Chip Control: A Readers’ Digest Version
- August 30, 2021
Recommendations on chip management from the experts
Chip control is a key attribute of stable, predictable and efficient processes. Achieving it, however, remains elusive for many shops, which is why we’ve collated the following list of tips and techniques from the experts on breaking, blasting, and carrying away all that productivity-busting swarf. It’s by no means complete, but should be a good start to help anyone struggling with bird’s nests and chip recutting improve their machining processes.
Randy McEachern, a product and applications specialist for holemaking and tooling systems at Sandvik Coromant Canada In., says that effective chip management in drilling operations depends on a number of factors, but starts by looking at the chips. With most indexable drills, there’s only one insert working at the nominal diameter, and this should produce a cone-shaped chip, with chips shaped like “Cs or 6s” coming from the peripheral insert(s).
Solid carbide or exchangeable tip drills, on the other hand, provide a more balanced cutting action that produces similar chips from both flutes. In either case, it’s imperative that machinists “drill one or two holes, stop the process, review the chips, check the hole size and finish, then make any required changes to the drilling process.”
An article McEachern wrote for Shop Metalworking Technology (find it at: https://shopmetaltech.com/machining-technology/cutting-tools/managing-your-chips.html) provides a host of timeless advice on ways to achieve these desirable chip shapes, extend drill life, and improve hole quality.
Milling is a big topic in any shop. Unfortunately—at least for job shops and others that machine a wide variety of materials—effective chip management might require investment in material-specific cutting tools. “Selecting the right geometry is dependent, in part, on the material you’re cutting,” says Tim Aydt, product manager for indexable milling tools, Seco Tools Inc. “When you consider different materials, each require different geometry forms for different types of operations you’re performing in a machine.”
Alyssa Walther, applications engineer for milling products at OSG USA In., says advanced flute geometries are ground into many cutting tools because of their ability to curl and cut chips more effectively for better chip evacuation. “The design of a flute dictates how well the chip curls,” says Walther, “Chip curl is important because you don’t want chips to stick to the tool. The correct flute form helps you to achieve a smoother curl, generate less heat, and throw the chips out faster.”
Cut thin to win
Aydt speaks to the importance of cutting tool lead angles in milling and turning operations: “If you’re taking a 3 mm depth of cut with a tool with a 90° lead angle, 3 mm of that edge is in the cut,” he says. “But if you take a 45° lead angle at the same depth of cut, more of the insert is engaged in the cut at this angle than the 90° one. So you have thinned out the chip with the 45° lead angle so the average chip thickness starts to go down, which means you can increase the feed rate.”
“This is the basic principle behind high feed milling,” adds Tungaloy Canada’s general manager, John Mitchell. “Due to the lead angle, a typical high feed milling cutter will produce an average chip thickness of less than 20 per cent of the programmed chip per tooth, calling for extremely high feed rates.”
Lumps and bumps
Of course, there’s little chance without the correct chip-breaker, either, according to Kurt Ludeking, director of marketing for Walter USA. He explains that effective chip control often comes down to proper placement of bumps and waves on the surface of the turning insert. “These serve to fold the metal, cold-working it into a shape that causes it to break away,” he says. “A specific amount of edge rounding is also needed, to reinforce the cutting edge according to the cutting conditions. A roughing insert, for example, requires a stronger edge than a finishing insert, and therefore requires additional honing.”
Gary Kirchoff agrees, but suggests that selecting the wrong chipbreaker is often just as bad as no chipbreaker at all. “It’s very important to choose a chipbreaker designed to effectively curl and break the chip,” says Kirchoff, a product specialist at cutting tool manufacturer Dormer Pramet. “If the depth-of-cut (DOC) and feedrate are proportioned correctly to the width of the T-Land and chipbreaker groove, the material enters the groove and is curled properly. The chip is broken and the chipbreaker does its job. But if the T-Land is too wide, or a DOC and feedrate too small in relation to it, the material does not reach the chipbreaker groove, and it cannot do its job.”
Enough, but not too much
As hinted at earlier, stocking all these different geometries, grades, and chip-breakers can be a pain for shops that machine aluminum one day, carbon steel the next, and superalloy the day after that. Walter’s Ludeking says not to worry. “Most cutting tool suppliers can suggest four or five geometries that will handle 90 per cent of applications pretty well. For the rest, a few feed and speed tweaks should do the job,” says Ludeking.
David Vetrecin, holemaking product manager at Iscar Tools Canada, says he can appreciate concerns over too many part numbers in the tool crib. Aerospace, mould and die, and especially automotive shops typically cut the same kinds of materials on a constant basis, however, making it easier to streamline the number of inserts in stock while still achieving maximum performance and reduced cycle times. “However, many of the job shops that have a variety of materials at any given time want a general purpose insert to keep inventories low,” he says. “This can create a balancing act between performance and cycle time vs. carrying inserts in stock to accommodate a specific material.”
Vetrecin reiterates that a little feed and speed tweaking can go a long way towards effective chip control, even when the chipbreaker is less than ideal. Shops that cut titanium, however, should take care. “TiC and TiN inserts use titanium as one of the ingredients in their coatings. This is why Iscar recommends an un-coated insert for this material and has seen up to three times the tool life as a result,” he says. “That said, small adjustments in feeds and speeds can improve chip control and tool life, but there is still no replacement for using the proper insert for a material.”
Iscar, Walter, Sandvik—indeed, most cutting tool manufacturers—offer toolholders with built-in precision coolant channels. These are effective at chip-breaking, especially when high pressure cutting fluid is applied. “Consider superalloys, where you not only need a very strong, sharp cutting edge, but also a geometry that can cold work the metal enough to make it break away,” Ludeking says. “Without it, you’ll end up with a giant bird nest of chips. This is one area where toolholders with integrated coolant really shine, as they remove heat very effectively from the cutting zone.” “Apart from better chip control, we’ve seen a substantial improvement in tool life and productivity—up to 150 per cent in some cases.” That’s according to Abhay Chaubal, product manager for North America at Seco Tools LLC, who recommends cutting fluid pressures of at least 300 psi to be effective, with 1,000 psi more than sufficient for most applications. “However, even with the low-pressure pump that comes standard on most machine tools, precision coolant delivery provides a host of benefits. These include less built-up edge (BUE), as well as reduced flank wear, chipping, and deformation.”
Fast and furious
Ron Parker, national product manager for high pressure coolant systems at LNS North America, says the traditional low pressure approach to cutting fluid delivery is “unacceptable,” providing little to no lubrication in the cutting area, extreme and inconsistent temperatures, and inefficient chip removal. “Flood coolant typically turns to super-heated steam before it can reach the tip of the cutting tool. The result is poor tool life and potential damage to the workpiece.”
At pressures of 1,000 psi (70 bar) or higher, cutting fluids can reach the work zone and get forced into the area between the cutter and workpiece. Not only does this increase lubrication where it’s needed most, but the lower temperatures eliminate the “steam effect” while also shortening the chip’s shear zone, which helps to break them up. Chip evacuation becomes easier, tool life improves and grows more predictable, and feeds and speeds can generally be increased, leading to higher productivity.
Bill Fiorenza, die and mould product manager for Ingersoll Cutting Tools, is a big advocate of education for cutting tools. “When customers are looking for chip management or require extended reach applications, I usually suggest a particular insert in our milling line to begin with. The reason I do this is because you have to learn how a cutter performs, since all cutter geometries perform differently in milling applications,” he says. SMT