The die has a specific contour or cavity shape, and the contour shape with cutting edge can separate the blank according to the contour shape, that is, the punch; The shape of the inner cavity can make the blank obtain the corresponding three-dimensional shape. By the way, molds are divided into two categories abroad: molds and dies. Mold means "mold, mold cavity", which means plastic mold, casting mold, etc. DIE means "metal die, stamping die", that is, stamping die, forging die and the like. The difference is simple: first, the material is heated and melted and poured into the mold cavity; second, the material is pressed into the required shape by external force. )
Mold is generally divided into moving mold and fixed mold, or male mold and female mold, which can be separated or combined. When separating, the blank is loaded or the workpiece is taken out, and when closing, the workpiece and the blank are separated or formed. In the process of blanking, forming stamping, die forging, cold heading, pressing and compression molding, the external force required for separation or forming is applied to the blank through the die; In the process of extrusion, die casting and injection molding, external force is applied to the blank by air pressure, plunger and punch, and the die bears the bulging force of the blank.
In addition to the mold itself, it also needs a mold base, a mold base, a guide device and a product ejection device. These components are usually made into universal types to be suitable for a range of different molds.
Moulds are widely used. A large number of molds are used to manufacture electromechanical products, such as automobiles, bicycles, sewing machines, cameras, motors, electrical appliances, meters and so on. And household appliances.
Mould is basically produced in a single piece with complex shape, which requires high structural strength, rigidity, surface hardness, surface roughness and machining accuracy, so mould production needs a high technical level. The timely supply and quality of molds directly affect the quality, cost and development of new products. Therefore, the mold production level is one of the important symbols of the mechanical manufacturing level.
The dies for processing metal are classified according to the processing technology adopted, and commonly used are: stamping dies, including blanking dies, bending dies, drawing dies, hole-turning dies, shrinking dies, corrugated dies, bulging dies, forming dies, etc. Forging dies, including forging dies for die forging and upsetting dies; As well as extrusion dies and die-casting dies. The molds used to process nonmetals and powder metallurgy are named and classified according to the processing objects, including plastic molds, rubber molds and powder metallurgy molds.
Stamping die is used for stamping and separating sheet metal. The mold for forming has a cavity, and the mold for separating has a cutting edge. The most commonly used stamping die has only one station to complete a production process. This kind of die is widely used, simple in structure and easy to manufacture, but its production efficiency is low. In order to improve productivity, multiple stamping processes such as blanking, drawing, punching and trimming can be arranged on one die, so that the blank can complete multiple stamping processes on one station. This kind of mould is called compound mould.
In addition, blanking, bending, stretching, punching and trimming are arranged at different stations of the die. In the stamping process, the blank goes through several stations in turn for continuous stamping and finally becomes a part at the last station. This kind of die is called progressive die, also called continuous die.
The characteristics of stamping die are: high precision, accurate size, and the gap between punch and die of some stamping dies is close to zero; The stamping speed is fast, and it can be stamped dozens to thousands of times per minute; The die life is long, and the life of some silicon steel sheet blanking dies is more than several million times.
Forging die is a die used to forge hot metal. In die forging, the blank is often deformed many times before it can be made into forgings, which requires carving several cavities on a module. Metal is sent to each cavity in turn, flows plastically in the cavity, and finally fills the cavity to make forgings. In die forging, it is difficult for the blank to be equal to the cavity volume in the final forging process. In order to avoid waste, a slightly larger blank is often selected. Therefore, a flash groove is set around the cavity of the interface between the upper and lower dies of the final forging die to store excess metal, and the flash is cut off after forming.
The technical characteristics of forging die are: more complex cavities; The working conditions are bad, and the red steel above 1000℃ deforms and flows in the die cavity; The die should bear the high-speed impact of the forging hammer or the reduction of heavy load; In the process of use, it is often in a state of rapid cooling, rapid heating and alternating cold and hot. Therefore, the mold material should have high strength, toughness and wear resistance. Hot forging must also have high temperature strength and hardness and undergo toughening heat treatment.
Extrusion die is a die used to extrude metal. The positive extrusion die has a stationary female die, an extrusion cylinder for placing the blank and a punch for applying pressure to the blank. The extrusion barrel of the reverse extrusion die is a female die and the punch is a male die. Because the metal needs to be extruded from the female die under great pressure, the extrusion cylinder and the female die for reverse extrusion need high strength, so the multi-layer prestressed composite structure is often adopted. The working length of punch and punch should be short to avoid instability and bending under high pressure stress.
The die casting die is installed on the die casting machine, which can inject liquid metal into the cavity under high pressure and keep the pressure until the metal solidifies and forms. Mainly used for aluminum, zinc, copper parts, but also for steel parts. The structure of the die casting mold is similar to that of the plastic injection mold. It consists of a moving die and a fixed die, and the core is used as the cavity of the casting. After the metal is cooled and solidified in the cavity, the core is taken out and the mold is separated.
Die castings are generally thin, hollow, with many platforms and ribs, complex shape and structure, accurate size requirements and smooth surface. Because metal is formed at high temperature, the die-casting mold needs to be made of high-temperature resistant materials.
Plastic mold is a mold used for plastic molding. With the development of plastic industry, the demand for plastic molds is increasing day by day, and its output has occupied the first place in all kinds of molds. Commonly used plastic molds include injection mold, compression mold and extrusion mold.
When the plastic mold works, the pressure and temperature it bears are not high, but there are many parts, and the surface requirements are particularly smooth. Therefore, the mold material can be pre-hardened steel, that is, the mold is heat treated first, then cut to prevent deformation after heat treatment, and finally polished to improve surface quality.
Rubber molds are mainly used for molding rubber products such as tires, automobile battery cases and soles. Generally, rubber material is sandwiched in a mold and heated by steam. There are also rubber injection molds similar to plastic injection molds.
Powder metallurgy die is a die for powder pressing solid metal. When working, metal powder is quantitatively poured into the lower die, then the upper die is pressed down for closed molding, and then the preform is ejected by the ejector and sent to the sintering furnace for sintering, thus making powder metallurgy parts.
Generally speaking, the gap of powder metallurgy parts is large, accounting for about 15% of the total volume, and the forming pressure is not large, the die structure is simple, the requirements for precision and surface roughness are general, and there is no special requirement for the die. In order to reduce the gap and improve the density and strength, the sintered blank is hot forged again, which is called powder forging. The die used is similar to the die forging die.
Because the mold is a molding tool, it requires accurate size, smooth surface, reasonable structure, high production efficiency and easy automation. But also is easy to manufacture, long in service life and low in cost; In addition, it is also necessary to consider that the design meets the technological needs and is economical and reasonable.
The structural design and parameter selection of the die must consider the factors such as rigidity, guidance, unloading mechanism, positioning mode and gap size, and the wearing parts on the die should be easy to replace. For plastic molds and die-casting molds, we should also consider the reasonable gating system, the flow state of molten plastic or metal, and the position and direction of entering the cavity. In order to improve productivity and reduce the pouring loss of runner, multi-cavity mold can be used, that is, multiple identical or different products can be completed in one mold at the same time.
Mold production is generally a single piece and small batch production, which requires strict and accurate manufacturing. Therefore, precision machining equipment and measuring devices are often used. According to the structural characteristics, dies are generally divided into flat blanking dies and concave dies with spaces.
The plane blanking die can be initially formed by EDM, and then the precision can be further improved by the methods of form grinding and coordinate grinding. Coordinate grinding machines are generally used for accurate positioning of molds to ensure accurate aperture and hole spacing. You can also grind the punch and die of any curved surface with the computer numerical control continuous trajectory coordinate grinder.
Cavity mold is mainly used to shape three-dimensional workpiece, so it has size requirements in three directions: length, width and height, and its shape is complex and it is difficult to manufacture. Such as cold extrusion mold, die casting mold, powder metallurgy mold, plastic mold, rubber mold, etc. They all belong to cavity dies, and the cavity dies are mostly made by copying milling machine, electric spark and electrolytic machining. Combining copying milling with numerical control and adding three-way translation head device in EDM can improve the machining quality of cavity.
Computer numerical control multi-axis milling machine, coordinate grinder and machining center machine tool are important equipment for cavity mold processing. Generally, electric or pneumatic tools are used to grind and polish the surface of the cavity, and various grinding wheels and grinding paste powder are used, or ultrasonic grinding, extrusion honing, chemical polishing and other methods are used. Coordinate measuring machine and optical projection comparator are commonly used precision measuring equipment in mold manufacturing.
Mould is a precision tool, which is expensive, and its service life must be prolonged as much as possible. The common failure forms of molds mainly include wear, collapse and fracture, adhesion and so on. The failure forms of dies for different purposes are also different. The main way to improve the service life of the die is to reasonably select the die steel and determine the heat treatment specification according to the service conditions.
Choosing a material with high strength at the temperature can prevent collapse; Increasing die hardness can reduce wear rate; High toughness and fatigue resistance, as well as the elimination of hardened layer and machining residual stress, can hinder the occurrence and development of cracks and prevent them.
Surface treatment, lubrication and selection of mold materials with good adhesion resistance are important measures to prolong the life of mold. The requirements of the working face and the matrix of the die are very different, so it is difficult to meet them completely and reasonably with one material. However, the comprehensive performance of the die can be improved by insert, surfacing, spraying and local strengthening. In addition, reasonable operation and use is another way to eliminate abnormal faults and slow down normal faults.