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Coating technology trends
The right coatings can enhance performance and prolong the life of tools and component according to international specialist IHI Hauzer Techno Coating
Michiel Eerden and Gabriela Negrea
Tool life improvement is the result of several upgraded functionalities, depending on the use of the tool. 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 realize a tool life that is ten times longer than uncoated tools.
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 tetrahydral amorphous carbon (ta-C) coating, which is a hydrogen-free diamond like carbon (DLC) coating with a low coefficient of friction.
It is a practical example of a crossover development originated from tribology and applied in the tool coating market. In tribological applications this hydrogen-free 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.
In every industry cost efficiency is a driving factor that needs constant attention. The tool industry is no exception. The cost of the tool coatings 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 characterized by short batch times, high target efficiency and smooth coatings that need minimal post-treatment. CARC+ technology is nowadays proven technology for nitride coatings, including a highly functional AlCrN coating for hobs used in gear cutting.
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 larger speed and feed. Some coated tools can achieve not only longer cutting lengths, also a larger depth of cut per contact will be possible, saving time and energy along the way. The meters 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.
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 component materials and coatings that can withstand the high temperatures. Component 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 operating temperature maximum 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. Hauzer has developed silicon containing nanocomposite coatings and is fine-tuning AlTiN for specific applications.
Trends such as the use of lightweight and high strength materials, the need for high temperature resistance materials and the drive towards sustainability and cost efficiency strongly influence tool coating developments. Hauzer is convinced that by joining tool production and application knowledge such as geometry, substrates and cutting materials with knowledge about deposition technology, coatings and building machines with a low cost of ownership, a lot of progress can be made. Innovative, highly functional and affordable coatings will be the result.
January 7, 2016
Michiel Eerden and Gabriela Negrea
7 January 2016