High-performance tool coatings provide vital protection

Because machine tools repeatedly remove material, frequently at high spindle speeds, to shape a workpiece, carbide cutting tools are often applied instead of HSS ones to retain a sharp cutting edge and extend tool life. However, when machining highly abrasive materials, such as carbon fiber-reinforced polymer, glass fiber-reinforced plastic, graphite, aluminum alloys or ceramics, even carbide tools can rapidly wear.

In these cases, further hardening carbide cutters with specialty coatings can significantly improve wear resistance and service life. For extremely expensive cutting tools, this not only reduces costs but shortens cycle times. These coatings come in a variety of types, from physical vapor deposition coatings to proprietary diamond coatings.

Greater Abrasion Protection

In a growing number of industries, including automotive and aerospace, manufacturers continue to place more emphasis on design and weight reduction. Designers subsequently increasingly use composite fiber-reinforced plastics in many parts, but these composites are exceedingly rough on cutting tools.

For cutting tools to withstand heavy wear, a specialty coating with a very high resistance to abrasion is needed. Image courtesy of Oerlikon Balzers

“The problem with the carbon and graphite fibers is that they are very high strength and extremely abrasive,” said Volker Derflinger, senior manager at Balzers, Liechtenstein-based Oerlikon Balzers, which has produced coatings for components and tools for more than 30 years. “For cutting tools to withstand heavy wear, it needs a specialty coating with a very high resistance to abrasion.”

In industries like automotive that require strong, lightweight materials, parts are also made of aluminum-silicon alloys. However, the higher the silicon content, the more abrasive the material.

“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.”

When it comes to machining very abrasive materials, uncoated carbide tools experience accelerated wear. To increase tool life, high-performance coatings provide a vital protective barrier. He said the ideal coating would have a very hard, protective surface that simultaneously maintains the sharp cutting edges that enable clean, precise cuts while boosting productivity.

PVD Coatings

One coating type increasingly being utilized in these industries is strong, nonhazardous PVD. PVD describes a variety of vacuum deposition methods that can deposit thin coatings. The process typically coats tools and components at relatively low temperatures from 150° to 500° C, which avoids altering the fundamental material properties.

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 suitable for machining nonferrous materials, including aluminum alloys with up to 12% silicon content.

Balinit Hard Carbon by Oerlikon Balzers is deposited on tools to machine nonferrous materials, including aluminum alloys with up to 12% silicon content. Image courtesy of Oerlikon Balzers

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

The Balinit Hard Carbon coating has high hardness—40 to 50 gigapascals—making it appropriate for applications that require enhanced wear protection. In addition, the thin, smooth application helps maintain sharp cutting edges. For example, at a Malaysian manufacturer producing aluminum hard disk drive baseplates, a coated carbide endmill exhibited less abrasive wear and produced 95% more parts with 55% lower production costs than an uncoated tool.

The combination of coating hardness and a low friction coefficient can also dramatically improve production even when dry machining. In an application machining CFRP and thermoplastics, for instance, a Balinit Hard Carbon-coated countersink produced 180% more parts than an uncoated tool. In another case, a coated carbide endmill doubled the parts produced when dry machining compared with an uncoated tool using lubricant.

Diamond Coatings