Six kinds of injection molding sharing and six common injection molding processing technologies for

Time:2020-06-17 09:25:06 / Popularity: / Source:

Six kinds of injection molding sharing

01 Injection compression molding

Injection compression molding:
Injection compression molding is an advanced form of traditional injection molding.
It can increase flow length ratio of injection molded parts; use smaller clamping force and injection pressure; reduce internal stress of material; and increase processing productivity.
Injection compression molding is suitable for a variety of products made of thermoplastic engineering plastics, such as large-size curved parts, thin walls and miniaturized parts, optical lenses, parts with good impact resistance requirements.
Injection compression molding 
Picture shows a schematic of injection compression molding:
As we all know, optical lenses have very high requirements for their geometric accuracy. They must be accurate in size and small in deformation, which is difficult to achieve in general injection molding.
Injection compression molding 

02 Exhaust injection molding

Exhaust injection molding:
Purpose of "Exhaust" procedure is to allow volatile fission products produced during polymerization-solidification process to escape. If these gases cannot be discharged from cavity, result will be incomplete products or air bubbles in closure.
1. When injection volume reaches about 80% -95%, injection is suspended;
2. Open mold about 0.1-0.2mm to allow volatile gas to be discharged;
3. Perform secondary mold clamping and remaining injection amount is injected.
Exhaust injection molding 
Picture shows exhaust injection molding
Product: Filter plate for filter press 1500x1500
Number of cavity: 1 cavity
Raw material: PP + 6% (flow index 0.2 high viscosity)
Injection molding machine: BU4000 with 6800T storage tank
Molding process: injection compression molding
Exhaust injection molding 
Exhaust injection molding 
Filter plate

03 Low pressure injection molding

Low-pressure injection molding process is a packaging process that uses a very low injection pressure to inject hot-melt material into a mold and rapidly cures. With excellent sealing properties, excellent physical and chemical properties of hot-melt material to achieve insulation, temperature resistance, impact resistance, vibration damping, moisture resistance, water resistance, dust resistance, chemical resistance and other effects, it has a good protection of electronic components .
Sensitivity of leather, wood, fiber fabrics, PVC / TPO / PUR decorative films requires reduced injection pressure.
Car pedal sensor
Low pressure injection molding 
Picture shows car pedal sensor, following picture shows components before and after injection

04 Gas assisted injection molding

Gas assisted injection molding process:
Injection stage(part) - inflation stage(N2) - gas holding stage(constant cooling pressure) - decompression stage - demolding stage
Gas assisted injection molding device composition:
Gas pressure generator, gas control unit, gas injection device, gas recovery device
gas assisted injection molding 
Picture shows principle of gas assisted injection molding
gas assisted injection molding 

05 Water assisted injection molding

Water assisted injection molding technology is an advanced injection moulding process in which a part of melt is injected into a mold cavity, and then high-pressure water is injected into melt through a device to finally shape workpiece.
Due to incompressibility of water, front end of water forms a solid interface, which squeezes inner wall of product into a cavity, and front end of water also plays a role of rapid cooling. Therefore, water assist has many incomparable advantages of gas assist. Research and application show that water assist can generate thinner and more uniform cavity walls, and inner wall surface of runner is very smooth. Especially for thick-walled workpieces, cooling time of water-assisted compared with gas-assisted can be greatly reduced.
Water assisted injection molding 
Picture shows principle of water assisted injection molding
Water assisted injection molding 
Pictures of auto parts

06 High gloss injection molding

Basic process of high gloss injection molding is to quickly heat mold surface by using high temperature and high pressure water vapor before injection molding, so that surface temperature of molding cavity reaches above glass transition temperature (Tg) of resin plastic, and then inject plasticized plastic melt into closed mold cavity. During injection phase, mold temperature is kept constant by high-temperature and high-pressure water vapor. When injection is completed, gas supply is stopped, and water vapor in pipeline is blown out by air pipe pressure. Then cooling water is passed to make temperature of mold drop rapidly, until product is cooled and opened.
High gloss injection molding 
High gloss injection molding 
High gloss injection molding 
Miphone tablet uses high gloss injection molding

Six common injection molding processing technologies for plastic products for home appliances

Molding and processing methods of plastic products for home appliances mainly include injection molding, extrusion molding, thermoforming, hollow molding, lamination molding, compression molding, transfer molding, foam plastic molding, casting molding, insert casting, sealing casting, etc., of which injection molding is mainly used.
In recent years, some new plastic processing technologies and new equipment have been widely used in molding of home appliance plastic products, such as precision injection molding, rapid prototyping technology, fuse core injection technology, gas assisted/water assisted injection molding technology, electromagnetic dynamic injection molding technology and laminated injection molding technology.

1. Precision injection molding

Can guarantee products with high precision and high repeatability in terms of size and weight. Injection molding machine using this technology can achieve high pressure and high speed injection. Because its control mode is usually open-loop or closed-loop control, it can achieve high-precision control of injection molding process parameters. Generally, precision injection molding requires higher precision in the mold. At present, China has been able to produce small and medium-sized precision injection molding machines.

 2. Rapid prototyping technology

It is rapidly developed along with diversification of home appliance varieties and continuous upgrading, and is mainly used to prepare plastic housings for home appliances. Advantage of this technology is that small batches of plastic parts can be achieved without need for a mold. At present, more mature rapid prototyping technology include laser scanning molding and liquid light curing molding. Among them, laser scanning molding method is widely used. Laser scanning device is composed of a laser light source, a scanning device, a dusting device and a computer. Processing process is that computer-controlled laser head scans according to a certain trajectory. At the position where laser passes, plastic micropowder is heated, melted and bonded together. After each scan, micropowder device sprinkles a thin layer of powder. After repeated scanning, products with a certain shape and size are formed. At present, some domestic enterprises have been able to produce laser scanning molding machines and plastic powders, but performance of equipment is unstable, and types of powders are also small.

 3. Fuse core injection technology

It is usually used to form special-shaped cavity products with high requirements on cavity roughness and accuracy, which cannot be processed by hollow forming or rotary forming methods. At present, application of this technology has been relatively mature in foreign countries, but it is still in an individual application state in China. Processing principle of this technology is that core shape that forms cavity is formed first, and then core shape is used as an insert for injection molding. Under heating action of injection molded parts, core is melted and flowed out, thereby forming a cavity. The most important point to use this technology is to know melting point of core materials and plastic parts. Generally, core material can be selected from general-purpose plastics, thermoplastic elastomers, or low-melting-point metals such as lead and tin according to specific conditions.

4. Gas assisted / water assisted injection molding

It has a wide range of applications and can be used to form many types of injection molded parts. Its typical product is a TV casing. During injection, gas or superheated water can be injected into cavity almost simultaneously with plastic melt. At this time, plastic melt is coated with gas or superheated water, and formed plastic product has a sandwich structure. After plastic part is shaped, gas or water can be released and mold can be demoulded. Such products have advantages of material saving, small shrinkage, good appearance and good rigidity. Key part of molding equipment is gas or water assisted device and its control software. In recent years, although there have been many domestic studies on this, application speed is fast, domestic equipment is still unstable.

5. Electromagnetic dynamic injection molding technology

It was invented by Mr. Qu Jinping of South China University of Technology. This technology causes screw to reciprocate in axial direction through effect of electromagnetic force. Because plastic is micro-plasticized in pre-plasticizing stage, structure of plastic part in holding stage is more compact, and internal stress of product is reduced. This technology can be used to form more demanding products such as optical discs. When used in molding of ordinary products, it can improve quality of products.

6. Laminated injection molding technology

Application of this device in foreign countries has been relatively mature. When using this technology, it is necessary to clamp a special printed decorative plastic film in a mold before injection molding, and then injection molding. Printed film can be adhered to surface of plastic after being deformed by heat, which is not only beautiful and firm, but also eliminates post-decoration step.
In general, plastic molds for household appliances have a very large demand for plastic molds. For example, a refrigerator or a fully automatic washing machine usually requires more than 100 molds, an air conditioner requires more than 20 pairs, and a color TV The machine requires 50-70 pairs of plastic molds. At the same time, technical requirements for plastic molds are relatively high, often requiring mold processing cycle to be as short as possible, thereby greatly promoting development of mold design and modern mold manufacturing technology. In addition, some difficult molds, such as hot runner injection molds and laminated injection molds, are gradually increasing in domestic applications.

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