Laser surface texturing of a WC-CoNi cemented carbide grade: surface topography design for honing application

Abrasive effectiveness of composite-like honing stones is related to the intrinsic surface topography resulting from the cubic boron nitride (CBN) grains protruding out of the metallic matrix. Within this framework, Laser Surface Texturing (LST) is implemented for replicating topographic features of a honing stone in a WC-base cemented carbide grade, commonly employed for making tools. In doing so, regular arrays of hexagonal pyramids (similar to CBN grains) are sculpted by a laser micromachining system. Micrometric precision is attained and surface integrity does not get affected by such surface modification. Finally, potential of laser-patterned cemented carbide tools, as alternative to conventional honing stones, is supported by successful material removal and enhanced surface smoothness of a steel workpiece in the abrasive testing.Peer ReviewedPostprint (author's final draft

Assessment of wear micromechanisms on a laser textured cemented carbide tool during abrasive-like machining by FIB/FESEM

The combined use of focused ion beam (FIB) milling and field-emission scanning electron microscopy inspection (FESEM) is a unique and successful approach for assessment of near-surface phenomena at specific and selected locations. In this study, a FIB/FESEM dual-beam platform was implemented to docment and analyze the wear micromechanisms on a laser-surface textured (LST) hardmetal (HM) tool. In particular, changes in surface and microstructural integrity of the laser-sculptured pyramids (effective cutting microfeatures) were characterized after testing the LST-HM tool against a steel workpiece in a workbench designed to simulate an external honing process. It was demonstrated that: (1) laser-surface texturing does not degrade the intrinsic surface integrity and tool effectiveness of HM pyramids; and (2) there exists a correlation between the wear and loading of shaped pyramids at the local level. Hence, the enhanced performance of the laser-textured tool should consider the pyramid geometry aspects rather than the microstructure assemblage of the HM grade used, at least for attempted abrasive applications

Wear Characterization of Cemented Carbides (WC–CoNi) Processed by Laser Surface Texturing under Abrasive Machining Conditions

Cemented carbides are outstanding engineering materials widely used in quite demanding material removal applications. In this study, laser surface texturing is implemented for enhancing, at the surface level, the intrinsic bulk-like tribological performance of these materials. In this regard, hexagonal pyramids patterned on the cutting surface of a tungsten cemented carbide grade (WC–CoNi) have been successfully introduced by means of laser surface texturing. It simulates the surface topography of conventional honing stones for abrasive application. The laser-produced structure has been tested under abrasive machining conditions with full lubrication. Wear of the structure has been characterized and compared, before and after the abrasive machining test, in terms of changes in geometry aspect and surface integrity. It is found that surface roughness of the machined workpiece was improved by the laser-produced structure. Wear characterization shows that laser treatment did not induce any significant damage to the cemented carbide. During the abrasive machining test, the structure exhibited a high wear resistance. Damage features were only discerned at the contacting surface, whereas geometrical shape of pyramids remained unchanged

Analysis of different surface structures of hard metal guiding stones in the honing process

Honing is a precise abrasive machining process with high standards for the resulting form, dimension, and surface quality. Additionally, honing further improves geometrical tolerances of the machined workpieces, especially when compared to the drilling process. In order to achieve a high adherence it is essential that the honing tool and the workpiece interact accordingly. The following paper will describe the static and dynamic correlations of the process forces of a honing tool equipped with one honing stone and two guiding stones for bores with small diameters (less than 20 mm). When working with bores of such small diameters, a direct measurement of the process forces with an integrated sensor is usually difficult to realize. Therefore, a theoretical model will be used to calculate the process forces within the honing tool. Missing coefficients of friction or tangential force coefficients (TFC) within the system will be determined with the help of an external test bench. Moreover, guiding stones made of hard metal with two different types of surfaces will be investigated and then compared with conventional guiding stones. The following measurement results are based on a MATLAB® simulation calculating the forces of the honing and guiding stones.Peer ReviewedPostprint (published version

Wear characterization of cemented carbides (WC-CoNi) processed by laser surface texturing under abrasive machining conditions

Cemented carbides are outstanding engineering materials widely used in quite demanding material removal applications. In this study, laser surface texturing is implemented for enhancing, at the surface level, the intrinsic bulk-like tribological performance of these materials. In this regard, hexagonal pyramids patterned on the cutting surface of a tungsten cemented carbide grade (WC-CoNi) have been successfully introduced by means of laser surface texturing. It simulates the surface topography of conventional honing stones for abrasive application. The laser-produced structure has been tested under abrasive machining conditions with full lubrication. Wear of the structure has been characterized and compared, before and after the abrasive machining test, in terms of changes in geometry aspect and surface integrity. It is found that surface roughness of the machined workpiece was improved by the laser-produced structure. Wear characterization shows that laser treatment did not induce any significant damage to the cemented carbide. During the abrasive machining test, the structure exhibited a high wear resistance. Damage features were only discerned at the contacting surface, whereas geometrical shape of pyramids remained unchanged.Peer ReviewedPostprint (author's final draft

Design Study for Multifunctional 3D Re‐entrant Auxetics

The increasing demands of safety, cost reduction, or weight reduction on components call for new, multifunctional materials. Mechanical metamaterials, such as auxetic materials, provide enhanced properties due to a specially tailored microstructure. The negative Poisson's ratio of auxetics, for instance, increases the impact and thermal shock resistance. Herein, a parametrized model of a modified auxetic structure is simulated using the finite-element software ABAQUS. Three out of five geometry parameters are varied between a minimum and maximum value to establish their impact on the energy absorption capacity and the Poisson's ratio using design of experiment (DoE). All eight resulting structures are additively manufactured by selective laser melting (SLM) and experimentally investigated under uniaxial compression to validate the simulations. The size of a unit cell has the biggest impact on both target values. Energy absorption capacity and Poisson's ratio are directly competing in optimization; hence, a compromise is necessary. The quasistatic compression experiments verify the simulation results up to the first collapse. Afterward, the specimens are brittle, which is not accounted for in the simulations, and this may result from the high process complexity of SLM manufacturing

Influence of Cutting Speed in Turning and Force in Subsequent Diamond Smoothing on Magnetic Properties of Steel 100Cr6

Magnetic properties are known to be crucial in the application of electrical steel and they are therefore covered by manifold studies. Other ferromagnetic materials are out of scope in this respect, even if the importance of magnetism of conventional steel is evident. Additionally, there is a contradiction regarding the major influence on magnetic properties. Machining, transport, and storage are possible influencing variables. In the experimental investigations, specimens consisting of the bearing steel 100Cr6 are machined by turning and partly by subsequent diamond smoothing. While machining using several cutting speeds and smoothing forces, the thermoelectrical voltage, current, and the components of the resultant force are recorded. The results show how the nearsurface plastic deformations evolve throughout the machining process. Additionally, it was found that the magnetic properties and other properties of the surface layer are influenced in different ways depending on turning and diamond smoothing parameters. Correlations between in situ and ex situ measured values are shown. This study aims to solve the aforementioned question by quantification of machining impacts of cutting speed in turning and force in diamond smoothing and its dependence on transport and storage

Investigating the energy consumption of the PECM process for consideration in the selection of manufacturing process chains

The initial planning of manufacturing process chains provides the opportunity to sustainably influence the energy requirement for the manufacturing of industrial products by selecting the process chain with the lowest energy consumption. However, the task is still challenging due to the need for energy consumption data of manufacturing equipment. In this paper, the analysis of the energy consumption of a manufacturing process is illustrated by the example of the Pulse Electrochemical Machining (PECM) process. A comparison of two machine tool generations of the same manufacturer shows the improvement in energy consumption. Based on the information gained from the analysis, an approach for the provision of energy consumption data is presented

Ablation investigation of cemented carbides using short-pulse laser beams

As an excellent engineering tool material, cemented carbides are capable to shape and cut metallic materials with high surface finish quality and precision. However, in regard to conventional abrasive methods cemented carbides are difficult-to-machine materials due to their extreme hardness combined with relatively low toughness. In contrast, laser beam machining is an advanced non-contacting cutting method which is therefore suitable for shaping hard materials. In particular, the application of short-pulse laser beams enables the cutting of hard materials meeting high precision requirements. Moreover, it can effectively reduce defects induced by mechanical contacts and thermal reactions. In this paper, a general study of the ablation mechanism of cemented carbides using short-pulse laser is conducted. Special attention is paid to the correlation between the material ablation and machining parameters within the nanosecond regime: pulse number and pulse energy. In doing so, two cemented carbide grades with similar composition but different grain size have been chosen as investigated materials. An experimental set-up equipped with a nanosecond laser and an auto-stage is implemented to produce dimples on the cemented carbide surfaces with variable pulse number and pulse energy. The experimental design and characterization of geometrical features of produced dimples are presented and discussed. The work is complemented with a thorough surface integrity assessment of the shaped materials. It is found that ablation increases proportionally with the pulse number and applied energy. Regarding microstructural effects, ablation is discerned to be more pronounced in the coarse-grained grade as compared to the medium-sized one.Postprint (author's final draft

Impact of the Process Parameters, the Measurement Conditions and the Pre-Machining on the Residual Stress State of Deep Rolled Specimens

Mechanical surface treatments, e.g., deep rolling, are widely spread finishing processes due to their ability to enhance the fatigue strength of the treated materials with means of cold working and inducement of favorable compressive residual stresses. Despite of the clear advantages of deep rolling, the controlled generation of compressive residual stresses is still a challenging task, as the process can be influenced by the pre-machining stress state of the treated material. Additionally, the exact characterization of the induced residual stress field is impacted by the specific characteristics of the applied measurement technique. Therefore, this paper is focused on the X-ray diffraction residual stress analysis of deep rolled specimens, pre-machined to achieve rough or polished surface. The deep rolling process was realized as a single-trace to avoid the influence of the other process parameters and the resulted residual stress field on the surface and in depth was investigated. Additionally, the surface residual stress profiles were determined using two different measuring devices to analyze the impact of the different measurement conditions