Analysis of methods to improve service life of molds (4)

Overall toughening process of mold

Main causes of material failure are stress concentration and fatigue fracture when it comes to produce office equipment plastic parts. In order to increase toughness, reduce brittleness and fracture of ordinary cold work die steel, low temperature quenching and low temperature tempering process can be used; high temperature quenching and high temperature tempering process can significantly enhance toughness and thermal stability of hot work die steel. When mold cavity is large and wall is thin, upper limit of normal quenching temperature is required to increase amount of retained austenite so that mold does not swell. Rapid heating method has a short heating time, a reduced tendency to oxidative decarburization, a small grain size, quenching deformation of large tool of carbon tool steel is small. High-speed steel adopts low quenching and high-returning process, quenching temperature is low, tempering temperature is high, which can greatly improve toughness. Although hardness is reduced, mold can be improved in resistance to fracture and fatigue damage. In order to reduce residual stress, mold should be tempered after quenching. Effect of tempering is to release material due to internal stress generated by quenching in a short time. Tempering should be sufficient, and tempering is insufficient to cause pre-grinding cracks.

Surface strengthening heat treatment process of mold

It has been found that wear and adhesion occur on surface of mold, common fatigue and fracture often start from surface. In order to improve life of mold better and make better Custom Plastic Parts, it is necessary to enhance wear resistance of surface of part, and surface strengthening treatment of main forming parts is the most direct way. Surface strengthening process of mold mainly includes gas nitriding, ion nitriding, electric spark surface strengthening, boronizing, thermal diffusion carbide coating, chemical vapor deposition, physical vapor deposition, laser surface strengthening, ion implantation, plasma spraying, and so on. In actual production, different surface strengthening processes are adopted according to different uses of mold. For example, in order to enhance wear resistance and compressive strength of surface layer of blanking die for mold manufacturers in china, a strengthening method such as electric spark or hard alloy surfacing may be adopted; for surface of hot working die (die-casting mold, plastic mold), nitriding method may be used to enhance wear resistance, heat fatigue resistance and corrosion resistance; drawing die and bending die are mainly wear caused by friction in production, and sulfur permeability process can be used to reduce friction coefficient in order to enhance wear resistance of material. Carbonitriding is suitable for surface strengthening of various types of molds. PVD and CVD in surface coating hardening technology have made great progress in recent years. Vacuum evaporation, vacuum sputtering and ion plating are commonly used in PVD. Among them, ion plating has strong adhesion, fast deposition speed, no pollution. Etc. Ion plating process can plate tic and TIN on surface of mold, and its service life can be extended several times to several tens of times.

(source:https://www.hthc-tech.com/analysis-of-methods-to-improve-service-life-of-molds-4/)