Costs slashed by plastics ingenuity

Tom Shelley reports on a moulder that has moved into leading edge R&D with a focus on biochemical and medical developments



A plastics moulder in Herefordshire has transformed its business by focusing on developing ingenious designs that slash manufacturing costs in critical applications.
AK Industries began life as an established moulding business but since a management buy-out in 1996 has realised that competing on cost grounds is unworkable. Instead, it focuses on developments in conjunction with high technology research partners. In some cases, components for the medical and instrument markets can be made for a fraction of their original cost.
A typical development programme is the Tepnel allergen testing kit, which detects a variety of trace substances. The original kit consisted of five parts, including a sampler that was dipped into the liquid under investigation, then re-inserted to contact a test strip. Colour changes were viewed through a port in the side.
The new design is made out of polypropylene and consists of a single moulding with a living hinge. This allows the two parts to be folded over and clicked together to trap the test strip, whose colour change is still viewed through a port in the side. Dipping the end of the device into the liquid of interest draws up a small amount by capillary action to make contact with the test strip. An important part of the product development is that the testing kit is now supplied in a range of colours, according to which test is incorporated – so there is little chance of users picking up the wrong one.
“Such products do not necessarily demand the use of high strength engineering materials,” joint managing director Allen Green told Eureka. “As well as being inexpensive, polypropylene is also an excellent material for making living hinges.”
Manufacturing advances are key to cost cutting in some of the re-designs – such as the Malvern Instruments Zetasizer Nano ZS, which uses a laser system and transparent measurement cells to measure particles in the size range 0.6nm to 6 microns. In order to eliminate cross-contamination, the measurement cells should be low enough in cost to be disposable. Each polycarbonate cell incorporates a channel through which liquid is pumped; at the same time, two sprung gold plated electrodes must stand out clear of the sides, so that the measuring instrument can detect that a measurement cell has been correctly inserted.
The design previously used two mouldings that were subsequently put into another tool and over-moulded. The process was expensive led to lots of rejects, according to Green. The solution was to make two mouldings that are now ultrasonically welded together with laser cut steel mould tool carriers, into which the electrodes are slid so that only the protruding parts get moulded into the sides of the cells.
Fitting must be exact, so there are no gaps through which plastic can penetrate. The moulding tools have to be polished so that a laser beam can pass through the sides of the cell at the base of the ‘U’ shaped channel. Malvern is now developing a new machine that will require even smaller test cells.

All done by magnets
Even more ingenious is the design and technology used to mould vials used by Molecular Dimensions for its protein crystallisation X-Ray diffraction machines. The vials, made from polypropylene, protect protein growth during transportation. The vials must be automatically placed for testing, identified, then returned to a holding unit. This requires the use of a pole-oriented, ferromagnetic ring, which is insert-moulded by AKI in order to retain a cap from which the sample is suspended and is also used to retain the vial in its basket. Also, a zinc-plated, ferromagnetic disk at the bottom of each vial enables positive manipulation with a magnet. The vials must be compatible with liquid nitrogen temperatures, and cheap enough for the customer to sell at £62.50 for 50 items. A particular challenge was set by the fact that the magnetic rings have to be the right way round.
“The tool has two nickel-plated, iron-neodymium-boron sintered magnets,” said Green. “The first is located on the moving half of the tool and is at the base of the core that creates the vial form. This magnet is polarised such that it will attract the magnet that is inserted and moulded into the product.”
If the magnet to be insert-moulded is positioned with the wrong polarity, it will be repelled by the magnet in the tool. The second magnet is located inside the tool cavity on the fixed half. The purpose of this magnet is to retain the ballast weight that is insert moulded into the base of the vial.
For Green, this approach typifies the companies refocused approach.
“In the past, we did all the items above production for nothing,” he said. “Now we are trying to move into design and development as a business.”

Pointers

* AK Industries is moving from supplying moulding advice – in the hope of gaining moulding work – to researching and developing manufacturing techniques for making novel plastic products

* Magnetic inserts are held in mould tools by magnets to ensure correct orientation of products

* The company is also working on research projects involving nano-clays, finely adjustable vacuum valves, smart pharmaceutical packaging and single piece pumps

Author
Tom Shelley

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