Plastics & Rubber World - November/December 2019 - 54

case study

efficiency by design
details of how Hexagon
manufacturing software
products supported
development and
production of a new
medical device

Richard Brown, Fenton Precision
Engineering

WWW.PRW.COM | november/december 2019

RBR Active is the manufacturer of Legflow,
a device designed to reduce the possibility of suffering deep vein thrombosis. According to the manufacturer, completing
three simple foot exercises during long
periods of inactivity, such as air travel or
office working, can result in an 11-fold increase in blood flow to the lower limbs.
Tooling to manufacture the device
was produced by Fenton Precision Engineering. Designed in VISI, the mould uses
P20 tool steel machined on a Dugard CNC
unit programmed with WORKNC. Both of
these are software solutions from Hexagon Manufacturing Intelligence's Production Software business.
When Paul Westerman, managing director of RBR Active, first approached
Fenton, it was to produce tooling for an
overmoulded device prototype. "We suggested it would be better to mould it as
a one-piece product," said Richard Brown,
Fenton's technical director. "VISI's reverse-engineering capability was essential to take the point data from our CMM,
combine surfaces and solids, and seamlessly work between the two."
The section at the top of two dome
structures on the product had to be particularly thin to allow flexibility. "But there's
obviously a limit as to how thin we could
make the wall," explained Brown. "We got
the optimum thickness through VISI Flow
Lite, which simulates the filling phase of
the injection moulding process."
Continuing, Brown described the
mould tool as being "straight open and
close," with two cavity plates, support
plates, and back plates. In total, the tooling comprises around 30 different components. "One of the design challenges

was to ensure there were no side actions
or lifters," he added.
The complete tool manufacturing
process took about six weeks; the cores
and cavities were machined through
WORKNC, with each plate taking around
25 hours. A further 20 hours was needed
for the build.
"It was quite a complex format, with a
lot of small solid carbide cutters from a variety of suppliers," Brown noted. "We also
used shrink fit tooling to ensure greater
accuracy, balanced chip loads, better
finishes, and increased speed and feed
rates." The ability of WORKNC to produce
a high-quality surface finish reduced additional polishing to a minimum.
On Fenton's recommendation, SteriTouch antimicrobial masterbatches were
added to protect the product against
bacteria, biofilm, fungi and mould for its
entire lifetime.
In total, the full project was completed
in approximately 11 months.
Fenton designs all their mould tools
in VISI, machining them on one of their
six 3-axis Dugard, Mazak and Mikron
CNC mills. "WORKNC readily reads native VISI files, so it's a seamless transition
from CAD to CAM. Once we save the VISI
work file we simply open it in WORKNC,"
Brown said.
Fenton has moulding facilities in Northamptonshire and Leicestershire, where
the polypropylene RBR Legflow is dual-pad printed on a 120-tonne Yizumi machine. In total, the company has a fleet of
33 moulding machines, comprising such
brands as Yizumi, Negri Bossi, Arburg,
Borche and Demag. Sizes range from 25
to 500 tonnes.

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Plastics & Rubber World - November/December 2019

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