Robust Schedules for Spot Welding Zinc-Coated Advanced High-Strength Automotive Steels

Spot  welding  is  the  prominent  joining  process  for  assembling  steels  in  vehicles.  Spot weldability  is  measured  in  terms  of  weld  lobes.  A  wider  (robust)  lobe  represents  better weldability.  Unfortunately,  recently  developed  advanced  high-strength  steels  (AHSS)  exhibit poor  spot  weldability  (narrow  weld  lobes)  with  conventional  weld  schedules.  The  present work  is  thus  aimed  to   develop  a  robust   spot   welding  schedule  for  selected  AHSS combinations.

Weld  lobes  were  plotted  with  upsloping  pulse,  single  pulse  and  multiple  pulse  weld schedules.  Nugget  growth  study  for  zinc  coated  Dual  Phase  (DP)  600  was  conducted.  Fast nugget  growth  in  DP600  steels  was  controlled  by  interrupting  the  heat  input  during  a  weld pulse.  An  enhanced  weld  schedule  consisting  of  two  pulses  with  reduced  current  on  the second  pulse  was  designed.  It  was  found  that  the  first  pulse  removed  zinc  and  the  second pulse  controlled  the  nugget  growth.  The  enhanced  weld  schedule  showed  a  considerable increase in the lobe width over the conventional weld schedule for DP600 steels.