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PWL#105 - Improving GMAW Performance, Brazing Nickel, New FCAW Specification, Low Load Vickers Hardn
May 01, 2012
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PWL#105
Practical Welding Letter No. 105
May 2012

PWL#105 - Improving GMAW Performance, Brazing with Nickel AWS BNi-2/AMS 4777, New FCAW Specification AWS A5.36, Low Load Vickers Hardness Testing, Invitation to ITA Titanium Welding Workshop, High Energy Beam Processing, New Contact Us Form and much more...


May 2012 - Practical Welding Letter - Issue No. 105


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This publication brings to the readers practical answers to welding problems in an informal setting designed to be helpful and informative. We actively seek feedback to make it ever more useful and up to date. We encourage you to comment and to contribute your experience, if you think it may be useful to your fellow readers.
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TABLE of CONTENTS
1 - Introduction

2 - Article - Improving GMAW performance

3 - How to do it well: Brazing with Nickel AWS BNi-2/AMS 4777

4 - A new Open Specification for FCAW Filler Metals

5 - Online Press: recent Welding related Articles

6 - Terms and Definitions Reminder

7 - Article - Low Load Hardness Testing

8 - Site Updating: Beam Processing, New Contact Us (R) Form

9 - Short Items

10 - Explorations: beyond the Welder

11 - Contributions: Invitation to a Titanium Welding Workshop

12 - Testimonials

13 - Correspondence: a few Comments

14 - Bulletin Board


1 - Introduction

This new Issue No. 105 of Practical Welding Letter opens with a note relating the information recently presented in two published articles. Progress in GMAW performance occurs not only in research institutions but can appear even in modest shops, if daring minds are ready to initiate trials following hints devoted to improve profitability. Such improvements may become most effective.

Nickel base brazing for high temperature applications may be quite disturbing if center cracks keep appearing in brazed parts. Special attention to the brazing clearance may be all that is needed to obtain strong joints.

Specifications are frequently updated. Less often are new specifications being written to satisfy advanced requirements and new applications. This is the case with a new open specification on flux cored arc welding for many different materials, to be introduced in the near future and to supersede older classification in a matter of a few years. Keeping up to date may be not only useful but even essential.

A short review follows of a long article reporting studies performed to solve ancient discrepancies in interpretation of results of low load hardness tests. Most interesting is the conclusion that all differences will finally be resolved once the well known Scanning Electron Microscope will be slightly modified to provide the definite objective measurements required.

In the Site Updating section a new page is announced explaining some unusual processing feasible with high energy beam sources. In certain cases this could be the most effective application. The other page is an updated form to collect queries and feedback from readers, by implementing a few rules in view of weeding out useless unfocused questions.

We are glad to be able to invite our readers to participate in a day long workshop on Welding of Titanium. It is a very good opportunity to learn basic facts or to refresh essential knowledge. It could be a profitable investment too. See details in section 11.

Regular features are found at their usual place. Feedback, requests, comments and contributions are requested, at least from those readers who testified that they read PWL with some interest.

If you are pleased with what you read here, you might as well spread to your friends and associates the notion of this website and of this publication. Thanks.


2 - Article - Improving GMAW performance

Two articles, recently published in the April 2012 issue of the Welding Journal, stress the point that modern power sources based on inverter technology, are most probably under exploited.

There is a diffuse opinion, mainly with experts and equipment manufacturers, that the available excess fine tuning of controls is overwhelming for most of users, who tend to stay with the few welding schedules providing acceptable results.

Both articles try to motivate the lucky owners of modern equipment to explore uncharted fields for a more thorough understanding of available features and for improved exploitation of capabilities.

The first article, at page 28 of that magazine, reports on a sponsored project concerned with shipbuilding, aimed at increasing productivity and throughput of mechanized GMAW, by low-cost modifications to existing equipment/parameters.

While the project examined also extensive equipment modifications with great potential for remarkable improvements, it seems that most interesting results can be obtained with regular inverter technology power sources, by using new parameters ranges that increase weld speed while limiting heat input.

In the quoted research paper by Dr. Hudec, he explains that operation in regions of instability in older GMAW power supplies might be possible and useful with modern inverters. One such solution is in a "short-spray" parameter region at lower voltages than those used in the past in spray-arc GMAW.

The tests confirmed that drastically reducing voltage and increasing weld speed produced an acceptable symmetrical fillet leg length of 0.125 in. as required, at optimum weld speed of 55 in./min. (~1.40 m/min).

The article remarks that the limited scope of the project did not permit extensive testing. The point of the effort was to show that higher weld speeds and lower heat inputs are enabled with many of the current generation of inverter power supplies. Therefore the potential for significant improvement in welding operations may already exist on the shop floor of many fabricators.

The second article at page 48 of the same issue explains why the new sources make it easier to perform with pulsed GMAW. The standard recommendation with traditional power sources is to use direct current electrode negative only when low penetration is required, as for surfacing.

This article notes that direct current electrode negative with traditional power sources tends to produce a ball at the electrode end, that makes proper welding quite difficult. Much better control is achieved with pulsed power. The power delivered to the arc is adjusted in real time to allow the formation of molten metal that will then transfer across the arc into the pool in a controlled, uniform manner.

By utilizing this technology, GMAW can weld in the DCEN mode while providing a stable arc, good bead appearance, and little to no spatter. The great benefit of this process variant is the welding of thin materials with large root openings without melting through or cutting the workpieces.

Newer power supplies can provide the ability to vary the pulse peaks in a defined sequence, adjusting the percentage of time when the electrode is connected to negative polarity. In this state, more heat goes to the electrode, increasing the rate of melting, while decreasing heat input to the workpiece. This results in a GMA weld with the appearance of a gas tungsten arc (GTA) weld.

The author notes that GMAW is generally considered easier to apply than GTAW, and also more productive, being performed at higher speed, even with a larger diameter electrode, especially if the pulse sequence parameters are selected carefully.

Other advantages claimed as consequences of variation in the peak pulse levels are low frequency agitation, helping in floating out porosity and in promoting solidification of small grains, that improve resistance to cracking.

With modern technology it is easier to control pulses switching rapidly from EN to EP and vice versa. It is also easier to test quickly the results of change in the various proportions and duration of peaks, a first screening being made by instant visual inspection.

The most important recommendations gathered from the two recent articles quoted here is to learn from all available sources and to experiment by changing parameters with the purpose to reduce heat input and increase weld speed and productivity, while assuring the best possible quality. There is space for improvement, but one must work to realize it.

Interested readers are urged to seek the original articles, and to send us their feedback reflecting their practical experience on the suggestions reported above.


3 - How to do it well: Brazing with Nickel AWS BNi-2/AMS 4777

A quite common question from shops using AWS BNi-2/AMS 4777 nickel base filler brazing alloy to join elevated temperature resistant alloys in vacuum furnaces, refers to the frequent appearance of a center crack right through the brazing material.

ANSI/AWS A5.8M/A5.8:2011
Specification for Filler Metals for Brazing and Braze Welding
Edition: 10th
American Welding Society / 17-Jun-2011 / 62 pages
Click to order.

The brazing range of this filler metal is given as 1010-1175 0C (1850-2150 0F), relatively low, due to melting point depressants included in its composition.

The added elements performing this function (boron, silicon, phosphorus) also reduce the ductility of the brazing alloy. As the solidification occurs in the direction from the outside toward the central part of the brazing gap, and as these elements are the last ones to freeze, it so happens that their concentration is higher in the center.

The location of concentration of those elements is also a weaker point because of their reduced ductility, prone to cracking in service but also, occasionally, during solidification.

If the capillary clearance existing at the brazing temperature results larger than 0.1mm (0.004"), then there are good chances that the brittle constituents solidify at the joint center, visible in a metallographic section as a dark line, indicating a continuous layer likely to crack.

If however the said clearance is smaller than that, the brittle parts solidify preferably as separated islands in a more ductile matrix, capable of sustaining minor strains without cracking.

Therefore, for successful brazing with this brazing alloy, besides all other precautions it is essential to control the actual capillary gap at brazing temperature, to keep it consistently smaller than 0.05mm (0.002").


4 - A new Open Specification for FCAW Filler Metals

Advance notice of a new Specification named AWS A5.36, to be officially issued shortly, was given in the March 2012 issue of the Welding Journal at page 51.

This new document, developed by the AWS A5M Subcommittee, will be issued as AWS A5.36/A5.36M, Specification for Carbon and Low-Alloy Steel Flux Cored Electrodes for Flux Cored Arc Welding and Metal Cored Electrodes for Gas Metal Arc Welding.

While largely accepted and used for current practice, the older specifications include "fixed" classification systems with defined requirements for weld metal tensile strength, Charpy V-notch toughness, condition of heat treatment, etc.

However they do not adequately provide for the classification of new electrodes designed for enhanced weld metal properties, for use with other commonly used shielding gases, for alternate conditions of heat treatment, or for use with advanced power sources.

The new document introduces an Open Classification System to address jointly old and new electrode types and alternate weld deposit requirements.

It seems that the main drive to the issuance of the new Specification was to simplify the reference, by unifying under the same document different electrodes presently meeting different specifications.

The other purpose was apparently to promote innovation and progress, by establishing an accepted method to characterize new electrodes designed to meet new and advanced requirements, by encouraging developers and manufacturers to make reference to the new document.

The major features of this document are:

  • It provides for the classification of both the carbon steel and low-alloy steel flux cored electrodes previously classified separately,

  • It does the same for classification the carbon steel and low-alloy steel metal cored electrodes previously classified separately,

  • It retains the fixed classification system for those carbon steel flux cored and metal cored electrodes for which there is wide acceptance with their existing classification requirements,

  • It introduces an "open" classification system to address new electrode types and alternate weld deposit requirements.

This classification system is similar to that already used in AWS specifications for the classification of submerged arc flux and electrode combinations.

According to the current practice, two versions the A5.36 specification will be introduced.
One utilizes a classification system based upon U.S. Customary Units.
The other, identified as A5.36M will utilize a system based upon the International System of Units (SI).

The different identifiers are briefly introduced in the above article and a few examples are presented. Shielding gases, single or as identified mixtures, shall be included when used.

Readers using flux cored and/or metal cored electrodes covered by the old specifications are advised to stay tuned to the new specification release, to acquaint themselves with the new identifiers, and to seek the above referenced article for further information.


5 - Online Press: recent Welding related Articles

Combustible Dust Explosion at Pasta Plant
OHS.

Welding Process Planning and Parametric Pricing Software Solution for SMEs
Cordis.

US Navy to build ship hull from titanium
Steel Guru.

Offline programming and simulation in robotic welding
The Fabricator.

Connect - Issue 177 March/April 2012
http://www.twi.co.uk/news-events/publications/connect/march-april/


6 - Terms and Definitions Reminder

Governing metal thickness in resistance welding, is the sheet thickness on which are based the requirements for nugget size and depth of fusion.

Level wound is spooled or coiled filler metal, wound in distinct, touching adjacent layers.

Metallic bond is the principal force that holds metals together. It is a primary bond resulting from increased spatial extension of valence electron wave function when metal atoms are brought close together.

Preweld interval in resistance welding is the time between the initiation of squeeze time and the beginning of the weld time.

Root bead is a weld bead that extends into or includes the root joint partially or totally.

Stranded Electrode is a composite filler metal electrode made of stranded wires, that may mechanically enclose materials to improve properties, stabilize the arc or provide shielding.

Thermal cutting is a group of cutting processes that separate metal parts by melting, burning or vaporizing, by heating the metal locally over melting temperature.

Weld Interval in resistance welding multi-pulse cycle, describes the sum of heat and cool time, including upslope time.


7 - Article - Low Load Hardness Testing

The Macro Vickers Hardness test is normally performed with a load between 1 and 50 kgf. It is explained quite thoroughly in our book on Hardness Testing Made Simple that every reader can download upon subscribing to Practical Welding Letter.

The same test can be performed with lower loads for testing small areas (grains) or very thin specimens. In principle, if the material is quite homogeneous, all the results should be identical, within statistical variation, because the shape of the Vickers indentation is geometrically similar at whatever test load, over a very wide test load range.

We all recall the general assumption that low load microindentation Vickers Hardness testing tend in general to display higher results than the normal load test on the same materials and condition.

It appears that such an assumption is not universally accepted and other conclusions have been reported by different researchers, as explained in the article quoted hereafter.

In the past the difference in hardness at decreasing loads was attributed to the "indentation size effect" or ISE, thought to be dependent on fundamental characteristics of the material.

A recent article by the renowned expert metallographer George F. Vander Voort, published in the ASM International Magazine Advanced Materials and Processes in the April 2012 Issue on page 28, reports on extensive research performed on the subject and presents qualified conclusions.

The author stresses the importance of proper specimen preparation, especially if they are intended for low load microindentation hardness testing, because of the critical sensitivity to preparation damage.

Besides this, various Round Robin test series involving numerous test laboratories and experimenters, all testing the same specimens, produced a large number of data, reported in quoted research papers.

It was confirmed that the best operators, repeating many times the same measurements on the same indentations, reach at best ±0.5 microns variation, while multiple operators can deliver at best ±1.0 micron over time. At low loads such uncertainties have large effects on hardness.

The analysis of the results demonstrates that the indentation size effect is not a characteristic of the material, but is due to visual perception problems associated with sizing small indents.

A perplexing source of uncertainty derives from the fact that the edges of the lowest load impressions, when examined with good quality lenses in a light optical microscope at high enlargements, can be brought to focus with minimal adjustments. Focus, it should be stressed, is not a unique value, it depends on personal judgement.

It appears however that those same focus changes produce an appreciable difference in the measurable diagonal of the indentation. In these conditions different hardness results could be obtained for equally acceptable focus settings, which cannot be correct.

It could be agreed to accept as a definite result the maximum (or the minimum) possible diagonal measurement obtained in a series, but this uncertainty is unacceptable.

The way to a solution is suggested in the same article: find a verified procedure to perform the indentation measurement by a machine, independent of operator's personal judgement.

By adapting the Scanning Electron Microscope (SEM), through endowing it with minor adjustments (tilt) to enhance image contrast, it is hoped to free the measurements and their uncertainties from human judgement, provided the actual magnification is known to a very high precision, maintained even as the working distance is changed.

Because of the importance of the argument treated, interested readers are urged to seek the original article at the reference given above, and let us have their feedback.


8 - Site Updating: Beam Processing, New Contact Us (R) Form

The Pages of this Month are a new one and an updated one. The new page explains a few important uses (other than for welding or cutting), of high energy beams sources. In particular existing equipment may be used for heat treatment hardening of suitable materials, and also for introducing or modifying favorable patterns of residual stresses.

It is reachable at Beam Processing.

The other page is an updated form to be used when contacting this website. Following explanations exposed in our previous PWL issue, a few new requests are introduced to discourage useless questioning of unclear problems, not sufficiently elaborated. Reference was also added to the Feedback page, intended to learn how useful were the answers provided.

It is found at Contact Us.

New pages appear in the Blog page. They are also listed in our Site Map and in the Index Page.


9 - Short Items

9.1- Electromagnetic Radiation consists of Energy propagated at the speed of light by an electromagnetic field. The electromagnetic spectrum includes different wavelength regions, from Gamma-ray, X-ray, Ultra violet (far and near), Visible, Infra-red (near, middle, far), Microwave and Radio-wave.

9.2 - Freezing Range is the temperature interval between liquidus and solidus temperatures of alloys, in which molten and solid constituents coexist.

9.3 - Grinding Sensitivity is a qualitative feature of a material, expressing its susceptibility to surface damage such as grinding cracks. Affected by such factors as composition, manufacturing history, hardness, microstructure, hydrogen content, and residual stresses.

9.4 - Isothermal Transformation describes a change in phase that takes place at a constant temperature. The time required for transformation to be completed, and in some instances the time delay before transformation begins, depends on the amount of supercooling below (or superheating above) the equilibrium temperature for the same transformation.

9.5 - Microindentation is the small residual impression, left in a solid surface when an indenter, typically a pyramidal diamond stylus, is withdrawn after penetrating the surface when applied with a low load. Typically, the dimensions of the microindentations are measured to determine the hardness of the material feature under investigation by microindentation. See the article in Section 7 above.

9.6 - Parting Line is the intersection of the parting plane of a casting or plastic mold or the parting plane between forging dies with the mold or die cavity, and the residual impression visible on the part.


10 - Explorations: beyond the Welder

What Happens Inside the Large Hadron Collider? (Video)
SA1.

Electron Splits into Quasiparticles
SA2.

New Technology Allows Better Extreme Weather Forecasts
SA3.

Melting Glaciers Liberate Ancient Microbes
SA4.

How Do They Do It: Jet Engines (Video)
ASM.


11 - Contributions: Invitation to a Titanium Welding Workshop

PWL was recently informed of a "Welding of Titanium" workshop, hosted by the International Titanium Association (ITA) (www.titanium.org).

The workshop will be held on June 26, 2012 at the
Edison Welding Institute
1250 Arthur E. Adams Dr.
Columbus, Ohio 43221
USA
1-614-688-5000

Information on the workshop, open to the public, and called
How to Weld Titanium - Full Day Course
can be found on the page of the Event. (Click on the link.)

From that page download also the TITANIUMWeldingBrochure by clicking on this name under the page Title.

The published program promises to be most informative, with 4 hours of classroom study and 3 hour hands-on exercises that will follow for a full day workshop.

Interested readers of Practical Welding Letter are urged not to miss this exceptional occasion, and to participate by Registering, through the contact form provided in the above page or by phone as hereafter.

PWL readers will be able to attend this workshop at the discounted ITA Member rate of $539. This saves PWL readers $110 off the Non-Member rate of $649. When registering, use Discount Code: 883289W. Call 303-404-2221 to register.

Readers can download the last Newsletter dedicated to Titanium, the April 2012 issue at
http://www.titanium.org/files/ItemFileA4864.pdf

The official ITA website offers also a few Books for Sale and an On-Line Titanium Library that requires agreement to certain conditions for obtaining the right to download the available publications.

Readers are urged to profit of all learning opportunities opened to them.

For nearly three decades ITA instructed thousands of professionals in all aspects of titanium usage. They look to educate welders, engineers, designers and industry professionals on titanium’s superior properties and explain how those properties can be exploited to enhance products and services.

They also strive to advance ideas in research, design, metallurgy and engineering, and serve as the leading forum to cultivate the exchange of ideas and support a diverse, dynamic, global industry.

Participating readers are asked to kindly report to PWL on their experience with the workshop and on the benefits, in terms of knowledge and practice, they gathered from the Event.


12 - Testimonials

On Mon Apr 02 15:22:55 2012, the following results were submitted from the "Form 5" on welding-advisers.com:

Name: Henry Martin
E-mail Address: removed for security
Country: United States
Introduce Your Organization: National Metal Fabricators
Describe Your Responsibility: Seek out internet advertising opportunities.
Questions and Feedback : Hi,

I thought your website http://www.welding-advisers.com/Welding-plan-blog.html would be a great place to advertise for a client of mine in the metal fabrication industry [...]


Name: Mike Postorino
E-mail Address: removed for security
Country: United States
Introduce Your Organization: Mesothelioma Center
Describe Your Responsibility: National Awareness Coordinator
Questions and Feedback : Hi,
My name is Mike Postorino and I'm the National Awareness Coordinator for the Mesothelioma Center (Asbestos.com). While I was browsing through a number of construction safety sites I came across your site and was impressed by the information you have listed. [...]


13 - Correspondence: a few Comments

13.1 - As already noted above, the new Contact Us form has been updated, to weed out waste of time questions. Experience will tell if and how much serious inquirers appreciate the opportunity to better explain their needs and to obtain more useful answers.

13.2 - This author has sometime naive expectations as to inquirers' reactions. It happens that an equipment manufacturer offers to perform a trial weld at no cost or obligation. It seems obvious that such an offer should be well accepted to check if certain welding performance is adequate or not to given requirements. Unfortunately however, such offers remain often unanswered, it is not clear why, even if this behavior does not seem to be in the inquirer's best interest.

13.3 - Inquirers are encouraged to send their questions, but they should show that the answer is needed for some useful purpose, not for idle, unfocused curiosity. They should also appreciate that details should be provided to clarify the issue and to get pertinent answers.

The use of the Feedback Form is encouraged to evaluate the acceptance of answers.


14 - Bulletin Board

14.1 - AWS Weldmex
May 2–4. Mexico City, Mexico
www.weldmex.com

14.2 - 17th Beijing-Essen Welding and Cutting Fair.
June 4–7. New China Int’l Exhibition Centre, Beijing, China.
www.cmes.org/essen/en/index.htm.

14.3 - AeroMat 2012 Conference and Exposition
June 18-20, 2012 - Charlotte Convention Center, Charlotte NC, USA
http://www.asminternational.org/content/Events/aeromat/welcome.jsp

14.4 - 65th Annual Assembly of the International Institute of Welding (IIW)
July 8–13. Hyatt Regency Hotel Denver and Colorado
Convention Center, Denver, Colo.
www.iiw2012.com

14.5 - Visit Now the BlockBuilder 2 Page

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