Trends in tool coating technology

Hardness, temperature resistance and the contact between the tool and the material that needs to be cut or formed can be positively influenced. In some cases coated tools can realise a tool life that is ten times longer than uncoated tools.

Lightweight materials

One important trend that is influencing tool coatings is the cutting of lightweight materials. In the automotive industry, lightweight materials are being chosen because of less fuel consumption and less CO2 emissions. As a result, materials such as aluminium, magnesium and carbon reinforced plastics are gaining importance. Apart from the reduced weight, these materials have one thing in common, they have the tendency to stick to the cutting tool resulting in shorter tool life. This trend has stimulated the development of tetrahedral amorphous carbon (ta-C) coating, which is a hydrogen-free diamond like carbon (DLC) coating with a low coefficient of friction.

Crossover tribological applications

It is a practical example of a crossover development originated from tribology and applied in the tool coating market. In tribological applications this hydrogenfree diamond like carbon (DLC) coating is used to reduce wear and friction. Applied to the tool industry, ta-C coatings have proven to be extremely suitable for cutting lightweight metals and fibre reinforced plastics that tend to stick to the tool. A ta-C coating for tools is much thinner with a typical layer thickness of 0.5 μm. With ta-C coating the tool life can be significantly increased. The coatings are deposited with a circular arc technology, guaranteeing a strong adhesion of the coating itself.

Cost efficiency

In every industry cost efficiency is a driving factor that needs constant attention. The tool industry is no exception. The cost of the tool coating is only a small part of the total cost of a tool, but because the coating is positioned at the end of the production line, it is very important that the coating is of high quality. Therefore, in tool coating reliability is as important a factor as costs. When Hauzer developed their new circular arc technology CARC+ for depositing nitride coatings in the Hauzer Flexicoat® 850, they succeeded in making many cost of ownership factors more efficient than ever before. CARC+ is characterised by short batch times, high target efficiency and smooth coatings that need minimal posttreatment. CARC+ technology is nowadays a proven technology for nitride coatings, including a highly functional AlCrN coating for hobs used in gear cutting.

Sustainability

The awareness of sustainable production methods becomes more and more mainstream, also in the tool industry and related fields up and down the supply chain. Important factors here are the future scarcity of raw materials, energy consumption, renewable energy, toxicity of materials and recycling in biological or industrial circles. In the tool industry some answers to these challenges are found in higher speed and feed. Some coated tools can achieve not only longer cutting lengths, also a larger depth of cut will be possible, saving time and energy along the way. The metres per minute are deciding and speed meets performance in the Hauzer Flexicoat® 850 with CARC+ technology, so that can be a contributing factor. Another trend that is driven by sustainability as well as cost efficiency is less use of cooling liquids. Dry cutting or minimum quantity lubrication (MQL) are trending, which leads to increased temperatures of the tool cutting edges and hence a need for improved oxidation resistance.

Temperature resistance

The trends in the tool industry are all related. The trends for cost efficiency and environmental awareness lead to lower use of cooling fluids, which in turn leads to higher temperatures during cutting. The industry answers with a different choice of substrate materials and coatings that can withstand the high temperatures.

Workpiece materials such as titanium (Ti) and nickel (Ni) alloys are difficult to cut because of their sticking tendency and toughness, but ta-C coating will not bring any solutions here because of its maximum operating temperature of around 500 °C. CARC+ coatings are therefore a better solution. These nitride coatings can function at operating temperature levels of up to 1100 °C or even 1500 °C. Application directed development has been done to adapt the coatings made with CARC+ technology to specific applications, such as high speed milling and roughing finishing. For cutting titanium the TiAlN coating can give excellent results. Hauzer has developed silicon containing nanocomposite coatings and is fine-tuning its coatings for specific applications.

Aluminium oxide coatings

Another possibility to deal with temperature resistance is the use of aluminium oxide (Al2O3) coatings. The biggest challenge when depositing oxide coatings is in controlling the sputtering process. An Al2O3 coating is made by sputtering from an aluminium target in an argon (Ar) and oxygen (O2) atmosphere.

When using a single magnetron cathode during the deposition, the anode area surrounding the cathode will slowly become non-conductive resulting in unstable cathode behaviour. Hauzer has chosen Dual Magnetron Sputtering (DMS) technology to overcome this problem. Two magnetron sputtering cathodes on opposite sides of the PVD system are connected to one AC power supply. When one cathode is running on negative potential, the other cathode is positively charged, effectively acting as anode. In this way, a stable anode is established continuously during the complete deposition cycle. Hauzer’s proven T-mode technology deals with another challenge of Al2O3 coatings: balance in the oxygen flow. T-mode technology introduces a loop on each of the two sputter cathodes to achieve this and prevent the target from being poisoned.