Top ten plastic molding processes

June 26, 2019

 Top ten plastic molding processes

 

First, injection molding

 

(1) Injection 
Injection : also known as injection molding, the principle is to add granular or powdery raw materials into the hopper of the injection machine, the raw material is heated and melted in a flowing state, and is poured by the nozzle and the mold under the push of the screw or piston of the injection machine. The system enters the mold cavity and hardens and shapes in the mold cavity.

Factors affecting the quality of injection molding: injection pressure, injection time, injection temperature

 

Process characteristics:

 

Advantages:
1. Short molding cycle, high production efficiency and easy automation
2, can form plastic parts with complex shapes, accurate dimensions, with metal or non-metal inserts
3, product quality is stable
4, a wide range of adaptation

 

Disadvantages:

1, the price of injection equipment is higher

2, the injection mold structure is complex

3, high production cost, long production cycle, not suitable for single-piece small batch production of plastic parts

 

application:

In industrial products, injection molded products are: kitchen supplies (garbage cans, bowls, buckets, pots, cutlery and various containers), electrical equipment shells (hair dryers, vacuum cleaners, food blenders, etc.), toys and games, cars Various industrial products, parts of many other products, etc.

 

(2) Insert injection molding
Insert injection molding: Insert molding refers to a molding method in which a resin is injected into a mold and a resin is injected into the mold, and the molten material is bonded and solidified to form an integrated product.

 

Process characteristics:

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

2. The combination of the moldability and flexibility of the resin and the rigidity, strength and heat resistance of the metal complements the compact and intricate metal-plastic integrated product.

3. In particular, the combination of the insulating properties of the resin and the electrical conductivity of the metal can be used to satisfy the basic functions of the electrical product.

4. For the rigid molded product and the curved elastic molded product on the rubber gasket plate, the integrated product is formed by injection molding on the substrate, which can eliminate the complicated operation of arranging the sealing ring, and make the automatic combination of the post process easier.

 

 

(3) two-color injection
Two-color injection molding: refers to the molding method of injecting two different color plastics into the same mold. It can make plastics appear in two different colors, and can make the plastic parts have a regular pattern or irregular cloud-like colors to improve the usability and aesthetics of the plastic parts.

 

Process characteristics:

1. The core material can use low viscosity materials to reduce the injection pressure.

2. From the perspective of environmental protection, the core material can use recycled secondary materials.

3, according to different use characteristics, such as thick pieces of finished leather layer using soft materials, core materials using hard materials or core materials can use foam plastic to reduce weight.

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

5, the cortical material or core material can be used expensive and have special surface properties, such as anti-electromagnetic interference, high electrical conductivity and other materials to increase product performance.

6. The proper cortex material and core material can reduce the residual stress of the molded product, increase the mechanical strength or the surface properties of the product.

 

 

(4) Microfoam injection molding process
Microfoam injection molding process: It is an innovative precision injection molding technology that fills the product by the expansion of the pores and completes the molding of the part under a low and average pressure. The microcellular foaming process can be divided into three stages: first, a supercritical fluid (carbon dioxide or nitrogen) is dissolved in a hot melt to form a single-phase solution; and then a switch type nozzle is used to inject a mold having a lower temperature and pressure. The cavity, due to the instability of temperature and pressure, causes molecular instability to form a large number of bubble nuclei in the article, and these bubble nuclei gradually grow to form minute holes.

 

Process characteristics:

1. Precision injection molding;

2, breaking through the limitations of traditional injection molding, can significantly reduce the weight of the parts, shorten the molding cycle;

3. Greatly improved the warpage deformation and dimensional stability of the workpiece.

application:

Car dashboard, door panel, air conditioning duct, etc.

 

 

(5) Nano Injection Molding (NMT)
NMT (Nano Molding Technology): It is a combination of metal and plastic technology. After the metal surface is nano-treated, the plastic is directly injected and formed on the metal surface, so that the metal and plastic can be integrally formed.

Nano-forming technology is divided into two types of processes based on the location of the plastic:

1. Plastic is a one-piece molding

2, plastic is the one-piece molding

Process characteristics:

1. The product has a metallic appearance texture.

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

3, reduce production costs and high bonding strength, and significantly reduce the use of related consumables

 

Suitable metal and resin materials:

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

2. The adaptability of aluminum alloy is strong, including 1000 to 7000 series;

3. The resin includes PPS, PBT, PA6, PA66, PPA;

4. PPS has a particularly strong bond strength (3000 N/cm2).

 

application:

Mobile phone case, laptop case, etc.

 

 

Second, blow molding
 

Blow molding: a molten thermoplastic raw material extruded from an extruder is sandwiched into a mold, and then air is blown into the raw material, and the molten raw material is expanded by air pressure to be bonded to the wall surface of the mold cavity, and finally cooled. A method of curing into the desired product shape.

 

Blow molding is divided into two types: film blowing and hollow blowing:

 

1, film blow molding

Film blowing is to extrude molten plastic from a circular thin tube in the annular gap of the die of the extruder head, while blowing compressed air from the center hole of the machine head into the inner cavity of the thin tube to inflate the thin tube into a diameter. Larger tubular film (commonly known as a bubble tube), which is taken up after cooling.

 

2, hollow blow molding

Hollow blow molding is a secondary molding technique in which a rubber-like parison closed in a mold cavity is inflated into a hollow product by means of gas pressure, and is a method for producing a hollow plastic product. Hollow blow molding has different manufacturing methods for parisons, such as extrusion blow molding, injection blow molding, and stretch blow molding.

1) Extrusion blow molding: Extrusion blow molding is to extrude a tubular parison by an extruder, sandwich it in a mold cavity and heat the bottom, and then inject a compressed air into the inner cavity of the tube blank to form a blow molding.

2) Injection blow molding: The parison used was obtained by injection molding. The parison is left on the mandrel of the mold, and after the mold is closed by the blow mold, compressed air is introduced from the core mold to inflate the parison, and after cooling, the product is obtained after demolding.

advantage:

The product has uniform wall thickness, small weight tolerance, less post-processing and small waste corner; suitable for producing small-sized fine products with large batch size.

3) Stretch blow molding: the parison which has been heated to the stretching temperature is placed in a blow mold, longitudinally stretched with a stretching rod, and laterally stretched and inflated with blown compressed air to obtain a product. method.

 

application:

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

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

 

 

Third, extrusion molding (profile)

Extrusion: Also known as extrusion molding, it is mainly suitable for the molding of thermoplastics, and is also suitable for the formation of thermosetting and reinforced plastics with better fluidity. The molding process uses a rotating screw to extrude the heated and melted thermoplastic material from a machine head having a desired cross-sectional shape, and then shaped by a sizing device, and then chilled and hardened by a cooler to obtain a desired cross section. product.

 

Process characteristics:

1. Low equipment cost;

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

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

4. Products or semi-finished products of various cross-section shapes can be formed by changing the die of the machine head.

 

application:

In the field of product design, extrusion has a strong applicability. Extrusion products include pipes, films, rods, monofilaments, flat belts, nets, hollow containers, windows, door frames, plates, cable clads, monofilaments and other profiles.

 

 

Four, calendering (sheet, film)

Calendering: A method in which a plastic material is passed through a series of heated press rolls to join a film or sheet under extrusion and stretching.

 

Process characteristics:

 

Advantages: good product quality, large production capacity, and automatic continuous production;

 

Disadvantages: large equipment, high precision requirements, many auxiliary equipment, product width is limited by the length of the calender roll.

 

 

application:

Mostly used in the production of PVC soft film, sheet, sheet, artificial leather, wallpaper, floor leather and so on.

 

 

 

Five, press molding

Press molding: mainly used for the molding of thermosetting plastics. According to the properties of the molding materials and the characteristics of the processing equipment and process, press molding can be divided into two types: compression molding and lamination molding.

 

1. Molding

Molding, also known as compression molding, is the primary method of forming thermoset plastics and reinforced plastics. The process is to pressurize the raw material in a mold that has been heated to a specified temperature, so that the raw material is melted and uniformly filled into the cavity, and the raw material is formed into a product under a condition of heating and pressurization for a certain period of time.

 

Process characteristics:

The molded product has compact texture, accurate size, smooth and smooth appearance, no gate mark and good stability.

application:

In industrial products, molded products include electrical equipment (plugs and sockets), handles, handles for tableware, bottle caps, toilet bowls, non-breaking plates (Melamine), carved plastic doors, and the like.

 

2, laminate molding

Lamination molding: a method in which two or more layers of the same or different materials are combined into one body under heat and pressure using a sheet or fibrous material as a filler.

 

Process characteristics:

The laminating process consists of three stages of impregnation, pressing and post-processing, and is used to produce reinforced plastic sheets, pipes, rods and model products. The texture is compact and the surface is smooth and smooth.

 

 

Six, injection molding

Injection molding: It is a molding method of thermosetting plastic developed on the basis of compression molding, also known as transfer molding. The process is similar to the injection molding process. During injection molding, the plastic is plasticized in the feeding cavity of the mold, and then enters the cavity through the casting system, and the injection molding is plasticized in the barrel of the injection molding machine.

The difference between injection molding and compression molding: the compression molding process is to first close the mold after feeding, and the injection molding generally requires the mold to be closed after feeding.

 

Process characteristics:

 

Advantages: (compared to compression molding)

1. The plastic has been plasticized before entering the cavity, and it can produce plastic parts with complex shape, thin wall or large wall thickness and fine inserts.

2. Shorten the molding cycle, improve production efficiency, and improve the density and strength of plastic parts.

3. Since the mold is completely closed before the plastic molding, the flash edge of the parting surface is very thin, so the precision of the plastic part is easy to ensure the surface roughness is also low.

 

Disadvantages:

1.