00:42 Oct-07-1998 James Dolfi Director ford, USA, Joined Oct 1999 8
Ultrasonic testing of spot welds
(Here is the completed version of the message 2 days ago)
The following is quoted from the paper on testing of autobody spotwelds.
'A modified ultrasonic testing method clearly detects stick welds and cold welds, this is not possible with normal ultrasonic methods. When testing under production conditions, 98% of the welds tested are correctly evaluated, i.e. values obtained from the ultrasonic test satisfactorily corresponded to the results from the teardown test.' The link to the paper is: http://www.ndt.net/article/0498/spotw/spotw.htm
The above quoted statement would be true of most testing of autobody spotwelds for the following reason.---
The body welding performance is typically very high and can reach 98% or more. When an operator calls all welds good he can only be wrong 2% of the time. If the report claims 98% correlation or 98% reliability I believe that is misleading the readers to believe the testing system is capable of accurately detecting both good and bad welds (with one calibration setting). I have read detailed reports that do just as outlined above. They report 98% accuracy but the item under test had 98% good items (welds) in the test population. I could claim the same accuracy and be correct by simply reporting all welds are good!
The way to present reliability data is to include the ALPHA and BETA error data along with the claim of reliability for the test system. As mentioned in other articles, the way to report could be:
1-ALPHA * 1-BETA = TEST RELIABILITY
Where: ALPHA is the proportion of good called bad BETA is the proportion of bad called good
I believe that a standard method of reporting or at lease the computational method used to establish reliability should be included in any such report.
Is there a standard with which you expect data to be reported? Would you please comment on the appropriate measure of a checking-gauge's performance?
Note: My concern is that the measurement system should reject bad items and not reject good items. Any checking system looses effectiveness when it begins to reject good or accept bad items. My present requirement for testing is 3% alpha (max) error and 15% beta (max) error (without re-calibrating the system). Using the above 3% and 15% requirements, the system only has to be about 82% reliable.
Re: Ultrasonic testing of spot welds dear,i studid your paper and enjoyed that.please send me more information about the method of your testing and describe me how did you do that.my email is firstname.lastname@example.org thanks alot.