plastic forming processes for formed parts
by Lushi-Molding  | April 19th. 2020  |  Tags: Molding Technology

8 commonly used processes for plastic forming

Plastics has nowadays become an indispensable part of our daily life, and also in industry, they are everywhere. Plastic forming refers to the production of formed parts, semi-finished products, films, fibers, etc. which are made of plastics. Plastics in the chemical industry exist in the form of granules, powders, foils or sheets that through various molding processing to reach the parts with specific shape and structure, such as injection molding, extrusion, calendering, blow molding, etc. Using shapeless materials such as powder or melt to create solid geometry, this is the primary forming process that can produce parts of various shapes, such as shell parts, pipes and packages and other plastics; this is very suitable for mass production. In the following, Lushi-Molding will introduce 8 common ways for plastic forming.

Injection molding

Plstic injection molding process is the most commonly used method in the production of plastics, accounting for 70% of all plastics. Firstly, the granular raw materials are loaded into the funnel, heated, plasticized, and then injected into the cavity of the mold under high pressure. Through the cooling system the required parts will be formed. During the molding process, the mold and injection molding machines are needed. Its advantage is that it can carry out mass production of products, which is conducive to reducing costs. Besides, it is suitable for all kinds of plastic, such as thermoplastic and thermosets.

injection molding is the most common forming process for plastics

Extrusion injection molding

The extrusion process using a system called an extruder. At first, raw materials of plastic enter the barrel through the funnel. The material is melted, homogenized and compressed. And then the melt is extruded through the shaped nozzle head at the end of the extruder. According to the shape of the nozzle head, different products can be made. This process is very similar to injection molding, but the main difference is that extrusion molding is a continuous process. The disadvantage is that extrusion molding cannot produce complicated plastic parts, but injection molding can do.

extrusion injection molding technology

Calendering

The calendering process, also known as the rolling process, is used to produce films. The calender consists of several highly polished rollers with fast rotation speed. The rolls can be cooled or heated as needed. Especially when the specification of the film thickness is in a particularly narrow, calendering is an excellent way to make it. A special calendering helps make films with certain embossing or other patterns.

plastic forming using calendering to make folie

Rotomolding

Rotational molding is general manufacturing used to produce large, hollow, and seamless plastic parts. First, the plastic material is added to the mold, which is continuously rotated along two vertical axes and heated. And then, under the gravity and heat energy, the plastic raw materials in the mold are gradually uniformly coated, melt-adhered to the entire surface of the mold cavity to get the desired shape. Through the cooling and demolding, the product is finally is obtained. Due to the nature of the rotary tool, different wall thicknesses can also be achieved within a single shape. Applications include large enclosures and shipping containers.

rotational molding process to make bottles and packages

Foam molding

Foaming is a process for producing foam. In the foam molding process, the foamed polymer material participates in the reaction by adding a physical foaming agent or a chemical foaming agent, thereby forming a honeycomb or porous structure. The basic steps of foam molding are the formation of the nucleus, the growth and the stabilization. Under the given temperature and pressure conditions, the solubility of the gas decreases and reaches saturation, which will cause the excess gas to be eliminated and form bubbles, thereby achieving nucleation.

Chemical foaming process: the added chemical foaming agent is decomposed by heat to produce gas generated by the chemical reaction so that the plastic melt fills the cells—for example, the production of polyurethane foam.

Physical foaming process: First, the low-boiling liquid is added to the reaction mixture. These gases evaporate during the polymerization process, forming typical bubbles.

Mechanical blowing process: Stir the plastic melt while blowing gas into the melt to form the foaming method of the cells.

foam forming process in the molding industry

Injection blow molding

The blow molding process is used to produce hollow bodies. Blow molding is often carried out by extrusion blow molding. First, use an extruder to press a tube into a two-part die. Then, the compressed air enters the tube and is pressed against the cold wall of the molded part. After cooling, the molded part is separated and the hollow body can be taken out. In the packaging industry, the blow molding process is mainly used to produce plastic bottles.

injection blow molding for bottle manufacturing

Compression molding

thermoset is a hard plastic, usually glass fiber reinforced polymer material. Under pressure and high temperature, plastics undergo cross-linking in chemical reactions. Once the thermosetting plastic has hardened, it can no longer be molded. Thermosetting plastics are used in applications requiring high heat resistance, chemical resistance, and electrical insulation. The advantage is that thermoset parts have excellent dimensional stability, maintain electrical and dielectric properties, and are resistant to chemical or organic solvents even at high temperatures. Therefore, even without halogen flame retardants can meet the fire rating requirements.

Compression molding is to add powdered or loose granular solid plastics directly to the mold, gradually soften and melt them by heating and pressing, and then shape them according to the shape of the mold cavity and solidify into plastic parts.

In the first step: Powder, granular, crumb or fibrous thermosetting plastic raw materials are directly added to the open mold charging chamber.

In the second step: The mold is then heated to melt the plastic. Under the effect of the mold clamping pressure, the molten plastic fills the cavity, and then the molded part is held in this position until it hardens.

In the third part: At this time, the plastic in the cavity produces a chemical cross-linking reaction, which gradually turns the molten plastic into an infusible hardened and shaped plastic part. Finally, the formed plastics are removed from the mold.

compression molding technology for thermosetting forming

Plastic vacuum casting

The discontinuous casting process is used for thermosetting materials. Liquid substances (reactants) are evenly mixed and chemical reactions occur. The reactive mixture is then poured into the mold, and on this basis, the cavity can be filled with vacuum assistance. The mixture reacts in the mold to form a thermosetting plastic, hardens in the pattern, and then it will be demolded.

vacuum casting for plastic forming

Lushi-Molding has more than 10 year experience in the molding industry with high expertise. We can give you the best suggestions, which meet your project requirements, to achieve the top quality of forming plastics, ensuring with effective project cost.


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Email: jonas@lushimold.com
Jonas Zhan
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