Introduction to plastic die casting process 1

2022-06-23
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Introduction to plastic die casting process

in the die casting process, thermosetting resin is added into a separate material cavity, often called a material trough, and then forced into one or more closed molds for polymerization (curing)

material channel, also known as injection channel and runner, enables the material to flow from the material trough to the mold cavity, and pass through the restrictor or gate before entering the mold cavity. Many die cavities have a single chute. The air in the material chamber is replaced by the incoming material and discharged through a specially placed exhaust port

when the material is put into the trough, measure the material in a compact measuring device, and then preheat it to close to the polymerization temperature. Only add enough injection quantity once at a time

the force to send the preheated raw material out of the chute sends it to a feeder, which is installed on the chute immediately to prevent material leakage from the gap between the piston and the edge of the chute. The gland is usually clamped into the injector to further prevent leakage

the surface of the material trough, injector, gate, runner and mold cavity maintains a certain temperature that can rapidly solidify the raw materials. The temperature is 280 ~ 380 ° f according to the material properties, mold design and workpiece geometry

when the die-casting material reaches the end of the curing period, the complete die-casting material is demoulded, including removing the solidified material pad (called residual material) from the gate, runner, runner and trough

preheating of materials is very important in die casting. The cold material flows slowly, and the material entering the mold cavity may polymerize before it reaches its end point. In case of the above situation, the product quality is poor, which is not only the appearance, so the following points should be paid attention to before electroplating of metal parts, but also the 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 furnace, but the effective and common method is to use a dielectric heater specially made for plastic molding

screw type plasticizing heating of thermosetting materials is also commonly used nowadays

this kind of equipment can be combined with the molding equipment, or it can be independent. It has the advantages of reducing the volume and accurately measuring the material quantity of the electrical parts. In other systems, it must be combined with the preform

type of die-casting die

the word "die casting with integral feed chute" was first used because the feed chute and the injection rod were made together as a whole of the die. The most commonly used is the circular chute, or other shapes may 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 overall chute die frame is a three plate type with the chute in the middle. The feeding injection rod is installed at the top of the mold frame, and the mold cavity is at the bottom

the area occupied by the material trough shall be at least 10% larger than the total mold area in the mold cavity section (the horizontal plane in contact with the plastic material). This can prevent excess clamping force from causing mold overflow

after the material is cured, the parts will be demoulded by moving the pressure of the demoulding rod, but the waste and runner residues are still kept at the bottom of the injection rod by one or more molded "dovetails"

use a wooden rod or a soft hammer to remove the waste and to clean the mold

when a single chute is used to generate large waste, sometimes a double chute can be used to feed the multimode cavity. At this time, although the weights of the two material grooves are slightly different, a horizontal plate is still needed to balance the pressure in each material groove

the pressure bar die-casting die is also called the injection bar die. It uses an auxiliary pressure plunger to force the injection bar into the material groove (or barrel), and takes out the material from the material groove and moves it to the mold cavity. The die-casting pressure and speed are easy to control and have nothing to do with the clamping pressure

the size of the material groove (which determines the size of the waste) in the pressure plug die-casting die only needs to be large and deep enough to meet the exact feeding amount

the maximum chute area is determined by the force (in tons) given by the auxiliary plunger of the die casting machine and divided by 3.5. This ensures that a pressure of 3.5 T/in2 is used as the molding pressure, which is sufficient for most die-casting grade formulations

the auxiliary plunger is usually installed on the upper fixed pressing plate and acts downward. Punch the plunger to make the lower die plate move upward to close the die. When the die is clamped, the raw material is loaded into the chute and the auxiliary plunger applies force. The force ratio applied by the clamping plunger and the auxiliary plunger is generally 3:1 or 4:1

After the

material solidifies, the auxiliary plunger returns and the die casting machine opens. Molded parts, waste materials and channel cold materials are sent out by the demoulding rod at the same time

a deformation of this kind of casting mold is a three plate injection rod die-casting mold, in which there is a floating channel plate to distribute the materials into the material channel that directly feeds the mold cavity

this method is applicable to the places where the clamping line can not open the runner, or the places where the core and parts are very irregular and the layout is very disturbed

there are several types of specially designed die-casting machines:

1) the bottom extrusion rod die-casting die is installed in the die-casting machine, in which the auxiliary plunger is installed in the clamping plunger with optical transparency only in the main elimination crystallization area. If there is enough space between one or more die-casting units, the auxiliary plunger is installed on the lower platen

the advantage of this method is that the material can be loaded into the material trough when the mold is opened

this design is slightly faster than the design of waiting for the die to close before loading into the chute. And the stroke of the auxiliary plunger can be shortened, and each cycle can save several seconds

the above die-casting machine can be used as the top plunger injection rod die-casting mold, but the pre pressed ingots should be aligned to ensure that the materials are well fed into the material trough, otherwise it is difficult to close the mold

2) the die casting machine with multiple auxiliary plungers feeding to multiple material slots has a long and curved flow channel that can fill multiple mold cavities, does not produce waste and does not need low efficiency

3) the small-sized powder die-casting machine can be used for automatic die-casting, which can be operated horizontally or vertically. There is an auxiliary plunger perpendicular to the clamping plunger, which is used for the clamping line injection of raw materials

4) for the prefabricated monolithic molding compound (BMC), usually the polyester filled with glass fiber, there is a horizontal die-casting machine with feeding accessories to compact the material and then send it to the die-casting barrel

5) die casting machine is the prototype of thermosetting resin injection molding machine. This machine combines screw plasticizing with preheating the mold

the preheated material is sent to the mold closing line or the Qing casting cylinder under the tight grid mold county

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