Benchtop injection moulding process using MCP Minimolder enhances artificial eye production, modernising a process that has changed little in 80 years
Part of the Blackpool Wyre and Fylde Community Health Services NHS Trust, the National Artificial Eye Service (NAES) is involved with up to 5000 new patients each year.
Artificial eyes are manufactured at its Blackpool laboratory for patients who are seen at 16 regional centres and 57 satellite clinics around the country.
Some of the manufacturing processes involved in artificial eye production have not changed significantly since 1918 when the NAES was established.
Ocular technicians still apply artists' oil colours to an acrylic disc to achieve the correct colouration of the iris, and a mix of water colour and fine red silk threads are sealed onto the scleral surface of the acrylic eyes to replicate vascularisation.
In order to enhance productivity, technical manager Mervyn Stewart has recently introduced benchtop injection moulding technology to replace labour intensive manual production of two acrylic components.
The MCP Minimolder was originally specified to produce acrylic, single use "iris buttons" which are set into the original wax impression of the eye socket taken at the clinic. Back at the laboratory, these are placed inside surgical plaster moulds to identify the location of the iris and to fabricate a corneal shape before the acrylic is added.
After curing, the stem of the button provides a locator for the painted iris disc, which is eventually covered with an artificial cornea created from clear acrylic in the same mould.
Before the NAES took delivery of the benchtop injection moulder, each iris button was made by hand, one at a time, and took around 30 minutes to cure.
They were then hand finished to remove flash.
Now the same number of buttons made over six months by hand can be injection moulded in just one day! At a cycle time of around 22 seconds, single impressions are made from a multi-cavity tool, manufactured by Sprint Tool and Die of Telford, which carries all 6 button sizes. Surface quality is of a consistently high standard.
Manual production of the individual iris "discs" was even more labour intensive with a 60% reject rate of the very fragile acrylic discs, (0.9mm thick x approximately 11 mm diameter) as they were removed from the mould and hand finished before painting.
These are now also injection moulded using a 10 impression tool, manufactured by Fylde Precision Tools of Poulton-le-Fylde, Lancashire, reducing production time per disc dramatically from "hours to seconds".
To provide patients with a temporary shield against infection, and a cosmetic solution during the 8 weeks or so required to manufacture their own artificial eye, a range of "stock" half spheres is also manufactured by the NAES. Currently produced by hand, production manager Larry Snarr says, these are also parts which could be injection moulded in the future subject to the appropriate bonding technology being developed to incorporate the iris and cornea." The benchtop injection moulder was supplied by MCP Equipment.
One of a range of benchtop machines, each is ideally suited to the production of small precision engineered parts and, because they are all cleanroom compatible, are used widely in the manufacture of medical devices.
Parts from 0.2 grams to 12 grams can be produced in a wide range of engineering thermoplastics, including acrylic, glass filled nylon, ABS, noryl, polycarbonate, acetal, PBT, peek and PPS - plus biodegradable materials.
If required, the machines can deliver sprueless or runnerless mouldings by injecting right up to the cavity with the machines integral hot tip, which significantly reduces material waste and component handling problems.
Screw plasticising with a choice of screw ratios, and plunger injection controlled by linear transducers ensures and maintains high shot accuracy.
Using only compressed air, single phase power and a supply of chilled water, the Minimolders are cost effective and easy to install.
Tool changes take only five minutes and material changes as little as ten, reducing downtime significantly.
A PLC driven touch screen control panel allows quick and easy setting of all moulding parameters.
