The shape of things to come - distortion control by multimedia

TWI Bulletin, September - October 1998

Martin Bourton is a senior software engineer in the Technology Transfer Department at TWI, which he joined in 1987. Much of his work has been concerned with expert systems and multimedia development.

Geert Verhaeghe is a project leader in TWI's Arc Welding section, where he has been involved in development and application of arc welding process technologies, and distortion studies.

Distortion is a recurring and costly problem in industrial metalworking processes using heat, such as welding and cutting. ^[1] For these processes distortion is prevalent because the heat source is so concentrated. Martin Bourton and Geert Verhaeghe describe the development of a multimedia program on the complex subject of distortion control.

Distortion of a welded structure is the result of the non-uniform expansion and contraction of a weld and surrounding base material caused by heating and cooling during welding or cutting. ^[1] Four separate types of distortion can be distinguished; transverse shrinkage, angular distortion, longitudinal shrinkage and bowing distortion. In most fabrications, more than one of these types occurs simultaneously.

It should be underlined that distortion cannot be prevented, only minimised. Each fabrication requires separate consideration to determine the ideal conditions for minimising distortion. However, often only a few key personnel hold the expert knowledge needed to avoid or correct unacceptable levels of distortion. TWI recognised the need to disseminate this invaluable expert know-how and has developed the multimedia program Staying in Shape to help tackle the problem of welding and cutting distortion. The system covers the following:

• The different types of distortion and when they occur
• The factors in welding affecting distortion
• Prediction of distortion and practical steps to reduce distortion
• Precautions for specific welding and cutting scenarios and actions to correct distortion after welding

This report describes the development of a multimedia training package on the topic of welding and cutting distortion.

Objectives

To build up expertise in the techniques required to develop multimedia training software.

To develop a multimedia computer program to provide practical training and advice on how to handle the problem of welding and cutting distortion.

Multimedia

Computer software, video clips, animations, audio - as commentary, music or sound effects, scanned photographs, computer graphics and text make up a multimedia program. ^[2] Due to the large amounts of memory required to store multimedia, it is usually delivered on CD-ROM.

Multimedia is often used in training applications and promotional activities, as it has high impact and aids memory retention. Because of the large data storage capacity of a CD-ROM, multimedia reference disks are also commonplace. ^[3]

There are similarities in the way that information is presented in a television programme and in a multimedia program, they both use movie, animation and audio. However, television programmes comprise full screen images, one following another. In contrast, multimedia programmers can mix and match different media (stills images, video, animation, narrative and text) in any way and in any part of the screen, interactively. So unlike television, the viewer is an active participant in the process.

On a multimedia CD-ROM a user has control of where they go, so it is vital that the software has a navigation structure that allows users to move around the material (Fig.1). It is very easy to become lost within a non-linear system. So the programmer must impose some order, but without making the system entirely linear, otherwise the benefit of CD-ROM is lost.

There are different approaches to designing a navigation structure. In many programs the structure forms a contents list, much like in a book, and the user can jump to a particular chapter. Other types of navigation structure might be a 'time line' or a 'virtual landscape', where a user would click on an object for more information. 

Staying in shape

In order to communicate effectively the complex issues covered by the CD-ROM, Staying in Shape uses all the media previously listed (Figs 2-7):

• A video clip depicting a number of the industry sectors that experience problems with distortion, introduces the software.
• 3-D animations explain the four basic types of distortion (longitudinal, transverse, angular and bowing).
• An audio soundtrack accompanies the on-screen presentation.
• Scanned photographs show the welding and cutting processes that create distortion.
• Computer generated graphics are used as illustrations throughout the program, often emphasising the feature under examination.
• Blocks of text and bullet points provide the user with an opportunity to browse through the information.

Staying in Shape is essentially a database, but the information is presented visually. By clicking on an option the user can see pictures of distortion related topics, with accompanying commentary. It is similar to the user looking up the information in a book, but the user gets more of a feel for the scale of distortion, the different types of distortion and when they could occur. It is more like the student is doing their own research. Users can follow their own interests and thoughts. They do not have to follow the same path as another student. Furthermore, a student has the freedom to move at his or her own pace.

Distortion is a complex phenomenon and has been dealt with in many papers and books. Staying in Shape aims to provide practical information to the end user and avoid the highly technical issues such as weld pool behaviour,strain-stress analysis or temperature distribution in the welded structure. In order to define the scope of the software, the problem of welding and cutting distortion was examined from different perspectives (see Fig.8).

The following list summarises the topics covered by the Staying in Shape CD-ROM:

• Introduction
• Types of distortion
• Factors affecting distortion
• Prediction of distortion
• Practical steps to avoid distortion
• Specific precautions to avoid distortion
• Actions to correct distortion after welding
• Recommendations for good practice

Each chapter contains a number of quiz questions and some form of user interaction, so that a student can test their understanding of the information presented. A representative quiz question asks the student to rank a series ofwelding processes, in order of preference to minimise distortion. A typical user interaction involves the student positioning a number of heat spots on a fabrication, in order to remove out-of-plane distortion.

The software also contains a terms and definitions section, that allows the student to look up the meaning of technical terms used during the on-screen presentation, or as part of the audio commentary.

Staying in Shape has been designed for a multimedia PC meeting the following specification:

• Pentium Processor
• 16Mb RAM
• 800 x 600 pixels, 65k colour display
• Quad speed CD-ROM drive
• Sound card and speakers
• Windows version 3.11 (or above)

Discussion

In order to develop an effective educational package, it is imperative to understand at the outset what the objectives are and how multimedia technology can be used to enhance traditional teaching methods, without losing focus,clarity or detail.

When developing a multimedia application it is essential to map out the structure and content of the program before the implementation stage is started. Unless the multimedia program is precisely defined, by clearly identifying the user requirements and a software design specification to meet these requirements, it is highly likely that the project will not run to the allotted time scale and budget. Implementing a multimedia program that will require substantial alteration, will almost certainly lead to an unsatisfactory conclusion.

The development of the Staying in Shape CD-ROM included defining and implementing the following:

• Verified knowledge base
• Navigation structure or flow diagram
• Screen designs (video, animation, scanned photographs, graphics)
• Audio script
• Test questions and user interactions
• Dictionary of terms
• On-line user help text
• Test strategy

Recommendations

Verified knowledge base

Defining the scope of the knowledge base must be the first task. Software that tries to cover too much, in insufficient detail, will be of little worth.

Navigation structure or flow diagram

Keep the navigation structure as simple as possible. Having more than two or three levels can lead to confusion.

Screen designs

Reserve a section of the screen for static objects, such as the program title and the navigation buttons. Then, media can be created to fit into the remaining dynamic region (Fig.9). A full screen scanned photograph may have maximum clarity, but it leaves no space for anything else.

A CD-ROM can store a maximum of 650Mb of data. Text consumes relatively little disk space, but still images and moving pictures make huge storage demands. There is always a trade off between media quality and file size. A system developer must try to find a compromise, using media of an acceptable standard and realistic amounts of memory.

Audio script

Write the commentary in a conversational style. Long convoluted sentences acceptable for technical reports, do not lend themselves to effective oral communication.

Test questions and user interactions

Give the student the opportunity to interact with the material, this will reinforce their understanding. Try to discover novel user interactions, this will aid memory retention. A long series of multiple choice questions will be monotonous and easily forgotten. For instance one Staying in Shape user interaction asks, 'Drag the weld beads on to the fabrication to show a typical skip welding sequence'.

Dictionary of terms

Use a dictionary of terms to define terminology unfamiliar to the student. Hypertext, where the user clicks on a word for more information provides an instant reference.

On-line user help text

Provide the student with a friendly help text that aids running the software. Include how to install the software, a tutorial and a minimum PC specification.

Test strategy

Thoroughly test the software throughout its development. This is of paramount importance in all multimedia applications, and especially so in an educational framework. Programmers can easily lose sight of the user's requirements, as they are forced to concentrate on the detailed coding phase of the project. Feedback from typical end users is the only method of obtaining a useful guide to whether the software is meeting the original objectives.

Conclusions

Multimedia techniques have been used to provide an effective training system on the topic of distortion produced by welding and cutting. During the development of Staying in Shape, it was concluded that:

• Selecting the appropriate media can keep the coursework interesting and aid knowledge retention. For example, the introductory video shows a range of industries affected by welding distortion when presenting the general problem of welding and cutting distortion.
• If designed correctly, multimedia software can put across complex issues in a simple manner. For example, the 3-D animations show the different types of distortion individually. In a real situation two or more types would usually interact, potentially causing confusion.
• Students can work at their own pace, completing the course in a number of sessions, if leaving their day to day activities for long periods is unacceptable. In Staying in Shape, a student can easily return to the appropriate point in the course.
• The interactive nature of multimedia training retains the user's attention, more than a passive presentation. In Staying in Shape, the user must actively select a path through the system.
• Students can select the topics relevant to them. Unlike a video cassette, there is no need to view irrelevant material. For example, in Staying in Shape, the actions to correct distortion after welding chapter can be used directly to obtain advice on a specific problem.
• Test questions and interactivity can be used to judge to what level the user has understood the coursework. Twenty-nine test scenarios are used in Staying in Shape to provide feedback of the user's understanding.

In a practical sense, one of the main advantages of using software training systems is that many personnel can be trained for the cost of one CD-ROM.

Future Developments

PC technology is moving forward all the time, increased processor speeds will make multimedia web pages, broadcast quality full-screen video, speech recognition and virtual reality landscapes commonplace. All of these innovations are sure to find application in the field of materials joining and could be included in a Staying in Shape upgrade.

Acknowledgements

This work was carried out within the TWI Core Research Programme, as part of the projects 'Software with Advanced User Interfaces' and 'Predicting and Reducing Distortion Due To Welding'. It was funded by the Industrial Members of TWI.

The authors would like to thank Vic Wright for compiling the distortion knowledge base, Lynda Godden for developing the multimedia software and John Dadson for preparing the script.

References