Accuracy and Productivity with Modular Workholding

Röhm's Power Grip Zero Point Clamping System is designed to reduce setup times by easing the alignment process.

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Advanced modular palletized workholding technologies take the headache out of machine setups. These systems revolutionize the alignment process, may reduce setup times by as much as 90 percent, and provide safe clamping forces as well as tighter tolerances and higher transfer repeatability.

One such high-tech modular clamping solution is the Power Grip Zero Point Clamping System, from RÖHM Products of America, that uses a single locating point in the center of the base unit as the absolute zero reference point for the whole system. This center position always remains constant, and even remains unaffected by thermal deviations. This system also has multiple power clamp units (usually as many as four), however, with each power clamp unit the location is set at the time the system is manufactured, again, based on the zero-point center retention principle.

Conventional pallet systems, on the other hand, set their system zero point fixed at one of their multiple power clamp positions. This setup references dimensions from the zero holder to the other power clamp positions as well as to the center of the pallet itself. Such systems are susceptible to location errors when exposed to thermal deflections.

Conversely, shops can easily align zero-point clamping systems because once the base holder is set and located on the machine tool, the system is ready.

In addition to hassle-free part location, the Power Grip Zero Point Clamping System self-centers for fast and accurate loading. Pallets can be as much 2 mm off center from the base unit, and the system will still locate and clamp the pallet properly. These systems are also self-balancing to further enhance accuracy and precision, making them highly suitable for automation-integrated handling.

One of the major advantages of advanced zero-point clamping solutions is the tremendous force that secures each clamping unit. On that system, pneumatics in each clamping unit secure the pallet to the base with as much as 1,700 daN (3,740 lbf) without re-clamping, and with as much as 2,800 daN (6,160 lbf) at 6 bar of air pressure with re-clamping, per each clamping unit. This equates to a total of more than 11 tons, or 26,640 lbf of clamping force to hold down the 4-clamp pallet.

With all that force securing the pallet, these systems are well suited for very tight tolerance applications that demand a high degree of repeatability. For instance, a milling machine equipped with a zero-point clamping system will produce parts with as little as 2 µm of transfer location repeatability through 750,000 clamping cycles, air-cushioned with conical centering and a leveling system.

Pallets of all types expand and contract during use due to temperature shifts. However, with one zero point, advanced pallet solutions maintain their position throughout machining, which means that workpieces are free from the errors that would otherwise occur due to incorrect offsets.

In conventional systems, the occurrence of thermal expansion can throw off the zero points for the holder positions and the pallet itself. A central zero point, on the other hand, stabilizes the pallet and eliminates errors caused by thermal changes.

Base units of zero-point clamping systems are typically carriers that get bolted on to a machine’s standard table or rotary table or directly on a turning machine’s spindle for applications as high as 6,000 rpm. Four clamping units secure pallets to the base. The pallets hold vices and chucks as well as parts clamped directly to the pallet.

Pallets with different capacities can mount onto individual locating pins in various configurations to suit the needs of various applications. For instance, the base unit can hold one four-position pallet or two two-position pallets. Shops can also machine their own pallets tailored to their specific applications and purchase a separate centering and locking bushing to make those custom pallets compatible with the Power-Grip Zero Point system.

Today’s advanced clamping solutions can be used on machine tools, EDMs and measuring systems. This flexibility allows shops to quickly transfer parts from one process to another without spending significant time setting up parts on different tables. Such zero point systems are also readily incorporated with automation and end-of-arm robotic gripping technologies.

The strong clamping forces, high repeatability and short setup times of zero-point clamping systems make them particularly effective for shops in the automotive, medical, aerospace and watchmaking industries. Parts for these sectors are frequently made from tough materials and demand extreme precision and high-quality surface finishes, along with, in the case of automotive, high-volume production. Zero-point systems enable shops to overcome all of these challenges.

Whether used in high-volume/low-mix or low-volume/high-mix environments, zero-point clamping systems streamline production. With short run parts, shops can waste a lot of time setting up multiple machines, each with a different type of workholding. Modular zero-point clamping systems enable shops to set up parts offline to increase overall spindle utilization. Additionally, zero-point clamping systems can exceed other conventional pallet systems in terms of accuracy and advanced capabilities.