Failure mode and analysis of aluminum alloy casting die
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Aluminum alloy plays a decisive role in modern manufacturing industry, the main reasons are as follows:
(1). high dimensional precision and good surface quality;
(2). high material utilization rate;
(3). can produce complex shape, clear contour, deep cavity thin wall die casting;
(4). the die casting has compact structure and high strength and hardness;
(5). high production efficiency, easy to achieve mechanization and automation of production.
(6). with good economic benefits, the parts of other materials can be directly embedded in the die-casting, saving valuable materials, especially the automotive industry has adopted a large number of aluminum alloy parts to achieve the purpose of weight reduction and energy saving.
Die - casting die is very important for aluminum alloy forming. Aluminum melting temperature is 680 ℃, due to the die casting when temperature is high, plus the filling pressure is big, makes the service life of aluminum alloy die casting mould is very low. According to the field statistics, the common failure forms of die casting die are cracking, cracking, erosion, adhesion and deformation, etc., of which cracking, cracking, erosion and adhesion mainly occur in the mold cavity surface.
1. The checking
In each die-casting cycle, due to the existence of intense heat exchange, the temperature of the mold changes dramatically, and the resulting thermal stress leads to thermal fatigue on the surface of the mold cavity and the formation of microcracks. With the increase of the number of die casting cycles, the microcracks further expand and form cracks. This is the main failure form of aluminum alloy die - casting die.
2. The cracking
In die casting production, in addition to the thermal stress, due to the high pressure impact of liquid aluminum in the mold also produced other stresses. Cracking occurs when these stresses exceed the fatigue limit of the die material, especially at the sharp corners where stress concentration is likely to occur. The possibility of cracking is greater.
3. The erosion
Heat generated by friction during high-speed cavity filling of liquid aluminum makes the surface temperature of the area facing the inner sprue on the surface of the mold cavity be high, coupled with the fierce impact of liquid aluminum, so the surface protection layer of this part is easy to be destroyed, and the liquid aluminum further reacts with the exposed metal matrix to generate harder compounds. In the process of removing these compounds, it is easy to take away the matrix material and expose the fresh surface, which, in turn, aggravates the damage of the cavity surface and forms severe erosion.
4. The adhesion
Aluminum alloy mold filling injection process, the moment on the surface of the cavity temperature above 600 ℃, the mold material and the affinity of liquid aluminum big strong adhesion force, easy to form the cavity adhesion.
5. The deformation
In the process of die casting, the die casting mold bears the action of various stresses such as clamping force, injection pressure, etc. If the rigidity of the template is not enough, the mold will produce bending deformation under the long-term action of these stresses.
6. The movement block
Due to the large temperature difference between inside and outside the die, the thermal deformation of each part of the die is different. Different thermal deformation leads to different sizes of the parts of the mold, which changes the cooperation between the parts of the mold. The change of the matching relation may cause the relative motion of the mould parts to produce obvious motion obstacle.