By Quy Te
I had never been to a plastics manufacturer before, my first experience has been during a Hillside Product Design visit to Hymid. They are a Torquay based injection moulding company who specialise in technical plastic injection moulding. Greg (Hillside Senior Product Designer) and I were first greeted by Andy Tettmar (Design Director at Hymid) who was took us on a full tour at Hymid’s premises.
During my time as a product design student at Bournemouth University I have been learning about a variety of manufacturing processes including injection moulding; however up until this point I had not witnessed the process first hand. So when I walked into the shop floor I was excited to see the injection theory that I had studied at university, come to life.
I saw the process from start to finish. Beginning with the plastic granules drying, this is necessary as some plastics are hygroscopic and take on moisture. Removing moisture is necessary to prevent against unwanted effects including those that reduce quality of surface finish. Once the granules were in the feeder hopper they fell into the cylinder containing the screw. The granules were made molten from shear forces as the screw rotates and heat from elements around the cylinder. The screw then moves forward to inject plastic, this molten plastic travels down the sprue and gate to fill the tool cavity. Once the part is sufficiently cooled it was pushed out of the tool by ejector pins and a robotic arm removed the components from the tool. At the same time the gates and sprue had separated from the part and fell into a container for collection.
Two-shot injection moulding
I also saw two-shot injection moulding. This allowed for the part to have a secondary material moulded over the first. The first material is usually PC, ABS, PC/ABS, PP with the secondary material normally being a TPE. This was achieved by one cavity of the tool receiving a shot of plastic. The tool then opened and instead of ejecting the moulding from the first cavity the tool rotated 180 degrees and closed again. This allowed for the moulding to receive a secondary shot of TPE. The 2 shot part was now carefully removed from the tool, trimmed, checked for quality and packaged.
I learnt that material selection is key to the two shot process. Expertise is needed to make sure that the two materials achieve a satisfactory bond strength. These materials often need to have other properties such as being food-grade, anti-static, readily available and in specific colours.
Advantages of two shot moulding
• Improved process and part consistency
• Improved bonding between materials
• Faster processing time
• Reducing number of mould tools necessary
• Well suited to adding dustproof, waterproof, shockproof functionality to a part
Broader Perspective – product design
I was made aware of spark erosion and wire EDM which was completely new to me. I learnt how these processes were integral to tool-making. I also learnt to appreciate the attention to detail required for designing parts for injection moulding and how knowledge of the processes involved influence part design. Furthermore I saw how organisation and controlled conditions lead to efficiency and high standards. Walking through the manufacturing floor was amazing and has given me more perspective when considering product design.
I enjoyed my visit at Hymid and feel that it has been an invaluable experience to see how technical mouldings are manufactured. Thank you Hymid for having us.
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