A Robust Design Perspective on Factors Influencing Geometric Quality in Metal Additive Manufacturing

Additive manufacturing (AM) for metals is a widely researched, continuously enhanced manufacturing process and is implemented across various industries. However, the AM process exhibits variation that affects the geometric quality of the end product. The effect of process variation on geometric quality is rarely considered during design stages. This paper discusses the various sources that contribute to geometric variation and the prospect of applying robust design method to produce geometry assured AM products. A framework for geometric robustness analysis of AM products is presented as an outcome. This framework would facilitate development of methods and tools to produce geometry assured AM products. The prospects of variation simulation to support geometric robustness analysis and the challenges associated with it are discussed.

TIE POINT GENERATION IN HYPERSPECTRAL CUBES FOR ORIENTATION WITH POLYNOMIAL MODELS

This paper presents a technique for tie point generation in hyperspectral images collected by a camera with time-sequential principle for band acquisition (i.e., non-synchronized bands). In mobile applications, each band is acquired at a different time, which generates different camera positions and attitude angles. Due to the large number of bands, a bundle adjustment with polynomial models can be applied to sample bands and then, EOP of other bands are interpolated. The determination of homologue points in all sample bands is required to ensure geometric robustness. A procedure was developed to extract tie points from a reference band which were then transferred to the other sample bands. The technique uses a Helmert geometric transformation combined with majority voting to estimate point transfer functions, followed by area-based matching. Experiments with image orientation were conducted to apply and assess the technique. The tests showed an increase in height discrepancy when tie points are not located in all sample bands highlighting the relevance of the proposed filtering. The accuracy of the technique achieved less than 1 GSD in planimetry and 2 GSD in altimetry using the tie points with the maximum number of rays. Thus, the polynomial approach enables interpolation of other bands according to the parameters of the polynomial function.

Efficient Compliant Variation Simulation of Spot-Welded Assemblies

During product development one important aspect is the geometric robustness of the design. This is due to the fact that all manufacturing processes lead to products with variation. Failing to properly account for the variability of the process in the design phase may lead to expensive redesign. One important tool during the design phase in many industries is variation simulation, which makes it possible to predict and optimize the geometric quality of the design. However, despite the increase in computer power, calculation time is still an obstacle for the wider use of variation simulation. In this article, we propose a new method for efficient compliant variation simulation of spot-welded sheet metal assemblies. The method is exact, and we show that the method leads to time savings in simulation of approximately 40–50% compared to current state-of-the-art variation simulation.

Robust Design by Support of CAT Tools

This paper describes how currently available tools for computer aided tolerancing (CAT), can be used in a two step procedure to increase the robustness of a design and when allocating proper tolerances. The first step is to increase geometric robustness by minimizing the number of parameters controlling a critical characteristic. This is closely related to the philosophy behind axiomatic design, see Suh (1990) and is performed during concept design. In this step, the CAT tool is used to analyze the general stability and sensitivity of an assembly in order to detect the sources of variation, KC:s, on an overall product characteristic, PKC. This step is performed with equal tolerances applied to all geometrical part features, which enables the designer to detect geometrical couplings and evaluate general assembly robustness. The second step is to assign tolerances on the final geometry. This is done with respect to final geometrical sensitivity, manufacturing capability and manufacturing cost and is performed during detail design. At this stage, the final variation of overall product characteristics may be simulated, and part tolerances may be adjusted with respect to final sensitivity and cost. If loss functions for the PKC:s are available, the total quality level of a concept may be analyzed.