When the Chair Mould(FURNITUREMOULD) is operated at high hardness, the mould steel has high yield strength and low fracture toughness. High yield strength is beneficial to delay the generation of fatigue cracks, but low fracture toughness accelerates the expansion rate of fatigue cracks, reduces the critical length, and greatly shortens the fatigue crack growth cycle. Therefore, the fatigue life of the cold work dies mainly depends on the fatigue crack initiation time.
Hot work dies are typically used for medium or low hardness conditions, and chair mould fracture toughness is much higher than cold work dies. Therefore, in the hot work die, the fatigue crack growth rate is lower than that of the cold work die, and the critical length is greater than the cold work. The subcritical expansion period of the hot mould fatigue crack is much longer than that of the cold mould. However, the surface of the hot work die is susceptible to rapid cooling and rapid heating. The fatigue crack initiation time of hot work die is much shorter than that of cold work die. Therefore, the fatigue fracture life of many hot moulds mainly depends on the time of fatigue crack growth.
Common forms of fracture failure are: fragmentation, caries, splitting, fracture, cracking, etc. The driving force for different mould fractures is different. Cold working dies are mainly subjected to mechanical forces (impact pressure). In addition to mechanical forces, hot moulds also have thermal stresses and microstructure stresses. Many hot working dies have higher operating temperatures and forced cooling. Internal stresses can far exceed mechanical stresses. Therefore, the fracture of many hot moulds is mainly related to excessive internal stress.
There are two types of chair mould fracture processes: one-time fracture and fatigue fracture. A one-time break is a mould that sometimes breaks suddenly during the stamping process, and once cracks begin, it becomes unstable and expands. The main reason for this is the severe overload or severe embrittlement of the mould material (eg overheating, insufficient tempering, severe stress setting and severe metallurgical defects).