G. R. Wilms

Bio: G. R. Wilms is an academic researcher. The author has contributed to research in topics: Machining & Surface finish. The author has an hindex of 1, co-authored 1 publications receiving 7 citations.

Anisotropy in machining of steel plates

Abstract: The influence of microstructural directionality on machining behaviour is examined for two commercial steel plates with respect to both ferrite-pearlite banding and inclusions, using orthogonal cutting tests. In relation to machining forces, chip morphology, and surface finish, one steel exhibited marked anisotropy, and comparisons with a non-banded steel indicated that the anisotropy was primarily due to the presence of ferrite-pearlite banding. Reasons for the anisotropy are briefly discussed in terms affracture energy, and the difficulties of machining in certain directions and relevance of the results to practical machining operations are also highlighted.

Evolution of Microstructural Banding during the Manufacturing Process of Dual Phase Steels

Abstract: The segregation of manganese during solidification from casting is responsible for banding problems of dual phase steels. Microstructural banding lasts during all the manufacture process, producing the deterioration of the material, so the final ductility and impact toughness of the sheets are decreased due to the high level of anisotropy. To avoid or reduce the problem of microstructural banding, it is proposed to modify the hot rolling parameters so the formation of ferrite-pearlite microstructures is avoided and thus the presence of banding. The study of the microstructural evolution during the whole manufacturing process reveals that the increase of the cooling rate during the hot rolling leads to a significant decrease of martensite banding in the microstructure of dual phase steels for sheets used in the automotive industry.

Assessment of pearlite banding using automatic image analysis: application to hydrogen-induced cracking

Abstract: Methods to quantify ferrite-pearlite banding using automatic image analysis have been proposed and tested, for example, in relation to classical banding charts. The method that is found to have the most general applicability is based on the measurement of the Feret's diameter distributions in two directions parallel and perpendicular to the rolling direction. The quantity related to banding is the ratio between the slopes of the cumulative frequency distribution curves. Structural steels with banded ferritic-pearlitic structures were investigated with regard to hydrogen-induced cracking (HIC) in previous work. The results show that the development of HIC depends on microstructural heterogeneities such as pearlife banding and inclusions. In the present work, the quantitative relationship between HIC parameters and banding is investigated. Banding quantification was used to interpret results of HIC tests. It was found that there is a significant correlation between banding and HIC in the National Association of Corrosion Engineers solution. No corresponding correlation was observed for the less acidic British Petroleum solution.

Assessment of Banding in Steels by Using Advanced Image Analysis

Abstract: Three methods for quantitative assessment of banded and oriented structures using advanced image analysis are proposed and tested. In method 1, local Fourier transforms are used to extract the locally dominant orientation. The distribution over all possible orientation angles is referred to as the local orientation distribution function. Methods 2 and 3 are based on global Fourier transforms. In method 2, banded structures are quantified by using the difference in projected grey level distribution of the Fourier spectrum in two orthogonal directions. In method 3, the directional image energy as a function of orientation is studied. The image energy, defined by grey level variations, is given by the square of the Fourier spectrum. The concept of energy distribution function is introduced. The methods are successfully applied to two types of materials: pearlite banded structural steels and ferritic-austenitic stainless steels. The proposed methods show good correlation with previously developed methods by Komenda and Sandstrom for assessing banding based on the Feret slope ratio or the chord slope ratio. It is concluded that all methods give a similar ranking of banded structures.

Machining of directed energy deposited Ti6Al4V using adaptive control

Abstract: Additively manufactured (AM) components possess microstructures different from conventional forms in the same material and as a consequence, the mechanical properties and machinability of components produced using these technologies differ. Also, the microstructures from these processes are often anisotropic and as such different regions possess varying properties and hence varying response during post process machining. An adaptive control (AC) machining system for addressing this variation in microstructures during post process machining is developed here and its use demonstrated in this paper. The adaptive control system is used in milling and drilling trials for machining components manufactured by Directed Energy Deposition (DED). Surface roughness and residual stress analysis in the ‘as built’ state and after post process machining with the prevailing cutting forces are also presented here. Microstructures of the deposited material and the subsurface effects at the machined region due to the action of the cutting tool is also analysed. Milling trials are investigated from the standpoint of the use of adaptive machining for the removal of the outermost layer of DED produced Ti6Al4V and in the machining of bulk regions after preliminary machining of the undulating layer. Drilling experiments are carried out for investigating the effects of the machining process on the resulting surface condition, comparing the process with and without adaptive control. The effects of variation in cutting forces during drilling through the different material systems comprising of the DED region and the wrought substrate is also discussed. The effect of periodic changes in cutting forces during machining due to the variation in microstructure along the build direction is analysed and discussed. The use of adaptive control machining for post processing is shown to improve surface finish as it reduces the initiation and generation of chatter marks on the machined surface resulting from material anisotropicity.

Influence of Build Orientation on Machinability of Selective Laser Melted Titanium Alloy-Ti-6Al-4V

Abstract: Selective laser melting (SLM), a promising additive manufacturing (AM) technology, has a huge potential in the fabrication of Ti-6Al-4V near-net shape components. However, poor surface finish of the components fabricated from this technology requires secondary machining to achieve the desired accuracy and tolerance. Therefore, a systematic understanding of the machinability of SLM fabricated Ti-6Al-4V components is paramount to improve the productivity and product quality. Considering the significance of machining in SLM fabricated Ti-6Al-4V components, this research aim is to study the influence of build orientation on machinability characteristics by performing low speed orthogonal cutting tests. In addition, the machinability of SLM fabricated Ti-6Al-4V is compared with conventionally produced wrought Ti-6Al-4V to understand the influence of SLM technology on machining. This paper is an attempt to provide evidence to the hypothesis associated that build orientation influences cutting forces, chip formation and surface integrity during orthogonal cutting of SLM Ti-6Al-4V samples. Results obtained from the low speed orthogonal cutting tests highlight the practical importance of microstructure and build orientation on machinability of SLM Ti-6Al-4V. Keywords—Additive manufacturing, build orientation, machinability, titanium alloys (Ti-6Al-4V).