Another Level of Workholding: Zero-Point Clamping

What do you think of when you think workholding? A vise, hydraulic clamps, vacuum plates, toe clamps, magnets, glue? Absolutely, but this is only half of the equation. What about the interface between these components and the machine tool? This is...
by Michael Guance
Jun 18, 2018

What do you think of when you think workholding? A vise, hydraulic clamps, vacuum plates, toe clamps, magnets, glue? Absolutely, but this is only half of the equation. What about the interface between these components and the machine tool? This is equally important, if not more important because it dictates the time it takes to change your workholding, which in turn has a significant impact on your spindle up-time. By investing in a quick-change pallet system (aka zero-point clamping system), most companies report a return on their investment in only a few months! From then on, it is pure cost savings year over year.

When workholding needs to be changed on a typical t-slot table, a skilled operator must unfasten the workholding with the many screws holding it in place, clean the table, load the new workholding, and then indicate it in thus re-establishing the off-sets. Not only are the people capable of doing this becoming a scarce resource, but it takes time no matter how skilled your operator is. Depending on the complexity of the setup and the skill level of the operator, this could take anywhere from 45 minutes to 3 hours, during which time the spindle is idle. Machine tools are becoming more and more capable every year, and companies are now buying one multitasking, 4-6 axis machine to take the work of three machines. This single machine tool not only necessitates a higher hourly rate, but it also demands more flexibility out of the workholding due to the wide variety of parts flowing through the machine.  In order to mitigate this downtime, job shops from five employees to production facilities of 1,000 employees are utilizing quick-change pallet systems in order to capitalize on both their human resources as well as their capital resources. By using quick-change pallet systems, the employees have more time to tend to more jobs, and the spindles stay running longer.

There are many different types of zero-point clamping systems out there. They can be operated manually, pneumatically, or hydraulically, and can be used on milling centers, turning centers, multitasking machines, indexing machines, inspection tables, the list goes on. Quick-change pallet systems are simply a way of standardizing the mechanical interface across a shop. The typical repeatability of these systems is 0.005mm (0.0002”), which means once the initial program is created for a particular fixture/workholding device, it never has to be indicated again. Zero-point clamping is being used successfully on everything from drill-tap machines to large bridge-mill machines, turning centers with A2-6 spindles to 2-meter VTL’s, for pocket watch components to 767 wing spars.

Now that the industry is familiar with the standard application of the technology, we are seeing it being applied in more and more creative ways in industries new and old. Many automotive manufacturers are designing the zero-point clamping interface directly into their components, including engine blocks, cylinder heads, and transmission housings. The first operation on these components is to prepare it for the clamping pins. From then on, the zero-point clamping offers the most repeatable, stable, and best part access for processing the workpiece. Part presence detection and workpiece clamping confirmation can all be integrated into the clamping system. We call this form of clamping direct workpiece clamping, and it is being applied in many industries, most notably structural aerospace, large-block machining (fluid ends for fracking), and on tool & die components.

By investing in a system that is controlled pneumatically or hydraulically, it also means that when (not if) you decide to automate your shop in the future you are already one step ahead. As we transition to industry 4.0, and the internet of things (IoT) begins to creep into manufacturing, it becomes more and more important to be able to control all levels of the shop via PLC. A zero-point clamping system is certainly a piece of that puzzle. This is of course the ultimate realization of manufacturing in this moment in time, but the nice thing about a quick-change pallet system is that it is easy to get started. The payback on a system for a small machine is only a matter of a few months, and can be spread across a shop as slow or fast as is necessary.

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Author
Michael Guance
Workholding Group Manager
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