by Jim Barnes
Focus on the basics for profitable and productive grooving
Grooving is a well-established machining operation, but that does not mean everyone does it as efficiently as possible. Especially in the current economic environment, people may not be paying enough attention to the details.
“A lot of times when people think about productivity in a variety of machining processes, they think of cranking parts out and getting the job done. With grooving–like other processes–that will cause some issues. Changing feeds and speeds affects you in multiple ways,” says Eric Jenkins, senior applications engineer, Kyocera Cutting Tool Div., Hendersonville, NC.
Some shops increase speeds, planning to trade tool life for output. However, feeds and speeds affect chip control and quality. “If it’s too fast, too much heat goes in the material and some materials might get soft,” explains Jenkins. “It becomes a little more plastic and doesn’t break as easily.”
Others set speeds too low, trying for a better finish. That also causes chip control problems. “Instead of getting a clean cut, you cause the chips to drag through the cut and damage the finish,” says Jenkins. “You have to find that sweet spot, between achieving a high finish and maintaining chip control.”
“Some people actually clamp off the rpms with a G50 command,” notes Todd Hayes, technical specialist, Horn USA Inc., Franklin, TN. If a user has 8,000 rpm on a 32 mm Swiss machine and does not have the straightest bars, he could get a lot of noise–especially if the bar feeder is not aligned correctly. “So, a lot of people limit it to 4,000 or 5,000 rpm,” says Hayes.
Working with very small diameter parts, some shops are not getting the surface footage they need from their machines. “They’re not getting enough heat into the tool. People use inserts with advanced coatings, but they don’t realize they need a certain amount of heat for the coating to work properly,” says Hayes.
Part of the problem comes from older machines. “Some of [these shops] know they have limitations on rpms and machine accuracy, but they have to use the machines they have… They’re trying to get jobs in the door,” says Hayes.
The problem might be maintenance. “Inserts wear,” says Ken King, chief operating officer, Kaiser Tool Co. Inc., Fort Wayne, IN. “Is your toolholder in as good condition as you think it is? Did you crash the machine on another application? Are the headstock, tailstock and spindle still aligned? Start with the basics.” Even a new machine coming into the shop might not be perfectly aligned.
Rigid toolholding is essential and you have to spec the toolholder carefully.
For example, when a shop does deep grooves 10 or 20 per cent of the time, some users consistently use a holder with a deep reach. “They think, ‘I’ll never have to change my setup,'” says Jenkins. The downside? “When you have an insert that sticks out farther, that greater reach is not as well-supported,” he says. “It’s going to create chatter issues for 90 per cent of your grooves, just so it is available for that 10 per cent of the time that you need it.”
One trend is to cut deeper grooves with replaceable blades. “Grooving tools get crashed quite often. It’s just the nature of shoving a stick into metal,” says Jenkins. “Being able to replace the portion that holds the insert is cost-effective for the customer and permits some versatility from the manufacturing standpoint,” says Jenkins. “We can allow the use of multiple insert widths by changing the blade. That lets us swap out to either a wider insert or the same width insert, but with a deeper reach.”
Chip control can be problematic, especially in machining IDs Programming and tool geometry are keys to chip control.
“A lot of the geometries that we put in the faces of our grooving inserts actually thin that chip down and make it narrow. Not only does it break it up into smaller sections, it also keeps it from scratching or marring the finish on the flanks of the groove. It allows it to be washed out; you don’t have to worry about a piece of chip being caught in the groove because it’s the same size as the groove,” says Hayes.
Keep cutting load in mind. “Moulded chip breakers with unique contours are generally going to create more cutting force, as well. In terms of a smaller-diameter workpiece in Swiss applications, that can be a challenge,” notes Jenkins.
The toolpath is another factor. “With wider grooves and multiple plunges, the easy way to program is to start on one side of your large width and make successive passes, one on top of the other,” says Jenkins. However, that means you are mostly using one edge of your cutting tool. “It’ll affect your chip control, because you’re not really engaging the insert and allowing the chip breaker to function properly. You might just be using one side of it,” Jenkins adds.
“We recommend that users make plunges opposing each other. If your groove width requires three plunges– one on the left, one on the right, and one in the middle–you’ll get better tool life and chip control than if you make three successive passes, one on top of the other,” says Jenkins. This also helps the chip to curl as it is forced out of the groove.
The key to success with grooving “…is basics. Sometimes, the production environment takes you away from basics, because there’s a lot of pressure to get things done,” says King. SMT
Jim Barnes is a contributing editor. [email protected]