Abrasive Waterjet Cutting
Abrasive waterjet cutting utilizes a high velocity coherent stream of water and abrasive that can be used to cut almost any materials. Water at 40,000 to 60,000 psi accelerates through a sapphire, ruby or diamond orifice. The stream passes through a mixing chamber where a vacuum, induced by the stream, sucks in abrasive. Momentum of the water stream accelerates abrasive as it passes through the nozzle.
The stream exits the nozzle as a three phase mixture of air, water and abrasive particles with a cutting diameter of 0.020" to 0.060". The high velocity abrasive particles impact the kerf face and do the actual cutting. Kerf material is removed as microchips, with no negligible affects on the material. The cutting stream carries 0.5 to 1.5 pounds per minute of abrasive. The cut diameter, as well as the quantity of abrasive is dependent on the cutting stream size, which is selected based on the material to be cut. Garnet is by far the most commonly used abrasive. It is an environmentally clean process, containing no free silica, it combines cutting ability with reasonable wear on the consumables. Other less commonly used abrasives are olivine sand, silica sand and slag by-products. The above emphasized characteristics make abrasive waterjet make it a successful, cost effective method for processing metals, rubbers, plastics, and more. See our material selection page for help when trying to decide between the different cutting methods.
To see a complete list of key terms and definitions, visit our manufacturing glossary page.
Benefits of Abrasive Waterjet Cutting
Abrasive waterjet offers many advantages not found in other cutting techniques, such as:
- No heat affected zone (HAZ)
- Low contact force of cutting stream
- No distortion and warping
- Burr-free parts
- Near net shape cutting eliminates secondary operations
- Can achieve high accuracies of up to +/- 0.001"
- Material thickness of 0.0005" to 12" can be processed
- Small kerf width allows for tight nesting and optimal material usage
Most Commonly Cut Materials
Materials that are reflective, conductive, heat resisting, or heat sensitive are ideal candidates for abrasive water jet cutting. As the material thickness increases, abrasive waterjet becomes the preferred cutting technique, especially where accuracy must be maintained. Heat sensitive and heat resisting materials such as stainless steel, alloy steel, titanium, inconel and hastelloy can be cut with no material effects. Some distortion may occur due to the residual stresses already present in the material. In thicker materials (over ¼") the edge finish and cut accuracy are superior to heat cutting methods. There is no burr or dross that may require secondary operations. Conductive materials such as aluminum and copper also cut well. Abrasive waterjet cutting is the superior cutting method for aluminum because of its high cutting speed. Since abrasive waterjet is a mechanical cutting process, materials of low hardness and density cut faster.
Reflective materials such as polished stainless steel and polished brass are cut without discoloration along the cut, though there may be slight frosting along the cut. This is usually not significant enough to require masking. Hard plastics are also good candidates for abrasive waterjet cutting. Polycarbonate (LexanTM) is an excellent cutting application since it can be cut without edge discoloration, as seen when cut by laser. Acrylic (PlexiglassTM) can be cut but it is prone to chipping during piercing. Soft plastics, foams and rubbers can be cut with no abrasive in the cutting stream, known as non-abrasive waterjet cutting.
Other materials that are brittle such as stone, ceramic and glass can be cut. Piercing may cause chipping which can be alleviated by piercing at reduced pressure. Abrasive waterjet cutting of inlaid patterns with stone is a growing market for businesses and residential homes. The results are beautiful and unique.
Typical Applications for Abrasive Waterjet Cutting
Abrasive waterjet has the ability to cut almost all materials and thicknesses. Most applications of abrasive waterjet are for cutting of specialty materials such as stainless steel and aluminum. Its flexibility makes it useful for all applications. The following is a list of applications where waterjet is the best cutting method:
- Shape cutting of ¼" and thicker aluminum
- Net size cutting of ½" and thicker stainless steel
- Blank cutting of parts for final machining
- Short run lots of sheet metal parts
- Screen cutting
- Converting plate stock to bars
- Precision cuts in ½" and thicker mild steel
- Hardened materials
- Intricate shapes in delicate materials
- Custom shims in stainless steel and exotic materials
Cut Geometry
Abrasive waterjet cuts have straight edges with a slight amount of taper. Kerf width is controlled by the orifice/nozzle combination. Cuts in thicker materials generally require larger combinations with more abrasive usage. The kerf width can be as small as 0.020" for thin materials and up to 0.055" in thick materials.
The minimum inside corner radius is controlled by the nozzle diameter and therefore is 0.010" to 0.030". Inside corners may have digs on the bottom of the cut in thick materials. This is due to the exit of the stream lagging behind the entrance side of the stream and can occur as the jet exits from corners. Reducing the feed rate or adding a radius of at least 0.5" can eliminate this in thick materials.
The abrasive waterjet can pierce or drill holes smaller than 0.060" diameter. Interrupted cuts can be performed if the distance between the top and bottom layer is less than 1.5". For example 1.00" OD x .125" wall 304 tubing can be cut to length. The benefit of this approach is that there are no burrs as there would be with saw cuts.
Cut Quality (Kerf and Taper)
Cut quality describes the kerf edge and taper, and the feed rate controls the amount of jet lag. Cutting speed and edge quality are directly related. At high feed rates, the jet has increased curvature as it passes through the cut. Reduced cutting speeds can result in a good edge finish of 125 microinch, having a ground appearance and minimal taper. High feed rates for separation cuts give striations through the full cut depth. Edge quality is defined with a scoring system with the numbers 1 through 5.
| Edge Quality | Cut Appearance |
|---|---|
5 |
Excellent, no striations, most accurate |
4 |
Very good, minimal striations |
3 |
Good, striations on bottom half of cut, most commonly used |
2 |
Fair with through striations |
1 |
Poor and rarely used |
Edge Taper and Total Part Accuracy
The following chart gives part accuracy and edge taper per side for
high accuracy (Quality=5) and normal accuracy (Quality=3) feed rates.
| Material | Edge Taper | Part Accuracy | ||
|---|---|---|---|---|
| Thickness | Quality=5 | Quality=3 | Quality=5 | Quality=3 |
| 0.12 | 0.002 | 0.005 | +/-.003 | +/-.005 |
| 0.25 | 0.0035 | 0.0075 | +/-.005 | +/-.010 |
| 0.5 | 0.003 | 0.01 | +/-.007 | +/-.005 |
| 0.75 | 0.0035 | 0.012 | +/-.010 | +/-.020 |
| 1 | 0.004 | 0.014 | +/-.015 | +/-.030 |
| 1.5 | 0.006 | 0.016 | +/-.020 | +/-.040 |
| 2 | 0,008 | 0.018 | +/-.025 | +/-.045 |
| 3 | 0.01 | 0.02 | +/-.030 | +/-.050 |
| 4 | 0.012 | 0.02 | +/-.035 | +/-.055 |
Comparing Abrasive Waterjet Cutting to Other Cutting Methods & Techniques
Abrasive waterjet cutting is an important, no-heat shape cutting technique. Generally, it cuts with higher quality than heat cutting methods and with less cost and quality than electrical discharge machining (EDM). The following are key points of comparing abrasive waterjet to other cutting techniques:
- The accuracy and edge quality of abrasive waterjet cutting is similar to laser for thin sheet metal and superior to all other shape cutting methods, except electrical discharge machining (EDM), in thick materials.
- Abrasive waterjet cutting is slower than heat cutting techniques in non-conductive materials and similar for conductive materials like aluminum.
- Abrasive waterjet has almost unlimited thickness capability whereas high powered plasma is limited to about 2" and laser to about 0.75" thick.
- In steel and stainless steel, for thicknesses where they compete, the cost per inch of cut for abrasive waterjet is higher than laser and plasma because of its lower cutting speed and higher cost of operation.
- Abrasive waterjet does not create a burr or HAZ as the heat cutting processes do. This saves customers the expenses of secondary operations.
Good abrasive waterjet applications take advantage of its unique capability to cut with high accuracy without using heat. These applications justify themselves based on high part quality and the elimination of secondary operations. When all the costs are factored in, abrasive waterjet cutting is the most cost-effective solution for many different applications.
