Walter launches Tiger·tec® Silver with PVD coating technology

The Tiger surpasses itself

Walter AG, the Tübingen-based carbide specialist, is giving its "PVD Tiger" a new skin. The high-performance cutting material with PVD aluminium oxide coating has been given a silver outfit, making it a "PVD Silver Tiger". Tiger·tec® Silver PVD, to give it its official designation, offers an increase in performance of around 30%.

Jörg drobniewski, head of cutting tool material and coating development at walter ag in tübingen: the performance increase offered by tiger·tec® silver pvd is based on the greater hardness and improved surface structure of the aluminium oxide.	     image: läppleWhen Walter presented a new Tiger·tec® cutting tool material with PVD aluminium oxide coating at EMO 2005, it was a world first. A new technology made it possible for the Tübingen-based specialists to apply the Al2O3 hard layer using the PVD process (physical vapour deposition) for the first time. Until then, it had only been possible to apply the hard layer using the CVD process (chemical vapour deposition). The advantage: Indexable inserts with PVD aluminium oxide combine the properties of classic, nitride-based PVD-coated materials and classic CVD coatings. This means that they offer extreme heat resistance thanks to the Al2O3, while at the same time also providing good toughness properties. This is due to the fact that the PVD process requires significantly lower process temperatures of around 500°C. The CVD process, on the other hand, requires temperatures of around 800°C to 1,000°C. High process temperatures make the carbide substrate more brittle. In addition to this, CVD coatings also display undesirable residual tensile stresses. PVD coatings are subject to residual compressive stress, so there is significantly less influence on the properties of the substrate. The PVD-Al2O3 coating therefore creates a carbide cutting tool material that comes closer to the ideal cutting tool material or "rubber diamond" (which obviously only exists in theory) than all other known materials to date.

Walter is initially supplying the tiger·tec® silver pvd cutting tool material in the form of grooving inserts. however, the range is set to be further extended over the next two or three years to also include indexable inserts for iso turning and milling.	image: walter agFour years later, in 2009, Walter then launched Tiger·tec® Silver, a completely new generation of CVD grades. This cutting tool material also set new standards immediately. The gold-black appearance was replaced by a silver-black look. According to Walter, the silver colouring of the flank face improves wear detection. Using a special surface treatment allowed the developers to noticeably increase the resistance to both wear and cracking. The toughness increased and the excellent high temperature resistance remained fully intact.

The goals of the cutting tool material experts can be seen in both lines of development. The objectives here are to optimise PVD coatings in order to achieve high temperature resistance and to optimise CVD coatings for improved toughness. The gap between CVD-coated and PVD-coated cutting tool materials would therefore become ever larger. In other words, an approximation to the ideal cutting tool material comes from two directions. As such, crossing PVD aluminium oxide technology with the Tiger·tec® Silver technology represents a logical next step for Walter. PVD Tiger·tec® and Tiger·tec® Silver then come together to create Tiger·tec® Silver PVD.

Comparison of conventional pvd coating (left) and tiger·tec® silver pvd coating (right). the improved surface structure of the tiger·tec® silver pvd indexable inserts reduces friction and thereby ensures reduced heat build-up. with conventional pvd coatings, there is a great inflow of heat into the carbide. on the new tiger·tec® pvd coatings, the al2o3 acts like a protective heat shield, thereby guaranteeing longer tool life.		          image: walter agHowever, the new cutting tool material is more than just a mix of familiar technologies. "We have increased the hardness of the aluminium oxide, while at the same time further improving the microstructure of the coating surface," explains Jörg Drobniewski, head of cutting tool material and coating development at Walter AG, adding that "this provides us with a particularly smooth rake face with extremely low friction. These optimisations make Tiger·tec® Silver PVD the new top-level cutting material for the increasingly difficult tasks being encountered in machining technology which require indexable inserts to be extremely tough and also offer high temperature wear resistance." This is, for example, the case with materials that are difficult to cut, such as titanium-based or nickel-based alloys. As was also the case with its predecessor, Walter recommends the "PVD Silver Tiger" for machining ISO-S and ISO-M materials. However, it is also used for ISO-P materials, in particular when using unstable clamping arrangements or producing interrupted cuts. Thanks to the aforementioned new features, users benefit from an increase in performance of around 30%.

It all starts with grooving

The Tübingen-based company is launching the new cutting tool material for all machining technologies in a step-by-step approach. This starts with grooving in the quartet of WSM13S, WSM23S, WSM33S and WSM43S. The two middle grades actually already cover the majority of all grooving applications. This is particularly true of the WSM33S grade, which Walter recommends for most "standard conditions". It offers the ideal combination of hardness and toughness for most applications. The hard grade WSM13S, on the other hand, offers maximum performance for applications with stable machining conditions, e.g. finishing operations on Inconel turbine blades. The particularly tough WSM43S grade has been designed for unstable conditions or interrupted cuts. All four cutting tool material grades are equally suitable for all material groups. When grooving, the working conditions are always specific, so the otherwise ubiquitous ISO material group classification plays less of a part here. Grooving operations generally require a high level of toughness, meaning that high-performance cutting materials such as Tiger·tec® Silver PVD can also play to their strengths when processing standard steel. Machining operators then make the necessary fine adjustments to specific process conditions or material characteristics by selecting the appropriate geometry. With the four aforementioned high-performance cutting materials, the Tübingen-based manufacturer provides a broad range of geometries for parting off, grooving and recessing.

No other cutting tool material with pvd coating is currently able to combine optimum toughness properties with improved high temperature wear resistance like the tiger·tec® silver pvd.											image: walter agIn a benchmark test, the new WSM33S grade competed against its predecessor, the WSM33, and against other products. The task was to cut a groove in ball bearing races made of 100Cr6 material (1.3505). The new "PVD Silver Tiger" clearly had its nose in front in terms of tool life, as it produced 950 components, some 150 more than its predecessor. Other conventional PVD cutting tool materials only achieved a maximum tool life of around 450 components. According to Jörg Drobniewski, "The benchmark test demonstrates that we have surpassed our own top performance with the Tiger·tec® Silver PVD; as such, we are further building on our leading position in the market for PVD-coated cutting tool materials already occupied by our former PVD Tiger. And there is currently nothing that would suggest any risk of this position being jeopardised by other products in the market. We actually consider our PVD aluminium oxide technology a USP that sets Walter apart in the international tool market."

So what happens next in terms of launching the new "PVD Silver Tiger"? The cutting tool developer explains: "We are set to launch corresponding grades for milling and ISO turning over the course of the next two or three years. Our ultimate strategy is to switch over all previous Tiger·tec® PVD grades to Tiger·tec® Silver PVD."

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