In the brave new world of smart factories, Internet 4.0 and highly automated machines and cells, workholding rarely gets top billing. It’s surprising that workholding gets so little attention, given the profound impact it can have on reducing cycle times, scrap, and ultimately, cost per workpiece. Fortunately, most gear manufacturers in recent years have begun to take notice, as a new generation of these under-appreciated components doing the “dirty work” prove their worth — and help manufacturers “clean up” like never before.
The Flexibility of ‘Fluids’
As awareness of workholding’s importance has grown, so has customers’ willingness to explore alternative clamping solutions, all in the quest for more flexibility, reliability, and economy. Hydraulically actuated workholding solutions for bores and shanks, for example, are now being developed by Gleason for applications once considered strictly the domain of better-known traditional mechanical clamping systems.
Most recently, Gleason has developed hydraulic workholding systems for applications ranging from hobbing automotive transmission gears in high volumes to power skiving large internal gears in lots of one or two, to high-precision hob sharpening operations. These systems are capable of performing as well or better than their mechanical counterparts. Most importantly, they offer a host of characteristics unique to hydraulic systems that are increasingly desirable across this wide application spectrum. For example:
Hydraulic workholding solutions offer attractive benefits to manufacturers producing families of parts with various bore or shank diameters, and/or producing multiple parts in a stacked configuration. The new-design Gleason hydraulic production expanding arbor is available for, but not limited to, the most common size range of automotive cylindrical gears from 12 mm to 100 mm in diameter. It delivers a powerful and consistent clamping force when hydraulic fluid pressure is applied to a thin-walled expansion sleeve, precision-machined out of tough tool steel. The sleeve expands as required by the application uniformly over its entire chucking length. This gives a single arbor the inherent flexibility to meet the requirements of, potentially, a variety of parts with different bore diameters.
The ability to produce uniform clamping force across the entire length of a gear’s bore also makes it an ideal solution for the machining of both thin-walled and multiple-stacked parts. In the case of multi-stacking applications, the sleeve can be designed with multiple expansion zones so that even parts with different diameters can be stacked together and clamped with great precision.
The hydraulic system is also a good alternative for parts with small bore diameters, since it eliminates the challenges that exist in producing small precision collets for mechanical systems.
Note that the automatic chucking system is designed with a pressure balance feature to prevent over-expansion. It can also be expanded without a workpiece with no risk of damage, since its maximum expansion range can’t be exceeded.
These hydraulic workholding systems apply clamping forces in a completely enclosed system that’s inherently impervious to the dirt and swarf contamination that can plague much more exposed mechanical systems. In high-volume, dry-cutting operations, the periodic downtime required for routine maintenance, cleaning, and lubrication can be an enormous burden on both productivity and manpower. The same problems exist in large-part production as well, and particularly so with internal gears where effective chip evacuation can prove more difficult.
Additionally, Gleason’s use of new FEA design tools, precision machining, and heat-treat resources, and our extensive workholding “know-how,” have enabled the company to manufacture hydraulic workholding for greater reliability and for applications requiring extreme accuracy. Gleason is now able to build longer service life into all the wear components of its latest hydraulic systems with these state-of-the-art, in-house manufacturing resources. Improvements in design and manufacturing have also resulted in particularly reliable, repeatable performance. Gleason’s standard hydraulic production expanding arbors, for example, deliver the standard accuracy and repeatability levels — 5 microns (0.0002”) TIR (Total Indicator Reading) — of their mechanical counterparts, but can also be designed for applications where the quality bar is even higher.
Gleason’s hydraulic hob sharpening arbor is one such example. This type of high accuracy production arbor typically has two expansion zones delivering an accuracy of 0.00005” (0.0013mm) or better. In the case of a typical shell-style hob with two location bores with a relief between them, the arbor expands into the hob bore to clamp, leaving zero clearance. A typical mechanical system would require a small clearance, thereby compromising accuracy. Additionally, a mechanical system requires an axial clamping element, whereas the hydraulic system’s very high bore clamping forces eliminate this need. The hydraulic arbor can also be used for hobs with different lengths as well, with no additional setup.
Fast and Economical
Finally, hydraulic workholding can offer attractive economies, both in terms of cost and delivery. Meeting on-going new-part clamping requirements often requires production of new, high-precision mechanical collets that are both expensive and typically require lead times of many weeks or months. This situation is exacerbated when it involves larger parts. In the case of the large-part power skiving application cited previously, Gleason’s hydraulic workholding system was the perfect solution to meet the needs of the customer’s ambitious multi-part family production requirements. Just two large chucks, with adapting sleeves, accommodate a range of workpiece diameters from 200 mm to 400 mm. They can operate with less maintenance required as well, sealed against all the considerable volumes of chips and swarf produced in this highly productive soft cutting/hard finishing power skiving environment.