Workholding is an essential element in any manufacturing process. Andrew Allcock catches up with latest product developments and applications, discovering that energy-saving is one development driver
Hainbuch (01543 478710) is using high-tech, lightweight materials more associated with the motorsport, aerospace and sporting goods sectors in its latest products. But for manufacturing and machining, says the company, concern over rising maintenance and energy costs is increasingly becoming a central issue, with power costs having seen high levels of increase recently. "Hainbuch has addressed these issues early, and responded to the challenges of lightweight clamping devices and their special manufacturing processes by devoting research and development resources in these areas," explains the company's UK general manager, Nick Peter.
So, what are the key attributes of a lightweight clamping device? The objective is to keep the construction as slender as possible, and avoid unnecessary wall thicknesses and reduce mass, but still maintain strength. In addition to using lightweight metallic materials and high performance plastics composites, Hainbuch relies on carbon fibre as the main material for the new lightweight generation of clamping devices, some of which can be as much as 70% lighter than their 'heavyweight' precursors. Steel is now the material employed in the lowest proportion – used only if components slide on each other or for accuracy when joining individual parts. Hainbuch manufactures all parts for these new clamping devices in-house.
Image: Carbon fibre workholding solutions are lightweight
Benefits from the new lightweight products are not only in energy saving, but also in performance enhancement. For highly dynamic machining, low moving mass is key, for example, while for rotating, spindle-held workholding, spindle acceleration can be up to 30% faster, with a higher top speed also possible, compared to a steel counterpart.
As an example, on a CNC lathe, simply replacing a clamping device made of steel with its equivalent lightweight clamping device made of carbon fibre can reduce the time for spindle acceleration from stop to maximum speed by 30%, with braking time also reduced. So the cycle time for each complete part is reduced by as much as 6%, meaning hundreds or even thousands of extra parts produced per annum, offers Hainbuch.
Another benefit is that there is a recommended 15 kg maximum weight limit, with regard to manual handling, which a lightweight solution can help achieve.
Not billed as an energy-saving development, but one which does, nevertheless, have that benefit is Enerpac's new Collet-Lok technology (0121 505 0787), a claimed unique combination of hydraulic and mechanical clamping to retain holding force.
Image: Hydraulic pressure puts the force on, but it is held mechanically thereafter, avoiding on-machine hydraulics and problems of pressure loss
A wedge, driven by hydraulic pressure, clamps a plunger in position and maintains clamping force at 100%, even after clamping pressure is released. This eliminates the risk of reduced clamping force due to leakage or pressure loss.
An important advantage of the Collet-Lok technology is that workpieces awaiting machining may be clamped ready for processing – once locked, the Collet-Lok requires no hydraulic pressure. Of course, without the need to maintain hydraulic pressure during machining, no complex on-machine hydraulic system is necessary.
The new system also provides for greater security than does an accumulator-based solution – an accumulator will only make up for a slight drop in clamping pressure caused by a leak in the circuit. However, it is essential to maintain hydraulic pressure and, hence, the clamping force, during machining.
Of course, if a hydraulic fixture used on a machine tool must remain in place, then hydraulics remain a necessity. But the workholding set-up need not be complex, as an arrangement at California-based machine tool maker Haas Automation demonstrates. The company has automated the milling of the drive 'dogs' on the end of its machining centre spindles, with help from a Kurt HDM 690 hydraulic vice (Carillon Industrial Services, 01480 225850), fitted to a Haas VF4SS vertical machining centre, which is part of a cell that also includes two lathes, all three serviced by a Motoman robot for load/unload operations.
The vice supports complete automation of the process. "The goal with the new workholding set-up was to automate the milling operations used to produce our machining centre spindle shafts in a cell with two lathes and a milling machine tended by a Motoman Hp 165 robot," Phillip Linscheid, Haas machine shop manager, explains. "The robot provides the load/unload operations for each of the three machines. There is no fixture set-up labour required. The cell operates automatically during the 8 hour day shift and continues to run unattended through the night. We're operating continuously, 20 to 21 hours a day, with this new cell, depending on quantities required. We're achieving two to three times greater output for different size spindle shafts versus the previous set-up and able to get that kind of productivity increase without needing a machine operator for the night-time hours."
Image: Kurt is supporting unmanned automation at California-based Haas Automation
The Kurt vice is located on a 90° angle plate – the vice top surface facing towards the operator – such that the spindle shaft is held vertically in machined vice jaws. Using hydraulic pressure, the new double-acting vice design ensures that the moveable jaws open and close precisely, with up to 26.7 kN clamping force, actuated by the machining centre's CNC. The vice holds tolerances of +.005 - 0.000 in, without any variations to date, it is reported.
Box item
Product developments in brief
[] The Lehmann series 500, gear-driven rotary tables (Avon CNC, 0560 1766265) cost up to 30% less than previous generations. They are available in the four sizes 507, 510, 520 and 530 mm, with peak heights of 110 to 240 mm, suitable for face plates from 100 to 500 mm. With these four installation sizes, over 170 variants and combinations can be created – from simple one spindle 4th axis, right up to a 4-spindle turntable layout, offering 4th and 5th axis capability.
[] Roemheld (0121 453 1414) has introduced a new self-centring vice to provide quick, simple fixturing for concentric machining of different sized workpieces. The new Bock vice features an adjustable Gib design for increased accuracy and is available with a universal base that is easy to mount directly to machine tables. Its fully sealed, patented leadscrew assembly ensures long, maintenance-free service and contains cleverly located openings that allow chips to flow out of the vice base. Hardened steel rails provide precise location, resist wear and offer strong support to jaws. The Roemheld self-centring vice has a maximum clamping force of 2,000 kgf and offers repeatability of 0.005 mm. It comes complete with aluminium soft jaws, which are fully machineable and reversible.
Image: Quick, simple fixturing for symmetrical parts
Also from Roemheld, a new Bock hydraulic vice column has patented swivel coupling that prevents twisting of hoses, and saves time and money. In-house testing showed up to a 50% reduction in production time when compared to the manual version performing the same tooling operation. The Bock vice offers a consistent clamping force, up to 4,700 lbs.
[] Following the introduction of the Erowa self-centring vice, REM Systems (01452 314100) now offers two more variants, one with the Erowa standard 148 mm pallet and one for direct mounting to larger pallets or machine tables.
Image: Erow's self-centring vice now in two additional variants
