Frequently Asked Questions

Rubber and other flexible parts... Should I Injection mould or Compression mould?

Flexible components are present in most assemblies. Whether you want a simple gasket, a seal, a more intricate connector, or a bellows, the common denominator is that the part is required to flex in its operation or assembly.

Compression Moulded PartMaterial options

Materials that can flex are frequently referred to generically as rubbers. However, there are two basic categories simply differentiated by their processing technique, thermoplastic and thermoset.

Thermoplastic elastomers (TPE’s) are copolymers that are a blend of rubber and plastic, processed by injection moulding or extrusion. Within TPE’s there are six sub sets, which is where names like TPU and TPV come from.

Rubbers are thermosets, processed by compression moulding.

Silicones may be single or two part and processed by compression moulding or injection moulding (LSR).

The decision on whether to injection mould using TPE or to compression mould using rubber is usually a function of quantity and service environment.

Quantity is important

Quantity is important as the cycle times of the two processes are wildly different. Rubber (whether synthetic or natural) is a thermoset and as such must cross link during processing  - which is referred to as vulcanisation. Depending on a variety of parameters, vulcanisation can take from minutes to hours.

In contrast TPE’s are processed on conventional injection moulding machines with cycle times similar to moulding conventional thermoplastics.

Flexible PartsTooling is a requirement

Tooling is a requirement to process either option. A large range of rubbers including silicone, nitrile, neoprene, EPDM and Viton can be moulded in compression tooling. This is relatively simple compared to injection mould tooling and multiple cavities can be used to offset longer cycle times.

In contrast TPE’s require tooling designed and manufactured to injection moulding standards. Material is processed and injected in the same way as ABS or PC would be for rigid parts. It is more sophisticated than compression mould tooling and as a result more expensive.

Thus for a low call off of say 100 parts per year, the lower tool cost and greater cycle time of compression moulding is unlikely to be an issue. As the quantities rise, the number of cavities in a tool can be increased, so a ten, twenty or more cavity tool is possible (geometry permitting).

However, ultimately the additional expense of injection mould tooling and faster cycle time will pay off, and needs to be considered. (material properties being equal)

Environment and exposure

Service environment is also important and both maximum and minimum operating temperatures as well as exposure to solvents need to be taken into consideration. Some rubbers can be better at retaining there elastomeric properties, particularly in high temperature environments and silicones excel in situations where the material must be highly inert.

Compression Moulded flexible partSustainability

If you need your component to be recyclable, then thermoplastics are your only option. Rubbers being a thermoset means components are destined for landfill at the end of their life.

Prototyping flexible parts 

Prototyping flexible parts can be a challenge. Whilst it is possible to 3D print materials that demonstrate a level of elongation in a variety of harnesses’, their properties fall well short of production intent materials.* Vacuum Casting can offer a better solution, although more costly, again in a range of harnesses’.

However neither of these options will truly emulate a production TPE or rubber, especially in areas such as elongation, temperature resistance or stiction. Thus if the goal is to create anything more than a visual prototype there is little option but to manufacture a bridge tool and prototype in the production intent material.

Plunkett Associates can support both your prototyping requirements and production requirements, in either class of materials. Drawing on strengths in both tooling and moulding, we will ensure you get to market on time. 

*(Note flexibility can be achieved through additive techniques but tear strength, chemical resistance and elongation to break will be significantly reduced.)

  • “Plunkett Associates have excellent breadth of experience, work with high quality partners and have a flexibility that we have found enables challenges to be met successfully, cost effectively and in a timely manner.”
    Nick Skaer, CEO, Orthox Ltd
  • Plunkett associates always find a solution. Whatever we need to prototype, they have a great grasp on the technologies available, costs and lead-times so we get the right solution tailored to the project needs. Have always delivered and never let us down.
    Naim Audio
  • “I can’t recommend Tim and his team highly enough. We ended up with a design which can be produced and assembled quickly, efficiently and reliably, in volumes that make sense”
    Simon Leggett, Director, Olivewood Technology
  • "Tim's experience, expertise and supplier base have been fundamental to us getting this project off the ground."
    Sam Pearce, Jelly Products Ltd
  • “We were really surprised at how quickly they turned round such a high quality prototype and the parts certainly proved their worth. They were of high enough quality to provide a fantastic visual representation and to undergo rigorous testing."
    Stuart Wilson, Design Director, TRT Lighting
  • “Accuracy, finish and delivery all first class.”
    Andrew Peters, JMDA Ltd
  • “We use Plunkett Associates because we want someone we can trust, that knows what they’re talking about, has all the contacts, will provide reliable advice and feedback and will get the right result for us.”
    Jim Copestick. Design Manager, Thorlux Lighting
  • “We always know exactly what we’re getting and we know we won’t be let down on quality, price or lead times.”
    Mark Williams, Research and Development Director, Johnson Safety Products
  • “Plunkett Associates truly offer a complete turnkey solution with Speed, Effectiveness and Precision.”
    David Harden, Director, Enica Ltd
  • “Kirintec were thrilled with Plunketts. They made a complex process simple and we were just amazed at the lead times achieved. Plus, every single deadline was met without any drama.”
    Penny While, Marketing Director, Kirintec
  • “Thanks to Plunkett Associates flexible, bespoke and cost effective service I was able to produce the objects that I had originally had in mind.”
    Simon Ryder, Artist
  • To create such a consistent quality finish in chrome was an amazing achievement and the prototypes really gave our stand the wow factor.
    James Clark, Group Commercial Director, The Airdri Group
  • Interestingly, people who look at it in its own right with little knowledge of what it does, just like it! It’s tactile and it looks good…
    Tim Collings, Operations Director, Troika Systems Ltd
  • "With their simple to understand language, willingness to go the extra mile and approachability, Plunkett Associates were a great partner for our company. We couldn’t be happier with the results of our project. (A working prototype that they got right first time, by the way). Thank you!"
    Carolina Ballon-Forrester, Director, Kittyrama Ltd
  • Plunkett Associates worked on the design and production of titanium frames for an artificial heart valve where precision and consistency was paramount. Communications were efficient and productive with concepts readily incorporated into the final design, and suggestions for improvements all highly appropriate. The quality of the end product was ideal and I have no doubt that I will use the advice and expertise of Plunkett Associates again.
    David Wheatley, Wheatley Research Ltd
  • “Thanks for the present that arrived this morning, as promised. Parts look first class, as always.”
    Jon Todd, Design Manager, PHS Group
  • “Plunkett Associates have a fantastic supply chain, work with all sorts of production processes and will always do their utmost to solve a problem.”
    Naim Audio
  • “ Plunketts developed a solution that met our precision requirements at a cost significantly lower than alternative manufacturing approaches we had investigated”
    Nick Skaer, CEO, Orthox Ltd
  • “Doing business with you has been an absolute pleasure. You have made my goals a reality. You have been patient, helpful and above all, responsive. Best service that I have experienced in ages. I consider Plunkett Associates to be an integral part of my business plan moving forward.”
    Jet Cooper, Sculptor
Related Processes

Injection Moulding

Produces production intent material properties. Injection Moulding is used for development as well as production parts.

more info

Compression Moulding

Compression Moulding is a great process that is commonly used for thermoset materials, such as silicone and a variety of rubbers.

more info

Vacuum Casting

Ideal for producing small quantities of plastic and flexible rubber parts, especially if aesthetics are important.

more info

3D Printing

Fused Deposition Modelling (FDM), Polyjet, Digital Light Process (DLP); all are quick and provide a degree of accuracy that satisfies most design requirements. But which is the best option?

more info

Read more expert articles in our FAQ section where we discuss topics on materials, methods and products.

Back to FAQs
  • “Plunkett Associates have excellent breadth of experience, work with high quality partners and have a flexibility that we have found enables challenges to be met successfully, cost effectively and in a timely manner.”
    Nick Skaer, CEO, Orthox Ltd
    Nick Skaer, CEO, Orthox Ltd
  • Plunkett associates always find a solution. Whatever we need to prototype, they have a great grasp on the technologies available, costs and lead-times so we get the right solution tailored to the project needs. Have always delivered and never let us down.
    Naim Audio
    Naim Audio
  • “I can’t recommend Tim and his team highly enough. We ended up with a design which can be produced and assembled quickly, efficiently and reliably, in volumes that make sense”
    Simon Leggett, Director, Olivewood Technology
    Simon Leggett, Director,  Olivewood Technology
  • "Tim's experience, expertise and supplier base have been fundamental to us getting this project off the ground."
    Sam Pearce, Jelly Products Ltd
    Sam Pearce, Jelly Products Ltd
  • “We were really surprised at how quickly they turned round such a high quality prototype and the parts certainly proved their worth. They were of high enough quality to provide a fantastic visual representation and to undergo rigorous testing."
    Stuart Wilson, Design Director, TRT Lighting
    Stuart Wilson, Design Director, TRT Lighting
  • “Accuracy, finish and delivery all first class.”
    Andrew Peters, JMDA Ltd
    Andrew Peters, JMDA Ltd
  • “We use Plunkett Associates because we want someone we can trust, that knows what they’re talking about, has all the contacts, will provide reliable advice and feedback and will get the right result for us.”
    Jim Copestick. Design Manager, Thorlux Lighting
    Jim Copestick. Design Manager, Thorlux Lighting
  • “We always know exactly what we’re getting and we know we won’t be let down on quality, price or lead times.”
    Mark Williams, Research and Development Director, Johnson Safety Products
    Mark Williams, Research and Development Director, Johnson Safety Products
  • “Plunkett Associates truly offer a complete turnkey solution with Speed, Effectiveness and Precision.”
    David Harden, Director, Enica Ltd
    David Harden, Director, Enica Ltd
  • “Kirintec were thrilled with Plunketts. They made a complex process simple and we were just amazed at the lead times achieved. Plus, every single deadline was met without any drama.”
    Penny While, Marketing Director, Kirintec
    Penny While, Marketing Director, Kirintec
  • “Thanks to Plunkett Associates flexible, bespoke and cost effective service I was able to produce the objects that I had originally had in mind.”
    Simon Ryder, Artist
    Simon Ryder, Artist
  • To create such a consistent quality finish in chrome was an amazing achievement and the prototypes really gave our stand the wow factor.
    James Clark, Group Commercial Director, The Airdri Group
    James Clark, Group Commercial Director, The Airdri Group
  • Interestingly, people who look at it in its own right with little knowledge of what it does, just like it! It’s tactile and it looks good…
    Tim Collings, Operations Director, Troika Systems Ltd
    Tim Collings, Operations Director, Troika Systems Ltd
  • "With their simple to understand language, willingness to go the extra mile and approachability, Plunkett Associates were a great partner for our company. We couldn’t be happier with the results of our project. (A working prototype that they got right first time, by the way). Thank you!"
    Carolina Ballon-Forrester, Director, Kittyrama Ltd
    Carolina Ballon-Forrester, Director, Kittyrama Ltd
  • Plunkett Associates worked on the design and production of titanium frames for an artificial heart valve where precision and consistency was paramount. Communications were efficient and productive with concepts readily incorporated into the final design, and suggestions for improvements all highly appropriate. The quality of the end product was ideal and I have no doubt that I will use the advice and expertise of Plunkett Associates again.
    David Wheatley, Wheatley Research Ltd
    David Wheatley, Wheatley Research Ltd
  • “Thanks for the present that arrived this morning, as promised. Parts look first class, as always.”
    Jon Todd, Design Manager, PHS Group
    Jon Todd, Design Manager, PHS Group
  • “Plunkett Associates have a fantastic supply chain, work with all sorts of production processes and will always do their utmost to solve a problem.”
    Naim Audio
    Naim Audio
  • “ Plunketts developed a solution that met our precision requirements at a cost significantly lower than alternative manufacturing approaches we had investigated”
    Nick Skaer, CEO, Orthox Ltd
    Nick Skaer, CEO, Orthox Ltd
  • “Doing business with you has been an absolute pleasure. You have made my goals a reality. You have been patient, helpful and above all, responsive. Best service that I have experienced in ages. I consider Plunkett Associates to be an integral part of my business plan moving forward.”
    Jet Cooper, Sculptor
    Jet Cooper, Sculptor