Our guide to Thermoplastic Injection Moulding
Are you considering using plastic injection moulding for your medical device or just interested in what thermoplastic injection moulding is? This guide will explain the basics of thermoplastic injection moulding, its uses in industry, how it works, types of plastics to consider, the advantages and limitations of the injection moulding process.
What is Thermoplastic Injection Moulding?
Thermoplastic injection moulding is a manufacturing process in which melted polymer is injected under high pressures into pre-made moulds. It is used to produce a wide range of solid plastic parts and products. The industry has evolved quickly from initially producing small and simple plastic parts like buttons to manufacturing today’s intricate medical equipment.
What Industries Use Thermoplastic Injection Moulding?
Injection moulded parts can be found across many industries. For example, within the automotive industry, injection moulded components can be found in instrument panel components, shifter knobs and door handle components. Injection moulded components can also be found throughout much of our daily lives. Remote controls, computers, televisions, earphones, sensors, cell phone components and medical equipment all contain injection moulded parts.
How Does the Thermoplastic Injection Moulding Process Work?
The injection moulding process can be broken down into 5 simple steps:
- The raw material, usually plastic beads or fragments, enter a heating barrel
- The barrel heats the polymer to its melting point
- A rotating screw pushes the melted polymer into the mould to fill all cavities
- Polymer remains under pressure until cooled to a solid state
- Hardened material is removed from the mould, typically by ejector pins
Image courtesy of Technology Student
What Type of Plastic is Typically Used?
A variety of polymers can be used for plastic injection moulding but there are a few important considerations when selecting your plastic for the injection moulding process. These are:
- ● Aesthetic: The desired colour, texture and/or transparency of the finished product
- ● Physical: The desired strength, flexibility or rigidity required of the finished product
- ● Durability: The desired resistance to corrosive materials or extreme temperatures of the finished product.
- ● Service life: The desired length of time the component is expected to last given standard usage
- ● Industry: Regulations the component will be subject to e.g. FDA, ISO
Some of the materials commonly used for injection moulding are:
- ● HDPE (High Density Polyethylene)
- ● PP (Polypropylene)
- ● HDPE (High Density Polyethylene)
- ● MDPE (Medium Density Polyethylene)
- ● LDPE (Low Density Polyethylene)
- ● LLDPE (Linear Low Density Polyethylene)
- ● PC (Polycarbonate)
- ● ABS (Acrylonitrile Butadiene Styrene)
- ● TPV (Thermoplastic Vulcanizate)
Advantages of Thermoplastic Injection Moulding
Thermoplastic injection moulding creates consistent, high quality units and there are several other reasons why the process is chosen by many manufacturers around the world for manufacturing complex components and parts.
Scalability
Thermoplastic injection moulding is one of the best ways to adapt your process and scale up production. Injection moulding is one of the fastest manufacturing processes with a typical cycle taking less than a minute. With each cycle capable of producing multiple parts combined with the low cycle time, the output can be significant.
Low waste
Thermoplastic is more efficient than other manufacturing processes such as CNC machining. Unlike CNC machining, which cuts away plastic from a large block or sheet, plastic injection molding produces very little waste material. On average out of 100g of original plastic material, only 20g becomes waste, and this waste can be ground up and reused. In the Aerospace and Medical industries however, regrind material is not typically allowed, but this excess material can be sold to other manufacturers, further reducing costs of excess wasted materials.
Consistent Quality
Thermoplastic injection moulding is the ideal process in terms of consistent manufacturing as it is a highly repeatable process. Injection Moulding machines can produce thousands of components in just one day and they will be virtually identical to the others in the manufacturing run. Provided your mould design, material selection and product design is properly set up from the outset, the process capability for thermoplastic injection moulded parts can be excellent. If consistency is key to your project, injection moulding is an ideal solution for you.
Complex parts
Plastic injection moulded components can be intricately designed and executed with pin-point accuracy. This level of detail can cut down on the number of parts needed for an object, reducing overall production time. Additional features of injection moulding such as unscrewing fixtures or core pulls can eliminate secondary manufacturing operations.
Long Term Savings
When the process is running, it is very cost effective. The two main reasons for this is the recyclable material and level of automation:
- Automation: The injection moulding process involves a high degree of automation, which can provide significant savings in production costs. A single operator set up the machinery, reducing labour costs and overhead. Over time the high production rate will pay for tooling cost.
- Recyclable Material: Leftover plastic from the injection moulding process is called “re-grind” as it can be ground up and re-used. In the case of Medical and Aerospace manufacturers, the regrind can be sold to manufacturers with low cosmetic requirements, making the overall process even more affordable.
Limitations of Thermoplastic Injection Moulding
Starting your thermoplastic injection moulding process can be costly, especially as the moulds have to be precisely machined. Here’s a few of the limitations of thermoplastic Injection Moulding:
Speed
The speed of the process is an advantage when producing large quantities of components; however, for prototyping thermoplastic injection moulding will take much longer than other types of manufacturing. For example, additive manufacturing such as 3D printing could produce a prototype in hours, but an injection moulding process will be much longer due to the time needed for tooling.
Long Lead Times
An injection moulding tool is usually made of a metallic alloy that has to be precisely machined. A multi cavity tool for example will have to go through designing, prototyping, building and testing phases that can take a long time. A typical build can take between 4-20 weeks, depending on the complexity of the component. However, once these phases are complete a plastic injection mould can produce millions of components in its lifetime. The initial upfront costs and loss of time will be outweighed in the long run. If you are considering using thermoplastic injection moulding for your component, it is important to give the tool maker time for manufacturing.
Upfront Cost
One of the biggest limitations to the thermoplastic injection moulding process is the cost. Tooling and the time needed for mould creation can be expensive, something that developers should keep in mind when designing new components. The two main steps where expensive costs can be avoided is in the designing and prototyping phase.
- Designing: Make small changes to lower the tooling costs in the design phase. Changing a design on computer software such as CAD is much easier and cost effective than altering a physical object.
- Prototyping: Best practice is to create a prototype of your mould. Creating a 3D printed prototype could save you the full tooling cost on a mould that doesn’t work. Putting your part through a DFM (design for manufacturing) process with a tolling expert is recommended. These experts will be able to identify any issues with your design that will lead to cosmetic and filling issues.
Is thermoplastic injection moulding right for your manufacturing process?
In short, if you are looking to switch to thermoplastic injection moulding for your components or parts you are going to need some expert guidance. Thermoplastic injection moulding reliably produces components efficiently and economically. There are also a range of materials and multiple design options to choose from. The benefits of cost, durability and scalability outweigh the limitations of thermoplastic injection moulding. As with any manufacturing process, mistakes can happen, and with thermoplastic injection moulding these mistakes can be costly. That’s why it’s important to go with a trustworthy, experienced company for your production needs.
Advant Medical’s Thermoplastic Injection Moulding Expertise
Advant Medical is a specialist provider of Precision Injection Moulding Services to the Medical Device Industry. Our injection moulding team is ready to respond to your complex moulding challenge. We provide dedicated client support which will navigate you through all stages of your injection moulding project including initial design, validation, production and supply chain management. Advant Medical’s injection moulding operates from our state-of-the-art Class 8 Cleanrooms. Our specialist moulding team and advanced technologies ensure we can support a turnkey solution in product design, packaging and assembly of your Class I, II, III medical device. Our flexible and service-oriented approach has contributed to Advant Medical being a multiple ‘Supplier of the Year’ award winner. Talk to an injection moulding expert today.
