Choosing the Correct Piercing Technique
Piercing material on a waterjet cutting system is often the first step in successfully creating a part. In order to maximize productivity and reduce costs, it is important to recognize the different types of piercing techniques and when to use them.
In one test cut, linear piercing was nearly 10x faster than stationary piercing.
Static piercing (also known as stationary piercing) is the most basic method of piercing with a waterjet. With this technique, the cutting head remains in a fixed position while the cutting stream works its way through the material. Although not the fastest piercing method, it is extremely useful due to the simplicity of programming and the fact that it creates the smallest hole when compared to the other piercing techniques. Static piercing should be used when:
- Cutting thin materials (<1/4”), as time savings using other methods would be negligible
- Creating holes with very small diameters (a static pierce will create a hole just slightly larger than the diameter of the cutting stream)
- Cutting valuable material in order to minimize the amount of scrap
Note: Static piercing creates a hole with a very small diameter, restricting the amount of water and abrasive that is able to get in and erode the material. For this reason, static piercing may not be successful on some thick materials. In these instances, alternative piercing methods must be used.
By adding slow, linear motion to the cutting head, a larger channel is created for the water and abrasive to get into. This allows the cutting stream to erode the material quicker. To achieve a successful linear pierce, a lead-in of about 0.2” is necessary. The short lead-in will ensure that the cutting stream has enough time to fully pierce the material before reaching the start of the cut. Linear piercing should be used:
- If there is sufficient room for a lead-in
- If the material is relatively inexpensive, as lead-ins can create more scrap
- If cutting many parts and a reduction in overall pierce time can lead to cost savings
Small, circular motion can be added to the cutting head to reduce pierce time. Circular piercing utilizes the same principles as linear piercing but with a different range of motion. This method is slower than linear piercing but creates less scrap material. Use circular piercing when:
- There is not enough room for a lead-in
- A relatively small hole is needed
- Working with expensive material
When working with brittle or composite materials, the initial impact of a standard pierce can crack or delaminate the workpiece. By lowering pump pressure during the pierce, the likelihood of damaging the workpiece can be greatly reduced. Low-pressure piercing can be used in conjunction with any of the other piercing methods to increase the efficiency of the pierce. Use low-pressure piercing when working with:
- Brittle materials such as glass, ceramics, and stone
- Materials that are at risk of delaminating, such as fiberglass, carbon fiber, or G-10*
Piercing carbon fiber.
*Note: Always perform a test cut to determine the viability of a low-pressure pierce. Depending on the composition of the workpiece, it is still possible for delamination to occur. To prevent this, a pneumatic drill may be used.
Most waterjet cutting systems can be outfitted with a pneumatic drill. The drill is mounted to the side of the cutting head and can produce consistent, accurate holes in many different materials. Most commonly these drills are used to prevent delamination in composite materials. Situations that would call for the use of a drill include:
- When processing composite materials that can be damaged by the waterjet piercing process
- When many precise holes are needed
Choosing the correct piercing method for your application can save time, material, and money. Many CAM programs have the ability to automatically implement various piercing techniques, but experimenting with different speeds and abrasive feed rates can often times optimize a pierce for maximum efficiency.
If you would like to learn more about the waterjet cutting process, contact WARDJet at (330) 677-9100 or visit www.wardjet.com/get-in-touch.