Plastic Injection Mold

Plastic Injection mold is assorted with plastic forming machines in plastic processing industry, making plastic products with complete configuration and precise dimension. Based on different forming methods, plastic mold can be classified into several categories to meet different requirements of techniques, mainly including plastic injection mold, plastic extrusion mold, plastic suction mold and high foaming polystyrene mold.

1. Plastic injection mold

Plastic injection mold is one of the most commonly used molds in manufacturing thermoplastic products. The processing equipment matching with plastic injection mold is plastic injection molding machine. Firstly, plastic is heated and melt in bed charge cartridge heater of injection molding machine. Then, the plastic enters into cavity of mold though nozzle of injection molding machine and gating system of mold, under the promotion of screw or plunger of injection molding machine. The plastic is cooled and hardened for molding, ejected for products. The structure generally consists of molding parts, gating system, guiding parts, ejecting mechanism, exhaust system and supporting parts. Making materials usually adopt plastic die steel, mainly including carbon structural steel, tool carbon steel, tool alloy steel and high-speed steel. Injection molding is only suitable for manufacturing thermoplastic products. Thermoplastic products made by injection molding are quite wide. Daily necessities, complicated machineries, parts on electric appliances and vehicles are molded by injection mold. It is the most widely used in manufacturing plastic products. 

2. Plastic compression mold

Plastic compression mold is classified into compression molding and pressure casting molding, which is mainly used for thermosetting plastic. Equipment matched with the mold is pressure forming machine. The principle of compression molding is that heat the mold to forming temperature (generally 103℃~108℃), then, put metrological compression molding powders into mold cavity and feed compartment. Closing the mold, the plastic becomes soft and plastic flow under high pressure and high temperature. After a time, plastic is solidified in required shape of products. What the difference between compression and pressure casting molding is that pressure casting molding does not need sole feed compartment. The mold is closed firstly before forming. The plastic is preheated to plastic flow in feed compartment. Under pressure, plastic is adjusted and extruded into mold cavity, hardening and forming. Compression mold is also used to form some special thermoplastic plastics which are to be melt, such as PTFE workblank (cold press molding), resin lens having high optical performance and mild foaming steering wheel made of nitrocellulose. Plastic compression mold mainly consists of cavity, loading chamber, guide mechanism, extrusion parts and heating system. Pressure casting mold is mainly used for packaging electrical apparatus elements. The materials used for plastic compression mold are the same as those used for injection mold. 

3. Plastic extrusion mold

Plastic extrusion mold is a mold used to manufacture and form plastic products having continuous shapes, also called as extrusion head, widely applied in processing tube, stick, filament, sheet, thin film, coating layer of cable and profiled bar. Equipment matched with the mold is plastic extruding machine. The principle is that solid plastic is melted and plasticized under heating and screw of extruding machine. It forms continuous plastic products through neck mold having specific shape so that the shape of products is the same as neck mold. The materials mainly contain carbon structural steel and tool alloy steel. Some extrusion molds are inset with diamond or other wear-resistant materials on wear-resistant parts. Generally, extrusion mold is only used for manufacturing thermoplastic plastic products. The structure of extrusion mold is obviously different from injection mold and compression mold.     

4. Plastic blow mold

Plastic blow mold is a mold used for forming hollowed plastic containers (such as beverage bottle and package of daily chemical products. Based on different technical principles, forms of blow molding are mainly classified into extrusion hollow blow molding and extrusion injection molding, including extrusion blow hollow molding, blow hollow injection molding, injection blow molding, multilayer hollow blow molding, sheet hollow blow molding. The equipment matched with blow molding is plastic blow molding machine. Plastic blow mold is only suitable for thermoplastic products. The structure of blow mold is quite simple. Carbon steel is mostly used as materials.

5. Plastic suction mold

Plastic suction mold is a mold that forms simple plastic products made of plastic plate and sheet. The principle is that use vacuum or air compression to fix plastic plate or sheet on die or terrace die. Under heating and softening, plastic deforms and paste on cavity of mold, forming into required products. The mold is mainly used for manufacturing packaging of daily necessities, food and toys. Due to lower pressure during forming, plastic suction mold is mainly made of cast aluminum or non-metallic materials. The structure is quite simple. 

6. High foaming polystyrene forming mold

The mold is a mold that uses expandable polystyrene to form required foamed plastic packaging materials. The principle is that use expandable polystyrene is formed by steam in mold, including simple manual operation mold and hydraulic press cut-through foaming plastic mold. The mold is mainly used for manufacturing packaging products of manufactured goods. Cast aluminum, stainless steel and bronze are mainly used for manufacture the mold.

Plastic Molding in China

Compared with stamping mold and die casting mold, plastic molding has 5 development features in China.

1. Cavity and core showing tridimensional molded surface
External and internal shape of plastic parts is directly formed by cavity and core. These complicated tridimensional molded surfaces have larger processing difficulty, especially blind hold molding surface processing. If traditional processing methods are adopted, it not only requires workers with high technical level, many auxiliary tools, but also requires long processing cycle. 

plastic molding

2. Higher requirements for precision, surface quality and service life
At present, dimensional precision of common plastic parts is required to IT6-7, surface roughness Ra0.2-0.1mm. Dimensional precision of matching plastic molding parts is required to reach IT5-6, and surface roughness should be below than Ra0.1mm. Roughness of laser disc recording surface should reach to level of mirror finishing, 0.02-0.01mm. So, the surface roughness of mold should be lower than 0.01mm. Plastic injection mold having long service life is essential for improving efficiency and reducing cost. Now, the service life of injection mold is required to be used for more than one million times. Precise injection mold should use mold base having large rigidity to increase thickness of template, increasing bearing post or cone setting element to prevent mold from deforming after being pressed. Sometimes, internal pressure can reach to as high as 100MPa. Ejector is an important factor having influence on product deformation and dimensional accuracy. For this, the ejection points must be chosen for even demold. The structure of high precise injection mold mostly uses splicing and full splicing which requires that processing precision and interchangeability of mold parts should be highly improved.

3. Long technological process and limited manufacturing time
For plastic molding parts, most of them are composed into complete parts with other parts. And in many cases, other parts have been finished, urgently waiting for plastic parts. The requirements for shape and dimensional precision of products are high, and characteristics of resin materials are varied. Repeat trial and modification are needed after manufacturing mold, making limited development and delivery time.

4. Distributed design and manufacturing
Making mold is not the final objective. The users come up with design of final products, and the mold manufacturers design and making mold based on users’ requirements. In most of cases, injection molding is also carried out by other manufacturer. So, product design, mold design and product manufacturing are carried out in different places. 

5. Professional division of labor, dynamic combination
Mold manufacturing has few batches, generally one piece production. However, mold needs a lot of standard parts, including mold base and centre. All of parts cannot be finished solely by only one manufacturer. Besides, manufacturing technology is complicated. The utilization of common equipment and CNC equipment is imbalanced.