Stamping is mainly used in the production of large volume parts. Therefore, stamping dies become an indispensable equipment in the process of stamping production, which belongs to technology-intensive industry.

 

The design and manufacture of dies are directly related to the quality, production efficiency and production cost of stamping parts. In other words, the level of design and manufacturing technology of die is also a comprehensive measure of an enterprise's technical ability, and plays a decisive role in the process of new product development.

 

In the stamping production, once the mold has problems, it will directly affect the delivery cycle and production cost. Therefore, the design stage is very important, and the good or bad design directly affects the production and the cost.

 

1. Overview of stamping and tooling

 

1.1 Introduction of tooling 

 

In modern industrial production, die is one of the important process equipment. Moulds occupy an important position in all walks of life, especially in the stamping process and shaping molding forming process. Comprehensive view, in all walks of life in China, the stamping die accounts for 50%, can be seen its importance. Since China's reform and opening up, with the rapid development of China's economy, China's market demand for mold is also growing, mold industry also developed rapidly. 

 

Type of mould: The type of mould is various, mainly single process mould, compound mould and progressive mould. To determine the form of the die, must be based on the requirements of the stamping workpiece, the number of batches required to be produced, and the conditions of the die processing. There are many forms of stamping dies, and according to the nature of the work, the construction of the die, and the material used in the die, the stamping dies can be classified into three main categories. 

 

According to the nature of the die process, it can be divided into punching die, bending die, drawing die and forming die. Punching die is a kind of die that separates the material along the semi-closed or open contour line; bending die is a kind of die that bends the material along the straight line; drawing die is a kind of die that changes the shape and size of the stamped parts by making the open hollow shape or further deforming the cast hollow; forming die is a kind of die that reproduces the semi-finished products directly according to the concave-convex die, but the material is only partially deformed. The forming mold is a mold that directly replicates a semi-finished product, but only partially deforms the material.

 

According to the degree of process combination, it can be divided into single process die, compound die, progressive die and transfer die. A single process die is a die that performs only one stamping process in one stroke of the press; a compound die is a die that performs two or more stamping processes in one stroke of the press when there is only one working position; a progressive die is a die that performs two or more stamping processes in one stroke of the press when there are two or more working positions; and a transfer die is a die that combines a single process die with a single process die. The transfer die is a combination of a single process die and a progressive die. 

 

It can also be divided into punching and shearing dies, bending dies, drawing dies, forming dies and compression dies according to the processing method of the product. 

 

1.2 Introduction of stamping dies 

 

Stamping dies, which can be called cold stamping dies, are also commonly known as cold punching dies. Stamping die is a relatively special process equipment, is in the process of cold stamping processing, the material is processed, and finally processed into parts or semi-finished products. The material can be metal or non-metal material. Stamping is a method of pressure processing, which is carried out at room temperature, and the press is equipped with a die to apply pressure to the material, causing separation or plastic deformation of the material to obtain the desired part. 

 

The design of the stamping process and the design of the die structure are the two aspects of the design of the stamping die structure. In the production process of stamping parts, the main application of stamping process design is the process of stamping process design, which mainly includes the plan of the process, how to arrange, the size of the process, what kind of equipment and die type to be used, and the technical and economic indexes, and the comprehensive overall planning of these aspects. The design of stamping die structure is to design the specific structure and shape of the required die according to the above requirements of stamping process design, and also draw the assembly drawing of the die and the parts drawing of the die. 

2. Material selection of stamping die design

 

2.1 Materials of stamping dies 

 

The materials for manufacturing stamping dies are steel, carbide, steel-jointed carbide, zinc-based alloy, low melting point alloy, aluminum bronze, polymer material and so on. At present, most of the materials used in the manufacture of stamping dies are mainly steel, and the common types of materials used for working parts of dies are: carbon tool steel, low-alloy tool steel, high-carbon high-chromium or medium-chromium tool steel, medium-carbon alloy steel, high-speed steel, matrix steel, and cemented carbide, steel cemented carbide, etc. 

 

2.2 Stamping die material selection principle 

 

Among the materials used in stamping dies, it can be various metal materials or various non-metal materials, which mainly include carbon steel, alloy steel, cast iron, cast steel, cemented carbide, low melting point alloy, zinc-based alloy, aluminum bronze, synthetic resin, polyurethane rubber, plastic, laminated birch board and so on.

 

The material used to make the mold is also very strict. Not only the hardness, strength and wear resistance of the material should be very high, but also appropriate toughness, and hardenability should also be very high as well as heat treatment without deformation and quenching is not easy to crack and other properties. 

 

To ensure the service life of the mold should be reasonable selection of mold materials and heat treatment process to the correct implementation. The selection of the correct steel and heat treatment process should correspond to the different uses of the die, in addition to its working condition, stress conditions and the performance of the processed material, production volume and productivity and other comprehensive factors, and should focus on the performance of the above requirements. 

 

3. Structure of stamping die

 

 

Before determining the structure of the stamping die, it is necessary to determine the feeding method of the stamping die, the unloading method, and the form of the die holder of the stamping die. 

 

4. Design of stamping die

 

4.1 Determination of stamping gap 

 

Stamping clearance is the difference between the dimensions of the concave and convex die edges of the stamping die. The size of this gap has a great influence on the single-sided quality of the stamped part, the size of the punching force, and the life of the die. Therefore, one of the important process parameters in the design of stamping dies is the stamping gap. Therefore, it is important to choose a suitable stamping gap when designing a die to ensure good quality of the stamped part, a smaller punching force and also the service life of the die. The appropriate gap value is based on different criteria for different data, as long as the selected gap is in the right range for the production. The minimum value in this suitable range is called the minimum reasonable clearance value and the maximum value is the maximum reasonable clearance value. In the process of using the die, it is possible that the die will wear out and the clearance will become larger, so the minimum reasonable clearance should be used when designing a new die.

 

4.2 Determining the profile of the concave and convex die

 

The size of the working edge of the concave and convex die for stamping dies is determined after careful calculations. 

 

1) Concave die 

The structure of the concave die of a stamping die should be made according to the needs of the part, and the method of making it should be according to the above description. The concave die is usually fixed directly to the convex die. 

For example, how to determine the thickness of a concave die in the manufacturing process of a blanking die. The thickness of a die is the length of the die edge from the outer edge. Therefore, the dimensions of the concave die are determined using the empirical formula for concave die dimensions, which is H=Kb (H≥15mm). k represents the coefficient, which is available in the book, and b represents the maximum width of the concave die hole. In manufacturing engineering, it is necessary to calculate not only the thickness of the concave die, but also the data related to it around the die. In this way, a suitable combination of mold structures is formed with the already determined main structures of the mold. In this way, the mold design is greatly simplified. 

 

 

2) Convex die 

The structure of the convex die of a stamping die is also made according to the needs of the stamped part, and the method of making it is based on the data pressed out by counting. The convex die will be fixed by rivets in general, or it can be fixed by low soluble point alloy or low melting point welding agent. 

After that, just install the position of concave die and convex die and other related parts according to the drawing. 

 

5. Future development trend of stamping dies

 

The future development of stamping die technology should be based on "fast delivery", "high precision", "high quality" and "low price" of die products. " as the requirement standard. How can we reach this point? To achieve this series of standard requirements must be timely development of these items. 

 

Vigorously promote the mold CAD/CAM/CAE technology. Mold CAD / CAM / CAE technology can be called the future development trend of mold design. With the continuous development of microcomputer software and continuous progress, has reached the basic conditions of maturity so that mold CAD/CAM/CAE technology to popularize, each mold industry and enterprises will also increase the training of CAD/CAM technology and the development of its technical services; a greater range of CAE technology to expand the application. 

 

Speed up the speed of milling processing. In recent years, the rapid development of foreign milling industry, to a large extent, the efficiency of processing can be improved, not only this can also make the surface finish to a very high degree. In addition, the processing of high hardness modules also has the advantages of low temperature rise and small thermal deformation. The rapid development of milling technology, the automotive industry, large and medium-sized home appliance industry cavity mold manufacturing note also added fresh impetus. In terms of the current degree of development it has been to the agile, intelligent, integrated higher direction. 

Make mold scanning and digitalization. High-speed scanning machine and mold scanning system provides a lot of functions needed from the model or physical scanning to process the desired model, greatly reducing the mold in the development and manufacturing cycle. Some fast scanning system, can be quickly installed in the existing CNC milling machine and machining center, to achieve rapid data acquisition, automatically generate a variety of different CNC system processing procedures, different formats of CAD data, used in the mold manufacturing industry, "reverse engineering". Mold scanning system has been in the automotive, motorcycle, home appliances and other industries have been successfully applied, I believe that in the "Tenth Five-Year" period will play a greater role. 

 

EDM milling. EDM milling technology is also known as EDM into the processing technology, which is an alternative to the traditional molding electrode processing cavity of the new technology, it is a high-speed rotation of a simple tubular electrode for three-dimensional or two-dimensional profile processing, so no longer need to create complex molding electrodes, which is obviously a major development in the field of EDM forming process. This is obviously a major development in the field of EDM. Foreign countries have used this technology in the application of machine tools in mold processing. It is expected that this technology will be developed. 

Improve the standardization of stamping dies. The degree of standardization of stamping dies in China is still at the stage of continuous improvement, although the coverage rate of standard parts of stamping dies in China has reached about 30%, but compared with other countries, especially developed countries, it is still a big distance away, at present, the coverage rate of stamping dies in developed countries abroad is generally can reach about 80%. 

 

The choice of materials of high quality and treatment of surface technology advanced. The selection of high-quality materials and the application of corresponding advanced surface treatment technology to improve the life of stamping dies is very necessary, such as the selection of high-quality steel materials. The key to the performance of stamping die steel material lies in the ability to make the heat treatment and surface treatment of the stamping die more. The future development trend of stamping die heat treatment is to use the technology of vacuum heat treatment. Not only to develop the surface treatment technology of stamping dies but also to develop advanced technology such as vapor deposition (TiN, TiC, etc.), ion spraying and other advanced technology.

 

The grinding and polishing of stamping dies will be automated and intelligent. The quality of the surface of the stamping die can be said to have a greater impact on the service life of the stamping die, the quality of the appearance of the stamping parts and other aspects, research and invention of automated, intelligent grinding methods and polishing methods to replace the current manual operation methods, so as to improve the quality of the surface of the stamping die, which is also an important future development direction of the stamping die 

Develop the system of automatic processing of dies and moulds. The development of automatic processing of stamping dies can be said to be the long-term development goal of China's mold industry. The automatic processing system of stamping dies mainly adopts the reasonable combination of multiple machine tools to work; and is equipped with jigs or positioning discs for accompanying positioning; the CNC library of stamping dies' machines and tools is also quite complete; the CNC flexible synchronization system is also complete; and a quite perfect monitoring control system is set up for quality. 

 

6. Conclusion

 

Since the 1990s, the rapid development of automobile, home appliance, communication and other industries has driven the rapid development of mold industry at the same time. In the international demand for mold development is very obvious. Today, China's mold industry has achievements, relative to some mold industry developed countries, China's mold technology still has not reached the advanced level. Our country in the mold industry still need greater reform, the related industries also need to improve. This not only need mold design talent training also need the government to give policy support.

Mold design level and manufacturing level is also a measure of the country's manufacturing capacity, so to a very large extent on the quality of products, efficiency and new product development capabilities are playing a decisive role. Therefore, related industries and enterprises should improve the design and manufacturing ability of moulds.