Anisotropy of functional surfaces can in many practical cases significantly influence the surface function. Tribological contacts in sheet forming and engine applications are good examples. This article introduces and exemplifies a method for visualization of anisotropy. In a single graph, surface texture properties related to the anisotropy as a function of scale are plotted. The anisotropy graph can be used to explain anisotropy properties of a studied surface such as texture direction and texture strength at different scales of observation. Examples of milled steel surfaces and a textured steel sheet surface are presented to support the proposed methodology. Different aspects of the studied surfaces could clearly be seen at different scales. Future steps to improve filtering techniques and an introduction of length-scale analysis are discussed.

The evolvement of product requirements in the automotive industry, e.g. reduced weight, means that the use of advanced high strength steels (HSS, EHSS,UHSS) in automotive applications is continuously increasing. The introduction of high strength steels in production implies increased tool wear and calls for functional tool surfaces that are durable in these severe tribological conditions. In this study the influence of tool surface topography on friction has been investigated. The frictional response was studied in a Bending Under Tension test. The results did show that a low frictional response was generated by low slope of roughness profiles combined with a strong anisotropy applied perpendicularly to the sliding direction. An improved machining strategy has a high potential to significantly reduce the need for manually polished surfaces.

The friction in stamping is an important process parameter to control the flow of material in the tool. Consequently, it is also an important parameter in the design process of new stamping tools when numerical simulations of the forming operations are performed. In this work an advanced friction model is evaluated, which considers properties of surface topography, lubricant, sheet material, and process parameters such as sliding speed and pressure. The evaluation is made by comparing theoretical results with experimental ones obtained in a bending-under-tension friction test. The results show conformance in behaviour between the friction model and the experimental work. Furthermore, a model, which considers the influence of bulk plastic strains on the real area of contact, is investigated. The developed model predicts that the effective hardness of a surface is reduced by the presence of underlying plastic flow. It is found that when the strain rates are increased, the Stribeck curve becomes flatter and mixed lubrication is introduced at lower Hersey values. The friction model clearly shows the potential of improving the FE simulations of sheet metal forming operations, in comparison to the use of the classical Coulomb's friction model.

The friction is of critical importance to sheet metal forming operations. It affects the flow of material in the tool and thereby the scrap rate and final quality of products. In the experimental work the frictional response was measured in a bending under tension (BUT) test under mixed lubricated conditions. The study includes stainless steel, but previous research on carbon steels, coated and uncoated, are discussed also. The experimental results could be explained by the theory of pad bearings. The frictional response showed a correlation to the surface topography, e.g. the amplitude parameter (Sq) and texture aspect ratio parameter (Str). When predicting the frictional response of surfaces with multi-component distributions, the standard deviation of the distribution above the mean line could be used.

During the past years, large efforts have been made, to analyze and evaluate the surface quality of dies manufactured in nodular iron (GGG70L). The variation of quality in respect of wear resistance hardenability and micro cracks are the main issues. It results in bad surface quality on the formed parts (scratches) which gives break down in the production and increases the maintenance (repolishing of tool surface). The spread in wear resistance depends on that the parameters for a functional working surface combined with and the lubrication is not clarified and thus not been able to be specifie . The main parameters for a functional working surface are among other things the amount of nodules (n), size, shape (style), how the exit side (in draw direction) of the nodule crater looks like. Different qualities in respect to size, amount and shape of the nodules in a nodular iron have been tested against uncoated sheet material (H300LA, t=1.5mm) in semi-industrial test equipment (OSAS U-bend). The surface conditions of the nodular iron are laser or induction surface hardened. The result in this investigation shows that nodular iron (GGG70L) with high nodule count and small nodule size in the working surface gives a significant improvement of the resistance to adhesive wear.

The higher product requirements (reduced weight, increased safety, lower emissions…) have meant that a larger number of car body parts must be made in advanced high strength steels. With a reduced lifecycle of a car model from 7 to 5 years this leads to a need for reducing the manufacturing cost and lead time for the tool and die design and manufacturing. The main purpose of this investigation is to establish cost- and lead-time reducing guidelines for selection of tool concepts (choice of die materials, hardening methods and geometry) for different production volume scenarios with respect to sheet materials quality (MS-UHSS) and thickness, without increased die maintenance costs. In this study the cutting edge geometry has been evaluated in respect to the cutting edge radius and the angle of the upper tool. Experimental testing together with FE simulation has been used. Results show that an angle of 93° on the upper cutting edge initially can reduce the cutting work by 14%. Results also shows that by using a cutting edge radius of 80µm, the tool “wear in phase” can be more controlled. Wear test up to 150 000 strokes have been made to evaluate different tool concepts using laser hardened cast iron, cast steel and wrought steel as die material. Sheet material tested was 220RP, DP600, DP800, 700MC and DP1000, with a thickness of t=2mm. The result leads to recommendations for industrial verification. Results among other recommendations are: laser hardened EN-JS-2070 up to 500 000 parts against 220RP and Sleipner up to 1 500 000 parts against 1000DP.

Tribology is the science of friction, wear, and lubrication; the interaction of surfaces in relative motion. The tribological conditions in sheet metal forming influences the flow of material in forming operations, the strain distributions of sheet material, extent of wear, and thereby the quality of products. The purpose of the thesis is to increase the knowledge of why and how sheet surface topography influence the frictional response in stamping, to characterise the geometrical properties, and make results applicable for industry. The frictional response of different surface topographies have been measured in a Bending Under Tension test under mixed lubricated conditions. The studied materials have been stainless steel sheets and uncoated and coated carbon steel sheets. The results did show the influence of roughness, skewness, and anisotropy of surface topography. The findings could be explained by the theory of pad bearings. A new functional 3D parameter (Sq>0) was developed for pressing performance that is sensitive to the effects of roughness and skewness. The texture-aspect ratio parameter (Str) was found to be correlated to the anisotropical behaviour of the frictional response. The results are very tangible and mean increased control of stamping operations. An initial step was taken to introduce more advanced tribological models in FE simulation of sheet metal forming operations. The aim is to decrease the trial-and-error time in the design process of dies and tools. A friction model considering surface topography (Sq>0), sliding velocity, lubricant viscosity, and apparent pressure, was successfully implemented. Simulations of a part were evaluated with real stamping tryouts. The results did show the potential of improving the precision in forming simulations with more advanced tribological models. Finally, theory and characterisation methods of active micro-oil pockets in the contact zone of tool and sheet were investigated. The real contact area was shown to be the critical feature to determine. Therefore, two topographical methods and one microscope-imaging processing technique were studied, but no method was found to be viable. However, the experimental results did not confirm the importance of microoil pockets in mixed lubricated regime.