Technical Discussions: Re: Electrical resistance measurements

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Re: Electrical resistance measurements
Posted by: S.V.Swamy (PID_839), E-mail: svswamy@gmail.com, on December 07, 2004 at 17:40 :
In Reply to: Re: Electrical resistance measurements posted by : Richard Kazares , E-mail: rkazares@ndtautomation.com, on December 06, 2004 at 15:58 :
----------- Start Original Message -----------
: Please note the comments of Phil Thayer - the M100A (current designation of product - with several generations of improvements) is available through Physical Acoustics Corp.
: I mustm however take exception to Mr. Swamy's comments (below). While EVERY test method has its advantages and limitations, in the case of the M100A - it is currently being used by at least 2 MAJOR INTERNATIONAL auto manufacturers to inspect laser and laser-like (resistance and other methods) welds IN PRODUCTION!!
: Both major manufacturers (that I know of) ran months (and in one case, YEARS) of testing the M100A methodology against other competing technologies and products - many cost as much as 200 TIMES the cost of the M100A. In every case the results of the M100A were as reliable as the competing methods.
: Notice, I didn't necessarily say "BETTER" - simply that EACH METHOD has its share of "issues" - but that at the price point of the M100A, coupled with the simplicity, time to measure and ease of use - the M100A was the more cost effective solution, WITHOUT any lose (and in many cases - actual gains) in reliability and accuracy - compared to other methods.
: PLease contact me directly via e-mail if you would like additonal information about the M100A product.
: : : : Does any one know where I can get hold of a piece of equipment called the 'AT&T Microhmeter'. This was produced 15 yrs ago for spot weld inspection (amongst other things). Unfortunately, the AT&T subsidary went into liquidation after a few years.
: : : : I would assume it may be available second-hand, or that some company is still producing a similar device.
: : : : Would be most interested to hear of what is happening in this field.
: : : : regards
: : : : John Turner
: : : The subject ATT device was not effective at determining weld quality. It used a four point system where test current was injected into the surface and the voltage was measured with two probes. The resistance is not an effective method for determining welds in many materials due to several factors.
: : : Materials will exhibit relatively good conductivity even when the fusion is not sufficient for a strong weld. Additionally, materials that are coated with zinc can be soldered together at the faying surface with zinc and exhibit good conductivity. They may also only be slightly bonded by diffusion. Resistance welds of this type will not survive even moderate impact and fatigue loads.
: : : The risk you take is assuming a weld is good until it shows poor conductivity. In my opinion, you will only detect welds that are completely unacceptable while passing welds that are not fit for service grouped along with welds that are acceptable.
: : : Our tests at a major automobile producer site did not show the resistance check method to be sufficiently robust for acceptance. If you are not going to test resistance spot welds then the device may be useful for other applications.
: : : I am not aware of anyone still producing the resistivity weld checker commercially. You should be able to make one easily from commercially available equipment if you are handy designing and assembling electro-mechanical equipment. A suitable 100 A (max) power supply is available from RoMan Mfg. 861 47th St. SW, Grand Rapids, Mi 49509 Michigan, USA. The probe would have to be custom made.
: : : The origginal unit was very portable. The power supply from RoMan will be rather large perhaps 15 kg.
: : :
: : :
: : Dear John,
: : If your interest in that equipment is for inspection of spot welds, I would recommend an ultrasonic test instead of weld resistance. Pl. contact me if you need more details.
: : Swamy
: : India
------------ End Original Message ------------
Dear Richard,
Did I give an impression that ultrasonic test is superior to weld resistance measurement? I reread what I wrote but didn't understand it that way. I meant that if testing of spot welds is the area of interest, a simple ultrasonic test technique is available. And we used a very simple set-up. I have no commercial interest in any test method or equipment.
I will be happy to know more about the two applications that you mentioned.
Regards.
Swamy

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----------- Start Original Message ----------- : : Please note the comments of Phil Thayer - the M100A (current designation of product - with several generations of improvements) is available through Physical Acoustics Corp. : : I mustm however take exception to Mr. Swamy's comments (below). While EVERY test method has its advantages and limitations, in the case of the M100A - it is currently being used by at least 2 MAJOR INTERNATIONAL auto manufacturers to inspect laser and laser-like (resistance and other methods) welds IN PRODUCTION!! : : Both major manufacturers (that I know of) ran months (and in one case, YEARS) of testing the M100A methodology against other competing technologies and products - many cost as much as 200 TIMES the cost of the M100A. In every case the results of the M100A were as reliable as the competing methods. : : Notice, I didn't necessarily say "BETTER" - simply that EACH METHOD has its share of "issues" - but that at the price point of the M100A, coupled with the simplicity, time to measure and ease of use - the M100A was the more cost effective solution, WITHOUT any lose (and in many cases - actual gains) in reliability and accuracy - compared to other methods. : : PLease contact me directly via e-mail if you would like additonal information about the M100A product. : : : : : Does any one know where I can get hold of a piece of equipment called the 'AT&T Microhmeter'. This was produced 15 yrs ago for spot weld inspection (amongst other things). Unfortunately, the AT&T subsidary went into liquidation after a few years. : : : : : I would assume it may be available second-hand, or that some company is still producing a similar device. : : : : : Would be most interested to hear of what is happening in this field. : : : : : regards : : : : : John Turner : : : : The subject ATT device was not effective at determining weld quality. It used a four point system where test current was injected into the surface and the voltage was measured with two probes. The resistance is not an effective method for determining welds in many materials due to several factors. : : : : Materials will exhibit relatively good conductivity even when the fusion is not sufficient for a strong weld. Additionally, materials that are coated with zinc can be soldered together at the faying surface with zinc and exhibit good conductivity. They may also only be slightly bonded by diffusion. Resistance welds of this type will not survive even moderate impact and fatigue loads. : : : : The risk you take is assuming a weld is good until it shows poor conductivity. In my opinion, you will only detect welds that are completely unacceptable while passing welds that are not fit for service grouped along with welds that are acceptable. : : : : Our tests at a major automobile producer site did not show the resistance check method to be sufficiently robust for acceptance. If you are not going to test resistance spot welds then the device may be useful for other applications. : : : : I am not aware of anyone still producing the resistivity weld checker commercially. You should be able to make one easily from commercially available equipment if you are handy designing and assembling electro-mechanical equipment. A suitable 100 A (max) power supply is available from RoMan Mfg. 861 47th St. SW, Grand Rapids, Mi 49509 Michigan, USA. The probe would have to be custom made. : : : : The origginal unit was very portable. The power supply from RoMan will be rather large perhaps 15 kg. : : : : : : : : : : : Dear John, : : : If your interest in that equipment is for inspection of spot welds, I would recommend an ultrasonic test instead of weld resistance. Pl. contact me if you need more details. : : : Swamy : : : India : Dear Richard, : Did I give an impression that ultrasonic test is superior to weld resistance measurement? I reread what I wrote but didn't understand it that way. I meant that if testing of spot welds is the area of interest, a simple ultrasonic test technique is available. And we used a very simple set-up. I have no commercial interest in any test method or equipment. : I will be happy to know more about the two applications that you mentioned. : Regards. : Swamy ------------ End Original Message ------------

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