Weld Stepper Validation in production weld-cells
- Thread starter dtrebel
- Start date
Spotweld Applications
Resistance spotwelds on automotive sub-assy's. The requirement is to validate the complete stepper routine quarterly.My inquiry stems from multiple robotic welders producing 2 [1 LH & 1 RH] finished assemblies. There are a total of 26 weld on each finished part, one center robotic welder applies 12 welds on both lh & rh, while 4 other robotic welders [2 per lh 2 per rh] complete the part by applying 7 spotwelds to each side. All weld electrode tips are changed together [@stepper-end] approx 3000 welds. I need to validate the entire stepper program which has a total of 5 steps and a 17% increase in current over these steps.
The confusion stems from The center [common] robotic welder applying more welds than the others. Do I validate the cell as a whole [per part countx welds] or have to go through the lengthy method of validating each weld operation???
Resistance spotwelds on automotive sub-assy's. The requirement is to validate the complete stepper routine quarterly.My inquiry stems from multiple robotic welders producing 2 [1 LH & 1 RH] finished assemblies. There are a total of 26 weld on each finished part, one center robotic welder applies 12 welds on both lh & rh, while 4 other robotic welders [2 per lh 2 per rh] complete the part by applying 7 spotwelds to each side. All weld electrode tips are changed together [@stepper-end] approx 3000 welds. I need to validate the entire stepper program which has a total of 5 steps and a 17% increase in current over these steps.
The confusion stems from The center [common] robotic welder applying more welds than the others. Do I validate the cell as a whole [per part countx welds] or have to go through the lengthy method of validating each weld operation???
I've been through some weld validations and there are so many variables that it has always been a case by case basis determined during the planning stages. But often what we thought we would look at during the early planning stages changed when we did the runoff as problems arose which caused us to change what we thought would be appropriate. Differences such as metal thickness, alloy, etc make it hard to give a blanket answer.
If I read you correctly, you're saying you change tips on all at the same time but some tips weld more spots (and/or at a higher current) than others. The assumption would be the tips with the most welds (or higher current) would guide your replacement PM schedule. I don't see that as part of the validation issue.
In similar situations I looked at several variables at the end of the process:
1. Correct number of welds per part and each side or piece.
2. Welds each tested (pull apart or pushout - depending on the part).
3. Visual or cross section (depending on criticality of weld) for weld penetration.
4. Within dimensional tolerence (sometimes an external fixture but I have seen the weld holding fixture its self calibrated and used).
5. All parts /holes present.
That would be validating the group of cells. Whether or not you would want to look at individual cells and their individual steps would be something to consider but it depends upon the situation. During trial runs I'd look closely at each step, but normally I would validate the process as a 'system' - or at least base inspection checks on the process as a system. I would watch internal and external nonconformance feedback and any that point to failures in the weld operations might lead me to want to investigate and revalidate each cell / step.
Putting dimensional aspects aside, the requirement is probably a weld separation issue such as xx pounds to pull the assembly apart. Many times assemblies are designed with enough over engineering that one weld of five failing to completely penetrate (as an example) will not cause the assembly to fail the pull apart test. Center welds are often less critical because end and side welds, if penetration is not complete, will tend to allow a part to bend if it 'unsticks', if the metal is somewhat thin.
I have seen issues where a welder was set for a higher current at one step than another using the same weld head. A problem was the current difference was enough to make it difficult to balance - one spot would burn and the other would be OK, OR one spot would be OK while the other often didn't penetrate.
These are just some thoughts.
If I read you correctly, you're saying you change tips on all at the same time but some tips weld more spots (and/or at a higher current) than others. The assumption would be the tips with the most welds (or higher current) would guide your replacement PM schedule. I don't see that as part of the validation issue.
In similar situations I looked at several variables at the end of the process:
1. Correct number of welds per part and each side or piece.
2. Welds each tested (pull apart or pushout - depending on the part).
3. Visual or cross section (depending on criticality of weld) for weld penetration.
4. Within dimensional tolerence (sometimes an external fixture but I have seen the weld holding fixture its self calibrated and used).
5. All parts /holes present.
That would be validating the group of cells. Whether or not you would want to look at individual cells and their individual steps would be something to consider but it depends upon the situation. During trial runs I'd look closely at each step, but normally I would validate the process as a 'system' - or at least base inspection checks on the process as a system. I would watch internal and external nonconformance feedback and any that point to failures in the weld operations might lead me to want to investigate and revalidate each cell / step.
Putting dimensional aspects aside, the requirement is probably a weld separation issue such as xx pounds to pull the assembly apart. Many times assemblies are designed with enough over engineering that one weld of five failing to completely penetrate (as an example) will not cause the assembly to fail the pull apart test. Center welds are often less critical because end and side welds, if penetration is not complete, will tend to allow a part to bend if it 'unsticks', if the metal is somewhat thin.
I have seen issues where a welder was set for a higher current at one step than another using the same weld head. A problem was the current difference was enough to make it difficult to balance - one spot would burn and the other would be OK, OR one spot would be OK while the other often didn't penetrate.
These are just some thoughts.
A
Arvind
Start from Voice of customer
It is a good idea to start from voice of customer. What concerns does your internal/external customer has with your output?
You may further break that down into
a) Low time in service defects
b) High time in service issue or durability issues which often are design or robustness issues.
Low time in service issues are something you can influence quickly.
Arvind
It is a good idea to start from voice of customer. What concerns does your internal/external customer has with your output?
You may further break that down into
a) Low time in service defects
b) High time in service issue or durability issues which often are design or robustness issues.
Low time in service issues are something you can influence quickly.
Arvind
weld validations
First of all thanks for the input...
We have discussed the difference betwen the initial start-up of a weld program @PPAP which includes validating every weld operation (tips, weld schedule, equipment, weld stepper validation etc...) to the preventative quarterly weld validations which are based on the entire weld-cell. The output of the cell is what is being validated not the individual welders directly, (that has already been accomplished @PPAP).
so my company has asked me to outline the procedure based on the stepper cycle and parts produced. Parts will be inspected before and after each of the lead welder (the weld operation that governs the entire weld-cell tip change) steps.
ie: new tips/ 3000 welds produced / (5 step) stepper ends
each part produced has 26 spotwelds.
3000 welds divided by 26 welds per part = 2 samples are taken every 115 parts (before and after a theoretical step)
-this example covers the validation of the entire cell and includes consideration for the steppers.
what do you think?
First of all thanks for the input...
We have discussed the difference betwen the initial start-up of a weld program @PPAP which includes validating every weld operation (tips, weld schedule, equipment, weld stepper validation etc...) to the preventative quarterly weld validations which are based on the entire weld-cell. The output of the cell is what is being validated not the individual welders directly, (that has already been accomplished @PPAP).
so my company has asked me to outline the procedure based on the stepper cycle and parts produced. Parts will be inspected before and after each of the lead welder (the weld operation that governs the entire weld-cell tip change) steps.
ie: new tips/ 3000 welds produced / (5 step) stepper ends
each part produced has 26 spotwelds.
3000 welds divided by 26 welds per part = 2 samples are taken every 115 parts (before and after a theoretical step)
-this example covers the validation of the entire cell and includes consideration for the steppers.
what do you think?
