The most common injection molding processes for plastic molding

Plastic molding processes include: injection molding, extrusion molding, compression molding, blow molding, calendar molding, rotational molding, vacuum molding (blister molding), casting molding (cast molding), slush molding, tape molding , foam molding, transfer molding (injection molding), winding molding, etc.

This article will briefly introduce the processes, advantages and disadvantages, and application areas of the 8 most common plastic molding methods.

Ⅰ. Injection molding

Injection molding: It 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 and die-casting. Injection molding machine (referred to as injection machine or injection molding machine) is the main molding equipment for making thermoplastic or thermosetting materials into plastic products of various shapes using plastic molds. Injection molding is achieved through an injection molding machine and a mold.

Injection molding process:

a. Mold clamping. The mold is closed to form a space for injection molding.

b. Filling. The molten plastic is injected into the mold under pressure and stops after filling 95% of the mold cavity.

c. Keep pressure. Continuously apply pressure to compact the melt and make the molded part structurally tight.

d. Cool. Cooling the molded parts until they can be demolded takes up 70% of the entire process.

e. Cool and demould. The mold is opened and the product is ejected using an ejector pin or stripping plate. Factors that affect the quality of injection molding: injection pressure, injection time, injection temperature.

Injection molding process features:

advantage:

1. Short molding cycle, high production efficiency, easy to realize automation

2. Can form plastic parts with complex shapes, precise dimensions, and metal or non-metal inserts.

3. Product quality is stable

4. Wide adaptability

shortcoming:

1. Injection molding equipment is more expensive

2. The injection mold has a complex structure

3. The production cost is high, the production cycle is long, and it is not suitable for the production of single-piece and small-batch plastic parts.

application:

Among industrial products, injection molded products include: kitchen supplies (trash cans, bowls, buckets, pots, tableware and various containers), casings of electrical equipment (hair dryers, vacuum cleaners, food mixers, etc.), toys and games, automobiles Various industrial products, parts for many other products, etc.

Ⅱ. Insert injection molding

Insert injection molding: Insert molding refers to a molding method in which pre-prepared inserts of different materials are installed in the mold and then resin is injected. The molten material joins and solidifies with the insert to form an integrated product.

Process features:

1. The pre-molding combination of multiple inserts makes the post-engineering of product unit combination more rational.

2. The easy formability and bendability of resin and the rigidity, strength and heat resistance of metal can be combined and complement each other to make complex and exquisite metal-plastic integrated products.

3. Especially by utilizing the combination of the insulation of resin and the conductivity of metal, the molded products can meet the basic functions of electrical products.

4. For rigid molded products and bending elastic molded products on rubber sealing gaskets, after the integrated products are made by injection molding on the base body, the complex work of arranging the sealing rings can be omitted, making the automated combination of the post-process easier.

Ⅲ.Two-color injection molding

Two-color injection molding: refers to a molding method in which two plastics of different colors are injected into the same mold. It can make plastic appear two different colors, and can make plastic parts show regular patterns or irregular moiré-like colors to improve the usability and aesthetics of plastic parts.

Process features:

1. Low-viscosity materials can be used as core materials to reduce injection pressure.

2. From the perspective of environmental protection, recycled secondary materials can be used as core materials.

3. According to different usage characteristics, for example, soft materials are used for the skin material of thick finished products, hard materials are used for the core material, or foamed plastic can be used as the core material to reduce the weight.

4. Lower quality core materials can be used to reduce costs.

5. The skin material or core material can use expensive materials with special surface properties, such as anti-electromagnetic wave interference, high conductivity and other materials to increase product performance.

6. Appropriate combination of skin material and core material can reduce the residual stress of the molded product and increase the mechanical strength or surface properties of the product.

Ⅳ. Micro-foam injection molding process

Micro-foam injection molding process: It is an innovative precision injection molding technology that relies on the expansion of pores to fill the product, and completes the molding of the product under low and even pressure. The microcellular foaming molding process can be divided into three stages: first, the supercritical fluid (carbon dioxide or nitrogen) is dissolved into the hot melt glue to form a single-phase solution; then the mold with lower temperature and pressure is injected through the switch-type nozzle. Due to the decrease in temperature and pressure, the instability of molecules triggers the formation of a large number of bubble nuclei in the product, and these bubble nuclei gradually grow to form tiny holes.

Process features:

1. Precision injection molding;

2. Breaking through many limitations of traditional injection molding, it can significantly reduce the weight of parts and shorten the molding cycle;

3. Greatly improve the warpage deformation and dimensional stability of the parts.

application:

Car dashboards, door panels, air conditioning ducts, etc.

Ⅴ.Nano injection molding (NMT)

NMT (Nano Molding Technology): It is a method of combining metal and plastic using nanotechnology. After the metal surface is nano-treated, the plastic is directly injection molded on the metal surface, so that the metal and plastic can be formed into one piece. Nanomolding technology is divided into two types of processes based on the location of the plastic:

1. The plastic is integrally formed on the non-appearance surface.

2. The plastic is integrated into the exterior surface.

Process features:

1. The product has a metallic appearance and texture.

2. The design of product machine components is simplified, making the product lighter, thinner, shorter and smaller, and more cost-effective than CNC processing.

3. Reduce production costs and achieve high bonding strength, and significantly reduce the usage rate of related consumables.

Applicable metal and resin materials:

1. Aluminum, magnesium, copper, stainless steel, titanium, iron, galvanized sheet, brass;

2. Aluminum alloys have strong adaptability, including 1000 to 7000 series;

3. Resins include PPS, PBT, PA6, PA66, and PPA;

4. PPS has particularly strong bonding strength (3000N/c㎡).

application:

Mobile phone cases, laptop cases, etc.

Ⅵ. Blow molding

Blow molding: The molten thermoplastic raw material extruded from the extruder is clamped into the mold, and then air is blown into the raw material. The molten raw material expands under the action of air pressure, adheres to the wall of the mold cavity, and is finally cooled. A method of curing into the desired product shape. Blow molding is divided into two types: film blow molding and hollow blow molding:

1. Film blow molding

Film blowing is to extrude molten plastic into a cylindrical thin tube from the annular gap of the die of the extruder head. At the same time, compressed air is blown into the inner cavity of the thin tube from the center hole of the extruder head to inflate the thin tube to a diameter of Larger tubular films (commonly known as bubble tubes) are rolled up after cooling.

2. Blow molding

Also known as hollow blow molding, it is a rapidly developing plastic processing method. The tubular plastic parison obtained by extrusion or injection molding of thermoplastic resin is placed in a split mold while it is hot (or heated to a softened state). After the mold is closed, compressed air is immediately introduced into the parison to blow the plastic parison. It expands and adheres closely to the inner wall of the mold. After cooling and demoulding, various hollow products are obtained.

1) Extrusion blow molding: Extrusion blow molding uses an extruder to extrude a tubular parison, clamp it in the mold cavity while it is hot and seal it at the bottom, and then introduce compressed air into the inner cavity of the tube parison to blow it into shape.

2) Injection blow molding: The parison used is obtained by injection molding. The parison remains on the core mold of the mold. After closing the mold with the blow mold, compressed air is introduced from the core mold to inflate the parison, cool it, and after demoulding, the product is obtained.

advantage:

The product has uniform wall thickness, small weight tolerance, less post-processing, and small waste corners; it is suitable for producing small refined products in large batches.

3) Stretch blow molding: Place the parison that has been heated to the stretching temperature in the blow mold, use a stretch rod to stretch it longitudinally, and use blown compressed air to stretch and blow it transversely to obtain the product. method.

application:

1. Film blowing is mainly used to manufacture thin plastic molds;

2. Hollow blow molding is mainly used to make hollow plastic products (bottles, packaging barrels, spray cans, fuel tanks, cans, toys, etc.).

Ⅶ.Extrusion molding (profiles)

Extrusion molding: Also known as extrusion molding, it is mainly suitable for the molding of thermoplastic plastics, and is also suitable for the molding of some thermosetting and reinforced plastics with good fluidity. The molding process is to use a rotating screw to extrude the heated and molten thermoplastic raw material from the machine head with the required cross-section shape, then shape it by the shaper, and then pass it through the cooler to cool and solidify it into the required cross-section. product.

Process features:

1. Low equipment cost;

2. The operation is simple, the process is easy to control, and it is convenient to realize continuous automated production;

3. High production efficiency; uniform and dense product quality;

4. By changing the die of the machine head, products or semi-finished products with various cross-sectional shapes can be formed.

application:

In the field of product design, extrusion molding has strong applicability. The types of extruded products include pipes, films, rods, monofilaments, flat ribbons, nets, hollow containers, windows, door frames, plates, cable cladding, monofilaments and other special-shaped materials.