Identifying process parameters influencing gear runout

The hardening distortions with respect to base body, clutch teeth and helical gears are investigated for a serial‐produced main shaft gear of a 20NiCrMoS6‐4 steel. The influences of casting geometry, annealing heat treatment and stress relief annealing of blanks, as well as vertical and horizontal loading arrangements during case hardening, are studied. The concentricity, roundness and runout of clutch teeth and helical gears are measured in the soft machined, hardened and hard‐machined conditions. The Brinell hardness is measured on blanks obtained from different manufacturing routes showing differences in hardness and scatter. Stress relief annealing lowers the hardness and the scatter for all groups, but has no significant effect on distortions. The case depth, core hardness and surface hardness are measured after hardening. The study shows that the surface hardness correlates with the oil flow measured in the quench tank. The effect of casting geometry is stronger for the clutch teeth compared to the helical gears. For the clutch‐teeth roundness and runout, significantly lower values are found for square geometry compared to rectangular. It is also seen that the major part of the runout comes from roundness errors which are mainly induced by the hardening. Horizontal loading reduces roundness errors and runout but produces conical base‐bodies with worse backplane flatness.     

Ultrasonic Assisted Electrical Discharge Machining of Ti–6Al–4V Alloy

In this research, an attempt was made to investigate the influence of copper tool vibration with ultrasonic frequency on output parameters in the electrical discharge machining of Ti–6Al–4V. The selected input parameters for the experiment comprise of ultrasonic vibrations of tool, current and pulse duration and the outputs are tool wear ratio (TWR), material removal rate (MRR), and stability of machining process and surface integrity of a workpiece, including surface roughness, thickness of recast layer, and formation of micro cracks. Scanning electron microscope and X-Ray diffraction were employed to examine the surface integrity of the workpiece. The results revealed that tool vibration with ultrasonic frequency enhances MRR via increasing normal discharges and decreasing arc discharges and open circuit pulses. Also, by using ultrasonic vibrations in finishing regimes, the density of cracks and TWR decrease while in roughing regimes, the thickness of recast layer, density of cracks, and TWR increase.     

Hardening distortions of serial produced crown wheels

The hardening distortions of serial produced crown wheels are studied with respect to gear runout, inner diameter and back‐face tilt. The data analysed originates from a production data base from ordinary production as well as from directed experiments carried out in production, resulting in a large set of data. Strong influences are found for steel plants, position of material in ingots and stacking levels on hardening trays. It could be concluded that rectangular strands have a detrimental effect on gear runout, which, however, can be strongly decreased by disabling the magnetic stirring during casting. Furthermore, the inner diameter after quenching is influenced by the stacking level on the hardening tray when free‐hardening or when using a segmented central expander during press quenching. This influence is attributed to variations in hardening temperature. When press quenching using a fixed mandrel, the effect of stacking level disappears. Moreover, it is found that the back‐face tilt strongly depends on the position in the ingot as well as on the stacking level on the hardening tray.     

Vibration Suppression of Thin-Walled Workpiece Machining Based on Electromagnetic Induction

Thin-walled workpieces are largely manufactured in the aerospace industry. The manufacturing process has been a problem due to its flexibility, and chatter vibrations are apt to occur, which restricts the machining efficiency and quality. A vibration suppression device for thin-walled workpieces is presented based on the electromagnetic induction principle, which utilizes machining vibrations to generate resistant force on the workpiece. The formulated force varies with the workpiece vibration velocity, but in an opposite direction. Excitation tests using the electromagnetic shaker illustrate that the device is effective in vibration attenuation. Finally, machining tests are carried out with applications to two thin-walled structures for further verification. The machining vibrations and surface quality demonstrate the damping promotion of the workpiece assembly, and milling stability limit is increased by more than twofold.     

Dry forming of aluminum alloys – Wear mechanisms and influencing factors

Tribological contacts in sheet metal forming are accompanied by several wear phenomena. One of which is the transfer of material from the softer sheet material to the harder tool surface, namely adhesive wear. Forming of aluminum alloys makes high demands on forming processes. Aluminum alloys show a strong tendency of adhesion on common tool materials. Adhesions on tools reduce the surface quality, the dimensional accuracy of the parts and the process stability. In order to avoid adhesive wear during forming, nowadays a high amount of lubricant is applied to the aluminum sheets. Though economically and ecologically attractive, dry forming processes with aluminum sheets seem not to be possible. In order to develop advantageous tribological systems a comprehensive understanding of the acting mechanisms is necessary. This paper discusses the influence of the alloy composition and the influence of oxide layers on the adhesive wear in aluminum forming.     

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.     

The study of the influence of wear of the cutting tool with an insert of cBN-based composite material on the tool vibrations in finish turning of hardened steels

It has been found out that wear of a cutting tool with an insert of cBN-based composite material has an effect on the tool vibrations in finish turning of hardened steels with various hardness values. The influence of the tool vibrations on the machined surface roughness has been studied.     

Influence of surface residual stresses on gigacycle fatigue response of high chromium cold work tool steel

The effect of surface compressive residual stresses (RS) induced by surface grinding and polishing on the gigacycle fatigue behavior of medium‐carbon high‐chromium alloy cold work tool steel was evaluated. Two test series were performed: Specimens of series I revealed high compressive RS of about ‐800 MPa at the surface, resulting from grinding with fine emery paper, which treatment had definitely a beneficial influence on the fatigue endurance strength. The existence of surface RS was also revealed to be responsible for the location of the fatigue crack initiation. High compressive RS favored internal crack origins. In this case crack nucleation sites were primary carbide clusters in the interior of the specimen, forming so‐called fish‐eyes at the fracture surface. In contrast, specimens of test series II had only very low RS, which enabled crack initiation near/at the surface at primary carbides/clusters. Furthermore, it has been shown that the high initial RS are prone to partial relaxation through cyclic loading for which the mechanisms are currently unknown. In this case near‐surface induced failure was obtained. It was possible to confirm the experimentally obtained data by the use of the concept of local fatigue strength as function of effective RS. The relaxation of high initial RS was experimentally confirmed through RS measurements at runout specimens (10¹⁰ cycles without failure).     

Materials and machining trends in terms of the existing axioms of the machining theory

The paper provides new insight into existing axioms of theory of machining. The existing theory of metalworking was based on the development of cutting materials during the 20^th century. In particular, the improvement of cutting materials, the new special materials and progressive technologies and the trends to increase cutting speed call for a review of existing definitions and relations. Appling previously defined relations between cutting conditions and results of machining, the inaccuracies occur and this may lead to an incorrect choice of cutting conditions in the specific conditions of machining. The paper analyses existing well‐known equations used in practice and on the basis of extensive experimental analysis it modifies them. Furthermore, the paper concerns the evaluation of physical and technological parameters, such as chips compression, machined surface roughness, cutting forces, cutting tool‐wear and tool‐life.     

Oberflächen‐ und Dünnschichtanalytik – unverzichtbares Werkzeug für Schichtentwicklung und ‐produktion

Surface and thin film analysis – indispensable tool for coating development and ‐production Development and production of thin films for functional coating on special materials is unalterable combined with a permanent quality control and therefore use of sophisticated analysis and measurement techniques. The field of interest is belonging to all steps of the production chain, starting with the characterization of the substrate surface (e. g. glass, plastics), followed by polishing and cleaning processes up to depth profiling of complex multilayers. The typical analyses are focused onto topographical and chemical features and their influence onto the product functionality. The use of surface and thin film analytics for problem oriented characterization is demonstrated by a few examples, which deal with surface roughness, contamination, impurities and dopand profiles as well as composition variations in the surface near region.     

Simulation der Wärmebehandlung von Stählen am Institut für Werkstoffkunde I

Simulation of the heat treatment of steels at the Institut für Werkstoffkunde I The simulation of manufacturing processes is an important tool in simultaneous engineering. The aim is to cut the time necessary for development and to optimize processes by simulation of the complete manufacturing chain. The field of heat treatment offers a large variety of applications for the use of simulation tools. The geometry of the part, the composition of the material, the heat treatment process as well as the initial state of the parts interact with each other in complex ways and have an influence on the distortion of the part. The calculation of the microstructure and of the hardness distribution helps to determine suitable charging and quenching conditions as well as plant engineering. Calculated residual stresses and distortions can be taken into account in the development and construction of new parts. The Institut für Werkstoffkunde I of the Universität Karlsruhe (TH) is engaged in research programms in this field dealing with numerical as well as experimental problems for almost 30 years.     

An industrial approach of laser polishing with different laser sources

Surface finishing of dies and molds is one of the most interesting applications of laser polishing process. Because of the variety of materials used in die and mold manufacturing, as well as the different surface topographies, in each case, it is necessary to use appropriate process parameters. The presented work focuses on the study of laser polishing process on three commonly used materials in the manufacture of dies and molds, such as tool steels AISI D2 and AISI P20, ductile cast iron GGG70L and LaserForm ST‐100, a specific material developed for plastic injection mold making. Experimental studies were carried out determining the influence of the energy density on the roughness reduction rate. A key point that has a direct impact on the resulting surface roughness is the initial surface finishing of the material before laser polishing. In order to determine the degree of influence, experimental studies were conducted on two steels, AISI H13 and AISI P20, which are typically used in mold making industry. The experimental tests showed that a random distribution of peaks and valleys allows more homogenous material melting and gives as result a smoother surface after laser polishing.     

A freeform surface manufacturing approach by integration of inspection and tool path generation

Freeform surfaces have been widely used in various engineering applications. Increasing requirements for the accuracy of freeform surfaces have led to significant challenges for the manufacturing of these surfaces. A method for manufacturing of freeform surfaces is introduced in this paper by integrating inspection and tool path generation to improve manufacturing quality while reducing manufacturing efforts. Inspection is conducted by comparing the digitised manufactured surface with the design surface to identify the error regions. In this new inspection technique, the areas on the manufactured surface that are beyond the design tolerance boundaries are used as the objective function during the localisation process, in order to minimise post-inspection machining efforts. The tool path generation methods are then selected based on the geometric characteristics of the identified error regions, for creating tool paths to remove the errors. Computational efficiency, machining efficiency, and quality are considered in this integrated method.     

Grundlagen,Herstellung und Anwendungsaspekte des Supersolidus Flüssigphasensinterns von hochlegierten Werkzeugstählen und Metallmatrix‐Verbundwerkstoffen

Principles, manufacturing and application aspects of super solidus liquid phase sintering of high‐alloyed tool steels and metal matrix composites Iron‐based metal matrix composites (MMC) are applied for abrasive wear resistant applications. A common production route uses hot isostatic pressing (HIP) of metal and carbide powders, a comparatively cost intensive process. Using high‐alloyed tool steels as matrix materials it is possible to obtain dense materials by liquid phase sintering with an internally formed liquid phase. This contribution describes the basic principles of densification of the matrix materials taking thermodynamic calculations into consideration. It points out a production route for processing particulate reinforced, high wear resistant composite materials by sintering. Beside the sintering behaviour concepts for heat treatment as well as the abrasive wear resistance are discussed.     

On selective laser melting of ultra high carbon steel: Effect of scan speed and post heat treatment

Selective laser melting is a laser‐based additive manufacturing process applying layer manufacturing technology and is used to produce dense parts from metallic powders. The application of selective laser melting on carbon steels is still limited due to difficulties arising from carbon content. This experimental investigation aims at gaining an understanding of the application of the process on ultra high carbon steel, which is a special alloy with remarkable structural properties suitable for different industrial applications. The feedstock ultra high carbon steel (2.1% C) powder, 20 μm to 106 μm was prepared by water atomizing technique. This powder was used for the selective laser melting to build specimens 10×10×40 mm in dimensions. To decrease the thermal stresses during layer by layer building, laser scanning was done through 5×5 mm random island patterns while layer thickness was 30 μm. Laser beam diameter, maximum power output, layer thickness and scan speed range were 0.2 mm, 100 W, 30 μm and 50–200 mm/s respectively. The process was done inside high purity nitrogen environment, with less than 0.5% oxygen content. The results illustrate the influence of scan speed from 50 to 200 mm/s on product geometry and dimensions, surface roughness, internal porosity and cracks, microstructure and surface hardness. The effect of post heat treatment by heating and holding for one hour (annealing) at different temperatures of 700°C, 750°C, 950°C is studied. The results indicate that selective laser melting is able to produce near to 95% density of ultra high carbon steel parts with acceptable geometry and surface quality. Porosity cracks, and microstructure formed during the process could be controlled through proper selection of process parameters and post heat treatment. Industrial ultra high carbon steel products can be rapidly fabricated by selective laser melting.     

Impact experiments and finite element simulation of surface roughness reduction by machine hammer peening

Machine hammer peening (MHP) is a mechanical surface treatment that employs a tungsten carbide tool to hammer the surface of a work piece. It was the goal of this study to find relations between the process parameters and the surface smoothing effect of MHP by finite element simulations. Impact experiments have been conducted in order to find suitable load‐deformation‐relations for a selection of work piece materials and to validate the model. A finite element model has been established with good agreement to the experimental results. Simulations have been conducted to investigate the influence of main process parameters on the surface roughness reduction. Additional simulations were performed and a way of creating uniform smooth surfaces with respect to small duration of surface treatment is presented.     

Integrated approach for prediction of stability limits for machining with large volumes of material removal

High-speed machining of thin-walled structures is widely used in the aeronautical industry. Higher spindle speed and machining feed rate, combined with a greater depth of cut, increases the removal rate and with it, productivity. The combination of higher spindle speed and depth of cut makes instabilities (chatter) a far more significant concern. Chatter causes reduced surface quality and accelerated tool wear. Since chatter is so prevalent, traditional cutting parameters and processes are frequently rendered ineffective and inaccurate. For the machine tool to reach its full utility, the chatter vibrations must be identified and avoided. In order to avoid chatter and implement optimum cutting parameters, the machine tool including all components and the work piece must be dynamically mapped to identify vibration characteristics. The aim of the presented work is to develop a model for the prediction of stability limits as a function of process parameters. The model consists of experimentally measured vibration properties of the spindle-tool, and finite element calculations of the work piece in (three) different stages of the process. Commercial software packages used for integration into the model prove to accomplish demands for functionality and performance. A reference geometry that is typical for an aircraft detail is used for evaluation of the prediction methodology. In order to validate the model, the stability limits predicted by the use of numerical simulation are compared with the results based on the experimental work.     

Löten und Härten im Vakuum zur Herstellung leistungsfähiger Gesteinwerkzeuge

Brazing and hardening in vacuum for manufacturing of high‐performance tools for construction applications High‐performance tools for applications in construction industry are used under severe service conditions. Huge amounts of construction materials have to be removed in short times with long service times. By sophisticated heat treatment processes or combination of materials construction tools are optimized for the dedicated application. Vacuum brazing is a proven technology to join different materials. Case studies will be presented where vacuum hardening of tool steel and vacuum brazing of hard metal to steel improve tool performance significantly.