Weld procedure development with OSLW

Weld procedure development with OSLW

Keywords: Welding, Sandia

Phillip W. Fuerschbach and G. Richard Eisler of Sandia National Laboratories,and Robert J. Steele of the Naval Air Warfare Center have developed computer models for CO₂ laser beam welding based on dimensionless parameter correlations derived from solutions to moving heat source equations. They expect their optimization software for laser welding (OSLW) to be extended to many different materials.

Finding the best automated welding parameters to achieve a specific weld size on a new material is usually an expensive and time consuming task. To determine a weld procedure, engineers must consider many competing factors including productivity, thermal input, defect formation, and process robustness. The tradeoffs between these factors can be substantial as well as hard to quantify.

For example, process robustness might be expected to be inversely proportional to productivity, but in fact, the result depends on the defect being considered. Humping and undercut are defects that occur primarily at high feedrates, however, thermal damage and base metal distortion are deficiencies that tend to occur at lower feedrates.

Choosing among numerous weld procedures can be hastened with computer models that find parameters to meet selected weld dimensional requirements while simultaneously optimizing important figures of merit. Two fundamental figures of merit for fusion welding processes are the energy transfer efficiency and the melting efficiency.

Energy transfer efficiency indicates what fraction of the energy incident on the workpiece is actually absorbed by the metal. Melting efficiency quantifies the fraction of net heat input to the workpiece that is used to produce melting,rather than unnecessary heating of the metal that can lead to thermal damage and distortion.

Other figures of merit are the physical extent of the heat affected zone or the fusion zone size tolerance to a changing base metal temperature. Desktop computer models to quantify these and other figures of merit for the numerous welding processes in use today present a formidable task that has only recently been undertaken[1-3].

For laser beam welding, a dimensionless parameter model[4] has been shown to be effective in relating melting to power, speed, and the material thermophysical properties. By combining this thermodynamic based relationship with additional correlations for penetration depth, weld shape, spot size, and energy transfer efficiency, a computer model of the continuous wave CO₂laser welding process has been developed.

The authors say continued development will yield similar models for other welding processes. As the models evolve, better optimization strategies may result in even more robust weld procedure parameters. The authors expect that users of this type of software will increase as the advantages of model based weld procedure selection are realized. Someday, they hope, weld procedure development for automated processes utilizing software such as OSLW will be common.

Notes

• 1.

  Reutzel, E.W., Einerson, C.J., Johnson, J.A., Smartt, H.B., Harmore, T. and Moore, K.L. (1995), “Derivation and calibration of gas metal arc welding dynamic droplet model”, Trends in Welding Research, ASM,Gatlinburg, Tennessee, pp. 377-84.

• 2.

  Sudnik, V. (1997), Modelling of the MAG Process for Pre- Welding Planning,pp. 791-816; Mathematical Modelling of Weld Phenomena 3, Institute of Materials.

• 3.

  Eisler, G.R. and Fuerschbach, P.W. (1997), “SOAR: an extensible suite of codes for weld analysis and optimal weld schedules”, Seventh International Conference on Computer Technology in Welding, NIST, San Francisco, California, pp. 257-68.

• 4.

  Fuerschbach, P.W. (1996), Welding Journal, Vol. 75 No. 1, pp. 24s-34s.