Compression injection molding is a more traditional injection molding method
Principle:
First inject molten material into mold cavity, when molten material enters mold lung. Mold is opened a little under its pressure knife; after molten material fills cavity, mold is locked with high pressure to obtain desired product. Second step is compression molding. Since molten material enters cavity when mold has been slightly opened, required mold force is relatively small.
When molding, screw no longer injects material into mold cavity, but mold is locked by high pressure so that force Lf is pressed against plastic to form, so orientation of product is small and internal stress is low. This method is especially suitable for products with small volume and high transparency requirements;
Advantage:
It can increase flow length ratio of injection molded parts; use smaller clamping force and injection pressure; reduce material internal stress; and improve processing productivity.
Injection compression molding is suitable for products made of various thermoplastic engineering plastics; such as large-sized curved parts, thin-walled, miniaturized parts, optical lenses, and parts with good impact resistance requirements;

 

Principle:
When injection molding volume reaches about 80%-95%, injection molding is suspended; mold is opened about 0.1-0.2mm to discharge volatile gas; second mold is closed, and remaining injection volume is injected.
Advantage:
Gas-assisted injection molding parts have lower injection pressure, and equipment with lower clamping force can be selected to form larger parts.

 

Principle:
Pressure injection molding process is a packaging process that uses a very low injection pressure to inject hot-melt materials into mold and solidify quickly. Excellent sealing and excellent physical and chemical properties of hot-melt materials are used to achieve insulation, temperature resistance, impact resistance, vibration reduction, moisture-proof, waterproof, dust-proof, chemical corrosion resistance, etc., play a good role in protecting electronic components.
Advantage:
Equipment cost of low-pressure injection molding process is low;

 

Injection molding stage (partial) - inflation stage (N2) - gas pressure holding stage (cooling pressure constant) - depressurization stage - demoulding stage
Advantage:
Assisted injection molding technology has many incomparable advantages. It not only reduces manufacturing cost of plastic products, but also improves some of its performance; In the case that parts can meet same use requirements, use of gas-assisted injection molding can greatly save plastic raw materials, and saving rate can be as high as 50%. Reduction in the amount of plastic raw materials reduces the time of each link in the entire molding cycle;

 

Water-assisted injection molding technology is an advanced injection molding process that injects part of melt into mold cavity, injects high-pressure water into melt through equipment, and finally shapes workpiece.
Advantage:
Due to incompressibility of water, front of water forms a solid interface, extruding inner wall of product into a cavity, and front of water also plays a role in rapid cooling. Therefore, water assist has many incomparable advantages over gas assist. Research and application have shown that water assist can produce a thinner and more uniform cavity wall, and surface of inner wall of flow channel is very smooth. Especially for thick-walled workpieces, water-assisted cooling time can be greatly reduced compared with gas-assisted.

 

Basic process of high-gloss injection molding is to rapidly heat up surface of mold by using high-temperature and high-pressure steam before injection molding, so that surface temperature of molding cavity reaches above glass transition temperature (Tg) of resin plastic, then inject plasticized plastic melt into seal mold cavity. During injection stage, temperature of mold is kept constant by high-temperature and high-pressure water vapor. When injection is completed, air supply is stopped, water vapor in pipe is blown away by air pressure of air pipe, then cooling water is introduced to make mold temperature drop rapidly until it cools down and mold is opened to take out product.
Advantage:
Compared with ordinary injection molding, it can effectively eliminate defects such as weld lines, ripples, silver lines, and floating fibers on product surface, improve product quality and strength, and completely solve product surface marks.

Injection molding is a method of producing shapes for industrial products. Products usually use rubber injection molding and plastic injection molding. Injection molding can also be divided into injection molding molding method and die casting method.
Injection molding machine (referred to as injection machine or injection molding machine) is main molding equipment for making thermoplastic or thermosetting materials into various shapes of plastic products using plastic molding molds. Injection molding is realized through injection molding machines and molds.
Several injection molding processes that affect strength of injection molded parts:

 

Compared with other hard rubber materials, PP materials are more elastic, so density of injection molded parts will increase with increase of pressure, which is relatively obvious. When density of plastic parts increases, its tensile strength will naturally increase, and vice versa.
However, when density increases to maximum value that PP itself can achieve, tensile strength will not continue to increase when pressure is increased, but will increase residual internal stress of injection molded part and make injection molded part brittle, so it should be enough.
Other materials have a similar situation, but degree of obviousness will vary.

Nylon and POM materials are both crystalline plastics. Mold is injected with hot oil by a hot oil machine, which can slow down cooling speed of injection molded parts and improve crystallinity of plastic. At the same time, due to slowing down of cooling rate, residual internal stress of injection molded parts is also reduced. Therefore, impact resistance and tensile strength of nylon and POM parts injected with hot oil by hot oil machine will be improved accordingly.
It should be noted that size of nylon and POM parts injected with hot oil by a hot oil machine will be slightly different from that of water injection molded parts, and nylon parts may be larger.

Usually, pvc90 degree material is injected at 180 ℃, temperature is enough, and generally there will be no problem of raw rubber. However, it is often due to reason that operator did not pay attention, or to speed up production to speed up melting speed, so that screw retreats very fast. For more than one-third of position, time for heating and stirring PVC material is seriously insufficient, resulting in problem of melt temperature and uneven mixing of raw rubber, making strength and toughness of injection molded parts quite poor.
Therefore, when injecting PVC materials, be careful not to adjust speed of melt to more than 100 rpm. If it must be adjusted quite quickly, remember to increase temperature of material by 5 to 10℃, or increase back pressure of melt adhesive appropriately to match, and also pay attention to frequently checking whether there is any rubber problem, otherwise it is very likely to cause heavy losses.
Regarding this issue, because most people don't pay much attention to it, it is specially proposed here to remind you to pay attention to it during production, and remember to do a good job in inspection.
On the contrary, it should also be noted that if melt speed is too slow, even if it is 180-degree injection molding PVC material at 90 degrees, it will cause problem of glue burning, especially for transparent PVC, there will be many black spots and air marks on injection molded parts.