Injection moulding is a manufacturing process for producing parts by injecting material into a mould.
Injection moulding is one of the chief processes for producing plastic items. It is a fast process that can deliver a large numbers of identical items - from high precision engineering components to small disposable consumer goods.
The use of this process has enabled the extension of boundaries of design in plastics, and also helped in the substitution of conventional materials, thereby reducing the weight of the end product and providing immense design freedom.
Companies Involved in Injection Moulding
The following are some of the major companies involved in injection moulding:
- Ferromatik Milacron GmbH, Malterdingen, Germany develops, manufactures, and sells injection molding machines. The latest creation is the modular F-Series, which can be configured as an all-electric, hydraulic, or hybrid machine. The company is a part of the American Milacron group.
- KraussMaffei is one of the world's leading manufacturers of injection moulding machinery. The injection moulding machine ranges provided by the German company are AX series, CX series, CX-ClassiX, EX series, GX series, MX series, and C3 series.
- Sumitomo (SHI) Demag Plastics Machinery GmbH, Schwaig/Germany, is a Japanese-German company dealing with the manufacturing of injection moulding machines. They provide all-electric, hydraulic and hybrid injection moulding machines with clamping forces of between 180 and 20,000 kN.
- German company, Arburg is one of the world’s leading manufacturers of high-end injection moulding machines for plastics processing. They cater to industries such as electronics, packaging, automotive, medical/optical, and many others as well.
- AIM Plastics caters to the wide range of sectors including healthcare/medical, electrical / electronic, automotive/auto aftermarket , commercial/consumer, aerospace/defense, and action sports. They are located in Michigan, USA.
Recent Improvements in Injection Moulding
The following are some of the key improvements in injection moulding:
- Multiple component injection technologies - Under the spectrum of multiple component injection technologies are the sandwich technologies. Sandwich technologies comprise co-injection, mono-sandwich, gas injection technique (GIT) and water injection technique (WIT). In the co-injection method, two melts are injected into the machine’s cavity through one gate, one after the other. In mono-sandwich method, two materials are injected with one injection unit via one passage into the cavity. In GIT, the gas used is mostly nitrogen, which is injected into the part to replace the melt in the core and create a hollow space. GIT enables production of parts with high wall-thicknesses and/or material accumulations. It provides increased strength and stiffness at lower or equal part weight. It enables reduction of weight up to 50% and decreasing of the material costs. Likewise it enables reduction of the cooling/cycle time up to 50%, lowers clamp force and machine costs. GIT enables less sink marks, parts with less distortion, and improved part quality. In WIT, there are two processes - the short-shot process and the full shot process. In the short shot process, high speed shooting is required during the filling process in a transparent tool. Many consider WIT to have relatively more advantages than the GIT. WIT provides lesser cycle times, smaller and constant wall thickness with less warpage, large part diameters, and smoother inner surfaces. Additionally, water is cheaper than gas and is incompressible.
- Micro injection moulding - To produce very small components using the injection moulding process requires maximum possible accuracy and precision. The core of the processing of plastics of minimal size is the micro injection unit. Sumitomo (SHI) Demag is one such company that caters to the field of miniaturisation by providing customized plastification systems for shot weights of 5 to 0.1 g. their micro injection unit can be integrated in any standard machine for a clamping force up to 500 kN.
- Modern day injection moulding machines are controlled by a built-in computer. The computer controls all the actions of the machine based on sensor fed information, thereby ensuring consistent output and shot to shot quality.
Dual-Shot Injection Moulding
‘Two-Shot’ injection moulding or dual-shot injection moulding is a method to produce simple to complex parts comprising two different polymers even with two different colours during one machine cycle.
The ‘Two-Shot’ mould consists of two separate cavities that are used for making a single part. The first step in the process is to create a substrate in the first cavity, which receives material from one of the two injection units. The tool then opens to allow for a 180° rotation to a secondary position after the finished part is removed from the second stage cavity. As the tool closes, the second step commences by positioning the previously molded substrate into the second cavity. The second cavity receives the material from the second injection unit completing a finished part, this occurs simultaneously as the substrate for another part is being molded.
When the tool opens again, the finished part is ejected, and another substrate is ready to receive its over-mold. Therefore by applying alternating rotary motion of the tool, this simultaneous process enables continuous manufacturing operation.
The key benefits of the ‘Two-Shot’ injection moulding are as follows:
- Soft touch features and multi-color on handles, grips, devices, enclosures, and other components
- Back-lit buttons, dials and other instrumentation products
- Noise/vibration dampening and isolation
- Air/water seal
- Shock absorption and protection
- Movable segments or components such as living hinges and spring type mechanisms
Applications of Modern Injection Moulding
Injection mouldings account for nearly most of all plastics products. Almost all manufacturing sectors use injection moulded parts due to their flexibility in size and shape.
The following is a list of basic products that can be injection moulded:
- Power-tool housing
- Telephone handsets and DVDs
- Television cabinets
- Electrical switches
- Automotive bumpers and dash boards
- Battery casings
- Drug inhalation units
- Disposable razors and syringes
- Washing-up bowls
- Wheelie bins and crates/recycling boxes
- Bottle lids/closures
However, this list is not comprehensive as there are many more products that can be created using injection moulding.
Sources and Further Reading