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Category: Machinery
Volume: 40
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Article No.: 5691

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Vacuum Tables Hold Down Costs

For more than half a century industrial engineers have been utilizing vacuum technology to achieve effective and reliable holddown of various materials for printing, cutting, machining, measuring, application of coatings and adhesives, and many other types of processing without the use of clamps or chucks. The advantages inherent in vacuum workholding are clear: setups are faster and more accurate, the entire surface of the workpiece can be accessed, handling of the material, and potential damage to the material and the machine is minimized. These advantages have driven the expansion of vacuum workholding systems into numerous businesses and industries.

Vacuum technology is efficient, flexible, and adaptable to a wide range of materials and processes. From large industrial facilities cutting and machining steel, to plastic fabrication shops using CNC routers, to cleanrooms recording precise measurements of aerospace grade composites, to museums and art restoration studios, vacuum table systems provide logistical solutions and operational advantages and are regarded as vital tools for success.

Although the principles of operation are the same in all vacuum table systems, the design and construction of vacuum tables varies widely depending on the application. Small tabletop systems may have a vacuum surface area of just one square inch while modular systems for industrial use may be expanded to hundreds of square feet. Stainless steel and aluminum are the most common surface materials and generally preferred for heavy-duty usage, but common variants include anodized aluminum, Formica®, and even plastic surfaces to accommodate specific materials and processes.

The precision of computer-controlled industrial processes such as CNC mills, lathes, and routers, plasma cutters, and EDMs has led to an exponential increase in the use of vacuum table systems over the last two decades. At the same time, the development of high-tech composites and synthetic materials has created a demand for clamp-free workholding solutions. It may require on-site adjustment to make a vacuum system perform seamlessly with an existing process, but such system calibration is usually fairly simple and straightforward. Vacuum technology is the state of the art for precision workholding in science and industry and system design continues to evolve as new technologies and markets develop, ensuring its continued dominance.

Peak performance under pressure
A vacuum table system typically consists of a penetrable flat, rigid work surface, usually perforated or grid-style depending on the application; a plenum or vacuum chamber; and a vacuum pump large enough to create a sufficient pressure differential between the chamber and the ambient or atmospheric pressure at the surface to hold a workpiece in place during processing. Strictly speaking, it is not pure vacuum that holds the part in place but the force (in this case suction) created by this pressure differential.

Hoses and clamps are used to connect the vacuum pump to a port or series of ports on the vacuum table, typically on the sides or bottom of the table. These connections must be tight, unobstructed, and as short as possible for optimal system performance. In a properly configured and calibrated vacuum workholding system a high level of hold down force may be generated with a relatively small pressure differential. Balancing suction and system airflow achieves the best results. Working in only one zone of the vacuum table surface requires effectively blocking the unused zones with gaskets or air dams to eliminate air leakage.

If the process in question generates excessive heat it may require the application of coolant during processing. If the process generates excessive scrap material it may require cleaning during processing with blasts of compressed air.

In such instances it is advisable to use a grid-style vacuum surface with larger air holes and vacuum ports and integral drainage channels. Because it is vital that no coolant flow back into the vacuum pump, these systems typically utilize some form of coolant collection system to protect the pump from damage.

Most commonly associated with metal processing, woodworking, and the processing of various high-grade plastics and composites, vacuum workholding systems have revolutionized production in many industries and disciplines.

“I don’t even know all of the potential customers, because I regularly hear from people in new industries with new applications,” says Michael Green, president of Graphic Parts International (GPI), a division of the Chicago-based A.W.T. World Trade Group, which manufactures vacuum tables for a wide range of clients in numerous fields, including many custom designs. “Meeting the specific needs of new customers has led to some of our most important design innovations.”

G.P.I.’s customers demonstrate the versatility and variety of vacuum workholding solutions. A local high-end bass guitar maker with an international reputation and elite clientele uses vacuum table systems for complex routing of hardwood guitar bodies. Multi-national aerospace and high technology manufacturing corporations such as Boeing, GE, and Agfa utilize vacuum tables in their close-tolerance and highly regulated manufacturing operations both in the U.S. and around the world. Another emerging use for vacuum tables is in the high-quality artistic and photographic restoration conducted by universities, museums, and art galleries. Vacuum tables are also extensively used for precision measurement of both flat and three-dimensional objects. In these instances the systems can be optimized to accommodate delicate materials. Whether a process involves plastics, composites, stainless steel or wood, there is a vacuum system suitable to the specified material.

Look out for Leaks
The evolving nature of vacuum system technology, combined with the fact that vacuum systems are typically ancillary to larger operations and the fact that vacuum holddown is used so differently across so many different industries, has created a situation in which even as vacuum tables become more ubiquitous there remains a lack of comprehensive information and expertise available to production managers seeking to implement vacuum workholding systems to improve their operations.

Even technicians who understand basic vacuum concepts may fail to appreciate the importance of carefully configuring each system for efficient operation to create adequate hold down force at the work surface. Air leaks and airflow inefficiencies account for the vast majority of problems users encounter when calibrating vacuum workholding systems. These problems will not be solved by simply adding a larger vacuum pump.

A vacuum table system draws air through the spoilboard (usually MDF if one is used), the table surface, the plenum, a sequence of ports, flanges, hoses, valves, and fittings to the vacuum pump. To achieve optimal system operation there must be no air leaks at any juncture in the configuration. Moreover, the hoses and fittings must be connected tightly, with the shortest runs possible, no kinks or obstructions and minimal use of elbows and sharp changes of direction.

Again, efficient holddown of the workpiece is achieved by balancing suction and system airflow. For this reason it is critical that the part be flat against the vacuum table surface. It is also important that the plenum be deep enough and fittings be large enough to prevent reduction of the necessary pressure differential to maintain holdown of the part as it is processed. An improperly configured or installed system may not achieve adequate suction until such errors are corrected. Vacuum table systems should be regularly tested to ensure system integrity. Vacuum gauges and ultrasonic leak detection devices may be used for this purpose.

An airtight case
With an appropriate system properly configured and installed, and all the kinks worked out, business owners and production managers should rapidly reap the many rewards of vacuum workholding technology in the form of tangible workflow improvements and lower costs.

Clamps, chucks, fasteners, and adhesives can be eliminated along with the time-consuming manual processes these items entail. Handling of delicate substrates, production materials, and costly components is minimized or eliminated. Production quality and consistency are enhanced.

For plastic fabricators it means faster setups and changeovers, along with reduced downtime and wastage. In any application, versatile, safe, stable, and efficient vacuum tables and vacuum workholding systems deliver higher quality results and increased productivity across all platforms, leveraging a reliable technology that is being expanded, improved, and adapted to new industries and processes all the time.

For more information, contact Graphic Parts International, Inc. (G.P.I.) manufacturers of custom vacuum workholding systems. Written by Michael Hurley of G.P.I.

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