Die Casting

Article Tour:

What is Die Casting;

Advantages and disadvantages of die casting;

Material of Die Casting;

Application of Die Castings;

Process of Die Casting.

What is Die Casting:

Die casting is a widely used casting process: it fills liquid, semi-solid metals or alloys and liquid metals or alloys containing reinforcing phases into the cavity of the die-casting mold with a high speed under high pressure by using the die-casting machine to solidify a metal or alloy under pressure to form a casting. The pressure commonly used in die casting is 4-500MPa, and the metal filling speed is 0.5-120m/s.

Advantages and Disadvantages of Die Casting:

Advantages:

1. During die casting, the metal liquid is under high pressure and has a fast flow rate;

2. The quality of die castings is good, the dimensions are stable, and the interchangeability is good;

3. The production efficiency is high, and the die-casting mold is used many times;

4. It is suitable for mass production and has good economic benefits.

Disadvantages:

1. Castings are prone to some pores and shrinkage.

2. The plasticity of die castings is low, and it is not suitable to work under impact load and vibration;

3. When the high melting point alloy is die-casting, the life of the mold is low, which affects the expansion of die-casting production.

Material of Die Casting

The most commonly used is the aluminum alloy; followed by magnesium alloy, zinc alloy, and copper alloy.

Application of Die Castings

In addition to being used in automobiles and motorcycles, instrumentation, and industrial appliances, die castings are also widely used in household appliances, agricultural machinery, radio, communications, machine tools, transportation, shipbuilding, cameras, clocks, computers, textile equipment, and other industries. Among them, automobile and motorcycle manufacturing is the most important application area, with automobiles accounting for about 70% and motorcycles accounting for about 10%. Some of the die-casting parts currently produced are as small as a few grams, and the largest aluminum alloy castings have a mass of 50kg and a diameter of 2m.

Process of Die Casting:

Die Casting Machine Debugging

Commissioning the die-casting machine ensures that it can work stably and continuously.

Die-casting mold design and manufacture

According to the drawings, use the mold design software to design the 3D mold's model, use the mold steel as the material, and use the CNC machining center to complete the manufacture of the die-casting mold.

Die Casting Mold Installation

Install the finished metal mold on the die-casting machine and complete the commissioning work.

Coating Formulation

In the die-casting process, to avoid the welding of the casting and die-casting mold, reduce the frictional resistance of the casting ejection and prevent the die-casting mold from being overheated, paint is used.

Requirements for Coatings:

1) At high temperatures, it has good lubricity;

2) Low volatilization point, the diluent can volatilize quickly at 100-150℃;

3) No corrosive effect on die-casting molds and die-castings;

4) The performance is stable in the air, and the diluent should not be excessively volatilized and thickened;

5) Will not release harmful gas at high temperatures;

6) No fouling will occur on the surface of the die-casting cavity.

Mold Cleaning

To complete the cleaning of the mold needs before starting processing. Ensure the cleanliness of the mold.

Mold Preheating, Coating

Should preheat Die-casting molds to a particular temperature before use. The methods are using gas, blowtorch, electrical, or induction heating.

In continuous production, the temperature of die casting molds tends to increase, especially for die casting high melting point alloys, which increases temp rapidly. In addition to making the liquid metal sticky when the temperature is too high, the cooling of the casting is slow, and the grains are coarse. Therefore, when the die-casting mold's temperature is too high, should adopt cooling measures. The methods usually are cooling with compressed air, water, or chemical media.

Closed the Mold

Alloy Smelting and Heat Preservation

The die-cast alloy is heated to a predetermined temperature and kept stable.

Casting Injection

The pouring temperature refers to the average temperature of the liquid metal when it enters the cavity from the press. Because it is inconvenient to measure the temperature of the liquid metal in the pressure chamber, it is generally expressed by the temperature in the holding furnace.

If the pouring temperature is too high, the shrinkage will be high, which will make the casting prone to cracks, large grains, and stickiness. Therefore, should consider the pouring temperature at the same time as the pressure, the temperature of the die casting mold, and the filling speed.

The time required from the liquid metal entering the cavity to the filling of the cavity is called the filling time. The length of filling time depends on the size and complexity of the casting volume. For large and simple castings, the filling time is relatively long, and for complex and thin-walled castings, the filling time is shorter. The filling time is closely related to the cross-sectional area of the gate or the width and thickness of the gate and must be determined correctly.

Insert Preparation

Improve and improve local process properties on castings, such as strength, hardness, wear resistance, etc.

Some parts of the casting are too complicated, such as hole depth, inner concave, etc., which cannot be out of the core and use inserts.

Several parts can be cast in one piece.

Pressure Holding

The duration from the liquid metal filling the cavity to the complete solidification of the inner gate is called the pressure holding time. The length of the pressure holding time depends on the material and wall thickness of the casting.

After holding the pressure, the casting should be opened and taken out. The time from the end of the injection to the opening of the die-casting is called the opening time, and the opening time should be controlled accurately. If the opening time is too short, due to the low strength of the alloy, it may cause deformation when the casting is ejected and the die is dropped; but if the opening time is too long, the temperature of the casting will be too low, and the shrinkage will be large. The resistance is also great. Generally, the opening time is calculated according to the casting wall thickness of 1 mm and takes 3 seconds, and then adjusted by trial.

Open The Mold, Pull The Core, and Take Out The Parts

Surface Quality Inspection

Clean Up (Refurbishment)

The cleaning of castings is very heavy work, and its workload is often 10 to 15 times that of die casting. Therefore, it is very important to realize the mechanization and automation of the casting cleaning work with the increase in the productivity of the die casting machine and increase the output.

Casting Infiltration, Shot Peening

Surface cleaning mostly adopts ordinary polygonal roller and vibration buried cleaning devices. For simple and small pieces with small batches, a polygonal cleaning roller can be used, and decorations with high surface requirements can be polished with a cloth or leather polishing wheel. For mass-produced castings, screw-shell vibration cleaning machines can be used.

The cleaned castings can also be surface treated and impregnated according to the requirements of users to increase gloss, prevent corrosion and improve air tightness.

Final Inspection

Ensure that the shape, size, corrosion resistance, mechanical properties, and other parameters of the die casting meet the requirements.