Product category:
Tubeworking: bending, cutting-off, profiling and end working
News Release from: Kasto | Subject: BEMA 'Reverse 25' seven-axis CNC tube bender
Edited by the Manufacturingtalk Editorial
Team on 07 June 2001
Reversing tube bender solves headrest
problem
RSM Industries' existing tube benders could not cope with the complexity of tubular steel headrest frames. A BEMA 'Reverse 25' 7-axis machine solved the problem.
When second tier supplier RSM Industries was awarded the contract in 1999 to manufacture the tubular steel headrest frames for the five-seater Nissan Almera, the existing tube bending and endworking plant at the subcontractor's Coventry factory could not cope with the complexity of the two rear outer headrests The problem was that the last of the six bends needed a reversal in the direction of bending to avoid the tube hitting the tooling
This article was originally published on Manufacturingtalk on 23 May 2001 at 8.00am (UK)
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A turnkey machine tool package supplied by the Italian company BEMA through its UK agent, Rivers Machinery, proved to be the answer.
Key was the ability of the 'Reverse 25' seven-axis CNC tube bender to complete all six bends in one hit.
Although a standard BEMA product, it is able to change the direction of bend during a cycle.
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Competitive machines either could not do this, or would have been special products and hence more expensive and on longer delivery.
Moreover, BEMA was the only one of six suppliers able to offer both the tube bender and the endworking machine, the latter comprising the other half of the production cell.
In addition to supplying metal pressings and welded assemblies, RSM specialises in manipulation of many grades of steel tube with the emphasis on automotive work.
In addition to headrest frames, other components regularly manufactured are seat impact bars and parcel shelf reinforcements.
The company has handled Nissan work for many years, notably producing headrest frames for the Primera for which a U-bender and a notching and doming machine from BEMA plus a separate cranking machine have been used since the early 1990s.
The production sequence in the new cell for a rear outer headrest frame starts with feeding 800\mm lengths of steel tube, 12.7mm diameter / 1.6mm wall thickness, down an inclined magazine to the electro-hydraulically actuated Reverse 25.
The machine's loading arm picks up a tube and presents it to a sequence of tooling sets supplied by BEMA which complete the six bends.
The 'U' and crank angles are formed in a fully automatic cycle of just under 30 seconds prior to ejection of the part-finished component.
At the adjacent BEMA BS50x2 end forming and notching machine, two of the U-shaped components are loaded by hand, clamped, and the four legs presented simultaneously to tooling which forms the appropriate number of height adjustment notches, then presses a dome on the ends.
The BS50x2 has spare capacity as it processes two frames in tandem in a similar cycle time to that of the Reverse 25, so another job is also carried out on the endworker during the factory's two-shift working, 6.00 am to 10.30 pm.
Batch size is between 12,000 and 15,000 frames, representing a three-week production run before resetting for another Almera headrest.
There is considerable variation between them; for instance, there are six height adjustment notches in the front and just one in the back of the car.
The centre back frame has just four bends.
There is also a front seat variant known as an active headrest, which has a larger crank angle to assist in minimising whiplash injury during an accident.
Both BEMA machines are required to work to tight tolerances.
The pitch between the two legs of the frame, after bending, has to be within +/-2mm.
Formed domes, on the ends of the legs, have a drawing tolerance of 9.5 +/-0.5mm.
The notch depth accuracy is surprisingly stringent at +0/ -0.2mm.
Metal inserts have historically been used to achieve this level of precision, although RSM has found that they can be eliminated using a mandrel prior to forming.
Quality control is achieved by checking the first-off from each new batch of tube, then taking five samples per hour during production and measuring all critical features using bespoke fixtures and conventional metrology equipment including height gauges and verniers.
A statistical process control chart indicates when dimensions are drifting out of tolerance and the machine programs are adjusted accordingly, typically a couple of times a day.
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