Boosting Machining Productivity with the aid of coatingsSince the introduction of the first PVD coatings in the 1980s, more than 70 coating materials for tools

have been developed. Oerlikon Balzers now aims to alleviate the ordeal of choice, at least for drilling tools.

The company presented a new coating solution at EMO 2011 that covers all drilling applications.

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ApplIcAtIon

Boosting efficiency, ensuring processes, dealing with manufacturing costs for com-ponents, striving for the utmost precision and handling innovative materials are the megatrends driving innovations in produc-tion technology – and in the field of PVD coatings for tools too. At the same time, the further development of coatings is not pro-ceeding merely in parallel with the demands emanating from production technology.

The objective of the developer has always been to contribute to the advancements achieved in economic efficiency as well as production reliability. In this regard, a gen-eral rule applies that a significant reduction in costs relating to the mechanical process-ing can only be realised through stepped-up productivity of the tools utilised.

This is manifested in a simple calcula-tion. For example, a 50 % increase in the service life of the tool leads to cost savings of merely 1 % per component. Even a 30 % reduction in the cost of the tool results in savings amounting to the same extent, at best. On the other hand, improving the cutting parameters by 20 % can reduce the manufacturing costs by 15 % and more. However, specific circumstances apply depending on the relevant application, 1.

drIllIng tools

Increasingly demands on drive train com-ponents for years have justified the use of

innovative, more high-performance materi-als. Some examples include austenitic duc-tile iron and vermicular grey cast iron. The high degree of tensile strength and abra-siveness of these special iron-based materi-als pose significant challenges for the coated tool. At the same time, the automo-tive industry requires that such materials are processed at the same costs as conven-tional materials. In order to ensure that this requirement is fulfilled, the technology of high-performance drills – with accelerated cutting speeds and feed rates – is regarded as the process of choice for boosting pro-ductivity and thus reducing the production costs associated with drilling. The use of conventional drilling tools at vc = 80 m/min is giving way to a new generation of high-performance drills with accelerated cutting speeds of up to vc = 200 m/min.

Quasi-dry processing also promises sav-ings potential through minimum quantity lubrication (MQL), based on the fact that with conventional cooling lubrication sys-tems the costs for the cooling lubricant itself as well as the expenses relating to disposal of the cooling lubricant must be taken into account. The use of MQL can lead to a con-siderable reduction in this cost component.

In order to take into account the vast array of applications and materials, numer-ous standardised PVD coatings have been developed in recent years. In fact, just one coating material was available in 1980, while in the interim there is a selection of more than 70 to choose from. Added to

dr. WolfgAng KAlssis Market Segment Manager for

cutting Tools at Oerlikon Balzers ag in Balzers (liechtenstein).

auThOr

❶ Development of cutting performance of end mill cutters

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that are many additional application-spe-cific coatings directly from small coating technology firms and tool manufactures. Just for the drilling segment, there is a selection of coatings available based on titanium aluminium nitride (TiAlN), alu-minium titanium nitride (AlTiN) and aluminium chromium nitride (AlCrN) – and featuring monolayer, multi-layer and nano-composite versions as well.

Consequently, this initially led to a vast degree of variance in the production proc-ess due to diverse drilling geometries as well as a variety of coatings possibly origi-nating from different providers. This is exemplified by the mechanical engineering sector, where a company may utilise a total of 780 drills in the production process var-ying according to length, diameter, geome-try and coating. However, this vast degree of variance must also be factored into the tool processing and procurement activities.

Oerlikon Balzers aims to provide a con-tribution towards alleviating the situation with the introduction of a new, all-around coating for all applications in the automo-tive industry. Indeed, the company is the leading provider of coatings for drilling tools, with historically evolved know-how revolving around coating materials. Hence, Oerlikon Balzers has succeeded in achiev-ing advances in the oxidation resistance and temperature hardness of PVD coatings in recent years. The most significant achievements are coatings based on alu-minium chromium nitride (AlCrN) – such as Balinit Alcrona Pro or Alnova – and the targeted development of hard-material coat-ings aimed at influencing oxidation resist-ance and high-temperature parameters.

However, the greatest challenge is find-ing the right balance between hardness and residual stress. This affects not only the abrasion resistance of the coating, but also the drilling performance with through-holes, drilling through casting surfaces and under less stable cutting conditions. Multi-layer coatings can also provide an advantageous effect. The indi-vidual coating layers absorb the energy of the fissures, thus preventing widening of the fissure into the substrate and, as a result, extending the tool’s service life, but particularly the tool’s reliability too.

Oerlikon Balzers has continued to con-sistently further develop this concept, incorporating technical material know-how, analytical analyses with, among other things, a transmission electron microscope as well as extensive simulations and cutting tests in in-house laboratories. These activi-ties cleared the way for a transformation of the multi-layer concept into the nano-layer concept with optimum layer intervals.

The concept offers numerous advantages. The new coating is actually a coating solu-tion that covers all drilling applications, including moderate to high-speed cutting for drilling through steel. Due to the very smooth surfaces, the coating is also suitable for deep-hole drilling as well as for process-ing demanding casting applications, 2.

geAr tools

Advanced surface technology has also been regarded as “the enabling technology” and the key to stepped-up productivity in the gear manufacturing sector for more than 25 years, which is attributable to the typical cost allocation. Merely 8 % of costs are

incurred directly by the tools, while 12 % – depending on the system – must be used for cooling. The set-up incurs roughly 24 % of the costs, with 26 % allocated to other expenses that are not directly controllable. Finally, the largest single cost item relates to the cutting operations, 3.

However, extending the cutting parame-ters results in a more pronounced mechani-cal and thermal burden on the cutting mate-rial. Hence, the tool materials as well as coatings are playing an increasingly signifi-cant role. Already in the late 1980s, the first PVD coating based on titanium nitride (TiN) enabled considerable acceleration of cutting speeds. At the same time, this extended the service life of the tools as well, which could be traced to the improved sur-face hardness realised through the PVD coatings. Consequently, this, in turn, led to higher abrasion resistance, better cutting processes and reduced heating of the tools.

The first titanium carbon nitride (TiCN)-based coatings developed at the beginning of the 1990s paved the way for the next step on the path toward accelerating cut-ting speeds. The next milestone followed in 1996, with titanium aluminium nitride (TiAlN)-based coatings, which already more than doubled the boost in perform-ance versus untreated tools. In 2004, Oer-likon Balzers provided another answer to the demand for further improvements on the market: the aluminium chromium nitride (AlCrN)-based coating Balinit Alc-rona, promising extended service life with high-speed cutting process and significant process reliability as well as re-coating without reducing performance, 4.

The AlCrN-based coatings offer better performance and higher productivity com-

2 Drill coated with Balinit helica

3 factors influencing production costs

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pared with their predecessors. Key fea-tures such as temperature hardness, ther-mal shock stability and abrasion resist-ance have been further optimised in order to realise favourable results in the cutting and forming processes – even under extreme conditions, 5.

Oerlikon Balzers took a further step in 2010 with Balinit Alcrona Pro, based on the Balinit Alcrona coating. Optimising the process parameters and modifying the coating structure led to significant improvement in the coating’s residual stress profile and temperature change resistance. Depending on the application, the coating can achieve a boost in per-formance of 20 % and more compared

with its predecessor, at moderate cutting speeds (vc = 110 to 160 m/min) and wet processing as well as at high cutting speeds (vc = 160 to 220 m/min) and dry processing.

Current developments relate to further improvement in the high-temperature properties of the coatings and additional boost in cutting speeds. The target calls for >250 m/min for tools made of pow-der-metallurgical high-speed steels as well as >500 m/min for carbide tools.

outlooK

Developments of recent years show that target-specific modification of the coating

properties through the composition of the coating materials and/or the process parameters is possible during deposition. Essential coating properties, such as abra-sion resistance, temperature hardness, thermal conductivity as well as adhesive performance and coating roughness, can be specifically influenced, paving the way for the design of coating systems for the respective application.

The periodic table of the elements still offers numerous opportunities for improv-ing PVD coatings. Target-specific measures for optimisation are possible through in-depth comprehension of the correlations between the cutting process, mechanical and thermal properties of coatings, and the respective coating parameters. Close coop-eration with universities and research facil-ities involving theoretical models as well as experiments have led to the efficient short-ening of innovation cycles.

At the same time, the performance of coatings is inextricably linked to the surface quality of the substrate material. First of all, the ideal interaction of all parameters ena-bles the coating to develop its full potential.

Advanced surface technology can ulti-mately provide significant contributions to resource-saving and energy-efficient pro-duction as well. At the same time, the enhanced utilisation of the coating materi-als used in the process – so-called targets – harbour the greatest potential in terms of efficient use of resources. Enormous amounts of funds have been invested in order to exploit this potential: for example, Oerlikon Balzers invested several million euros just in the years 2007/2008 in rele-vant technological improvements aimed at converting and upgrading its coating centres.

The positive impact on the environment of PVD technology has been determined by taking into consideration the ecological balance. For instance, the use of resources with PVD coatings amounts to merely 10 % compared with the manufacture of a carbide tool. Furthermore, ecologically relevant potential is also derived through application-specific uses: for example, modern AlCrN-based PVD coatings signifi-cantly extend the service-life of tools and therefore save the corresponding energy and resources in the production process. And with the higher the quality of the coating, this savings potential becomes even greater.

4 Development in gear cutting

5 Balinit alnova – improved hardness at application temperature (source: university of cleveland Ohio, Oerlikon Balzers)

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