Injection moulding (or Injection Molding) is a manufacturing technique for making products from plastic resin. Injecting the molten plastic resin at high pressure into a mould, which is the inverse of the desired part shape, the part shape was created by designer using some CAD design software, The mould is made by a mould maker (or toolmaker) from metal material, usually either aluminum or steel, and precision-machined to form the features of the desired part by some high technical machine like CNC machine, EDM machine, lather machine grinding machine, wire-cutting machine etc, step by step to make final mould cavity base on exactly desired part shape and size. Injection moulding is very widely used for manufacturing a variety of plastic parts, from the smallest component to entire body panels of cars. It is the most common method of production on the world today, with some commonly made items including bottle caps, food containers, bucket, storage bins, house cooking equipment, outdoor furniture, more and more.
If you want to run your business with injection moulding, below some basic information you may need to know
- 1 Types of Injection Molding
- 2 Injection molding equipment
- 2.1 Injection molding machine
- 2.1.1 Horizontal or vertical machines
- 2.1.2 Clamping unit
- 2.2 Injection mold
- 2.1 Injection molding machine
- 3 Injection molding process
- 3.1 Injection Molding Cycle
- 3.2 Molding trial
- 3.3 Molding defects
Types of Injection Molding
Basically 7 type of injection moulding process as below
- Reaction injection molding
- Liquid injection molding
- Gas assist injection molding
- Co-injection molding
- 2-Shot Injection Molding (or double injection molding)
- Fusible core injection molding
- Rapid injection molding
Injection molding equipment
Injection molding machine
Injection molding machines, also known as presses, hold the molds in the press which the components are shaped. Presses are rated by tonnage, which expresses the amount of clamping force that the machine can generate. This pressure keeps the mould closed during the injection process. Tonnage can vary from less than 5 tons to 6000 tons, with the higher figures used in comparatively few manufacturing operations.
Horizontal or vertical machines
Injection molding machines can fasten the molds in either a horizontal or vertical position. The majority is horizontally oriented but vertical machines are used in some niche applications such as insert molding, allowing the machine to take advantage of gravity. there are some injection machine can old two color or three or four color at one step, we call double injection molding machine or 2K molding machine( more color will be 3K or 4K),
Machines are classified primarily by the type of driving systems they use: hydraulic, electric, or hybrid. Hydraulic presses have historically been the only option available to molders until Nissei introduced the first all electric machine in 1983. The electric press, also known as Electric Machine Technology (EMT), reduces operation costs by cutting energy consumption and also addresses some of the environmental concerns surrounding the hydraulic press. Electric presses have been shown to be quieter, faster, and have a higher accuracy, however the machines are more expensive. Hybrid injection molding machines take advantage of the best features of both hydraulic and electric systems. Hydraulic machines are the predominant type in most of the world, with the exception of Japan.
Considerable thought is put into the design of moulded parts and their moulds, to ensure that the parts will not be trapped in the mould, that the moulds can be completely filled before the molten resin solidifies, to compensate for material shrinkage, and to minimize imperfections in the parts, which can occur due to peculiarities of the process. read more information about injection mold
Injection Mouding process
Injection Molding Cycle
The basic injection cycle is as follows: Mold close – injection carriage forward – inject plastics – metering – carriage retract – cooling (cold done) – mold open – eject part(s)
The molds are closed shut by hydraulics or electric molding machine, and the heated plastic is forced by the pressure of the injection screw to take the shape of the mold. Some machines are run by electric motors instead of hydraulics or a combination of both. The water-cooling channels then assist in cooling the mold and the heated plastic solidifies into the part. Improper cooling can result in distorted molding or one that is burnt. The cycle is completed when the mold opens and the part is ejected with the assistance of ejector pins within the mold.
When filling a new or unfamiliar mold for the first time, where shot size for that mold is unknown, a technician/tool setter usually starts with a small shot weight and fills gradually until the mold is 95 to 99% full. Once this is achieved a small amount of holding pressure will be applied and holding time increased until gate freeze off has occurred, then holding pressure is increased until the parts are free of sinks and part weight has been achieved. Once the parts are good enough and have passed any specific criteria, a setting sheet is produced for people to follow in the future.
Plastic processing troubleshooting
Injection moulding is a complex technology with possible production problems. They can either be caused by defects in the molds or more often by part processing (molding)