III. Basic Components of Tool Coating Equipment
(1) Vacuum Chamber
Coating systems mainly include continuous production lines and single‑chamber coaters. Due to complex shapes, high heating requirements, and diverse dimensions of tools and molds, single‑chamber machines are more widely used.
(2) Vacuum Generation
High vacuum is essential for strong coating adhesion. No single pump can cover the full pressure range from atmosphere to ultra-high vacuum, so combined systems such as mechanical pumps and molecular pumps are typically used.
(3) Vacuum Measurement
Vacuum gauges monitor pressure inside the chamber. Different types are used across different pressure ranges, as no single gauge can measure the entire vacuum spectrum.
(4) Power Supply System
Target power supplies include DC and mid-frequency units. Workpieces are usually powered by DC, pulsed, or RF (radio frequency) sources.
(5) Process Gas Supply System
Process gases include Ar, Kr, N₂, C₂H₂, CH₄, H₂, and O₂, supplied from cylinders through pressure regulators, valves, flow meters, solenoid valves, and piezoelectric valves.
Independent gas lines for each machine simplify maintenance and reduce interference. Centralized gas systems save space but increase leakage risks and mutual interference between machines. Cylinder replacement requires all systems to be non-operational.
(6) Mechanical Rotation System
Uniform coating thickness requires three rotational motions: main turntable rotation, satellite holder rotation, and workpiece rotation. For molds, two rotations are often sufficient but require higher load-bearing gear systems.
(7) Heating and Temperature Measurement
Uniform heating is critical for tool and mold coating. Equipment usually includes dual heaters and thermocouples. However, thermocouple readings may not represent actual workpiece temperature.
Surface thermometers provide a practical solution: they record peak temperature during heating and retain the value after cooling, allowing accurate post-process reading.
(8) Ion Evaporation and Sputtering Sources
Arc evaporation sources are typically round targets. Rectangular arc targets have also been developed but show limited improvement. Targets are mounted on water-cooled copper cathodes with adjustable magnets to control arc spot motion. Tin spacers may be used to improve electrical and thermal conductivity. Magnetron sputtering uses rectangular or cylindrical targets.
(9) Water Cooling System
High-power operation requires effective cooling of cathodes and chamber walls. Process temperatures commonly range from 400°C to 500°C. Chilled water at 18–20°C is recommended. To prevent condensation when opening the chamber, the system should switch to 40–45°C warm water approximately 10 minutes before venting.
IV. Development Trends
(1) Diversified and Composite Coating Compositions
First-generation PVD coatings were dominated by TiN, followed by TiC, TiCN, ZrN, CrN, WC, and other single‑layer coatings. The introduction of aluminum led to TiAlN, TiAlCN, and other multi-component coatings with significantly improved wear resistance and red hardness, supporting higher cutting speeds such as 150 m/min in hobbing.
Layered composite structures, such as TiN‑TiCN‑TiN, TiN‑TiAlN, and TiAlN‑WC/C, have become mainstream.
Recently, advanced pulsed coating technologies have been commercialized, including Balzers' P3E (Pulse Enhanced Electron Emission) and Cemecon's H.I.P. (High Ion Pulse). These processes enable deposition in oxidizing environments, allowing nearly all metal oxides such as Al₂O₃, ZrO₂, Cr₂O₃, and Ta₂O₅. Al₂O₃ coatings are now under practical testing and will soon be widely applied.
(2) Application‑Specific Coating Development
Coatings are increasingly designed for dedicated applications including drilling, milling, dry hobbing, stamping, and deep drawing.
Successful examples include:
High-aluminum TiX (Al:Ti = 2:1) coatings for milling
AlCrN coatings for high-speed dry hobbing
CrN‑TiSiN coatings for drilling
TiN‑TCX coatings for deep drawing dies
Specialized coatings such as corrosion-resistant Crₓ, self-lubricating WC/C, soft-machining MoS₂, and superhard CBN and diamond coatings are already widely used. Further innovations will continue to replace existing solutions.
(3) Nanoscale Coating Microstructures
Nanocoatings have attracted extensive attention due to improved adhesion, reduced interlayer stress, and smoother surfaces. Most current coatings still contain relatively large particles, resulting in higher roughness.
Future development will focus on stable nano-grained and nano-layered coatings, especially for mirror-finish applications. This will enhance performance, expand precision molding applications, and improve surface quality.
(4) Lower Deposition Temperatures
CVD temperatures near 1000°C have been reduced to around 500°C in PVD and PCVD, expanding applicable materials. However, 500°C can still cause distortion and hardness reduction, requiring tempering temperatures above coating temperature.
Future coatings will operate below 200°C, eliminating thermal deformation, broadening material selection, and enabling flexible combinations of surface treatments. Low-temperature processes also reduce energy consumption, shorten heating and cooling cycles, and improve production efficiency. Thus, low-temperature PVD will become a key development direction.
