Precision investment casting at home: technology, advantages and disadvantages. Manufacturing of casting molds for aluminum casting

To produce small quantities of plastic blanks, vacuum casting into silicone molds is most often used. This method is quite economical (making a metal mold requires more time and Money). In addition, silicone molds are used repeatedly, and this also significantly reduces the cost of production.

Plastic molding

The essence of the casting technique is as follows. The molten material is located in the unit’s screw (special equipment for casting into silicone molds). Under the influence of the piston, the mass moves along the sprue channels, then fills the mold space. This way you can get a casting. When plastic is heated, the atoms that make it up begin to move chaotically and randomly. However, upon cooling, crystallization centers begin to form. Crystal growth occurs near the walls of the mold, and then the same process occurs inside the casting. At this stage it is very important to comply temperature regime, choose the right exposure time. Otherwise, casting plastics into silicone molds will be of poor quality, with visible traces of defects. But, first of all, the molds themselves must be made into which the mass for crystallization will be poured.

Technology for creating molds for casting

There are several ways to create silicone molds. The first one is a solid fill. This method is suitable for simple designs: reliefs, souvenirs, two-dimensional parts. The model is placed in formwork and filled with silicone. Split molds are made similarly to the previous ones and are used for more complex shapes. Two-part molds are produced in several stages. First, the first half of the workpiece is poured, after the silicone has hardened, the mold is turned over and the second part is made in the same way. Very important when this method on the basis to designate special locks (casting in silicone mold of this type should occur without its displacement). The “spread” form most accurately replicates all the details of the workpiece. A fairly viscous silicone is applied to the part using a brush. The process takes place in several stages, this is necessary to completely repeat all the small nuances of the product. At the same time, the form itself is quite thin - from 3 mm. To keep it in shape, final stage an outer hard shell is created.

Silicone for making molds

Vacuum casting in silicone molds involves the use of various materials to create matrices. One of them is Mold Star type silicone. It is used for continuous filling, it is quite durable and flexible. Hardening occurs when room temperature. For the “spread on” technique, the Rebount series is most often used. This silicone has a high viscosity, which can be controlled using a thickener. Casting in a silicone mold of this kind allows you to obtain a high-quality, durable matrix, and, accordingly, an ultra-precise part. There are also translucent silicones that are ideal for cut forms.

Casting materials

As a rule, polyurethane is used to make the parts themselves. The material has high impact strength, hardness, and elasticity. Polyurethane rubbers have higher tensile strength and tear strength. They are used in the manufacture of various tapes, cylinders, dies, gaskets, and bushings. It is also used for casting and is quite resistant to ultraviolet rays and retains its transparency even when stained. Area of ​​application: lenses for various tests, prototypes in medicine, production of souvenirs, etc. As a rule, casting in silicone mold involves the use of two-component mixtures, which directly include plastic and a catalyst.

Small-scale production of cast blanks is a technological process that allows you to produce a batch of exact copies of a part of any complexity. Very often, the technique is used to obtain prototypes that are tested before launching mass production, testing appearance, design.

Industrial plastic molding equipment in silicone molds provides the following: vacuum chamber(injection molding machine), heating cabinet, vacuum mixer (mixer). Silicone is first prepared in a vacuum chamber, where the process of degassing the material occurs. This is necessary to prevent the formation of bubbles on the mold. Once the casting mold has been made and preheated, the polyurethanes (or resins for the final part) are mixed directly. This process takes place in a vacuum chamber. The mixture is poured into the mold through the sprue. For final processing, it is necessary to place the workpiece in a special heating cabinet, where the final hardening of the product occurs at a temperature of 70°C.

Vacuum chamber. Main characteristics

As a rule, automatic casting into silicone molds is used on a production scale. The equipment, namely a vacuum chamber, allows you to control both the temperature and the casting speed. The operator does not require special skills and knowledge, since all control comes from operating system, which has both automatic and manual switching. It is also possible to edit a given program. Various modifications of cameras are capable of producing workpieces up to 5 kg (for example, camera ST-02). The installation is equipped with a lift for lifting silicone molds. It is worth noting that the ST-02 system allows the use of both small and fairly heavy matrices.

Another option is the MCP camera. This equipment for casting in silicone molds makes it possible to produce parts with thin walls and complex configurations. This process is carried out thanks to differential pressure. The resulting casting is then removed and subsequently hardened in air. For some, vacuum casting into silicone molds is completed in ovens, which ensure uniform heating of the air and, accordingly, the workpiece.

Final processing of the cast workpiece

After the plastic mass has completely hardened, it is carefully removed from the mold. The surface is mechanically processed, protrusions are removed and cleaned, and irregularities are ground. If necessary, the workpiece is coated with either paint or other protective material. Needs to be cleaned and silicone mold, remove any remaining plastic. Next, it is washed, preparing for subsequent use. It is worth noting that casting plastic into silicone molds involves repeated use of matrices (from 20 to 80 times).

The main advantages of the method

Small-scale production is developing dynamically, it allows you to qualitatively evaluate the sales market, test products, and create unique original works in small quantities. Silicone molds, which are used for plastic molding, make it possible to completely copy the texture, shape, and design of the workpiece. The part is easily released from the matrix, which can also be used repeatedly. Castings have minimal amount surface defects, optimal physical and mechanical properties. In addition, in some cases, even metal can be poured into silicone molds.

But the main advantage that casting in silicone molds has is the price. Providers of this service indicate that the final cost of the workpiece will depend on both the plastic material and the volumetric parameters of the part (for example, a workpiece measuring 10*10*10 cm can cost 1,500 rubles). Silicone itself can be purchased from 500 rubles per kilogram, plastic - from 700 rubles. The cost of metal forms is quite high, and sometimes their use is simply ineffective (if the circulation is several units). And silicone matrices are also suitable for home use, there is no need to buy expensive equipment. All you have to do is make a layout yourself, take into account the lifetime of polyurethanes (the period when they remain liquid and suitable for pouring), observe all technological nuances- and casting in silicone mold can be done even at home. According to calculations, the cost of one piece in this case is about 70-140 rubles.

The world around us consists of details, most of which we will not notice as long as they modestly perform their function. But as soon as one of them breaks or becomes unusable for another reason, its irreplaceability becomes obvious.

Some spare parts are not so easy to obtain and replace, for example, plastic parts k, the model of which has already been discontinued. It’s even worse if we are talking about a serial breakdown, and the company that previously produced the necessary spare parts has changed its profile. What to do? Set up own production missing parts! Thanks to this, you can solve your own problem and even make money.

Silicone casting allows you to make fragile plastic gears, fasteners and other similar little things at minimal cost and with virtually no defects. This material has a number of irreplaceable qualities, including flexibility, strength, and low adhesion (in the solid state) to other materials. It is so easy to use that casting into a silicone mold can be mastered even at home. However, to establish mass production, first of all, it is necessary to purchase special equipment for casting into silicone molds, as well as for the manufacture of these molds themselves.

Our company is ready to offer you the best price-quality ratio of silicone casting equipment with a guarantee and subsequent maintenance.

We help set up the casting of plastics into silicone molds

For thin-walled, fragile products that require special care, it is difficult to find anything other than silicone. The molds made from it are very flexible, therefore, when removing finished products, you can not be afraid of damaging the silicone patterns. Made from quality raw materials, they can be used dozens of times. In addition, casting plastics into silicone molds does not require much time.

In order to cope with this simple but responsible task, you need a little experience. And, of course, it will be required for casting plastics into silicone molds. You can purchase it from us, including the highest German quality, and at a very attractive and fair price.

We don’t just sell equipment, but also install it, teach how to use it, and then provide technical support. The price of our services is minimal, and the quality is trustworthy. We suggest you master profitable production together with us!

Molding plastic into silicone molds: work without errors

Like any other production, casting plastic into silicone to produce thin-walled parts and spare parts requires not only knowledge of technology. High-quality equipment that works exactly like a clock is one of the components of a successful and profitable business.

The operation of such units in high degree automated. So, the worker only places the custom-made mold into the chamber and connects the supply hoses liquid material- everything else is done by machines, including in silicone molds in a vacuum.

Only under vacuum conditions, that is, airless space, can products of the desired strength be obtained, since the content of air bubbles in the source material significantly increases their fragility.

In molding silicone, into which production raw materials are poured, airiness is also extremely undesirable, which deteriorates the quality of both the mold itself and the final product. However, the technology we offer eliminates the occurrence of such problems.

The ROSAL plant uses several technologies that have proven themselves in the production of aluminum alloys throughout Russia. They allow us to produce both single castings and set up serial production of aluminum parts to order.

Die casting of aluminum and aluminum alloys

The mold is a reusable form (up to 10,000 pours) and is ideal for organizing serial and large-scale production. Basic operations and processes: cleaning the chill mold from old cladding, heating it to 200-300°C, covering the working cavity with a new layer of cladding, installing rods, closing parts of the mold, pouring metal, cooling and removing the finished casting. General requirements to castings obtained in molds - this is a streamlined configuration without sharp corners, sharp transitions from one surface to another, without high ribs and protrusions, deep holes and pockets.

• Minimum permissible thickness walls of aluminum castings – 3 mm;
• The weight of produced aluminum castings is from 20 g to 50 kg;
• Surface roughness of castings according to GOST 2789-73 Ra = 4 - 20 microns;
• Accuracy class of the resulting aluminum castings according to GOST R 53464-2009: 6-10.

Die casting of aluminum and aluminum alloys

Injection molding produces thin-walled castings various shapes and configurations with high-quality surface relief that practically does not require mechanical processing. The high rate of heat transfer from the casting to the mold necessitates rapid filling (less than 0.1 s.) of the latter. Such filling is provided by special casting machines A711A08, which are equipped at ROSAL production. In these machines, molten aluminum poured into the pressing chamber is pressed into a mold under high pressure (30...100 mn) and at high speed (up to 100 m/s). High intake flow rates contribute to high-quality design casting relief.

• The minimum permissible wall thickness of aluminum castings is 0.8-1.2 mm;
• The weight of produced aluminum castings is from 5 g to 12 kg;
• Surface roughness of castings according to GOST 2789-73 Ra = 3.2-10 microns;
• Accuracy class of the resulting aluminum castings according to GOST R 53464-2009: 3-8.

In our production we use various aluminum alloys, each of which has its own special characteristics and requires compliance certain rules casting Aluminum-based alloys are complex systems of two or more metals. Aluminum alloys may contain silicon, copper, magnesium, and zinc. Below are examples of aluminum alloys that can be used to produce various parts: Alloy – aluminum-magnesium system: AMg6l, AMg7 (AL29); Alloy – aluminum-silicon-magnesium system: AK7, AK12, AK7ch (AL9), AK8l, AK9ch; Alloy – aluminum-copper-magnesium system: D16 (duralumin); Alloy – aluminum-silicon-copper system: AK5M, AK6M2; Alloy – aluminum-copper system: AM5 (AL5); It is possible to manufacture products from aluminum alloys proposed by the customer. SolidWorks and Pro/ENGINEER programs are used to simulate foundry processes. Castings are put into production only after receiving simulation results confirming that the developed casting technology guarantees the absence of any casting defects. Used for casting aluminum alloys in pigs with a guaranteed chemical composition GOST 11069-2001, GOST 1583-93; During the melting of aluminum alloys, they are cleaned with special fluxes, refined with special additives, and purged with an inert gas. The main processes of the casting production cycle are automated, which eliminates manual production errors.

Aluminum is a metal that is widely used in industry and everyday life.

It is used to produce not only aircraft and ship parts, but also dishes and other utensils. Therefore, there is often a need to independently manufacture aluminum parts that have failed.

Its ability to produce cast products in artisanal conditions allows it to be produced at relatively low temperatures. In order to independently produce cast aluminum products, you need to know the behavior of this metal at high temperatures and its physical and chemical properties.

The melting point of aluminum depends on the purity of the metal and is approximately 660 °C. Its boiling point is 2500 °C.

Aluminum is distinguished by its lightness and ductility, so it bends well and can be processed.

This metal is an excellent conductor of heat and actively enters into a chemical reaction at high temperatures with atmospheric oxygen, forming an oxide film on the surface. It protects aluminum from further oxidation, but when scrap melts, it significantly affects the composition of the alloy. During the metal smelting process, the structure of aluminum changes.

If it cools suddenly, it may cause internal stresses and shrinkage of the resulting alloy. This must be taken into account when working with aluminum at home.

Technologies for home aluminum casting and necessary equipment

The principle of casting aluminum at home should be based on the technology for its production in production, adjusted for conditions that can be used at home.

Aluminum products are produced by casting in several ways. In domestic conditions, the most common and in a convenient way is the technology of casting molten aluminum into specially manufactured molds.

Therefore, to carry out the process, two things must be ensured:

• build a furnace for melting aluminum scrap;
• create the desired shape to produce a cast alloy or a separate part.

The casting process must include several stages:

1. Preparation of aluminum scrap, including cleaning from dirt, impurities and various fillers, as well as grinding it to a small size.
2. Carrying out the smelting process in the planned way. When the metal is completely melted, slag formations must be removed from its surface.
3. Filling the prepared mold with liquid aluminum melt. After solidification, the ingot is freed from the molding mass.

Let's consider how to melt aluminum at home, what designs of furnaces for melting metal can be used, as well as options self-made forms.

Homemade furnaces and methods for melting aluminum

In order to melt aluminum, you need to heat it to a temperature close to 660 °C. On open flame a fire cannot reach such a temperature. Therefore it is necessary closed space, which a homemade stove can provide. It can be heated by burning coal and wood or using natural gas.

You can also use an electric muffle furnace if you have one on the farm.

For a self-made stove, you need to ensure forced ventilation to maintain the combustion process.

1. The simplest version of a homemade fireplace can be made from old pots.

Its design is as follows:

• As a frame, use a steel container, for example, an old pan, on the side of which you need to make a hole to supply air through a connected metal pipe.
• Air can be forced through the hose using a vacuum cleaner.
• Coal is placed inside the device.
• Then the coal is set on fire and air is supplied to keep the fire from going out.
• A container for melting aluminum is first placed inside an improvised furnace structure and lined with coal on its sides. When it burns, uniform heat distribution is ensured.
• To prevent heat from being lost to the surrounding air, the top of the “pan” stove should be loosely covered with a lid, leaving a small gap for the smoke to escape.

An ideal design would be a firebox with an oval arch made from a masonry mixture used for heat-resistant bricks. You can use it as a frame to create an oval arch. flower pot the right size.

After the mixture dries, a good firebox is obtained that can withstand several heats.

2. The second version of the furnace involves using the flame of a household gas burner to heat aluminum.

It can only be used for piece products made of aluminum weighing no more than 150 grams. An imitation oven is created by using two containers inserted into each other with a small gap. It could be ordinary cans from canned food.

The outer jar should be larger. A hole with a diameter of about 4 cm is made in it to ensure the supply of flame to the inner can.

The flame jet should be directed towards the opening of the can. Only the inner container is heated directly, and the outer one serves as a shell that retains heat. The top of the structure must be covered with a simulated lid, leaving a gap for the removal of combustion products.

This design is disposable and can only be used for one heat, since the tin is thin and can quickly burn out.

Methods for creating a mold for casting aluminum

One of the main tasks of home aluminum smelting is preparing the mold into which the molten metal is poured. Exist different variants pouring aluminum melt. The main ones are open and closed method casting

Open casting

The simplest is to pour the liquid metal into a handy form, such as a metal mug or can.

After the alloy has hardened, the blank is removed from the container. To facilitate this process, tapping is performed on the form that has not completely cooled down.

If you do not need to give the casting a clear shape, you can simply pour the liquid melt onto a prepared combustion-resistant surface.

Closed form

If it is necessary to obtain a complex casting, a mold is first made for it that meets all the parameters of the part. To ensure strict compliance of the product with the specified parameters, it is made from composite molding parts.

Materials for casting molds

With the open pouring method, the simplest material that is always at hand is often used, this is silica. First, the earth is laid with layer-by-layer compaction. A casting model is placed between the layers, which, after careful compaction, leaves an imprint in the silica. This mold is carefully removed and aluminum is poured in its place.

Some craftsmen use molds when preparing the base river sand with addition liquid glass. A mixture of cement and brake fluid is also sometimes used.

Plaster molds

When making a model of complex shape, gypsum is often used, which can mainly serve for one-time process casting When casting aluminum into a plaster mold, paraffin or foam plastic is used as models.

The wax model of the product is filled with plaster and, after drying it, high temperature melts and drains through a special hole.

If the model is made from foam plastic, it is poured gypsum mixture and leave in it until the mold completely hardens. Hot aluminum melt is poured directly onto the foam. Due to the high temperature of the metal, the foam melts and evaporates, and its place is taken by an aluminum melt, taking the shape specified by the foam.

When using polystyrene foam as a model, work must be carried out in an open space or the room must be well ventilated, since the combustion products of polystyrene foam are harmful to humans.

Lost wax casting (LMC) is an industrial process also called wax casting or frangible mold casting. The mold is destroyed when the product is removed. Lost wax models are widely used in both mechanical engineering and art casting.

Application area

Features of the technical process make it possible to use the LVM method in a wide range: from large enterprises to small workshops. Lost wax casting is also possible at home, for personal and commercial purposes to produce detailed figurines, souvenirs, toys, structural parts, and jewelry. Almost all metals can be used as filler:

• steels (alloy and carbon);
• non-ferrous alloys;
• cast iron;
• alloys that cannot be machined.

However, the technology is universal - it is quite possible to produce relatively large structures of complex shapes. To facilitate the technical process, use specialized equipment for investment casting and 3D modeling using specialized programs.

Ceramic casting

Depending on the requirements for products, various, most suitable technologies. Precision investment casting (PLMC) allows you to produce the most complex casting configurations with high precision, with minimum thickness walls and surface roughness. For TLVM, the wax model is immersed in a ceramic-based liquid mixture. The ceramic mixture dries and forms the shell of the casting mold. This process is repeated until the desired thickness is achieved. The wax is then removed in an autoclave. However, this method is characterized by high cost, duration technological process, highlighting harmful substances in the production area and pollution environment remains of ceramic molds.

Casting into CTS molds

In many cases, when making crafts at home, castings of complex configurations are not required to have low roughness, and for a number of artistic castings, a surface with uniform roughness is not only acceptable, but is design solution. In this case, it is advisable to use lost wax casting.

Technology developed for products that do not require smooth surfaces, is quite simple. Such a surface can be obtained by casting into molds from cold-hardening mixtures (CMC). This process is much simpler, cheaper and more environmentally friendly.

However this method Lost wax casting does not allow the production of complex castings using lost wax patterns. This is explained by the fact that when melting figures Substantial part The model composition remains in the mold cavity and can only be removed by calcination. Calcination, that is, heating to the ignition temperature, of the model composition leads to the destruction of the CTS resin binder. When metal is poured into a mold with the remains of the model composition, they burn, leading to metal emissions from the mold.

Using liquid glass mixtures

Lost wax casting into liquid-glass mixtures with a liquid catalyst (LCS LC) allows the disadvantages of CTS technology in the manufacture of certain types of castings to be mitigated. These mixtures containing liquid glass in an amount of 3-3.5% and a catalyst of about 0.3% by weight of the sand base began to be used abroad in the early 80s and are still used today. According to research, these mixtures, unlike the first generation of LSC, are distinguished by their environmental friendliness, good knock-out properties and insignificant burns on the castings.

Lost wax casting: technology

The LVM process includes the operations of preparing model compositions, making models of castings and gating systems, finishing and controlling the dimensions of models, and further assembly into blocks. Models, as a rule, are made from materials that are multi-component compositions, combinations of waxes (paraffin-stearin mixture, natural hard waxes, etc.).

In the manufacture of model compositions, up to 90% of the waste collected when melting wax models from molds is used. The return of the model composition should not only be refreshed, but also periodically regenerated.

The production of models consists of six stages:

• preparation of the mold;
• introducing a model composition into its cavity;
• holding the model until hardening;
• disassembling the mold and extracting the model;
• cooling it to room temperature.

Features of the technical process

The essence of the LVM is that a silicone or wax model is melted from a workpiece by heating, and the free space is filled with metal (alloy). The technical process has a number of features:

• In the manufacture of molding sand, suspensions consisting of refractory fine-grained materials held together by a binder solution are widely used.
• For pouring metals (alloys), one-piece molds are used, obtained by applying a fire-resistant coating to the model, drying it, then heating the model and calcining the mold.
• For castings, disposable models are used as they are destroyed during the mold making process.
• Thanks to fine-grained refractory dust-like materials, a sufficiently high quality of the surface of the castings is ensured.

Advantages of LVM

The advantages of lost wax casting are obvious:

• Versatility. You can use any metals and alloys for casting products.
• Obtaining configurations of any complexity.
• High surface cleanliness and manufacturing precision. This makes it possible to reduce subsequent expensive metalworking by 80-100%.

Disadvantages of LVM

Despite the convenience, versatility and decent quality of products, it is not always advisable to use lost wax casting. The disadvantages are mainly due to the following factors:

• The duration and complexity of the casting production process.
• Inflated cost of molding material.
• Great burden on the environment.

An example of making a product at home: preparatory stage

Lost wax casting at home does not require in-depth knowledge of metallurgy. First, let's prepare a model that we want to replicate in metal. The finished product will serve as a mock-up. You can also make a figurine yourself from clay, sculptural plasticine, wood, plastic and other dense plastic materials.

We install the model inside a collapsible container fastened with clamps or a casing. It is convenient to use a transparent plastic box or a special mold. To fill the mold, we will use silicone: it will provide excellent detail, penetrating into the smallest cracks, holes, depressions and forming a very smooth surface.

Second stage: filling with silicone

If precision investment casting is required, to make a mold without liquid rubber not enough. Silicone is prepared according to the instructions by mixing different components (usually two) and then heating. To remove the smallest air bubbles, it is advisable to place a container with liquid rubber in a special portable vacuum apparatus for 3-4 minutes.

We pour the finished liquid rubber into the container with the model and re-vacuum it. Subsequent hardening of the silicone will take time (according to the instructions). The translucent materials used (containers and silicone itself) allow you to observe with your own eyes the process of forming the mold.

We remove the set rubber with the model inside from the container. To do this, release the clamps (casing) and separate the two halves of the box - the silicone easily comes away from the smooth walls. It will take 40-60 minutes for the liquid rubber to completely harden.

Third stage: making a wax model

Lost wax casting involves melting out fusible material and replacing the resulting space with molten metal. Since wax melts easily, we use it. That is, the next task is to make a wax copy of the originally used model. This required the creation of a rubber mold.

Carefully cut the silicone blank lengthwise and take out the model. There is little secret: in order to accurately connect the shape later, it is recommended to make the cut not smooth, but zigzag. The applied parts of the mold will not move along the plane.

We fill the resulting space in the silicone mold with liquid wax. If the product is being prepared for yourself and does not require high precision in pairing the parts, you can pour wax separately into each half, and then, after hardening, connect the two parts. If it is necessary to accurately replicate the silhouette of the model, the rubber halves are connected, secured, and hot wax is pumped into the resulting void using an injector. When it fills the entire space and hardens, we disassemble the silicone mold, take out the wax model and correct the flaws. It will serve as a prototype for the finished metal product.

Fourth stage: molding

Now you need to form from the outer surface wax figure a heat-resistant durable layer, which, after melting the wax, will become a mold for a metal alloy. We will choose the lost wax casting method using a cristobalite mixture (quartz modification).

We form the model in a metal cylindrical flask (a device that holds the molding mixture as it is compacted). We install the soldered model with the gating system into the flask and fill it with a mixture based on cristobalite. To force out air pockets, we place it in a vibrating vacuum apparatus.

Final stage

When the mixture is compacted, all that remains is to melt the wax and pour metal into the free space. The process of investment casting at home is best done using alloys that melt at relatively low temperatures. Casting silumin (silicon + aluminum) is perfect. The material is wear-resistant and hard, but is fragile.

After pouring the molten silumin, wait for it to harden. Then we remove the product from the trench, remove the sprue and clean it of any remaining molding sand. Before us is an almost finished part (toy, souvenir). Additionally, it can be sanded and polished. If foundry residues are firmly stuck in the grooves, they must be removed with a drill or other tool.

Lost wax casting: production

LVM is carried out a little differently for the manufacture of critical parts that have a complex shape and (or) thin walls. Casting a finished metal product can take from a week to a month.

The first step is to fill the mold with wax. For this purpose, enterprises often use an aluminum mold (analogous to the silicone mold discussed above) - a cavity shaped like a part. The output is a wax model slightly large sizes than the final part.

The model will then serve as the basis for a ceramic mold. It should also be slightly larger than the final part, since the metal will shrink after cooling. Then, using a hot soldering iron, a special gating system (also made of wax) is soldered to the wax model, through which hot metal will flow into the mold cavities.

Making ceramic mold

Next, the wax structure is dipped into liquid ceramic mortar, called slip. This is done manually in order to avoid defects in the casting. To ensure the strength of the slip, the ceramic layer is strengthened by spraying fine zirconium sand. Only after this is the workpiece “trusted” to the automation: special mechanisms continue step by step process spraying coarser sand. Work continues until the ceramic-sand durable layer reaches the specified thickness (usually 7 mm). In automated production this takes 5 days.

Casting

Now the workpiece is ready for melting the wax from the mold. It is placed for 10 minutes in an autoclave filled with hot steam. The wax melts and completely flows out of the shell. The result is a ceramic mold that completely matches the shape of the part.

When the ceramic-sand mold has hardened, metal casting is carried out using lost wax models. The mold is first heated for 2-3 hours in an oven so that it does not crack when pouring metals (alloys) heated to 1200˚C.

Molten metal enters the mold cavity, which is then left to cool and harden gradually at room temperature. Cooling of aluminum and its alloys requires 2 hours, for steels (cast iron) - 4-5 hours.

Finishing

Actually, lost wax casting ends here. After the metal hardens, the workpiece is placed in a special vibrating machine. Due to gentle vibration, the ceramic base cracks and crumbles, but the metal product does not change its shape. Subsequently, the final processing of the metal workpiece takes place. First, the metal filling system is sawed off, and the place of its contact with the main part is carefully ground.

Finally, inspectors check that the dimensions of the product correspond to those specified in the drawing. Aluminum parts are measured cold (at room temperature), steel parts are preheated in an oven. Specialists use it for control and measurement work various instruments: from simple patterns to complex electronic and optical systems. If a discrepancy with the parameters is detected, the part is either sent for rework (reparable defect) or for remelting (irremovable defect).

Gating system

The design of the gating-feeding system plays a leading role in the LVM. This is due to the fact that it performs three functions:

• In the manufacture of mold shells and model blocks, gating systems are load-bearing structures that support the shell and models.
• Through the sprue channel system liquid metal when pouring, it is brought to the casting.
• During solidification, the system performs the function of profit (a feeding element that compensates for metal shrinkage).

Shell casting

In the LVM process, the key is to create the shell layers of the form. The shell manufacturing process is as follows. A continuous thin film of suspension is applied to the surface of the model block, most often by dipping, which is then sprinkled with sand. The suspension, adhering to the surface of the model, accurately reproduces its shape, and the sprinkling sand is introduced into the suspension, wetted by it and fixes the composition in the form of a thin facing (first or working) layer. The non-working rough surface of the shell formed by quartz sand promotes good adhesion of subsequent layers of suspension to the previous ones.

Important indicators that determine the strength of the form are the viscosity and fluidity of the suspension. Viscosity can be adjusted by adding a certain amount of filler (fullness). At the same time, with an increase in the filling of the composition, the thickness of the layers of the binding solution between the powder particles decreases, shrinkage and the negative effects caused by it decrease, and the strength properties of the mold shell increase.

Materials used

Materials for the manufacture of the shell are divided into the following groups: base materials, binders, solvents and additives. The first include dust, used for preparing suspensions, and sand, intended for sprinkling it. They are quartz, chamotte, zircon, magnesite, high-alumina chamotte, electrocorundum, chromium magnesite and others. Quartz is widely used. Some shell base materials are obtained in a ready-to-use form, while others are pre-dried, calcined, ground, and sifted. Significant disadvantage quartz are its polymorphic transformations, which occur with changes in temperature and are accompanied by a sharp change in volume, ultimately leading to cracking and destruction of the shell.

Smooth heating of the molds in order to reduce the likelihood of cracking, which is carried out in the supporting filler, increases the duration of the technological process and additional energy costs. One of the options for reducing cracking during calcination is to replace pulverized quartz sand as a filler with dispersed quartz sand polyfractional composition. At the same time, the rheological properties of the suspension are improved, the crack resistance of the molds is increased, and defects due to blockages and breakdown of shells are reduced.

Conclusion

The LVM method has become widespread. It is used to produce complex parts in mechanical engineering, in the production of weapons, plumbing, and souvenirs. To make jewelry from precious metals, lost wax jewelry casting is used.