Die casting is a metal casting process, which is characterized by the use of the mold cavity to apply high pressure to the melted metal, the mold is usually processed with a higher strength alloy, this process is similar to injection molding, then, follow the small series together to understand the following 8 notes on die casting processing: die casting processing

(1) Choice of die casting machine

In the organization of many varieties, small batch production, generally choose a simple hydraulic system, strong adaptability, can quickly adjust the die casting machine, in the organization of a few varieties of mass production, to choose a variety of mechanized and automated control mechanism with high efficiency die casting machine; A special die-casting machine can be used for the mass production of a single variety of castings.

Casting shape inch, weight, wall thickness and other parameters have an important impact on the selection of die casting machine, casting weight (including pouring system and overflow trough) should not exceed the rated capacity of die casting machine, but can not be too small, so as not to cause the waste of die casting machine power string.

The rated capacity of the general die-casting machine can be checked in the manual, the die-casting machine has a certain maximum and minimum distance, so the thickness of the mold and the height of the casting must have a certain limit, if the thickness of the die-casting mold or the height of the casting is too large, the casting may not be taken out.  

(2) The choice of pressure and speed

The choice of injection pressure should be determined according to the structural characteristics of different alloys and castings. For the selection of filling speed, generally for castings with thick walls or high internal quality requirements, lower filling speed and high booster pressure should be selected; For castings with thin wall or high surface quality requirements and complex castings, high specific pressure and high filling speed should be selected.  

(3) Casting temperature selection

The casting temperature is too high, the shrinkage is large, so that the casting is easy to crack, the grain size is large, and the viscosity can be caused; Casting temperature is too low, easy to produce cold insulation, surface pattern and insufficient pouring defects. Therefore, the pouring temperature should be considered at the same time as the pressure, die casting mold temperature and filling speed.

(4) The temperature of the die casting mold

The casting mold should be preheated to a certain temperature before use, generally multi-purpose gas, blowtorch, electrical appliances or induction heating, in continuous production, the temperature of the die casting mold often rises, especially the die-casting high-melting point alloy, which rises quickly.

In addition to making the liquid metal sticky, the casting cooling is slow, so that the grain is coarse, so when the die casting temperature is too high, cooling measures should be adopted. It is usually cooled by compressed air, water or chemical media.  

(5) Filling time

Since the liquid metal begins to enter the cavity to fill the cavity, the required time is called the filling time, and the length of the filling time depends on the size and complexity of the volume of the casting.

For large and simple castings, the filling time is relatively long, and for complex and thin-walled castings, the filling time is shorter. Filling time is closely related to the size of the cross-sectional area of the inner gate or the width and thickness of the inner gate, and must be correctly determined.  

(6) Holding pressure and opening time

When the liquid metal filling cavity is completely solidified from the inner gate, the continuous duration under the action of the injection punch is called the holding time, the length of the holding time depends on the material and wall thickness of the casting, and the casting should be opened after the holding pressure.

The time from the end of injection to the opening of die casting is called the opening time, and the opening time should be controlled accurately. The opening time is too short, because the alloy strength is still low, it may cause deformation when the casting ejection and the self-pressing casting fall; However, if the opening time is too long, the casting temperature is too low, the shrinkage is large, and the resistance to core-pulling and ejecting the casting is also large, the general opening time is calculated according to the casting wall thickness of 1 mm for 3 seconds, and then adjusted by trial.  

(7) Paint for die casting

In the process of die casting, in order to avoid the welding of the casting and die casting mold, reduce the friction resistance of the casting ejection and avoid excessive heat of the die casting mold, paint is used. Requirements for coatings: good lubricity at high temperature; The volatilization point is low, and the diluent can volatilize quickly at 100 ~ 150℃; It has no corrosion effect on die casting mold and die casting parts; Stable performance In the air diluent should not volatilize too much and become thick; It will not precipitate harmful gases at high temperatures; No accumulation of scale on the surface of the die casting cavity.

(8) Casting cleaning

Cutting gate and flash, the equipment is mainly punch, hydraulic press and friction press, in a large number of production parts, according to the casting structure and shape of the design of the special mold, in the punch to complete the cleaning task, surface cleaning using ordinary multi-angle roller and vibration embedded cleaning device.

For simple small pieces with small batches, multi-angle cleaning rollers can be used, decorations with high surface requirements can be polished by polishing wheels made of cloth or leather, and spiral shell vibration cleaning machines can be used for mass production of castings. The cleaned castings can also be surface treated and impregnated according to the requirements of use to increase luster, prevent corrosion and improve air tightness.