1 working conditions and performance requirements
Die casting is a basic tool for pressure casting production, is formed in high pressure 150 ~ 500MPa under the high temperature of 1000 DEG C molten metal die-casting, machining objects lead, zinc and aluminum, magnesium, copper and other alloy etc.. Because of these metals and alloys with different melting points, the mold performance requirements are not the same.
1.1 die working conditions
(1) compared with other mold, die-casting mold working condition is very bad, because of different metal die-casting, should bear 150 ~ 500MPa high pressure.
(2) work, often with 300 DEG to 1000 DEG C molten metal contact, die casting alloy of different pouring temperatures are also different. And the repeated heating and cooling, a large temperature gradient along the section.
(3) die cavity from 150m/s ~ 70m/s high speed injection of molten metal contact, will cause serious wear.
(4) the cavity in the liquid metal erosion and erosion, easy to make the metal adhesion in the mold cavity on the surface (especially Aluminum Alloy more prominent), even into the die face or die face metal chemical changes and die surface corrosion.
1.2 die of other performance requirements
Pressure casting can be cast with complex shapes, high precision, low surface roughness and good mechanical properties of parts. So, die casting mould has the following performance requirements:
(1) the high temperature strength and high toughness
Die casting under high temperature, high pressure and heat of molten metal into the stress effect, easy deformation, and even cracking.Therefore, the mold material should have high strength and enough toughness at the working temperature, and high hardness.
(2) excellent high temperature wear resistance and oxidation resistance and tempering stability
High temperature of the molten metal into the mold and casting speed after demoulding, produce friction effect is larger, in order to ensure the long-term use of mold, mold should have high wear resistance under working temperature. Die casting mould in continuous mass production, a long time in a certain temperature, should continue to maintain its high hardness, but also should not stick mode and does not produce oxide. Therefore, the mold also has anti-oxidation and good temper stability.
(3) the good performance of thermal fatigue
Die casting die surface repeatedly by high temperature heating and cooling, expansion, contraction, alternating thermal stress. The stress exceeds the elastic limit of mold material, had repeated plastic deformation caused by thermal fatigue. At the same time, the mold surface by long time corrosion and oxidation of molten metal, will gradually produce micro cracks, in most cases, thermal fatigue is one of the most important factors to determine the service life of die casting die.
(4) high melting damage
With the large-scale die casting machine, die casting pressure is also increasing, from the low of 20 ~ 30MPa, 150 ~ 500MPa high pressure to improve. High temperature and high pressure casting can produce obvious melting damage, mold has greater resistance to this. Therefore, the mold material must have high strength high, the smaller of the molten metal affinity, mold roughness is smaller, and with a proper oxidation mode, the nitride layer protection layer, and there is no decarburized layer.
(5) good hardenability, heat treatment deformation
Manufacturing method of die casting mould is the general mold material carving in the annealed state cavity, and then get the required heat treatment, hardness, or the first mold material for heat treatment, to obtain the required hardness, carving cavity. The first method of carving manufacturing cavity after heat treatment, high hardness and strength, not easy to produce melting loss and thermal fatigue. Heat treatment of either method, obtain uniform hardness is necessary, so the requirements of good hardenability, especially after the first carving cavity subjected to heat treatment to deal with small deformation material for heat, this is particularly important for die size.
Kunshan cold die steel