Plastic die casting process introduction

In the die casting process, the thermosetting resin material is added to a separate chamber, often called a chute, and then forced into one or more closed molds for polymerization (curing).

Channels, also known as sprues and runners, allow material to flow from the chute to the mold cavity and through the restrictor or gate before entering the mold cavity. Many mold cavities have a single chute. The air in the chamber is displaced by the incoming material and exits through a specially placed vent.

When the material is placed in the chute, the material is measured in a compact measuring device and then preheated to near the polymerization temperature. Add only enough shots at a time.

The force of feeding the preheated material out of the chute is then sent to a feeder which is mounted on the chute to prevent leakage from the gap between the piston and the sides of the chute. Sealing sleeves are usually snapped into the feeder to prevent further leakage.

The surface of the chute, feeder, sprue, runner, and mold cavity maintains a certain temperature at which the raw materials are rapidly solidified. The temperature is 280-380°F depending on the material properties, the design of the mold, and the geometry of the product.

When the die casting reaches the end of the curing period, the next complete die casting is demolded, including the formation of a solidification pad (called a residue) in the gate, flow path, sprue, and chute.

In die casting, the warm-up of the material is very important. The cold material flow is slow, and the material that enters the mold cavity has not yet reached its end point, that is, it may be polymerized. If the above situation occurs, the product quality is poor, not only the appearance but also the mechanical performance. Some exceptions, such as a small amount of injection, or some low viscosity materials. Heating lamps or stoves can be used for heating, but an effective and common method is to use dielectric heaters made specifically for plastic molding.

Screw-type plastic heating of thermosetting materials is also commonly used.

This device can be combined with molding equipment or it can be stand-alone, with the advantages of reduced volume and accurate determination of feed volume, and must be combined with pre-molding in other systems.

The type of die-casting mold was originally used as the term "unitary die-cast die-casting" because the trough and the injection bar were made together as a whole. The most common is a circular trough, but other shapes may also be used to suit the requirements of a particular gate to produce less waste.

A simple compression molding press can be used with a die casting machine. The overall slot mold frame is a three-plate type with a feed slot in the middle. Feeding rods are mounted on the top of the mold and the mold cavity is at the bottom.

The area occupied by the chute is at least 10% greater than the total mold area in the cavity section (horizontal contact with the plastic material). This prevents excess mold clamping force from causing the mold flash.

After the material has solidified, the part is demoulded by moving the pressure of the stripper bar, but the scrap and sprue residue is still held at the bottom of the injection bar by one or more molded "pigeons".

Use a wood or soft hammer to remove the waste and clean mold.

When using a single chute to produce large waste, it is sometimes possible to feed the multi-cavity chamber with a double chute. At this time, even though the weights of the two tanks are slightly different, a crossbar needs to be used to balance the pressure in each tank.

The press rod die casting mold is also called injection rod mold. It uses an auxiliary pressure plunger to force the injection rod into the trough (or the barrel) and remove the material from the trough into the mold cavity. Die-casting pressure and die-casting speed are easy to control, regardless of clamping pressure.

The size of the chute (which determines the size of the waste) in the die-cast die-casting molds need only be large and deep enough to satisfy the exact amount of feed.

The maximum chute area is determined by the force (in tons) imparted by the auxiliary plunger of the die casting machine and is divisible by 3.5. This assures a pressure of 3.5 tons/in2 for molding pressure, which is sufficient for the formulation of most die casting grades.

The auxiliary plunger is usually mounted on the upper fixed platen and acts downwards. Punching the plunger moves the lower platen up and closes the mold. After the mold is clamped, the raw material is loaded into the trough and the auxiliary plunger applies force. The force ratio applied by the mold clamping plunger and the auxiliary plunger is generally 3:1 or 4:1.

After the material is cured, the auxiliary plunger is retracted and the die casting machine is opened. Molded parts, scrap, and runner cold material are simultaneously delivered by the ejector pin.

A variant of this casting mold is a three-plate injection rod die casting mold in which a floating runner plate distributes the material into a channel directly feeding the mold cavity.

This method is applicable to the place where the mould line cannot open the flow channel, or to move the core and the workpiece on the plane of the mould line, which is very irregular and disturbing the layout.

Specially designed die casting machines come in the following types:

1) The bottom extruding rod die casting mold is installed in the die casting machine, wherein the auxiliary plunger is installed in the main mold clamping plunger. If there is enough space between one or more die casting units, the auxiliary plunger is installed on the lower pressing plate .

The advantage of this method is that the mold can be charged with the mold open.

This design is slightly faster than waiting for the closed mold design before loading the chute. And the auxiliary plunger stroke can be shortened, saving a few seconds per cycle.

The above die casting machine can be used for injection molding die of the top plunger injection rod, but the pre-pressed material spindle should be aligned to ensure that the material enters the material trough well, otherwise it is difficult to close the die.

2) A die casting machine with a multi-auxiliary plunger for feeding a plurality of chutes, having a long, curved flow path that can charge a plurality of mold cavities, does not generate waste, and does not require low efficiency.

3) Small-sized powder die casting machine can automatically die-cast, and it can be operated horizontally or vertically. There is an auxiliary plunger perpendicular to the mold-clamping plunger, which is used for injection molding of raw materials.

4) For prefabricated integral molding compound (BMC), usually glass fiber-filled polyester, there is a horizontal die casting machine, with a feeding attachment to compact the material, and then sent to the die casting cylinder.

5) The die casting machine is a prototype of a thermosetting resin injection molding machine. This machine combines screw plasticizing and preheating molds.

The preheated material is sent to the molding mold line or in the clear casting cylinder below the mold county