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PWL#110 - Planning Welding Inspection, Welding Bolts, Stainless SAW Cladding,Friction Stir Spot Weld
October 01, 2012
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PWL#110
Practical Welding Letter No. 110
October 2012

Planning Welding Inspection to improve Productivity, Welding Bolts may affect strength, Stainless SAW Cladding new insight, Friction Stir Spot Welding for automotive manufacturing, Correct Heat Input Calculations for waveform controlled current, Oxyacetylene Welding Tips (R), Welding Qualification (R) and much more...


October 2012 - Practical Welding Letter - Issue No.110


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TABLE of CONTENTS

1 - Introduction

2 - Article - Early Inspection for Higher Productivity

3 - How to do it well: Welding bolts of ASTM A320L7

4 - Filler Metals for SAW cladding with 309LMo

5 - Online Press: recent Welding related Articles

6 - Terms and Definitions Reminder

7 - Article: Friction Stir Spot Welding and Refill

8 - Site Updating: Oxyacetylene Welding Tips (R),
Welding Qualification (R)

9 - Short Items

10 - Explorations: beyond the Welder

11 - Contributions: ASME IX Code Changes of Heat Input Calculation

12 - Testimonials

13 - Correspondence: a few Comments

14 - Bulletin Board


1 - Introduction

This 110th Issue of Practical Welding Letter proposes subjects that busy readers may have missed, despite their efforts to stay updated.

We open with an article dealing with inspection and productivity. Many may think that the two are opposed, as one can harm productivity by concentrating in inspection performed too late in the manufacturing process.

As productivity should be one of the main worries of most of those that work with welding, the publication referred to may be important for their information.

The answer to a reader's query provides the opportunity to deal with the weldability of low alloy steels used for high strength bolts: right precautions should avoid that mechanical properties become compromised by welding.

Useful information in stainless cladding is reported from a renowned expert in stainless steel welding that, answering a specific question, provides deep insight in the subject of SAW cladding with 309LMo.

A recent development of friction stir welding seems to be an interesting alternative to resistance spot welding, especially for aluminum and for dissimilar lap joints of incompatible materials.

Heat input calculations play an important part in certain Welding Procedures Specifications (WPS) and Procedure Qualification Records (PQR) for demanding applications.

The simple calculation that uses Amperage and Voltage does not represent adequately the actual heat input of welding sources that support waveform control.

Measuring instruments capable of sampling actual values at high frequency are now available. Therefore the ASME IX Code was updated to include more precise calculations of actual heat input, when required.

Revised pages on Oxyacetylene Welding Tips and Welding Qualification were introduced in the website and are presented hereafter. The usual columns are appearing at their place.

Please send us comments, feedback and contributions using the Contact Us Form. Don't use Reply!

To remain updated with new and revised pages, browse regularly through the Site Map, the Index Page or subscribe to our RSS service just below the NavBar in every page.


2 - Article - Early Inspection for Higher Productivity

The problem of welding productivity seems to remain one of the subjects least understood and acted upon.

A recent article proposes to introduce a revolutionary attitude to the traditional way taken by management confronting issues of improving quality and increasing productivity.

In normal administration, the request to improve quality is followed by an increased inspection effort with more people, less productivity, increased costs and additional time.

Limiting the inspection function to verifying if quality requirements were met at the end of production "is totally backward".

The article was published in the September 2012 Issue of the Welding Journal at page 26. Although not new in the welding fabrication industry, the principles of Planning, Cost Analyzing and Production Monitoring receive in this clear exposition a character of urgency, to which no involved manager can remain unmoved.

Design for Manufacturing is invoked to assure that the planned processes produce the needed results. The cost of quality is monitored in four classes (prevention, analysis, repair, and scrap). Monitoring production is then implemented to track equipment uptime, productivity and quality to allow for continuous improvement.

Analysis of historical data helps in establishing robust processes that will handle manufacturing variability. Preventing or identifying a problem as soon as possible, improves productivity and quality. Introducing maximum automation reduces human variability and speeds up execution.

Gathering of historical process performance data helps in determining the achievable productivity. If Welding Procedures Specifications (WPS) are developed under lab conditions, the variability on the production floor may show that instructions are inadequate to assure acceptable welds.

The article then goes on to recommend a number of steps intended to help develop improved welding processes, starting with the establishment of benchmark conditions at the time of the initial investigation.

The use of a portable laser scanning weld inspection system is advocated as a useful tool to determine variability of preceding operations (stamping tolerances, assembly gaps, mismatch etc.) and to determine the main problems of each stage in the process.

The analysis of the basic data may point to the way to improve results, by way of introducing new methods, techniques, equipment, people, or processes. The laser scanning system is quoted again as a help to check if any of the changes introduced improved in effect the quality level.

Also it is indicated as a help in screening candidate welders and to score their performance. Finally, when mounted on robots, laser scanners are used to establish the actual process capability. The records of automated inspection scans help in improving processes by reducing variability.

Interested readers are urged to seek the original article quoted above.


3 - How to do it well: Welding bolts of ASTM A320L7

Question: What are the problems when welding bolts made of ASTM A320 grade L7?

Answer: This material is intended for low-temperature service down to -150°F (-101°C) and has a minimum Charpy impact value of 15 ft-lb at this temperature. Sizes 2-1/2 in. and under. Bolts are heat treated to Tensile Strength 125 ksi min (860 MPa min), Yield Strength 105 ksi min (725 MPa min), Elongation 16% min, Reduction of Area 50% min.

Welding this bolt material will affect mechanical properties: depending on applications one should make sure that suitability is not compromised.

From the large range of carbon content (0.38-0.48 %C) one can see why three AISI steels, classified as chrome-molybdenum steels, are reported as equivalents, namely 4140, 4142, 4145.

The higher the carbon the higher the susceptibility to hardening and to cracking.

Welding requires the use of low hydrogen electrodes, suitable preheating to reduce risk of cracking, and determination if properties after welding are sufficient for the purpose.

A summarized yet thorough treatment of Hydrogen Induced Cracking was given (4) in PWL#044. Click on PWL#044 to see it.

A practical approach to the problem is presented in the Hydrogen Embrittlement website page.

If mechanical properties after welding are insufficient for the purpose, then full re-heat treatment may be required.

For establishing correct heat treating procedures, one should first perform chemical analysis of the material batch in question, to calculate the carbon equivalent,
(see http://www.welding-advisers.com/Welding-alloy-steel.html).

Precautions should be taken to avoid decarburization during heat treatment.


4 - Filler Metals for SAW cladding with 309LMo

As I remarked more than once, the Welding Journal's Q&A Column on welding stainless, by Damian J. Kotecki, is always interesting, helpful and informative.

All involved with welding stainless steels would benefit most by reading regularly the columns and assembling them in a file in their computer until a collection of all such columns is gathered in a volume to be published.

In the September 2012 WJ Issue, at page 16, a reader describes the problem. In the past some cladding had been done with covered electrodes (SMAW) of AWS A5.4 Class E309LMo-16.

Now, to try cladding by Submerged Arc Welding (SAW), they purchased continuous wire material: but it did not meet AWS A5.9 Class ER309LMo composition requirements. In particular, the chromium was low (~21%) and the nickel was high (~15%).

Kotecki explains with his usual grace and clarity why such a material is hard to find. It is simply too expensive to draw. Why then the covered electrodes are possible? Because critical elements are added in the covering, not in the drawn metal...

But he adds also the metallurgical reasons requiring a high ferrite content to allow for dilution with the base metal and to reduce risk of cracking.

Kotecki suggests to look for metal-cored EC309LMo, with metallic content in powder form, that circumvents the difficulties of drawing solid wire.

Summarizing the explanations would not make justice to the beauty of the original article. Therefore I urge interested readers to seek it, to enjoy reading and learning for their benefit.


5 - Online Press: recent Welding related Articles

Collaboration between EADS and KUKA:
License for DeltaN friction-stir welding technology from EADS planned

4 Traders.

Honda develops technology to weld steel and aluminium together
Magazine.

New process to prevent cold cracking in high-strength steel
http://phys.org/news/2012-09-cold-high-strength-steel.html

Selecting, installing, and maintaining
a through-arm robotic GMAW gun

The Fabricator.

TWI Connect - Issue 179 - July/August 2012
http://www.twi.co.uk/news-events/publications/connect/july-august/?locale=en


6 - Terms and Definitions Reminder

Continuous Wave Laser has output operating in continuous, not pulsed mode, or pulsed with period longer than 25 milliseconds.

Electron Beam Braze Welding, is a process variation where the heat is supplied by an electron beam.

Long Electrode Extension, in processes with continuous filler metal, is an increased length of electrode protruding from the contact tip, for increasing resistance and heating for improved flux activation. It is intended to provide adequate shielding or increased weld deposition rate. Be advised that arc current is affected by changing electrode extension.

Pressure Gas Welding is an oxyfuel gas welding process realized by heating the faying surfaces and then pressing them against each other without filler metal.

Resistance Welding Upslope Time is the time, measured from the beginning of the welding cycle, during which the current continuously increases.

Self-fluxing Alloy in thermal spraying, is a surfacing material that wets the substrate and coalesces when heated to its melting point, with no additional flux except boron and silicon contained in the alloy.

Theoretical Electrode Force is that available at the electrodes of a resistance welding machine. Friction and inertia are neglected, system mechanical advantage is included.

Ultraviolet Light Source is a lamp generating intense invisible light, to excite fluorescent pigments used in magnetic particle testing and in liquid penetrant testing for revealing thin cracks.


7 - Article: Friction Stir Spot Welding and Refill

Under the pressure to reduce car weight, manufacturers have devised, tested and applied new processes to assemble sheet metal parts.

While resistance spot welding (RSW) has been successfully applied for years on steel sheets, it is not easily usable on aluminum alloy sheets because of the limited electrical resistance of the lighter metal.

Different processes were developed in Europe as substitutes to RSW, like self-piercing rivets, adhesive bonding, bolts, laser brazing, clinching, and arc welding. When considering the increased possibility of design calling for dissimilar materials joining, the drive is strong for developing alternative economic technologies.

A variant of friction stir welding (FSW), friction stir spot welding was developed, tested and applied in specific car production designs. A graphic description of the process can be seen in a page found at
http://www.mek.dtu.dk/Forskning/Projekter-phd/phd_trinecoldinglomholt.aspx

The process in general was dealt with in pages Friction Stir Welding, and Friction Stir Welding Equipment and in several articles in PWL.

To overcome the problem of the hole left in the upper panel as the plunge tool is removed, a further variant, called Refill Stir Spot Welding (RSSW) was developed, whereby a special tool and a longer welding cycle permits to fill the void space before ending the weld.

The process needs optimization to minimize the few welding defects that were found to appear in some of the developmental applications. Therefore research is continuing to improve the technology.

According to literature reviews, it seems that friction stir spot welding, as compared to existing processes, is likely to provide comparable strengths with improved flexibility and consistent joint quality. Further improvements and applications are believed to increase in the future.


8 - Site Updating: Oxyacetylene Welding Tips (R),
Welding Qualification (R)

The Pages of this Month are revisions and updated versions of older publications.

Oxyacetylene Welding Tips (R) provides essential information on this old but highly successful manual process that is still much used for repair jobs, for hobby welding and for brazing.

Those using the equipment, especially if at home, should be especially alert to the safety rules, published by different sources and available also as posters from equipment distributors.

The revised page can be seen at Oxyacetylene Welding Tips.

Welding Qualification (R) explains the reasons for the requirements established by welding Codes. Even if not required to do so, any conscientious welder should check his/her own production to make sure that no harmful flaws find their way into production. Simple destructive tests of suitable test pieces maybe all that is needed.

The revised page is found at Welding Qualification.

For searching the Welding Advisers Website, besides using a search engine, one may use the Site Map and follow updates by subscribing to the RSS service under the Navigation bar on the left side of every website page.


9 - Short Items

9.1 - Tooth is a projection on a multipoint tool (such as on a saw, milling cutter, or file) designed to produce cutting by removing shavings. Or, on the periphery of a wheel (or segment thereof, as on a gear, spline, or sprocket), an element designed to engage another mechanism and thereby transmit force or motion, or both.

9.2 - Uniform Strain, in a tension test, is the strain to maximum load, occurring before the beginning of localization of strain (necking)

9.3 - Vapor Plating consists in the Deposition of a metal or compound on a heated surface by reduction or decomposition of a volatile compound, at a temperature below the melting points of the deposit and the base material. The reduction is usually accomplished by a gaseous reducing agent such as hydrogen. The decomposition process may involve thermal dissociation or reaction with the base material.

9.4 - Wet Blasting is a process for cleaning or finishing, by directing a slurry of abrasive dispersed in water, at high velocity, against the workpiece surfaces.

9.5 - X-ray Spectroscopy is a collective name for several spectroscopic techniques (mainly wavelength dispersive or energy dispersive) for characterization of materials by using x-ray excitation.

9.6 - Zinc Worms are surface imperfections, characteristic of high-zinc brass castings, that occur when zinc vapor condenses at the mold/metal interface, where it is oxidized and then becomes entrapped in the solidifying metals.


10 - Explorations: beyond the Welder

Skilled Work, Without the Worker
NY Times.

Autonomous Robot Completes “Full Day’s Work” Unassisted
Trends.

How Astronauts Used a Toothbrush to Fix Space Station
SA1.

The Sky Is the Limit for Wind Power
SA2.

Weird Planets (Video)
http://www.youtube.com/watch?v=Cl5EknhEsSQ


11 - Contributions: ASME IX Code Changes of Heat Input Calculation

Readers with practical experience with Heat Input Calculations meeting ASME IX Code changes, are welcome to contribute their knowledge to this publication, for the benefit of all others who risk to get lost.

Heat Input is an essential variable only for selected applications, if the fabrication code requires impact testing. For welding ambient temperature piping/vessels, changes in heat input are not essential variables. The same applies for welding the typical power plant ferrous materials (Cr-Mo and CS [carbon steel]).

Creep strength enhanced ferritic steels and duplex stainless steels need more careful review for establishing specified ranges of heat input to meet code requirements.

The changes were introduced when it was realized that Heat Input from new power supplies, capable of pulse welding or of waveform control, cannot be represented adequately by the simple formula, called Equation 1 per ASME Section IX QW-409.1(a).

This gives Heat Input as equal to Voltage per Amperage x 60 divided by travel speed in linear distance units per minute.

Advanced manufacturers enabled their equipment to provide the required heat input information by sampling both voltage and amperage at high frequency, and by displaying either energy values or power values.

Therefore two new formulas were added to the controlling document, both giving equivalent results. The first, called Equation 2 per ASME Section IX QW-409.1(c)(1), simply gives energy in Joules divided per weld bead length.

The second called Equation 3 per ASME Section IX QW-409.1(c)(2) multiplies the Power in Joules per second (watts) per arc time in seconds, and again divides the power result in watt by weld bead length.

A draft of this paragraph can be seen online at
http://www.lincolnelectric.com/en-us/equipment/Documents/RevisedASMEcode.pdf

The 2010 edition of ASME Section IX, includes the new formulas of the variable QW 409.1, and provides instructions for calculation of heat input that takes into account waveform control, when required.

Significant differences in heat input calculations were found in practical trials, depending on the measuring methods. The new methods of monitoring heat input provide a much needed control tool for those cases where this variable is critical for assuring sound welds.

A Welding Journal article on New Code Requirements for calculating Heat Input is available online at
http://files.aws.org/wj/2010/06/wj201006/wj0610-61.pdf


12 - Testimonials

On Wed Sep 05 03:09:38 2012, the following results were submitted from the "Form 5" on welding-advisers.com:

Name: Mahsa Seyyedian
E-mail Address: removed for security
Country: Iran
Organization: University of Applied Science and Technology
Your Task: Assistant Professor
Subject: Welding joint design problem

Thank you so much for your time and help. The suggestion was useful.


On 18 Sep 2012, 11:41:33 AM, the following results were submitted from the "Form 5" on welding-advisers.com:

Name: Dean Hardy
E-mail Address: removed for security
Country: United Kingdom
Subject: RE: weldability

Hi Elia,

Just wanted to thank you for the prompt response and the excellent feedback.
It is, as I may have suspected, a potential issue. [...]

Kind Regards,
Dean Hardy


13 - Correspondence: a few Comments

Many readers kindly ordered from this Website my Encyclopedia Online. I compiled it quite some time ago with much attention to the details, caring to assemble information likely to be of use to those who look for it.

I hope it was appreciated by readers but I did not get any comment. I would be most obliged if some of those who got it would kindly comment on the use and benefit they gained from it. I am not looking for advertisement.

I am sincerely interested in evaluating the acceptance of the work by those who perused my labor, and in finding ways to improve the results by providing new subjects likely to be requested, in usable format.

I will be obliged to get comments, requests and suggestions. A short note should not be hard to write. Please do this for me. Thanks.


14 - Bulletin Board

14.1 - TITANIUM 2012, 28th Annual Conference and Exposition.
International Titanium Association.
Oct. 7–10. Hilton Atlanta Hotel, Atlanta, Ga.
www.titanium.org.

14.2 - ASNT Fall Conference
American Society for Nondestructive Testing.
Oct. 29–Nov. 2. Rosen Shingle Creek Resort, Orlando, Fla.
www.asnt.org/events/conferences/fc12.htm.

14.3 - ASME Section IX Code Clinic.
American Welding Society.
Nov. 12, 13. Las Vegas Convention Center, Las Vegas, Nev.
www.fabtechexpo.com; www.aws.org/conferences;

14.4 - Explore the best overall introduction to SBI!
SBI!.

14.5 - Visit Now the BlockBuilder 2 Page


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