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Technical Discussions
James Dolfi
Director
ford, USA, Joined Oct 1999, 8

James Dolfi

Director
ford,
USA,
Joined Oct 1999
8
01:11 Apr-05-1998
UT of resistance spot welds

Recently I had a specialist for Genk come to the United States and evaluate the effectiveness of our inspectors and equipment used for UT of resistance spotwelds made in zinc coated steel used in our auto body assemblies.

The results were disappointing. The inspection system could not accurately detect welds in the materials used. The very qualified expert having the state of the art equipment on hand and the best probes (20 MH) specially designed for the purpose was only able to detect about 75-85% of the "cold or undersized" welds.

How is it that European inspectors are above 90% on detecting bad welds?


####

I will not mention the experts name as he is involved with the UT community in Europe and believes the technology is progressing - we do not want to stop that and many of the major users would do just that since they have spent big $ to support development already. (over 12 years)




    
 
 Reply 
 
James Dolfi
Director
ford, USA, Joined Oct 1999, 8

James Dolfi

Director
ford,
USA,
Joined Oct 1999
8
01:13 Apr-05-1998
Re: UT of resistnace spot welds - correction
: Recently I had a specialist for Genk come to the United States and evaluate the effectiveness of our inspectors and equipment used for UT of resistance spotwelds made in zinc coated steel used in our auto body assemblies.

: The results were disappointing. The inspection system could not accurately detect welds in the materials used. The very qualified expert having the state of the art equipment on hand and the best probes (20 MH) specially designed for the purpose was only able to detect about 75-85% of the "cold or undersized" welds.

: How is it that European inspectors are above 90% on detecting bad welds?

:
: ####

: I will not mention the experts name as he is involved with the UT community in Europe and believes the technology is progressing - we do not want to stop that and many of the major users would do just that since they have spent big $ to support development already. (over 12 years)




    
 
 Reply 
 
Ed Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1268

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1268
06:02 Apr-06-1998
Re: UT of resistnace spor welds
: Recently I had a specialist for Genk come to the United States and evaluate the effectiveness of our inspectors and equipment used for UT of resistance spotwelds made in zinc coated steel used in our auto body assemblies.

: The results were disappointing. The inspection system could not accurately detect welds in the materials used. The very qualified expert having the state of the art equipment on hand and the best probes (20 MH) specially designed for the purpose was only able to detect about 75-85% of the "cold or undersized" welds.

: How is it that European inspectors are above 90% on detecting bad welds?

:
: ####

: I will not mention the experts name as he is involved with the UT community in Europe and believes the technology is progressing - we do not want to stop that and many of the major users would do just that since they have spent big $ to support development already. (over 12 years)

Mr. Dolfi:
Your question seems to be based on a statistical analysis of which youhave
provided no details. In some of the replies from last month's forum you
will note that UT techniques on automotive spot resistance welds are still
something of a challenge for the industry and MANY different techniques can
be applied.

Whichever technique was applied in your situation would also have variables
to consider. Since you are providing us with two values (75-85% versus over
90%) we must look at all possible sources including the lot sampling size.

Was the technique 1. pulse-echo multiples, 2. pulse-echo C-scan, 3. through
transmission compression mode, or horizontal Lamb? or something else??

Was the coupling method immersion, contact or gap?

Was the nugget surface roughness EXACTLY the same roughness for both sets of
statistics?

Was the nugget grain structure the same for both sets of statistics? (i.e.
was the welding process identical in ALL respects??)

What were the systems calibrated the same (on a target?, time (velocity),
frequency content?)

Were the tolerances used for accept/reject identical for both sets of
statistics?

Based on the "success of detection" I would think that the analysis
techniques indicate that; had the "expert" been able to set up on the same
type of weld conditions as was used in Europe then the "evaluation"
statistics would have been even closer if the sample size was large enough.

Your question also indicated that the "expert" was to evaluate the
inspectors. You provided no information on the background to this variable.
What is being evaluated in the inspector review?

Your question also states the that the qualified expert had the state of the
art equipment on hand and the best probes (20 MH) specially designed for the
purpose. This assumes that the equipment you were using was state of the
art, but is it identical in all ways and used set up on the same
calibration targets as the equipment used to obtain the statistics of over 90%?


If amplitude methods are used in the accept/reject criteria I would expect
any one of the above parameters to provide statistical deviation comparable
to the 5-10% you indicated. In fact, considering the variety of parameters
to control I would consider the 5-10% deviation quite good. To try to point
a finger of blame or ridicule is certainly not an effective method of
finding the root cause of statistical variation. If you are truely
interested in improving your "statistical" results I suggest you look at the
REAL causes of statistical variation....physical parameters.


E.G.



    
 
 Reply 
 
Rolf Diederichs
Director,
NDT.net, Germany, Joined Nov 1998, 608

Rolf Diederichs

Director,
NDT.net,
Germany,
Joined Nov 1998
608
04:26 Apr-24-1998
Article: Quality assurance of spot-welded joints - use of high frequency ultrasonic technology
ality assurance of spot-welded joints, use of high-frequeny ultrasonic technoloy.
(Qualitätssicherung von Punktschweissverbindungen -
Einsatz hochfrequenter Ultraschalltechnik)

By Dipl-lng. Silvio Schulz and Dipl.-lng. Stefan Langrock, Halle (schulz@slv-halle.de, http://www.schweissen.de/slv-halle/)

Schweissen & Schneiden (English supplement Welding & cutting) ISSN 0036-7148, Issue 2 1998

English text at E34 - E 35.
2 figures and references at the German text section (pp.114 -116).

Author Abstract:
The non-destructive ultrasonic testing of spot-welded joints is suitable for plants with series production as a cost-favourable solution. However, the clear reproducibility of the test results must be guaranteed. Since manual ultrasonic tests cannot guarantee this, a testing device was developed and built in order to accommodate and guide the probe. Specially manufactured probes made it possible to compensate for the surface unevenness of spot welds. The reliability of the testing method was tested on various steels and aluminium alloys and was checked by means of accompanying me/allographic investigations, radiographic inspections and tensile-shear tests.

Summarize by Rolf Diederichs:
The authors stated in the introduction that the industry was extremely hesitant in accepting this procedure are to be found not only in difficulties related to the reproducibility of the probe-to-specimen contact conditions but also in problems with regard to the interpretation of the ultrasonic results and to the varying stipulation of limiting values. There has been no satisfactory solution until now.

The objectives of a research project at the SLV Halle dealt with the problems associated with the ultrasonic testing of spot-welded joints.

The testing programme used several materials (unalloyed steel, austenitic chrome-nickel steel, ferritic chrome steel, aluminium alloys) and plate-thickness between 1.5 mm and 8 mm.

The investigations were carried out using a digital ultrasonic testing device (Krautkramer , Type: USD15S) with large visible screen area which permits improved horizontal resolution.

Because of a modified screen, this device is especially suitable for such testing tasks. The visible screen area of 100 mm x 195 mm is considerably larger than in the case of conventional ultrasonic testing devices and probes crystal sizes of 5.0 mm, 6.1 mm, 7.1 mm and 9.0 mm with a very high frequency of 20 MHz were used.

A simple testing device was developed and built in order to guarantee clear reproducibility. This serves to accommodate and guide the probe and guarantees a defined position in relation to the surface of the spot.

Finally it was stated that the testing of spot-welded joints using ultrasound no longer represents any problem for the materials investigated here. However, this statement was linked to compliance with certain boundary conditions, e.g. it was seen the reproducibility of the test as extremely important.

Rolf Diederichs


    
 
 Reply 
 
narasimhan
narasimhan
02:07 Nov-17-2000
Re: Article: Quality assurance of spot-welded joints - use of high frequeny ultrasonic technoloy
SIr
i introduce myself asa M.tech student in NDT. atpresent iam doing project quality evaluation of spot welded joints. for ultrasonic testing i have only 15 MHZ probe and delay shoe. kindly send me the reference journals or procedure to do the test successfully to find out stick weld coldweld and no weld . thanking you
expecting your reply





    
 
 Reply 
 
Sadegh Saiidi
Sadegh Saiidi
00:54 Jun-02-2002
Re: Article: Quality assurance of spot-welded joints - use of high frequeny ultrasonic technoloy
: : Recently I had a specialist for Genk come to the United States and evaluate the effectiveness of our inspectors and equipment used for UT of resistance spotwelds made in zinc coated steel used in our auto body assemblies.

: : The results were disappointing. The inspection system could not accurately detect welds in the materials used. The very qualified expert having the state of the art equipment on hand and the best probes (20 MH) specially designed for the purpose was only able to detect about 75-85% of the "cold or undersized" welds.

: : How is it that European inspectors are above 90% on detecting bad welds?

: :
: : ####

: : I will not mention the experts name as he is involved with the UT community in Europe and believes the technology is progressing - we do not want to stop that and many of the major users would do just that since they have spent big $ to support development already. (over 12 years)

: See below a summarize of a recent literature concerning our spot weld discussion:

: Quality assurance of spot-welded joints, use of high-frequeny ultrasonic technoloy.
: (Qualitätssicherung von Punktschweissverbindungen -
: Einsatz hochfrequenter Ultraschalltechnik)

: By Dipl-lng. Silvio Schulz and Dipl.-lng. Stefan Langrock, Halle (schulz@slv-halle.de, http://www.schweissen.de/slv-halle/)

: Schweissen & Schneiden (English supplement Welding & cutting) ISSN 0036-7148, Issue 2 1998

: English text at E34 - E 35.
: 2 figures and references at the German text section (pp.114 -116).

: Author Abstract:
: The non-destructive ultrasonic testing of spot-welded joints is suitable for plants with series production as a cost-favourable solution. However, the clear reproducibility of the test results must be guaranteed. Since manual ultrasonic tests cannot guarantee this, a testing device was developed and built in order to accommodate and guide the probe. Specially manufactured probes made it possible to compensate for the surface unevenness of spot welds. The reliability of the testing method was tested on various steels and aluminium alloys and was checked by means of accompanying me/allographic investigations, radiographic inspections and tensile-shear tests.

: Summarize by Rolf Diederichs:
: The authors stated in the introduction that the industry was extremely hesitant in accepting this procedure are to be found not only in difficulties related to the reproducibility of the probe-to-specimen contact conditions but also in problems with regard to the interpretation of the ultrasonic results and to the varying stipulation of limiting values. There has been no satisfactory solution until now.

: The objectives of a research project at the SLV Halle dealt with the problems associated with the ultrasonic testing of spot-welded joints.

: The testing programme used several materials (unalloyed steel, austenitic chrome-nickel steel, ferritic chrome steel, aluminium alloys) and plate-thickness between 1.5 mm and 8 mm.

: The investigations were carried out using a digital ultrasonic testing device (Krautkramer , Type: USD15S) with large visible screen area which permits improved horizontal resolution.

: Because of a modified screen, this device is especially suitable for such testing tasks. The visible screen area of 100 mm x 195 mm is considerably larger than in the case of conventional ultrasonic testing devices and probes crystal sizes of 5.0 mm, 6.1 mm, 7.1 mm and 9.0 mm with a very high frequency of 20 MHz were used.

: A simple testing device was developed and built in order to guarantee clear reproducibility. This serves to accommodate and guide the probe and guarantees a defined position in relation to the surface of the spot.

: Finally it was stated that the testing of spot-welded joints using ultrasound no longer represents any problem for the materials investigated here. However, this statement was linked to compliance with certain boundary conditions, e.g. it was seen the reproducibility of the test as extremely important.

: Rolf Diederichs

thanks



    
 
 Reply 
 
N. Azarov
Engineering
GosNIIGA, Russia, Joined Jan 2000, 12

N. Azarov

Engineering
GosNIIGA,
Russia,
Joined Jan 2000
12
04:43 Jun-03-2002
Re: Article: Quality assurance of spot-welded joints - use of high frequeny ultrasonic technoloy
: : : Recently I had a specialist for Genk come to the United States and evaluate the effectiveness of our inspectors and equipment used for UT of resistance spotwelds made in zinc coated steel used in our auto body assemblies.
.
: : : The results were disappointing. The inspection system could not accurately detect welds in the materials used. The very qualified expert having the state of the art equipment on hand and the best probes (20 MH) specially designed for the purpose was only able to detect about 75-85% of the "cold or undersized" welds.
.
: : : How is it that European inspectors are above 90% on detecting bad welds?


Dear Mr Saiidi.
At 70-80 years in Russia was tested high-frequency (10-20 MHz) ultrasonic method of quality control of spot welding and also was installed it low reliability. In this connection in Research Institute of Aviation Technologies (Moscow) the method and equipment of a ultrasonic control of spot welding during process of welding with the help of ultrasonic transducers, built-in in electrodes of the welding machine, was developed . The given method and equipment ensure possibility of measurement of a diameter of a kernel of spot welding, allow to determine other imperfections (flaws) of welding with a high reliability (more than 90 %) and were introduced in an aviation industry of Russia.
Yours faithfully, N. Azarov.



    
 
 Reply 
 
Sean S. Franklin
Sean S. Franklin
03:28 Jun-04-2002
Re: Article: Quality assurance of spot-welded joints - use of high frequeny ultrasonic technoloy
: : : Using (micro) resistivity as a non-destructive testing method for helping to determine weld (spot/laser) quality (ultimate bond strength) has been very effective and efficient in the automobile industry – particularly in Europe, where many resistivity systems are currently in production use.

Electrical pulses of a rapid reversing direct current are induced into metal using a specially designed probe assembly (may be manual or automated) in order to measure the metal's local resistance to current flow. The (very) small differences between the resistivity of the unwelded metal and the welded seam/spot (or between various seams and spot welds) can be statistically correlated to weld size and quality (including such factors as weld penetration, area of weld (for spot weld), porosity, etc.)

A database of information correlating resistivity-determined weld quality to actual strength of the weld is accumulated through destructive testing of a statistically relevant number of samples.

Once the correlation between resistivity and strength is established, information can be stored and a cutoff point between acceptable and unacceptable welds can be established.

Resistivity methods offer an economically attractive blend of speed and accuracy for data acquisition and quality feedback in a production environment. Further customization permit data acquisition rates into the hundreds of readings per minute and customized probes that can take multiple readings on each cycle are available – thus providing the capability for multiple welds (spot or laser seams) to be analyzed on each cycle.

For more information (or if you have further questions), please contact me:

Sean Franklin
Physical Acoustics Corporation
609-716-4088
SFranklin@PACNDT.com

I’d be happy to provide additional details.


ntly I had a specialist for Genk come to the United States and evaluate the effectiveness of our inspectors and equipment used for UT of resistance spotwelds made in zinc coated steel used in our auto body assemblies.
.
: : : The results were disappointing. The inspection system could not accurately detect welds in the materials used. The very qualified expert having the state of the art equipment on hand and the best probes (20 MH) specially designed for the purpose was only able to detect about 75-85% of the "cold or undersized" welds.
.
: : : How is it that European inspectors are above 90% on detecting bad welds?
.
: : :
: : : ####
.
: : : I will not mention the experts name as he is involved with the UT community in Europe and believes the technology is progressing - we do not want to stop that and many of the major users would do just that since they have spent big $ to support development already. (over 12 years)
.
: : See below a summarize of a recent literature concerning our spot weld discussion:
.
: : Quality assurance of spot-welded joints, use of high-frequeny ultrasonic technoloy.
: : (Qualitätssicherung von Punktschweissverbindungen -
: : Einsatz hochfrequenter Ultraschalltechnik)
.
: : By Dipl-lng. Silvio Schulz and Dipl.-lng. Stefan Langrock, Halle (schulz@slv-halle.de, http://www.schweissen.de/slv-halle/)
.
: : Schweissen & Schneiden (English supplement Welding & cutting) ISSN 0036-7148, Issue 2 1998
.
: : English text at E34 - E 35.
: : 2 figures and references at the German text section (pp.114 -116).
.
: : Author Abstract:
: : The non-destructive ultrasonic testing of spot-welded joints is suitable for plants with series production as a cost-favourable solution. However, the clear reproducibility of the test results must be guaranteed. Since manual ultrasonic tests cannot guarantee this, a testing device was developed and built in order to accommodate and guide the probe. Specially manufactured probes made it possible to compensate for the surface unevenness of spot welds. The reliability of the testing method was tested on various steels and aluminium alloys and was checked by means of accompanying me/allographic investigations, radiographic inspections and tensile-shear tests.
.
: : Summarize by Rolf Diederichs:
: : The authors stated in the introduction that the industry was extremely hesitant in accepting this procedure are to be found not only in difficulties related to the reproducibility of the probe-to-specimen contact conditions but also in problems with regard to the interpretation of the ultrasonic results and to the varying stipulation of limiting values. There has been no satisfactory solution until now.
.
: : The objectives of a research project at the SLV Halle dealt with the problems associated with the ultrasonic testing of spot-welded joints.
.
: : The testing programme used several materials (unalloyed steel, austenitic chrome-nickel steel, ferritic chrome steel, aluminium alloys) and plate-thickness between 1.5 mm and 8 mm.
.
: : Theinvestigations were carried out using a digital ultrasonic testing device (Krautkramer , Type: USD15S) with large visible screen area which permits improved horizontal resolution.
.
: : Because of a modified screen, this device is especially suitable for such testing tasks. The visible screen area of 100 mm x 195 mm is considerably larger than in the case of conventional ultrasonic testing devices and probes crystal sizes of 5.0 mm, 6.1 mm, 7.1 mm and 9.0 mm with a very high frequency of 20 MHz were used.
.
: : A simple testing device was developed and built in order to guarantee clear reproducibility. This serves to accommodate and guide the probe and guarantees a defined position in relation to the surface of the spot.
.
: : Finally it was stated that the testing of spot-welded joints using ultrasound no longer represents any problem for the materials investigated here. However, this statement was linked to compliance with certain boundary conditions, e.g. it was seen the reproducibility of the test as extremely important.
.
: : Rolf Diederichs
.
: thanks
.



    
 
 Reply 
 

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