Shape error modelling and analysis by conditional simulations of Gaussian random fields for compliant non-ideal sheet metal parts

Accurate modelling of geometric and dimensional errors of sheet metal parts is crucial in designing correct GD&T and preventing unnecessary design changes during the development and launch of a new assembly process. A novel conditional simulation based methodology to probabilistically model and generate non-ideal sheet metal part geometric variations is developed. The methodology generates part geometric variations, which accurately emulate part fabrication process in terms of covariance of generated deviations. The methodology uses as inputs one or more of the following: measurement data of current parts, historical measurements of similar parts or FEM-based simulations. The proposed methodology emulates real processes and products accurately by generating non-ideal part representatives based on the aforementioned input data. Results provide an easy engineering interpretation to the designer. The methodology is demonstrated using automotive door hinge reinforcement

Quality and productivity driven trajectory optimisation for robotic handling of compliant sheet metal parts in multi-press stamping lines

This paper investigates trajectory generation for multi-robot systems that handle compliant parts in order to minimise deformations during handling, which is important to reduce the risk of affecting the part’s dimensional quality. An optimisation methodology is proposed to generate deformation-minimal multi-robot coordinated trajectories for predefined robot paths and cycle-time. The novelty of the proposed optimisation methodology is that it efficiently estimates part deformations using a precomputed Response Surface Model (RSM), which is based on data samples generated by Finite Element Analysis (FEA) of the handled part and end-effector. The end-effector holding forces, plastic part deformations, collision-avoidance and multi-robot coordination are also considered as constraints in the optimisation model. The optimised trajectories are experimentally validated and the results show that the proposed optimisation methodology is able to significantly reduce the deformations of the part during handling, i.e. up to 12% with the same cycle-time in the case study that involves handling compliant sheet metal parts. This investigation provides insights into generating specialised trajectories for material handling of compliant parts that can systematically minimise part deformations to ensure final dimensional quality

Fixture capability optimisation for early-stage design of assembly system with compliant parts using nested polynomial chaos expansion

AbstractThis paper introduces the novel concept of fixture capability measure to determine fixture layout for the best assembly process yield by optimizing position of locators and reference clamps to compensate stochastic product variations and part deformation. This allows reducing the risk of product failures caused by product and process variation. The method is based on three main steps: (i) physics-based modelling of parts and fixtures, (ii) stochastic polynomial chaos expansion to calculate fixture capability, and (iii) fixture capability optimisation using surrogate modelling. The methodology is demonstrated and validated using the results of an aerospace wing sub-assembly joined by riveting technique

Root cause analysis of product service failure using computer experimentation technique

Improvement of product quality and reliability following field failures of products is a well-researched area. The feedback from the service in the form warranty / field performance is important in guiding design and manufacturing changes. Traditionally, efforts in this area have been limited to analysis of warranty data for evaluating warranty policies, estimating field reliability, predicting failures etc. Also some research has been done on performing corrective actions in manufacturing via process adjustments by linking warranty failures with manufacturing Key Control Characteristics (KCCs). However there is also need to develop the systematic approach of doing Root Cause Analysis (RCA) and Corrective Actions in design. This research proposes a novel methodology of performing RCA and CA in design by linking warranty failures with the product design parameters such as Geometric Dimensioning and Tolerance (GD&T). An analytical approach based on computer experimentation technique performs effective Root Cause Analysis (RCA) of product failures by linking warranty failure modes with the design parameters and identifies the analytical relationship between them. The method focuses on identifying root cause(s) to address in tolerance product design faults. Warranty failures modes are represented by Key Failure Characteristics (KFCs) and the geometrical design parameters are represented by Key Product Characteristics (KPCs). The proposed methodology establishes the analytical relationship between the KFCs and KPCs using variation mechanistic models to identify the dimensional variations which caused the failure. A case study on automotive ignition switch demonstrates the methodology

The Effects of Laser Welding Direction on Joint Quality for Non-Uniform Part-to-Part Gaps

Controlling part-to-part gaps is a crucial task in the laser welding of galvanized steel sheets for ensuring the quality of the assembly joint. However, part-to-part gaps are frequently non-uniform. Hence, elevations and depressions from the perspective of the heading direction of the laser beam always exist throughout the gap, creating ascending, descending, and flat travelling paths for laser welding. In this study, assuming non-uniform part-to-part gaps, the effects of welding direction on the quality of the joint of galvanized steel sheets-SGARC440 (lower part) and SGAFC590DP (upper part)-were examined using 2-kW fiber and 6.6-kW disk laser welding systems. The experimental analysis of coupon tests confirmed that there is no statistically significant correlation between the direction of welding and weld pool quality if the gap exceeds the tolerable range. However, when the gap is controlled within the tolerable range, the welding direction can be considered as an important process control variable to enhance the quality of the joint.ope

Laser dimpling process parameters selection and optimization using surrogate-driven process capability space

Remote laser welding technology offers opportunities for high production throughput at a competitive cost. However, the remote laser welding process of zinc-coated sheet metal parts in lap joint configuration poses a challenge due to the difference between the melting temperature of the steel (∼1500 C) and the vaporizing temperature of the zinc (~907 C). In fact, the zinc layer at the faying surface is vaporized and the vapour might be trapped within the melting pool leading to weld defects. Various solutions have been proposed to overcome this problem over the years. Among them, laser dimpling has been adopted by manufacturers because of its flexibility and effectiveness along with its cost advantages. In essence, the dimple works as a spacer between the two sheets in lap joint and allows the zinc vapour escape during welding process, thereby preventing weld defects. However, there is a lack of comprehensive characterization of dimpling process for effective implementation in real manufacturing system taking into consideration inherent changes in variability of process parameters. This paper introduces a methodology to develop (i) surrogate model for dimpling process characterization considering multiple–inputs (i.e. key control characteristics) and multiple–outputs (i.e. key performance indicators) system by conducting physical experimentation and using multivariate adaptive regression splines; (ii) process capability space (Cp–Space) based on the developed surrogate model that allows the estimation of a desired process fallout rate in the case of violation of process requirements in the presence of stochastic variation; and, (iii) selection and optimization of the process parameters based on the process capability space. The proposed methodology provides a unique capability to: (i) simulate the effect of process variation as generated by manufacturing process; (ii) model quality requirements with multiple and coupled quality requirements; and (iii) optimize process parameters under competing quality requirements such as maximizing the dimple height while minimizing the dimple lower surface area

Role activity diagram-based discrete event simulation model for healthcare service delivery processes

In case of healthcare systems, discrete event simulations are useful techniques to identify problematic process issues. However, currently available simulation models often use a simplified flow chart as an input which represents patient flow obtained from on on-site observations and interviews complemented with historic patient data. This is insufficient in modelling important interactions between clinical staff, equipment and patients causing the resultant models to be incomplete and unrealistic. This in turn leads to oversimplified outputs from any simulations. This paper presents a systematic methodology for the development of discrete event simulation model from process mapping model based on the Role Activity Diagram (RAD) notations. RAD allows complex collaborative healthcare service delivery processes to be modelled as roles, interactions, actions, and decision questions. The workflow simulation modelling methodology based on RADs includes: (i) development of RAD model of the service delivery process; (ii) data model for RAD based service delivery process; (iii) developing DES model based on RAD; and, (iv) adding dynamic attributes and validating DES model. The methodology is demonstrated through a case study of magnetic resonance (MR) scanning process of radiology department in a large hospital

Challenges and opportunities in laser welding of 6xxx high strength aluminium extrusions in automotive battery tray construction

Laser welding has been increasingly adopted into the automotive sector due to its competitive processing speed, less restrictive single-sided access requirements and improved process flexibility. These benefits notwithstanding, laser welding still remains susceptible to the weld cracking especially for 6xxx high strength aluminium extrusions, which are widely used in the automotive industry for body-in-white and battery tray manufacturing. This paper reviews current challenges and opportunities for construction of battery tray using aluminium alloys with laser welding process. It aims to provide a view on the selection of welding equipment in terms of beam oscillation, power modulation, beam shaping, filler wire and shielding gas, and analyze their impact on joint integrity for 6xxx grades aluminium extrusions. The driving idea is to control the thermal history in and around the molten pool and to modify the chemical composition in the fusion zone to reduce the formation of solidification cracks. Results of the study have shown that the modification of chemical composition by the use of filler wire is currently the most efficient approach to improve joint strength. Further results evidences also showed that beam shaping with adjustable ring mode laser helps to stabilize the keyhole and achieve a wider molten pool and weld interface width. Manufacturing implications are reviewed and discussed throughout the paper

A novel hybrid shell element formulation (QUAD+ and TRIA+) : a benchmarking and comparative study

This paper introduces a novel hybrid finite element (FE) formulation of shell element to enable assembly process simulation of compliant sheet-metal parts with higher efficiency and flexibility. Efficiency was achieved by developing both new hybrid quadrilateral and triangular elements. Quadrilateral element (QUAD+) was formulated by combining area geometric quadrilateral 6 (AGQ6) nodes and mixed interpolated tensorial components (MITC) to model membrane and bending/shear component respectively. Triangular element (TRIA+) was formulated by merging assumed natural deviatoric strain (ANDES) for membrane and MITC for bending/shear component. Flexibility was addressed by developing an open-source C++ code, enhanced by the OpenMP interface for multiprocessing programming. Tests and benchmarks were compiled and executed within Matlab using the MEX API interface. Extensive benchmark studies were accomplished to evaluate the performance of the proposed hybrid formulation and the shell formulations used in three FEM packages - ABAQUS, ANSYS and COMSOL- under static linear elastic condition with small strain assumption. It was observed that the proposed QUAD+ and TRIA+ elements performed better amongst the FE packages, especially when there was in-plane mesh distortion, with errors below 3%. It was also identified that the best efficiency is obtained by adopting dominant QUAD+ elements compared to the TRIA+ when working on complex geometries. This paper also contributes to present a wide set of benchmark studies required to verify new release of FE packages using shell element or evaluate the performance of new shell formulations