Cutting is a critical component of metal fabrication and machining. One method, waterjet metal cutting, offers advantages over other processes, depending on the project. This cutting method has become increasingly popular for metalwork due to its ability to cut complex shapes with minimal heat distortion and burring. Waterjet cutting provides many advantages for cutting thicker metals over traditional machining techniques such as laser or plasma cutting, including greater accuracy, improved edge quality, faster speeds, and no need for secondary finishing operations.
A waterjet used in metal fabrication is a CNC-controlled cutting machine with a table supporting the material and a gantry-mounted cutting head. Waterjet metal cutting uses a high-pressure water stream to cut through sheet metal. A high-pressure pump forces through a narrow, gemmed orifice. The orifice is typically made of diamond, ruby, or sapphire, which are highly resistant to heat, pressure, and corrosion and have a low coefficient of friction. This is critical because friction creates heat, and when coupled with high pressure, it could cause part failure or reduce efficiency.
The jewels also help to focus the stream down through the nozzle. If an abrasive is used to aid in the cutting process, the nozzle will have an inlet to let it flow in. the water stream rapidly accelerates the flow of the abrasive, which mixes with it. Whether or not abrasive is used, the water is forced out the tip of the nozzle and cuts the sheet metal. The water pressure is between 60,000 psi and 94,000 psi.
This cutting process offers a much higher level of precision than traditional methods due to its ability to precisely control the angle at which the jet hits the material being cut, resulting in more intricate designs without sacrificing accuracy or speed. It is up to four times more accurate than a plasma cutter. They can also maintain tight tolerances, which is critical for many applications.
One of the main advantages is that it is a cold-cutting process. Cutting processes that generate heat can create a heat-affected zone (sometimes abbreviated as HAZ). Plasma cutters, lasers, and torches create a heat affected zone because they cut by melting the material in a controlled manner. The heat-affected zone is the area of metal adjacent to the cut that is not melted but has had its microstructure and properties altered by heat-intensive cutting operations. The heat from the cutting process, followed by subsequent cooling, causes this change and can be recognized by color changes in the metal. The extent and magnitude of property change depend primarily on the base material and can have an adverse impact on the metal’s strength. Because waterjet cutting does not generate heat, parts come off the table in pristine condition with a smooth, clean edge.
Waterjet cutting is a highly versatile process. It is not limited to cutting on two axes, so it can cut any shape. Waterjets can cut materials from 1/16 inch to over 10 inches thick and just about any metal used in fabrication, including aluminum, copper, tin, stainless steel, titanium, and brass. Comparatively, laser cutters cannot be used to cut reflective materials like brass and aluminum.
Another advantage of waterjet metal cutting is that it does not generate hazardous waste or fumes like other processes. Additionally, material waste is reduced because the small kerf means less material is washed away during cutting, potentially allowing more parts to be cut per sheet or more material to be recycled.
The setup is fast, and starting holes do not need to be predrilled as the waterjet pierces the metal as part of its operation. When cutting with a waterjet, the piece is ready to go as soon as it is cut. There are no secondary processes. When changing materials to cut, there is no need to change gases or optics like other methods.
While the waterjet can cut nearly any material with a wide range of thicknesses, some limitations make other cutting options ideal. The pros and cons should be weighed when determining which cutting technique is used.
The inside corners will not be perfectly sharp and have a contour that matches the jet. This may not be significant but should be considered when designing the part.
The waterjet is most effective and cutting all the way through the material. If a partial cut is desired, it may be difficult to do it accurately.
The water doesn’t travel in a straight line through the metal. There are three types of tapers. V-shaped taper is the most common. It is wider on the top, where the force of the water is more powerful. Generally, the taper will be more pronounced with a faster cutting speed. Very slow speeds or very soft materials may have a reverse taper. The jet stream expands as it gets further from the nozzle and removes more material from the bottom. Really thick materials may have a barrel taper where the cut is wider in the center than in the top or bottom. However, tapers are barely noticeable on materials less than 1/8 inch thick, and modern waterjet machines often compensate by tilting the nozzle.
At CMD, we use a powerful 94,000 PSI waterjet that provides unmatched accuracy and speed – in fact, it is three times faster and more accurate than a conventional waterjet. While we use it to cut all metal over two inches thick, we can easily cut materials up to 12 inches thick. Depending on the application, we can run it with pure water or garnet abrasive and have the option of using a ruby, sapphire, or diamond jewel orifice.
When you need custom machining that includes cutting thick metals, we have the expertise to deliver to spec with a waterjet cutting tolerance of ±0.003”. Contact us for a quote on your next project.