Heat-shrink’s grip tightens

Heat-shrink tool/toolholder technology is well proven and widely used in the aerospace and mould and die sector, but the process really came to the fore in 2000 in the German and American auto industry for transfer line and flex-line type machining installations, according to Juergen Meyer, milling specialist at LMT (UK), Coventry. The adoption was in response to the trend to ensure predictable performance of the equipment and processes, in order to maximise spindle utilisation, process reliability and machine uptime. So, along with tool pre-setting, it rapidly gained acceptance to ensure that minimal production time was lost due to tool changing and also that maximum rigidity was maintained in the tool to spindle assembly. But it is largely the adoption of high-speed machining that has drawn attention to the advantages of heat-shrink, in preference to traditional collets and hydraulic chucks, with shanks up to 32 mm typically catered to. Now, according to Mr Meyer, users are looking for other applications of the technology and adopting it for use with drills and taps between M5 and M20, especially as holders are now available with built-in length adjustment and through-tool coolant feed. Yet LMT (UK) toolholding manager Bob Osborne observes that: "Many still view heat-shrink as the domain of industries such as aerospace where very expensive high-speed machining applications using spindle speeds of 20,000 to 60,000 rpm are the order of the day. But, today, even for general machining, faster accelerations and higher spindle speeds with improved tool performance are bringing heat-shrink into higher demand." And although people view the technology as expensive, versus a hydraulic toolholder a heat-shrink holder costs half as much and can be used for thousands of gripping cycles. heat-shrink holders also overcome the problem of permanent damage to the internal membrane or a burst hydraulic bladder if the hydraulic holder is closed without a tool being present. And on the cost of the ancillary heat-shrink unit, Mr Meyer says that "cost is relative", adding that: "A machine and a selection of backends would easily be justified in under a year just on the payback generated from improvements in the life of the cutting tools without the additional benefits." And a toolholder is capable of going through 5,000 heat-shrink cycles without showing any signs of degradation, or any loss concentricity or elasticity, he adds. As to the cycle time, to remove and replace a tool in the holder should take less than 30 secs, it is claimed. The assembly is re-heated, the tool to be replaced picked out and the new tool inserted, with the assembly then automatically quenched. "What is not generally realised is that the effective working life of cutters is being seriously shortened when using collet holders that enable the tool to run-out, leading to uneven loading of its cutting edges," he says. "A simple check of the run-out of a cutter in the spindle will reveal all. The greater the eccentricity, the quicker the cutter will wear as one tooth takes the majority of loading. This means tool costs escalate and quality levels in production suffer." Image: LMT (UK)'s ISG-3200WK shrinking machine (pictured) has a 10 kW high frequency generator, with a tool capacity between 3 mm and 32 mm diameter in solid carbide, and 6 mm to 32 mm in high speed steel. Tools can be up to 450 mm long, requiring a single heating coil. A fully programmable (menu with graphics display) automated process monitors the temperature, ready for the tool shank to be inserted, with manual override for full adjustment to the generator included He puts a conservative estimate that for every 10 microns of run-out at the tool tip shown on the dial indicator, the effective cutting life will be reduced by around 10 per cent due to the uneven load. This also has a direct influence on the machining process by intensifying noise and vibration and has a detrimental effect on surface finish. There are other issues for consideration between heat-shrink and collet systems, too. It is very difficult to remove a broken cutter from a collet and, in any case, the collet should be immediately discarded. Should a tool work loose or drop out, the internal gripping area of the collet becomes damaged and again should be replaced. Also, prevention is better than cure – collets wear, especially the critical first 10 mm of the gripping zone, due to radial forces generated during the milling process – but collets are rarely checked until problems arise. And problems are exaggerated when longer length tools are in use. Indeed, in such applications, a further positive advantage of using heat-shrink is that very slim yet rigid holders are available that improve access to difficult-to-machine component areas. Mr Meyer is adamant that too often, the choice and usage of tool holding system is down to custom and practice, and is not seen in its true light as playing a critical part in optimising the cutting process. The advantage of heat-shrink is that it provides a rigid monoblock connection between the cutting edge and the spindle, he underlines. And that rigidity is even more important today as exotic materials, such as high performance alloy steels, titanium, Inconel and high strength steels, are machined in ever-greater quantities. And while, for example, heat-shrink holders being used on titanium at 500 rpm is a far cry from high speed cutting, Mr Meyer says: "The production engineering logic is the same in determining security of process." Box item> Other suppliers of heat-shrink technology * Fenn Tool (Zoller and Haimer systems) www.fenntool.com * Gewefa www.gewefa.co.uk * Guhring www.guhring.co.uk * Kelch www.kelch.de * Schunk-Intec (Celsio) www.schunk.com * Seco Tools www.secotools.com/uk * YMT www.ymtltd.co.uk Image: Seco is another tooling supplier able to offer heat-shrink tooling technology A claimed alternative to heat-shrink systems is Rego-fix's powRgrip toolholding system from Brunner Machine Tools (www.brunnermachine.co.uk). The system claims to offer advantages over conventional collet chucks and heat-shrink cutting toolholder systems, such as: higher transmittable torque; runout of 0.003 mm; tool change in less than 30 seconds; room temperature operation – no heat involved, so no delay for 'cool down'; easy to balance where high speed spindles are in use – just fit the balancing rings; works with 'through coolant ' cutting tools. The system claims a higher transmittable torque than all other systems – for a 25 mm tool shank, this is over 1,000 Nm for powRgrip, while Rego-fix puts the heat-shrink comparison at just over half this. While offering a heat-shrink system, Schunk-Intec (www.schunk.com) also highlights its Tendo hydraulic clamping system as an alternative. When the company launched its HSK-A63 Tendo E Hydraulic toolholders system, it stated that, unlike heat-shrink systems, it requires no additional external peripherals. On performance, it highlighted test results of three totally different systems using a finish milling cutter of 20 mm diameter to machine several horizontal paths in a test material (16MnCrS5k). With a cutting depth of 20 mm, contact width 0.6 mm and cutting speed of 180 m/min speed, the test was stopped as soon as the width VB (flank wear) exceeded the value of 0.3 mm. The tool life travel of a standard ER collet chuck was 230 m, while a heat-shrink toolholder machined 240 m. However, the Tendo Hydraulic Toolholder achieved almost 360 m; 56 per cent more than the collet chuck and 50 per cent more than the heat-shrink toolholder. Article first published in Machinery, May, 2009