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The basic factors that affect the mould life

Posted by admin on Jun 26th, 2015

Mold design, mold material, hot and cold processing, heat treatment, grinding, adjustment and operation of the machine,  the nature and status of processing of materials, and die lubrication service environment are the eight fundamental factors affect tool life.

1. Mold design.

Irrational structure design is often caused by mold early failure and an important factor in heat deformation cracking. The structural design of the mold should avoid sharp corner and over large cross-sectional changes. Concentrated stress caused by sharp rounded up to 10 times the average calculated stress. When due to the requirements of the mold structure, when a sharp corner is not allowed to eliminate, you can change the composition or the overall structure of the fillet on the final heat treatment after machining. As in the square head bolts, the original design made by cold heading die upsetting, life 500, the punch rounded transition stress concentration broken; later to improve the design and increase the radius of rounded transition parts by R = 01127mm increased to 01381 ~ 015mm, life expectancy has increased to 12,000 to 27,000, still rounded transitions failure; the second designed to improve the composition, life expectancy increased to 100,000, and ultimately to wear failure [3]. To prevent heat deformation and cracking, even sought to cross-sectional dimension, shape and strive to symmetry and simple, blind holes as possible to open a through hole, the hole can be opened when the process necessary for the complex shape of the mold can be easily deformed crack into modular.

2. Mold material and heat treatment

Mold material impact on die life is reflected in the choice of mold material is correct, the material is good and reasonable use of three aspects. When the selection must take into account the performance requirements of mold. Die should be the main consideration for the strength of steel, toughness and wear resistance. Often shift between strength and toughness and wear resistance and toughness. When the primary failure mode of the mold is brittle cracking may consider choosing a lower intensity but better toughness of the material or to establish a reasonable heat treatment process to improve the toughness of the steel can also choose to have a high strength and high toughness according to the actual situation of advanced alloys steel. From the perspective of both toughness and wear resistance in addition to the overall selection and reasonable, it can also be considered to ensure toughness while using reasonable surface treatment to improve the wear resistance of the mold. Plastic mold steel to take into account when selecting its strength, wear resistance and corrosion resistance at the plastic molding temperature, taking also into account its workability and mirror degrees.

Improper heat treatment is an important factor leading to early failure of the mold. Effect of heat treatment on the life of the mold heat treatment technology is mainly reflected in the quality of heat treatment demands are unreasonable and bad aspects. Statistics show that since the selection and improper heat treatment, resulting in mold early failure of about 70%.

3. hot and cold processing

Effect of forging and machining of die life, and often overlooked, is not correct
Forging and machining indeed often a key cause of early failure of the mold. In Cr12MoV steel, for example, that steel is one of the most commonly used cold work tool steel and high-carbon high-chromium ledeburite, rich in primary and secondary carbides, segregation greatly. Therefore, improving the distribution of their carbide become an important part to improve die life.

Incorrect machining may result in the following three aspects of early failure of the die: ¹ improper cutting, forming a sharp corner or too small radius is often caused by stress concentration, so that the mold early failure; º surface finish is not enough, there is not a allow the marks, often due to early fatigue failure of the mold and failure; »machining is not completely removed even decarbonization layer formed by rolling and forging, heat treatment causes the mold to form a soft spot and excessive residual stress leading to early failure of the die .

4. Grinding and EDM

Grinding metal surfaces may cause overheating, resulting in high surface residual stress and organizational changes, the result may lead to grinding cracks. Often
See grinding defects, grinding metal burns caused by excessive speed; grinding cracks caused by improper use or overload with a blunt or too small grinding wheel grinding wheel and the coolant. Fine grinding cracks are difficult to observe with the naked eye, the required magnetic particle or cold dilute nitric acid erosion can only be displayed. Light grinding cracks often distributed in the grinding direction perpendicular parallel, severe crack-like form grinding cracks. These grinding cracks can even be removed by light grinding, but hazards still exist, often leading to mold early failure in service.
EDM is often used as a mold finishing operations. EDM can be quenched martensite formed white layer on the surface of the quenching and tempering of the mold, due to the inherent brittleness and microcracking presence of high carbon martensite, often leading to early failure of mold cracking. In addition, the EDM in the mold surface formation of undesirable residual stress, reduced life of the mold.

5. Adjustment and operation of the machine

Excellent material, design right, good hot and cold processing, heat treatment and reasonable mold, due to improper use of the machine to adjust and operate, service may still be in the process of early failure. Machine adjustment and operational factors include precision, rigidity, gap adjustment machine, positioning allowed and occasional overload. Seriously these factors will help to identify the real cause of die failure, the greater volatility in the life of the mold production, often with the machine to adjust and use the operating factors, must be given adequate attention.

In addition to these factors, the lubrication conditions and the material, hardness, size and flatness of the end face of the mold materials processing external factors, it will affect the life of the mold.

posted by Hillary Wang

Huangyan Zhilian Mould & Plastic Co., Ltd.

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