TWI Industrial Member Report Summary 529/1995
T B Layzell
Work was carried out from 1989 to 1991 to convert the electrons which are backscattered from the workpiece during electron beam welding, into an electrical signal to provide video information. During this period pictures of the workpiece were obtained by sharing the beam between welding and scanning duties in such a way that neither the joint nor the scanned surface suffered any detriment. This early work was limited to power levels of up to 6kW, using the small beam diameters obtainable from an unpulsed triode gun structure and high quality pictures were obtained.
The present report describes advances made in the use of unpulsed diode guns at power levels up to 75kW. It describes the problems of vapour deposition on optical surfaces associated with closed circuit television and other optical systems when used for viewing the electron beam welding process and shows the progress made towards developing a better alternative method for use in industry. It describes the work of designing, building and testing of the equipment. The full report includes twelve photographs of the images obtained, the design methodology of the detector and timing diagrams for the system and calculations of the necessary spot velocity to prevent melting.
The main achievement during the period 1992 to 1994 has been to develop equipment which can scan the beam fast enough to prevent it melting the workpiece and to capture the wider frequency spectrum video signals generated by these rapidly scanned backscattered electrons.
The objectives of this work were:
- To develop an improved vision system for in-vacuum electron beam welding, which can operate continuously at all beam powers up to 75kW without any image deterioration due to metal vapour deposits and which does not need to pulse the electron gun during imaging.
- To make the vision system mechanically and electrically rugged and easily installed in new equipment by electron beam manufacturers or retrofitted at a later date.