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Resistance welding toolkit - A computer knowledge base, covering design and manufacturing considerations for resistance spot welding

   
H J Powell

This paper was presented at 'Materials for Energy-Efficient Vehicles/Paint and Powder Coating Applications for the Automotive Industries', 30th International Symposium on Automotive Technology & Automation, Florence Italy, 16-19 June 1997.

Abstract

One of the major challenges faced by automotive manufacturers and suppliers is the achievement of lean, agile product development processes, combined with a manufacturing environment conducive of continuous product and process improvement. A significant factor in achieving this goal is rapid access to knowledge and expertise, often only present in the form of 'experience' and generally associated with a declining population of technical specialist engineers.

This paper presents the concept and functionality of a 'user-friendly' computer knowledge base, designed for use by product design engineers, manufacturing engineers and production personnel concerned with process and quality control. Information and quality knowledge presented within the system includes database functions, spreadsheet calculations and hypertext documentation. The factors covered in the program include:

  • Joint design feasibility: A database of different joint configurations, materials thicknesses, coatings and index relating to technical suitability
  • Weld parameter guidelines: Database of suggested weld parameters, with output based on information given in joint design feasibility
  • Joint quality and performance: Database of approximate joint quality and performance based on information given in joint design feasibility
  • Process cost analysis: Process costing methodology using embedded spreadsheets
  • Troubleshooting: Hypertext documentation using case studies to illustrate common quality related problems and improvement actions. Documentation on weld quality and the achievement of best practice.
  • Equipment and standards: References to equipment and standards

Introduction

The work presented in this report has concentrated on the development of a practical methodology for resistance spot welding, addressing welding system design, process control and technical-economic considerations. It has resulted in the design and specification of a 'user-friendly' computer knowledge-base designed for use by product design engineers, manufacturing engineers and production/shop floor personnel concerned with process and quality control.

The Resistance Welding Toolkit software resembles an electronic book, incorporating data-base functions with simple user interfaces, spreadsheet calculations and hypertext documentation.

Design Issues

Rapid application development (RAD)

Recent advances in the speed of computers and user interface techniques have led to the development of a number of programming tools which use a technique called Rapid Application Development. These tools, which include Visual Basic, Delphi, and Visual C++, allow the user interface for a system to be designed on-screen, very quickly. Facilities are provided by the system to produce windows, text boxes, pictures, menus etc. These functions are selected from a menu and then sized and placed on the screen. As a result, prototype systems, looking exactly like the finished product, can be easily developed in a very short timescale.

Traditional QA systems for software development discourage any coding before the software design is complete and has been verified. This is to avoid having to discard and restructure the code because a key element of the design has not been incorporated.

In Rapid Application Development (RAD), the user interface of the system is designed first, and any complex functions designed later. These functions are 'attached' directly to buttons or menu options on the screen, and the code structure is handled automatically by RAD tool.

Visual basic, which uses RAD techniques, was chosen to develop the Resistance Welding Toolkit, and the Windows environment was considered to offer a user friendly interface. A timescale of approximately 9-12 months would normally be associated with the development of the software using conventional design and programming approaches. A significant reduction in the design lead time was anticipated by the use of RAD for this application.

System design

The following sections present the top level design of the system, and the main modules that make up the system. The main design issues for each module are listed in Table 1.

Table 1: Main Toolkit Modules

LevelDescription
Introduction Banner
Main Screen Ishikawa diagram of factor affecting process variability, with hypertext links to best practice guide of key factors. Selection buttons to separate modules
Joint Design Feasibility Database of different joint configurations, materials, thicknesses, coatings, and index relating to technical suitability.
Welding Parameter Guidelines Database of suggested weld parameters, with output based on joint configuration selected in Joint Design Feasibility.
Joint Quality & Performance Database of approximate joint performance characteristics, with output based on joint configuration selected in Joint Design Feasibility
Joining Process Economics Process costing methodology, using embedded spreadsheet
Trouble Shooting Hypertext documentation, using case-studies to illustrate common quality related problems and improvement actions
Standards Hypertext documentation, listing current relevant industry standards for resistance spot welding
Welding Equipment Hypertext documentation, listing key suppliers of process and quality related equipment

Toolkit main screen

When the user selects the Toolkit programme, the following main screen is presented as follows:

Figure 1: Image of Toolkit main screen
Figure 1: Image of Toolkit main screen

The screen is split into three areas:

  • A 'header box' with the system name and logos.
  • A 'button box' containing links to the other modules of the system, which is displayed permanently.
  • A 'window' in which the information relevant to the selected module is displayed.

The main screen displays an Ishikawa diagram (ref. 3), illustrating the main factors that affect resistance welding process variability. Each of the main factors is displayed in green, which is a standard Windows format for showing a hypertext link to further information about that topic. This technique has been used extensively throughout the Resistance Welding Toolkit.

Joint feasibility

This module determines the suitability of each of the main resistance welding processes (spot, projection and seam) to the application. Up to four sheets can be defined in terms of generic material type, thickness and coating(s), and a suitability index, measured on a scale of 0-100 is displayed for each process type. Engineers at TWI have generated the rules of thumb, or heuristics, which are used to determine these aspects.

Figure 2: Image of feasibility module
Figure 2: Image of feasibility module

In this case, the system reports that for a joint between two sheets all processes can be used, but projection welding is slightly less suitable than spot or seam welding.

The values entered in this module are used in a number of other modules in the system.

Welding parameters

This module indicates suitable welding parameters for the application defined in the Joint Feasibility module. The data is stored in tabular form, covering all combinations of thickness, material and coating, and was taken from both published data, and in-house expertise.

Figure 3: Picture of parameter module
Figure 3: Picture of parameter module

In this case, the system is recommending a practical range of parameters for the spot welding application configuration described in the previous section.

Joint performance

This module indicates anticipated performance data, in terms of joint strength (shear and cross-tension), peel and fatigue properties. As with the weld parameters module, the data is stored in tabular form, covering all combinations of thickness, material and coating, and taken from both published data and in-house expertise.

Figure 4. Picture of joint performance module
Figure 4. Picture of joint performance module

The example illustrated in Fig. 4 shows the anticipated range of joint performance characteristics for the spot welding application described in the Joint Feasibility section.

Economics

A spreadsheet approach was used to model the cost of ownership associated with resistance spot welding. The user supplies information about the application to be joined, which supplements the information already entered in the Feasibility module, and the system determines the cost of making the joint in that way. The system incorporates a number of default values, which can be accepted, to reduce the number of user inputs required, or overridden, if more information is known.

One of the major benefits of such an approach is that the user can perform very fast 'what-if' analyses to assess the impact of various manufacturing scenarios on the operational cost of manufacture and the most economic way of making the joint.

Figure 5. Image of the economics module
Figure 5. Image of the economics module

In this case, the system is displaying the results of a spreadsheet analysis, showing a summary of the cost of ownership.

Troubleshooting

This module gives guidance on avoiding manufacturing and quality-related problems. A hypertext technique has been used to navigate through the information in this module, so in practice, the user simply clicks on keywords highlighted in green to identify the problem and the system gives remedial advice. The contents of this module are presented in a case study format.

Standards

Listings of national and international Process Standards relevant to resistance welding have been included in this module. Hypertext links have been used to enable the relevant standard(s) to be identified quickly.

Welding equipment

This module provides quick and rapid access to listings of suppliers and manufacturers of resistance welding equipment using hypertext documentation.

Concluding remarks

A user friendly computer knowledge-base for resistance spot welding has been successfully developed.

An methodology for assessing the 'cost of ownership' for resistance spot welding (including cost per weld, machine utilisation, piece-part costs) has also been developed and incorporated within the Toolkit Software.

Rapid Software Application Development techniques have been successfully applied, enabling the development of significantly complex software programme within a 3 month timescale (as opposed to a 9-12 month timescale associated with conventional methods).

The object orientated structure of the system allows relatively easy modification and incorporation of additional modules.

Acknowledgements

This work was carried out within the Core Research Programme of TWI, which is funded by the Industrial Members of TWI.

References

authortitle 
1 H J Powell, S A Westgate, K Wiemer A Practical Guide to Process and Quality Control for Resistance Spot Welding, TWI Industrial Members Report No. 569 - August 1996  
2   Guide to Software Quality Management System Construction and Certification Using EN 29001, Issue 1.1, September 1990, DTI.  
3 Ishikawa K Guide to Control, Chapter 3, Asian Productivity Association, Tokyo.  

Published with permission of Automotive Automation Limited, Croydon, UK (e-mail - 100270.1263@compuserve.com)

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