Sheet metal stamping technology. Equipment. Presses for cold and hot stamping of sheet metal CNC machine for making molds

The production of parts using stamping occupies a leading place in the technology of metal forming and is used in various industries.

Of particular importance is the stamping of metal products from sheet metal. It is based on the plastic deformation of the metal without heating it with the help of special stamps. This method of plastic deformation of parts is widely used for the manufacture of parts of different sizes and complex shapes with high accuracy, which cannot be done using other processing methods.

They are used to assemble large-sized products in the engineering industry, in the automotive and shipbuilding industries, as well as in the instrument-making and household industries, where various miniature parts are often required.

Stamping is the process of giving parts the desired shape and obtaining a certain size by documents by mechanically acting on them using pressure. The main direction of stamping is the production of parts from blanks, which are used as sheet metal. Under the action of a compressive force, the workpiece undergoes deformation and acquires the desired configuration.

Distinguish between hot forging with heating of the workpiece and cold forging without preheating it. Stamping of sheet metal parts is carried out without their preheating.

Pressure deformation with billet heating is used in the manufacture of metal parts that do not have sufficient ductility, and is mainly used in the production of small batches of bulk products from a metal sheet having a thickness of 5 millimeters.

The technological process of hot metal stamping largely coincides with the sequence of operations of cold workpieces. The difference lies in the preliminary heating of the initial workpieces in furnaces to a temperature that ensures the plasticity of the metal. This takes into account the degree of warping of the part during cooling, as well as its tightening during deformation processing, which affects its size. To avoid deviations from the required dimensions for parts obtained by hot stamping, large tolerances are made.

In the production of stamped sheet metal parts, the cold stamping method is mainly used.

Cold stamping sheet metal

The technology of cold deformation of sheet metal using stamps involves changing the shape and dimensions of the product while maintaining its original thickness.

As a material for producing cold stamped products, strips, sheets or thin strips are used mainly from low-carbon and ductile steels, as well as copper, brass (containing over 60% copper), aluminum, magnesium, titanium and other ductile alloys. The use of alloys with good ductility for stamping is due to the fact that they are easily amenable to deformation change.

To carry out cold stamping of sheet metal, various operations are used, which depend on the task of achieving a certain shape of the workpiece. They are divided into separating and form-changing effects.

1. During separating deformations, the workpiece material is partially separated along a given contour. The separation is carried out by shifting a part of the metal in relation to the main workpiece. Such operations are cutting, punching and others.

Let us consider how some separation operations are carried out.

cutting

When cutting, a certain part is separated from the part by cutting it along a curly or straight line. Such a separating operation is performed using a press made in the form of a different design.

Such an operation is intended mainly to prepare the workpiece for other processing methods.

Punching

An operation called punching is used to create holes of various shapes in the workpiece. Part of the metal during punching is completely removed from the workpiece, and its weight is reduced.

The figure shows a diagram of the punching process.

felling

With the help of the process of punching a metal part, a finished product with a closed contour is given.

The figure shows a scheme for manufacturing a part using punching.

2. Form-forming deformations include a change in the shape and dimensions of the product when its individual areas are moved, which does not lead to its general destruction. These include drawing, bending, embossing, twisting, crimping and other operations.

Consider some types of operations that do not lead to the physical destruction of the form.

Hood

With the help of an extract from sheet flat blanks, hollow volumetric products are obtained. For example, parts having the shape of a hemisphere, cylinder, cone, cube and other types are made in this way. The figure shows different versions of the hood.

bending

With the help of the operation, the product is given a given shape of its bend. Depending on the type of bending, this operation makes it possible to obtain curved products of various configurations. Some of them are shown in the figure.

relief molding

This type of operation implies a modification of the local parts of the product, its external configuration remains unchanged. The figure shows a diagram of some molding operations:

It is also possible to use combined operations, including the separation and shaping of one part.

The technological process of cold stamping consists of stages that are associated with the nature of the deformation operation and depend on the type of stamping equipment used.

The development of the technical process is carried out in the following sequence:

The structure of the main operations is indicated, including their nature, quantity and sequence of execution.
The calculation of the initial, intermediate and finished dimensions of the part, as well as the necessary deformation forces to achieve the desired result, is performed.
Documentation of the technological process is carried out.

Additional operations can be introduced into the technological process, with the help of which the workpiece is brought to a form convenient for processing. These include cleaning, straightening sheets, lubricating and other operations.

Metal stamping press

All cold stamping operations can be carried out with special equipment, the main of which is a stamping press. Its device can be based on mechanics, or using hydraulics.

Mechanical types include:

eccentric presses;
presses using a crank mechanism.

A crank-type punching press is used to carry out punching, punching and drawing operations.

The device and principle of operation of the crank type press

Any press designed for stamping products includes the main components, which include: a mechanism that drives it and a device that performs direct stamping.

The operating mechanism is a crank shaft, which is driven by an electric drive. To do this, the electric motor, during the rotation of the flywheel, transmits rotation to the crank mechanism using a gear train.

Performing reciprocating actions, the crank slider activates the stamping device, which, with a pressure force, performs plastic deformation.

The main parts of such a press are made of high-strength steels and are additionally reinforced in order to give the necessary rigidity.

Hydraulic press device

The hydraulic type metal stamping press is used to create three-dimensional shapes by punching metal.

The principle of operation of such a mechanism is based on the pressure of a liquid placed in two tanks, which are equipped with pistons. The tanks are connected by a pipeline. As a result of the pressure in the liquid that occurs at the moment it is injected into the cylinder from another reservoir, it is transferred to the slider and sets it in motion. When moving, the slider pushes the workpiece with great effort.

Production of dies for cold metal stamping

The working device of any press machine is the stamp itself. It includes two working parts, called a matrix and a punch. In the process of work, only the upper part of the stamp is movable - a punch fixed on a slider. The matrix is located below and remains motionless.

The deformation of the sheet is carried out while pressing the punch to the matrix with the workpiece located on it.

The development of drawings and the manufacture of dies for the press are subject to increased requirements, since the correctness of the formation of the product depends on their accuracy.

Such work is carried out in stages in the following sequence:

a sketch of the stamp is drawn up;
with the help of a computer scheme of the stamp, compiled according to a special program, a check is made of the rational cutting of the material;

Request a call back:

A mold is a complex device designed to produce products of various configurations from rubber, metals, plastics and many other materials using the action of pressure, which is created on special injection molding machines. Molds are typical for both mass and serial production. They are used in injection molding of metals and polymeric materials, in investment casting, as well as in the pressing of polymeric materials.

The process of manufacturing molds is laborious, because it has a rather complex specificity and requires significant material costs. Therefore, it is extremely important to choose reliable performers who successfully carry out their production in order to obtain high-quality and durable products.

Production of molds at Spetsstanmash Plant LLC

Specialists of Spetsstanmash Plant LLC have impressive experience in the production of technological equipment for casting products from various materials.

At our plant, molds are designed and manufactured, while work of any complexity is carried out in a timely manner by highly qualified professionals. For production, we use exclusively modern, multifunctional and state-of-the-art machines that allow us to produce forming parts as quickly and efficiently as possible. Our company is ready to provide guarantees for the long-term operation of molds and the accuracy of products cast with their help.

The minimum production time is 10 working days and depends on the characteristics of a particular product, the availability of a suitable blank and other factors.

Mold making steps

At Zavod Spetsstanmash LLC, the production of molds takes place in several stages:

Transfer of a drawing or sample model, according to which your product will be manufactured;
Preparation of technical specifications for the mold, taking into account all your requirements;
Creation of a drawing for a mold;
Mold making process;
Sample production;
Elimination of comments, if any, and casting of a control batch of the product;
Delivery of the device by a transport company to any point in Russia.

If you need to order the production of molds of varying complexity in compliance with impeccable quality and at the best price, then contact us at the contacts indicated on the website.

In the shortest possible time you will be able to get those products that meet all your requirements and needs. We work with individuals and legal entities.

Stamping, for which a metal press is used, is one of the most common technological operations for processing this material. The essence of this procedure is to give a workpiece made of metal the necessary shape, for which plastic deformation is used, extruding a certain relief, patterns or punching holes. Presses for metal processing, depending on the list of tasks for which they are intended, differ from each other both in their technical parameters and in their design.

Types of stamping technological operations and equipment

Stamping as a method of processing metal blanks can be:

hot;
cold.

The first implies that the metal is processed in a heated state. The big advantage of hot stamping is that when it is performed, the characteristics of the workpiece are improved (in particular, the metal structure becomes denser and more uniform). Meanwhile, no scale layer is created on the surface of metal blanks processed using the technology, while the dimensions of finished products are more accurate, and their surface is smoother.

According to the type of workpiece subjected to stamping, such a technological operation can be sheet or volumetric. Stamping of the first type is used for processing sheet metal blanks; this technology is used to produce:

dishes;
jewelry;
weapon;
medical equipment and instruments;
parts of clocks, household, climatic equipment and electrical equipment;
parts for a complete set of automotive equipment;
details of machine tools and other engineering products.

Finished metal products obtained by technology do not need further development. The formation of their geometric parameters during forging occurs in special forms in which hot or cold metal is subjected to punching.

The press machine is usually used for:

production of metal blanks by forging;
pressing in and pressing out shafts, bearings and gears;
performing stamping of sheet and volumetric type.

According to the principle of operation, pressing machines can be of a mechanical or hydraulic type, perform metal processing by static or impact methods.

Pressing equipment of a mechanical type in its design can be:

eccentric;
crank.

Crank machines are used for both cold and hot. This stamping equipment is also used to perform such technological operations as drawing, punching and punching. The hydraulic press is used for stamping and forging technological operations with bulk metal blanks.

According to their functionality, pressing machines are divided into the following types:

universal;
special;
specialized.

The universal pressing machine has the widest functionality; such equipment can be used to perform almost any forging operation. Specialized dies or presses are used to implement one technological process. The minimum functionality is possessed by special presses that are used for stamping products of the same type, while their work is based on one technology.

The design and principle of operation of the press equipment

The design of any equipment for stamping consists of the following elements:

drive motor;
movement transmission mechanism;
actuating mechanism.

Depending on how the drive motor of the press is connected to its actuator, machine tools with communication are distinguished:

mechanical;
non-mechanical, carried out by liquid, gas or steam.

Traverses, a slider, rolls, rollers and women can act as an actuator, which is equipped with equipment for stamping.

Crank type presses

The main structural element of these presses is the crank mechanism, which converts the rotational movement received from the drive into the reciprocating movement of the slider. The actuator, which is equipped with a stamping press of this type, is connected directly to the slider, capable of developing a force of up to 100 tons. The movement of the slider in such presses is carried out with the same frequency.

Crank type presses can be single type, double or triple acting. Using such machines, you can perform the following technological operations:

stamping using matrices of open and closed type;
sheet metal cutting;
firmware;
the formation of the finished product by extrusion;
combined processing.

In cases where more powerful equipment is required to form a finished product from a metal billet, hydraulic-type machines are used.

Hydraulic presses

Using a hydraulic press, it is possible to press both larger and thicker-walled metal parts. Such equipment for sheet stamping, forging, forging, bending and other technological operations, depending on the specific model, can develop forces from 150 to 2000 tons or even more.

The main structural elements that any is equipped with are two cylinders of different diameters that are filled with a working fluid and communicate with each other. In each of these hydraulic cylinders, a piston is installed that creates pressure of the working fluid or moves under its influence. It is the movement of the pistons in the hydraulic cylinders that ensures the movement of the actuator of the equipment. The amount of force that such a stamping press can create is determined by the difference in the diameters of its hydraulic cylinders.

Radial forging presses

A radial forging machine is a molding press on which preheated metal ingots are turned into finished products of a cylindrical configuration. The design of this type of press is:

induction furnace, in which the workpiece is preheated;
a conveyor for feeding the workpiece into the processing zone;
gripping mechanisms, with the help of which the workpiece made of metal, constantly rotating, passes through the forging zone;
worm gear connected to the electric motor and responsible for the operation of the gripping mechanisms;
four shafts with eccentric axle boxes transmitting movement to a connecting rod with a striker, between which a slider is fixed (the shafts themselves receive rotation from the drive motor by means of a V-belt transmission);
copy drums responsible for the synchronous approach of the strikers and the subsequent movement of the workpiece;
spring clutch providing braking of the part at the moment of its processing by strikers.

Press forms

TO category:

Production of precision castings

Press forms

The main prerequisite for obtaining an accurate casting is an accurate model with a flawless surface, with precisely maintained dimensions, which meets all the technological features that appear in the production of castings. For the manufacture of such a model, a precisely made mold is used. Often, when choosing an investment casting method, the cost of the master model and mold is decisive. Sometimes it may even be that the cost of making a master model and a mold will be higher than the savings obtained by switching the part from machining to casting.

Molds for casting investment models must meet the following basic requirements: ensure the production of high-quality models (with a given accuracy and surface finish, without defects); minimum cooling time of the model.

According to the intended purpose and use of the mold, they are divided into:
a) for the manufacture of actual models;
b) for the manufacture of auxiliary technological parts (risers, collectors, profits, etc.).

According to the design of the mold, they are classified into single-cavity (single-seat); multi-cavity, not connected by a gating system; multi-socket with replaceable inserts for assembly in conductors.

According to the degree of mechanization, molds are simple, with the removal of models (manually); simple, with manual removal of models using a push system; complex, with removable rods. Molds are assembled with cores and mold parts and disassembled manually or with the help of mechanisms; fully mechanized or automated.

According to the manufacturing methods, molds are classified into mechanically processed; cast from fusible alloys; cast zinc alloys; molded plastics; cast from plaster; cast or pressed from rubber (rubber); processed by electroforming or metallization methods.

The cost of a mold mainly depends on its complexity; which determines the complexity of manufacturing and the material of the mold. These factors are decided by the technologist and designer. When designing a mold, the technologist and designer are guided by the requirements for castings and the number of castings in a series.

Rice. 1. Mold made by machining

Molds made by machining (Fig. 1) are widely used for the manufacture of investment models. The entire mold is made on machining machines without the use of a master model. The design of molds for simple castings (without internal cavities) is relatively simple, as is its manufacture. It is much more difficult and expensive to manufacture molds for castings with internal cavities or with a figured parting plane. Models with internal cavities or with profile joints (the axes of which are not parallel to the direction of opening of the mold or run outside the plane of the parting) must have retractable cores, the exact manufacture and fitting of which in the mold is very laborious. These molds are made from steel and aluminum alloys. Aluminum alloys are preferred as they have high thermal conductivity. In cast billets made of aluminum alloys, pores and ripples are often found, which degrade the quality of the surface of the models.

The molds are made according to the 6th IT accuracy class with a surface roughness of 0.4-0.8 µm according to Hsk. Model sites should be equipped with modern precision metal-cutting machines. Models made in such molds are distinguished by high accuracy, and the molds themselves are durable.

Molds from low-melting alloys (Fig. 2) are made by pouring a low-melting alloy onto a metal master model installed in a steel frame. Each half of the mold is filled with different alloys, differing from each other in melting point. With a flat part, the model is molded in a steel shell with a sand mixture consisting of quartz sand with 3% bentonite; humidity of the mixture 3.5-5.0%, green strength 0.8-1.0 N/cm2.

With a curved connector, the model is fixed in a false gypsum slab. Before pouring with plaster, the surface of the model is lubricated with oil. After the plaster has set, the connector is cleaned for easy removal of the model. Then, a second shell is installed on the shell with a false plate and a model, and the assembled set is slowly heated to the temperature of pouring the fusible alloy. For casting the first metal half, an alloy with a higher melting point is used. The temperature of the model and false plate is controlled by chips of the cast alloy poured onto the model. The temperature must be such that the chips melt to form molten alloy balls. A fusible alloy should not be overheated by more than 30-40 ° C above its melting point. Otherwise, the elements of the alloy will burn out and it will cease to be eutectic. The use of non-eutectic alloys results in a rough mold surface.

Before pouring, oxide films and impurities are removed from the molten alloy mirror. After pouring, the shell is gently tapped to remove adhering air bubbles from the model, and the mirror of the poured metal is carefully heated to prevent its premature hardening. After cooling the metal, the mold is disassembled and the model is removed from it. The mold connector is cleaned and technological cavities are made in it (gating channel, collector, etc.). Rods, pushers and centering pins are machined on machine tools. The holes for the pushers are obtained by pouring the pushers themselves or auxiliary pins in the manufacture of the second half of the mold. The model must be firmly connected to the pusher so that it does not skew.

Rice. 2. Low-melting alloy mold

Rice. 3. Zinc alloy mold

The second half of the mold is filled with an alloy with a lower melting point than the alloy used for the first half of the mold. The surface of the first half of the mold is smoked with soot from burning oil before pouring. After pouring and cooling the second half of the mold, the model is removed and, if necessary, the cavity and the mold connector are corrected (adjustment of both halves of the mold). Minor defects in the cavity are corrected by soldering or sealed with resin.

For the first half of the mold, an alloy consisting of 80% lead, 14% antimony and 6% zinc with a melting point of about 250 ° C is usually used. The second half of the mold is cast from a low-melting alloy containing 51% tin, 31% lead and 18% cadmium with a melting point of 150 °C.

The surface of the working cavity of the mold is scraped and polished. This technology allows you to get a mold with an accuracy of 8-9 class IT. Master models are usually made from medium carbon steel. The surface of the model is polished. When making a model consisting of several pieces, it is not recommended to fasten them by soldering hard and soft solders.

Low-melting models obtained in cast molds have a high-quality surface and satisfactory dimensional accuracy. However, molds fail quickly, so it is recommended to use them for the manufacture of a small series of castings. Cast molds made of low-melting alloys are not advisable to use for the manufacture of large models due to the significant cost and high consumption of low-melting alloys.

Zinc alloy molds (Fig. 14) are made by pouring a master model with zinc alloy in a steel shell.

In the manufacture of complex molds or molds that are subject to increased requirements for accuracy, pressure is applied to the mirror of the cast zinc alloy until the alloy is completely solidified. Compared with low-melting alloy molds, zinc alloy molds are harder, stronger, wear out and deform less upon impact, i.e., the durability of a zinc alloy mold is somewhat higher than that of a low-melting alloy.

The process of making molds from zinc alloys, hardening under pressure in the first phase, is similar to the process of making molds from low-melting alloys. First, a polished zinc or steel model is made. The model is molded with a sand mixture and deepened from the parting plane by 1 mm. Before pouring, the sand mold is smoked with soot, then a steel flask is installed on it and the set is heated to 260-280 ° C. Zinc alloy, overheated to 410-430 ° C, is poured into the shell. If the model is made of zinc alloy, then initially the entire set is cooled to room temperature, and then the model is heated again to 100-200 ° C for its better extraction.

The half-mold released from the model is mechanically processed along the connector and the model is inserted into it, followed by smoking with soot. Then the second half of the shell is installed and the whole set is heated in the oven to 260-280 °C. The heated set is placed under a press, filled with a zinc alloy and pressed with a punch with a force of at least 10 kN, depending on the size of the mold, until the alloy is completely solidified. After cooling to room temperature, the kit is heated again to 100-200 °C to facilitate its disassembly.

The cast first half of the mold is processed, and two or three blind holes are drilled on the parting plane for fixation with the second half of the mold. The pushers are fixed in the mold by casting with an alloy or a hole is drilled for them in the mold.

The second half of the mold is cast in a similar way. The mold is brought to the required dimensions by machining, the gating system is milled, pushers, rods are made and clamping devices are installed.

For the manufacture of molds from zinc alloys without pressure, a split model is used. Both of its halves are installed separately on the plates in the shell, heated to 420 ° C and filled with zinc alloy at a temperature of 470-490 ° C. After hardening and cooling, the shell is removed, the plate is removed and the model is removed. The mold parting plane is processed and both halves are connected along the centering pins. Auxiliary parts of molds, such as pushers, rods, centering pins, etc., are usually made of machined steel. It is relatively easy and cheap to make molds from zinc alloys without pressure, but this method is used with a simple parting plane.

Rice. 4. Plastic mold

Molds made of zinc alloys are quite durable, provide high quality models and are relatively inexpensive. They are suitable for making castings in large series, but are almost unsuitable for models with large cavities or with side and inclined rods. The wage cost of making zinc molds is higher and the material cost is lower than that of fusible alloy molds.

The molds obtained by pouring the master model with plastics (Fig. 4) are very easy to manufacture and therefore cheap. They are not durable enough, and therefore they are used in the manufacture of castings of small series. Mold materials are dentacryl or epoxy resins. Given that plastics are less thermally conductive than metal, they should be used for small molds with a uniformly distributed mass so that the model composition hardens evenly. To increase thermal conductivity, it is recommended to introduce fillers into resins - metal powders or shot.

The best master models are metal, polished; for less critical castings, wooden models are used. In practice, various materials can be used for models that do not deform when poured with plastics. Plaster models produce lower quality prints than wooden ones, and even more so metal ones.

Before pouring, the model is lubricated with a thin layer of a release agent to better separate the master model from the poured mass. Lubricants that have proven themselves well are: 2% solution of silicone oil in trichlorethylene; A 2% solution of beeswax or carnauba wax in gasoline and a solution of castor oil in methyl or ethyl alcohol. The lubricant is applied with a brush or a spray gun in a very thin layer so that the accuracy of the smallest elements of the model surface is not violated.

The process of manufacturing molds from plastics is similar to the process of manufacturing using liquid metal melts. It is most expedient to use a false gypsum plate. The plastic is poured at maximum speed in a continuous stream so that air bubbles do not mix in the mass. A jet of plastic is directed to the parting plane, the rising liquid level calmly covers the model. Air bubbles from resin filled with metal powder or shot are removed by vacuum or vibration.

It is recommended to use a mass consisting of CHS Epoxy 1200 resin, in which 80% (by mass) of steel shot with a size of 0.3-0.5 mm is replaced. The mixture is heated to 50 °C with stirring, hardener P1 is added to it in the ratio of 7 hours per 100 hours of Epoxy 1200 resin, and the resulting mixture is thoroughly mixed again.

Molds made of metal-filled epoxy resins are often used to refine casting technology or to obtain small series of investment models. This method does not require much time, is cheap and is always applied without mechanical processing. The disadvantage of plastic molds is the lower accuracy and low thermal conductivity of molds compared to metal molds.

Gypsum molds can be used to produce individual models without special requirements for their dimensional accuracy. The resistance of such forms is very small, but, given the insignificant costs of their manufacture, they are often used to test technological solutions. The molds are detachable, and both halves are cast in wooden or metal collapsible shells. The second half of the mold is poured over the first, as if it were a false plate. So that the gypsum does not stick, the connector of the first mold is lubricated with a release agent (a solution of wax in trichloroethane, in gasoline or silicone oil; a solution of petroleum jelly in gasoline). Gypsum molds are not suitable for pressing the model composition into them under pressure. The model composition is poured into molds in a molten state by free pouring.

Molds made by pouring a master model with silicone rubber are used to make investment models that do not require accuracy, such as models of decorative objects or models to check the casting technology being developed (for example, the density of castings with a selected gating system). Such forms are elastic, so they can produce models with negative slopes.

Silicone rubber molds can also be made without a false plate by pouring the whole model. After curing, the silicone rubber sheath is cut at the connector. A fake slab is best made from gypsum.

Guide pins can be poured into both halves of the mold; in addition, it is possible to make a gating channel model from the model composition and mold it simultaneously with the model. Rubber molds in metal shells can be used to make models by pressing the model composition at low pressure. In forms without shells, only free pouring of the model composition is allowed. The very low thermal conductivity of rubber molds lengthens the entire cycle of model making, but allows you to get models with a clear imprint and high surface quality.

Electroformed molds can be used for very precise and complex medium weight models. Such molds are not suitable for the manufacture of models with deep pockets, grooves and holes, their production is relatively expensive, requires special equipment and therefore is not widely used in Czechoslovakia.

Molds made by metallization have not yet been tested in production, but have been considered by the authors from the technical and economic side with the previously given methods.

The basic principle of metallization is the application of liquid metal particles by a gas stream onto the prepared surface of an object using a metallization gun. The metal wire in the gun is melted either by a flame, most often oxy-acetylene, or by an electric arc. Upon impact, under the influence of kinetic energy, metal particles are deformed, adhering to each other and to the surface of the material, and form a firmly bonded mass that accurately reproduces the shape of the model object. This method is not used for all types of models. Planes deposited at an angle to the flow are more difficult to metallize or not metallized at all at large sizes of their area or at a very sharp angle of attack.

Any mold (steel, fusible or zinc alloys, plastic) can be simple, complex and with varying degrees of mechanization. The mold can be designed only for a specific model configuration or be universal with interchangeable inserts. The mold can be provided with a water cooling device, and finally it can be used to make models or gating systems.

Of course, in the manufacture of models of small series or in single production, highly mechanized molds are not used. The technology and costs for making molds from different materials are different.

When designing molds for investment models, it is necessary to take into account the design features of their elements, which can significantly affect the operation of the entire mold. Such elements are, for example:
1) actual half-moulds, depending on the configuration of the casting (a mold without detachable inserts or with collapsible elements);
2) rod (movable or stationary);
3) pushers;
4) mold cooling system;
5) system for supplying model composition to the central collector (assembly of model links);
6) model composition supply system for individual models (soldered models);
7) air exhaust system for molds.

In molds without inserts, the model is formed either in both halves, or in one, usually the lower half of the mold. Both halves of the mold must be matched to each other along the parting surface, which can be flat or profiled. The mold cavity must be designed in such a way that when the mold is opened from both halves, the model can be easily removed.

In a collapsible mold with a complex cavity profile, to extract the model, it is necessary to extract inserts, rods and other elements from it before opening the mold. Such solutions are used only in cases where the configuration of the casting is very complex and it is impossible to make the parting plane of the mold without detachable parts.

The complex shape of cavities or holes in the model is obtained using rods that are placed perpendicular or parallel to the parting plane; in the latter case, side rods. Rods with a perpendicular arrangement relative to the parting plane, if the configuration of the casting allows it, are recommended to be fixed in the lower half-mould. Side rods with a small series of castings should be removed manually; very small rods are removed from the mold along with the models.

Rice. 5. Metal composite rod that forms a complex configuration of the cavity

Rice. 6. The location of the pushers in the mold

Pushers serve to push models out of the working cavity of the mold; they are located in the lower half of the mold (Fig. 17). The parting plane must be chosen so that when the mold opens, the model remains in the lower half. Since the pushers leave an imprint on the models, they should be placed, if possible, on the surfaces to be machined.

The pushers must have a locking device, or special plates are made in the mold to prevent the movement of the pushers during the pressing of the model composition. Profile pushers are fixed in the mold (due to their possible rotation around their axis). Gray cast iron has proved to be the best material for pushers, designed for bearing bushings according to CSN 42 2456. Pushers are driven by a pressure plate through a hydraulic actuator or manually. The pushers return to their original position in most cases with a compressed spring.

In many cases, models can be removed without pushers using compressed air supplied through a gas-permeable insert (Fig. 7).

To shorten the hardening cycle and eliminate external local shrinkage on the surface of the molds, the molds should be cooled. Cooling the mold with cold water is most effective. In molds without inserts, cooling channels are made in one or two half-moulds; in molds with inserts, insert slots are additionally cooled. The dimensions of the cooling channels are usually not calculated, and the designer determines them according to his experience and, if possible, their placement in the mold. Channels are necessarily provided near the most massive parts of the model. Drinking water is often used for cooling. The water temperature varies depending on the weather, which does not allow you to set a single cooling mode. It is desirable to carry out cooling in a special refrigeration device and maintain a constant water temperature.

Rice. 7. Extraction of the model from the mold with compressed air: 1 - SUPPLY of compressed air; 2 - gas permeable insert

It is necessary to fix the upper and lower half of the molds between each other in the plane of the connector. This is ensured in most cases by centering pins or by a protrusion-cavity design in molds made of fusible alloys or plastics (Fig. 8). Zinc alloy halves are fixed by drilling a cavity in one half of the mold before pouring the other half.

Rice. 8. Fixing the halves of the molds with a ledge

Molds of large sizes or molds for making models in large series are fixed on the plates of the pressing device, so the designer needs to provide a method for attaching the molds to the platen of such a device. Molds of small sizes or for models of small series are not fixed, but are installed and removed from the pressed device manually.

Air is removed from the mold through the gaps between the guide bushings and pushers along the parting plane or along specially made grooves.

Press floats with full mechanization and automation of assembly and disassembly are suitable for the manufacture of models of large series or for mass production. Investment casting foundries in Czechoslovakia do not yet produce such types of molds, since castings are produced in relatively small batches. The use of automated molds requires high-capacity press-in equipment and appropriate transport devices to transfer molds from assembly, press-in, cool-down and disassembly positions.

If different types of pressing equipment are used in foundries, then the corresponding mold designs are also used. This creates certain difficulties, since in each foundry it is necessary to design and manufacture different designs of molds. Therefore, each precision casting foundry should have its own technology for making molds, which depends on the equipment and various devices necessary for one or another type of production.

Economic comparison of individual mold making methods. Initially, investment molds were made from metals by machining. In order to reduce production costs and expand the use of investment casting, other, cheaper and faster methods of making molds have been developed and proposed.

In this table, wage costs are systematized in relation to the costs (taken as 100%) for the manufacture of steel molds by machining. Payroll costs reflect the costs associated with making the same simple molds in different ways. The degree of accuracy is classified according to a five-point system. The difference between the individual scores is not equivalent. For example, the difference in accuracy between 1st and 2nd scores, or 2nd and 3rd scores, is smaller than between 4th and 5th scores. The solidification time was determined experimentally based on the results of observations of the cooling of identical investment models in molds of various types.

This is the time required to keep the model in the mold and then remove it without the risk of damage and deformation during further technological operations. This information is for informational purposes only. There may be deviations from the given values. This depends, for example, on the modeling composition used and its pressing temperature.

The last column of the table. 13 contains information about the resistance of molds. The resistance of molds made using the same technology depends on many factors: the size of the models; the position of the parting plane in the mold, especially when the parting plane passes over a surface that does not have a machining allowance; the number and quality of the pushers and, finally, the thorough care of the mold during its operation, regulation and adjustment, as well as the condition of the pressing equipment. The data is taken from practical experience in investment casting foundries, where molds were made according to the given technological processes.

In practice, machined molds will also be used, as this is the only production method for manufacturing molds for models of large overall dimensions and weighing more than 10 kg. The same molds will be used to produce the most complex models with a complex parting plane and detachable parts. Models of castings, produced in large series with high requirements for surface cleanliness and dimensional accuracy, are made in steel-> x molds obtained by machining.

Fess molds made of fusible alloys are used in the manufacture of castings of small series. This is a relatively fast and reliable method, which, for the reasons already mentioned, always finds application in investment casting.

If it is necessary to check the designed technological process in the manufacture of single castings, for example for repair needs, molds made of gypsum or silicone rubber are suitable. Molds made of epoxy resins are used in the urgent production of single castings.

From a review of the merits and demerits of molds made by various methods, it cannot be assumed at present and in the near future that only one method of making investment molds is used in any foundry. It is economically profitable to manufacture molds not only by machining, but also mainly from zinc and low-melting alloys. To what extent the described methods will be used will depend on the production program, on the configuration and overall dimensions of the castings to be produced.

If a technologist develops a technology for a new casting, he must know all the circumstances that affect the choice of a mold. This is the only way to design a mold that will ensure maximum economic production of a new casting.

When designing different types of molds, the following criteria are decisive:
1) the size of the series and the estimated number of castings;
2) configuration and overall dimensions of castings;
3) required dimensional accuracy of castings;
4) thermophysical properties of the mold material;
5) the cost of making molds;
6) equipment for pressing the model composition into a mold.

The main documentation that the technologist develops and submits to the designer for the manufacture of drawings, molds, is a drawing of a casting or a drawing of a master model with detailed instructions on the type and method of manufacturing a mold.

Today we will tell you about the features of the production of molds, as well as their main components.

Direct assembly of a new mold begins after its drawings are ready and a 3D model is prepared. It is the design stage that allows you to outline the entire scope of work for the manufacture of a mold, and also determines the necessary set of standard and special elements necessary for its assembly (you can read more about mold design).

Standard and special mold elements

Any mold consists of more than 50% of standard elements (this figure can even reach 95%). These details include:

forming plates and other parts of the forming structure: columns, guide bushings, retainers, springs, inserts, etc.;
parts of the extracting mechanism: tubular and slotted pushers, double stroke shanks, gears, bearings and many other small components;
gating system elements: nozzles, gating bushings, injectors, filters, manifolds;
fittings, couplings, gaskets and rods of the cooling system and much more.

There are many companies that specialize in the production of standard mold elements. Therefore, they try not to make them on the spot, but to buy them separately. When designing a mold, developers strive to use as many standard elements as possible. This allows you to save on its manufacture and assembly, as well as significantly speed up this process.

The special elements of the mold include:

movable and fixed plate (box forming the shape of the product). They define the outer and inner contour of the casting;
a punch that presses the molten metal into the mold cavity;
other elements involved in the creation of the casting mold, and designed to remove it from the mold.

Special elements are usually designed and created directly at the plant from which the mold was ordered.

CNC machines

Special mold elements must be manufactured with the highest precision. Otherwise, it will not be possible to achieve the necessary pairing between them, and the workpiece may be damaged. At the moment, almost all manufacturers use numerical control (CNC) milling machines to create these parts. Such equipment makes it possible to manufacture metal components with an accuracy of 1 micron, which is quite enough for installation in a mold and casting.

Is it possible to make a mold on a 3D printer?

At the moment, 3-D printing technology does not yet allow the production of molds for metal castings. First, modern 3-D printers cannot print metal products. Secondly, even plastic products from a 3-D printer so far have a slightly larger accuracy error than is acceptable for casting complex metal molds. However, with the help of such printers, some simple molds are already being created for the production of small batches of plastic products. One mold made on a 3-D printer can withstand approximately 100-150 castings.

However, this issue should not be considered closed. Technology is advancing at a dizzying pace these days, and this allows us to hope that in the future it will be possible to abandon CNC machines in the production of molds and significantly save time and money.

It might be useful to read: