Different types of steel are used as
plastic molds, and their chemical composition and mechanical properties are different, so plastic cnc machining routes are different; similarly, different types of plastic mold steels use different heat treatment processes. This section mainly introduces the manufacturing process route and the characteristics of the heat treatment process of the plastic mold.
1. Explanation of heat treatment terms
1. Annealing
(1) Concept: The heat treatment process of heating steel to an appropriate temperature, keeping it for a certain period of time, and then slowly cooling (usually cooling with the furnace).
(2) Purpose:
a. Increase the hardness of low steel to increase its plasticity (to facilitate cutting);
b. Refine the grains, and even the structure and composition of the steel;
(3) Classification: complete annealing; spheroidizing annealing; stress relief annealing
2. Normalizing
(1) Concept: The process method of heating steel to 30～500C above Ac3 or ACcm, holding it for an appropriate time, and cooling it in air.
(2) Purpose: It is basically the same as the purpose of annealing, but the normalizing cooling rate is slightly faster than annealing, so the pearlite structure obtained after normalizing is relatively fine, and the strength and hardness are higher than that of annealed steel.
Normalizing has a shorter production cycle than annealing and has low cost and easy operation. Therefore, normalizing is preferred under possible conditions, but annealing should be used for complex parts.
3. Quenching
(1) Concept: The heat treatment process of heating steel to a certain temperature above Ac3 or Ac1, holding it for a certain period of time, and then cooling at an appropriate speed to obtain martensite or bainite structure.
(2) Purpose: In order to obtain martensite, improve the strength and hardness of steel.
4. Tempering
(1) Concept: a heat treatment process in which the quenched steel is heated to a temperature below the Ac1 point, held for a certain period of time, and then cooled to room temperature.
(2) Purpose:
a. Eliminate internal stress;
b. Obtain the required mechanical properties (improve the toughness of the steel, appropriately adjust the strength and hardness of the steel);
c. Stable organization and size
1. Low-carbon steel and low-carbon alloy steel molds
For example, the process route of 20, 20Cr, 20CrMnTi and other steels is: blanking→forging die blank→annealing→mechanical rough machining→cold extrusion forming→recrystallization annealing→mechanical finishing→carburizing→quenching, tempering→grinding and polishing →Assemble.
2. High-alloy carburized steel mold
For example, the process route of 12CrNi3A and 12CrNi4A steel is: blanking→forging die blank→normalizing and high temperature tempering→mechanical rough machining→high temperature tempering→finishing→carburizing→quenching and tempering→grinding and polishing→assembly.
3. Quenched and tempered steel mold
For example, the process route of 45, 40Cr and other steels is: blanking→forging die blanks→annealing→mechanical rough machining→tempering and tempering→mechanical finishing→dressing, polishing→assembly.
4. Carbon tool steel and alloy tool steel molds
For example, the process route of T7A～T10A, CrWMn, 9SiCr and other steels is: blanking → forging into die blank → spheroidizing annealing → mechanical rough machining → stress relief annealing → mechanical semi-finishing → fine
cnc machined parts → quenching, tempering → Grinding and polishing → assembly.
5. Pre-hardened steel mold
For example, 5NiSiCa, 3Cr2Mo (P20) and other steels. For those directly processed with bar stocks, they have been pre-hardened due to the supply status, and can be directly processed and formed, then polished and assembled. For those that need to be forged into blanks and then processed into forming, the process route is: blanking→forging→spheroidizing annealing→planing or milling six sides→pre-hardening treatment (34～42HRC)→mechanical roughing→stress relief annealing→ Mechanical finishing → polishing → assembly.
