by Kip Hanson
Still using copper lines and modular plastic tubing to keep turning tools cool? It’s time to lose the hoses
CNC turning is challenging enough without worrying about cutting fluids. All it takes is one stringy chip wrapped around one of those flexible plastic hoses to make today a really bad day as coolant goes flying everywhere, the turning tool burns up, the workpiece morphs into your newest paperweight. Copper lines are more predictable, although these can eat up precious machine time as the operator struggles to get them aimed in just the right direction, or digs in his or her toolbox for the perfect length of tubing. Isn’t there a better way?
As it turns out, there is. A number of cutting tool providers have addressed this all too common problem with internally-plumbed turning tools that not only direct coolant in an accurate and reliable manner, but do so from both sides of the tool simultaneously. What’s more, they support another critical component of modern cutting fluid application—high-pressure coolant (HPC).
Someone call a plumber
Iscar Tools Inc., for instance, offers its Jet-Cut High Pressure tooling technology with frontal (under) and external (over) coolant ports. Ashok Guruswamy, product manager of Grip/Turn/Thread for Iscar Canada, says cutting fluid—properly applied—has a positive influence on chip formation. When metal is being cut, he explains, temperatures often reach 500° to 900º C (932° to 1652º F); by reducing or controlling this heat, chips become more ductile and easier to break.
Lowering temperatures at the cutting edge also protects it from thermal shock and breakage, while inhibiting flank wear. Furthermore, the shorter chips will not tangle around the tool, workpiece or machine components, thereby improving workpiece surface quality and further reducing machine downtime. The result? Significantly extended insert life, lower manufacturing costs and more predictable processes.
“Cutting fluids are essential to most machining applications, but particularly so with parting off and deep grooving operations,” Guruswamy says. “In this instance, coolant applied to the top of the insert loses its effectiveness as the tool plunges deeper, but if you can deliver it through a “frontal” port underneath the insert, coolant can reach the work zone regardless of groove depth. This is why we provide both upper and lower coolant ports, so that machinists can determine which will be most successful for any given situation.”
The pressure’s on
Whether grooving, threading, parting or turning, he adds, effective cooling can mean the difference between profit and loss, and one of the best ways to achieve this is with HPC. This is especially true with difficult to machine alloys such as Inconel, titanium, Hastelloy, Monel and others.
These nickel and chromium-based materials tend to form built-up edge (BUE) due to their elastic, sticky and ductile properties, and machining them without accurate HPC delivery is nearly impossible, as the high temperatures and BUE can otherwise cause instantaneous wear and premature failure for carbide inserts. “By using HPC with Jet-Cut High Pressure tooling, we’ve seen up to 200 per cent increases in cutting speeds in these and other alloys, as well double the tool life, greatly improved chip control and safer, more stable processes,” says Guruswamy.
Iscar’s not alone. Sarang Garud, product manager for Walter Tools USA LLC, offers several reasons why it’s important for shops to upgrade their outdated cutting fluid delivery methods. “With Walter’s precision cooling turning, grooving, and parting tools, the coolant is introduced very near the actual cutting zone, so there’s no loss of pressure by the time it reaches the workpiece,” he says. “The overhead port is responsible for cooling and lubricating the insert’s rake face, while the lower port cools the clearance face and assists with chip breakage and evacuation.”
A high bar
Garud notes that with precision cooling, the fluid is always aimed directly at the cutting zone; this is not always the case with external coolant, or internal adjustable jets that don’t utilize over and under technology. In either case, proper aiming depends on the operator’s skill, and his or her remembering to adjust the nozzle during setup. If either of these fails to occur, or if the depth of cut and other machining parameters change, internal coolant becomes ineffective. “With precision cooling, these adverse situations are avoided, since the coolant is always directed at the cutting zone by design,” he says.
Like the others named in this article, Garang is a strong proponent of HPC, recommending at least 10 bar (150 PSI) and up to 138 bar (2000 psi) for maximum performance. He also recommends using inserts designed specifically for precision coolant flow. “We’ve introduced new ISO turning insert geometries with features on the rake face that act as coolant channels, helping to guide the high-pressure coolant and better target the cutting zone,” he says. “This leads to superior cooling of the insert edge, increasing tool life up to 100 per cent or more.”
Sandvik Coromant product and industry specialist Kevin Burton agrees, listing off numerous examples of process improvements made possible with one of the tooling provider’s precision coolant solutions, especially when HPC was used: a customer cutting grooves in 27MnCrB5-2 (a type of wear-resistant steel) saw tool life jump from 90 to 219 pieces with a 23 per cent reduction in cycle time. Another more than quadrupled tool life to 670 pieces per edge by using precision coolant when parting 304 stainless steel. Still another enjoyed double the tool life, 50 per cent higher cutting speeds and no more problems with chips sticking to the top of the insert while cutting 8-pitch threads in 400 series stainless.
Pouring on the coals
Despite these success stories, Burton says precision coolant and HPC aren’t always a case of “more is better.” Depending on the cutting conditions, material and specific failure modes, turning off the upper or lower (or even both) might provide better results. This is why it’s important to find a tooling system that’s flexible, with multiple ways to quickly and securely plumb its various ports. It’s also important to find a qualified application engineer or technical sales person who can explain how to most effectively use over and upper coolant (or better yet, attend a training session) so as to achieve the desired results.
That said, Sandvik Coromant’s and its competitors’ high performance coolant systems almost always provide unprecedented opportunities for process improvement. The ability to replace unpredictable and ineffective hoses and lines with high pressure, accurate and easy-to-use cutting fluid delivery systems is a game-changer for anyone doing CNC turning.
“Practically every aspect of turning is greatly improved, including chip control, tool life, productivity and part quality,” says Burton. “There’s no more time lost adjusting or bending hoses, so machine utilization is better. Perhaps most important of all, the process becomes much more predictable and secure. Considering the relatively small investment in new toolholders and a high pressure pump—an investment that’s often recouped in months or even weeks—there’s simply no reason not to pursue a precision coolant solution.” SMT
