Die casting is a kind of pressure casting parts, is to uses the installed pressure casting mold casting machine die casting machine, the heating liquid copper, zinc, aluminium or aluminium alloy of metal poured into the die casting machine into the mouth; the die casting machine die casting, casting the shape and dimensions of the mould limit of copper, zinc, aluminium or aluminium alloy parts, such parts are often called die casting. Die-casting parts have different names in different places, such as die-casting parts, pressure castings, die-casting parts, die-casting aluminium, die-casting zinc, die-casting copper, copper die-casting, zinc die-casting, aluminium die-casting aluminium die-casting, aluminium die-casting alloy castings, aluminium die-casting parts and so on.
Die-casting parts design
Shape structure of die casting
1.Eliminate internal side concave; Simplified mold structure, die casting mold temperature is relatively high, the internal structure is easy to expand and lead to stuck;
2.Avoid or reduce the core pulling part;
3.Avoid core crossing; the Reasonable structure of die casting can simplify the structure of die casting mold, reduce manufacturing cost, and improve casting quality.
The wall thickness of die casting has a great influence on casting quality. When the casting wall is too thin, the metal welding is not good, which affects the strength of the casting, and brings difficulties to the moulding; If the wall thickness is too large or seriously uneven, it is easy to produce shrinkage and cracks. With the increase of wall thickness, the defects such as porosity and shrinkage porosity in the casting also increase, which also reduces the strength of the casting. Therefore, under the condition of ensuring sufficient strength and rigidity of the casting, the wall thickness should be reduced as far as possible, and the wall thickness of the die-casting parts should generally be 2.5 ~ 4mm, and the parts with wall thickness more than 6mm should not be die-casting.
Casting rounded corners
The intersection of each part of the die casting should be rounded (except the parting surface) so that the metal filling flow is stable, the gas is easy to discharge, and can avoid cracking due to acute Angle. For die castings requiring electroplating and finishing, the rounded corners can be uniformly coated to prevent paint accumulation at sharp corners.
The fillet radius R of die casting should not be less than 1mm in general, and the minimum fillet radius is 0.5mm.
Inclination of drawing die
When designing die casting, there should be a structural slope on the structure. When there is no structural slope, there must be a demoulding process slope where necessary. The direction of the slope must be consistent with the direction of the casting release.
The role of reinforcement is to improve the strength and rigidity of the parts after the wall thickness is thinned, reduce the shrinkage deformation of the casting, and avoid deformation when the workpiece is pushed out from the mould. It is used to act as an auxiliary circuit (the path of metal flow) when filling;
The thickness of the die-casting bars should be less than the thickness of the wall, generally taking 2/3~3/4 of the thickness of the place, the setting of reinforcement bars can increase the strength and rigidity of the parts and improve the process of die-casting. But a few points must be noted:
1.The distribution should be uniform and symmetric;
2. the root connected with the casting should have rounded corners;
3. Avoid multiple tendons crossing;
4.The width of the tendon should not exceed the thickness of the wall to which it is connected. When the wall thickness is less than 1.5mm, it is not suitable to use reinforcement;
5. The release slope of the reinforcement should be greater than the allowable casting slope of the casting cavity.
The ratio of the maximum wall thickness to the minimum wall thickness should not be greater than 3:1 (the wall thickness should be uniform to ensure sufficient strength and stiffness).
Die-casting parts design matters that need attention.
The design of die casting involves four aspects
1.Requirements of shape and structure of parts for pressure casting;
2.Process performance of die casting;
3.Dimensional accuracy and surface requirements of die casting parts;
4.Determination of die-casting parting surface;
Die casting parts design is an important part of the die casting production technology; the design must consider the following questions: the mold parting surface selection, gate opening, the choice of position of the plunger, the contraction of the casting, the casting dimension accuracy assurance, prevention of internal defects of castings, cast hole of the requirements, the related requirements of contraction deformation and the size of the machining allowance, etc.;
Structural design principles of die castings
1.Choose the material for die casting correctly;
2.Reasonably determine the dimensional accuracy of die casting;
3.try to make the wall thickness distribution uniform;
4.Add craft park corners at each corner to avoid sharp corners
Process principles of die-casting structure
1. Eliminate the inner side concave of the casting as far as possible to make the mold structure simple.
2.Try to make the wall thickness of the casting uniform; you can use reinforcement to reduce the wall thickness and the porosity, shrinkage, deformation and other defects of the casting.
3. Try to eliminate the deep hole and cavity on the casting. Because the small core is easy to bend and break, the deep cavity is filled, and the exhaust is poor.
4.The designed casting should be convenient for demoulding and core pulling.
5.Uniformity of meat thickness is necessary.
6.Avoid sharp corners.
7.Pay attention to the drawing Angle.
8. Pay attention to the tolerance marking of products.
9.Too thick and too thin are not suitable.
10. Avoid dead corner chamfering (less is less).
11.Consider the difficulty of post-processing.
12.Minimize the cavity in the product.
13.Avoid weak shapes with peninsular parts.
14.Too-long forming hole or too-long forming column are not suitable
How to improve the processing technology level of die-casting production?
Single liquid heat treatment of mold steel
The die steel or parts are heated to mart sensitization and quenched into water, oil or other cooling substances. The die steel is air-cooled by cooling for a certain time (cooling to less than the temperature area of ferritin shape change or austenite change temperature area). Because the whole process of die steel cooling is carried out in a single refrigerating substance, called single liquid heat treatment.
Double liquid heat treatment of die steel
To put it bluntly, the whole process of heat treatment and refrigeration of die steel is realized by coordinating two refrigeration substances (commonly water and oil). The whole process of refrigeration is ideal: rapid refrigeration in the ferrite change area and slow refrigeration in the austenite change area.
The specific method is to heat the mould steel or parts to the mart sensitization temperature, first quenched into a high temperature and quick cooling of a substance (usually water or salt solution) to suppress the ferritic change of low-temperature martensite; when the cooling to less than 100℃, quickly removed to the ultra-low temperature zone slowly cooling of another substance (usually oil). Because the austenite change is carried out under a relatively relaxed refrigeration standard, deformation and cracking can be reasonably reduced or avoided, known as water-quenching oil cooling.
This method must be a higher method of operation, sometimes interpreted as three substances: water first, oil, and gas.
Ejection heat treatment of steel in the mold
Large and medium-sized complexes, especially the thin and thick difference between zinc alloy die casting and die steel, to make the cooling symmetry, prevent excessive heat treatment internal stress, control the cooling rate of different parts of the whole process of refrigeration, different parts of the body. The method has spray (water or solution), sprayer (air compression and water will do atomization spray to parts in different positions), gas quenching and other various methods; its characteristics are: can manipulate different substances or different total flow, working pressure to control and adjust the cooling rate of each temperature area; Or change the total number and parts of different sprinkler heads; Can make the cooling symmetrical. At present, vacuum pump high-pressure gas quenching is popular in the heat treatment process of die casting.
Die steel grading quenching method
The mould steel or product workpiece warmed to mart sensitization temperature is quenched into the cooling material (commonly salt bath), whose temperature is around the austenite changing temperature, and retained for some time, so that the surface layer and core temperature of the product workpiece gradually tend to be the same. The air cooling is removed, and the austenite change is carried out at a low heat loss rate. This method can reduce the deformation and improve the toughness of die-casting steel. It is one of the common heat treatment methods for die-casting parts.
There are two kinds of temperature selections for die steel grading quenching. One is to take the Mahalanobis change gradually temperature (Ms point) above 10~30℃ of the steel product grade to be solved; The other is to choose Ms point below 80~100℃. Grade classification of the stay time also needs to grasp; if it is too short, the temperature is not symmetrical and can not achieve the purpose of grading quenching; If it is too long, it is likely to produce non-austenitic changes and reduce the strength.
Die steel isothermal process heat treatment method
The die steel product workpiece warmed to mart sensitization temperature is quenched into the heat bath with a temperature slightly higher than the Ms point of the quenched steel grade. The isothermal process is retained to obtain the lower martens mechanism or the mixing mechanism of lower martensite and austenite. This method has the advantages of reducing deformation, cracking and less stress in heat treatment, and it has similar strength and toughness to quenched austenite.
It is also certain to prevent deformation and cracks in the application process of die steel. It is also certain to refrigerate die steel after the heat treatment process, making it not easy to deform die steel.
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