Many metal parts today are made from sheet or thin plates. These parts may end up as an electronics panel, or an aircraft structural component made from aluminum or composite. There are many ways to hold parts, however, sheets and plates are most often held using vacuum chucks. Why? What are today’s best techniques to hold this material and get the part out quickly and effectively?
The Basics on Vacuum Chucks
We all want to make parts as quickly as possible. That means we want the raw material as accessible as possible to do our cutting without multiple setups. No clamps, if possible. So, for a large sheet or plate, vacuum provides an excellent workholding method. The vacuum presses down on the sheet and generates high holding forces without clamps. But what type of vacuum chuck works best for holding plates? It depends upon required features. Let’s review some specific types of vacuum chuck designs for holding large plates or sheets.
Dedicated Vacuum Chuck
In a perfect world, we would use one vacuum chuck to hold every part we make. For some, there are features that cannot be done on a universal chuck. The part may have multiple windows cut through or other penetrations that would be difficult to produce with a standard, grid type chuck. Although it is possible to support a few penetrations using a standard chuck, for special part configurations a dedicated vacuum chuck is sometimes the only solution. However, having a dedicated chuck for every part is not practical. They are costly to produce, tie up capital, and require storage space and maintenance.
General Purpose Grid Type Vacuum Chuck
The most common type of vacuum chuck uses a grid cut into a plate. The plate may be made from steel or aluminum, but typically aluminum. The grid can be made in a small or large pattern. An O-ring gasket material is pressed into the slot in the grid pattern, surrounding the part, to provide a seal between the part and the chuck. This works best for large parts, and is a very flexible design that can hold a wide variety of similar parts. This type of vacuum chuck also provides very high accuracy as the part locates against the chuck surface. This can be ground to a tight tolerance if needed. However, this type of chuck is limited if the part has windows or drilled holes required. A window or drilled hole will break the vacuum seal and release the holding force. And, it is not easy to cut the periphery without damaging the chuck. For those requirements, there are other chuck systems that provide a solution.
Special Vacuum Workholding Systems for Plates and Sheet
The aerospace industry was frustrated by not being able to completely machine an aircraft part in one setup. The traditional approach used required multiple vacuum chucks to get the job done.
A unique work holding system, the Vac Mat, was created to solve this problem. While we don’t typically talk about our specific products in our blogs, we don’t have much of a choice here since it’s truly a unique solution.
The system uses a molded, plastic mat that holds sheets and plates. The mat has suction cups on the top. On the bottom, vacuum is distributed to each suction cup. As the part material is placed upon the Vac Mat pad, each suction cup providing holding force to the part. However, unlike a standard vacuum chuck that must maintain a single seal between the part and the chuck, the Vac Mat system relies upon the total holding force of many suction cups. And, all of the open suction cups do not need to be covered.
Mats are placed on a modular base plate large enough to support the part size. The best parts are larger than 8” x 8”. The complete part can now be cut, with flood coolant, including windows and through drilled holes. The outside of the part can also be completely finish cut because the pads can be cut up to .010” deep. When cutting occurs into the Vac Mat, that single suction cup will no longer provide holding force. However, as long as enough cups are intact the part will be securely held. At the end of machining, the used pads are discarded, and new pads are used for the next part.
Another benefit of the system is reduced material waste and cost. On many aircraft components, additional material is required for clamping. When the part is done, the excess material is scrapped. This system does not require external clamps.
The Vac Mat system is used today by major aircraft companies worldwide to successfully produce aluminum components, panels and shims. It is a general-purpose vacuum chuck system that replaces many dedicated chucks which saves setup time, storage and maintenance costs.Conclusion
Holding flat sheets of material with a vacuum chuck is not difficult, mainly due to the high holding force generated by the large surface area. However, the features required (windows, cut outs, drilled holes, external and internal contouring) will dictate if a general-purpose chuck can be used, or, a dedicated vacuum chuck must be used. And, there are solutions available that supply unique, cost saving solutions for many parts made today.