1. The main causes of mold cracking are as follows.
1. 1 Reasonable selection of materials according to requirements is the most critical first step.
After the material 1.2 is determined, the metallographic structure is the key to determine the properties.
1.3 in order to ensure a good metallographic structure, we should strengthen control from the following aspects:
1.3. 1 Formulate a reasonable forging process.
1.3.2 The heat treatment process after forging should meet the actual requirements and control the metallographic structure in the best state.
1.3.3 The formulation of heat treatment process for finished products includes chemical heat treatment and ice cooling treatment in addition to quenching and tempering.
1.4 The flatness and roughness of die grinding are unqualified.
1.5 The design strength of the mould shall fully meet the requirements of use.
1.6 The mold structure should be reasonable.
1.7 effective treatment measures should be taken for wire cutting dies.
1.8 peeling is not smooth. There is no demagnetization treatment before production, no waste products, etc.
1.9 When the blanking is not smooth, there is no chip leakage or chip rolling.
1. 10 production: lamination stamping, poor positioning, etc.
Step 2 equip
The precision and rigidity of stamping equipment have great influence on the life of stamping die. The stamping equipment has high precision and good rigidity, and the service life of stamping die is greatly improved. For example, the die material of complex silicon steel sheet is Crl2MoV, and the average regrinding life is1~ 30,000 times when used in ordinary open press, while the regrinding life of the die can reach1.2000 times when used in new precision press. Especially for small gap dies, cemented carbide dies and precision dies, we must choose equipment with high precision and good rigidity, otherwise the service life of the dies will be shortened or even damaged.
3. Mold design
3. 1 Accuracy of mold guide mechanism
Accurate and reliable guidance has a great influence on reducing the wear of die parts and avoiding the damage of punch and die, especially for small gap blanking die, compound die and multi-position progressive die. In order to improve the service life of the die, it is necessary to correctly select the guide form and determine the accuracy of the guide mechanism according to the requirements of process properties and parts accuracy. Generally speaking, the precision of guide mechanism should be higher than that of male die and female die.
3.2 Geometric parameters of cutting edge of dies (punch and die)
Shape, fit clearance and fillet radius not only have great influence on stamping parts forming, but also have great influence on die wear and life. For example, the fit clearance of die directly affects the quality of blanking parts and the life of die. If the accuracy requirement is high, a smaller clearance value should be selected; On the contrary, the gap can be appropriately increased to improve the service life of the die.
4. Stamping process
4. 1 raw materials for stamping parts.
In actual production, due to the large tolerance of raw material thickness, large fluctuation of material properties, poor surface quality or poor cleanliness of external pressed parts, die wear will be aggravated and edges will easily collapse.
4. 1. 1 Use raw materials with good stamping process as much as possible to reduce stamping deformation force;
4. 1.2 Before stamping, the brand, thickness and surface quality of raw materials should be strictly checked, and the raw materials should be wiped clean, and surface oxides and rust should be removed if necessary;
4. 1.3 According to the stamping process and the types of raw materials, softening treatment and surface treatment can be arranged when necessary, and the appropriate lubricant and lubrication process can be selected.
4.2 Layout and hem.
Unreasonable reciprocating feeding layout and too small overlap value will often cause severe wear of the die or damage of the convex and concave die. Therefore, while considering improving the utilization rate of materials, it is necessary to reasonably select the layout method and overlap value according to the processing batch, quality requirements and mold fit clearance of the parts to improve the life of the mold.
5. Mold materials
Correct selection of materials is the key to improve die life. Such as chemical composition, metallographic structure, hardness and metallurgical quality. The service life of dies made of different materials is often different. Therefore, mold materials should be strictly controlled in the following two points.
5. 1 The material should have high hardness and strength, high wear resistance and sufficient toughness, small heat treatment deformation and certain thermal hardness;
5.2 Good process performance. The manufacturing technology of stamping die is generally complex, and it must adapt to various processing technologies, such as malleability, machinability, hardening ability, hardenability, low sensitivity to quenching cracks, good grinding processability and so on. Usually, according to the material characteristics, production batch and precision requirements of stamping parts, considering its manufacturability and economy, the die material with excellent performance is selected.
6, hot processing technology
Practice has proved that the hot working quality of die has great influence on the performance and service life of die. According to the analysis and statistics of the causes of mold failure, the "accident" of mold failure caused by improper heat treatment accounts for more than 45%. The quenching deformation, cracking and early fracture of the die are mostly related to the hot working technology of the die.
6. 1 forging process. This is an important link in the mold manufacturing process. For the die of high alloy tool steel, it is usually required to have metallographic structure such as carbide distribution. In addition, the forging temperature range should be strictly controlled, the correct heating specification should be formulated, the correct forging method should be adopted, and the forgings should be slowly cooled or annealed in time.
6.2 preheating treatment. According to the material and requirements of the die, the preliminary heat treatment processes such as annealing and tempering are respectively adopted to improve the structure, eliminate the structural defects of forgings and blanks, and improve the processability. After proper preheating treatment, high carbon alloy die steel can eliminate network carbide, spheroidize and refine carbide, and promote the uniformity of carbide distribution. This is beneficial to ensure the quenching and tempering quality and improve the service life of the die.
6.3 Quenching and tempering. This is the key link of mold heat treatment. If overheating occurs during quenching and heating, it will not only make the workpiece brittle, but also easily cause deformation and cracking during cooling, which will seriously affect the service life of the die. When quenching and heating dies, special attention should be paid to prevent oxidation and decarbonization, and the technical specifications of heat treatment should be strictly controlled. If conditions permit, vacuum heat treatment can be used. Tempering should be done in time after quenching, and different tempering processes should be adopted according to technical requirements.
6.4 Stress relief annealing. After rough machining, the die should be annealed to eliminate the internal stress caused by rough machining and avoid excessive deformation or crack caused by quenching. For molds with high precision requirements, it is necessary to carry out stress relief tempering after grinding or electrical machining, which is beneficial to stabilize the mold precision and improve the service life.
7, processing surface quality
Die surface quality is closely related to die life. Especially the surface roughness has a great influence on the service life of the die. If the surface roughness is too large, stress concentration will occur when working, and cracks will easily occur at its tiny sharp corners, which will affect the durability of the mold and the corrosion resistance of the workpiece surface and directly affect the service life and accuracy of the mold.
7. 1 The mold must be prevented from overheating and annealing during grinding, and the grinding process conditions and methods (such as grinding wheel hardness, particle size, coolant, feed speed and other parameters) must be strictly controlled;
7.2 Macro defects such as knife marks, interlayers, cracks and impact scars should be prevented during processing. The existence of these defects will cause stress concentration, become the root of fracture, and lead to early failure of the mold;
7.3 Finishing and finishing such as grinding, grinding and polishing are adopted to improve the surface roughness and prolong the service life of the mold.
8. Surface strengthening treatment
In order to improve the performance and service life of the die, the surface strengthening treatment of the die has been more and more widely used. Commonly used surface strengthening treatment methods include nitrocarburizing, nitriding, boronizing, vanadizing, BRN treatment, chemical vapor deposition (CVD), physical vapor deposition (PVD) and surface carburizing (TD). Improving its fatigue strength is beneficial to improve the service life of the die.
9, WEDM metamorphic layer control
The cutting edge of stamping die is mostly machined by wire cutting. Due to the thermal effect and electrolysis of WEDM, a metamorphic layer with a certain thickness is produced on the die surface, which leads to the decrease of surface hardness and the appearance of micro-cracks, which makes WEDM die prone to early wear, directly affects the maintenance of die blanking gap, and is easy to collapse and shorten the service life of the die. Therefore, reasonable process parameters should be selected during on-line cutting to minimize the depth of metamorphic layer and remove metamorphic layer.
10, used correctly and maintained reasonably.
In order to ensure normal production, improve the quality of stamping parts, reduce costs and prolong the service life of stamping dies, it is necessary to use and maintain the dies correctly, strictly implement the "three inspections" system of stamping dies (pre-use inspection, in-use inspection and post-use inspection), and do a good job in the use and maintenance of stamping dies. Its main work includes the correct installation and debugging of the mold; Strictly control the depth of the punch into the die; Control and correct bending, cold extrusion, forming, etc. Re-grinding and polishing its cutting edge in time; Pay attention to keep the mold clean and properly lubricated. Correct use and reasonable maintenance of dies are of great significance to improve the life of dies.
In a word, advanced manufacturing technology and total quality management should be applied to the whole process of design, manufacture, use and maintenance to improve the service life of molds, which is an effective guarantee to improve the service life of molds. In addition to the standardization of parts, there are also standardization of design parameters, combination forms and processing methods, so as to continuously improve the design and manufacturing level of molds and help to improve the service life of molds.