Five precautions for using die casting die

When using die-casting film, attention should be paid to: the use characteristics of die-casting die, the temperature of alloy melt, the working temperature of die, the lubrication of die-casting die and the adjustment content of die-casting die.
1、 Application characteristics of die casting die
In the process of die-casting production, the forming conditions of die-casting die parts are extremely bad. They are subjected to repeated effects of mechanical abrasion, chemical erosion and thermal fatigue.
1) Liquid metal enters the mold cavity under high pressure and high speed, which will produce fierce friction and impact on the surface of the mold cavity, resulting in erosion and wear on the mold surface.
2) Molten metal is inevitably brought in during pouring. Molten slag has complex chemical effects on the surface of formed parts. Aluminum and iron compounds, like wedges, accelerate the formation and development of cracks in die-casting dies.
3) Thermal stress is the main cause of cracks on the surface of die-casting parts. In the production process of each die-casting part, in addition to the high-speed and high-pressure scouring of liquid metal, the surface of the formed part also absorbs the heat released by the metal in the solidification process, resulting in heat exchange. In addition, due to the heat conduction of the die material, the temperature of the surface layer of the formed part rises sharply, resulting in a large temperature difference with the interior, resulting in internal stress. When liquid metal fills the cavity, the surface of the cavity first reaches high temperature and expands, while the inner mold temperature is low and the relative expansion is small, resulting in compressive stress on the surface. After the mold is opened, the surface of the cavity is in contact with air and is cooled by compressed air and coating to produce tensile stress. This alternating stress increases with the continuation of production. When the fatigue limit of the die material is exceeded, the surface layer of the die will produce plastic deformation and crack.
In order to maintain the durability of the profile, the profile is required to have thermal fatigue resistance, wear resistance, non sticking mold and easy to take off parts. Therefore, the formed parts are made of 4Cr5MoSiV1 (H13) material which is well used at present.
2、 Temperature of alloy melt
During the production of die-casting die, in order to better fill all concave holes and depths of die-casting die and ensure the mutual integration of metal during flow, the pouring temperature of metal should be correctly selected when using die-casting die. The pouring temperature of alloy die-casting liquid is as follows:
Material name: die casting liquid temperature / ℃
Zinc alloy 420-500
Aluminum alloy 620-690
Magnesium alloy 700-740
Copper zinc alloy 850-960
Selection principle of die casting alloy temperature:
1) The lower the pouring metal temperature, the longer the service life of the die casting die;
2) With low temperature die casting, it is possible to reduce the increase of the depth of the exhaust slot and the risk of liquid metal splashing;
3) Low temperature die casting can reduce the chance of tight engagement between the pressure chamber and the ejector rod;
4) Low temperature die casting can reduce shrinkage holes and cracks in castings.
In short, when the process conditions permit, the temperature of die-casting alloy is better to choose low-temperature die-casting.
Three. Temperature of mould work
The working temperature of die-casting die varies according to its die-casting alloy. The following are the recommended values of several alloy dies for selection:
Mold name working temperature / ℃
Zinc alloy die
Aluminum alloy die 180-225
Magnesium alloy die 200-250
Copper zinc alloy die 300
Selection principle of working temperature of die casting die:
1) The mold temperature is too low, the internal structure of the casting is loose, the air is difficult to discharge, and it is difficult to form;
2) The mold temperature is too high and the internal structure of the casting is dense, but the casting is easy to be "welded" to the mold cavity and stick to the mold
It is not easy to unload the casting. At the same time, too high temperature will expand the mold itself and affect the dimensional accuracy of the casting.
3) The mold temperature should be selected in an appropriate range. Generally, after the test is appropriate, it is better to control the constant temperature.
4、 Lubrication of die casting die
1. Purpose of lubrication
Lubrication is used as parting agent for die casting die and die casting, which is convenient for die casting die unloading; As the lubricant of the moving part of the die-casting die and press, it can reduce friction and improve the service life of the die-casting die; In addition, it can also be used as the coolant of the die-casting die, reduce the thermal fatigue of the die due to long-term work, and prolong the service life of the die.
2. Lubricant requirements
The selection of lubricant shall meet the following requirements:
a. The die castings cannot adhere in the cavity;
b. Do not corrode the steel on the die surface;
c. Can not produce toxic gas;
d. No ash can be generated when heated;
e. After lubrication, it should be evenly attached to the cavity and working surface without being washed away by high-pressure metal.
3. Preparation of lubricant
a. Total loss system oil 85% - 90% + graphite 10% - 15%;
b. Heavy oil 100%;
c. Paraffin 30% + yellow wax 30% + vaseline oil 14% + graphite 26%;
d. Graphite 25% + glycerol 20% + water glass 5% + water 50%;
4. Precautions when using lubricant
a. Lubricant can be used on the surface of cavity and movable part;
b. The amount of lubricant sprayed should be less each time, and it should be uniform. After spraying, it is best to form a layer of film on the mold surface.
5、 Adjustment contents of die casting die
After the die-casting die is made, it should be adjusted through die test, and the correct die-casting conditions and process parameters should be selected in order to achieve stable die-casting and produce qualified castings.
Before the mold test, the mold test personnel shall check the alloy raw materials for die casting in advance to understand the characteristics of alloy materials and die casting characteristics; We should also understand the structure of the die, the performance of the die-casting machine, die-casting conditions, die-casting process and operation methods.
Correct selection of die casting forming conditions is the key to die test adjustment. Such problems are often encountered. Even if the design and manufacture of the die are very correct, due to the improper selection of die-casting conditions, qualified castings can not be produced. On the contrary, in some cases, the defects of the die can be overcome by adjusting the die-casting conditions, and the qualified castings can be extruded. Therefore, the die test personnel must be familiar with the function and relationship of various die-casting forming conditions and the action principle of the die, so as to correctly select and reasonably adjust various die-casting forming conditions.
The adjustment of die casting forming conditions includes: material melting temperature, die temperature and melt temperature during injection; The determination of injection pressure, mold locking force and mold opening force of die casting machine, and the injection ratio and injection speed required according to the condition of parts. Finally, the condition of die-casting products should be repaired before perfect die-casting parts can be obtained.