The combination of coating hardness along with a low-friction coefficient also can dramatically improve production even with dry machining. In an application involving CFRP and thermoplastics workpieces, for instance, a hard carbon-coated countersink tool produced 180% more parts than an uncoated tool. In another comparison, a coated carbide end mill doubled the parts produced with dry machining, compared to an untreated tool using lubricant.

The main obstacle in the New England rebuilder’s effort to raise capacity of its screw machine fleet was the boring sequence, which represented more than half the total machine time.  The shop still used conventional, negative-rake boring tools, a carryover from the time when most of the work they took in involved free-machining mild steels.  When more work came in that called for long-chipping 8620 steel, they simply accepted as an unavoidable detail the 100% operator attention for chip clearance.

“Titanium just complicates ID work with conventional tooling because of its unhelpful chipping characteristics,” said Ingersoll’s Darrell Boatwright. “The aggressive chipbreakers on the new Gold-Duty tool make short work of long chips in OD turning, and soon for ID work as well.”

Because the action of machine tools is constant, cutting and grinding away material at high RPMs to shape workpieces, carbide cutting tools often are selected instead of hardened steel, to retain a sharp cutting edge and prolong tool life. However, when highly abrasive materials like carbon-fiber reinforced polymer/glass-fiber reinforced polymer sandwich materials (CFRP/GFRP), graphite, aluminum alloys, and ceramics are machined — even carbide tools may be prone to rapid wear.

The incoming castings had the usual, wide piece-to-piece dimensional variations and yet needed a lot of stock removed depending on those inconsistencies. “Definitely not the ideal candidates for a first stab at a new kind of process,” said Commerford.

High-performance coatings — When it comes to machining very abrasive materials, uncoated carbide tools experience accelerated wear. To increase tool life, high-performance coatings can provide a vital protective barrier. According to Derflinger, the ideal coating would have qualities such as a very hard, protective surface that maintains the sharp cutting edges, allowing clean and precise cuts while speeding production time.

Diamond coatings. When carbon content in composites or silicon content in aluminum alloys becomes too high, cutting tools typically require a diamond coating to prevent premature wear. Traditionally, polycrystalline diamond (PCD) cutting tools have been used in such instances. PCD is a composite of diamond particles sintered together with a metallic binder. Diamond is the hardest of all materials, and therefore the most abrasion-resistant, too.

Derflinger noted that standard PVD-applied metal-doped carbon coatings have a hardness of approximately 15 GPa, whereas a “diamond-like” carbon coatings range from 20 to 50 GPa. In comparison, a diamond coating reaches a hardness of 80 to 100 GPa.

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In terms of satisfying such qualities, BALINIT Diamond Micro and Nano coatings are examples of PACVD-based diamond coatings formulated specifically according to the needs of a wide range of highly-abrasive, nonferrous materials. While both are well suited to machining GFRP, CFRP, and ceramics, the rougher “micro” formulation is ideal for graphite.

The bottom line — Some manufacturers may be inclined to use uncoated carbide cutting tools or traditional coatings because of their familiarity with such methods. However, those that take advantage of the superior capabilities of high-performance hard-carbon PVD and diamond PACVD coatings will significantly harden carbide cutting tools and improve part quality. This will enhance production and tool service life, which also improves the bottom line.

As a cutting tool material, PCD has good wear-resistance but it lacks chemical stability at high temperatures and dissolves easily in iron. So, PCD-coated tools usually are limited to cutting materials such as high-silicon aluminum, metal matrix composites (MMC), and CFRPs.

Micor, which built its reputation machining difficult metals, was only midway through a 150-piece rush job turning titanium, and was running late already.  But, the tools they were using, with conventional two-sided negative rake inserts, broke whenever they tried to run any faster than 130 SFM/0.010 IPR/0.200 DOC. That operation, on a Mazak Quik Turn 450, was taking 45 minutes per piece, while the finishing machine nearby stood idle, waiting for feedstock.

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Finally, in the machining of ceramics, typically for the dental industry, both PACVD-based diamond coatings can substantially boost production and extend tool life while improving the surface quality of the workpiece. As an example, when a micro ball-nose end-mill tool was used to machine a zirconium oxide workpiece for a dental application, a PACVD-based diamond coating produced about 900 finished parts, compared to about 100 parts for an untreated tool.

For example, at a Malaysian manufacturer producing HDD aluminum alloy baseplates, coated-carbide end-mill tooling exhibited less abrasive wear and produced 95% more parts, with 55% lower production costs than untreated tooling.

The PACVD process allows the diamond coating to be applied at varying thicknesses (6 μm to 12 μm), which can be customized to suit the application.

“Even if the cutting tool is expensive, you can put a hard coating on it and you will get a much better performance out of it,” said Derflinger. “That is why in the future more and more tools are going to have specialty coatings.”

However, many auxiliary spindles are designed for light duty, unable to deploy the full capabilities of the high-performance face mills available today.  “The trick in live turning is to find a cutter able to take deep cuts, yet hold down cutting forces,” said Ingersoll field engineer Brian Winterlin, who worked on the DeZurik live turning project.

Ingersoll’s Brian Winterlin made a counterintuitive recommendation: a Hi-QuadF high-feed style cutter and taking off the stock in a single pass.  That’s definitely beyond the ‘comfort zone’ for conventional high-feed cutters, which are known for fast feeds and shallow cuts.  But the tool — though primarily a high-feed insert — had worked in similar high-depth applications “This is really an all-purpose cutter,” Winterlin added.

In an application where a Duralcan composite workpiece comprised of ceramic particle-reinforced aluminum materials was drilled, a PACVD-based, diamond-coated cutting tool drilled 20 times more holes compared to even very hard “diamond-like” carbon coatings.

With the original Hi-Quad F insert, edges lasted through two complete parts, or four flanges.  Recently the company switched to a tougher insert grade with an improved coating treatment, IN4005.  The change notched edge life up another 50% at the same removal rates. Edges now last through three complete parts.

It should come as no surprise that live turning speeds up a roughing operation on any machine with a C axis.  The process gets two spindles working simultaneously, with tools having multiple cutting edges rather than just one.

With the PACVD coating process, a carbide cutting tool is sequentially coated by two different gasses in a heated vacuum container, assisted by plasma. Each alternating cycle that builds the atomic layer on the surface and the number of cycles thus controls the thickness of the final coating.

The “nano” coating also works well with abrasive CFRP and GFRP materials. In one example, production significantly increased when a tool manufacturer drilled holes in CFRP/Al composite workpieces with the PACVD-based diamond coating. Compared to about 60 holes drilled with untreated tooling, approximately 380 holes were drilled with the PACVD-based diamond coating.

With its advanced design, substrates, and coatings, the Ingersoll Gold-Duty line of rough turning inserts is a generation ahead of the field in large scale turning, according to Ed Woksa, Ingersoll national turning product manager.  The inserts are physically much thicker and stronger than conventional turning inserts.  Their unique seating scheme enables more efficient top-face geometries in two-sided inserts for the first time.  ‘Rest pads’ on the insert faces mate with bumps in the seat pocket to lock them in place (see diagram).  It’s the rest pads that bear the clamping forces, not the cutting edges on the reverse side. This is what enables 5-7 degree positive rakes and aggressive chipbreakers in a two-sided insert. Recessed clamping provides a flush surface for unimpeded chip evacuation.

DeZurik-APCO-Hilton, in Sartell, Minn., improved a host of valve-turning operations with the move to live turning at rates some people think could damage the spindle.  On the first job, facing time on a large valve flange was reduced from 18 minutes to three, yet the spindle load reading rarely exceeded 50%. The C-axis spindle is equipped with an Ingersoll Hi-Quad F high-feed face mill that doubles as a full-depth face mill capable of depths of cut up to 0.200 in.

The same types of tooling also increased OD removal rates, enabling the whole fleet of screw machines to reach the shop managers’ goal of 30% higher capacity with no capital expenditures.  “Even in miniature precision screw machine work, today’s higher-rake, chipbreaking inserts with advanced coatings can make a material difference,’ said Ingersoll’s Matt Hagenow, who worked on this project.

For instance, in an application drilling Duralcan composite workpieces, comprised of ceramic particle-reinforced aluminum materials, a PACVD-based diamond coated cutting tool drilled 20 times more holes compared to even very hard “diamond-like” carbon coatings.

Now, the DeZurik operation runs securely, cutting cycle time for a typical 36-in. flange from 18 minutes to three and leaving a perfectly flat mating surface. As the part rotates slowly on the machine table, the facemill works much like a woodworking router, rotating at 785 SFM and feeding outward from the center bore at 403 IPM. Synthetic oil is delivered through the spindle.

“The hard carbon coating works on CFRP and GFRP, but only when the fiber content is on the lower side,” Derflinger reported. “The more fiber content, the more abrasive the material is and then you will need an even harder coating.”

In the automotive and other industries that require stronger, lighter materials, aluminum-silicon alloys are used, too. However, the higher the silicon content, the more abrasive becomes the material.

“The Mazak is a big ticket item with a high hourly burden, so it’s vital to get the most out of it,” said Chandler Commerford, manufacturing engineer.  But, the Minnesota shop had no experience with the live turning process.

In a live-turning setup like this, the cutting forces are lighter than you might think, Winterlin explained. “As the tool rotates, its eleven inserts engage sequentially, dividing the cutting forces uniformly over them all. The stock comes off as a lot of small chips rather than the fewer thumb-size chips they were getting by turning with a stick tool.”

“Within any cutting process, the coating is constantly being removed. The thicker the coating, the longer it takes to wear it off,” Derflinger explained. “Once you are into the carbide, the wear is accelerated further. So, a thicker coating normally gives a longer tool life, which then lowers manufacturing costs.”

“As a cost effective, high-performance alternative, specialized PACVD-based diamond coatings can increase the service life of the tool,” Derflinger stated.

“With aluminum-silicon alloys, there are very hard silicon particles embedded in the aluminum,” Derflinger said. “When you have to cut the material, the silicon content is extremely abrasive and can rip up the carbide tool. Even tooling with typical protective hard coatings can degrade very quickly.”

In addition, PCD tools are geometrically limited in structure, and may be too rough or unrefined for the optimal machining of the wide range of nonferrous materials.

When it comes to machining aluminum alloys, including those with high silicon concentrations (AlSi-17 or higher) and ceramic particles, the “nano” diamond coating can replace more expensive PCD tools.

The Hi-QuadF face mill features an extra-thick insert with the usual high-feed radius, extremely rigid seating, free cutting geometry and a 12-degree lead angle for lower lateral forces at entry and exit.  It is so free-cutting that, in similar applications elsewhere, it has doubled throughput without the spindle-load needle even budging.

Micor standardized on those settings for the balance of the job, and delivered the job three days early as a result.  “Despite the higher removal rates, the inserts lasted 33% longer,” King added.  He estimated that, with an annual volume of 400-500 pieces, Micor would save $13,000 a year on that one titanium job.  Consequently Micor is standardizing on Gold-Duty tooling for all rough turning and facing, for a projected $60,000 annual savings.

“The problem with the carbon and graphite fibers is that they are very high-strength and extremely abrasive,” explained Volker Derflinger, a senior manager for Oerlikon Balzers, which has been producing specialized coatings for components and tools for over 30 years. “For cutting tools to withstand heavy wear, a specialty coating with a very high resistance to abrasion is needed.”

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Finally, PCD cutting tools can be quite expensive. As an alternative, plasma-assisted chemical vapor deposition (PACVD) can be used to apply crystalline diamond structures in varying thicknesses and roughnesses. This can be highly advantageous for machining fiber-reinforced plastics, graphite, nonferrous materials, and ceramics. The diamond coating extends tool life while also improving cutting quality and surface finish.

Up in New England, a screw machine reconditioning shop boosted capacity by 30% on its fleet of Swiss Automatics using Gold-Duty CNMX 43.52 inserts.  Their applications involve OD and ID work on wrought 8620 steel.

Switching to Ingersoll TCMT boring inserts with higher rakes, more aggressive chipbreakers and the proprietary TT8125 coating led directly to 30% higher machining rates.  It also completely eliminated any ‘bird nests’ of chips and the labor involved to clear them.  Chips flow out as uniform C’s, easily cleared with a shot of compressed air.

The BALINIT hard-carbon coating is thin, smooth, and has high hardness (40-50 GPa) that makes the coating well suited to applications that require superior wear protection. In addition, the thin, smooth application helps to maintain sharper cutting edges.

The main concern was to remove 0.200-0.400 in. of stock fast without overloading the auxiliary spindle, especially laterally.  In flange work, low lateral forces are essential to keeping the flanges perfectly flat, preventing leaks when the valves go into service.

Need for greater abrasion protection — In a growing number of industries, including automotive and aerospace, manufacturers are emphasizing design and weight reduction. Consequently, designers increasingly are using composite fiber reinforced plastics in many parts. However, these composites are exceedingly rough on cutting tools.

Micor Industries, Decatur, Ala., reduced rough-turning cycle time on titanium from 45 to 30 minutes with another Gold-Duty insert, shipping a rush order three days sooner. They’ve since standardized on that tool for all rough OD work, and are collaborating with Ingersoll to develop an ID-machining version — projecting the savings at around $500,000 per year.

Among the PVD options are several carbon-based coatings that provide a unique combination of extreme surface hardness and low-friction coefficient properties. One example, BALINIT Hard Carbon, by Oerlikon Balzers is used to coat tools for machining nonferrous materials, including aluminum alloys with up to 12% silicon content (AlSi-12). The coating is ideal for CFRP and GFRP materials, if the volume of fibers is not too high.

In those cases, further hardening of cutting tools with various specialty coatings can significantly prolong wear-resistance and service life. For cutting tools that are extremely expensive, this not only reduces costs but speeds overall cycle time too. For applying to cutting tools like taps, reamers, end mills, drills, inserts, counter sinks, and others, these coatings come in a variety of styles from physical vapor deposition (PVD) coatings up to proprietary diamond coatings.

Until mid-2014, DeZurik rough-turned their big valve body workpieces with conventional stick tools on a heavy-duty VTL. Then, the company installed a large, five-axis Mazak mill/turn machine, which opened the door to live turning.

With this approach to machining, carbide tools can be coated to enable cutting of graphite workpieces with better quality and substantially greater speeds. Combined with significantly extended tool life, this allows even sophisticated workpieces and fine structures to be produced with a single cutter in a single clamping, which can help to eliminate cost-intensive reworking procedures.

You may think of rough turning as a bottleneck operation, maybe even a hazardous one, and rightly so.  But, across the country several alert machine shops have found different ways around both problems, according to Ingersoll Cutting Tools.  Users report material-removal rate improvements anywhere from 30% to 6-to-1 in OD and ID work, reliably longer tool life, and relief from ‘shrapnel’ flying from shattered tools.

“The Mazak had the power to cut faster; the bottleneck was the tool,” Ingersoll field rep Darrell Boatwright observed during a plant walk-through.  He brought in a Gold-Duty cutter he had in the trunk and they tried it out on the spot. By the end of the day, parameters were optimized at 100SFM/0.014IPR/0250 DOC.

The Gold-Duty tool easily handled the 33% higher machining rates with no pounding or scraping, the usual forerunners of an insert about to rupture.  “We slowed the surface speed but fed faster and cut deeper,” explained Micor programmer Joey King.

PVD coatings. One alternative that is increasingly being adopted in these industries are strong, non-hazardous, Physical Vapor Deposition (PVD) coatings. PVD describes a variety of vacuum-deposition methods that can produce thin coatings. PVD typically is used to coat tools and components at relatively low temperatures of 150-500°C, which avoids altering the fundamental material properties.