Where I come from spot welds are classified into different categories eg
Safety related parts- requiring a minimum nugget size, penetration ratio and defect level.
General use- requiring a minimum nugget size, penetration ratio and defect level but of different parameters to the above.
To determine the quality of your welds there is the old chisel test or the more modern ultrasonic procedures available in some countries.
I suggest that if your welds are burnt or undersize at the front end of a vehicle crash worthyness and possibly long term durability would be affected.
As gdodd stated most car manufactures have different ratings applied to different areas of the vehicle. Spot Welds that are deemed safety welds (i.e. welds that join together stampings in areas that dissipate impact energy) will be grouped together. The standards for these welds are much more strict than for general use welds. For example, in a grouping of 8 spot welds that join an impact beam (bumper) to a frame rail. No two consecutive welds can be done using the same weld schedule (this prevents someone from making a global change to all the weld schedules), there can be no failures of the first and last weld in the group, there can be no failures of any two consecutive welds. What the OEM has done is design the joint so that it would pass crash test with three spot welds then set a standard to make sure that there will always be at least five good welds and then put 8 welds on the joint. This is what is meant when people say the vehicle is overwelded. The weld controllers used by most OEM and Tier One/Two suppliers today are "smart" enough to stop the process when there is something wrong. However, if you are a supplier submitting parts for a crash test vehicle. I would suggest that you test every weld personally (chisel test or ultrasonic) on every part you submit. With crash tests costs near $1 million for each vehicle I wouldn't want to be the person responsible for having to do the test over.
