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Pentagon Plastics: Design for injection moulding masterclass 2014

Pentagon plastics visits 12th and 19th March 2014

All images are courtesy of Martyna Konopka and Chloe Fong.IMG_5574

Injection moulding is a fascinating technical area. It’s one we hear of constantly in the design world, and for most designers it’s the knee jerk response to the age old “how’s it made?” question when designing anything plastic (often without really thinking about if it really is the best way). But it’s only when you go and see a real injection moulding company, and get to talk to real experts that you find out how much goes into getting parts made this way.


On a hazy but sunny spring morning after a nice cruise through the Sussex countryside we were greeted by Gabby Day (Business Development Co-ordinator) and Paul Edwards (Managing Director) who whisked us up into their small but professional seminar room. Paul then spent a good 50 minutes giving us an overview of the business and a masterclass on his experiences in the injection moulding industry. The company is a proudly UK, family run business with 28 staff based in Horsham who specialise in production injection moulding of thermoplastics as well as the tool making for these moulds. This is a rarity, most companies tend to specialise in one or the other, not both. It has a real benefit for Pentagon, since they understand both sides of the coin, they can find the best ways to do production runs, and they can design tooling (and everything that goes with it) to fit these production needs. They take responsibility for key stages in the moulding process, they have good input into designs (and do some design work themselves), and they need to know their stuff inside out meaning that they need real expertise: and they’ve got it! What’s great about Pentagon is that they’re open minded, they’re happy to work with people to meet their needs, and they’re happy to open their doors and share their knowledge to disseminate best practice and ensure the best possible result for their customers, for themselves, and for the industry overall.


Design assistance

The company do design assistance to ensure that products that leave their factory are based on designs that are suitable for moulding, are well made and meet the overall needs of the client in order to be commercially viable. For instance, if a part has a hole, clip or undercut, then this may require an expensive side action on the tool, where it might be possible to redesign the component to minimise these tooling costs, or to setup the tooling to maximise the effectiveness of each shot. Often Pentagon finds that part materials can be over specified, with impressive materials that include high UV resistance or talc or glass fillers or other properties, which are often experimental or in some cases not necessary for the job and would bump up the cost of the parts considerably. They can also advise on the possibility of tool wear, and the implications that this might have for the costs down the line for the customer. For instance, if the material being used is a particularly hard thermoplastic and lots of parts are required for production, then the tool might be best designed with multiple cavities (e.g. to make 8 or 16 parts for every shot), or the tool might need to be reworked at some point down the line, or the tool might be best designed to have an insert that can be replaced later on once the tool wear gets beyond a certain tolerance. That’s where the experience and knowledge of the team at Pentagon come into their own, they are able to advise in such situations and work with customers to arrive at the best, most cost effective solution for the job.


On the back of such experience, Pentagon have produced their own Design Tips specifically for injection moulded parts, and also a useful Troubleshooting Guide to help understand some of the pitfalls and problems that occur with this process. These complement the guides produced by materials producers like Dupont and BASF, by big technology companies like GE and by other injection moulding companies like Protomold. Pentagon have kindly allowed me to publish them on my blog, and below are links to these:

Tool design

Pentagon typically offer two types of mould tool solutions for injection moulded parts.

Firstly, a basic mould tool which involves a straight pull action, where the tool simply opens and shuts and the part pops out (or is popped out by hand or with pins). These tools have no inserts and tend to be the simplest to setup but require the entire tool to be purchased.

Secondly, there’s the modular insert systems for relatively small parts, often with lots of detail. There are screw in or push in types, and this allows customers the option of buying either the whole tooling setup, or just the modular inserts for individual parts.

Pentagon have 9 impressive machines, with the ability to deliver shots of plastic ranging from 1/2g up to 500g in mass, in thermoplastics with melt ranges from 150degrees C (e.g. PP), up to 390degrees C (e.g. PEEK). The platens of these machines (what the mould tool is mounted to) can deliver loads from 22-280 tonnes of force, which is required to resist the pressure of the molten plastic as it’s inserted (remember that pressure = force/area, so the force required is injection pressure x the external surface area of the part!). These machines are mostly automated, but not always since parts can be removed by an operator when production numbers are low enough, and when there is a special requirement for this (e.g. when there is a side movement required or when a loose insert is to be placed in the tool).


On tour

According to Paul as we walk around the factory, the UK market for tooling and tool design is bouyant, since the lead time is actually better for tooling made in the UK (between 3-5 weeks quicker), when compared with the far east, and since some UK companies have had bad experiences with far east manufacturers, and UK manufacturers like Pentagon are now gaining from the reputation they’ve acquired as experts who’ve fixed problems that have been generated elsewhere. The other caveat that many UK companies have discovered over the years is that often tooling purchased in the far east doesn’t include ownership of the tools themselves, which often comes as a shock when attempting to move the tooling to a new manufacturer. Pentagon on the other hand don’t own the tools they have on the shop floor. There are over 2000 products made by Pentagon, all with tooling to go with them, and as we walked around inspecting the wide range of tools they have stored, it’s clear how much experience is available right there on the shop floor.


We are very grateful to Paul and Gabby and all the other staff at Pentagon who kindly took out so much of their time to share their knowledge, expertise and facilities with us over the period of two days.

Pentagon have also written a post about our visits to their facilities. To read their article, click here.

A gallery of some of the images (courtesy of Martyna Konopka, Sophie Douglas and Chloe Fong) are included below.



3 thoughts on “Pentagon Plastics: Design for injection moulding masterclass 2014

  1. Pingback: Pentagon Plastics: Design for injection moulding masterclass 2014 | Brighton Product Lab

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