How To Prevent Mold Cracking

1.Stamping equipment

The accuracy of stamping equipment (such as presses) and the impact of rigid on die life are extremely important. The precision of the stamping equipment is high, the rigidity is good, and the die life is greatly improved. Especially for small gap or gapless die, carbide die and precision die, it is necessary to select a press with high precision and good rigidity. Otherwise, the die life will be reduced, and the chess piece will be damaged in severe cases.

2. Mold design

(1) Precision of the guiding mechanism of the mold. In order to improve the life of the mold, it is necessary to correctly select the guiding form and determine the accuracy of the guiding mechanism according to the requirements of the nature of the process and the accuracy of the parts.

(2) Geometric parameters of the die (convex, concave die) edge. The shape of the convex and concave molds, the fit clearance and the fillet radius not only have a great influence on the forming of the stamping part, but also have a great influence on the wear and life of the mold. For higher precision requirements, a smaller gap value should be selected; otherwise, the gap can be appropriately increased to improve the life of the mold.

3. Stamping process

(1) Raw materials for stamped parts.

1) Use as much as possible of the stamping process of raw materials 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 treatment and surface treatment may be arranged as necessary, and a suitable lubricant and lubrication process may be selected.

(2) Layout and edging.

Unreasonable reciprocating feed patterning and too small edge values often cause sharp wear of the mold or bruises on the convex and concave molds. According to the processing batch size, quality requirements and mold matching clearance of the parts, the layout method and the edge value must be reasonably selected to improve the life of the mold.

4. Mold material

The material should have high hardness (58~64HRC) and high strength, high wear resistance and sufficient toughness, small heat treatment deformation, certain thermal hardness and good process performance.

5. The hot processing quality of the hot working process has a great influence on the performance and service life of the mold.

(1) Forging process. This is an important part of the manufacturing process of mold work parts. The forging temperature range should be strictly controlled, the correct heating specification should be established, the correct forging force method should be used, and the post-forging slow cooling or timely annealing should be carried out.

(2) Preparatory heat treatment. Pre-heat treatment processes such as annealing, normalizing or quenching and tempering should be used depending on the materials and requirements of the mold working parts to improve the structure, eliminate the structural defects of the forged blank, and improve the processing technology.

(3) Quenching and tempering. This is the key link in the heat treatment of the mold. Special care should be taken to prevent oxidation and decarburization during die quenching. The heat treatment process specification should be strictly controlled. Vacuum vacuum heat treatment can be used if conditions permit. After quenching, it should be tempered in time, and different tempering processes should be adopted according to technical requirements.

(4) Stress relief annealing. For molds with high precision requirements, it needs to be subjected to stress relief and tempering after grinding or electric machining, which is beneficial to stabilize mold precision and improve service life.

6. Control of wire cutting metamorphic layer

The die edge is mostly processed by wire cutting. Due to the thermal effect and electrolysis of the wire cutting process, a certain thickness of the metamorphic layer is produced on the surface of the die, resulting in a decrease in surface hardness and microcracking, which causes the die of the wire cutting process to be prone to early wear and directly affect the punching clearance of the die. Keep and the edge is easy to chip and shorten the life of the mold. Therefore, a reasonable electrical standard should be selected in the online cutting process to minimize the depth of the metamorphic layer.

7. Processing surface quality

(1) During the processing of the mold working parts, it is necessary to prevent the surface of the burned parts from being ground. The grinding process conditions and technological methods (such as grinding wheel hardness, particle size, coolant, feed rate, etc.) should be strictly controlled;

(2) During the processing, the surface of the working part of the mold should be prevented from leaving a knife mark. Macroscopic defects such as interlayers, cracks, and impact flaws. The presence of these defects can cause stress concentration and become the source of the fracture, causing early failure of the mold;

(3) Finishing and fine processing such as grinding, grinding and polishing to obtain a small surface roughness value and improve the service life of the mold.

8. Surface strengthening treatment

In order to improve the performance and service life of the mold, the surface strengthening treatment of the mold working parts is becoming more and more widely used. Commonly used and enhanced treatment methods are: liquid carbonitriding, ion nitriding, boronizing, vanadium and spark strengthening, as well as chemical vapor deposition (CVD), physical vapor deposition (PVD) and in salt baths. The surface of the workpiece is immersed in a carbide method (TD) or the like.

9. Proper use and reasonable maintenance

In order to protect normal production, improve the quality of stamping parts, reduce the cost, and extend the life of the die, the mold must be properly used and properly maintained, and the “three-check” system of the die (check before use, check during use and check after use) and do Good die and maintenance work.

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