Optimizing your waterjet production

Review best practices to ensure you get the most from your technology

Some software from OEMs includes stack height calculators that determine what the optimal stack size is for producing the most parts of a given material in the least amount of time.

The best abrasive waterjet machines on the market are designed for rigorous machining. A combination of meticulous mechanics, rigid construction, and velocity control from the software ensures the highest degree of repeatable precision in the machined parts. However, even with all that built in, you can hone the machining process further by using your waterjet to the best of its abilities.

All waterjet users can benefit from reviewing best practices to improve their results with the technology. Many of these considerations may seem basic, but it’s the fundamentals that make or break the efficiency of waterjet machining – and it’s never been easier to find tips and tricks to optimize your waterjet.

Physical Materials Optimization

Garnet. Abrasive is the biggest cost when it comes to operating a waterjet. Some bigger shops go through a semitruck load of abrasive every day. But using too much garnet is just wasting money and using too little is wasting time.

The operator sets the garnet flow rate based on the size of the machine’s nozzle orifice and mixing tube diameter. Whatever the garnet flow rate is set to, it will remain constant throughout the entire cut without specific programming. Generally, the higher the flow rate, the quicker the separation speed. This sounds counterintuitive since we are discussing reducing garnet use, but the key is to have greater control over separation speeds.

Using empirical data gathered through comprehensive testing, software can adjust the jet stream for whatever process is occurring at every single point along a toolpath. Using better computing processing power and a stronger understanding of corners and motion control, software allows for faster cutting and significant cost savings on water, electricity, and garnet usage. For example, while a 94-KSI intensifier pump with conventional control software can cut a 40-in. toolpath in 50 seconds using 1 lb. of abrasive, better software paired with a 60-KSI direct-drive pump takes only 41 seconds – and 0.68 lb. of abrasive – to cut the same path.

Mixing Tubes. The mixing tube on an abrasive waterjet is made from a high-strength composite carbide, but anything will wear with 60,000 PSI of abrasive running through it. To maintain the precision of finished products, you should change out your mixing tube every 45 to 80 hours. However, even with expected mixing tube use intervals, the accumulated barrelling will cause the jet stream to grow and deform, causing the kerf to widen. This will result in an elliptical shape that causes the tool offset to vary by a few thousandths of an inch (hundredths of a millimeter), depending on the orientation of the stream shape to the tool path. Rotating the mixing tube by 90 degrees for every eight to 10 hours of cutting allows the mixing tube to wear more evenly and last longer.

Cutting test parts and doing kerf checks on a regular basis allows you to see when cutting performance begins to degrade – provided you always measure with test parts cut using the same cutting quality and material as the actual part. If not enough material is being removed (hole too small or part too large), decrease the tool offset by half the dimensional error observed. If too much material is being removed, increase the offset by half the dimensional error. If the part has many intricate geometries, expect that the kerf will be slightly wider because of slower cutting while decelerating into corners.

Slats. Slats are the stainless steel plates that support materials being machined in an abrasive waterjet. Because waterjet users tend to place parts to be cut on one area of the table – such as the corner closest to the waterjet’s controls – slats will develop uneven wear over time, causing material to rock on the slats during machining. To ensure accurate cutting, it is important to maintain your slat bed.

You can greatly extend the working life of removable slats by periodically rotating slats as they erode over time. Weakened or severely worn slats and slat holders should be replaced. They may be flipped horizontally or vertically or moved to a different area of the table entirely. Create a schedule to inspect and rotate the slats at least once a month. New sets of galvanized steel slats can be ordered directly from the waterjet’s OEM.

Abrasive is the biggest cost when it comes to operating a waterjet. Some bigger shops go through a semitruck load of abrasive every day. But using too much garnet is just wasting money and using too little is wasting time.

Software Features for Optimization

Monitoring. System monitoring software enables you to connect operation controls with machine maintenance and upkeep for increased efficiency and reduced downtime. Some programs run in parallel with a machine tool’s controller software using MTConnect to maximize productivity. A good system monitoring and alert system allows fabricators, system designers, and service technicians to tailor the behaviour and experience of the software to their needs and application. Supervisors and maintenance staff receive automatic notification of important events to reduce downtime. Purchasers gain the data to maintain a lean but reliable inventory of spare parts. Operators can manage multiple machines more easily.

This level of flexibility makes it easy to meet your shop’s needs. In addition to the predefined maintenance schedules that OEMs may set, you can add your own maintenance tracking items, such as reference metrics like “pump hours” or “jet cycles,” or set up alerts for events like exceeding a certain weight threshold or if a certain number of hours remain before a planned maintenance task. And rather than a hard-copy log next to the machine, the data can be accessed anywhere, allowing for remote maintenance monitoring and the sharing of data with service technicians.

Stacking. If you cut a lot of very thin parts, stacking the material may be beneficial, especially if there is a lot of rapid traversing or workpieces that require time-consuming fixturing. Stacking cuts down on setup time for very thin materials, reduces the amount of rapid traversing per part, and can prevent taper and burr formation on the workpiece’s bottom edge. Some software from OEMs includes stack height calculators that determine what the optimal stack size is for producing the most parts of a given material in the least amount of time.

The optimal stack size for a given material, thickness, and pump setup depends on a number of factors. If a path has a lot of corners, for example, the slowdown in cutting speed expected as the waterjet head moves around corners will be even slower as a stack gets thicker. For a part with few corners, a thicker stack may be more reasonable. For this reason, effective stack height calculators use the actual toolpath itself.

Abrasive waterjet machines can help to truly transform a shop’s operations, and they only become more effective with optimal maintenance and processes. OEMs can support manufacturers with holistic options that cover the entire waterjet process, from the initial cutting program to the completion of finished parts, which allows the technology to truly shine. With effective software and a waterjet operated according to best practices, shops will have an easy time achieving optimal results – and profitable part production.

When and if you need help to push you over the line in maintenance, education, or operations, many OEMs have begun to offer extensive online resources ranging from one-on-one help to proctored training sessions. There has also been a rise of social media forums where waterjet operators discuss trends and techniques. Please check them outas a wealth of waterjet information is out there, and most of it is free.

Joshua Swainston is marketing and communications lead, OMAX Corp., 21409 72nd Ave. S., Kent, Wash. 98032, 253-872-2300, www.omax.com.

Because waterjet users tend to place parts to be cut on one area of the table – such as the corner closest to the waterjet’s controls – slats will develop uneven wear over time, causing material to rock on the slats during machining.