Digital light processing in the foundry. Additive technologies in foundry production. The main types of metal casting

The method of obtaining master models (RP-prototypes) by layer-by-layer synthesis for casting on burn-out models by the method of sterolithography using Digital Light Processing technology is considered. The possibility of obtaining models with an internal adjustable cellular structure in the form of a typical Wigner–Seitz elementary cell is determined. The crosslinked photosensitive polymer Envisiontec SI500 was used as the starting material. In this work, a computer 3D model in STL format was designed and a prototype was obtained, which is a shell filled with an adjustable cellular structure. The optimal illumination regimes and the thickness of the illuminated layer of the sample are determined, with the help of which it is possible to control the dimensions of the bridges of the cellular structure. The presence in the model of a structure in the form of an array of cells in the future will significantly reduce the amount of material used and reduce the pressure on the ceramic shell when it is removed.

digital light processing

synthesis models

honeycomb structure

photopolymer

master model

1. Vasiliev V.A., Morozov V.V. Production of steel castings according to photopolymer models by burning them in a mold / Int. STC "Modern problems of metallurgical production". Sat. work. - Volgograd. 2002. - S. 336-337.

2. Vasiliev V.A., Morozov V.V., Shiganov I.N. Using methods of layer-by-layer formation of three-dimensional objects in foundry production// Vestnik mashinostroeniya. 2001. - No. 2. - S. 4–11.

3. Evseev A.V. Operational formation of three-dimensional objects by laser stereolithography [Text] / A.V. Evseev, V.S. Kamaev, E.V. Kotsyuba and others // Sat. Proceedings of IPLIT RAS. – P. 26–39.

4. Zlenko M.A. Additive technologies in mechanical engineering [Electronic resource]: a textbook for universities in the direction of training masters "Technological machines and equipment" / M.A. Zlenko, A.A. Popovich, I.N. Mutylin. [SPb., 2013] URL: http://dl.unilib.neva.ru/dl/2/3548.pdf

5. Zlenko M. Rapid prototyping technologies - layer-by-layer synthesis of a physical copy based on a 3D CAD model // CAD/CAM/CAE Observer. 2003. No. 2 (11). pp. 2–9.

6. Skorodumov S.V. Layer-by-layer synthesis technologies for creating three-dimensional models for blank production. // Bulletin of mechanical engineering. - 1998. - No. 1. - S. 20–25.

7.S.O. Onuh., Y.Y. Yusuf. Rapid prototyping technology: applications and benefits for rapid product development. // Journal of Intelligent Manufacturing. 1999.V.10.PP. 301 - 311.

Modern 3D computer design systems can significantly reduce the time and cost spent on the development and design of new parts. The transition to digital product description - CAD and the resulting RP technology (RP technology for rapid prototyping) has revolutionized the foundry industry, especially in high-tech industries - aviation and aerospace, nuclear industry, medicine and instrumentation. traditional technologies, the use of new methods for obtaining casting synthesis models due to the technologies of layer-by-layer synthesis of photopolymer material made it possible to radically reduce the time for creating new products, improve the quality and accuracy of cast parts and reduce rejection.

Most widely, RP prototypes are used as investment casting patterns in foundries to produce high-precision and geometrically complex metal castings. The use of RP-models as burnt-out models in casting processes makes it possible to obtain geometrically complex metal castings with an accuracy of at least 12 quality and an average surface roughness of 7Ra. However, the use of synthesis models (RP prototypes) is often accompanied by cracking and subsequent destruction of the casting mold at the stage of high-temperature removal of the model mass.

The main reason for the destruction of ceramic molds in the process of removing the injection model is associated with the difference in the thermomechanical properties of the ceramic shell and the material of the prototype. One of the ways to reduce the contact stresses between the casting model and the ceramic mold in the process of thermal exposure is to replace the monolithic model with a model of an equivalent shape, which is a shell with a cellular filler of the internal cavity as a supporting frame that prevents the shell from losing stability from the effects of residual stresses. The design of such synthesis models includes the choice of the shape and geometric parameters of the cell, which, on the one hand, ensure the minimum level of contact stresses, and, on the other hand, maintain the specified accuracy parameters of the polymer model throughout the fabrication and molding process.

The purpose of this work is to study the possibility of obtaining RP prototypes with an internal adjustable structure in the form of cells of the Wigner-Seitz type.

Materials and methods of research

The starting material is Envisiontec SI500 crosslinked polymer, which is used in the stereolithography process. To obtain prototypes with a controlled internal structure, this work used the technological process of sterolithography, the scheme of which is shown in Figure 1. The main difference from classical sterolithography is the avoidance of using a scheme with a laser to initiate the photopolymerization reaction and replacing it with several digital video projectors using Digital technology. Light Processing (DLP). The developer of this technology is Enviziontec (Germany). Acrylic photopolymer is used as the starting material for creating the model. The essence of the process is to use the "mask" of each current section of the model, projected onto the working platform through a special system of very small mirrors using a spotlight (containing two lamps with high brightness of light). The platform after illumination of the layer descends exactly to the thickness of the next layer into the bath with liquid polymer. The formation and exposure of each layer to visible light occur relatively quickly. This explains the high speed of building models (on average, 1 cm per hour in height with a construction step of 50 µm).

Rice. 1. Scheme of operation of a stereolithography machine using DLP technology: 1 - projector; 2 - photomask; 3 - polymer alignment mechanism; 4 - bath with liquid polymer; 5 - lowered base; 6 - cured polymer model

When using a step of 25 μm, there are practically no steps from layers, typical for all technologies of layer-by-layer synthesis, on the models. This possibility makes it possible to obtain products with high surface quality with a roughness of up to Ra0.1 and a dimensional accuracy of up to 0.1 mm.

Research results and discussion

An Envisiontec Perfactory XEDE was used to produce prototypes with an internal adjustable structure. Works were carried out on modeling a sample, which is a shell with a wall thickness of 0.5 mm, filled with a cellular adjustable structure (Fig. 3). To fill the internal volume of the sample, an elementary unit cell of Wigner-Seitz was used, which is an array in the STL file. The experiments were carried out at different parameters of the exposure time of the sample of each subsequent polymerizing layer from 6.5 to 18 s.

Rice. 3. CAD model of a cube shell filled with honeycomb structure

As a result of the work carried out, a prototype was obtained with a shell wall thickness of 0.5 mm, filled with a cellular structure made of photopolymer material SI500 (Fig. 4). The exposure time of each layer is 18 s (both the shell and the cellular structure with a bridge thickness of 0.5 mm).

Rice. 4. Prototype with an organized cellular structure

By varying the illumination parameters of the polymerizing material layer, it is possible to obtain cells with a bridge thickness in the size range from 0.12 to 0.5 mm.

Conclusion

The technological possibility of developing the technology for obtaining complex geometric objects with an internal adjustable cellular structure has been established. The potential application of this technology is possible in the foundry industry, namely in casting on burnt patterns. By replacing a monolithic master model with a model representing a shell with an internal adjustable structure in the form of cells, it is possible to reduce the pressure of the burnt-out model composition on the ceramic mold by selecting the shell thickness, shape and size of the cells.

Reviewers:

Sirotenko L.D., Doctor of Technical Sciences, Professor, Perm National Research Polytechnic University, Perm;

Khanov A.M., Doctor of Technical Sciences, Professor, Perm National Research Polytechnic University, Perm.

Bibliographic link

Shumkov A.A. CREATING MASTER MODELS BY LAYER-LAYER SYNTHESIS OF PHOTOPOLYMER // Modern problems of science and education. - 2015. - No. 2-1 .;
URL: http://science-education.ru/ru/article/view?id=20538 (date of access: 01.02.2020). We bring to your attention the journals published by the publishing house "Academy of Natural History"

Many jewelers successfully use software-controlled milling machines in their work, which grind waxes for casting, and some devices - and immediately metal parts. In this article, we will look at 3D printing as an alternative and addition to this process.

Speed

When creating a part in a single copy, the CNC milling machine wins in speed - the cutter of the machine moves at a speed of up to 2000-5000 mm / min, and where the milling cutter can handle it in 15 minutes, the printer can print the part up to an hour and a half, sometimes even more.

This is true, however, only for simple and smooth products, such as a wedding ring of a simple shape and without a pattern, which do not require high surface quality, because. they are easy to quickly polish. The router cuts complex products as slowly as a 3D printer prints them, and often longer - processing time can reach up to six hours.

A photo @ FormlabsJp

When creating a series of products at once, the situation changes dramatically - in one pass, the printer is able to print a full platform of stencils - this is a platform (for example, the Form 2 printer) 145x145 mm, and they fit there, depending on the size of the models, up to 35 pieces. With a print speed of 10-30 mm/hour (and it prints in layers, immediately over the entire area of the platform), this gives a noticeable advantage over the router, which cuts out only one model at a time - this is either one complex part, or several simple, flat ones, from one cylindrical wax blank.

In addition, a 3D printer can print a tree of models for casting at once, without the need to assemble it from separate blanks. This saves time too.

A photo @ 3d_cast

Accuracy and quality

The positioning accuracy of the cutter in CNC machines reaches 0.001 mm, which is higher than that of a 3D printer. The quality of surface treatment by a router also depends on the size of the cutter itself, and the radius of the cutter tip is at least 0.05 mm, but the movement of the cutter is set programmatically, usually it is a step of a third or half of the cutter, respectively - all transitions are smoothed out.

A photo @ freemanwax

The layer thickness when printing on Form 2, the most popular but far from the most accurate printer, and hence the vertical accuracy, is 0.025 mm, which is half the diameter of the tip of any cutter. Its beam diameter is 0.14 mm, which reduces the resolution, but also allows you to get a smoother surface.

A photo @ landofnaud

In general, the quality of the products obtained on a photopolymer printer and top-end milling machines is comparable. In some cases, on simple shapes, the quality of the milled part will be higher. With the complexity of forms, the story is different - a 3D printer is able to print something that no router will ever cut out, due to design limitations.

Economy

The photopolymers used in stereolithographic printers are more expensive than regular jewelry wax. Large pieces of wax after the router can be melted into new blanks, although this is also time and extra steps, but also savings. Milled wax comes out cheaper, in terms of the cost of each single product of the same volume.

Wax is not the only consumable in the work of the router, the cutters also gradually wear down and require replacement, they last for 1-2 months of intensive work, but this does not greatly reduce the gap.

The work of the milling cutter, in terms of the cost of manufactured products, is cheaper.

A photo @ 3DHub.gr

Convenience and opportunities

The specificity of milling is such that even on a five-axis machine, the milling cutter is far from being able to reach everywhere. This forces jewelers to create composite models from several parts, which then need to be soldered, or even pre-finished by hand. A 3D printer, on the other hand, is able to print a model of an arbitrarily complex shape, including internal cavities and complex joints, in a single pass.

How does this happen

Printed models are soldered to a wax barrel, then the resulting structure is poured with gypsum or a special solution, after which the finished form is heated in a furnace and then filled with metal.

The wax material burns out without residue, allowing the metal to take all the vacant space and exactly repeat the shape of the workpiece.

More details:

1. The casting process begins with the printing of the model and standard post-printing processing - the printed part is separated from the supports, washed, subjected to a curing exposure in ultraviolet, if necessary, lightly polished.

2. Further, the process is similar to that used for casting using conventional stencils. The blanks are soldered to a wax gate, which will hold them in the correct position and create a channel for the distribution of the metal.

If the number and size of products allow, you can skip this step - if you print the products together with the sprue as a whole.

3. The sprue is fixed in the casting flask. If the flask is perforated, the holes should be closed, for example, with packing tape.

4. The filling solution is mixed in the proportions specified by the manufacturer.

Then it is poured into a flask with a sprue inside. Pour carefully so as not to damage the model and not to move the Christmas tree.

5. The flask is placed in a vacuum chamber for at least 90 seconds to remove all air from the solution. Then it is transferred to a place protected from vibration, for a speedy solidification.

6. Casting containers are placed in an oven, cold or heated to 167ºC, and the temperature is gradually raised until the plastic of the models is completely burned out.

Preheat - preheating.

Insert flask - place the flask in the oven.

Ramp - raise (change) the temperature.

Hold - keep the temperature (example: 3h = 3 hours)

7. Upon completion of this process, metal is poured into the mold.

8. After pouring, the mold is cooled, the filling material is washed out.

9. It remains only to remove the finished products, separate them and lightly polish.

Photos of products created by Top3DShop:

Conclusions:

Both technologies have their pros and cons. If a jewelry workshop already has a CNC milling machine, then it will cope with most of the tasks of manufacturing single copies. Moreover, if only single copies are made and not very often, then the machine wins here and in speed.

If there is no task to develop production, increase the volume of work, turnover of funds, raise the level of complexity of products, then a 3D printer will only be an additional financial burden.

With an increase in the pace and volume of work, with the constant introduction of new models, the advantages of a 3D printer will become noticeable immediately, in mass production, the difference in speed is serious. The printer is difficult to overestimate in rapid prototyping and production of batches of blanks.

If the enterprise fulfills both types of orders - both single and serial, it will be more efficient and cost-effective to have both devices on the farm, for different types of work, they will organically complement each other.

Equipment

Formlabs Form 2

Technology: SLA

Working chamber: 145 x 145 x 175 mm

Layer thickness: 25-100 microns

Laser Focus: 140 µm

Beam Power: 250mW

Price: 320,000 rubles

The Form 2 is a compact stereolithographic 3D printer that fits easily on your desktop.

Due to its accuracy (25-100 microns), it is very popular with orthodontists and jewelers, as it is able to print many products in one session.

A photo @ FormlabsJp

A photopolymer for printing burnt-out models costs 46,000 rubles for a 1-liter cartridge.

3D Systems Projet MJP 2500

Technology: MJM

Working chamber: 295 x 211 x 142 mm

Resolution: 800 x 900 x 790 dpi

Layer thickness: 32 microns

Price: 3,030,000 rubles

Multi-jet printer by 3D Systems, designed for printing molded blanks with VisiJet materials and functional parts with plastics.

MJP is inferior to stereolithographic printers in terms of compactness - it is much larger and cannot be placed on a desktop, but this is offset by print speed and a larger work area.

3D Systems ProJet MJP 3600W Max

Technology: MJM

Working chamber: 298 x 183 x 203 mm

Resolution: up to 750 x 750 x 1600 DPI

Layer thickness from: from 16 µm

Printing accuracy: 10-50 microns

Price: 7,109,000 rubles

The ProJet 3600W Max is an upgraded version of the ProJet 3500 CPX, a specialized 3D printer for printing cast wax. These are industrial 3D printers used in factories in continuous operation, with a large platform and high performance. The printers of this series use the technology of multi-jet modeling (Multi Jet Modeling, MJM), which increases the speed of work and allows the use of VisiJet materials specially designed for it.

Technology: DLP (digital light processing)

Printing area: 120×67.5×150mm

Layer thickness: 25-50 µm (0.025/0.05 mm)

Resolution: 62.5 µm (0.0625 mm)

Price: from 275,000 rubles

Hunter is a new DLP 3D printer from Flashforge. DLP is a stereolithographic technology that uses a projector instead of a laser.

This technology has its advantages - DLP printing is faster and is able to give great detail at ultra-small scales. On the other hand, DLP projection consists of pixels, if you need a perfectly smooth surface, it is better to choose an SLA printer, for example, Form 2.

Flashforge Hunter DLP 3D is compatible with the third generation of stereolithographic resins, which gives the user a wide choice of printing materials.

The printer uses a DLP module of the manufacturer's own design, the characteristics of which are optimized specifically for 3D printing. This component has greater linear accuracy than conventional DLP designed for consumer video projectors.

Wanhao Duplicator 7 v1.4

Print technology: DLP, 405nm

Maximum printing speed: 30mm/hour

Maximum printing area: 120x68x200 mm

Resolution: 2560x1440 pixels per layer

Accuracy: 0.04mm

Layer thickness: 0.035-0.5mm

Weight: 12 kg

Price: 35 900 rubles.

Wanhao Duplicator 7 is an inexpensive photopolymer printer for trying stereolithography. The disadvantages of this model are low stability, low resolution and problems with out-of-the-box repeatability.

A photo @

The article provides an analysis of computer technologies used in procurement, in particular foundry production, which make it possible to drastically reduce the time for launching new products. These technologies are of particular importance in the manufacture of foundry models, molds and tooling.

In the development and creation of new industrial products, the speed of passing the stages of R & D is of particular importance, which, in turn, significantly depends on the technological capabilities of pilot production.

In particular, this applies to the manufacture of casting parts, which are often the most time-consuming and costly part of the overall project. When creating new products, especially at the R&D stage in pilot production, which is characterized by variant studies, the need for frequent design changes and, as a result, constant correction of technological equipment for the manufacture of prototypes, the problem of rapid production of casting parts becomes key.

In pilot production, the traditional methods of manufacturing foundry tooling by hand or using machining remain predominant. This is due to the fact that at the R&D stage, when the design of the product has not yet been worked out, it is not advisable to create tooling for mass production for the manufacture of samples. Under these conditions, foundry tooling is a very expensive product, which, in fact, turns out to be one-time, which is not used in further work on the product due to changes in the design of the product during R&D. Therefore, each approximation of the part design to the final version often requires new tooling, and therefore traditional methods are not only expensive, but also time-consuming.

The transition to a digital description of products - CAD, and then additive technologies have made a real revolution in the foundry industry, which is especially evident in high-tech industries - aviation, aerospace, nuclear, medicine and instrumentation - those industries where small-scale, often piece production is typical. It is here that the departure from traditional technologies, the use of new methods for obtaining foundry synthesis molds and synthesis models using layer-by-layer synthesis technologies has radically reduced the time for creating new products. For the manufacture of the first prototype of the cylinder block

(Fig. 1) traditional methods require ≥ 6 months, and most of the time is spent on the creation of tooling.

The use of Quick-Cast technology for this purpose (growing a casting model from a photopolymer on an SLA machine, followed by casting according to a gasified model) reduces the time for obtaining the first casting from six months to two weeks!

Fig.1 Quickcast model (a) and casting of the cylinder block (b)

The same part can be obtained by a less accurate, but quite suitable technology - casting in grown sand molds, when there is no need to make a casting model at all: the "negative" of the part is grown - the mold. A mold for casting such a large part as a cylinder block is grown in fragments, then assembled in a flask and poured. The whole process takes several days. A significant proportion of "ordinary" castings, which do not have special requirements for accuracy or internal structure, can be obtained in the form of finished products within a few days:

direct waxing;
molding + mold drying;
calcination of the form;
and, in fact, obtaining a casting.

Total: 3 ... 4 days (each stage - one day), taking into account the preparatory and final time. Almost all automotive and aircraft companies in industrialized countries have dozens of AF machines serving R&D in their arsenal of pilot production. Moreover, these machines are beginning to be used as a "normal" technological

equipment in a single technological chain and for mass production.

Additive technologies (AT) and rapid prototyping Additive Fabrication (AF) or Additive Manufacturing (AM) are terms accepted in the English technical lexicon denoting an additive, that is, “adding”, method of obtaining a product, as opposed to traditional methods of machining by “subtraction” ( subtractive) material from an array of blanks. They are used along with the phrase Rapid Prototyping (or RP-technologies) - rapid prototyping, but have a more general meaning, more accurately reflecting the current situation. We can say that RP-technology, in the modern sense, is a part of AF-technologies, "responsible" for the actual prototyping by layer-by-layer synthesis methods. AF or AM technologies cover all areas of product synthesis, whether it is a prototype, a prototype or a serial product.

The essence of AF-technologies, as well as RP-technologies, is the layered construction of products - models, forms, master models, etc. by fixing the layers of the model material and connecting them in series with each other in various ways: sintering, fusion, gluing, polymerization - depending on the nuances of a particular technology.

The ideology of additive processes is based on technologies based on a digital description of a product, its computer model, or the so-called. CAD model. When using AF-technologies, all stages of project implementation - from idea to materialization (in any form - intermediate or finished product) are in a "friendly" technological environment, in a single technological chain, where each technological operation is also performed in digital CAD\CAM \CAE system. In practice, this means a real transition to “paperless” technologies, when, in principle, traditional paper drawing documentation is not required for the manufacture of a part.

Although there are various AF-systems on the market for the production of models using different technologies and from different materials, the common thing for them is the layer-by-layer principle of building a model. AT play a special role in the modernization of foundry production, allowing solving previously unsolvable problems, "growing" foundry models and molds that cannot be made by traditional methods. The terms of manufacturing model equipment have been radically reduced. The development of vacuum-film technologies according to the forms and models obtained by AT made it possible to reduce by several times and tens of times the time for manufacturing prototypes, and, in some cases, serial production. Recent advances in the field of powder metallurgy have made it possible to significantly expand the capabilities of AT for the direct "growing" of functional parts from metals and the production of new structural materials with unique properties (spray forming technologies, etc.).

Modern AT Centers often contain the words design and technology in their full name, thereby emphasizing the unity, and not the struggle of contradictions, between the designer and the technologist. Taking into account the specifics of Russian industry, where the production of a huge range of products from different materials is often concentrated within one enterprise, where many enterprises are forced to maintain their “subsistence economy”, this is a rational approach. Pilot foundries in the technologies for producing both metal and plastic products have much in common, and with the use of AT they are still approaching in terms of the equipment used, and in technological methods, and in the education and training of professional personnel.

AT and foundry

As already noted, AT is of particular importance for the accelerated production of casting parts, in particular, for obtaining:

foundry models;
master models;
foundry molds and foundry equipment.

Manufacturing of foundry synthesis models

Casting models can be obtained (grown) from the following materials:

powdered polystyrene (for subsequent LGM);
photopolymer compositions, in particular, using Quick-cast technology for subsequent LGM or MJ (Multi Jet) technology for investment casting.

Rice. 2. SLS-machine SinterStation Pro and turbine wheel model

Synthesis models from powdered polystyrene. Polystyrene is widely used as a model material for traditional LGM. However, due to the rapid development of layer-by-layer synthesis technologies, it has gained particular popularity for prototyping, as well as for the industrial production of piece and small-scale products. Polystyrene models are made on AF-machines using the SLS technology - Selective Laser Sintering - layer-by-layer sintering of powder materials (Fig. 2). This technology is often used when it is necessary to quickly make one or more castings of complex shape of relatively large dimensions with moderate requirements for accuracy.

Model material - polystyrene powder with a particle size of 50 ... 150 microns is rolled with a special roller onto a working platform installed in a sealed chamber with an inert gas (nitrogen) atmosphere. The laser beam “runs” where the computer “sees” the “body” in a given section of the CAD model, as if shading the section of the part, as the designer does with a pencil on the drawing. Under the influence of the heat of the laser beam, the polystyrene particles are sintered (~ 120°C). Then the platform is lowered by 0.1…0.2 mm, and a new portion of the powder is rolled onto the hardened layer, a new one is formed, which is also sintered with the previous one.

The process is repeated until the complete construction of the model, which at the end of the process is enclosed in an array of unsintered powder. The model is removed from the machine and cleaned of powder. The advantage of the technology is the absence of supports, since the model and all its layers under construction are constantly held by an array of powder.

The machines available on the market from 3D Systems and EOS make it possible to build fairly large models - up to 550 × 550 × 750 mm (which is important, since it is possible to build large models as a whole, without gluing individual fragments, which increases the accuracy and density of the casting). Very high detailing of model construction: surface elements (part numbers, conditional inscriptions, etc.) with a fragment thickness of up to 0.6 mm can be built, a guaranteed model wall thickness of up to 1.5 mm.

Rice. Fig. 3. Polystyrene model after cultivation (a) and infiltration (b) and cast iron (c)

Rice. 4. Polystyrene models (a) and castings from
Al-alloy (b)

Fundamentally, casting technologies for wax and polystyrene models do not differ (Figures 3 and 4). The same molding materials, the same foundry and auxiliary equipment are used. Is that the wax model - "smelted", and polystyrene - "burned out".

But working with polystyrene models requires attention when burning out: a lot of gases are released that require neutralization, the material partially burns out in the mold itself, there is a danger of ash formation and clogging of the mold, it is necessary to provide for the possibility of material draining from stagnant zones, calcining furnaces with programmers should be used, moreover , programs for burning out polystyrene and melting out wax are significantly different. But in general, with a certain skill and experience, LGM gives a very good result.

Technology Disadvantages

The powder sintering process is a thermal process with all its inherent disadvantages: uneven distribution of heat over the working chamber, over the material mass, warping due to temperature deformations.

Polystyrene powder does not fuse, as, for example, polyamide or metal powders, but sinter - the porous structure of the model is similar to the structure of foam. This is done specifically to facilitate the further removal of the model material from the mold with minimal internal stresses when heated.

The constructed model, in contrast to, for example, a wax one, requires careful handling both during cleaning and further preparation for molding.

To give strength and ease of working with it (joints with the gating system, molding), the model is impregnated at ~ 80 ° C with a special wax composition - the process is called infiltration. (Fig. 3 shows red infiltrated models, while white polystyrene models are removed from the machine). This also carries the risk of deforming the model and requires certain skills of the staff.

Recently, polystyrene powders have appeared that do not require infiltration. This alleviates but does not eliminate the problem. In addition, infiltrate in the form of wax is not always a harmful necessity. It melts in the flask when burning out before polystyrene, and when the latter becomes fluid, it contributes to its removal from the mold, thereby reducing the mass of the “burned out” part of polystyrene and reducing the likelihood of ash formation.

Rice. 5. SLS Camshaft Model and Sand Molding Box

Thus, when we talk about moderate requirements for accuracy when using SLS technology, we mean the noted reasons why the accuracy of products obtained by SLS technologies cannot be higher than when using other technologies that are not related to thermal deformations. as, for example, photopolymerization technologies (Fig. 5).

Speaking about the SLS technology, we note one more, not related to polystyrene, but "related" direction, sometimes used in the foundry. This is the cultivation of tooling from powdered polyamide. Polyamide is widely used for functional prototyping, durable polyamide models in many cases allow you to reproduce the prototype as close as possible to the finished product.

In some cases, it is advisable to use polyamide models as an alternative to wooden ones. The model is grown, as well as polystyrene. At the same time, if possible, make it hollow with the minimum possible wall thickness. Then the model, to give it strength and rigidity, is filled with epoxy resin, after which it is fixed in a flask, painted, and then traditional molding technology is used. An example of such a "quick" tooling for forming an internal combustion engine camshaft is shown in Fig. 5. Due to the large length, the model is grown from two parts, the parts are glued, filled with epoxy resin and fixed in the flask; duration of operations - two days.

Synthesis models from photopolymers. The essence of the technology is the use of special light-sensitive resins, which are cured selectively and in layers at points or places where a beam of light is supplied according to a given program. The methods of illumination of the layer are different (laser, ultraviolet lamp, visible light). There are two main technologies for creating models from photopolymer compositions: laser stereolithography or SLA technology (Steriolithography Laser Apparatus), or stereolithography - curing the layer with a laser, and "instant" layer illumination - curing the photopolymer layer with a flash of an ultraviolet lamp or spotlight.

The first method involves the sequential "running" of the laser beam over the entire surface of the formed layer, where the "body" of the model is in the section. According to the 2nd method, the curing of the entire layer occurs immediately after or during its formation due to radiation from a controlled light source - visible or ultraviolet.

The difference in the methods of formation of layers also determines the difference in the speed of building the model. Obviously, the growth rate of the 2nd method is higher. However, stereolithography has been and remains the most accurate technology and is used where the requirements for surface cleanliness and model building accuracy are basic and decisive.

Nevertheless, exposure-controlled technologies used, for example, by Objet Geometry and Envisiontec, in many cases successfully compete with stereolithography, leaving behind a clear advantage in the speed of construction and cost of models. A number of production tasks can be equally successfully solved with the help of AF-machines of different levels.

Thus, the optimal choice of technology for obtaining models and, consequently, prototyping equipment is often not obvious and must be carried out taking into account specific production conditions and real requirements for models. In cases where the variety of tasks to be solved is obvious, it is advisable to have two machines: for the manufacture of products with increased requirements and for performing “routine” tasks and replicating models.

Laser stereolithography. 3D Systems is a pioneer in the practical development of rapid prototyping technologies. In 1986, for the first time, it presented for commercial development the SLA-250 stereolithographic machine with the dimensions of the construction zone 250 × 250 × 250 mm. The basis in the SLA process is an ultraviolet laser (solid-state or CO2), where the laser beam is not a source of heat, as in SLS technology, but of light. The beam "hatches" the current section of the CAD model and solidifies a thin layer of liquid polymer. Then the platform on which the construction is performed is immersed in a bath with a photopolymer for the size of the construction step, where a new liquid layer is applied to the hardened layer: the new contour is “processed” by the laser.

When growing a model with overhanging elements, simultaneously with the main body of the model (and from the same material), supports are built in the form of thin columns, on which the first layer of the overhanging element is laid when the turn of its construction comes. The process is repeated until the completion of the model building.

Rice. 6. SLA-model (a) and casting ball, silver (b)

Then the model is removed, the remains of the resin are washed off with acetone or alcohol, and the supports are removed. The surface quality of stereolithographic models is very high, and often the model does not require post-processing. If necessary, the surface cleanliness can be improved, because the "fixed" photopolymer is well processed, and the surface of the model can be brought to a mirror. In some cases, if the angle between the model surface under construction and the vertical< 30 град., модель можно построить и без поддержек. И таким образом может быть построена модель, для которой не возникает проблемы удаления поддержек из внутренних полостей, что, в свою очередь, позволяет получать модели, которые в принципе нельзя изготовить никаким из традиционных методов (например, ювелирное изделие на рис. 6). Стереолитография широко применяется для: выращивания литейных моделей; изготовления мастер-моделей (для последующего получения силиконовых форм, восковых моделей и отливок из полиуретановых смол); создания дизайн-моделей, макетов и функциональных прототипов; изготовления полноразмерных и масштабных моделей для гидродинамических, аэродинамических, прочностных и других видов исследований. Но мы отметим лишь два направления.

Rice. Fig. 7. Quick-cast model (a), same with gating system (b) and casting of Al-cylinder head (c)

For the purposes of foundry production, the so-called. Quick-Cast-models (Fig. 7), that is, models for "quick casting". So called models, by which, by analogy with wax models, you can quickly get metal castings. But the Quick-Cast models have a honeycomb array wall structure:

the outer and inner surfaces of the walls are made solid, and the wall itself is formed in the form of a set of honeycombs, which has great advantages: the total mass of the model is significantly reduced by 70%, and, consequently, less material will need to be burned out;
in the process of burning out, any model material expands and presses on the walls of the mold, while the mold with thin-walled elements can be destroyed;
the honeycomb structure allows the model to “fold” inward during expansion, without straining or deforming the walls of the mold.

In some cases, SLA models, as well as SLS models, can be used not as casting models, but as tooling for obtaining a model when casting in a sand mold (SF) - fig. 8. In this case, casting slopes must be provided in the design of the model.

Rice. Fig. 8. CAD model (a), SLS model (b) and casting of the front cover of the DVO obtained in PF (c)

However, this method is rarely used due to the insufficient strength of the SLA model. The second, not in importance, but in the order of mention, advantage is the accuracy of building a model, under normal conditions, at room temperature, when there are no thermal stresses and deformations. A very small spot of the laser beam ∅ 0.1…0.05 mm allows you to clearly “work through” thin, filigree fragments of the model, which has made stereolithography popular in the jewelry industry. In Russia, there is quite a lot of experience in applying Quck-Cast technology in the aviation industry (Salyut, Sukhoi, UMPO, Rybinsk Motors enterprises), in power engineering (TMZ - Tushino Machine-Building Plant) - Fig. 9, some experience is also available in automotive research institutes. So, in NAMI, for the first time in Russia, such complex castings as the head and cylinder block were obtained using this technology. However, in other industries, this technology remains practically undeveloped.

Rice. Fig. 9. SLA-model (а) and casting of the impeller of the turbine unit (b), shell mold and casting of the turbine impeller of OAO TMZ (c)

The main manufacturer of SLA-machines is the American company 3D Systems, which produces a wide range of machines with different sizes of the construction zone, from 250×250×250 to 1500×570×500 mm. For foundry production in the world industry, iPro series machines are quite actively used (Fig. 10), the technical characteristics of which can be found on the campaign website www.3dsystems. com. Costs, both initial and in use, are perhaps the only drawback of this technology. The presence of a laser makes these installations relatively expensive and require regular maintenance.

Rice. 10. iPro 8000 machine (a) and SLA models (b)

Therefore, recently, when a lot of 3D printers have appeared, they are used to build especially critical products with increased requirements for accuracy and surface finish, primarily for the manufacture of Quick-Cast and master models. For other purposes, for example, design layouts, cheaper technologies are used. The cost of consumables is moderate - € 200 ... 300, and is comparable to the price of model materials from other companies. The model building time depends on the working platform load, as well as on the building step, but, on average, it is 4…7 mm/h along the model height. The machine can build models with a wall thickness of 0.05…0.2 mm. DLP technology The developer of this technology is the international company Envisiontec, which can be attributed to the newcomers to the AF market; it released its first machines in 2003.

Rice. 11. Models of Envisiontec (a) and castings of Al-engine parts (b)

The Envisiontec machines (Fig. 11) of the Perfactory family use the original DLP technology - Digital Light Procession, the essence of which is the formation of the so-called. masks of each current section of the model projected onto the working platform through a special system of very small mirrors, using a spotlight with a high brightness of light. The formation and illumination of each layer with visible light occurs relatively quickly, within 3–5 s.

Thus, if SLA-machines use the point principle of illumination, then in Envisiontec machines it is superficial, that is, illumination of the entire surface of the layer, which explains the high speed of building models - on average, 25 mm / h in height, with a construction layer thickness of 0, 05 mm. The support material is the same as the main material - acrylic photopolymer. Envisiontec models are used in the same way as SLA models - as master patterns and burnout casting patterns. Their quality is very high, but inferior in accuracy to SLA models, which is mainly due to the use of not low-shrinkage epoxy photopolymers, as in 3D Systems machines, but acrylic ones with a significantly higher, almost an order of magnitude - 0.6%, shrinkage coefficient at polymerization.

Nevertheless, their advantage is rather high accuracy and surface cleanliness, strength, ease of use, at a very moderate (compared to stereolithography) cost. Also, the undoubted advantages of Envisiontec technology are the high speed of building models and, consequently, the performance of the RP machine. The experiments carried out recently showed, in general, good burnout of models, low ash content. Conditional automotive castings were obtained, both by vacuum casting of Al-alloys into plaster molds, and by casting cast iron in PF (marshallite).

There is every reason to consider DLP technology promising and effective for foundry production, and not just for research and development. The time (taking into account the preparatory and final operations) of building the details of the inlet pipe with a height of 32 mm and the receiver with a height of 100 mm is 1.5 and 5 hours, respectively. Whereas on a Viper SLA machine (3D Systems) comparable in size, such models would be built in ≥ 5.5 and 16 hours. Of interest are the machines of the Extrim and EXEDE series, which are positioned as AF machines for mass production of master models and models for LGM. The peculiarity of these machines is that, unlike other technologies, they use not discrete (step by step), but continuous downward movement of the platform at low speed. Therefore, the models do not have pronounced steps characteristic of other construction methods. Models require post-processing - removal of supports and, in some cases, as in stereolithography - post-polymerization. The main characteristics of Envisiontec machines are shown in the table. A wide choice of materials for master models, models - burnout and for vacuum forming (can withstand up to 150°C), conceptual modeling makes these machines especially attractive when you need to produce a large number of models of a wide range. MJM (Multi Jet Modeling) technology for obtaining wax synthesis models. Models (Fig. 12) are built on 3D printers using a special model material, which includes a light-sensitive resin - an acrylic-based photopolymer (binder) and casting wax (50%). By means of a multi-jet head, the material is applied in layers on the working platform, curing each layer by irradiation with an ultraviolet lamp.

A feature of the technology is the presence of the so-called. supporting structures - supports for holding overhanging elements of the model during the construction process. The material is a wax polymer with a low melting point, which, after building the model, is removed with a hot water jet.

The disadvantage of the technology is the relatively high cost of consumables - $300/kg; advantages - the speed of obtaining a model and, no less important, the high quality of the model material, from the point of view of the investment casting technology itself (molding, melting the model).

	Dimensions of the construction zone, mm	Construction layer thickness, mm	Dimensions, mm	Weight, kg
standard	120´90´230	0.025¼0.150	480´730´1350
Zoom	190´142´230
Standard UV	175´131´230
Extreme	320´240´430	0.025¼0.150	810´730´2200
EXED	457´431´508	0.025¼0.150	810´840´2200

From synthesis master model to casting

Casting polyurethane resins and waxes into silicone molds. The second intensively developing area of using photopolymers is the production of high-precision master models, both for the subsequent production of wax models through silicone molds, and for casting polyurethanes. The use of silicone molds is extremely effective for piece and small-scale production of wax models, while their high quality is achieved.

Master models are usually grown on SLA or DPL plants, which provide the best surface finish and high model building accuracy. Models produced on 3D printers such as ProJet and Objet are of fairly high quality.

Rice. 13. Silicone mold (top), master model (bottom left), wax model (center), metal casting (right)

Master models are used to obtain the so-called. quick molds, in particular, silicone ones (Fig. 13), into which polyurethane resins or wax are then poured for subsequent casting of metals. The technologies of casting into elastic molds are widespread in the world practice. Various silicones with a low shrinkage coefficient and relatively high strength and durability are used as mold materials (here, silicone is a mixture of two initially liquid components A and B, which, when mixed in a certain proportion, polymerize and form a homogeneous, relatively solid mass).

Elastic molds are obtained by filling a master model with silicone in a vacuum, which is usually placed in a wooden flask, the flask is placed in a vacuum machine, where components A and B are mixed in a special container, then the silicone is poured into the flask. Vacuum is used to remove air from liquid components and to ensure high quality molds and castings. After pouring for 20 ... 40 minutes, the silicone polymerizes. The delivery set of equipment for vacuum casting, as a rule, includes the vacuum machine itself (one- or two-chamber) and two heating cabinets: for storing consumables at ~ 35°C and for holding molds at ~ 70°C; the latter is used for preliminary thermal preparation

silicone mold and casting materials immediately before pouring.

After pouring the polyurethane resin, the mold is returned to the resin curing oven. Therefore, the size of the second oven must match the dimensions of the vacuum chamber of the machine. Using special techniques, the mold is cut into two or more parts, depending on the configuration of the model, then the model is removed from the mold.

The usual form stability of 50–100 cycles is quite sufficient for the production of an experimental series of castings. These technologies have proved to be very effective for the production of pilot batches and small-scale products typical for the aviation, medical and instrument-making industries.

A wide range of both silicones and polyurethane resins makes it possible to produce castings with impact and heat-resistant properties, different hardness in a variety of colors. Modern investment casting enterprises usually have an AF machine for growing master patterns and a machine for vacuum casting into silicone molds as part of their technological equipment.

M.A. Zlenko - Doctor of Engineering Sciences NIImashTech ONTI SPbSPU.

P.V. Zabednov is an engineer at FSUE Vneshtechnika.

Colleagues, today we will talk about sore!

Namely, how some sellers of 3D printers try to sell you their product by hook or by crook....

First, let's talk about the two most common 3D printing technologies: DLP and SLA, these are the most common 3D printers in dentistry.

In the dental market today, printers using DLP and SLA printing technologies are the most popular, what is the difference between these two technologies?

Both (DLP and SLA) use “liquid plastic” as their printing raw material, in other words, a photopolymer that polymerizes and takes on a solid form under the influence of UV radiation.

A bit of history:

The pioneers in the development of dental 3D printing and the creation of a wide range of biocompatible polymers are the Dutch company Nextdent, formerly known to everyone as Vertex.

This winter, seeing the great potential of these biocompatible materials, Nextdent was bought by the father of 3D printing, 3D giant American company 3D Systems.

Getting certified for biocompatible materials is not easy, so Nextdent photopolymers are purchased by other companies and sold under their different brands: Formlabs, Novux and others.

Now back to 3D printing technologies.

DLP. Printing principle:

The program that comes with the printer breaks the printed object into layers with a given thickness.

A photopolymer (printing material) is poured into the bath of the printer with a transparent bottom.

A working table sinks to the very bottom of the bath, retreating from the bottom to one (first) layer of our object (in this “indentation” there is a liquid photopolymer).

The projector located under the bathtub projects the image of the first layer onto the bottom of the bathtub, and thanks to UV radiation, only the plastic on which the image from the projector has landed freezes.

This is how our printed object grows layer by layer, whether it is a model of the jaw or a temporary crown. SLA. Printing principle: The principle of printing is similar, but with the difference that it is not the entire layer that is projected, but a laser beam quickly passes through each point of the object, which polymerizes the liquid photopolymer (material)

Often, it is not easy for a buyer to understand all the properties of a 3D printer and its materials on their own, but there is one clear indicator that almost everyone is guided by. And of course, this indicator is mainly played by sellers of 3D printers.

Have you already guessed what is the main argument they give when selling you their printer?

Print Accuracy!

Let's then deal with this popular parameter, which is twisted in one direction or another intentionally or due to incompetence.

Print Accuracy.

This parameter depends on many factors, moreover, not only on the printer, but also on the material and environment.

How does it depend on the material?

The more opaque the material (filled with pigments and light blockers), the more accurate the products printed from it will be. This is due to the absence of light scattering during printing and polymerization of the material adjacent to the model.

How does it depend on the environment?

When printing with photopolymer, it is important to control its temperature during printing.

During polymerization, it is in DLP printers that a lot of heat is generated.

How does high temperature affect printing?

Very simply, the chemical reaction is accelerated and there is too much current light to polymerize the material.

The risk of polymerization of the boundary layer of the model increases (excessive plastic exposure), respectively, an increase in its size, in other words, a loss of accuracy.

In SLA printers, this is not so scary, since the laser has less power (it produces less heat), the volume of the bath for the material is usually much larger (than in DLP printers), which leads to the fact that the photopolymer in the bath heats up more slowly and there is no risk of overheating.

That is why SLA printing takes a little longer, but it does not have the risks of overheating and loss of accuracy, as in DLP printers.

So, in order to get the most accurately printed product, and it's hot in your room, control the temperature of the polymer used.

Cold is also not the best option, as the material may not have enough light strength, it will not fix on the print table and you will have to warm up the material and start the entire printing process from the beginning.

Of course, fussing with heated material is not very convenient!

But if your printer has the function of automatic material heating, you won't have to deal with it manually.

Additive technologies in pilot foundry. Technologies for casting metals and plastics using synthesis models and synthesis molds

(Scientific Supervisor of the Center for Additive Technologies of the Federal State Unitary Enterprise "NAMI", Doctor of Technical Sciences

Mikhail Zlenko; Pavel Zabednov, director of FSUE Vneshtechnika)

INTRODUCTION When developing and creating new industrial products, special

What matters is the speed of passing through the stages of R & D, which in turn significantly depends on the technological capabilities of pilot production. AT

variant studies, the need for frequent design changes and, as a result, constant correction of technological equipment for manufacturing

prototypes, the problem of rapid production of casting parts becomes key. In pilot production, traditional methods of making casting equipment (mainly wooden models) by hand remain predominant.

or using machining equipment, less often CNC. This is due to the fact that at the R&D stage, in conditions of uncertainty of the result, when the design of the product has not yet been worked out, not approved, for the manufacture of samples

it is not advisable to create "normal" technological equipment for serial

production. Under these conditions, a very expensive product - casting equipment, turns out to be, in fact, one-time, which is not used in further work on the product due to natural and significant changes in the design of the product during R&D. Therefore, each iteration, each approximation of the construction

details to the final version often requires new technological equipment,

since the alteration of the old one turns out to be excessively laborious or not possible at all. And in this regard, traditional methods are not only expensive in terms of material losses, but also extremely time-consuming.

The transition to a digital description of products - CAD, and appeared after CAD

(due to CAD!) additive technologies have made a real revolution in foundry, which is especially evident in high-tech industries - aviation and aerospace, nuclear industry, medicine and instrumentation, in industries where little serial is typical, often

piece (per month, year) production. It is here that the departure from traditional technologies,

the use of new methods for obtaining casting synthesis molds and synthesis models due to layer-by-layer synthesis technologies made it possible to radically reduce the time

to create new products. For example, typical for automotive

engine building detail - cylinder block. To make the first

prototype by traditional methods

it takes at least 6 months, and the main time costs

account for the creation

Quick-cast model and cylinder block casting (cast iron) pattern equipment for casting "into the ground".

The use of Quick-Cast technology for this purpose (growing a casting model

from a photopolymer on an SLA-machine with subsequent casting according to a burnt-out model)

reduces the time for obtaining the first casting from six months to two weeks!

The same detail can be obtained less accurate, but quite suitable for the data.

technology goals - casting in grown sand molds. According to this technology, there is no need to make a casting model at all:

the "negative" of the detail is grown - the form. A mold for casting such a large part as a cylinder block,

is grown in fragments, then collected in a flask and the metal is poured. The whole process takes several days. significant portion

"ordinary" casting products that do not have special requirements for casting accuracy or

Fragments of a sand mold internal structure, can be obtained in the form of finished products within a few days: direct wax model cultivation (1 day); molding + mold drying (1 day); calcination

molds and actual casting (1 day); total: 3-4 days, taking into account the preparatory-final time. Almost all automotive and aircraft building

companies in industrialized countries have in their arsenal of pilot production dozens of AF machines that serve R&D tasks. Moreover, these machines are beginning to be used as “ordinary” technological equipment in

a single technological chain and for mass production.

1. Additive technologies and rapid prototyping

Additive Fabrication (AF) or Additive Manufacturing (AM) - accepted in

English technical lexicon terms denoting additive, i.e., "adding", method of obtaining a product (as opposed to traditional methods of machining by "subtracting" material from an array of workpieces). They are used along with the phrase Rapid Prototyping (or RP -

technologies) - Rapid Prototyping, but have a more general meaning, more precisely

reflecting the current situation. We can say that Rapid Prototyping in the modern sense is a part of AF technologies, "responsible" for the actual prototyping by layer-by-layer synthesis methods. AF - or AM - technologies cover all areas of product synthesis, be it a prototype,

prototype or serial product.

The essence of AF-technologies, as well as RP-technologies, consists in layer-by-layer construction, layer-by-layer synthesis of products - models, forms, master models, etc. gluing, polymerization - depending on the nuances of a particular technology. The ideology of additive technologies is based on digital technologies based on

lies a digital description of the product, its computer model or the so-called. CAD model. When using AF-technologies, all stages of project implementation from idea to

materialization (in any form - in the intermediate or in the form of finished products) are in a "friendly" technological environment, in a single technological chain, where each technological operation is also performed in digital

CAD\CAM\CAE system. In practice, this means a real transition to “paperless” technologies, when, in principle, traditional paper drawing documentation is not required for the manufacture of a part.

Currently, there are various AF systems on the market that produce

models on various technologies and from various materials. However, they have in common the layer-by-layer principle of building a model. AF-technologies play a special role in the modernization of foundry production, they made it possible to solve previously unsolvable problems, to “grow” casting models and molds that are impossible

made in traditional ways. The terms of manufacturing model equipment have been radically reduced. Development of vacuum forming and vacuum forming technologies

casting according to molds and models obtained by additive technologies made it possible to reduce the time for manufacturing pilot, prototypes and, in some cases, serial products by several times and tens of times. Recent advances in the field

powder metallurgy have made it possible to significantly expand the possibilities of additive technologies for the direct "growing" of functional

metal parts and obtaining new structural materials with unique properties (spray forming technologies, etc.).

AF-technologies are justifiably referred to as technologies of the 21st century. Except

obvious advantages in terms of speed and, often, in the cost of manufacturing products, these technologies have important advantages in terms of environmental protection and, in particular, greenhouse gas emissions and "thermal" pollution. Additive

technologies have great potential to reduce energy costs for the creation of a wide variety of products.

"Under the pressure" of the global development of three-dimensional CAD / CAM / CAE technologies, modern foundry, and primarily pilot production, is undergoing significant modernization, which aims to create conditions for the full implementation of the principle of "paperless" technologies throughout the entire process of creating a new product - from design and development of CAD models, up to

final product, to be an integral part of the cycle of design and manufacture of prototypes, prototypes and small series of products for various purposes with a wide range of materials used. And for this purpose, "casters"

equipped with completely new equipment for them, giving them new

opportunities to satisfy the “whims” of designers, but at the same time requiring them to master new knowledge, forcing both technologists and designers to speak the same 3D language, while, if not eliminating, then significantly weakening the eternal confrontation between the technologist and the designer.

Modern Additive Technology Centers often in their full name

Russian industry, where often within the same enterprise

the production of a huge range of products from various materials is concentrated, where many enterprises, for various reasons, but are forced to maintain

their "subsistence economy", such an approach is quite rational.

Pilot foundry for the production of both metal and plastic

products have much in common, and with the use of AF technologies they become even more

similar both in terms of the equipment used, and in terms of technological methods, and in terms of

education and training of professional personnel.

2. Additive technologies and foundry production

As already noted, AF technologies are of particular importance for the accelerated production of casting parts. AF-machines are used to obtain:

- foundry models;

master models;

- foundry molds and foundry equipment.

* within one article it is impossible to describe all technologies and all machines for layer-by-layer synthesis. Here we will limit ourselves to only those technologies that are of the greatest interest in relation to mechanical engineering problems, omitting from consideration a fairly significant number of machines "sharpened" for solving special problems of general medicine, biology and dentistry, electronics or jewelry industry.

2.1. Production of foundry synthesis models can be obtained (grown) from:

- powdered polystyrene (for subsequent casting on burnt models);

- photopolymer compositions, in particular, according to the technology Quick-cast for post-casting on burn-out models or MJ technology (Multi Jet ) for

investment casting;

2.1.1 Synthesis models from powdered polystyrene

Polystyrene is widely used as a model material for traditional burnout casting. However, due to the rapid development

layer-by-layer synthesis technology has gained particular popularity in the field of prototyping, as well as for the industrial production of piece and

small-scale production. Polystyrene models are made on AF-machines using SLS technology - Selective Laser Sintering - layer-by-layer sintering of powder materials. This technology is often used when needed.

quickly make one or more castings of complex shape relatively large

	sizes	moderate

	requirements	by accuracy.
	The essence of the technology is
	next.	model
	material	polystyrene
	powder with particle size 50-
		rolls over
	special
SLS - SinterStation Pro machine and turbine wheel model		platform,
	established	in sealed

chamber with an atmosphere of inert gas (nitrogen). The laser beam "runs" where the computer "sees" in a given section of the CAD model "body", as if shading

section of the part, as the designer does with a pencil in the drawing. Here is the laser

the beam is a heat source, under the influence of which the polystyrene particles are sintered (operating temperature is about 120°C). Then the platform is lowered by 0.1-0.2 mm and a new portion of the powder is rolled over the cured one, a new layer is formed, which is also sintered with the previous one.

The process is repeated until the complete construction of the model, which at the end of the process

turns out to be enclosed in an array of unsintered powder. The model is retrieved from

			cleared of
			cleared of
		advantage
			technology
	is		absence
	supports - they are not needed,
	because the model and all its
	layers under construction during
	building		held
	array
Polystyrene model and casting of the cylinder head of the internal combustion engine	Available
	3D Systems machines

and EOS allow you to build fairly large models - up to 550x550x750 mm in size (this is important, it allows you to build large models as a whole, without the need

gluing individual fragments, which increases the casting accuracy and reliability,

especially vacuum casting). Very high detail of model building: surface elements can be built (part numbers, conditional inscriptions

and etc.) with fragment thickness up to 0.6 mm, guaranteed model wall thickness up to

Fundamentally, casting technologies for wax and polystyrene models do not differ. The same molding materials are used, the same foundry and

auxiliary equipment. Is that the wax model - "smelted", and the polystyrene model - "burned out". The differences are only in the nuances of molding and heat treatment of flasks. However, these nuances matter. Work with

polystyrene models require attention when burning out: a lot of gases (combustible) are released that require neutralization, the material

partially burns out in the form itself, there is a danger of ash formation and clogging of the form, it is necessary to provide for the possibility of runoff of material from stagnant zones, an unconditional requirement is the use of calcining furnaces with

programmers, and the polystyrene burning program is significantly different from the wax melting program. But in general, with a certain skill and experience, casting on polystyrene burnout models gives a very good result.

Polystyrene model (after cultivation and infiltration) and casting, cast iron

The disadvantages of the technology include the following. The process of powder sintering is a thermal process with all its inherent disadvantages: uneven distribution of heat over the working chamber, over the mass of material, warpage

due to temperature changes. Second. Polystyrene powder is not

alloys, such as polyamide or metal powders, which will be discussed

below, namely, it is sintered - the structure of the model is porous, similar to the structure

foam. This is done specifically to facilitate the further removal of the model material from the mold with minimal internal stresses when heated. The constructed model, in contrast to, for example, waxing, requires very careful handling both during cleaning and during further work in preparation for molding. For durability and ease of use

(joints with gating system,

molding) the model is impregnated

special composition on wax

basis - the process is called infiltration. The model is placed in a special oven and at a temperature

about 80 ° C impregnated with the indicated composition (the photograph shows infiltrated models of red

colors are extracted from the machine

Polystyrene models and castings, aluminum polystyrene snow models

white). This also carries the risk of deforming the model and requires

certain staff skills. Indeed, recently there have been

polystyrene model powders that do not require infiltration. This alleviates but does not completely eliminate the problem. In addition, infiltration in the form of wax is not always a harmful necessity. It melts in the flask when burned out first, before polystyrene and when the latter acquires fluidity,

contributes to its removal from the mold, thereby reducing the mass of the “burned out” part of the polystyrene and reducing the likelihood of ash formation.

Thus, when we talk about “moderate requirements for accuracy” when using SLS technology, we mean the noted objective reasons why the accuracy of products obtained by SLS technology cannot be higher than

when using other technologies not related to temperature deformations. Such, for example, is the technology of photopolymerization.

Speaking about the SLS technology, we note one more thing, not related to polystyrene, but


"related"		a direction sometimes used in foundry. it
			cultivation of foundry molding equipment
			from powdered polyamide. polyamide wide
			used				functional
			prototyping,			polyamide
			strong enough and in many cases
			allow		reproduce				prototype
			as close as possible to the "combat" product. AT
					turns out			economically
			expedient		apply			polyamide
			models as an alternative to wooden ones.
			The model is grown in the same way as
			polystyrene. At the same time, if possible
	SLS-model	distributive		her hollow with		minimum			possible
	shaft and mold box for		wall thickness (in order to minimize
	receiving		the above temperature deformations!).
						giving		strength and

rigidity is filled from the inside with epoxy resin. After that, they are fixed in a conventional molding box, painted and then - according to the traditional molding technology.

An example of such a "quick" tooling for molding

ICE camshaft is shown in the figure. Due to the long length, the model is grown in two parts, the parts are glued, filled with epoxy resin and fixed in a mold box; duration of operations 2 days.

2.1.2 Synthesis models from photopolymers

The essence of the technology is the use of special light-sensitive resins, which are cured selectively and in layers at points or places where a beam of light is supplied according to a given program. The methods of illumination of the layer are different (laser, ultraviolet lamp, visible light). There are two main technologies for creating models from photopolymer compositions: laser stereolithography or

SLA technology (from Steriolithography Laser Apparatus), or simply

stereolithography - curing the layer by means of a laser, and "instant" illumination of the layer - curing the photopolymer layer with an ultraviolet flash

lamps or spotlights. The first method involves the sequential "running" of the laser beam over the entire surface of the formed layer, where the "body" of the model is in the section. According to the second method, the curing of the entire layer

occurs immediately after or during its formation due to radiation from a controlled light source - visible or ultraviolet. The difference in the methods of forming layers also determines the difference in the speed of construction

models. Obviously, the growth rate of the second method is higher. However

stereolithography has been and remains the most accurate technology and is used where the requirements for surface cleanliness and model building accuracy are basic and decisive. However, exposure-controlled "flare" technologies, used for example by Objet Geometry and Envisiontec,

In many cases, they successfully compete with stereolithography, leaving behind a clear advantage in the speed of building and cost of models. A number of production

tasks can be equally successfully solved with the help of AF-machines of different levels. Thus, the rational choice of technology for obtaining models and, consequently, prototyping equipment is often not obvious and

should be carried out taking into account specific production conditions and real requirements for models. When the variety of tasks to be solved is

Obviously, it is advisable to have two machines: one for the manufacture of products with increased requirements, the second - for performing "routine" tasks and replicating models.

Laser stereolithography

3D Systems is a pioneer in the practical development of rapid prototyping technologies. In 1986, for the first time, she presented for commercial development the stereolithographic machine SLA-250 with the dimensions of the construction zone

250x250x250 mm. The basis of the SLA process is the ultraviolet laser.

(solid state or CO 2 ). The laser beam here is not a heat source, as in SLS technology, but a light source. The beam "shades" the current section of the CAD model and

solidifies a thin layer of liquid polymer in the places of its passage. Then the platform on which the construction is performed is immersed in the photopolymer bath by the magnitude of the construction step, and a new liquid layer is applied to the hardened layer, and the new contour is "processed" by the laser. When growing a model that has overhanging elements, simultaneously with the main body of the model (and

of the same material) supports are built in the form of thin columns, on which

the first layer of the overhanging element is laid when the turn of its construction comes. The process is repeated until the completion of the model building. Then the model is removed, the remains of the resin are washed off with acetone or alcohol, and the supports are removed. The surface quality of stereolithographic models is very high and often

the model does not require post-processing. If necessary, the surface finish can

be improved, the "fixed" photopolymer is well processed, and the surface of the model can be brought to a mirror. In some cases, if the angle between the model surface being built and the vertical is less than 30 degrees, the model can be built without supports. And thus it may be

built a model for which

there is no problem of removing supports from internal cavities, which in turn makes it possible to obtain models that, in principle, cannot be made by any of the

traditional methods

SLA - model and casting of the product "ball", silver (for example, jewelry

Stereolithography is widely used for:

- cultivation of foundry models;

Making master models (for the subsequent production of silicone molds, wax models and castings from polyurethane resins);

Creation of design models, layouts and functional prototypes;

- production of full-size and scale models for hydrodynamic,

aerodynamic, strength and other types of research.

But in the context of this work, we note the first two directions, which are important for the direct production of casting parts. For foundry purposes, the so-called Quick-Cast models are used, i.e., models for "quick casting".

This is the name of the models by which, by analogy with wax models, metal castings can be quickly obtained. In other words, these are models for casting on

the same technologies as wax and polystyrene models. But there is an important nuance. Quick-Cast models have a honeycomb structure of an array of walls: the outer and inner surfaces of the walls are made solid, and the wall body itself

formed as a set of honeycombs. This has a great advantage: firstly, the total mass of the model is significantly reduced by 70%, and, consequently, less

Quick-cast model, also with gating system and cylinder head casting (Al)

material will need to be burned out when preparing the mold for pouring metal. Secondly, during the burning process, any model material expands and exerts pressure on the mold walls, while a mold with thin-walled elements can

be destroyed. The honeycomb structure allows the model to “fold” inward during expansion, without straining or deforming the walls of the mold. This is the most important advantage of Quck-Cast technology.

Here we note that in some cases SLA-models, as well as SLS-

models can be used not as casting models, but as a tooling, molding model, for casting "into the ground". In this case, of course, casting slopes and radii must be provided in the design of the model for the model to exit the mold without

damage

last. However, this molding method is rarely used.

due to insufficient

strength SLA -

CAD-model, SLA-model and casting of the front cover of the internal combustion engine "into the ground" of the model.

In itself, obtaining an accurate high-quality model is a costly business, while the loss of a model, a form, and an olive becomes even more expensive and dramatic, especially when it comes to critical, complex details. Therefore, SLA-machines very quickly found their application in those nodes of technologies,

which were critical in terms of reliable production of complex casting products, primarily in aviation, military and space

industries, as well as in the automotive industry.

The second, not least, but in the order of mention, advantage is the accuracy of model building. The model is built under normal conditions with

room temperature. The thermal stress and strain factors mentioned above are absent. The very small diameter of the laser beam spot, 0.1-0.05 mm, allows you to clearly “work through” thin, filigree fragments of the model, which

made stereolithography a very popular technology in jewelry

industry.

In Russia, there is quite a lot of experience in applying Quck-Cast technology in the aviation industry (Salyut, Sukhoi, UMPO, Rybinsk Motors), in power engineering (TMZ - Tushino Machine-Building Plant),

some experience is also available in scientific organizations of the automotive profile. In particular, in NAMI, for the first time in Russia, castings were obtained using this technology.

such complex parts as the head and cylinder block of an automobile engine (see above). However, for other industries, this technology remains practically undeveloped.

SLA - model and casting of the impeller of the turbine unit (JSC "TMZ")

The main manufacturer of SLA machines is the American company 3D

Systems, which

produces a wide range of machines with

different zone sizes

construction, from 250x250x250 mm to

1500x570x500 mm. With technical

characteristics

cars can

familiarize

campaigns

www.3dsystems.com.

given

main

only one iPro 8000 machine each,

enough

iPro 8000 machine

and SLA models

used

industry

foundry production.

Main Parameters of iPro 8000 SLA Machine

Working size

Construction step, mm

Dimensional

models, kg

dimensions, mm

The cost, both initial and ownership, is perhaps the only

disadvantage of this technology. Due to the presence of a laser, these installations are relatively

roads require regular maintenance. Therefore, especially recently, when a lot of 3D printers have appeared, they are used for

construction of especially critical products with increased requirements for accuracy and surface finish, primarily for the manufacture of Quick-Cast - and master-

models. And for other purposes, for example, design layouts, cheaper technologies are used. The cost of consumables is relatively high - 200 ... 300 €, but comparable to the cost of model materials from other companies. Time

building a model depends on the load of the working platform, as well as on the step of building, but on average 4-7 mm per hour along the height of the model. The machine can build

models with a wall thickness of 0.1 ... 0.2 mm.

DLP Technology

The developer of this technology is the international company Envisiontec, which can be attributed to the newcomers to the AF market, it released its first cars in

2003 The Envisiontec Perfactory family uses the original

DLP - Digital Light Processing technology. Its essence lies in the formation

called "mask" of each current section of the model projected onto the working

Perfactory EXEDE

Envisiontec Models and castings of engine parts, aluminum

platform through a special system of very small mirrors using a spotlight with high light intensity. Shaping and illumination by visible light

each layer occurs relatively quickly - 3 ... 5 seconds. Thus, if in SLA-machines the “point” principle of illumination is used, then in Envisiontec machines it is “surface”, i.e., the entire surface of the layer is illuminated. This

the very high speed of building models is explained - an average of 25 mm per hour in height with a layer thickness of 0.05 mm. Support material is the same as

the main material is acrylic photopolymer.

Envisiontec models are used in the same way as SLA models - as master patterns and burnout casting patterns. The quality of the models is very high,

however, it is inferior to SLA models in terms of accuracy. This is mainly due to the use of not low-shrinkage epoxy photopolymers, as in 3D Systems machines, but acrylic,

having a significantly higher, almost an order of magnitude - 0.6%, shrinkage coefficient during polymerization. However, the advantage is a sufficiently high accuracy and surface finish, strength, ease of handling with very

moderate (compared to stereolithography) cost. The undoubted advantage of Envisiontec technology is the high speed of building

models and, consequently, the performance of the RP-machine.

Recently, NAMI has held

experiments that showed, in general, good burnout of models, low

ash content. Were received

quality castings of automotive parts both by vacuum casting of aluminum in plaster molds, and

atmospheric casting of iron

promising and effective for foundry purposes and not only for research and development. Time (taking into account the preparatory and final operations) of building the parts shown in the figure - an inlet pipe with a height

32 mm and 100 mm high receiver is 1.5 and 5 hours

respectively. Whereas on a comparable in size

SLA-machine Viper (3D Systems .) such models were built

would be at least 5.5 and 16 hours.

For industrial applications, machines of the Extrim and EXEDE series are of interest. These machines

positioned as AF - machines for industrial serial production of master models and models for metal casting on burnt models, as well as

high-performance machines for service bureaus specializing in the provision of services in the field of additive technologies. Extreme Machine has one digital spotlight with

resolution 1400x1050 pixels, EXEDE - two spotlights. Efficient working

the construction zone and the thickness of the construction layer are controlled by changing the lenses of the optical system.

A feature of the machines of the Extrim and EXEDE series is that, unlike other technologies, it uses not discrete, step-by-step, but continuous movement.