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News Release from: Unicut Precision | Subject: One-hit machining
Edited by the Manufacturingtalk Editorial
Team on 01 March 2007
One-hit machining on complex components
'One-hit' single machining cycles on very complex components has won Unicut Precision a long-term contract to produce batches of 250 flow control bodies.
Unicut Precision's production engineering culture of implementing 'one-hit' single machining cycles on very complex components has won it a long-term contract to produce batches of 250 flow control bodies that caused concern even to the supplier of the machines on which the parts would be processed But the final process developed by Unicut's Unit Business Manager Martin Branch, on the twin-spindle Miyano ABX-64 TH2 multi-axis mill/turn centre, has resulted in a fully-deburred part, washed and supplied to the customer, along with other components ready for final assembly
This article was originally published on Manufacturingtalk on 27 Apr 2004 at 8.00am (UK)
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The machining process involves all the 36 tool positions available on the Miyano's triple turret configuration, each of which have 12 driven stations.
Of the 36 tools employed, 18 tools are driven.
Two of the turrets have four axes of movement, with Y-axis cross feeds and a third is a single three-axis unit that is able to work with either spindle.
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From planning to first-off production of the part at the Welwyn Garden City site took a week (frequent interruptions were made, however, to meet normal day-to-day duties) and the part - made from 60 mm diameter, 316 stainless steel bar - was produced initially in 18 minutes.
It was then developed into a 15.5 min cycle time to result in a fully-deburred component that is subsequently ready for washing on the company's Durr programmable wash ready for despatch.
Mr Branch admits that the planning strategy 'numbed his brain' at times due to the number of tools and sequences required in order to maintain positional tolerances and compound angles, feature breakthroughs and the complexity of programming toolpath profiles for very consistent in-cycle deburring tasks.
He says: "Being able to start with a blank sheet of paper helped, and I carefully selected the best tools focusing on the latest tooling technologies because the flexibility of the Miyano gave me the production platform to fully exploit and appreciate any advantages in this respect." He maintains that to produce the part using a CNC lathe and machining centre at best, would require two turning operations and four machining centre operations if they had the availability of four axes.
Conventionally, the part would need at least a dozen operations and the holding of special, tighter, operational process tolerances for successive locations and positioning to meet the required tolerances.
Included in the Miyano cycle are turning, milling, grooving, counterboring, recessing, drilling, boring, reaming, pocket milling, screwcutting, profiling, thread milling, tapping and parting-off.
Several holes as small as 1 mm diameter are required as well as thread chasing of a special stub Acme thread of 30 mm diameter.
In planning the operation Mr Branch started with three tooling sheets, one for each turret, and he drafted out the tools required.
Some cycles were programmed off-line but most were performed step-by-step at the machine to optimise tooling performance.
He said: "I had a clear vision of what we needed to do, so it was really a matter of getting everything in the right order." For instance, there were four 1 mm diameter holes that were more like grooves by 8 mm deep.
These were required at quadrants around a front counterbore so the holes had to be pitch drilled then the counterbore machined to leave half of each hole in the wall of the material.
He explains: "The tool would be too weak to effectively endmill the holes if the counterbore was produced first." There were also two sets of three holes set in an arc in the counterbore at 9o to the centre line.
These holes have to break into each other in two kidney shaped slots machined in the main bore.
"We drilled the two outside holes first to prevent wander, then produced the centre hole.
However, the difficult part was these holes and the slot had to be fully deburred in-cycle by interpolating around the profile of each intersection to remove rags and sharp edges," he says.
In balancing the main and subspindle and overlapping operations, 60 per cent of the cycle is devoted to producing the component while it is attached to the bar.
These included rough and finish turning then roughing out a square on the outside of the component using the Y-axis crossfeed.
Then, using a 40 mm shellmill, the square is finished before a through coolant drill is used to drill out the centre bore.
A 5 mm endmill is then used to produce the two kidney shaped pockets and four mounting holes drilled through at 4 mm diameter followed by three clearance holes each 8 mm diameter.
The centre bore is opened out and an oil groove trepanned in the face and then, using two adjustable angle head drill holders set at 13o, a ballnose cutter is used to produce spot faces followed by two more at 9o with two 4 mm diameter holes also drilled.
Two further cross holes are drilled opposite each other on the square by drilling partway, indexing the main spindle 180o and drilling to break through, followed by the production of a counterbore on each side ready for thread milling 1/4 BSP threads at each position.
The subspindle with a square collet then synchronises with the main spindle and with the part supported on the milled flats, the part is parted from the bar.
The subspindle then retracts ready for the second operation to be performed simultaneously in-cycle while the bar is fed out and the next component started.
Initially the outside diameter is rough and finished turned in the sub-spindle, the part-off face machined to length and four 1 mm diameter holes drilled on a pitch circle in the face.
The counterbore is then drilled and bored to leave a section of half of the 1 mm holes in the wall of the material.
A 30 mm stub Acme thread is milled followed by the use of a slitting saw to radially mill a blunt start and run-out of the thread.
A face groove is then milled, internal scollops milled, the clamping holes counterbored to 8 mm diameter and an M12 internal screw threadmilled.
Amongst the tooling employed were new special coated end mills from WNT, special Titex Alpha TFL solid carbide, 'High Life' coated drills, Iscar Multi-Master interchangeable head milling cutters for producing the scollop shapes, and Q8 semi-synthetic coolant was applied at 70 psi through the turrets.
According to Jason Nicholson, joint managing director, the use of the recently installed OGP SmartScope programmable non-contact video and touch probe measurement centre proved critical in the initial machine setting, and Mr Branch maintains this equipment has generated dramatic savings on inspection times.
This, he outlines, reduced the need to cut and section parts to check intersections of holes and monitor the precise nature of the deburring cycles.
Typical of the Unicut philosophy, machine speeds and feeds were set for consistency of process rather than for the ultimate cycle time.
The maximum revolutions of the spindle were 3,000 revs/min and driven tools were run at a machine maximum of 5,000 revs/min.
The company operates 17 Citizen and two Star CNC sliding head autos and three other Miyano machines with long periods of limited supervision and unmanned cycles during the night and weekends.
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