1. Mold materials.
Due to the large extrusion pressure of cold mold, high strength, good toughness and good wear resistance are selected.Because the working condition of the punch mode is more likely to be affected by the eccentric force than the concave mode, the wear resistance of the punch material should be higher than the die material.
Ii. Heat treatment
Mold heat treatment includes: after the cold mold is forged, the mold is tempered in a timely manner to refine the grain, and the back fire after rough machining is used to eliminate the stress, the electric spark, and the post-cut stress low temperature tempering.Experience shows that the mould with a diameter of less than 80mm should be machined directly by rod, and no need to be forged, because it can cause the defects such as burning, coarse crystal and partial analysis.
The quenching cooling rate is too fast and the swimming temperature is too low.If the tempering temperature is too low and insufficient, the residual stress in the quenching process will not be eliminated, and the toughness of the die will be reduced, and the early fracture is easy to occur.
Three cold structure for the mold, mold design must have enough strength, stiffness, reliability, and good guidance, but the structure of the mould is not reasonable will directly affect the service life of mould.Working parts of die should be designed to be large enough radius, avoid sharp-angled transition to produce stress concentration, the width of the ligament should be reasonable design according to the metal flow situation, in order to minimize friction, generally between 1.5 to 3.5.
Iv. Mould processing.
The following measures should be taken in the process of cutting tools;Improve the surface roughness, grinding traces of micro cracks formation, transitional part to smooth, not organic processing tool marks and tiny flaws, to prevent the occurrence of stress concentration in use process lead to crack.