J. Manuf. Mater. Process., Volume 4, Issue 2 (June 2020) – 34 articles

AISI 52100 steel is often used as material for highly loaded rolling bearings in machine tools. An improved surface integrity, which can be achieved by means of mechanical surface layer finishing, can avoid premature failure. One of these finishing processes is machine hammer peening (MHP) which is a high-frequency incremental forming process and mostly used on machining centers. However, the influence of robot-guided MHP processing on the surface integrity of AISI 52100 steel is still unknown. Therefore, the objective of this work is to investigate experimentally the robot-based influences during MHP processing and the resulting surface integrity of unhardened AISI 52100 steel. The results show that the axial and lateral deviations of the robot due to process vibrations are in the lower µm range, thus enabling stable and reproducible MHP processing. By selecting suitable MHP process parameters and thus defined contact energies, even ground surfaces can be further smoothed and a hardness increase of 75% in the energy range considered can be achieved. In addition, compressive residual stress maxima of 950 MPa below the surface and a grain size reduction to a surface layer depth of 150 µm can be realized. Full article

Friction stir welding (FSW) has become an up-and-coming joining method with a wide range of industrial applications. Besides the unique weld seam properties, recent investigations have focused on the process-related tool wear of shoulder and probe, which can have detrimental economic and technological effects. This paper presents a systematic quantitative characterization of FSW tool wear using stripe light projection as a novel method to detect weight and form deviations of shoulder and probe. The investigations were carried out with a robotic welding setup in which AA-6060 T66 sheets, with a thickness of 8 mm, were joined by weld seams up to a total length of 80 m. During the experimental tests, geometrical deviations of the tool induced by wear were detected for varying weld seam lengths and different measuring points on the probe and shoulder. It was shown that wear depended on welding length which in turn caused significant deviations and weight losses on shoulder and probe. Furthermore, it was demonstrated that the wear on shoulder and probe can be considered separately. It was found that there is a progressive wear rate on the shoulder and a degressive wear rate on the probe depending on the weld seam length. To demonstrate the negative impact of tool wear on shoulder and probe after 80 m weld seam length, visual and metallographic inspections and tensile tests were carried out to detect resultant irregularities in the weld seam. Full article

Thermoplastic materials hold great promise for next-generation engineered and sustainable plastics and composites. However, due to their thermoplastic nature and viscoplastic material response, it is difficult to predict the properties of surfaces generated by machining. This is especially problematic in micro-channel machining, where burr formation and excessive surface roughness lead to poor component-surface integrity. This study attempts to model the influence of size effects, which occur due to the finite sharpness of any cutting tool, on surface finish and burr formation during micro-milling of an important thermoplastic material, polycarbonate. Experimental results show that the depth of cut does not affect either surface finish or burr formation. A proposed new sideflow model shows the dominant effect of cutting-edge radius and feed rate on surface finish, while tool edge roughness, coating and feed rate have the most pronounced influence on burr formation. Overall, a good agreement between the experimental data and the proposed size effect model for the machining of thermoplastic material was found. Based on these results, tool geometry and process parameters may be optimized for improved surface integrity of machined thermoplastic components. Full article

Numerical simulation of laser drilling is rapidly gaining interest in academia and industry since this process remains one of the most important and widely-used technologies in modern manufacturing. Meshfree methods such as Smoothed Particle Hydrodynamics (SPH) have proven to be successful as a numerical tool for the computation of the heat transfer and material removal associated with a laser drilling problem. Nonetheless, the vast majority of recent developments incorporate an inconsistent SPH kernel into their thermal simulations. In this paper, several enhanced schemes are implemented to address this problem by solving the heat transfer more accurately. These meshfree schemes can provide a second-order accurate discretization of the Laplace operator and abolish the inconsistency issue of the standard SPH kernels. An efficient approach is additionally suggested to handle the associated boundary conditions, which relies on the idea of the color function and particle label. The implementation is initially validated by a 3D benchmark study and then applied for the first time to a laser drilling problem. Full article

The present work characterized and modelled the interfacial heat transfer coefficient and friction coefficient of a non-alloy martensitic steel, for a novel Fast light Alloy Stamping Technology (FAST) process. These models were validated through temperature evolution, thickness distribution and springback measurements on experimentally formed demonstrator components, which were conducted on a pilot production line and showed close agreement, with less than 10% variation from experimental results. The developed models and finite element simulations presented in this work demonstrate that non-isothermal processes can be precisely simulated with implementation of the accurate thermomechanical boundary conditions. Full article

Hot metal gas forming (HMGF) is a desirable way for the automotive industry to produce complex metallic parts with poor formability, such as aluminum alloys. A simple hot gas forming method was developed to form aluminum alloy tubes using flame heating. An aluminum alloy tube was heated by a flame torch while the tube was rotated and compressed using a lathe machine and simultaneously pressurized with a constant air pressure. The effects of the internal pressure and axial feeding on expansion and wall thickness distribution were examined. The results showed that the proposed gas forming method was effective for forming aluminum alloy tubes. It was also indicated that axial feeding is a vital parameter to prevent reductions in wall thickness by supplying the material flow during the forming process. Full article

Refill friction stir spot welding (RFSSW) is an emerging technology for joining aerospace aluminum alloys. The aim of the study is to investigate the effects of the refill friction stir spot weld spacing and the edge margin on the mechanical properties of multi-spot-welded AA7075-T6 panels. AA7075-T6 is a baseline aerospace aluminum alloy used in aircraft structures. The study employs an innovative robotic RFSSW system that is designed and developed by Kawasaki Heavy Industries (KHI). The experimental strategy uses Design of Experiments (DoE) to characterize the failure loads of multi-spot-welded panels in terms of the spot weld spacing, edge margin, and heat-affected zone (HAZ) of the spot weld. The RFSSW process leaves behind a thermal “imprint” as HAZ in heat-treatable aluminum alloys. According to the DoE results, larger spot weld spacings with no HAZ overlap produce higher failure loads of multi-spot-welded panels. On the other hand, edge margins that are equal to or less than the spot weld diameter demonstrate abnormal plastic deformations, such as workpiece edge swelling and weld crown dents, during the RFSSW process. The larger edge margins do not demonstrate such abnormal deformations during the welding process. Full article

Shearing processes of high strength steel sheets increasingly applied to lightweight automobile parts were reviewed. With the increase in strength of the high strength steel sheets, shearing operations become hard. First, the sheared edge quality in shearing of high strength steel sheets and the effects on the formability and fatigue strength were shown. Next, ironing processes with a taper punch and a punched slug, a slight clearance punching with a punch having a small round corner and a thickening process of the sheared edge were explained as processes for improving the sheared edge quality. Finally, hydrogen-induced delayed fractures of cold-sheared ultra-high strength steel sheets and of hot-trimmed parts were evaluated. Full article

Deep hole boring using slender bars that have tuned mass dampers integrated within them make the boring process chatter vibration resistant. Dampers are usually designed using classical analytical solutions that presume the (un)damped boring bar which can be approximated by a single degree of freedom system, and the damper is placed at the free end. Since the free end is also the cutting end, analytical models may result in infeasible design solutions. To place optimally tuned dampers within boring bars, but away from the free end, this paper presents a receptance coupling approach in which the substructural receptances of the boring bar modelled as a cantilevered Euler–Bernoulli beam are combined with the substructural receptances of a damper modelled as a rigid mass integrated anywhere within the bar. The assembled and damped system response thus obtained is used to predict the chatter-free machining stability limit. Maximization of this limit is treated as the objective function to find the optimal mass, stiffness and damping of the absorber. Proposed solutions are first verified against other classical solutions for assumed placement of the absorber at the free end. Verified models then guide prototyping of a boring bar integrated with a damper placed away from its free end. Experiments demonstrate a ~100-fold improvement in chatter vibration free machining capability. The generalized methods presented herein can be easily extended to design and develop other damped and chatter-resistant tooling systems. Full article

The longitudinal and transverse beams of trucks are manufactured with a large number of holes to fasten brackets for springs, fuel tanks, batteries etc. The quality of the holes, which is particularly influenced by the manufacturing process, has a major influence on the fatigue strength of the beams and thus the service lifetime of the vehicle. In most cases, the holes are produced using the highly economical shear cutting process. Previous investigations have shown that the fatigue strength of thin sheets can be increased by adjusting the shearing parameters and using a two-stage shear cutting process. This paper discusses the difference between one- and two-stage shear cutting on the hole quality of components made of S500MC (1.0984, thickness 8 mm) and its resulting fatigue strength. The hole quality is characterized by the geometry of the shear cut surface, its roughness, microstructure, and microhardness. It was shown that the two-stage shear cutting process allows producing holes of better quality than the ones manufactured by a one-stage shear cutting process. Furthermore, this resulted in an improved fatigue behavior. Full article

In semi-solid metal high pressure die casting and in conventional high pressure die casting, it is common to find a defect band just below the surface of the component. The formation of these bands is not fully understood. However, there are several theories as how they occur, and it has been suggested that segregation is caused by the migration of aluminium-rich externally solidified crystals. In the present work the formation of these bands is investigated theoretically by reviewing suitable potential mechanisms for the migration of such crystals. Two mechanisms are identified as the most probable: Saffman lift force and the Mukai-Lin-Laplace effect. However, it was not possible to identify which of these two mechanisms acted in the case studies. Further testing is required to identify the mechanism that is causing the migration of the aluminium globules and suitable tests are proposed. Full article

The demand for inert bioceramics is always increasing in the dental field. Yttrium oxide tetragonal zirconia polycrystals (Y-TZP) are oxide ceramics which are currently used because of their interesting mechanical properties due to a toughening transformation. Industrially speaking, machining of the ceramic before sintering (green body) is very common because it allows a better productivity and it reduces crack probability during the sintering process. The goal of this paper is to determine the behavior of green ceramic during the machining operation. This study is carried out on several blanks with different binder percentages. The specific cutting energy (SCE) and the surface quality (R_a and R_z) are determined for several cutting speeds. The SCE follows a logarithmic evolution when the cutting speed increases. Despite this increase, the R_a are relatively stable whatever the cutting speed and the binder percentage. At a low cutting speed, a higher R_z value is observed caused by pullout of material. The increase of cutting speed allows to stabilize the R_z value whatever the binder percentage. This study shows that the green ceramic has a pseudo-plastic behavior whose machinability depends mainly on the interaction between the material and the cutting edge of the tool, so unlike pre-sintered ceramic or metallic part cutting speed has a low influence on the quality of the machined part. Full article

Distributed digital manufacturing offers a solution to medical supply and technology shortages during pandemics. To prepare for the next pandemic, this study reviews the state-of-the-art of open hardware designs needed in a COVID-19-like pandemic. It evaluates the readiness of the top twenty technologies requested by the Government of India. The results show that the majority of the actual medical products have some open source development, however, only 15% of the supporting technologies required to produce them are freely available. The results show there is still considerable research needed to provide open source paths for the development of all the medical hardware needed during pandemics. Five core areas of future research are discussed, which include (i) technical development of a wide-range of open source solutions for all medical supplies and devices, (ii) policies that protect the productivity of laboratories, makerspaces, and fabrication facilities during a pandemic, as well as (iii) streamlining the regulatory process, (iv) developing Good-Samaritan laws to protect makers and designers of open medical hardware, as well as to compel those with knowledge that will save lives to share it, and (v) requiring all citizen-funded research to be released with free and open source licenses. Full article

Due to their high speed and versatility, laser processing systems are now commonplace in many industrial production lines. However, as the need to reduce the environmental impact from the manufacturing industry becomes more urgent, there is the opportunity to evaluate laser processing systems to identify opportunities to improve energy efficiencies and thus reduce their carbon footprint. While other researchers have studied laser processing, the majority of previous work on laser systems has focused on the beam–material interaction, overlooking the whole system viewpoint and the significance of support equipment. In this work, a methodical approach is taken to design a set of energy modelling terminologies and develop a structured power metering system for laser systems. A 300 W fibre laser welding system is used to demonstrate the application of the power characterization system by utilizing a purpose-built power meter. The laser is broken down according to sub-system, with each part analysed separately to give a complete overall power analysis, including all auxiliary units. The results show that the greatest opportunities for efficiency improvements lie in the auxiliary units that support the laser devices as these were responsible for a majority of the electrical draw; 63.1% when the laser was operated at 240 W, and increasing as the beam power reduced. The remaining power draw was largely apportioned to electrical supply inefficiencies. In this work, the laser device delivered a maximum of 6% of the total system power. The implications of these results on laser processing system design are then discussed as is the suitability of the characterization process for use by industry on a range of specific laser processing systems. Full article

This paper investigates the quality performance of FDM 3D printed models with thin walls. The design of experiments method (DOE) was used and nine models of the same size were fabricated in a low-cost 3D printer using polylactic acid (PLA) material. Two limited studied parameters were considered (extraction temperature and wall thickness), each one having three levels. External X and Y dimensions were measured using a micrometer, as well as four surface roughness parameters (Ra, Rz, Rt, Rsm) with a surface tester. Two optimization techniques (the Taguchi approach and Grey relational analysis) were utilized along with statistical analysis to examine how the temperature and wall thickness affect the dimensional accuracy and the surface quality of the parts. The results showed that high extraction temperature and median wall thickness values optimize both dimensional accuracy and surface roughness, while temperature is the most important factor. Full article

A numerical model that incorporates temperature-dependent non-Newtonian viscosity was developed to simulate the extrusion process in extrusion-based additive manufacturing. Agreement with the experimental data was achieved by simulating a polylactic acid melt flow as a non-isothermal power law fluid using experimentally fitted parameters for polylactic acid. The model was used to investigate the temperature effect on the flow behavior, the cross-sectional area, and the uniformity of the extruded strand. OpenFOAM, an open source simulation tool based on the finite volume method, was used to perform the simulations. A computational module for solving the equations of non-isothermal multiphase flows was also developed to simulate the extrusion process under a small gap condition where the gap between the nozzle and the substrate surface is smaller than the nozzle diameter. Comparison of the strand shapes obtained from our model with isothermal Newtonian simulation, and experimental data confirms that our model improves the agreement with the experimental data. The result shows that the cross-sectional area of the extruded strand is sensitive to the temperature-dependent viscosity, especially in the small gap condition which has recently increased in popularity. Our numerical investigation was able to show nozzle temperature effects on the strand shape and surface topography which previously had been investigated and observed empirically only. Full article

The tribological effect of cutting fluids in the machining processes to reduce the friction in the cutting zone is still widely unknown. Most test benches and procedures do not represent the contact conditions of machining processes adequately, especially for interrupted contacts. This results in a lack of knowledge of the tribological behavior in machining processes. To close this knowledge gap, a novel experimental test bench to investigate the effects of cutting fluids on the frictional conditions in metal cutting under high-pressure cutting fluid supply was developed and utilized within this work. The results show that there is a difference between the frictional forces in interrupted contact compared to continuous contact. Furthermore, the cutting fluid parameters of supply pressure, volumetric flow rate, and impact point of the cutting fluid jet influence the frictional forces, the intensities of which depend on the workpiece material. In conclusion, the novel test bench allows examining the frictional behavior in interrupted cuts with an unprecedented precision, which contributes to a knowledge-based design of the cutting fluid supply for cutting tools. Full article

This paper deals with the development and comparison of prediction models established using response surface methodology (RSM) and artificial neural network (ANN) for a wire electrical discharge machining (WEDM) process. The WEDM experiments were designed using central composite design (CCD) for machining of Inconel 718 superalloy. During experimentation, the pulse-on-time (T_ON), pulse-off-time (T_OFF), servo-voltage (SV), peak current (I_P), and wire tension (WT) were chosen as control factors, whereas, the kerf width (Kf), surface roughness (R_a), and materials removal rate (MRR) were selected as performance attributes. The analysis of variance tests was performed to identify the control factors that significantly affect the performance attributes. The double hidden layer ANN model was developed using a back-propagation ANN algorithm, trained by the experimental results. The prediction accuracy of the established ANN model was found to be superior to the RSM model. Finally, the Non-Dominated Sorting Genetic Algorithm-II (NSGA- II) was implemented to determine the optimum WEDM conditions from multiple objectives. Full article

To evaluate the prediction accuracy of the anisotropic yield function, we propose an original cruciform hole expansion test. Displacements on two axes were applied to the cruciform specimens with a hole in the center. The thickness strain in the region near the hole was compared to the simulation results. Because this forming test is free of friction and bending, it is an appropriate method to assess the anisotropic yield function without the influences of friction or the Bauschinger effect, or the need to consider the stress-strain curve in high-strain region. Hill1948, YLD2000-2D, and spline yield function which is an improved version of the Vegter model were selected, and 6000 series aluminum alloy sheets (A6116-T4) were used in this study. The parameter identification method of the spline yield function also proposed in this paper using the pseudo plane strain tensile test and optimization software. As a result, the spline yield function has better predictive accuracy than the conventional anisotropic yield functions Hill1948 and YLD2000-2D. Full article

This work presents a comprehensive structure for evaluating the sustainability of machining processes. Industries can contribute towards developing a sustainable future by using algorithms that evaluate the sustainability of their processes. Inspired by the literature, the proposed model involves a set of metrics that are critical in evaluating the impact of a process on society, environment, and economy. The flexibility of this model allows decision-makers to use the available responses to identify the most favorable process. The entropy weight method was suggested for objectively calculating the weights of each indicator. A multi-criteria decision-making method i.e., Technique for Order Preference based on Similarity to Ideal Solution (TOPSIS), was used to rank processes in the decreasing order of their sustainability. The proposed algorithm was successfully validated with case studies from the published literature. A MATLAB code was also created so that industries may expeditiously apply this method to evaluate the sustainability of machining processes. Full article

Producing complex sheet metal components in fewer process steps motivated the development of the innovative forming process called sheet-bulk metal forming (SBMF). In this process, sheet metal forming and bulk-metal forming are combined to create a unique forming process in which a component with external and internal gearing is produced in three production steps. However, the high degrees of deformation that occur using high-strength steels and the number of different process steps result in high process forces, strongly limiting the service life of tools. To reduce the forming force during SBMF processes, tool and process modifications were investigated. Therefore, plane-strain compression tests were conducted to examine the influence of a CrAlN PVD coating and tailored surfaces produced by high-feed milling (HF) of tool-active elements on the material flow of the specimens. In addition to the tool-sided modifications, the influence of an oscillation overlay during the forming process was investigated. Based on the results of the compression tests, the surfaces of the active tool elements of the SBMF process were modified in order to transfer the basic experimental results to the production of a functional component. The friction is thus adapted locally in the SBMF process. Full article

In recent decades, beam welding processes have been set up as a key technology for joining applications in automotive engineering and particularly in gearbox manufacturing. Due to their high beam quality, energy efficiency, reliability as well as flexible beam guidance, modern solid-state lasers offer numerous advantages, but also pose increased requirements on the production and positional accuracy of the components for the joining process. In particular, small-focus diameters present a challenge for components with process-induced tolerances, i.e., disc carriers in automatic transitions. Furthermore, welding processes utilizing solid-state lasers show an increased spatter formation during welding at high welding speeds. Accordingly, the primary objective of the presented work consists in extending the current areas of application for solid-state laser beam welding in gearbox manufacturing through an improved process reliability regarding tolerance compensation and spatter formation. Therefore, this experimental study aimed to describe the effects of a dynamic beam oscillation in combination with a reduced ambient pressure in the process environment on both gap bridging ability and spatter formation during the laser beam welding of case hardening steel. For basic process evaluations, laser beam welding at reduced ambient pressure and laser beam welding with dynamic beam oscillation were initially studied separately. Following a basic process evaluation, samples for 2 mm full-penetration-welds with varying gap sizes were analyzed in terms of weld seam geometry and weld spatter formation. Full article

This article provides a comprehensive review of the advancements made in the diffusion bonding of titanium and its alloys to other advanced materials such as aluminium, stainless steel, and magnesium. This combination of advanced alloys has received considerable attention in different industries, including aerospace, petrochemical, and nuclear applications due to high specific strength, lightweight, corrosion resistance, and moderate to high mechanical properties. The mechanisms of bond formation are discussed based on the type of microstructures formed and the mechanical properties achieved. The scientific literature identifies various methods/processes for controlling the volume of intermetallic compounds formed within the joint regions, as well as ways of maximising the strength of the weld/joints. This paper discusses the relationship between weld/bond properties and bonding parameters such as time, temperature, surface roughness, pressures, interlayer composition, and thickness. The scientific literature also shows that the bonding mechanisms and microstructural evolution of the bond zone can be significantly affected by suitable optimization of the bonding parameters. Additionally, this is a method of maximising bond strength. Full article

Fused filament fabrication (FFF) is a cost-effective additive manufacturing method that makes use of thermoplastics to produce customised products. However, there are several limitations associated with FFF that are adversely affecting its growth including variety of materials, rough surface finish and poor mechanical properties. This has resulted in the development of metal-infused thermoplastics that can provide better properties. Furthermore, FFF-printed parts can be subjected to post-processes to improve their surface finish and mechanical properties. This work takes into consideration two commonly used polymeric materials, i.e., ABS (acrylonitrile butadiene styrene) and PLA (polylactic acid) and compares the results with two metal-infused thermoplastics i.e., copper-enhanced PLA and aluminium-enhanced ASA (acrylonitrile styrene acrylate). The four different materials were subjected to a post-process called annealing to enhance their mechanical properties. The effect of annealing on these four materials was investigated through dimensional analysis, ultrasonic testing, tensile testing, microstructural analysis and hardness testing. The results showed that annealing affects the materials differently. However, a correlation among ultrasonic testing, tensile testing and microstructural analysis was observed for all the materials based on their crystallinity. It was found that the semi-crystalline materials (i.e., PLA and copper enhanced PLA) showed a considerable increase in tensile strength post-annealing. However, the amorphous materials (ABS and aluminium-enhanced ASA) showed a comparatively lower increase in tensile strength, demonstrating that they were less receptive to annealing. These results were supported by higher transmission times and a high percentage of voids in the amorphous materials. The highest hardness values were observed for the ASA material and the lowest for the ABS material. This work provides a good comparison for the metal-infused thermoplastics and their applicability with the commonly used PLA and ABS materials. Full article

In recent years, additive manufacturing methods such as Fused Layer Modeling have been continuously improved by industry and research institutions. In many cases, the influence of process control on the mechanical component properties is being investigated. Influencing parameters include the infill and its orientation as well as patterns. Extrusion parameters such as the volume flow, which can be influenced by the speed, the line width, and the layer thickness, and the temperatures, which determine the interlaminar bonding between the lines and layers, are relevant as well. In this contribution, the influence of process control on the tribological properties of cylindrical tribo-test specimens made of polybutylene terephthalate is investigated. Using a reciprocating pin-on-plate tribo-tester, the static and dynamic friction forces as well as the linear wear is determined. The results show a significant influence of the orientation and density of the infill on the tribological properties. Due to the process-specific large degrees of freedom, the advantage of a load-compatible individualisation and consequently the optimisation of tribologically exposed components is given compared to conventional manufacturing processes. Full article

This work proposes an approach to fabricate micro patterned surfaces on PA2200 polyamide in order to improve its performance in terms of wettability and adhesion. In more detail, the present work aims to change the wettability of the surface and decrease their bacteria adhesion tendency. The experimental procedure consists of imprinting a set of different micro patterned structures over the polymer in order to verify the effectiveness of the methodology to change the contact angle of the surface, and in turn, reduce the occurrence of bacteria adhesion. Four different surface patterning were produced by laser ablation of a commercially pure titanium alloy, and then imprinted over the polyamide by surface stamping. The resulting surfaces were analyzed by topographical characterization and scanning electron microscopy. The wettability was probed by contact angle measurements while the bacteria adhesion was analyzed by adhesion test. The experimental results demonstrate the effectiveness of the method to modify the surface characteristics and to obtain a reliable patterned surface without using chemical hazardous material; opening to the possibility to replicate more complex structures and to obtain graded engineering surfaces. Full article

The surface roughness of the ground parts is an essential factor in the assessment of the grinding process, and a crucial criterion in choosing the dressing and grinding tools and parameters. Additionally, the surface roughness directly influences the functionality of the workpiece. The application of artificial intelligence in the prediction of complex results of machining processes, such as surface roughness and cutting forces has increasingly become popular. This paper deals with the design of the appropriate artificial neural network for the prediction of the ground surface roughness and grinding forces, through an individual integrated acoustic emission (AE) sensor in the machine tool. Two models were trained and tested. Once using only the grinding parameters, and another with both acoustic emission signals and grinding parameters as input data. The recorded AE-signal was pre-processed, amplified and denoised. The feedforward neural network was chosen for the modeling with Bayesian backpropagation, and the model was tested by various experiments with different grinding and neural network parameters. It was found that the predictions presented by the achieved network parameters model agreed well with the experimental results with a superb accuracy of 99 percent. The results also showed that the AE signals act as an additional input parameter in addition to the grinding parameters, and could significantly increase the efficiency of the neural network in predicting the grinding forces and the surface roughness. Full article

The increasing demand for complex and wear-resistant forming tools made of difficult-to-machine materials requires efficient manufacturing processes. In terms of high-strength materials; highly suitable processes such as micromilling are limited in their potential due to the increased tool loads and the resulting tool wear. This promotes hybrid manufacturing processes that offer approaches to increase the performance. In this paper; conduction-based thermally assisted micromilling using a prototype device to homogeneously heat the entire workpiece is investigated. By varying the workpiece temperature by 20 °C < T_W < 500 °C; a highly durable high-speed steel (HSS) AISI M3:2 (63 HRC) and a hot-work steel (HWS) AISI H11 (53 HRC) were machined using PVD-TiAlN coated micro-end milling tools (d = 1 mm). The influence of the workpiece temperature on central process conditions; such as tool wear and achievable surface quality; are determined. As expected; the temporary thermal softening of the materials leads to a reduction in the cutting forces and; thus; in the resulting tool wear for specific configurations of the thermal assistance. While only minor effects are detected regarding the surface topography; a significant reduction in the burr height is achieved. Full article

In large heavy-duty machine tool applications, the parametrization of the controller that is used for the positioning of the machine can affect the machine tool dynamics. The aim of this paper is to build a Multiple-Input and Multiple-Output model that couples the servo controller and machine tool dynamics to predict the frequency response function (FRF) at the cutting point. The model is experimentally implemented and validated in an electronically preloaded rack and pinion machine tool. In addition, the influence of each control parameter on the machine tool’s compliance is analysed. Full article

Metal additive manufacturing processes such as selective laser melting (SLM), laser powder bed fusion (L-PBF), electron beam melting (EBM) and laser metal deposition (LMD) can produce additively manufactured nearly fully dense parts with high geometrical complexity. These are often used as components in automotive, aerospace and medical device industries. Finish machining of these components is required to achieve the desired surface finish and dimensional tolerances. The investigations on additively manufactured alloys, as reported in the literature, indicate that a layer-wise scan strategy (orthogonal or layer-to-layer rotation) and process parameters have significant influences on the resultant microstructure which affects the final mechanical properties and fatigue life. The solidification microstructure depicts that growth directions of columnar grains and sizes of cellular grains that are affected by the layer-wise scan strategy. This paper presents experimental investigations on finish milling parameters on a nickel-based alloy manufactured with L-PBF using two distinct layer-wise scan strategies. The results reveal some effects of milling direction against the layer-wise build direction. The effects of cutting speed and feed rate on resultant cutting forces, chip formation, as well as surface finish at various cutting orientations in nickel-based alloy workpieces are reported. Full article