Showing papers in "Cirp Journal of Manufacturing Science and Technology in 2008"

Chatter stability of milling in frequency and discrete time domain

Abstract: Chatter stability of milling operations has been gaining significant attention with a view to improving the material removal rates in high speed machining of aluminum alloys and low speed milling of difficult to cut, thermal resistant alloys. This paper presents frequency and discrete time domain chatter stability laws for milling operations in a unified manner. The time periodic dynamics of the milling process are modelled. By averaging time varying directional factors at cutter pitch intervals, the stability lobes are solved directly and analytically. When the process is highly intermittent, which occurs at high speeds and low radial depth of cuts, the stability lobes are more accurately solved either by taking higher harmonics of directional factors in frequency domain, or by using semi-discretization method. This paper compares the stability solutions against the numerical solutions and experiments, and provides comprehensive mathematical details of both fundamental stability solutions.

Metal forming progress since 2000

Abstract: Considerable changes have occurred in metal forming in the last decade. A record of these changes can be found in keynote papers presented by the members of the Scientific Technical Committee—Forming, at the CIRP Annual General Meeting each year. The keynote papers are excellent references on important developments in metal forming and are used as a reference, globally. Not only is this paper a compendium of most of the keynotes presented, but from 2001 onward, it has updates on new information on five keynote subject areas. The authors of each keynote have written an update with new information that has developed since the writing of the keynote. The authors of each section are shown in order of presentation.

Helical milling of CFRP–titanium layer compounds

Abstract: Helical milling is used to generate boreholes by means of a milling tool being operated on a helical path into the workpiece. The bore diameter can be adjusted through the diameter of the helical path. In comparison to conventional drilling operations this process often results in lower burr formation and fiber delamination. Therefore helical milling is used in the aircraft industry for cutting composites and composite-metal compounds. One of these compounds, which is regarded as difficult to machine, is a layer compound consisting of unidirectional carbon fiber reinforced plastic (CFRP) and TiAl6V4. This paper presents the impact of the axial and tangential feed during helical milling on process forces and borehole quality is shown.

A perspective on manufacturing strategy: Produce more with less

Abstract: Over the last decade, the manufacturing landscape has changed worldwide. Parts of the traditional manufacturing activities have moved to world regions, away from the long-established industrial centres in Western Europe, North America and Japan. The demand for goods has been increased and so has the demand for natural resources and energy. However, since resources and energy are finite, new ways of producing more with less ought to be found. In this context, this work discusses the challenges to be addressed and focuses on the technologies, related to novel processes, materials and information/communication, which could deal with the issues pertaining to increased demand on manufacturing goods, the finite resources, and environment-conscious production.

Application of AE and cutting force signals in tool condition monitoring in micro-milling

Abstract: The paper presents acoustic emission and cutting force signals application in tool condition monitoring in micro-milling of cold-work tool steel. The results obtained revealed strong influence of tool wear on acoustic emission signal, providing acceptable results even while used separately. The signal was easy to register, and showed a very short reaction time to the tool–workpiece contact. As excitation frequency, equal to edge passing frequency, was much higher than in conventional milling, cutting forces, usually the best for this purpose, were strongly disturbed by resonance vibration of the table dynamometer. Despite these disturbances, the signals still show dependence on tool wear, making them useful for tool condition monitoring.

Investigations on reduction of tool electrode wear in micro-EDM using novel electrode materials

Abstract: In micro-electrical discharge machining discharge energies of less than We = 100 μJ per single discharge are used. Due to the short pulse durations in micro-EDM the tool electrode is usually charged as cathode to reduce tool electrode wear. Nevertheless, compared to conventional EDM, especially when relaxation generators are used, the relative wear can increase to more than 30%. In order to reduce the electrode wear, novel electrode materials can be applied. Experimental investigations aim to decrease the wear of tool electrodes by using boron doped CVD-diamond (B-CVD) and polycrystalline diamond (PCD). Both materials offer high thermal conductivity and a high melting/sublimation point which are general requirements for tool electrode materials. Until today there is a lack of knowledge regarding the process behaviour of both materials under conditions of micro-EDM with respect to the relative high specific resistance of diamond materials compared to those of copper or tungsten–copper. This paper gives an insight into latest research results regarding the process behaviour of B-CVD and PCD in micro-EDM as well as influences of electrode materials on tool electrode wear and surface formation processes.

Characterisation of chip formation during orthogonal cutting of titanium alloy Ti–6Al–4V

Abstract: The mechanics of segmented chip formation during orthogonal cutting of titanium alloy Ti–6Al–4V are studied in detail with the aid of high speed imaging of the chip formation zone. Cutting speeds from 4 to 120 m/min and feeds of 0.05, 0.075 and 0.1 mm were used. Segmented chip formation was observed throughout and detailed measurements of recorded video sequences examined the deformation within chip segments and within the shear bands separating the chip segments. The chip segment geometry was characterised in terms of the cutting parameters given above and the shear strains both within the chip segments and the shear bands were analysed. A thermal model of the process was developed and average temperatures for the primary shear zone and for the tool rake face were calculated.

Research on generation of three-dimensional surface with micro-electrolyte jet machining

Abstract: This paper proposes a method to generate three-dimensional surfaces with micro-electrolyte jet machining and discusses how to determine the nozzle path and scanning speed. In order to verify the effectiveness of the proposed method, calculated and machined results were compared. It was found that three-dimensional surfaces can be generated by superimposing elemental curved grooves, and good agreement between the cross-sectional shapes of the superimposed and machined surfaces with those of the target surface proves the effectiveness of the proposed method. In addition, layer-by-layer machining with optimized interval of the nozzle path is an effective way to reduce machining errors.

Toward value co-creation in manufacturing and servicing

Abstract: This paper surveys a prospect in manufacturing and service innovation by proposing a new concept of value co-creation. Starting with discussion of the analysis of existing things and the synthesis of new artifacts, a value-creation model is introduced based on the concept of emergent synthesis. The value-creation model includes three classes: Providing Value (Class I), Adaptive Value (Class II) and Co-creative Value (Class III). Class III is a novel concept to extend the value by co-creation among producers (providers) and customers (receivers). This paper also suggests a theoretical importance of the network externality which is a social effect on customer's utility, by showing a study example on value-creation in the market.

FEM-supported simulation of chip formation and flow in gear hobbing of spur and helical gears

Abstract: An integrated procedure for simulating the complicated chip formation and flow in gear hobbing is presented. The mathematical description of this manufacturing method is based on the calculation of penetrations between cutting teeth and gear gap, a solid modeling process and finally an implementation into a FEM code. Additionally, hobbing of spur gears and the four possible variations for manufacturing helical gears are investigated. A comparison of the calculated chips with the cut ones was conducted and revealed a sufficient similarity. Finally, visualization of phenomena such as of the chip collision with gear flanks during the chip flow in individual generating positions is provided.

Improvement of the numerical modeling in orthogonal dry cutting of an AISI 316L stainless steel by the introduction of a new friction model

Abstract: A better understanding of friction modeling is required to lead to more realistic finite element models (FEMs) of machining process. This work proposes to evaluate the performance of a new friction model depending on the local sliding velocity, compared to a standard approach considering a constant Coulomb friction coefficient. A finite element model, based on the Arbitrary Lagrangian–Eulerian (ALE) approach, was developed for orthogonal machining. This model has been applied to the investigation of an AISI 316L stainless steel in dry cutting. It has been shown that the material removal is very sensitive to the friction model. The flow of the workmaterial along the interfaces tool–workpiece–chip is very much disturbed by a variation of the friction model. The new friction model, previously published and introduced in this model, has shown its higher efficiency to reach reasonable data about the material removal phenomena.

Cutting edge preparation to improve drilling tools for HPC processes

Abstract: High material removal rate, high cutting parameters and, hence, high resultant forces are characteristics of high performance cutting. Due to these greater requirements on cutting tool material with respect to its strength and wear resistance, as well as the applied coating, the cutting edge design also gains in importance. By cutting edge preparation, the process reliability can be enhanced through a reduced chipping and a defined rounding along the cutting edge. In this research, the abrasive water jet blasting process was used to prepare different cutting edge designs of carbide twist drills prior to coating. Based on the results of drilling tests using high performance cutting conditions, it was determined that the high performance process can be effectively optimized with respect to workpiece quality and tool life by selectively varying the microscopic cutting edge form.

The influence of cutting edge sharpness on surface finish in facing with round nosed cutting tools

Abstract: The range of and particularly the minimum surface roughnesses achievable mainly with cemented carbide but also with single crystal diamond round nosed turning and facing inserts has been experimentally studied, machining aluminium and steel on engineering and precision lathes. Characteristic variations of machined surface profile with feed rate as well as insert edge sharpness and roughness measurements are reported. For aluminium faced by carbide inserts on precision lathes, insert edge radius (re) rather than feed marks determined Rz at low feeds, with Rz 0.02re. For steel work material, its properties rather than the insert edge radius became the Rz determining factor. 2008 CIRP.

Electrical probing for dimensional micro metrology

Abstract: Each dimensional measurement is based on probed points on the surface of the measured object. However, the well-established tactile and optical probing techniques face limitations when small and delicate objects with complex shape have to be measured. With tactile measurements there is always the danger of damaging the workpiece by the probing force and the measurable point rate is quite low. With optical probing there is a principal resolution limit and accessibility to complex surfaces is hindered by the limited acceptable surface slope. Also undercuts are not measurable. To overcome these limitations a probing system based on an electrical probing interaction with a direct current of a few nanoamperes has been developed, tested and compared with traditional technologies. With this probing system coordinate measurements of micro parts as well as nanometer resolved surface topography measurements are feasible. By applying a wide range of probes accessibility problems can be drastically reduced compared to tactile or optical micro probing systems.

Position-oriented process monitoring in freeform milling

Abstract: Today’s process monitoring applications in the area of five-axis milling are based on strategies developed for machining operations of one or maximum three effective degrees of freedom. Applied static and dynamic threshold monitoring can be used to detect excessive loads, but do not enable the basic evaluation of process behaviour. As alternating machining conditions do not allow a determination of the machining characteristics, it becomes apparent that a machining position-oriented monitoring solution would reveal a basic opportunity to improve the monitoring abilities in a freeform cutting process. In this paper a metrological solution is introduced, which allows a position-oriented inspection of a five-axis milling process. Measurement chains which have been integrated into a machining centre are described. Experimental results of measuring the processes’ cutting forces in parallel to the machine’s axes position and the needed technological environment and software solutions are presented.

Characterization and optimization of the dynamic tool path of a highly dynamic micromilling machine

Abstract: The miniaturization of components in the field of life science, consumer electronics and micro-electro-mechanical systems (MEMS) is becoming a part of our everyday life. As the manufacturing of these components demands in many cases the machining by micromilling with cutting tools down to 100 μm diameter, highly dynamic machine tools are needed to machine the more and more complex freeform surfaces at optimal process parameters. The paper describes the development of a highly dynamic milling machine which is equipped with linear direct drives in all axes with integrated impulse decoupling units to allow high dynamics and especially high jerks at low impact on the machine structure. Additionally the development of a metrology frame is detailed which can be used to characterize the dynamic tool path of machine tools to optimize its dynamic setup and to increase the work piece precision at minimized machining time.

Design of a virtual environment as a tool for diagnosis and monitoring

Abstract: This paper proposes a general methodology aiming at developing a virtual environment emulating the behaviour of a real machine-tool axis from a mechanical point of view. This design includes a modelling phase, taking into account bending modes, friction phenomena, inverters and servomotors and cascaded control strategy. Unknown parameters are further deduced from a global identification procedure, based on limited feasible experiments. This simulator can thus be used to evaluate mechanical parts, and is also an efficient tool which enables developing a procedure for a periodic diagnosis of the machine. This virtual environment is validated based on the particular example of a hobbing machine dedicated to gear cutting of car gearboxes.