The first thing they teach you in Sandvik Coromant’s Metal Cutting Technology course—right after they tell you that Sandviken means “the sandy bay” in Swedish— is that heat is what destroys a tool. So let’s begin our review of recent turning tool triumphs with advances in coolant delivery.
Cooling At The Cutting Edge
Done properly, 80% of the heat in a machining operation exits through the chip, with the rest split between the workpiece and the tool. While dry machining works in many applications, others require coolant for additional heat removal, chip evacuation, and lubricity. Walter USA LLC (Waukesha, WI) has introduced a new Walter Turn toolholder that delivers what it calls “precision cooling” in which internal coolant travels through the toolholder, comes up through the clamp, and jets right at the cutting edge. Kurt Ludeking, Walter’s director of marketing for its World West Region, explained that “this approach allows us to target the coolant more effectively and with better coolant pressure than other approaches. The farther your nozzle is back from the edge, the more a coolant jet fans out and loses pressure and effectiveness.”
He said it’s not a new concept, but “the difference is that the Walter design is very easy to use. It’s a standard D-style clamp with a single screw. Securing it with that one screw makes the connections to the coolant passages inside the toolholder. Operators like it because they index the insert the same way as with a regular D-style holder. There’s no difference in terms of the number of screws they have to deal with, messing with O-rings, none of that. It’s a very easy system to use.”
The system is so good that even relatively low pressure coolant systems deliver impressive results. “We’ve been telling each other in the industry that you need a coolant system in the high pressure range of 600 to 1000 psi [4137–6895 kPa] or more in order to see a benefit in wear resistance and chip control,” said Ludeking. “But most machines come with a coolant pump that delivers about 150 psi. This toolholder design improves chip control and boosts tool life 20 to 30% at 150 psi [1034 kPa], especially in austenitic stainless steels or superalloys. Even in normal steels like 4140 we’ll see improvements in tool life of 25 to 30% with coolant pressures as low as 175 to 200 psi [1210–1380 kPa].”
Ludeking said the toolholders have already achieved success in “all kinds of industries, from automotive to aerospace to general engineering. We’ve even put it into special tools for aerospace.” The toolholders are available for Walter Turn, Walter Capto (C4-C6) and Walter Cut ISO turning tools.
Over-Coolant, Under-Coolant, or Both?
Walter’s precision cooling system delivers both over- and under-coolant. The coolant that passes through the clamp hits the tool on the top for chip control. Another channel sends coolant from the bottom of the toolholder to the flank side of the insert, under the cutting zone, for heat removal via the coolant itself.
“There are always exceptions, but we find that adding under-coolant almost always helps increase tool life,” Ludeking said. “And if you don’t include over-coolant you don’t get any chip control advantages. Of course if you’re machining cast iron, you don’t need anything for chip control. But with most other materials in which chip control is an issue, top coolant really helps.” So Walter’s system is designed to cover the majority of machining circumstances, yet be extremely easy to use.
Sandvik Coromant (Fair Lawn, NJ) takes a somewhat more complex view of things, arguing that over-coolant may actually be detrimental when machining steel at higher rates. Specifically, it recommends only under-coolant when the feed rate exceeds 0.2 mm/revolution and the depth of cut (DOC) is larger than the nose radius of the insert. (In general, Sandvik Coromant recommends choosing a nose radius smaller than the cutting depth.) Under these conditions, over-coolant “might cause minor edge wear and increase crater wear in steel,” according to the company, adding that it might be difficult to evaluate this wear, which would lead to unpredictable and shorter tool life compared to using under- or external coolant. Conversely, if the DOC is either smaller than the nose radius or the feed rate is slower than 0.2 mm/revolution, using both over- and under-coolant is recommended, according to the company.
For example, in one automotive application (an outer CV joint) a Sandvik Coromant CoroTurn 300 insert with -L4 geometry was used to turn low-alloy steel (P2.1.Z.AN) with 3 bar (43.5 psi; 300kPa) of coolant pressure at a feed rate of 0.35 mm/revolution and a 2.5-mm DOC. While the CoroTurn (CT) insert delivered a 158% improvement in tool life versus an insert with -PF geometry, the same CT300 insert delivered a 200% tool life improvement using only under-coolant.
Linley Patterson, sales engineer, US Southeast Zone for Sandvik Coromant, said these guidelines are good starting points but “I’ve always found machinists and toolmakers push the envelope. The CT300 insert offers many possible variations to implement, including different radii and the -L4, -M5, and -M5W cross sections. Actual results depend upon actual operating parameters and the optimal solution is often not the obvious solution.”
Eight Edges, but Easy
Patterson said Sandvik Coromant’s new CT300 product has been a big hit for longitudinal and face turning of steel because it’s “easier to index and reposition than typical inserts and delivers 30% longer edge life for light- to medium-duty applications.” On top of that, it has eight cutting edges. The idea is to reduce the number of inserts you need to inventory and to decrease the amount of carbide per cutting edge, which reduces waste. Like Walter’s new toolholder, the available toolholders for the CT300 deliver both under-coolant and over-coolant. But if you determine you want only under-coolant you remove the set screw plug from the tool and replace the coolant nozzle. For over-coolant only you must remove the under plug and replace it with another special plug.
The CT300 family is available in insert grades GC4325 and GC4315 with Sandvik Coromant’s new Inveio coating, another big reason for the tools’ excellent heat transfer and wear resistance.
Super-Hard New Coatings Only a Chemist Can Pronounce
The new grades with Inveio coating have a carbide substrate, a layer of titanium carbonitride (TiCN), a layer of aluminum oxide (Al2O3) and a layer of titanium nitride (TiN). According to the company, the crystalline structure within the layer of aluminum oxide is unique in that the crystals are arranged “unidirectionally with the longest facets in a near parallel position. In addition, all of the crystals are oriented with the densest atomic plane toward the cutting surface. This ‘heads up’ orientation makes the aluminum oxide layer very hard, allowing it to resist wear exceptionally well.”
According to John Winter, Eastern US product manager for Sandvik Coromant, “the plane near the surface is very dense and deflects heat into the chip and coolant. At the same time, the heat that is absorbed by the insert is conducted to the less dense planes near the TiCN coating. The heat dissipates into this layer and the substrate underneath. By preventing heat buildup, the surface of the insert doesn’t get hot enough to lose its shape. In other words, we’ve prevented plastic deformation.”
Producing inserts with Inveio requires advanced control of the chemical vapor deposition (CVD) process that forms each layer of the coating. According to Sandvik Coromant, “the structure of the carbide substrate features a cobalt-enriched surface gradient zone that acts as a thin outer layer that is slightly softer than the inner core. This provides an impact-absorbing ‘padding’ for the coated layers. The inner core of the substrate however, retains its tough, wear-resistant properties derived from the fine grains of tungsten carbide and cobalt binder.”
For its part, Walter just introduced a new insert grade that uses High Power Impulse Magnetron Sputtering (HiPIMS), a new version of physical vapor deposition (PVD) coating that imparts a very smooth, very hard layer of titanium aluminum nitride (TiAlN). Ludeking said this coating allows the use of a thin layer, only about two microns thick, as opposed to standard PVD, which is usually five to six microns thick. “The thinner coating is smoother, giving us an advantage in machining sticky superalloys, nonferrous materials, stainless steel and titanium,” he said. “There’s much less tendency for buildup on the edge. And the heat resistance and hardness of the coating yield excellent tool life. We’ve been able to greatly improve tool life and increase machining speeds in a lot of really difficult applications.
“We’ve had particular success on the cobalt chrome alloys used in the medical industry,” Ludeking continued. “These alloys are particularly challenging because the cobalt has a high tendency to form edge buildup, while the chromium in it tends to be very abrasive. It’s a unique combination requiring a hard coating and a very sharp edge. HiPIMS’ thin coating really lends itself to holding on to a very sharp edge and gives us a big advantage in these cobalt chrome alloys.”
Walter’s HiPIMS technology can be found in its WSM01 grade inserts, which in turn can be configured in various geometries. For example, its MS3 geometry is ideal for machining ISO S materials with difficult cutting properties, such as high-temperature alloys, titanium alloys, cobalt-based alloys and nickel-based alloys (e.g. Inconel 718), according to the company. A secondary application of the new grade is in materials such as austenitic stainless steels, steel, and non-ferrous alloys. The geometry also provides low cutting pressure and excellent chip control, making it ideal for reducing vibration—especially on thin components, according to Walter.
A Simple Change in Tool Sizing Yields a Big Savings
Ed Woksa, national turning product manager for Ingersoll Cutting Tools (Rockford, IL), said the ongoing transition to near net shape workpieces—thanks to better casting and forging technology and the additive manufacturing boom—reduces the amount of material that needs to be removed. “And more and more customers are utilizing higher speeds and feeds, but not necessarily hogging the material with heavy DOCs as they have in the past,” he said. “Yet they’re using the same old CNMG432 inserts.
“I’ve been in many shops throughout North America where I see a coffee can full of ‘used’ inserts that barely show any wear due to the light cutting depth,” Woksa continued. “When we studied the market three years ago we found that 30% of customers using the general purpose CNMG432 insert were taking a DOC of 0.060” [1.5 mm] or less, and another 45% of customers using the same insert took a DOC of 0.125” [3.18 mm] or less. A CNMG432 insert has an inscribed circle (IC) of 0.500” [12.7 mm] and it’s 0.187” [4.75 m] thick, so these customers were paying for an insert that was much too large for their application.”
This realization led Ingersoll to introduce the Gold Rhino product line (CNMG332). Gold Rhino has a smaller IC than a CNMG432 insert (0.375 vs. 0.500”; 9.5 vs. 12.7 mm), yielding a cost savings of 20-30%. But Woksa said they “perform as well, and in many cases better, for these applications. And generally speaking there’s no need to modify the existing programs.” That’s because while previous attempts at smaller inserts scaled down the entire insert (CNMG322), making them both smaller and thinner, Ingersoll retained the same thickness as the CNMG432 (0.187″ thick) and didn’t change the chipbreaker. Ingersoll also “changed the insert hole from a straight design to a trumpeted shape, which allowed us to improve the clamping forces to be multi-directional with a single clamping motion,” said Woksa.
“In a thinner CNMG322 insert, heat transfer from one side to the other was excessive, reducing tool life on the second side,” he continued. “Also, the shorter chip breaker couldn’t handle the higher feed rates. Besides being thicker, Gold Rhino keeps the same chipbreaker so the user doesn’t have to reduce feed rates.”
It’s an admittedly easy idea to copy, and Woksa said other cutting tool manufacturers have since introduced similar inserts, “without the trumpeted screw hole, though. And we definitely have the largest product offering, primarily because of our belief that the trend towards near-net parts will continue. For example, we have since added compatibility with additional T-Type holders—most in the market call them D-Type holders—that provide the multi-direction clamping system that is also growing in the market.”
Cut-Off, Grooving, Turning, and Profiling in One Tool
Coming full circle to another solution that is very easy to use for a wide range of applications, Kennametal Inc. (Latrobe, PA) has a new platform called Beyond Evolution that, according to Carsten Gromoll, senior marketing manager for demand generation, “…does it all. Cut-off, grooving, deep grooving, face grooving, side turning, and profiling.”
The key is a proprietary Triple V holder in which the top, bottom, and backside of the seat are each V-shaped, creating a pull-in effect for exceptionally high stability. According to Kennametal, Beyond Evolution will groove deeper than double-ended systems, turn with 90% of the stability and allow interchangeability regardless of geometry or application. It offers tighter indexing tolerances, longer cutting depths, and new plunge and turn geometries.
Mark Filosemi, senior product manager for Kennametal, said customers “wanted to stop leafing through hundreds of pages of catalogs and thousands of items because it was difficult, time-consuming, and expensive.” Gromoll added that Beyond Evolution reduces the number of required items up to 35% compared to competitors. “This makes Beyond Evolution easy to choose in addition to easy to use, reducing inventory and expenses,” he said. “And where conventional product launches focus on a single line item, Beyond Evolution will be launched in multiple grades for dozens of applications—a full line offering that promises higher performance and reduced costs immediately.”
The Beyond Evolution products also deliver coolant into the work zone, aided by application-specific chip breakers and proprietary chip control for extended tool life, according to the company.