Developing Effective Parameters for Simulation of Self-Pierce Rivet Insertion
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DEVELOPING EFFECTIVE PARAMETERS FOR SIMULATION OF SELF-PIERCE RIVET INSERTION By: Zuzana Kotercova Faculty of Civil and Structural Engineering University of Sheffield A thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy Submission Date: May 2020 DECLARATION I, the author, confirm that the Thesis is my own work. I am aware of the University’s Guidance on the Use of Unfair Means (www.sheffield.ac.uk/ssid/unfair-means). This work has not been previously been presented for an award at this, or any other, university. This work includes nothing, which is the outcome of work done in collaboration except where specifically indicated in the text. It has not been previously submitted, in part or whole, to any university of institution for any degree, diploma, or other qualification. All sources of information have been acknowledged by references. Signed:______________________________________________________________ Zuzana Kotercova Date: 14th November 2019 i ABSTRACT The car manufacturing industry is going through a time of significant change under pressure to provide stronger crash safe structures while at the same time making car bodies lighter to enable electric drive. This is forcing car designers to choose very high strength materials and to use a mixture of steel for strength and aluminium for lightness. The result is a large number of riveted joint stack configurations on one car body each requiring different riveting parameters. The amount of physical testing required to find solutions has now become much bigger than the testing time available on the vehicle design programs. To solve this car manufacturers are keen to switch from physical lab testing to simulated joint testing. There is also pressure on rivet suppliers to rapidly develop new rivets designs for making the new joint stack combinations which are increasingly evolving into higher and higher strength materials. Simulation of rivet designs is needed to accelerate rivet development projects and to conduct process window testing to check the proposed new designs can cope with production variables. This project first created a validated base model for simulating rivet insertion and then applied this model to a number of research tasks. Through testing a large number of variety of rivet types, this work developed a set of friction parameters that have proven to work reliably for two different coatings, a standard SPR plating as well as low friction lubricant. The project also focused on accurately replicating the mid- clamping method used by AC setters with promising results. The developed base model been succesfully used to simulate several completely new SPR products that have not been simulated to date such as tubular rivets for standard and narrow flange and solid (swage) riveting. It has also been utilized in studies focusing on creating a process window for materials to account for manufacturing variables. And finally, the model was used in a study supporting rivet design by bringing together the worst possible combination of lowest rivet manufacturing tolerances in order to predict the worst case scenario in rivet production. The results of this study were particularly accurate and allowed for mitigation of the worst combination of tolerances by informing subsequent rivet geometry amendments. Following completion of this project, the simulation can be seen as particularly useful tool in design of new products by predicting trends and mapping out process windows for manufacturing variables of both geometries and materials and can potentially replace a large part of physical testing. ii ACKNOWLEDGEMENTS I would like to thank Atlas Copco IAS UK Ltd and EPSRC for sponsoring this PhD project via a EPSRC Case Award. I would also like to extend my thanks to the people that gave me technical guidance, including the academic supervisor Prof Luca Susmel, the industrial supervisor Dr Paul Briskham, and the team of riveting engineers in the applications lab and the R&D lab at the Atlas Copco site in Deeside who allowed me to conduct simulations on the live company projects, enabling me to ensure the PhD work was focussed on the latest new and novel aspects of benefit SPR technology. iii Word Template by Friedman & Morgan 2014 Morgan & Friedman by Word Template CONTENTS 1 INTRODUCTION & OBJECTIVES 1 1.1 Trend towards aluminium and mixed metal car bodies 1 1.2 PhD Objectives 4 1.2.1 Objective 1 – Selection and Evaluation of the simulation software. 4 1.2.2 Objective 2 – Development of the base model 4 1.2.3 Objective 3 – Application of base model 5 1.2.4 Objective 4 – Utilization of validated simulation models 7 1.3 Overview of the thesis structure 8 2 REVIEW OF SELF PIERCE RIVETING (SPR) 10 2.1 Self-Pierce Riveting - Introduction 10 2.2 Evolution of SPR from 1970 to present day 14 2.3 Rivet types 19 2.3.1 Rivet length 19 2.3.2 Rivet Types and Head Styles 20 2.3.3 Rivet diameter 21 2.3.4 Rivet hardness 21 2.3.5 Rivet hole style 23 2.4 Die types 23 2.5 Rivet Insertion Equipment types 24 2.5.1 Simulation of different rivet insertion equipment 24 2.5.2 Rivet insertion equipment used in this study for the physical lab tests 25 2.5.3 RivLite Portable Battery Tool 25 2.5.4 Hydraulic double acting and pre-clamping tools 25 2.5.5 Servo tools 26 2.6 Advantages and disadvantages of SPR 27 2.6.1 Versatility 27 2.6.2 Joint Strength and Fatigue Durability 28 2.6.3 Costs 30 2.6.4 Access 30 2.6.5 High force 31 2.6.6 Process limitations 31 iv 2.6.7 Permanency of the joint 31 2.6.8 Use of consumable (i.e. rivet) 32 2.6.9 Appearance 32 2.6.10 Not suitable for brittle materials 32 2.6.11 Each joint needs individual configuration 32 2.7 Physical joint assessment 33 2.7.1 Visual inspection of a joint 33 2.7.2 Cross sectioning 34 2.7.3 Force displacement curves 38 2.7.4 Tensile Strength 39 2.8 Types of testing in SPR 41 2.8.1 Feasibility testing 41 2.8.2 Further assessments 41 2.9 Current use of SPR 42 2.10 SPR innovations 42 2.10.1 Laser assisted SPR (LSPR) 43 2.10.2 Friction SPR (F-SPR) 44 2.10.3 Hydro-formed SPR (HF-SPR) 45 2.10.4 Adjustable die option 45 2.10.5 Kerb Konus Solid SPR (S-SPR) 45 3 REVIEW OF FINITE ELEMENT ANALYSIS (FEA) 47 3.1 What is Finite Element Analysis - Introduction 47 3.2 Brief history of Finite Element Analysis 48 3.3 Finite Element Analysis stages 48 3.3.1 Stage 1 – Pre-processing 48 3.3.2 Stage 2 – Solution 49 3.3.3 Stage 3 – Post-processing 49 3.4 Types of FEA 50 3.4.1 Static analysis 50 3.4.2 Dynamic analysis 51 3.4.3 Quasi static analysis 51 3.4.4 Implicit analysis 52 3.4.5 Explicit analysis 52 v Word Template by Friedman & Morgan 2014 Morgan & Friedman by Word Template 3.5 Specific methods used by Simufact software 53 4 REVIEW OF FEA IN CONTEXT OF SPR 58 4.1 Parameters to consider in FE analysis of SPR 58 4.1.1 Simulation process parameters 59 4.1.2 Process description 79 4.1.3 Material characterization 86 4.1.4 Rivets’, dies’, sheets’ and tools’ geometries 117 4.1.5 Friction, lubrication and coatings 119 4.2 FEA of SPR to date – Current state of the art 130 4.2.1 Software types 134 4.2.2 Different types of materials in simulation 135 4.2.3 Optimisation of rivet and die geometries 136 4.2.4 Areas for future development 137 5 RESEARCH METHODS 138 5.1 Physical SPR tests 138 5.2 FE analysis 140 5.3 Validation of simulation by experimental tests 142 6 EXPERIMENTAL STAGE 143 6.1 Simulation assessment and accuracy tolerances 144 6.1.1 Simulation assessment – Joint measurements 144 6.1.2 Simulation assessment – Joint visual attributes 146 6.1.3 Simulation assessment – Agreeability scorecard 147 6.2 Software selection 151 6.2.1 Evaluation of the software 152 6.3 Simulation process description 156 6.3.1 Friction 156 6.3.2 Clamping 184 6.3.3 Press selection 191 6.3.4 Mesh 202 6.3.5 Damage mechanics 209 6.3.6 Temperature effects 213 vi 6.3.7 Materials characterisation 224 6.3.8 Influence of geometries 243 6.4 Summary 253 7 PRACTICAL APPLICATIONS 257 7.1 Simulation of process window for sheet and rivet properties for BG rivet joining UHSS. 257 7.2 Simulation to aid design of fully tubular rivet for narrow flange joining 264 7.2.1 Test 1 – Narrowing down tolerance band 265 7.2.2 Test 2 – Coupled effect of rivet hardness and tip geometry 267 7.2.3 Test 3 – Process capability 271 7.2.4 Test 4 – Coupled effect of improved tip geometry and flare angle 274 7.3 Simulation of Solid SPR riveting joining process (Swage riveting) 275 7.3.1 Development of the swage simulation model 277 7.3.2 Validation of the swage model 281 7.4 Summary 286 8 DISCUSSION 289 8.1 Introduction 289 8.2 Selection and evaluation of out of the box version of the selected software (Objective 1A and 1B) 289 8.3 Development of the base simulation model (Objective 2) 290 8.3.1 Development of friction parameters (Objective 2A) 290 8.3.2 Effect of different joint clamping methods (Objective 2B) 292 8.4 Simulation of fully tubular rivets (Objective 3A) 294 8.5 Mixed material riveting of UHSS to aluminium and Process window for sheet and rivet properties (Objective 3B & 4A) 295 8.6 Simulation to aid design optimisation of new 4mm shank diameter T-rivets in combination with new narrow flange equipment (Objective 3C & 4B) 296 8.7 Swage solid SPR riveting joining process (Objective 3D) 298 9 CONCLUSIONS 299 vii Word Template by Friedman & Morgan 2014 Morgan & Friedman by Word Template 9.1 Conclusions 299 9.2 Recommendations for Future Work 305 10 REFERENCES 307 viii LIST OF TABLES TABLE 1, RIVET LENGTH AVAILABILITY TABLE (ATLAS COPCO RIVET BROCHURE 2019) ............................................