Product category:
EDM wire cutting
News Release from: Charmilles Technologies Corporation | Subject: Robofil 330F Wire EDM
Edited by the Manufacturingtalk Editorial
Team on 22 November 2002
Single-set up wire EDM replaces CNC
machining ops
Using a CNC wire EDM unit has replaced more conventional multiple set-up CNC turning and milling to produce hydraulic damping system stator's and rotors.
Horstman Defence Systems has realised significant production costs savings since employing Charmilles' Robofil 330F Wire EDM in a production environment The state-of-the-art wire EDM technology has replaced more conventional CNC turning and milling to produce hydraulic damping system stator's and rotors
This article was originally published on Manufacturingtalk on 22 Mar 2001 at 8.00am (UK)
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"We used to produce six different units of rotor and stator components, in small batches, by machining forgings in a number of set-ups in machining centres and turning centres," explained Horstman Defence Systems' Production Director, Peter Binns.
"Now we cut the components from billets in a Charmilles Robofil 330F wire EDM centre." In terms of actual machining times, the total cutting time for each rotor or stator component in the Robofil 330F is approximately equal to the cutting time in the four or five set-ups in machining centres and CNC lathes.
The savings accrue from the elimination of forgings and the virtual destruction of work-in-progress stocks and associated progress-chasing.
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"The EN 24 forgings were specified, not because we sought the extra structural strength, but so we could work from near-net shape stock to reduce machining content," said Peter Binns.
"We have now eliminated the costs associated with forging tool manufacture, forging costs and associated logistics." Horstman Defence Systems located in Bath, produces hydraulic suspensions, gas and pneumatic systems for a wide range of military and civil vehicles, including tracked ones.
Having long established itself as a World-wide O Centre of Excellence' in these industries, the company became a member of the Smiths Industries Group four months ago.
The rotor and stator components belong to a six different designs and sizes of a hydraulic suspension damping system.
They were traditionally produced from forgings, rough-milled, stress-relieved, finish-milled and profile-ground.
Batch sizes are 20-50 off.
"Our production here is predominantly CNC turning, milling and grinding," said Peter Binns.
"Our problem was, that we needed to reduce costs, and we were looking at reducing stocks and production inventories.
It so happened that one of the EDM suppliers had seen the rotors and stator's and said OHey - we can do this'."Intrigued, and with six new damping systems under development, Horstman Defence made arrangements for wire EDM trials to be carried out at Di-Spark in Horndean, Hants.
"We saw the process in action and gained a lot of support from Di-Spark." said Horstman Defence's Chief Production Engineer, Bob Copp.
He continued: "We were amazed at the accuracy and finish.
In general werequired an overall working tolerance of 10 microns and a surface finish of 4 micons Ra (16 microin).
These specifications are being achieved in our normal production by wire EDM and with very little effort.
We can load the Charmilles machine and let it run unmanned during the night, with the knowledge that the machine is being fully monitored.
If the cycle time is 6hours, we will know it will take 6hours." To put the job into clear perspective, Bob Copp described how a stator was produced before.
The largest stator is 300mm diameter and 100mm deep, with say a 14mm wall thickness.
The smallest is about 150mm diameter.
They are produced in five operations, namely: rough mill, stress relieve, finish mill, shape slots (in a gear shaper) and finish profile grind.
Total set-up time involved on the four machine tools was about 14hours.
Similar operations were carried out on the rotor, with the exception of the slotting.
To produce a rotor in the Robofil 330F - in one set-up - a turned, stress-relieved and ground billet is used.
Wire-feed holes are drilled in the billet and then it is mounted and clamped on tooling rails in the Charmilles machin'1s work area.
In the wire EDM operation, the wire feed nozzle first touches the end of the wire onto a setting bar, then the bar is removed, and the automatic cycle is initiated.
Wire feed is automatic.
The wire-feed nozzles are located within 0.010mm of the billet top and bottom surfaces.
Actual cutting time to produce the stator is about 7.75h.
"We are replacing five operations with just one," enthused Bob Copp.
He added: "The actual stator size produced is very accurate.
We have been running the Charmilles day and night, week-in, week-out.
The machining time is on par with milling, but we have no down-times and no tool wear to worry about.
If a wire break does occur, the machine automatically repositions, re-threads the wire and starts again." When asked about factory services, Bob Copp said that trouble-free production with wire EDM does depend on good water and air supply.
The water is heavily filtered and the machine has a large water reservoir built into the base.
Also, wire nozzles are replaced according to an established nozzle wear life.
Horstman Defence's Senior Chargehand, Steve Carpenter, said that the machine is using 0.010in (0.25mm) zinc-coated copper wire at an optimum roughing speed of 1mm/min and finishing speed of 5mm/min.
All the rotors are finish-cut.
"I used to work with the CNC lathes," said Steve Carpenter.
"It is quite a revelation to see how accurately the Charmilles machine can cut - and unmanned! We are very pleased with the surface finish and the very tight dimensional tolerances are being maintained." Bob Copp added: "Wire EDM has removed a lot of inter-operation inspection, and the repeatability of the process is really second-to-none.
We have wire-cut 80 sets of rotors and stators so far and have not had a single reject.
You just could not do that with CNC turning and milling." "We are now looking at other work for wire EDM, " continued Bob Copp.
"For example we machine large components - rather like cylinders - out of forged Ferralium nickel-base alloy.
These cylinders have covers - or Olug tops' - which are sliced from forged bar stock and profile-milled.
We have worked out we could produce 15 with wire EDM from the same stock needed to produce 12 by sawing.
We also aim to use wire EDM for prototyping and maybe replace subcontracted out gear cutting by wire EDM cutting them in-house." Horstman Defence is also examining the possibility of EDM wire-cutting a complete rotor/stator set from one billet.
As to programming, Bob Copp commented that there is a learning curve, "But that is no obstacle if an operator already has a programming background.
It is a new CNC concept for us, but the operator interface is quite user-friendly.
It features ISO programming, which the operators find easier to understand.
We like the graphics too, we can check up at any time on wire position and power, and the machine and process diagnostics are excellent." In operation, the Robofil 330F works unmanned.
On the day shift, operators merely Okeep an eye on it' while carrying out other work on manually-operated lathes or millers.
Back in Peter Binns' office, Peter Binns explained that Horstman Defence is reorganising the factory into cell operation over the next three years and plans to set up an expanded wire EDM cell.
"We are very pleased with the Robofil 330F installation.
It has proven to be a new manufacturing discipline for us all." .
(This was Manufacturingtalk's Top Story on 20 November 2002).
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