Considerations and Practices for Using Vacuum Clamps in CNC Machining

In CNC machining, workholding devices are important to ensure process stability. There are several methods to secure a workpiece, including clamping, pressing, supporting, magnetic holding, and vacuum suction. This article focuses on the application of “vacuum clamping” in machining. When applied properly, this method can become a highly effective workholding solution.

How do Vacuum Clamps Work?

Vacuum clamps secure workpieces by creating a close seal between the workpiece and the clamping surface. The process works as follows: a sealing strip is placed around the edges of the workpiece. Inside this sealing area, the clamp has pores or grooves connected to a vacuum pump. When air is removed, a vacuum (negative pressure) is created, holding the workpiece firmly in place.

Key Considerations for Using Vacuum Clamps

Using vacuum clamps in CNC machining requires attention to certain key factors to ensure effectiveness and prevent air leakage.

Workpiece Material

Vacuum clamp is particularly suited for soft metals and plastics. These materials will deform slightly during suction, which helps them form a tighter seal with the clamp. However, for harder materials with uneven surfaces, the suction may not be strong enough to correct the contact surface due to poor conform between the workpiece and clamps, which could lead to air leakage and inadequate holding.

Workpiece Structure

For the different structures, the vacuum clamp is most effective with thin, flat workpieces. Thin parts can conform more easily to the vacuum clamp’s surface, improving overall flatness during suction. Additionally, the larger surface area of plate workpieces increases the contact area with the vacuum, enhancing the suction force.

Different Types of Vacuum Clamps in Machining

There are several types of vacuum clamps, each suited to different machining needs and workpiece structures.

Figure.1: Multi-cavity vacuum clamp

1. One Mold with Multi-Cavity Vacuum Clamps (Fig. 1)

Figure 1 shows a vacuum clamp designed with multiple cavities, ideal for securing workpieces with pre-machined interiors. The clamp has independent vacuum sections in each cavity that can hold several components at once. For short machining cycles, this design allows stacking, reducing manual operation and improving machining efficiency.

Figure 2: Left-right sectioned vacuum clamp

2. Left-Right Sectioned Vacuum Clamp (Fig. 2)

The clamp in Figure 2 has two suction zones, which are ideal for sheet workpieces. The left section is suitable for the first machining route, providing strong suction to withstand roughing or heavy cutting. The right section is used for finishing the reverse side.

In this type of vacuum clamp, the workpiece is also suctioned as a whole before disconnecting the plate material. During this process, the suction force is also relatively strong. Once the primary features are machined, the part in the plate can be cut through, getting the finished products.

Figure 3: Standard vacuum clamp

3. Standard Universal Vacuum Clamps (Figs. 3)

Figures 3 and 4 show a standard universal vacuum clamp, suitable for prototype or small-batch workpieces. It is highly versatile and does not require custom design. Although it provides strong suction, it may not offer the same precision in repeat positioning or parallelism as custom vacuum clamps. Therefore, the choice of clamp should depend on specific machining needs.

Practical Case of Vacuum Clamps in Use

Figure 4: Machining Teflon parts with vacuum clamping

Figure 4 shows a Teflon plastic part with dimensions of 26.85×9.82×3mm. The part is small and features chamfered edges and two through-holes. So the traditional clamping methods are ineffective during the machining. However, by using a vacuum clamp, several parts were arranged into a single thin sheet. Not only it avoid deformation, but also allowing for stable quality, high efficiency, and ease of operation.

Conclusion

Vacuum clamps use negative pressure to hold workpieces, offering convenience, reduced human operation, and increased productivity. When designing a vacuum clamp, factors like the size of the contact surface, suction force, and seal integrity must be carefully considered to avoid air leaks during machining.

Like any other workholding method, vacuum suction has its limitations. Understanding various workholding techniques and machining principles is key to developing the optimal clamping strategy for any product.