Product category:
Special purpose joining equipment
News Release from: Leader Chuck Systems | Subject: Hainbuch collet chuck
Edited by the Manufacturingtalk Editorial
Team on 13 April 2001
Customised chuck improves friction
welder process
The use of a Hainbuch collet chuck on a friction welding machine has "significantly improved" process reliability for the critical welding of the Inconel turbine rotor to a steel shaft.
The use of a customised Hainbuch collet chuck on a friction welding machine has "significantly improved" process reliability for the critical welding of the Inconel turbine rotor to a steel shaft As a result of close collaboration between workholding specialist, Leader Chuck Systems, and turbocharger manufacturer, Holset, the use of a customised Hainbuch collet chuck on a British Federal friction welding machine has "significantly improved" process reliability for the critical welding of the Inconel turbine rotor to a steel shaft
This article was originally published on Manufacturingtalk on 3 Mar 2004 at 8.00am (UK)
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Designed to maximise the power output from car and diesel engines, turbochargers use the exhaust gases to drive a turbine that powers a compressor to force air into the induction system.
The turbine and compressor are directly coupled by a common shaft, and spin at around 100,000 revs/min.
So the kinetic energy is immense.
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The integrity of the manufacturing process is vital; not only do the rotating components need to be in perfect balance but the integrity of any joints must also be beyond reproach.
While the aluminium compressor stage is an interference fit on the shaft, the driving turbine rotor is friction welded to the end of the shaft prior to final machining.
This eliminates any risk of the rotor working loose in service due to differential expansion, and it allows machining and balancing of the rotor/shaft component as a unitary assembly to extremely tight tolerances.
Holset is a world leader in the design and manufacture of turbochargers for medium and heavy duty diesel engines in the automotive, industrial, marine and power generation markets.
It works closely with customers on the integrated development of engine systems, and is the pioneer of variable geometry turbocharger (VTG) technology.
This is where the characteristics of the turbocharger can be altered to provide effective boost over a much wider range of engine speed than fixed geometry designs.
Since 1973, when taken over by Cummins Engine Co, the company has expanded worldwide, and has manufacturing facilities in the UK, Brazil, India, China and the US.
At its Huddersfield headquarters, Holset manufactures thousands of units per week for most UK and European manufacturers of turbocharged engines.
Holset's manufacturing processes have to maintain extremely tight tolerances but also be capable of functioning for long periods without interruption.
In this respect, friction welding of the shaft to the rotor offers a near perfect joining process.
Because the materials are dissimilar, consumables-based processes are ineligible while laser or electron beam welding would be much slower.
The weld resulting from the process meets Holset's requirement to withstand a 150kN tensile loading and is also very fast, meeting production targets with ease.
The action of the friction welding process, in which the stationary captive rotor is indexed to contact the end of the rotating shaft, pushes the collet jaws back into the taper, tightening their grip on the shaft.
The friction this generates causes the materials to heat up, melt and fuse.
The upset generated by the welding process reduces the overall length of the assembly by about four millimetres.
Gary Waterhouse, the Holset project engineer, comments: "As originally constructed, the machine used a one-piece Hainbuch collet system to hold the shaft in place for friction welding.
Over time the collet faces - which have a dimple pattern to maximise grip on the shaft - wear." Occasionally, when the Inconel turbine rotor was pushed against the spinning shaft, instead of the shaft continuing to spin and heat up both materials to create the weld, the friction stopped the shaft.
The collet then proceeded to spin around the shaft until the shaft was welded into the collet.
With demand for Holset's medium range turbochargers running at 5,000/week, any interruption to production is obviously undesirable.
Removing a welded-up shaft and collet required extensive disassembly of the machine's headstock.
A parallel problem was that of unpredictable collet life, so Holset was unable to accurately predict when failure was likely to occur.
This ruled out a preventative maintenance-based approach.
"We worked together with Leader Chuck Systems - Hainbuch's exclusive UK agent - to improve the process reliability and the maintainability of the collet system," recalls Gary Waterhouse.
"And the result has been a vast improvement.
We now have a fully reliable process, and the new collet system is both more effective and much more maintainable.
And in the event of the shaft welding itself to the collet, the new system is much easier to replace." The new Hainbuch arrangement is based on a three-piece modular system comprising a solid outer clamping ring which attaches to the machine spindle, a central compressible ring with rubber inserts and sets of precision collet jaw inserts which have been re-profiled to improve grip.
An important aspect of the system is that it is fully compatible with the previous drawbar arrangement.
However, it can be fully assembled and disassembled from the front of the headstock in a few minutes.
Holset's redesigned system continues to exhibit the same high-accuracy clamping as a standard Hainbuch collet chuck - up to 0.004 mm TIR - plus clamping forces of up to 50 per cent higher than a conventional jaw or collet chuck using the same drawbar pull.
Another aspect of the project that is highlighted by Gary Waterhouse as a major success is the reprofiling of the gripping inserts.
"Life between seizures used to be unpredictable," he says, "but we now achieve a reliable six-month collet life.
As a result we can exchange the consumables in good time, so in-production seizures are a thing of the past.
"In addition, although the machine is dedicated to production of a single product it would now be very simple to alter it for a different shaft size if that were required.".
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