Ein neues Werkstoffkonzept zur trockenen Bearbeitung mineralischer Materialien

A new material concept for machining of mineral materials For the machining of mineral materials like rock, concrete and asphalt ultra hard cutting‐tools such as diamond tools are used. During the use diamond tools are cooled with water to remove the heat and to prevent an early deterioration of the diamonds. Without water cooling the diamonds at the cutting edge as well as in lower levels are damaged. For ecological and economic reasons a dry machining of mineral materials is of great interest. The consumption of coolant and the pollution of occupied buildings by alkaline water would be decreased. But specific diamonds tools are necessary to realise a dry machining. The Institute of Materials Engineering pursues a novel material concept for diamond impregnated composites to protect diamonds in deeper layers. Materials with a very low thermal conductivity are inserted in the diamond‐composites to protect the diamonds against heat and to reduce the deterioration of diamonds in lower levels. Cobalt and bronze (CuSn 85/15) with particle sizes of 45–90 μm and < 40 μm, diamonds with particle sizes of 300–450 μm and alumina with particle sizes of 350–500 μm, 150–210 μm and < 70 μm were used. The diamond‐alumina‐composites were powder metallurgically produced and were examined by light‐ and electron microscopy and digital image analysis.     

Beschichtungen lassen Werkzeuge kalt

Temperature of cutting tools by thin films During the cutting process, cutting tools are exposed to complex mechanical, thermal, dynamic and tribological loads. Especially in the case of dry machining the demands on cutting tools are very high. Dry machining becomes more and more interesting because of tightened up ecolaws and increased costs for the handling of coolants. Due to a renunciation on coolants the cutting tools need to be modified to the process of dry machining. Thereby modern plasma and ion based surface technologies can be used to deposit a thin film adopting the functions of coolants, e.g. cooling and lubricating. In this research project several coating types, e.g. titanium and chromium based coatings, where developed and characterized regarding their mechanical, tribological and thermal properties. For the research, four partners collaborated permuting all steps of surface and coatings design. Materials Science Institute (WW), Aachen University of Technology, performed the development of PVD coatings and the thermophysical characterization by thermal wave analysis. Surface modifications of uncoated and coated tools by ion beam assisted deposition were carried out at Stiftung Institut für Werkstofftechnik (IWT), Bremen. To determine the cutting properties of coated tools, practical tests were performed at Laboratory for Machine Tools and Production Engineering (WZL), Aachen University of Technology.     

Environment Friendly Machining of Ni–Cr–Co Based Super Alloy using Different Sustainable Techniques

In order to eradicate the use of mineral based cutting fluid, the machining of Ni–Cr–Co based Nimonic 90 alloy was conducted using environment friendly sustainable techniques. In this work, uncoated tungsten carbide inserts were employed for the machining under dry (untreated and cryogenically treated), MQL, and cryogenic cutting modes. The influence of all these techniques was examined by considering tool wear, surface finish, chip contact length, chip thickness, and chip morphology. It was found that the cryogenically treated tools outperformed the untreated tools at 40 m/min. At cutting speed of 80 m/min, MQL and direct cooling with liquid nitrogen brought down the flank wear by 50% in comparison to dry machining. Similarly at higher cutting speed, MQL and cryogenic cooling techniques provided the significant improvement in terms of nose wear, crater wear area, and chip thickness value. However, both dry and MQL modes outperformed the cryogenic cooling machining in terms of surface roughness value at all the cutting speeds. Overall cryotreated tools was able to provide satisfactory results at lower speed (40 m/min). Whereas both MQL and cryogenic cooling methods provided the significantly improved results at higher cutting speeds (60 and 80 m/min) over dry machining.     

陶瓷刀具切削304不锈钢时的磨损性能

采用Ｓｉ３Ｎ４陶瓷刀具切削Ｔｉ基陶瓷，ＹＴ１５硬质合金和高速钢四种刀具对３０４奥氏体不锈钢进行了切削试验，比较各种刀具的耐磨性能，并且用ＳＥＭ，ＥＤＸ等对刀具的磨损表面进行分析。     

Numerical analysis of coating–substrate systems

Coated tools having a higher edge life compared to uncoated ones are well suited for high speed or dry machining and produce a higher product quality. So coating technology gained a growing importance for industrial applications. To achieve further progress in the development of new coating systems, it is desirable to combine the experimental dominated developing process with numerical simulations for the influence of external loads on the stability of the coatings, which mainly depends on the deformation state and on the stress–strain situation inside the tool. These quantities are computable by 3D finite element simulations. Since the thickness of the coatings is tiny compared to tools' measures, such computations must be performed on highly graded meshes to lay hold of the tool's geometry as well as of the microscopic layers. Even when adapting the mesh density to the accuracy requirements in an optimal manner, the dimension of the FE systems, the computational effort and the storage requirements are extremely large, pushing the limits of standard hardware, even when advanced storage technologies and solvers for the FE matrices are used. On parallel computers, the runtime may be considerably reduced and the available storage is substantially enlarged.     

Identification of machining features based on available resources of cutting tools

In research on machining feature recognition, the problems of interacting features and availability of cutting tools are considered two major obstacles for developing industrial applications. In this research, a new machining feature recognition approach is developed to address these problems. In this work, a new concept called cutting mode is introduced to associate generic machining surfaces and cutting motions. In the feature recognition process, the machining surfaces of a part are first mapped to cutting modes, and these cutting modes are further mapped to available cutting tools. Among all the created candidate machining processes, heuristic rules are employed to identify the optimal solution that requires the minimum number of setups. When a number of machining surfaces are associated with a cutting tool in the same setup, these surfaces are grouped as a machining feature. Therefore the interacting features are recognised by the different cutting tools to produce these features. A database of available cutting tools is used to avoid the identification of features which cannot be machined in a machine shop. Three mechanical parts with interacting features are selected in the case studies to demonstrate the effectiveness of the developed approach.     

Diamond and cBN hybrid and nanomodified cutting tools with enhanced performance: Development,testing and modelling

The potential of enhancement of superhard steel and cast iron cutting tool performance on the basis of microstuctural modifications of the tool materials is studied. Hybrid machining tools with mixed diamond and cBN grains, as well as machining tool with composite nanomodified metallic binder are developed, and tested experimentally and numerically. It is demonstrated that both combination of diamond and cBN (hybrid structure) and nanomodification of metallic binder (with hexagonal boron nitride/hBN platelets) lead to sufficient improvement of the cast iron machining performance. The superhard tools with 25% of diamond replaced by cBN grains demonstrate 20% increased performance as compared with pure diamond machining tools, and more than two times higher performance as compared with pure cBN tools. Further, cast iron machining efficiency of the wheels modified by hBN particles was 80% more efficient compared to the tool with the original binder. Computational model of hybrid superhard tools is developed, and applied to the analysis of structure-performance relationships of the tools.     

Experimental studies on the cryogenic machining of biodegradable ZK60 Mg alloy using micro-textured tools

Reducing the contact area between the cutting tool rake surface and chip promotes the machining performance of the work material and increases the tool life. Magnesium alloys are ductile-lightweight materials that form continuous chips during machining. The present investigation discusses the orthogonal turning of ZK60 magnesium alloy with linearly textured cutting inserts under both dry and liquid nitrogen (LN₂) cooling conditions. Linear grooves that are parallel and perpendicular to chip flow direction were created using Nd-YAG laser on the tungsten carbide cutting inserts. The effect of texturing combined with the application of LN₂ cooling is studied by evaluating the machining temperature and forces, microhardness, surface roughness and tool wear. Textured tools considerably minimize the liaison area of the chip with the rake plane compared to non-textured tools, which resulted in favorable effects in machinability. In case of cryogenic machining, textured tools substantially minimize the friction by the coupled effect of micro-pool lubrication and the formation of thin-film lubrication between the tool–chip/tool–work interfaces. Parallel-textured tools aided with cryogenic cooling exhibit superior performance during machining among the different types of tools employed in the present investigation.     

Surface damages and tool wear mode in end milling of hastelloy‐C276 under dry and wet conditions

Hastelloy‐C276 is a nickel based superalloy that is widely used in chemical, petro‐chemical, environmental and nuclear industries due to its outstanding performance in a wide range of corrosive mediums. The superior properties of nickel based superalloys impair their machinability which increases the difficulty in obtaining a good surface finish. Because most of the components' failures are initiated from surface defects, several researchers have been concerned about surface integrity in machining aerospace superalloys particularly Inconel‐718. Due to the lack of studies done on machining corrosion‐resistant superalloys, this study aims to investigate surface damages and tool wear modes in milling Hastelloy‐C276 under dry and wet conditions. The absence of cooling and lubricating actions in dry machining resulted in the formation of craters, severe plastic deformation, voids, debris re‐deposition and materials drag. The breakage of the nucleated carbide phases resulted in the formation of nucleated cavities on the machined surface in both wet and dry machining. Adhesive tool wear was less in dry machining due to the formation of oxide layers on tool faces which suppressed the formation of built‐up edges due to the weak adhesion properties of oxide compounds which resulted in less surface roughness at v_c = 50 m/min. On the other hand, the higher temperature and friction in dry machining resulted in severer tool coating delamination.     

Comparative Wear Behavior of Ceramic and Carbide Tools During High Speed Machining of Steel

Two types of oxide-based ceramic cutting tools have been developed for high speed machining of hardened steel. These tools were made of alumina (A1₂O₃) and zirconia toughened alumina (ZTA). Commercially available tungsten carbide (WC)-based tools were also used during machining for comparison. In general, ceramic tools exhibited superior performance as compared to the WC tools, especially at higher machining speeds, both in terms of tool life and surface finish of the work-piece. The worn-out tools were observed under a stereo-microscope for studying the role of different wear mechanisms on the tool life. While severe crater wear was observed in the WC tools, only a small amount of edge chipping and nose wear occurred in the ceramic tools during high speed machining. The correlation between the mechanical properties of the tool material, the tool lives and their wear behavior was also studied.     

Evaluation of advanced alumina-based ceramic tool inserts when machining high-tensile steel

Three types of alumina-based ceramic tools (zirconia toughened, titanium-carbide reinforced and silicon-carbide-whisker reinforced) were used to evaluate their cutting performance when machining a high-tensile steel. Experimental studies were carried out at various cutting speeds, feeds and depths of cut, in dry conditions. The cutting performance of the alumina-based ceramic tools was judged by the cutting force produced during the process of machining, by the surface roughness of the workpiece and by the wear rate of the cutting inserts. The influence of the cutting parameters (that is, the cutting speed, feed rate and depth of cut) on the cutting performance is discussed.     

Tool life and surface integrity when milling inconel 718 with coated cemented carbide tools

Abstract

This paper presents a study of tool life and surface integrity while machining superalloy Inconel 718 using coated cemented carbide tools. In the machining of heat resistant superalloys used in aeronautical applications and classified as difficult‐to‐machine, tool life is an important parameter in evaluating the performance of the cutting tools. Surface quality of the workpiece is one of the important criteria in determining tool life. Our tests have been done under various combinations of speed, feed rate, and depth of cut to verify the change in surface roughness due to increasing tool wear. The behavior of the uncoated, TiN, and TiCN layers using various cutting conditions was analyzed. At the end, a choice of coating and optimization of the cutting conditions has been proposed.     

CrAlSiN nanocomposite thin films for high-speed machining applications

CrAlSiN nanocomposite thin films with varying film chemistry were developed on tungsten carbide (WC) specimens using cylindrical cathodic arc physical vapor deposition (c-CAPVD) technique. The physical, mechanical, and tribological properties of all the films were comprehensively investigated for arriving at the film chemistry leading to the best properties with respect to mechanical applications. The best tribo-mechanical properties were obtained in films with Cr/(Al+Si) ratio of 1.2. This coating with best properties was translated on to WC drill bits for machining tests. The Al and Si content has shown major influence on the adhesion strength and phase constitution of the films, with a considerable change in residual stress too. The superior properties achieved could be attributed to the formation of a near-perfect nanocomposite structure, with the crystalline CrAlN phase surrounded by an amorphous Si₃N₄ phase. The tool life of the coated CrAlSiN tools was investigated during dry machining of EN 24 material. In comparison to the tool life of an uncoated tool and a TiAlSiN-coated tool, the best CrAlSiN coatings synthesized in this study performed exceedingly well. The present study clearly demonstrates the advantages of CrAlSiN over other existing similar coatings for high-speed machining.     

Comparative study of the effect of surface texturing on cutting tool in dry cutting

Recent researches in the field of dry machining have indicated that surface texture has the potential to influence tribological conditions. Researchers have studied the application of controlled surface microtextures on cutting tool surfaces to improve machining performance by changing the tribological conditions at the interfaces of tool–chip and tool–work piece. An experiment to study the performance of the microtextured high-speed steel cutting implement within the machining of steel and aluminum samples was performed. Surface textures were introduced using Rockwell hardness tester, Vickers hardness tester, and by scratching with diamond dresser on the face of single point cutting tool. Machining in dry conditions was applied on mild steel (EN3B) and aluminum (AA 6351) samples using lathe machine with microtextured and traditional cutting tool for the constant range of feed, depth of cut, and for varying range of cutting speeds. Measurement of cutting force, cutting temperature, and surface roughness of the work surfaces after machining were made. The results showed reduction in cutting forces and cutting temperature with textured tools in comparison with those of the untextured tool. Chips collected from different samples were studied under a microscope and the results showed that textures created on the tool surface by various methods exhibited variations in chip formation. Cutting tools without texture and with texture were comparatively studied and the outcomes of the experimental study are presented in this paper.     

Properties,applications and manufacture of wear-resistant hard material coatings for tools

Wear processes during machining with cemented carbides and the effect of coatings on wear and on toughness are described. The requirements for coatings relating to optimum tool life are reviewed. Recently developed multilayer coatings with and without ceramic layers are described and examples for improvements in the tool lifetime are given. Additionally, some examples for the application of coatings for milling and chipless forming are presented.The wear-reducing effect of coatings on steel tools is described and possibilities for applications of steel tools coated using chemical vapour deposition (CVD) are elucidated. A number of examples for coated cutting and chipless forming steel tools are described.Finally, useful processes for the coating production are considered. A comparison between physical vapour deposition and CVD processes with respect to the coating temperature, the consistency and the adhesion of the coating is presented. The CVD process for economic production is considered and a suitable coating unit is outlined.     

Machining of high performance workpiece materials with CBN coated cutting tools

The machining of high performance workpiece materials requires significantly harder cutting materials. In hard machining, the early tool wear occurs due to high process forces and temperatures. The hardest known material is the diamond, but steel materials cannot be machined with diamond tools because of the reactivity of iron with carbon. Cubic boron nitride (cBN) is the second hardest of all known materials. The supply of such PcBN indexable inserts, which are only geometrically simple and available, requires several work procedures and is cost-intensive. The development of a cBN coating for cutting tools, combine the advantages of a thin film system and of cBN. Flexible cemented carbide tools, in respect to the geometry can be coated. The cBN films with a thickness of up to 2 µm on cemented carbide substrates show excellent mechanical and physical properties. This paper describes the results of the machining of various workpiece materials in turning and milling operations regarding the tool life, resultant cutting force components and workpiece surface roughness. In turning tests of Inconel 718 and milling tests of chrome steel the high potential of cBN coatings for dry machining was proven. The results of the experiments were compared with common used tool coatings for the hard machining. Additionally, the wear mechanisms adhesion, abrasion, surface fatigue and tribo-oxidation were researched in model wear experiments.     

Near-Cryogenic Machining of Polymethyl Methacrylate for Micromilling Tool Development

Micromilling tools with a diameter of 22 micrometers were developed to machine polymethyl methacrylate (PMMA) for micro systems applications. Due to the small diameter of the tool, and therefore its slow cutting speed, the specific cutting energy of PMMA in the near-brittle state was needed so the micromilling feed could be estimated. To determine the specific cutting energy in the near-brittle state, PMMA was cooled with liquid nitrogen and machined with diamond tools under normal machining conditions. Cutting forces and surface finish were measured from room temperature down to -53°C. It was found that as the temperature of the PMMA was reduced, the specific cutting energy increased linearly to approximately that of oxygen-free high conductivity copper. It was also found that the surface finish became rougher as the temperature decreased. Using these results, micromilling tools were fabricated using focused ion beam machining. The tools were used to micromachine PMMA electroforming molds with high precision, small features, and excellent surface finish. Using the feed indicated from the cryogenic machining and other tests, the micromilling tools did not break after extended periods of machining.     

Enriched machining feature-based reasoning for generic machining process sequencing

This paper presents an enriched machining feature (EMF)-based reasoning approach to generic machining process sequencing for distributed process planning (DPP). An EMF is represented by combining its machining volume with surface, geometric and volume features, as well as other technological information needed to machine the feature. The information embedded in the EMF is retrieved progressively for machining sequence generation. Following an introduction of EMF and its representation scheme, the problems in determining machine-independent feature groups (set-ups) in DPP and their machining sequences to be followed for a given part are investigated. Based on the EMF concept, five reasoning rules are formulated and the algorithms developed. As the set-ups and sequences are generated based on manufacturing constraints and datum references but separated from specific resources, they are generic and applicable to machine tools with varying configurations and capabilities. This approach is further validated through a case study.     

Setup and fixture planning in automated process planning systems

This research deals with the problems of setup and fixture planning for the machining of prismatic parts. The overall aim is to design the minimum number of setups that can be fixtured and machined using the available fixture elements and tools on the shop-floor. Setup planning takes into account machining sequence constraints, machine tools, as well as the feasibility of fixturing. A general scheme for search strategies in such planning is developed and implemented. The greater part of this work is aimed towards the development of an automatic fixture planner. A generalized representation scheme for a variety of fixture elements using geometric as well as functional properties is developed. A methodology is described to build up assemblies of fixture elements complete with the workpiece. The proposed approach has been implemented as part of an existing automated process planning system called the Quick Turnaround Cell.     

Development of ANFIS model and machinability study on dry turning of cryo-treated PH stainless steel with various inserts

This present investigation deals about the machinability comparison of cryogenically treated 15-5 PH stainless steel with various cutting tools such as uncoated tungsten carbide, cryogenic-treated tungsten carbide and wiper geometry inserts. Cryo-treated PH stainless steel is considered as the work material in this investigation and experimental trials were performed under dry turning condition. The machinability aspects considered for evaluation are cutting force (F_z), surface roughness (R_a) and tool wear. The outcomes of experimentation reveal that the tungsten carbide inserts which are cryogenically treated provide improved performance in machining while comparing with conventional and wiper geometry inserts at all machining conditions. The measured cutting force and the observed flank wear were less for the cryo-treated inserts. However, wiper tool produces a better surface finish during machining. An artificial intelligence decision-making tool named Adaptive Neuro Fuzzy Inference System has been evolved to determine the relation among the considered input machining variables and output measures, namely cutting force and surface roughness of the machined surface. An analysis has been performed to compare the results obtained from developed models and experimental results.