Finding a method to secure parts on the table of a machining center has been a challenge since before CNC was invented in the 1940’s. For years, there has been a very keen interest in vacuum table or vacuum chuck technology for securing material. Traditional vacuum systems, however, have a lot of limitations that often disqualify the technology for part holding.
Limitations of the Traditional Vacuum Table:
- Small parts don’t have enough surface area for the vacuum to hold them
- Parts with through cuts cause the loss of vacuum suction
- Parts that are not flat either can’t be held or require additional setup time – which is often too long, particularly in short run or low volume scenarios
Successful CNC Vacuum Table Design:
Fortunately, DATRON has developed a unique vacuum table that solves all these traditional vacuum table limitations. Here’s how each of the limitations mentioned above have been overcome.
Holding Small Parts with a Vacuum Table
One of the biggest limitations with traditional vacuum table technology is that parts are often too small or don’t have enough surface area for the vacuum to hold them securely on the table. This exact situation was presented to DATRON when a knife manufacturer contacted us with a requirement for both a high-speed machining center and efficient means of holding knife handles during the milling process. Adding to the challenge was the fact that the product line had many different sizes and shapes and was constantly changing.
The vacuum table solution that we delivered was inspired by elements used on vacuum tables for much larger router-type table formats. These large scale systems use a permeable wood fiber board with a large flow vacuum to hold or secure large sheets for machining. Our smaller vacuum table, made from aluminum, features a dense grid of small holes in the top plate. A special thin permeable substrate sits on top to distribute the vacuum evenly and allows us to hold much smaller parts than the conventional or larger scale vacuum tables. In cases, where the parts are particularly small, we have a special version of the permeable substrate with a light tacky surface (kind of like the adhesive on a Post-It note) which is enough to secure the parts. The combination of our vacuum table design, the substrate material and a powerful vacuum pump – all developed to secure knife parts for one customer, has ultimately become an integral CNC accessory for many other customers and different applications in the years that followed.
Milling Through Holes on Parts Held with a Vacuum Table
Another common problem associated with conventional vacuum tables is that when you cut through sheet material, you get a loss of vacuum. If open holes allow too much loss of vacuum and the parts let go, often damaging the cutting tool, the machined part and even the CNC equipment. With DATRON vacuum tables, you can have up to a 40% open area and still hold your parts. This of course varies depending on the part, but typically, you have no problem with through holes or profile cuts. This allows for the flexibility and efficiency of cookie cutting each of part out without special tabs, screws or second operations to remove the parts from the sheet. In the case of the knife manufacturer, they would typically lay down a 24” x 36” sheet of 1/8” aluminum, start the machine, and within a couple of hours, they’d harvest over a 100 pieces of finished parts simply by sliding the permeable sheet off the vacuum table. The permeable substrate also allows you to cut completely through the material without machining into the vacuum table top. The swapping out of sheets was usually less than a minute, so almost no production time was lost due to new material change-overs.
Holding Non-flat Parts with a Vacuum Table
But, not all materials are perfectly flat. Most machinists would never consider holding slightly warped material or objects like an aluminum extrusion with a protruding lip with a conventional vacuum system. However, the DATRON vacuum tables also accommodate a thicker version of the permeable substrate material that we call Magic Board. With a thickness of 1/8”, the Magic Board still allows for adequate vacuum suction while providing the flexibility to mill special pockets or contours into it that accommodate non-flat parts. Milling pockets or cavities in the material can also be a technique to secure or locate a nesting of preexisting parts. Additionally, the added thickness of this substrate also provides reduces the risk of cutting into the vacuum table when using cutting tools like drills or thread mills that need to penetrate through the work piece further than normal.
Reduce Setup Time with Vacuum Table Workholding
It is common with traditional vacuum table systems to spend a great deal of time setting up a job before getting started with the machining cycle. Dealing with cutting gasket material and having to place it correctly for your corresponding parts is often a very time consuming and tedious practice. In some cases, special custom tables need to be designed with supplementary screws, locating pins, guides, extra clamps, etc. to hold parts down properly or in the correct locations. In cases when a conventional vacuum table will not work, countless hours of applying double-sided tape is sometimes a method used to secure parts. This can create all sorts of issues such as coolant attacking the adhesive, glue getting on parts, or the tape simply letting go.
With the permeable substrate system, usually there is no setup involved. Quite often you simply load in the desired material, turn on the vacuum pump, and start machining right away. This saves many hours of setup time over a production week and reduces part rejection resulting from improper setups. The DATRON vacuum table is a revolutionary and unique design that reduces production time significantly in many applications. It also allows a greater flexibility and in some cases the capability to machine parts that otherwise were impossible. It often reduces part rejection rates and improves part quality. From small thin parts that cannot be mechanically mounted, to parts with free-form outside contours, the DATRON vacuum table offers unique machining advantages that provide a competitive edge.