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Title: Temperature and Material Flow Prediction in Friction-Stir Spot Welding of Advanced High-Strength Steel

Abstract

Friction-stir spot welding (FSSW) has been shown to be capable of joining advanced high-strength steel, with its flexibility in controlling the heat of welding and the resulting microstructure of the joint. This makes FSSW a potential alternative to resistance spot welding if tool life is sufficiently high, and if machine spindle loads are sufficiently low that the process can be implemented on an industrial robot. Robots for spot welding can typically sustain vertical loads of about 8 kN, but FSSW at tool speeds of less than 3000 rpm cause loads that are too high, in the range of 11–14 kN. Therefore, in the current work, tool speeds of 5000 rpm were employed to generate heat more quickly and to reduce welding loads to acceptable levels. Si3N4 tools were used for the welding experiments on 1.2-mm DP 980 steel. The FSSW process was modeled with a finite element approach using the Forge* software. An updated Lagrangian scheme with explicit time integration was employed to predict the flow of the sheet material, subjected to boundary conditions of a rotating tool and a fixed backing plate. Material flow was calculated from a velocity field that is two-dimensional, but heat generated by friction wasmore » computed by a novel approach, where the rotational velocity component imparted to the sheet by the tool surface was included in the thermal boundary conditions. An isotropic, viscoplastic Norton-Hoff law was used to compute the material flow stress as a function of strain, strain rate, and temperature. The model predicted welding temperatures to within percent, and the position of the joint interface to within 10 percent, of the experimental results.« less

Authors:
; ;
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1221502
Report Number(s):
PNNL-SA-107461
VT0505000
DOE Contract Number:  
AC05-76RL01830
Resource Type:
Journal Article
Journal Name:
JOM. The Journal of the Minerals, Metals and Materials Society, 66(10):2130-2136
Additional Journal Information:
Journal Name: JOM. The Journal of the Minerals, Metals and Materials Society, 66(10):2130-2136
Country of Publication:
United States
Language:
English

Citation Formats

Miles, Michael, Karki, U., and Hovanski, Yuri. Temperature and Material Flow Prediction in Friction-Stir Spot Welding of Advanced High-Strength Steel. United States: N. p., 2014. Web. doi:10.1007/s11837-014-1125-6.
Miles, Michael, Karki, U., & Hovanski, Yuri. Temperature and Material Flow Prediction in Friction-Stir Spot Welding of Advanced High-Strength Steel. United States. https://doi.org/10.1007/s11837-014-1125-6
Miles, Michael, Karki, U., and Hovanski, Yuri. 2014. "Temperature and Material Flow Prediction in Friction-Stir Spot Welding of Advanced High-Strength Steel". United States. https://doi.org/10.1007/s11837-014-1125-6.
@article{osti_1221502,
title = {Temperature and Material Flow Prediction in Friction-Stir Spot Welding of Advanced High-Strength Steel},
author = {Miles, Michael and Karki, U. and Hovanski, Yuri},
abstractNote = {Friction-stir spot welding (FSSW) has been shown to be capable of joining advanced high-strength steel, with its flexibility in controlling the heat of welding and the resulting microstructure of the joint. This makes FSSW a potential alternative to resistance spot welding if tool life is sufficiently high, and if machine spindle loads are sufficiently low that the process can be implemented on an industrial robot. Robots for spot welding can typically sustain vertical loads of about 8 kN, but FSSW at tool speeds of less than 3000 rpm cause loads that are too high, in the range of 11–14 kN. Therefore, in the current work, tool speeds of 5000 rpm were employed to generate heat more quickly and to reduce welding loads to acceptable levels. Si3N4 tools were used for the welding experiments on 1.2-mm DP 980 steel. The FSSW process was modeled with a finite element approach using the Forge* software. An updated Lagrangian scheme with explicit time integration was employed to predict the flow of the sheet material, subjected to boundary conditions of a rotating tool and a fixed backing plate. Material flow was calculated from a velocity field that is two-dimensional, but heat generated by friction was computed by a novel approach, where the rotational velocity component imparted to the sheet by the tool surface was included in the thermal boundary conditions. An isotropic, viscoplastic Norton-Hoff law was used to compute the material flow stress as a function of strain, strain rate, and temperature. The model predicted welding temperatures to within percent, and the position of the joint interface to within 10 percent, of the experimental results.},
doi = {10.1007/s11837-014-1125-6},
url = {https://www.osti.gov/biblio/1221502}, journal = {JOM. The Journal of the Minerals, Metals and Materials Society, 66(10):2130-2136},
number = ,
volume = ,
place = {United States},
year = {Wed Oct 01 00:00:00 EDT 2014},
month = {Wed Oct 01 00:00:00 EDT 2014}
}