Cutting metal with a waterjet machine offers many benefits, such as no heat-affected zone, the ability to cut exotic materials that are difficult to saw or machine, and a reduction or elimination of secondary operations to prep material for welding.
But waterjet does have a drawback. It’s slow, at least in comparison to other technologies, especially laser cutting. However, adding additional cutting heads to a waterjet system can help solve the technology’s too-slow problem.
Toymaker YOXO increased its productivity with a 10 cutting head Jet Edge waterjet shuttle system.
Pump it up
Deciding whether to purchase a waterjet with multiple cutting heads or add a head to an existing waterjet comes with many considerations. Pump size is one of them. Adding a cutting head requires increasing pump capacity. At a given pressure and orifice size of the head,a certain gallons per minute (gpm) rate is required. When you multiply that rate with multiple heads, depending on the number, the water rate grows in correlation to that, so the size of the pump has to be larger.
“Often, a single cutting head may require a 30-hp or 50-hp pump, given the orifice size used in the cutting head,” says Scott Wirtanen, Northeast regional sales manager for Jet Edge Inc. “When you increase the number of heads, you have to increase pump size.”
Trevor Burns, director of production for YOXO, demonstrates how to maneuver the Jet Edge waterjet shuttle.
When deciding on the pumps’ horsepower, the No. 1 issue is the application. What material is being cut and how thick is it?
“If the material is 2-in.-thick stainless steel, you want to put more water and abrasive into that cutting area to remove the material faster,” Wirtanen says. “With that single head, you’re going to require a 50-hp pump. When moving to the second head, you’re going to add 50 hp.”
In this scenario, as the number of cutting heads increases, the horsepower required doubles, so four heads, for example, require 200 hp. This means one larger pump or multiple pumps need to be integrated, depending upon the total number of heads.
Users must also consider the footprint of the overall system. It is not just fitting the water system, but the pumps that propel the water through the system. The closer the pumps are to the waterjet gantry, the better, because there’s a certain pressure loss per foot through the high-pressure tubing from the pump to the machine. Wirtanen adds that the pumps should be positioned no greater than 100 ft. away from the gantry.
A Jet Edge High Rail Gantry waterjet system with two cutting heads and a pneumatic drill for pre-piercing material that is sensitive to delamination.
While the actual cutting isn’t being performed any faster, having multiple cutting heads operating in tandem, attached to a gantry and cutting along the same X,Y axes, is what drives up productivity. To make this process easier, software can be used to nest parts to get the most from a single sheet of material. “Our software is designed specifically for waterjet applications,” Wirtanen says. “We are able to easily accommodate different numbers or combinations of heads, so that when we’re producing a nest, we’re simply inputting the total number of heads.”
Swapping runs of parts is also made easier with this software. If a user has a family of parts with a number of different combinations of parts, the cutting heads take care of the maximum number first, and then shut off automatically as needed to finish up the smaller number of parts.
Software can also aid when subsequent part runs have different parameters such as material thickness and type. To adjust for these material differences, the software can automatically adjust feed rates.
“As the user switches between different materials and thicknesses, there are associated feed rates to achieve the desired quality,” Wirtanen says. “For instance, cutting ¼-in. stainless steel is going to process much faster than say, 3-in. stainless steel, which would be much, much slower. As opposed to a user manually inputting the feed rates to process different materials, the software prompts the user to input the type of material, thickness and desired edge quality, and it automatically generates all of the straight line feed rates, and also all of the proper cornering and handling of the different cutting needed for that part.”
When utilizing multiple cutting heads, the amount of material and finished products to be loaded and unloaded increases. To better handle these goods, users can add shuttles to these waterjets. These systems can be automated or manual and are designed to reduce load and unload times. “The shuttles,” Wirtanen says, “provide a work surface that allows the operator to unload cut parts, and slide in a new plate underneath the heads so that they are always cutting even while the operator is loading or unloading a second plate.”
Jet Edge’s iP60-150 hydraulic intensifier pump for multiple cutting head waterjet is a 150-hp, 60,000-psi pump that produces up to a 3.2-gpm maximum flow rate.
Typically, when talking about cutting metal with water, it is actually a combination of water and abrasive. To accomplish this melding, hoppers containing the abrasive are used to input it into the water stream. With multiple cutting heads, the unit requires a bulk hopper that feeds the abrasive to mini hoppers positioned above each head. These mini hoppers control the amount of abrasive that is introduced into the water stream. “As you’re processing thinner materials, you may use less abrasive as opposed to thicker materials, where you would use more,” Wirtanen explains.
To understand this process, Wirtanen says that the stream is analogous to “putting your thumb on the end of garden hose and producing a jet of water. We’re forcing a volume of water through an opening that could range from 0.010 in. up to 0.015 in.”
The orifice constricts and produces the waterjet stream. From there, the abrasive is fed into the individual cutting heads. That mixture of water and abrasive is generally introduced into a mixing chamber and below the mixing chamber is a nozzle, approximately 3 in. or 4 in. long and three times the inner diameter of the orifice. “If the orifice is 0.010 in., the inner diameter of that nozzle is going to be 0.030 in., and that nozzle is what keeps the combination of water and abrasive in a tight, columned cutting stream,” he says.
In terms of maintenance, users should expect to replace the orifice anywhere between 800 hours and 1,500 hours of operation. The mixing chamber should last somewhere around 75 hours to 100 hours. When using multiple cutting heads, Wirtanen suggests changing the components at the same time so that they generally wear at the same rate.
The Jet Edge Edge X-5 5-axis waterjet in use at Jacquet, a metal processing company with six locations in the U.S.
Saving water and more
Reclaiming water might also be a consideration. Typically, this means disposing of the water as a company would dispose of its used, non-hazardous industrial water, through a sewer system. “There are two instances that the user may need to recover the process [cutting] water,” Wirtanen says. “The first is if the shop simply doesn’t have a drain to send the water down, then a closed-loop water filtration system is used to recover that water. The water is filtered, cleaned, deionized and sent back through the pump.”
The second instance is if a user is cutting a material that would become hazardous from the fines, which are the small particulates that are produced when cutting the material. “For instance, if a user is cutting a high-nickel alloy all day long, that water becomes hazardous and cannot be sent down the drain,” Wirtanen says. “It must go through a closed-loop water filtration system.”
These are just a few of the issues to consider when deciding on a waterjet system, and whether to invest in multiple cutting heads. When considering whether to go with multiple heads, users may think they shouldn’t because they only need the waterjet to cut small runs of parts or that the cost would be too great. However, according to Wirtanen, the cost to add an additional head is only about 10 to 15 percent of the machine’s cost.
“The way that I like to explain it to my customers is that upgrading to a system with a second cutting head will double their production, and the cost for this is minimal. Even if it’s a short run of parts, you’re getting that short run off the table and completing the job quicker,” Wirtanen says. “To me, it always makes sense from a math standpoint. Being that it’s only 10 or 15 percent of the overall investment to double your production, why not?”