Substrate Acts as a Holding Fixture

Machining parts from sheet or plate material is often the best approach for production runs of any size, from a single part to very high volume runs. In the past the biggest challenge has often been the workholding of small or thin parts.

Feedrates and productivity are influenced and often limited by the means used for securely holding the workpieces in place during the final stages of machining.

Double sided tape and spray adhesives are often used to accomplish this; however, neither of these methods are particularly desirable as they present their own problems.

Small and fragile parts are often difficult to remove and the adhesive requires a subsequent cleaning step, adding to the total cost of production.

For parts with sufficient surface area the vacuum will hold the workpieces securely in place. Even marginally-sized parts can often be machined this way if the feedrates are reduced. However, this also reduces productivity.

While small parts can be held in place by way of tabs or bridges, this method adds to the parts cost in several ways:

1. Parts need to be spaced farther apart for Substrate Acts as a Holding Fixture the tabs. The tabs cannot connect two parts. They need to connect the individual parts to the main sheet. More material is used, thereby increasing parts cost.
2. It requires the extra step of removing those tabs.
3. Hand deburring is often necessary.

Addressing the issue is a new approach called villmill that works to increase productivity levels and capabilities of CNC milling machines and CNC routers.

Vilmill, a product that is relatively new in the U.S., is used as a substrate between the sheet or plate material to be machined and the vacuum table or vacuum chuck acting as a holding fixture.

Vilmill is only 0.010" thick and has an adhesive coating on one side. The adhesive is activated by the heat generated in the machining process. Parts are bonded to the vilmill approximately 0.025" wide around the periphery and are held firmly in place during machining, allowing most parts to be machined in a single step. One method is to pull the vilmill over the edge of the machine table or a plate and the parts peel off, leaving no detectable residue.

Vilmill is becoming increasingly popular in aerospace for routing control panels, circuit boards, plaques, labels and more.

One major airplane maker in Europe uses this approach for all their aluminum sheet parts. They have automated the loading/ un-loading of their routers by using vilmill as a conveyor belt when one sheet is finished.

For machining metal, a very lean mist is used to keep the chips from building up on the router bit. For plastic, only a soft air blast is used to keep the chips airborne for easy extraction. Since the heat that is generated in the milling process is needed, no coolant can be used. This limits the use of vilmill to machining of non-ferrous materials such as aluminum, brass, copper and plastics. Vilmill does not work with foam materials.

Vilmill is available in rolls of different widths: 1.22m (48"), 1.5m (59") and 1.8m (71"). There are 100m (109 yards) to a roll.

Stackmaster Engineering Corp.
Menlo Park, CA
stackmaster.com