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Material requirements for blanking processing
The materials used for punching must not only meet the technical requirements of product design but also meet the requirements of the stamping process and the processing requirements after stamping (such as cutting, electroplating, welding, etc.). The basic requirements of the stamping process for materials are as follows.
- Good plasticity
For the stamping process, in order to facilitate stamping deformation and improve the quality of parts, the material should have good plasticity. For the separation process, materials with good plasticity can get better section quality. For the deformation process, the plasticity is good, and the allowable degree of deformation of the material is large, which can reduce the number of stamping processes and the number of intermediate annealing.
- Good surface quality
When stamping the materials, the surface of the stamping material is generally required to be smooth and smooth, free of oxide scale, cracks, rust spots, scratches, and other defects. The material with good surface quality, the workpiece is not easy to be broken during punching, and there is less waste. The mold is not easy to scratch, the service life is improved, and the surface quality of the parts is good.
- Thickness tolerance in accordance with national standards
The thickness tolerance of the material should comply with the national standards, and a certain mold gap is suitable for a certain thickness of the material. Too much thickness tolerance will affect the quality of the workpiece and may damage the mold and equipment.
Commonly used materials and mechanical properties of punching processing
The commonly used materials for stamping include metal materials and non-metal materials, and metal materials are divided into two types: ferrous metals and non-ferrous metals.
Commonly used ferrous metal materials are as follows.
- Ordinary carbon steel plate, such as Q195, Q235, etc.
- High-quality carbon structural steel plate. Such as 08, 08F, 10, 20, etc.
- Low alloy structural steel plate. Such as Q345 (16Mn), Q295 (09Mn2), and so on.
- Electrical silicon steel plate, such as DT1, DT2.
- Stainless steel plate, such as 1Cr18Ni9Ti, 1Cr13, etc.
Commonly used non-ferrous metals are copper and copper alloys. The grades are T1, T2, H62, H68, etc., which have good plasticity, electrical conductivity and thermal conductivity. There are also aluminum and aluminum alloys. The commonly used grades are 1060, 1050A, 3A21, 2A12, etc., with good plasticity, small and light deformation resistance.
Non-metallic materials include bakelite, rubber, and plastic boards.
The most commonly used material for stamping is sheet material, common specifications such as 710mm×1420mm and 1000mm×2000mm, etc., mass production can use special specifications of strip material (coil material), special circumstances can use block material, it is suitable for single-piece small batch Production and stamping of expensive non-ferrous metals.
According to the surface quality, the sheet material can be divided into three types: I (high-quality surface), II (higher-quality surface), and III (general-quality surface).
Aluminum killed steel sheets used for deep drawing of complex parts can be divided into three types: ZF (most complex), HF (very complex), and F (complex); general deep-drawn low-carbon thin steel sheets can be divided into Z( Deepest drawing), S (deep drawing), P (ordinary drawing); the supply state of sheet metal can be divided into M (annealed state), C (quenched state), Y (hardened state), Y2 (semi-hardened state, 1/2 hard), etc.; the sheet metal has two rolling states: cold rolling and hot rolling.
The mechanical properties of commonly used metal sheets are shown in Table 1-2.
Representation of commonly used materials in punching drawings
In the stamping process data and drawings, there are special regulations on the representation of materials, and examples are given here for illustration.
The characteristic shown is 08 steel plate, the sheet size is 1.0X1000X1500, ordinary precision, higher-level finishing surface, deep-drawn cold-rolled steel plate. For material grades, please refer to relevant information.
Commonly used materials for punch dies
The position of mold materials in the mold industry
The mold material is the basis of mold manufacturing. Mold material and heat treatment technology play an important and even decisive role in the service life, accuracy, and surface roughness of the mold. Therefore, select materials reasonably according to the use conditions of the mold, adopt appropriate heat treatment and surface engineering techniques, in order to give full play to the potential of the mold material, select a reasonable mold structure according to the performance characteristics of the mold material, and adopt corresponding maintenance measures according to the characteristics of the mold material Waiting is very important. Only in this way can the service life of the mold be effectively improved and the early failure of the mold can be prevented.
The performance of the mold material directly affects the quality and service life of the mold, and the process performance of the mold material affects the difficulty of mold processing, the quality of mold processing, and the processing cost. In-mold design, in addition to designing a reasonable mold structure, appropriate mold materials, and heat treatment processes should be selected to enable the mold to obtain good working performance and long service life.
Selection principle of die material
The materials used to make stamping dies include gray cast iron, cast steel, steel, steel-bonded cemented carbide, cemented carbide, low melting point alloys, plastics, polyurethane rubber, etc.
The mold material is directly related to mold life, mold manufacturing cost, and total mold cost. The following points should be fully considered when selecting mold materials.
- According to the nature of the punched parts, the type of process, and the working conditions and functions of the die parts, select the mold material. For example, whether the working conditions of the die working parts have stress concentration, impact load, etc., which requires the selected die material to have high strength and hardness, high wear resistance, and sufficient toughness; guide parts require wear resistance and relatively Good toughness, usually low carbon steel, surface carburizing and quenching.
- According to the size, shape, and precision requirements of the stamping parts, the material is selected. Generally speaking, for molds with simple shapes and small stamping parts, their working parts are usually made of high-carbon tool steel; for molds with more complex shapes and larger stamping parts, alloy tools with less heat treatment deformation are used for working parts. It is made of steel, and the working parts of precision die with high precision are often made of hard alloy with good wear resistance.
- Production batch of stamping parts. For mass-produced parts, the mold material should be made of better quality materials that can ensure the durability of the mold; for small-batch production parts, use cheaper and less durable materials.
- According to the production and supply of mold materials in my country, the material selection of the unit and the heat treatment conditions are considered.
Common materials and heat treatment of blanking die
The commonly used materials of some stamping dies are shown in Table 1-3 and Table 1-4. Since the materials used to make the convex and concave molds are tool steels, which are relatively expensive and difficult to process, the most suitable material is often selected according to the working conditions of the convex and concave molds and the size of the production batch of the parts.
Blanking and mold
Punching is a stamping process that uses a mold to separate the sheet material along a certain contour line. The die used in blanking is called a blanking die.
According to the different deformation mechanism, blanking can be divided into ordinary blanking and precision blanking. Generally speaking, blanking is ordinary blanking. The fine blanking section is smoother and more precise, but it requires special fine blanking equipment and molds. This chapter mainly discusses ordinary blanking. The die shown in Figure 1-5 is a typical structure of a punching die for stamping a plate-shaped part and the mutual size relationship of its parts.
There are many types of blanking processes. Commonly used are cutting, blanking, punching, trimming, notching, and cutting, among which blanking and punching are the most used. Blanking is punching along the closed wheel line of the shape of the workpiece, and the punched part is the workpiece. Punching is punching along the closed contour line of the inner shape of the workpiece, and the punched part is waste. The gasket shown in Figure 1-6 is completed by two processes of blanking and punching. Figure 1-6(a) shows blanking, Figure 1-6(b) shows punching, and Figure 1-6 (c) shows the finished gasket product. The deformation properties of blanking and punching are exactly the same, but when designing the mold, the method of determining the size of the mold is different. Therefore, the process must be distinguished as two processes.
Blanking process is one of the main methods of stamping production, mainly for the following purposes.
- Directly punch out finished parts
- Preparation of materials for other processes such as bending, deep drawing, and forming;
- Reprocessing the formed workpiece (such as trimming, cutting tongue, drawing parts, punching on bent parts, etc.).
Stamping deformation analysis
- Deformation process of blanking sheet
In the punching process, the convex and concave molds of the punching die to form the upper and lower cutting edges. Under the action of the press, the punch gradually descends, contacts, and pressurizes the material to be pressed, so that the material is deformed and separated. The blanking of the sheet is completed in an instant. When the mold gap is normal, the entire blanking deformation separation process can be divided into 3 stages, as shown in Figure 1-7.
- Elastic deformation stage (Figure 1-7(a))
When the punch begins to contact the sheet material and press down, the sheet material around the punch and the die edge will produce stress concentration, which causes the material to produce elastic compression, bending, deep drawing and other complex deformations. The sheet material is slightly squeezed into the cavity of the cavity. At this time, the material under the male mold is slightly bent, and the material on the female mold is upward. The larger the gap, the more serious the bending and upturning. As the punch continues to press in, until the stress in the material reaches the elastic limit.
- Plastic deformation stage (Figure 1-7(b))
When the punch continues to press down, the stress in the material reaches the yield point, and the material enters the plastic deformation stage. The punch is cut into the upper part of the sheet, while the lower part of the sheet is squeezed into the cavity of the concave mold. The edges of the shear surface of the sheet metal are rounded due to bending and stretching, and at the same time, a small section of bright and vertical straight edges are formed on the cut surface due to plastic shear deformation. As the depth of the punch into the sheet increases, the degree of plastic deformation increases, and the material hardening in the deformation zone increases, and the punching deformation resistance continues to increase until the material on the side near the cutting edge appears micro-cracks due to tensile stress. At the end of the plastic deformation stage, the punching deformation resistance reaches its maximum value. Due to the gap between the convex and concave molds, the sheet metal is also deformed by bending and stretching at this stage. The larger the gap, the greater the bending and stretching deformation.
- Fracture separation stage (Figure 1-7(c))
When the stress of the sheet material reaches the strength limit, the punch continues to press down, cracks occur in the side material near the edge of the concave die, and then the side material near the edge of the punch produces cracks. The formed upper and lower micro-cracks continue to expand into the material as the punch continues to press in. When the upper and lower cracks overlap, the sheet material is sheared and separated. Subsequently, the male mold pushes the separated material into the cavity of the female mold.
From the analysis of the above-mentioned blanking deformation process, it can be seen that the deformation of the blanking process is very complicated. In addition to shear deformation, there are also deformations such as deep drawing, bending, and lateral extrusion. Therefore, the plane of blanking parts and waste materials is not flat and often warps.