Heat Treatment Of Plastic Mold

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With the rapid development of my country’s plastics industry, plastic products have been widely used in every aspect of our lives, such as commodity packaging, building materials, auto parts and so on. In recent years, the demand for precision plastic products has continued to increase, and the market potential is huge. Correspondingly, the market for plastic molds in my country is also expanding, and the requirements for mold making technology are also increasing. The heat treatment process is a key link in the production of plastic molds and is closely related to the production quality and performance of plastic molds.

1. Important factors of heat treatment

1.1 Precision of plastic mold

The deformation produced during the heat treatment is the main problem that causes the accuracy of the plastic mold to decrease. Specifically, during the heat treatment of the mold, due to the difference in the heating rate and cooling rate of each surface, a temperature difference occurs on each surface. This leads to uneven volume expansion of the mold. Causes uneven transformation of the mold organization. As a result, tissue stress and thermal stress are generated. When the residual stress generated during the heat treatment exceeds the maximum bearing range of the mold, it will cause the mold to deform, reduce the accuracy of the mold, or even fail.

1.2 The strength of the plastic mold

The heat treatment process of the plastic mold is an important factor that determines its strength. Specifically, when the selection of the heat treatment process is unreasonable, the operation of the heat treatment process is not standardized, or the heat treatment equipment has obstacles, the strength of the plastic mold will be reduced, resulting in unqualified molds. Therefore, when producing plastic molds, manufacturers must adopt the corresponding heat treatment process according to the different strength requirements of the mold and the different mold materials.

1.3 The service life of plastic molds

The heat treatment process of the plastic mold is also a key factor in determining its service life. Specifically, when the heat treatment process is unreasonably selected or the operation is not standardized, it will cause problems such as unreasonable structure and excessive grain size of the mold during the heat treatment process, which will reduce the toughness of the plastic mold and the resistance to cold and heat fatigue. , The wear resistance becomes worse, which will eventually reduce the overall performance of the mold and affect the service life of the mold.

1.4 The production cost of plastic molds

The production cost of plastic molds is closely related to the heat treatment process. Specifically, when the mold uses an improper heat treatment process or the operation is not standardized, it will cause the mold’s wear resistance, corrosion resistance, cold and heat resistance, toughness, hardness and strength to decrease, and even cause the mold to deform , Invalidation. Therefore, the use of a reasonable heat treatment process can improve the production quality of plastic molds, thereby reducing the production cost of the molds and improving the economic benefits of manufacturers.

2. The key process of heat treatment

2.1 Normalizing process

The normalizing process is also an important part of the heat treatment process. It is similar to the heating temperature during annealing, but it uses a faster cooling rate than annealing. Specifically, when the metal mold is heated to a certain temperature (usually between 727 and 912 degrees Celsius), keep it warm for a period of time, and then let it cool naturally in the air, or accelerate the cooling by blowing, spraying, water spraying, etc. , And finally get the pearlite type tissue. The normalizing process is mainly to refine the grains in the metal mold, eliminate the residual stress generated in the heat treatment process, make the carbide structure distribution in the mold more uniform, and increase the hardness, toughness and strength.

2.2 Annealing process

The annealing process is the key link of the heat treatment process. Mainly used in metal molds. Specifically, when the metal mold is heated to a certain temperature, it is kept for a period of time, and then it is slowly cooled to room temperature to bring it close to the equilibrium structure. Master of annealing process

The main function is to remove the residual stress generated during the heat treatment of the mold, reduce the risk of their deformation, and improve its accuracy. In addition, the annealing process can also reduce the grain size, make the structure of the mold more reasonable, and increase the service life of the mold. According to the different heating temperature during heat treatment, we can divide the annealing process into four categories, namely complete annealing. Incomplete annealing, isothermal annealing and spheroidizing annealing.

2.3 Quenching process

Quenching process is the key link to strengthen the hardness of the mold during heat treatment. Specifically, when the metal mold is heated to a certain temperature (above the critical temperature Ac1 and Ac3), it is kept for a period of time, so that the structure of the mold becomes cold austenite. Then accelerated cooling is performed at a speed higher than the critical quenching rate. The mold structure is transformed from austenite to martensite or bainite. The quenching process must be based on the size and material of the mold to reasonably control the heating speed of the mold, the quenching temperature, the holding time and the cooling speed, otherwise it will cause internal stress during the quenching process. Leading to the deformation and cracking of the metal mold, in order to obtain the correct quenching cooling rate, it is necessary to use a suitable quenching medium. The commonly used media in industrial production are NaCl solution, NaOH solution, and various mineral oils.

2.4 Tempering process

The tempering process is also an important method to strengthen the hardness of the mold in the heat treatment. Most metal molds must undergo a tempering process after quenching. Specifically, when the quenched metal mold is heated to a certain temperature (below the critical temperature), it is kept for a period of time, and then it is allowed to cool naturally in the air, or accelerated cooling through water or oil injection, and finally the mold reaches steady state. The tempering process is mainly used to reduce the stress generated during quenching to enhance the toughness, strength and hardness of the mold. Make the performance of the mold meet the standard. According to the temperature during the tempering process, we divide the tempering into three types of processes, namely low temperature tempering, medium temperature tempering and high temperature tempering.

Generally speaking, the heat treatment process is a key link in the production of plastic molds, which directly affects the production quality and performance of plastic molds. In the process of manufacturing plastic molds, manufacturers must comprehensively consider various factors such as mold accuracy, strength, service life and production cost, and select appropriate normalizing, annealing, quenching and tempering processes to ensure the production quality and use of plastic molds performance.

Editor: Frank Lee

Copyright: SIMUWU Vacuum Furnace