Types of die casting process and points of attention

In the die-casting process, the thermosetting resin material is added to a separate material cavity, often called a material tank, and then forced into one or more closed molds for polymerization (curing). The sprue, also called sprue and runner, allows the material to flow from the trough to the cavity, and pass through the restrictor or gate before entering the cavity. Many cavities have a single trough. The air in the material cavity is replaced by the incoming material and is discharged through a specially placed exhaust port.

When the material is placed in the trough, the amount of material is measured in a compact measuring device, and then preheated to close to the polymerization temperature. Only add enough injection volume at a time. The force of sending the preheated raw material out of the trough sends it to an injector, which is mounted on the trough immediately to prevent leakage from the gap between the piston and the edge of the trough. The sealing sleeve is usually clipped into the injector to further prevent leakage.

When the die-cast product reaches the end of the curing period, demold the complete die-cast product, including removing the gate, runner, sprue and trough to form a solidified mat (called residual material). The surface of the chute, injector, gate, runner and mold cavity maintain a certain temperature that can quickly solidify the raw material. The temperature is 280-380°F according to the nature of the material, the design of the mold and the geometry of the part.

In die casting, preheating of materials is very important. The cold material flows slowly, and the material that enters the cavity first has not reached its end point, that is, it may polymerize. If the above situation occurs, the product quality is inferior, not only in appearance, but also in mechanical properties. There are some exceptions, such as a small injection volume or some low-viscosity materials. It can be heated by a heating lamp or a stove, but an effective and common method is to use a dielectric heater specially made for plastic molding.

Screw-type plasticizing and heating of thermosetting materials are also commonly used now. This equipment can be combined with the molding equipment, or it can be independent, with the advantages of reducing the volume and measuring the feed amount accurately, and must be combined with the pre-forming in other systems.

Types of die casting molds

The term integral trough die-casting was first used because the trough and the injection rod are made together as an integral part of the mold. The most commonly used is the circular trough, and other shapes may also be used to meet the requirements of special gates to reduce waste. A simple compression molding press can be used with a die casting machine. The integral trough mold frame is a three-plate type with the trough in the middle.

The feeding rod is installed at the top of the mold frame, and the cavity is at the bottom. The area occupied by the trough is at least 10% larger than the total clamping area (the horizontal plane in contact with the plastic material) in the cavity section. This prevents excessive mold clamping force from causing mold flash. After the material is solidified, the part is demoulded by moving the pressure of the ejector rod, but the waste and sprue residue are still held at the bottom of the injection rod by one or more molded dove tails.