Process and Characteristics of Precision Mold Processing

Posted on : July 27 , 2022 By  GREFEE

If you are looking for high precision injection molding, you need a set of the high precision mold. The high precision mold suppliers generally can meet your processing requirements. Before this, you need to communicate about the project to provide the drawing to the suppliers.

A set of mold is composed of multiple components and the quality is directly related to the mold quality. The quality of the end products is ensured with the high precision processing. Thus, the control of the high precision processing is essential. The precision mold suppliers usually use grinding,  electric machining and fitter treatment at the beginning. At this stage, the deformation, internal stress, and shape tolerance and dimension accuracy, and other coefficients of the part should be paid attention to.

China precision die processing process:

The manufacturing of the mold parts is according to the appearance of the parts, which can be classified into three types: plates, special-shaped parts and shafts. The common process is roughly as follows: rough machining – heat treatment (quenching and tempering) – fine grinding – electrical machining – fitter (surface treatment) – assembly processing.

1. Thermal treatment of parts

The process of the thermal treatment  of the part should ensure the dimension stability of the parts when processing, and the hardness and internal stress control also meet the standards. The treatment varies according to the material types.

The high strength and wear resistance can be obtained from the one-time hardening process, which is really effective to the mold with wear as the main failure form. Processing workpieces with many corners and complex shapes, tempering, stress relief annealing or multiple aging treatments are used together to eliminate the quenching stress. The secondary hardening process, start with quenching at 1050-1080 ℃ and then tempering at 490-520 ℃ for many times, it can produce the impact, toughness, and stability, suiting for molds with the main failure form of broken edges. Powder alloy steel are expensive but has performance. It is becoming a widely used trend.

2. Grinding of parts

There are three main types of lathes used for grinding: surface grinder, internal and external grinder and tool grinder. During finishing grinding, the generation of grinding deformation and grinding cracks should be avoided, even very small cracks will also be exposed in subsequent processing.

3. EDM control

EDM is indispensable for the modern mold manufacturers since it can process all types of abnormal and parts with high hardness requirement. It includes wire cutting and EDM.

4. Surface treatment and assembly

The tool marks and grinding marks left on the part surface during machining are the places where the stress is concentrated and the source of crack expansion. Therefore, it is necessary to strengthen the part surface and polish it after machining by fitter to eliminate the risks. Some edges, acute angles and orifices of the workpiece should be blunt and R-shaped. Generally, machined surfaces produce 6-10 μm the metamorphic hardening layer in gray white. The hardening layer is brittle and has residual stress. Make sure that the hardening layer is fully removed before using by polishing.

Based on practice, the good finishing process control can effectively reduce problems  like out of tolerance and scrapping rates. Besides, it can effectively improve the first-time success rate and mold service life.

Characteristics of high precision mold：

Compared to the ordinary mold, the high precision mold has higher requirement during the manufacturing, which is on its raw material, designing, processing, accuracy, dimension and other aspects. The processing process must be completed with the high precession processing molding technique. What are the characteristics of high precision mold, GREFF engineer team collects and concludes the relevant content.

Six molding requirements of high precision mold

1. Products specification: high accuracy and small dimension tolerance, with high premise specification limits.

2. The repetition precision standard of products is high with a day. month. year size reliability.

3. Good material with sufficient rigidity. The appearance dimension accuracy, smoothness and accuracy between templates of the female mold is high.

4. Select high precision plastics machine to replace the basic plastics machine.

5. Select high precision molding process.

6. Select raw materials integrated into high-precision forming.

The key of the precision mold processing must be on precision. Precision mold has extreme high requirements for dimensional tolerance, which is generally +/-0.005. The main specifications of many precision molds are without a slope. However, in the mold production, the tolerance grade plus a small slope will be flexibly used, such as the installation of transmission gear column head, etc. The operability and controllability of machining must be considered when designing the drawings of precision molds to ensure the smooth processing.

Four main characteristics of precision mold

1. Wear resistance

During the plastic deformation and transformation of the blank in the injection mold female mold, it flows and rolls along the surface of the mold cavity, generating the fierce friction between the surface of the mold cavity and the blank. It further results in the invalidation of the abrasive tool due to damage. Hence, the corrosion resistance is one of the most important features.

Strength also has a big impact on the wear resistance. Typically, the higher the mold strength, the smaller the wear possibility, the higher the wear resistance. Other than that, the wear resistance is also related to the type of cementite sum, shapes, dimensions and distribution.

2. Great ductility

Most of the mold working standards are extremely high because some molds need to bear a high impact load and become brittle after a long term of use. To avoid the brittle cracking in working, high hardness and ductility are required in the precision hardware mold.

The key of the ductility of the mold are the carbon content of the raw material. The size of the grains and structure status.

3. Fatigue cracking

In the mold working, the long term circulating pressure will lead to the fatigue cracking, which includes different types, like repeated impact with small kinetic energy leads to fatigue and fracture stretching fatigue rupture, touch fatigue rupture, and bending fatigue rupture.

The key to the mold fatigue cracking is the compressive strength, ductility strength and the ingredients the impurities in its raw materials

4. High temperature feature

When the mold working under a very high temperature, the strength and hardness will be decreased, leading to the damages in the first stage or invalidation due to the plastic deformation. Thus, the steel used in the precision hardware mold should have high reliability of quenching resistance to ensure that the mold is equipped with sufficient strength and compress strength to work under room temperature.

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