Several aspects of stress after casting molds
Stresses including thermal and mechanical stresses, mainly produced in mechanical, chemical, operational impact, heat. It describes several aspects of stress after.
First, the die-casting production process
1. The cooling temperature control system should be set up to keep the mold temperature within a certain range.
2. In the production process, the mold temperature rising, when the mold temperature overheat, prone to sticky mode, moving parts failed and caused damage to the mold surface.
3. In the pre-production mold should be preheated to a certain temperature, otherwise the chilled when hot liquid metal filling, leading to mold the inner and outer layers temperature gradient increases, the formation of thermal stress, the mold surface cracking, even cracking.
Second, the mold process.
1. steel quenching stress is the result of the cooling process of thermal stress and the stress phase transition superimposed, quenching stress is caused by deformation, cracking reasons, solid must be tempered to eliminate stress.
2. improper heat treatment, can cause mold cracking and premature retirement, especially using only tempered, not quench, then surface nitriding process, after thousands of die-casting mold views show surface cracking and cracking.
Third, in the mold manufacturing process
1. EDM stress. Mold surface layer of rich white light collector elements and dielectric elements, hard and brittle, will crack this layer itself, there is stress. EDM should use high frequencies, so to minimize the white layer must be polished to remove, and tempering, tempering at the tempering temperature.
2. rough forging quality problems.
Some molds can produce only a few hundred pieces of crack, and crack has developed rapidly. There may be only guaranteed when forging the dimensions, and the steel of the dendrites, the carbide inclusions, shrinkage, bubbles and other defects in the machine is extended loose stretched, forming a flow line, this flow line on the later final quenching deformation, cracking, embrittlement during use, failure tends to great impact.
3. produce hardened steel grinding grinding stress, frictional heat generated during grinding, producing softened layer, carbon layer, reducing the thermal fatigue strength, easily lead to hot cracking, early cracks. After grinding to h13 steel, it can be taken and heated to 510-570 ℃, to one hour per 25mm thickness of insulation stress relief annealing.
Cutting stress 4. When turning, milling, planing and other processing to produce the final, and this stress can be eliminated by intermediate annealing.