What is PVD coating

To provide the high performance solid carbide drills, Fidelity tools selects right carbide grade, grinding parameter and edge design, but most importantly we select the most suitable PVD coating solution for our solid carbide drills. Our PVD coating has a strong chemical stability, a low thermal conductivity and a high wear resistance at even 1100 degree.

What is PVD

Physical Vapor Deposition (PVD) is a method for producing metal-based hard coatings by means of generation of partially ionized metal vapor, its reaction with certain gases and by forming a thin film with a specified composition on the substrate, like solid carbide drills, inserts and mills.

Most commonly used methods are sputtering and cathodic arc. In sputtering, the vapor is formed by a metal target being bombarded with energetic gas ions. Cathodic arc method uses repetitive vacuum arc discharges to strike the metal target and to evaporate the material. Normally the coating thickness ranges from 1 to 6um.

The substrate materials include steel, non-ferrous metals, tungsten carbides as well as pre-plated plastics. The suitability of the substrate material for PVD coating is limited only by its stability at the deposition temperature and electrical conductivity.

The coatings can be deposited as mono-, multi- and graded layers. The latest generation films are nano-structured and super-lattice variations of multi-layered coatings, which provide enhanced properties. The coating structure can be tuned to producing the desired properties in terms of hardness, adhesion, friction etc. The final coating choice is determined by the demands of the application.

The key factors of PVD coating selection for solid carbide drills

Compare with 20 years ago, PVD TiN(Titanium Nitride) dominates in the PVD coatings, there are a number of PVD coatings available now, like CrN,AlCrNsi, AlTIN, AlTINSi, ZrN, and AlCrNsi+ etc. There are many factors for tools makers to consider to select the suitable PVD coating for their cutting tools like coating toughness, residual stress, coating deposition rate, coating adhesion, thermal stability and oxidation resistance etc. For drilling application, based on our past 15 years extensive hands on testing experience, there are four key factors for Fidelity tools to select the suitable PVD coating for the solid carbide drills.

  1. 1.Coefficient of friction
  2. Hot hardness&thermal stability
  3. Coating structure
  4. Wear resistance
  • 1.Coefficient of friction

There are many factors are important for drilling. Based on our experience, Coefficent of friction is the most important factor for two key reasons, one is chips moving the other is built-up edge.

Chip moving.

As for drilling, the drills is working in the hole, so chips formation and chip evacuation are critical issues in drilling. To avoid chip jamming, at Fidelity tools we use AlCrNSi multi-layers PVD coating with very smooth surface by our optimized layer configuration, coating composition and special treatment method, Coefficient of friction of the PVD coating can reach 0.2, which can provide nearly frictionless chip removal along the flute.

Bulit-up edge (BUE)

During machining, drills experienced built-up edge in the outer blade, inner blade and at the chisel. This BUE can be seen at both view, i.e. rake and flank sides. BUE is the most dominant deterioration and inevitably in drilling. Our smooth coating can minimize the BUE to keep the cutting edge sharp.

  • Hot hardness&thermal stability

High hot hardness – retain hardness at high temperature. To get good hot hardness performance, at Fidelity tools, we select the coating with low thermal conductivity and hot hardness stability

During machining process, heat originates from two fundamental sources: the mechanical energy to deform and fracture the workpiece material during chip formation and friction at contacting areas between the tool and the chip. The first term is a function of the strength and ductility of the material being cut, while the second term is dependent on the surfaces in contact. At Fidelity tools, we select the PVD coating can reduce friction forces considerably.

The flow of heat is also influenced by the thermal conductivity of the coating. For Fidelity tools solid carbide drills, the PVD coating is more insulating, therefore protect the drills better from being heat damage, thereby prolonging tool life.

Let me explain this in more details. The generated heat was absorbed by the tool , chips and work material. The coating alters the heat generation and heat transfer between chip and tool. As our PVD coating (AlCrN+) has low heat conductivity (below 5 W-m/K) which can make the heat mainly transferred to chips rather than the tools(Qs1 vs Qs2). Then the chips and heat will be removed as you can see from the picture below. finally, the tools can keep at lower temperature.

Besides, With the ALCrSi Chemical composition, The coatings have a very high oxidation resistance and maintain the hardness even at high temperature

  • Coating structure

The coatings can be deposited as mono-, multi- and graded layers. The latest generation films are nano-structured and super-lattice variations of multi-layered coatings, which provide enhanced properties.

Multilayer structure minimizes crack propagation along layer boundaries and provide the consistent prevention of crack growth , as we can see from the graph below.

Our Unique Multi-Layer PVD Coating with optimised layer configuration and coating composition assures an ideal balance between residual stress, hardness and fracture toughness, which resists chipping and cracking, for exceptionally long tool life

fidelity drills coating structure1

  • Wear resistance

At Fidelity tools, the PVD coatings of drills are using the Arc process, rather than the traditional sputter process. The Arc coating process produces excellent coating adhesion, especially when there are dynamic forces in the machining process. And the coating increases the surface hardness to approximately 3400 – 3600 Hv which greatly improves the resistance to abrasive wear.

Last but not least, at Fidelity tools, to get high performance at moderate and high cutting speeds drilling, we optimally balance between residual stress, hardness and fracture toughness of the PVD coating. This enables higher cutting speeds than with other coatings as well as extended tool lifetime, even when deep-hole drilling or using minimum quantity lubrication.

At Fidelity tools, with our knowhow on PVD coating, carbide grade, tools geometry design and edge preparation etc, Fidelity tools solid carbide drills has achieved excellent results at our customers side. As we can see from the test result in above graph from our customer in Auto industry, for the 5D deep hole machining, our drills can work more holes with much less VB wear, which help the customer save a lot.

At Fidelity tools we can not only provide standard stock for 3D, 5D & 7D drills but also can offer customized drills and reamers according to your requirement in the short lead time(less than 2weeks to manufacture). if you have any inquire, please feel free contact us.

Reference:

https://www.oerlikon.com/balzers

https://www.ionbond.com/

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