Product category:
Machining centres - all types
News Release from: Mori Seiki UK | Subject: Machining centres and CNC lathes
Edited by the Manufacturingtalk Editorial
Team on 23 July 2002
Titanium orthopaedic implants milled
reliably
The continuous production milling and drilling of forged titanium orthopaedic surgical implants requires a strong, rigid and reliably accurate machining centre to maintain working tolerances.
Titanium implants milled reliably The continuous production milling and drilling of forged titanium orthopaedic surgical implants requires a strong, rigid and reliably accurate machining centre to maintain close working tolerances When Stryker Osteonics Ireland was established in east Cork, the parent US company recommended the use of Pollard Mori Seiki machine tools to maintain the machined finish and accuracies specified
This article was originally published on Manufacturingtalk on 5 Jun 2001 at 8.00am (UK)
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Among the most recent Pollard Mori Seiki machining centres delivered to Styker's Carrigtohill factory are three SV 400 vertical machining centres (VMCs).
Stryker is operating 18 CNC lathes and machining centres of which Mori Seiki machines account for ten.
Stryker is producing the orthopaedic implants mostly for the Japanese market and is currently employing approximately 100 people on the Carrigtohill site.
Further reading
Compact CNC chuckers offer plenty of power
Pollard Mori Seiki's extremely compact CL Series of CNC chucking lathes offer superior rigidity to support continuous high speed machining of production components.
Long-bed machining centre is built for speed
A substantial three-way guideway system, which supports the longitudinal travel of a moving column, provides theSVL5020 long-bed VMC with plenty rigidity for the high speed milling.
High speed machining centre reduces downtime
Capable of machining workpieces up to 2000kg the Pollard Mori Seiki SH8000 horizontal machining centre offers faster traverses and tool-changing times and shorter pallet changeover cycles.
As well as machining, the company also carries out various assembly, coating and finishing techniques.
"Our experience with Mori Seiki's began with four machines supplied by the parent US company," said Mathew Colley.
"We were very impressed with the reliability of the machines and so we bought more through Wallace Machine Tools in Dublin - an agent for Fredk Pollard and Co in Leicester.
I personally have had a wide experience of different makes of machining centres and millers - lathes too - but I am impressed with the quality and repeatability of the Mori Seiki's performance.
They are reliable and accurate." The SV 400 machining centres are used mainly for the machining of ascetabular cups, which fit into the acetablum.
The cup mates with a head piece located on a femoral stem component driven into the femur to form the replacement joint.
Components are machined from near-net-shape titanium forgings.
A cup of the '542' family of 40-80mm OD in 2mm size range steps, can have clusters of five to nine holes drilled and counter-sunk with a circular profile.
Typically a cup with a 58mm outside diameter (OD) features a number of slots and barb profiles which have to be interpolation-milled into the pre-turned cup flange.
Slot depths are milled generally to 0.070-0.080in depth.
In a typical set-up in a Pollard Mori Seiki SV-400, cups are machined in pairs, held in a Nikken NC twin collet chuck trunnion fixture.
The fixture and collet chucks provide the two additional rotational axes for orientating the cups for drilling and counter-sinking.
Sets of chuck jaws are held in stock for each cup size range.
In the second collet chuck, the cup is inverted for location faces to be milled in the turned boss.
Machining time is generally 30min or 15min if no holes are to be machined.
The cups are produced in batches of 12.
Each batch of pre-turned cups is delivered to the SV- 400 with a bar-coded order form.
The operator scans the work order bar code, which is recorded, and the data automatically compared with the predator database.
The software selects the relevant sub-routines, pastes into one program and downloads it to the SV400's MSC 501 CNC.
The MSC 501 then splits up the pasted program according to the operation sheet data.
Predator Software Inc of Columbus, Ohio, US provided the DNC software run at the centralised programming station.
"Stryker chose this system to ensure that the operator can not run the wrong program," said support engineer, Mathew Colley.
"There is such a great variety of cups and individual specifications, that is why we use the Predator system." Machine operators are also responsible for tool setting, tool management, quality control and signing off the work done.
The factory generally works a double 8h-shift, or double 12h shifts as required.
Rough, finish and profile turning is performed in Pollard Mori Seiki DL and SL series CNC lathes.
The internal profile on the 58mm OD cups is machined to a radius of 1.014/1.016in, sweeping out from the boss bore of 0.500/0.505in and stepping out into a conical section which contains two parallel circumferential grooves.
The conical section blends into a machined flange of about 0.25in depth and 0.15in wall.
Overall machining tolerances are +/-0.001in.
After turning but before milling, the forged titanium cups are plasma-arc sprayed with titanium alloy to provide a rough outer face onto which the bone can grow.
The system was brought in-house last year.
The cups used to be plasma-arc sprayed in Switzerland.
Femoral stem forgings are machined in a Pollard Mori Seiki M400 machining centre - the M400 machines and taps a drive hole in the top of the stem and performs two counterboring operations.
The cups and stems were, at one time, machined all over from solid billets, but near-net-shape forging has achieved substantial materials costs savings.
Stryker plans to double the size of its Carrigtohill factory during 2002.
The American company originally came to Ireland approximately 20-25 years ago to set up a European operation in Limerick.
It acquired an increase in market share for orthopaedic implants from Halomedica, which was a much more research-focussed company, and set up a production site, four years ago, at Killbarry, near Cork.
The new site on the IDA Business Park replaces the Killbarry one and concentrates production on stems, arms and knees.
Factory expansion will add on production of hip, and other replacement joint components. Request a free brochure from Mori Seiki UK ...
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