Residual stress distribution in PVD-coated carbide cutting tools - origin of cohesive damage

PVD-coatings for cutting tools mean a substantial progress for tool lifetime and cutting conditions. Such tools, however, hold the risk of cost intensive sudden process breaks as a result of cohesive damage. This damage mechanism does not consist of a coating adhesion problem, but it can be traced back to the residual stress distribution in coating and substrate. This paper shows how residual stresses develop during the process chain for the manufacturing of PVD-coated carbide cutting tools. By means of different methods for residual stress determination it is shown that the distribution of residual stresses within the tool finally is responsible for the risk of cohesive tool damage.DFG/DE 447-50-

Changes of Residual Stresses in Surface Layers of Inserts after Application of Surface Treatments

Diplomová práce se zabývá problematikou zbytkových napětí v povrchových vrstvách vyměnitelných břitových destiček ze slinutého karbidu povlakovaných chemickou depozicí par (CVD). Teoretická část pojednává o vlivu zbytkové napjatosti na životnost řezných nástrojů a možnostech měření zbytkových napětí. Experimentální část se věnuje technologii mokrého pískování, kdy je zkoumán účinek procesních parametrů dané technologie na velikost a charakter zbytkové napjatosti v povrchové vrstvě řezného nástroje. Na základě získaných výsledků bude cílem vyhodnotit optimální parametry metody mokrého pískování, které zajišťují vysokou úroveň opakovatelnosti výroby, snadnou kontrolovatelnost a celkovou stabilitu výrobního procesu s ohledem na trvanlivost obráběcího nástroje.The Master thesis deals with issue of ressidual stresses in surface treatments cutting inserts of cemented carbide deposited by chemical vapour deposition. The theory part discribes technology of surface treatments on durability of cutting tools and possibility measurement of ressidual stresses. The experimental part is devoted to the technology of wet blasting, in which the effect of the process of parameters of the technology on the size and character of the residual stress in the surface layers of the cutting tool is investigated. On the basis of the obtained results, the aim will be to evaluate the optimal parameters of the wet blasting method, which ensure a high level of repeatability of production, easy controllability and overall stability of the production process with regard to the durability of cutting tools.346 - Katedra obrábění, montáže a strojírenské metrologievýborn

Effect of pre and post mechanical treatment on pvd coated tools' characteristics and machining performance

The current study investigates the influence of micro blasting as pre-treatment and post treatment technique separately and also in combined way on various characteristics of multilayer AlTiN and dual layer AlCrN/TiAlN coatings and compared the results with as deposited coating i.e. without any micro blasting either of substrate or coating. Pre and post micro blasting were carried out using Al2O3 granulates at different pressure for both the treatments. The changes in the microstructure, elemental composition and crystallographic phases of pre-treated, post-treated as well as combined in comparison with as deposited coated tools were examined using Scanning electron microscopy, Energy dispersive X-ray spectroscopy and X-ray diffraction test. Micro hardness test was carried out using Vickers hardness tester to determine the changes in the hardness value of the samples after surface treatment. The results revealed that both pre and post blasting have significant effect on physical, mechanical and machining characteristics of multilayer AlTiN and dual layer AlCrN/TiAlN coated tools. The results during dry turning of AISI 316L grade austenitic stainless steel with various pre and post treated coated tools revealed that reduction in flank wear upto maximum of 23.426 % and decrease in cutting force upto 32.315 % was observed for combined pre and post treated tool having layers of TiAlN/AlCrN and AlTiN coatings respectively

Effect of Micro-blasting on Characteristics and Machining Performance of PVD AlTiN Coated Cutting Tools

It is essential to sustain ever increasing challenges faced by cutting tool manufacturers in improving the performance of the tools during machining of difficult-to-cut materials which have been developed in recent times. Although coated tools have found wide application in industries, there still remains a considerable scope of improvement of the properties of coatings with a view to achieve environment-friendly dry machining. Surface treatment has been identified as one of the possible avenues which has the potential to augment properties and performance of coated tools in dry machining. The current research work has utilized micro-blasting of cutting tool substrates prior to coating deposition as well as coated surface in order to recommend optimal surface treatment technique for the development of a coated tool. AlTiN coating is deposited using cathodic arc evaporation and effect of micro-blasting both as pre-treatment as well as post-treatment methodology is investigated on micro-structure, crystallographic orientation, grain size, coating adhesion and hardness. Effect of surface treatment has been finally studied during machining of 17-4 PH martensitic stainless steel. As-deposited AlTiN coating without any treatment has all along been considered for comparison. Results have clearly indicated micro-blasting as pre-treatment technique considerably enhances coating adhesion while post-treatment results in increase in hardness. Since both the properties are essential in combating coating delamination and improving wear resistance, AlTiN coating with both pre- as well as post-treatment techniques has demonstrated excellent promise in dry machining application. Significant reduction in cutting force up to 27% is observed using AlTiN coated tool subjected to both pre- and post-treatment. The same tool is also successful in bringing down in chip reduction co-efficient. While tool wear progression of only pre-treated and pre- as well as post-treated tools are similar under lower cutting speed (120 m/min), the latter clearly outperformed all the tools under higher cutting speed (150 m/min)