Characterisation of Functional Pressing Die Surfaces

The manufacture of dies and moulds is a critical aspect of many production systems since the manufacturing and try-out of new dies and moulds often is essential in determining the lead-time and quality of a new production system. In the automotive industry, many new car models are introduced each year and for each of these models, a new set of pressing dies has to be designed and manufactured. The manufacturing of pressing dies consists of several different process steps of which machining and manual polishing contribute largely to the time and cost. To be able to improve the manufacturing processes rationally, for example by optimising the machining to reduce or eliminate the subsequent manual work, an appropriate specification of the required surface quality, using a relevant parametric description of the surface, is needed. In pressing dies, the effects of manufacturing processes on functional performance are not fully understood. One of the reasons for this is the lack of effective methods for characterisation. In the work described in this thesis, research is conducted to evaluate and establish such methods.It was found that surface roughness measurement of dies, with the purpose of manufacturing process development, requires 3D data. Replication often needs to be used in these cases since dies usually are too large to bring into a lab measurement equipment. The replication techniques tested in this thesis work adequately. For quality control in production 2D measurements from a handheld instrument are good enough if an appropriate measuring strategy is used and limits for the evaluated parameters are defined.Using a multi-scale approach when analysing roughness data it may be possible to find so called functional bandwidths. With the analysis focused on the functional bandwidth the characterisation is more effective and it is easier to identify roughness parameters which correlate to the functional property or the process parameter of interest. Such a method for functional filtering of roughness data is developed and presented in the thesis.Surface texture anisotropy has been found to be important for the function of a die surface. It has also been observed that texture anisotropy can vary depending on the scale of observation. The method developed in this work to analyse and visualise texture anisotropy as a function of scale can be a helpful tool when evaluating die surfaces, especially when analysing surfaces produced with different manufacturing methods to make sure that the manufactured surface has the required texture properties in the relevant scales

Multiscale characterizations of surface anisotropies

Anisotropy can influence surface function and can be an indication of processing. These influences and indications include friction, wetting, and microwear. This article studies two methods for multiscale quantification and visualization of anisotropy. One uses multiscale curvature tensor analysis and shows anisotropy in horizontal coordinates i.e., topocentric. The other uses multiple bandpass filters (also known as sliding bandpass filters) applied prior to calculating anisotropy parameters, texture aspect ratios (Str) and texture directions (Std), showing anisotropy in horizontal directions only. Topographies were studied on two milled steel surfaces, one convex with an evident large scale, cylindrical form anisotropy, the other nominally flat with smaller scale anisotropies; a EDMed surface, an example of an isotropic surface; and an additively manufactured surface with pillar-like features. Curvature tensors contain the two principal curvatures, i.e., maximum and minimum curvatures, which are orthogonal, and their directions, at each location. Principal directions are plotted for each calculated location on each surface, at each scale considered. Histograms in horizontal coordinates show altitude and azimuth angles of principal curvatures, elucidating dominant texture directions at each scale. Str and Std do not show vertical components, i.e., altitudes, of anisotropy. Changes of anisotropy with scale categorically failed to be detected by traditional characterization methods used conventionally. These multiscale methods show clearly in several representations that anisotropy changes with scale on actual surface measurements with markedly different anisotropies

Surface Topography of Nitrided Steel Surfaces

\ua9 Published under licence by IOP Publishing Ltd. The effect of nitrocarburizing were investigated for two different steels, 42CrMo4 and 25CrMo4, with objective to evaluate the influence of initial surface topography on the resulting nitrocarburized surface with regard to surface topography and thickness of the compound layer. It was found that the nitrocarburizing process has an impact on the surface topography. The process creates a short-wave isotropic structure on the original surface and this is particularly evident for the smoother original surfaces. No significant effect on the compound layer thickness depending on the surface topography before heat treatment could be observed

Detailed evaluation of topographical effects of Hirtisation post-processing on electron beam powder bed fusion (PBF-EB) manufactured Ti-6Al-4V component

Metal additive manufacturing surface topographies are complex and challenging to characterise due to e.g. steep local slopes, re-entrant features, varying reflectivity and features of interest in vastly different scale ranges. Nevertheless, average height parameters such as Ra or Sa are commonly used as sole parameters for characterisation. In this paper, a novel method for selecting relevant parameters for evaluation is proposed and demonstrated using a case study where the smoothing effects after three processing steps of the electro chemical post-process Hirtisation of a metal AM surface are quantified. The method uses a combination of conventional areal texture parameters, multiscale analysis and statistics and can be used to efficiently achieve a detailed and more relevant surface topography characterisation. It was found that the three process steps have different effects on the surface topography regarding the types and sizes of features that were affected. In total, Sdq was reduced by 97 %, S5v was reduced by 81 % and Sa was reduced by 78 %. A surface texture with much lower average roughness, less deep pits and less steep slopes was produced, which is expected to be beneficial for improved fatigue properties

Lead-Time Effect Comparison of Additive Manufacturing with Conventional Alternatives

This single case study used value stream mapping as input data to analyse alternatives for production of quenching tools in an on-site tool department of an automotive manufacturer. The existing manufacturing organised as a functional workshop was compared to the alternatives, adding an additive manufacturing cell or a conventional automated cell, with regards to lead-Time and needed process changes. The results indicate that lead-Time savings should not be the only reason for considering additive manufacturing. When it is beneficial for design and product functionality improvements, however, lead time improvements may give a contribution to the business case

Functional tolerancing of surface texture - A review of existing methods

Surface texture parameters can provide a link between texture, its processing and function. Recent surveys and industrial experience have shown that the ISO 25178 areal surface texture parameters have not received the level of traction in industry that was predicted when introduced despite the fact that the areal parameters were predicted to have more functionally relevant characterisations than the ISO 4287 profile parameters. The objective of the paper is to enable more functionally relevant specifications of surface texture to be taken up by industry and the scientific community by increasing the knowledge of the ISO 25178 texture and novel feature parameters, and their potential use, as well as knowledge about methods for establishing functionally relevant surface texture specifications. In the paper, existing methods for functional tolerancing of surface texture are reviewed and discussed, examples of applications are given and a direction for continued research is presented

Characteristics of a modified H13 hot-work tool steel fabricated by means of laser beam powder bed fusion

In the present study, a modified H13 hot-work tool steel (M-H13) was fabricated by laser beam powder bed fusion (LB-PBF). The effect of two types of post processing, direct tempering from as-built condition (DT) and conventional quenching followed by tempering (QT), on the microstructure and mechanical properties was evaluated. The typical microstructure in QT condition was tempered martensite with carbides along lath boundaries. In DT condition, melt pool boundaries and cellular structure from as-built condition were still observed. While comparable tensile properties and hardness were obtained, DT samples exhibited significantly lower impact toughness compared to QT samples. This was attributed to the difference in work hardening ability and strain rate sensitivity originating from different microstructures obtained under these two heat treatment conditions. The study was also focused on the softening behavior and the correlation with the microstructure of the two post treatments at the elevated temperatures. It was found that the DT samples showed lower thermal softening compared to QT samples. The evolution of carbides was discussed based on the microanalysis results and the JMatPro simulation

Efficacy, Immunogenicity and Safety of an Investigational Subunit Adjuvanted Herpes Zoster Vaccine in Adults Aged 60 Years and Older: Results From the ZOE-50 and ZOE-70 Efficacy Studies

n/

Determinants of serum levels of vitamin D: a study of life-style, menopausal status, dietary intake, serum calcium, and PTH

Background: Low blood levels of vitamin D (25-hydroxy D3, 25OHD3) in women have been associated with an increased risk of several diseases. A large part of the population may have suboptimal 25OHD3 levels but high-risk groups are not well known. The aim of the present study was to identify determinants for serum levels of 25OHD3 in women, i.e. factors such as lifestyle, menopausal status, diet and selected biochemical variables. Methods: The study was based on women from the Malmo Diet and Cancer Study (MDCS), a prospective, population-based cohort study in Malmo, Sweden. In a previous case-control study on breast cancer, 25OHD3 concentrations had been measured in 727 women. In these, quartiles of serum 25OHD3 were compared with regard to age at baseline, BMI (Body Max Index), menopausal status, use of oral contraceptives or menopausal hormone therapy (MHT), life-style (e. g. smoking and alcohol consumption), socio-demographic factors, season, biochemical variables (i.e. calcium, PTH, albumin, creatinine, and phosphate), and dietary intake of vitamin D and calcium. In order to test differences in mean vitamin D concentrations between different categories of the studied factors, an ANOVA test was used followed by a t-test. The relation between different factors and 25OHD3 was further investigated using multiple linear regression analysis and a logistic regression analysis. Results: We found a positive association between serum levels of 25OHD3 and age, oral contraceptive use, moderate alcohol consumption, blood collection during summer/autumn, creatinine, phosphate, calcium, and a high intake of vitamin D. Low vitamin D levels were associated with obesity, being born outside Sweden and high PTH levels. Conclusions: The present population-based study found a positive association between serum levels of 25OHD3 and to several socio-demographic, life-style and biochemical factors. The study may have implications e. g. for dietary recommendations. However, the analysis is a cross-sectional and it is difficult to suggest Lifestyle changes as cause-effect relationships are difficult to assess