The life of molds of different materials is often different. For this reason, two basic requirements are proposed for the material of the working parts of the die: the performance of the material should have high hardness (58-64HRC) and high strength, and have high wear resistance and sufficient toughness. The hot hardness; good process performance. The manufacturing process of die working parts is generally complicated, so it must have adaptability to various processing techniques, such as forgeability, machinability, hardenability, hardenability, quenching crack sensitivity and grinding processability, etc. .
Heat treatment: deformation caused by improper quenching and tempering process
Practice has proved that the thermal processing quality of the mold has a great influence on the performance and service life of the mold. From the analysis statistics of the cause of mold failure, we know that about 40% of the “accidents” caused by improper heat treatment are mold failures.
(1) Forging process This is an important part in the manufacturing process of mold working parts. For high-alloy tool steel molds, technical requirements are usually placed on the metallographic structure of the material carbide distribution.
(2) Preliminary heat treatment Depending on the material and requirements of the die working parts, preliminary heat treatment processes such as annealing, normalizing or quenching and tempering are used to improve the organization, eliminate the defects of the forged blank, and improve the processability. After proper pre-heat treatment, the high-carbon alloy die steel can eliminate the network secondary cementite or chain carbide, make the carbide spheroidized and refined, and promote the uniformity of carbide distribution, which is conducive to ensuring quenching and tempering Quality, improve mold life.
(3) Quenching and tempering This is a key link in the heat treatment of molds. If overheating occurs during quenching and heating, it will not only cause greater brittleness of the workpiece, but also cause deformation and cracking during cooling, which will seriously affect the life of the mold. Special attention should be paid to prevent oxidation and decarburization during die quenching and heating, and the heat treatment process specifications should be strictly controlled. Vacuum heat treatment can be used if conditions permit. After quenching, it should be tempered in time, and different tempering processes should be used according to the technical requirements.
(4) Stress relief annealing After rough machining of die working parts, stress relief annealing should be carried out, the purpose is to eliminate the internal stress caused by rough machining, so as to avoid excessive deformation and cracks during quenching. For the molds with high precision requirements, after grinding or electrical processing, they need to undergo stress relief and tempering treatment, which is conducive to stabilizing the mold accuracy and increasing the service life.
The flatness of the mold grinding is not enough, resulting in deflection deformation
The quality of the surface of the working parts of the mold has a very close relationship with the wear resistance, fracture resistance and adhesion resistance of the mold, which directly affects the service life of the mold, especially the surface roughness value has a great influence on the mold life. If the surface roughness value is too large, stress concentration will occur during work, and cracks are easily generated between its peaks and valleys, which affects the durability of the die and the corrosion resistance of the workpiece surface, which directly affects the service life of the die And accuracy, for this, the following should be noted:
(1) During the processing of mold working parts, the surface phenomenon of grinding and burning parts must be prevented, and the grinding process conditions and process methods (such as grinding wheel hardness, particle size, cooling liquid, feed rate and other parameters) should be strictly controlled;
(2) During the machining process, it should prevent macro defects such as knife marks, interlayers, cracks, and impact scars from remaining on the surface of the working parts of the mold. The presence of these defects will cause stress concentration and become the source of fracture, causing early failure of the mold;
(3) Adopt grinding, grinding, polishing and other finishing and fine processing to obtain a smaller surface roughness value and improve the service life of the mold.
Design process
The mold strength is not enough, the blade gap is too close, the mold structure is unreasonable, the number of template blocks is not enough, there is no pad foot, the mold is not guided accurately, and the gap is unreasonable.
(1) Layout and lap Unreasonable reciprocating feeding layout method, and too small lap value, will often cause sharp wear of the mold or convex and concave die bite. Reasonably choose the nesting method and edge value to increase the life of the mold.
(2) The precision and reliable guidance of the guiding mechanism of the mold has a great impact on reducing the wear of the working parts of the mold and avoiding the bite damage of the convex and concave molds, especially blanking dies, compound dies and multi-stations Progressive die is more effective. In order to improve the life of the mold, it is necessary to correctly select the guide form and determine the accuracy of the guide mechanism according to the requirements of the nature of the process and the accuracy of the parts.
(3) Mold (convex and concave) cutting edge geometry parameters.
Wire cutting process
Artificial ground wire cutting, wire cutting gap treatment is not correct, there is no impact on the metamorphic layer of angle cutting and wire cutting.
Die cutting edge mostly adopts wire cutting. Due to the thermal and electrolytic effects of wire cutting, a certain thickness of metamorphic layer is produced on the surface of the die processing, resulting in reduced surface hardness and micro cracks. The die of wire cutting is prone to early wear and directly affects the die gap Keeping and cutting edge easy to chip, shorten the service life of the mold. Therefore, in the online cutting process, a reasonable electrical standard should be selected to minimize the depth of the metamorphic layer.
Selection of punch equipment
Tonnage of punching machine, the punching force is not enough, and the die adjustment is too deep.
The accuracy and rigidity of stamping equipment (such as presses) are extremely important to the impact of die life. The punching equipment has high precision and good rigidity, and the die life is greatly improved. For example, the die material of the complex silicon steel sheet is Crl2MoV, which is used on ordinary open presses, and the average regrind life is 1-30000 times; while used on new precision presses, the regrind life of the die can reach 6-120000 times.
Stamping
The tolerance of raw material thickness of stamping parts is excessively poor, the material performance fluctuates, the surface quality is poor (such as rust) or unclean (such as oil stains), etc., which will cause the adverse effects of increased wear of the mold working parts and easy chipping. To this end, it should be noted:
(1) Use raw materials with good stamping process as much as possible to reduce the stamping deformation force;
(2) Before stamping, the grade, thickness and surface quality of the raw materials should be strictly checked, and the raw materials should be wiped clean. If necessary, the surface oxides and rust should be removed;
(3) According to the stamping process and the type of raw materials, softening and surface treatment can be arranged if necessary, and the appropriate lubricant and lubrication process can be selected
