Introduction to Injection Moulding

Introduction to Injection Moulding

Injection moulding enables complex shapes to be mass-produced with a high level of efficiency and manageable costs. A wide selection of materials allows engineers to exactly match the physical properties they require for any given product. Additionally, the application of multi-shot moulding techniques allows one to secure an appealing visual appearance, as well as incorporating additional functionality to the final product using materials that give high mechanical properties. Yet, the actual process can be quite multifarious, especially when it comes to achieving uniformity.

Injection Moulding Process

Plastic injection moulding allows to produce large numbers of parts with great accuracy and very quick cycle times from multi-cavity tools. The general process of injection moulding involves a certain amount of polymer materials being heated, melted, and injected into a mould under high pressure. Further into the process, main units of the injection moulding machine are: a) feed hopper; b) heated barrel; c) crew (known as the injection unit); d) clamp unit (which holds the mould together under the injection pressures); e) ejection unit (which removes the part from the mould).

The moulding process could be described by the following steps:

  • 1Thermoplastic granules are prepared according to the manufacturer’s guidelines. In some cases, this may mean that the material is dried in a desiccant dryer to remove moisture — if the moisture isn’t removed it could affect mechanical properties of the component. Once prepared, the material is poured into the hopper of the machine;
  • 2The material enters the throat of the barrel via the hopper. The plastic granules are collected by the helix of the rotating screw — the feeding zone of the screw;
  • 3The barrel is heated along its length using heater bands. There are a number of zones depending on the machine size. The zones have different temperatures along the length of the barrel. The temperatures are set in conjunction with the material supplier’s specification sheet;
  • 4The screw rotates, which moves the material forward with the pressure and determined rotational speed towards the compression zone. This zone of the screw is designed to put a shear heat into the plastic and to push the material against the barrel wall, giving it a consistent melt. As the material is pushed through, it enters the metering zone of the screw and fills the front of the barrel;
  • 5Once the material is injected via the nozzle at the end of the barrel, it enters the runner system of the mould tool;
  • 6The runner system allows the material to flow through a gate into the cavity of the mould tool, which forms the shape of the finished product;
  • 7The mould tool is held at a constant temperature, which, again, is defined by the material’s specification sheet. Keeping the tool at a constant temperature allows heat to be drawn from the plastic until it reaches its heat deflection temperature (HDT). The HDT is also defined via the material’s specification sheet;
  • 8Once the parts have reached the HDT, they will remain in a solid state. The mould tool can be opened;
  • 9Once ejected, the components fall into a boss. Parts also could be collected from the mould via a robot or a conveyor belt;
  • 10The tool closes and the whole process repeats.

“Injection Moulding is highly repeatable; this means that all the parts that are produced will be identical, which is especially convenient for brand consistency and part reliability in high volume production”

Advantages and Disadvantages of Injection Moulding

Injection moulding with extrusion capabilities ranks as one of the chief processes for manufacturing plastic articles. It yields low scrap rates unlike the traditional manufacturing processes such as CNC machining. Injection Moulding is highly repeatable; this means that all the parts that are produced will be identical, which is especially convenient for brand consistency and part reliability in high volume production.

Advantages of Injection Moulding:

  • 1Repeatable production;
  • 2Low serial production costs;
  • 3Design flexibility;
  • 4Multi-material accessibility;
  • 5No post-production scrap;
  • 6Colour control;
  • 7Enhanced product uniformity;
  • 8Reduced requirements for finishing;
  • 9Multi-dimensional control.

Disadvantages of Injection Moulding:

  • 1Relatively high initial tooling and machinery cost;
  • 2Occasional part design restrictions.

Industries where Injection Moulding is Used

Injection moulding is a highly effective tool that could be applied to any field one could possibly imagine. Precise and flawless results are highly appealing to many manufacturers in industries such as medicine, optics, cosmetics, electronics, etc. We’ve outlined the top four industries where injection moulding receives the biggest attention.

Medical Devices

Injection moulding has a set of finest practices that can help medical manufacturers and innovators design any device with unparalleled accuracy, strength and durability. Regulatory requirement and high-quality standards, such as ISO 13485, 14001, OHSAS 18001, that are necessary for the medical injection moulding; that is why not every manufacturer is able to compete in such intricate production.

Optics

Injection moulding provides the finest value to optical manufacturing. The most obvious advantage is automated series production for manageable costs. Optics manufacturing doesn’t tolerate any irregularity, which, de-facto, could be secured during the development phase: photometric simulations, feasibility studies and risk analysis are needed to optimize the lens.

Cosmetics

Plastic moulding guarantees standards of precision, which stands as a primary requirement for packaging in the cosmetic industry. To ensure that the beauty product stays securely sealed under specific conditions, many companies opt for injection moulding manufacturers to produce safe and secure packaging for cosmetic products.

Automotive Components

Safety is a key in the automobile industry. Plastic injection moulding must be carefully considered and researched prior to being used in the production of automotive components. Fortunately, 3D printing and rapid prototyping materials are able to replicate the qualities of production resins more easily than ever.

Consumer Electronics

Size and power are the two key drivers of consumer electronic features. As consumers grow more used to the all-in-one, integrated, connected devices in every area of their lives, plastic moulding must keep up. The ability to quickly and cost-effectively design, iterate, test and eventually manufacture, means that innovation occurs quicker and way more efficiently.

Plastic Parts Injection Moulding Polymermedics

Types of Injection Moulding

There are various types of injection moulding that are based on the specifics of any given product. Some prototypes require a water-free environment, while others need highly stable and timeproof materials. And, the versatility is yet another advantage of injection moulding.

Thin Wall Moulding

Thin wall moulding is an injection moulding technology that achieves a thin and light plastic part. Due to the size of the part, wall thickness could be significantly limited.  Wall thickness less than 0.025 inch could be considered as a “thin wall”. Compared with thicker walled plastic parts, thin wall moulding allows even faster cycle times. Often used in food packaging (e.g. margarine tubs, yoghurt pots), automotive industry (e.g. structural and non-structural parts), electronics (e.g. mobile phone and computer housings) etc.

Multi-material Injection Moulding (MMM)

When two or more different materials are moulded into a single plastic part at one time, the process is considered a MMM. MMM has a number of advantages over other production techniques, for example: a) creating parts with different regional polymer hardness by incorporating an elastic modulus that varies depending on the location on the part; b) it is possible to create a single-structure part with different regional polymer materials such as rubber and plastic; c) single part creations with varying polymer colours. The potential for applying these techniques range widely from relatively simple household items like toothbrushes to more complex constructions such as power tools.

Gas-assisted Injection Moulding

Gas-assisted injection moulding is a process where gas is introduced into the mould after the injection of the polymer. It is predominately used when the part has a uniform wall thickness, to eliminate sink marks and to get a smooth and finished appearance the of a part. It also enables high gloss levels and cosmetic finishes to be achieved using lower clamp pressures, and hence reducing costs, wear and tear of the injection moulding machine.

Metal Injection Moulding

Metal can also be injection moulded. The technology combines powdered metal with a binder material that are then used to create the so-called feedstock which is then applied to later manufacturing processes. Metal moulding is substantially more expensive than plastic injection moulding and usually serves a niche market for major industries as machinery and dentistry.

Liquid Injection Moulding (LIM)

LIM is a method that is used for processing Liquid Silicone Rubber. Suits for high volume disposable manufacturing even of the small parts with a complex geometry. The material also fits perfectly for two-shot moulding. Exceptional clarity allows to pigment the material in-line with a material flow to produce colours.  LIM is highly suitable for the production of durable parts. But even thought LIM has a lot of advantages, they are all followed by higher start-up/ shutdown costs.

“Injection moulding is considered to be the most versatile of the various moulding processes available”

Summation

Injection moulding is considered to be the most versatile of the various moulding processes available, due to its sheer variety of producible parts. Injection moulding also allows for a high level of customization to create unique parts to meet highly complex needs. Plastic injection moulding is an unfailing solution for manufacturing large numbers of precise and consistent components. It’s also more efficient and cost-effective than other moulding styles. As a result, injection moulding is most often used for the manufacture of high-quality parts in high volumes. To learn more about the services that we feature, please check our services page.

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