Increased material removal rates, extended tool life, fewer production line tool changes, reduced downtime, less wastage and improved precision and quality are common goals for manufacturers and engineering businesses. Physical vapour deposition (PVD) coatings applied to production tools often provide an appropriate productivity solution.
PVD is a vacuum deposition process that is carried out under vacuum in temperatures ranging from 450 to 600 degrees Celsius, where it produces a very hard thin film on the tool’s surface. For cutting tool applications, metals or alloys are either evaporated by heat or bombarded with ions (sputtered). A reactive gas is added which forms a compound with the metal vapour which is deposited on the tools as a thin, highly adherent ceramic coating. PVD methods include cathodic arc, electron beam, evaporative deposition, pulsed laser deposition and sputter deposition.
Not just for cutting tools
PVD may be applied to improve the wear performance of components, dental or surgical instruments or scientific tools and devices. According to Natalie Schembri of Surface Technology Coatings (STC), part of Sutton Tools, materials that can be coated include carbides, high speed steels, certain copper alloys, stainless steels and nitridable alloy steels.
“As well as PVD hard film coatings, Surface Technology Coatings offers high pressure quench vacuum heat treatment and plasma nitriding,” says Schembri. “This ensures work is carried out within a short turnaround time, while quality is assured through an ISO 90001:2008 Quality Assurance registration which ensures traceability of products through the entire process cycle.”
The different surface treatments include:
- Titanium Nitride (TiN). This general-purpose coating protects parts and tools from wear, extending tool life by three to eight times. It’s ideal for machining of iron based materials, die casting and plastic mould tooling. TiN treatment can improve performance of plastic moulds and moulding machine parts, slitting knives, wear parts, medical and dental instruments and forming tools.
- Titanium Carbonitride (TiCN). This process provides improved wear resistance over TiN. It is recommended for components and manufacturing applications such as punching and forming tools, and cutting tools for highly abrasive or gummy materials like cast iron, brass and some cast aluminium alloys. TiCN coating improves abrasion resistance to moulds and extrusion tools for plastics that contain more than thirty percent glass fillers.
- Chromium Nitride (CrN). This coating was developed to solve wear problems in special application areas where titanium based coatings were not optimal. CrN is recommended for its ability to provide resistance to wear, corrosion and oxidation in applications such as machining aluminium and copper and high temperature die casting. Benefits include enhanced thermal stability and excellent adhesion under high loads.
- Titanium Aluminium Nitride (Futura Nano – TiAIN). Used as a versatile coating for both HSS and carbide tools where there is a high thermal load, TiAIN has a nanolayered structure engineered for an optimum balance between hardness and internal stress. This process helps to reduce the propagation of cracks through a coating that delays the onset of failure. Typical treatments include tools for machining cast iron, heat treated steel and difficult to machine materials such as stainless steel, while benefits are higher speed and feed machining and reducing or eliminating the need for coolants.
- Aluminium Chromium Nitride (Alcrona – AICrN). A process for HSS and carbide tooling for forming, punching, blanking and hot forging operations, providing high wear resistance at lower speeds and under high mechanical loads. At higher speed processes, this coating provides protection up to 1,100 degrees Celsius and offers the benefits of improved tool performance when machining low alloy, high tensile and hardened steels up to 54 HRC.
- Steam Oxide (Ox). Ox is an environmentally friendly steam treatment of ferrous metals, forming a thin, well-adhered, blue-black oxide film called magnetite. The oxide layer is porous, enabling the retention of oil which lowers friction in ferrous applications. This avoids the problems of pick-up, cold welding on taps and ‘built-up edge’ on cutting edges and increased corrosion resistance.
- Aluminium Titananium Nitride (X.Ceed – AlTiN). Ceed (AlTiN) represents the pinnacle of titanium-based PVD coatings. AlTiN is a high-performance coating suitable only for carbide tools, due to its high deposition temperature, which gives improved adhesion in severe applications. For a titanium-based coating it has high hardness, excellent oxidation resistance and high service temperature. Good results have been obtained with this coating on tools used for machining Ti alloys, Inconel and other difficult to machine materials. AlTiN is also applicable in high-speed cutting and hard machining (> 52HRC).
“It is recommended that each new application should be evaluated jointly between the tool user and the coating centre specialist,”adds Schembri.