With the development of science and technology, the requirements for injection molding process are becoming higher and higher. The choice of injection molding mainly depends on the type of plastic, the initial shape, and the shape and size of the product. The common methods of injection molding include extrusion, injection molding, blow molding and calendering. Each method has its advantages and disadvantages, and is more suitable for specific applications.
injection molding
Injection molding: also known as injection molding, its principle is to add granular or powdery raw materials into the hopper of the injection machine. The raw materials are heated and melted to flow state. Driven by the screw or piston of the injection machine, they enter the mold cavity through the nozzle and the mold’s gating system, and then harden and shape in the mold cavity
Factors affecting injection molding quality: injection pressure, injection time, injection temperature.
injection molding
Advantage：
1. Short molding cycle, high production efficiency and easy automation
2. Be able to make plastic parts with complex shape, accurate size and metal or non-metallic inserts
3. Stable product quality
4. Wide adaptability
Application:
Among industrial products, injection molded products include kitchen supplies (trash cans, bowls, buckets, pots, tableware and various containers), shells of electrical equipment (hair dryers, vacuum cleaners, food mixers, etc.), toys and games, various products of the automobile industry, and parts of many other products
Two color injection molding
Two color injection molding refers to the molding method of injecting two kinds of plastics with different colors into the same mold. It can make plastic appear two different colors, and make plastic parts present regular patterns or irregular moire patterns, so as to improve the usability and aesthetics of plastic parts
Process characteristics:
1. The core material can use low viscosity materials to reduce the injection pressure.
2. Core materials can be recycled and reused.
3. According to different use characteristics, for example, soft
materials are used for thick finished products, hard materials are used for core materials, or foamed plastics can be used for core materials to reduce weight.
4. Lower quality core materials can be used to reduce costs.
5. The leather or core material can be used with high price and special surface properties to increase product performance.
6. Proper matching of the skin and core materials can reduce residual stress of the molded products, increase mechanical strength or surface properties of the products.
Nanometer injection molding (NMT)
NMT (NanoMoldingTechnology): It is a combination of metal and plastic with nanotechnology. After the metal surface is nano treated, the plastic is directly injected onto the metal surface, so that the metal and plastic can be formed in one.
Nanomolding technology can be divided into two types of processes according to the location of plastics: one is the integrated molding of plastics for non appearance surfaces; The other type is integrated molding with plastic as the exterior surface
Process characteristics:
1. The products have a metallic appearance,
2. The design of product mechanism is simplified, making the product lighter, thinner, shorter and smaller
3. Reduce production cost and high bonding strength, and greatly reduce the use rate of related consumables
Application:
Generally, electronic products such as mobile phone shell and laptop shell will use nano injection molding process
Blow molding
Blow molding is to place the processed raw materials in the split mold, inject compressed air, make the mold embryo cling to the inner wall of the mold, cool and demould. Blow molding is generally divided into film blow molding and hollow blow molding.
1. Film blowing
Film blowing is to extrude the molten plastic from the annular gap of the die of the extruder head as a cylindrical thin tube, blow compressed air into the inner cavity of the thin tube from the central hole of the die head, blow the thin tube into a tubular film (commonly known as a bubble tube) with a larger diameter, and roll it after cooling.
2. Hollow blow molding
Hollow blow molding is a secondary molding technology that uses gas pressure to blow the rubber like parison closed in the mold cavity into hollow products. It is a method to produce hollow plastic products. According to the different manufacturing methods of parison, hollow blow molding includes extrusion blow molding, injection blow molding, and stretch blow molding
advantage:
The wall thickness of the product is uniform, the weight tolerance is small, the post-processing is small, the scrap corner is small, and the production cost of the product is low; It has high resistance to tensile, impact, bending and environmental strains, and has good service performance. It is suitable for the production of small precision products with large batches.
Application:
1. Film blowing is mainly used to make plastic films;
2. Hollow blow molding is mainly used to make hollow plastic products (bottles, packaging barrels, watering cans, oil tanks, cans, toys, etc.)
Extrusion molding
Extrusion molding, also known as extrusion molding, is mainly suitable for the molding of thermoplastics, and also suitable for the molding of some thermosetting and reinforced plastics with good fluidity.
The molding process is to use the rotating screw to extrude the heated and melted thermoplastic raw materials from the die with the required cross section shape, and then shape them by the shaper, and then harden them through the cooler to become the products with the required cross section.
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; The product quality is uniform and dense;
4. Products or semi-finished products of various section shapes can be formed by changing the die.
Application:
In the field of product design, extrusion molding has strong applicability. The types of extruded products include pipe, film, bar, monofilament, flat strip, net, hollow container, window, door frame, plate, cable cladding, monofilament and other profiled materials
Calendering
Calendering refers to the method of connecting plastic raw materials into films or sheets under the action of extrusion and extension through a series of heated radiators
Process characteristics:
Advantages: good product quality, large production capacity, automatic continuous production;
Disadvantages: huge equipment, high precision requirements, many auxiliary equipment, product width, pressure and the limit of the length of the cylinder of the extension machine.
Application:
It is mainly used in the production of PVC soft film, sheet, sheet, artificial leather, wallpaper, floor leather, etc