Contaminants in your weld? Here’s how to prevent them

Sandwiches don’t mix well with welding.

I mentioned in blog 4 that contamination is a topic in itself.  Well, why not follow that train of thought?

Anything and everything that is not the “stuff” being welded is a potential contaminant.  Whether it be oil from machining, paper fibers, soapy water from a wash cycle, a sliver of plastic from your expensive non-marring table top, or even brown mustard from that London broil sandwich you had for lunch, these are going to put something unexpected into your end product.

Now, if you enjoy the smell of toasted brown mustard (yes, it has happened) and don’t much care about the quality of your welded parts, then don’t read anything more.  You’re done — wait for blog 6! 

If you want to know the implications of weld contamination and what to do about it, let’s go!

Let’s simplify things by breaking this down into 3 categories:

  • Organics – If it was ever alive, it will have carbon in abundance along with hydrogen, oxygen and nitrogen. Basically hydrocarbons.  Each of these components has its own effect on your weld. Carbon typically hardens iron-based alloys, increasing crack susceptibility.  Hydrogen often leads to embrittlement, oxygen has all sorts of effects good and bad, and nitrogen can be anything from harmless to utterly destructive. Examples are paper fibers, hydraulic oil, hair, a breadcrumb (really).
  • Inorganics – Things that aren’t primarily carbon. Silicon-based contaminants, dirt, silt, sand, glass – these all end up in parts, leading to porosity, cracking, and sometimes complete lack of fusion.  Ceramics from abrasives – some of these are innocuous, and others can lead to severe weld degradation and cracking, pitting, and general weakening of your precious parts.
  • Atmospherics – If your part is reactive, gasses and compounds floating around can wreak havoc in all kinds of ways through corrosion and conversion. These are complex problems and can really be tough to troubleshoot. 

What to do about weld contaminants

How you deal with a contaminant depends greatly on what it is.  Simple organic compounds can often be removed with an organic solvent like acetone, isopropyl alcohol, MEK, or something similar.  Soapy water can be effective for oils as long as no soap residue is left behind.  For some of the more persistent organics, an aggressive acid or alkaline cleaner may be necessary.

Inorganics like abrasive dust can be easy to remove by a quick dry wipe or with a lint free cloth and DI water. However for embedded particles, usually following a grinding operation, the solution can be quite challenging.  Often progressive polishing or machining is in order and will entail removing enough of the weld surface to ensure all of the inorganics are gone.

Of course, the best way to deal with contaminants is to NEVER introduce them to begin with.  My primary recommendation is to expose your parts to as few contaminants as possible.  Clean them thoroughly after inspection, then seal them in clean packaging so they can’t come in contact with anything until it’s time to weld.

As always, talk to a pro before putting those parts on a truck to your welder.   I’m sure we’ll touch on this topic again soon. 

Common weld defects and their causes: porosity

Alright, now that you’ve read the “Misconceptions About Welding” blogs, you want to know what else you might not know about welding, huh?  So, let’s talk defects.  In this blog we’ll discuss porosity.

I like to talk about porosity more than other weld defects because even though there are many contributing factors to it, at the end of the day it is always (did I use an absolute?) trapped gas in the solidifying weld.

-How do you trap gas in a solid material?  Well, start by making that solid a liquid.

-How do I do that?  Melt it.

-With what?  Doesn’t matter.  Porosity is a common problem across all types of welding, and other processes that involve molten metal as well – think casting.

-Where does the gas come from?  Lots of different places. Let’s list some:

  • The parent material. We already touched briefly on this in blog #2 (If it’s metal, I can weld it).  Some elements evaporate at the melting point of other elements.  These light elements turn into gas bubbles in the weld pool when they rapidly evaporate under intense heat.
  • The parent material. Yes, I wrote it twice.  During high energy density welding, i.e. laser welding or electron beam welding, some of the parent material goes beyond melting and actually evaporates.  Yes, you really can make metal vapor.
  • Dissolved gasses. Some alloys have gasses deliberately dissolved into them to add beneficial characteristics.  Heating these up is like shaking a bottle of soda then popping the top, except instead of a shower of sweet, syrupy liquid, there will be a shower of glowing, molten metal spraying in your direction.
  • Trapped atmosphere. During very high power welding, there can actually be enough of a crater in the weld that molten metal can “slosh over” and trap some of the local atmosphere in the weld.
  • Contamination. This is a topic in and of itself, but this could be oil, dirt, water, paper, tape, plastic — you name it, I’ve seen it.

-What does all this mean to me?  Well, that depends on what you want to accomplish.  It might be harmless, or it might be the initiation point of a catastrophic failure.  This is another case where you want to collaborate with someone in the know.  Put your design brains in the same room with the welding brains and talk through your options.

-What are my options?  That’s a topic for another blog, or series of blogs.  There are LOTS of ways to deal with common weld problems.  Stay tuned, we’ll touch on many of them in upcoming blogs.

Welding Myths Part 3: A weld is never as strong as the parent material

To go along with the last post on welding myths and non-weldable materials, I also often get grudging calls from a designer who has been “forced” to add a weld to a design.

Customer: “How much do I have to overdesign this part for this weld?”

Me: “Why do you want to overdesign?”

Customer: “Well, the weld is going to weaken the part!  I need to beef it up to compensate.”

Au contraire.  Weld strength, which by the way is an ambiguous term, is related to the parent material characteristics, part configuration and weld parameters.  So, to refer back to welding myth #2 (If it’s metal, I can weld it), if Mr. Customer designed his part out of 303 stainless steel, the weld is indeed going to be weaker than the parent material and will be a failure point.  However, that same part made from annealed 304L may actually be stronger at the weld.  SURPRISE!

Solutions for weld strength

It’s true that in many cases the weld will lead to softening or hardening of the material in the region in and adjacent to the weld, but very often this can be addressed by choosing a different material or by simply adding a post weld heat-treatment to restore characteristics to those of the parent material.

Quick example: A hot topic in the news right now is guns.  Believe it or not, modern guns are employing laser welding more and more frequently.

Well, guns are made from carbon and alloy steel (most of the time) and these materials don’t always play well after welding.  However, a few hours in an oven at a few hundred degrees will make the difference between a part that will survive a few tens of shots, or tens of thousands of shots.

The takeaway – Don’t fall into the trap of believing that a weld will be the weakest point of your part.  Talk to someone in the know, and use welding to make you look like a hero on your next “impossible” design.

New leadership series helps women advance their STEM careers

If you’re a woman in STEM (science, technology, engineering, math), how do you navigate a career with few role models or mentors?

According to the U.S. Department of Commerce, women are 50 percent of the overall workforce but only 24 percent of the STEM workforce. Moreover, 50 percent of women in STEM careers drop out in the first 10 years.

That’s a challenge that a Connecticut organization is working to address with a three-part professional development series for women called “B-Vibrant: Mastering Your Energy in the Technical Workplace.” The half-day workshops take place on May 23, June 7 and June 22 at multiple locations around the state.

The series is sponsored by BEACON (Biomedical Engineering Alliance and Consortium). Dave Hudson, President and CEO of Joining Technologies, serves on BEACON’s board of directors.

The “B-Vibrant” series is designed for women engineers, scientists, manufacturers, entrepreneurs and designers in all STEM-related roles. It includes sessions to help women define their vision and values for their career, overcome common barriers to success, and invest in their growth, development and connections.

BEACON Executive Director Terri Wilson said the idea for the workshops got started when an employee of a BEACON member company shared her frustration that women in technical environments have limited role models or mentors at the higher levels in their companies.

“While there are some diverse events for women, especially in colleges and universities for women entering technical fields, there seems to be a real gap in more robust training programs specifically targeting the professional development of mid-career women in manufacturing, engineering and STEM,” Wilson said.

For Caitlin Scott, Intellectual Property, Legal and Contracts Manager at Joining Technologies, having mentors at the company made a huge difference in developing her career. “Dave Hudson and Michael Francoeur (the company founder) have always been available when I want to strategize, need advice or to talk through a problem. We have a wonderful environment here for growing leaders, but not everybody is fortunate enough to have resources like that.”

Welding Myths Part 2: If it’s metal, I can weld it

 

This misconception about welding comes up far more often than I’d like.  An engineer calls in a rush to get a prototype stainless steel part welded.  To save time and cost, he had the parts made from free machining material.  Frantic on the phone, the conversation generally goes something like this:

Customer: “This is so and so, and I’ve got 3 stainless steel housings I need laser welded ASAP.  The machining is done, I just need a full penetration laser weld to hold them together, and they have to be absolutely leak tight.”

Me: “Ok, a couple of questions.  1 – What is the size and shape of the part?  2 – How much penetration?  3 – What grade of stainless?”

Customer: “It’s a round housing about 2 inches in diameter, it has a step behind the weld to align the parts.  The wall thickness at the weld is .030”, and the material is 303 stainless steel.”

Me: “Alright, a couple more questions now.  1 – Is there a cosmetic requirement for this part?  2 – Can you tolerate filler material in the weld?  3 – (in my head) Why did you make these out of 303?”

Customer: “Looks are very critical.  I need the weld very small, which is why I want laser welding.  I can’t tolerate filler material unless it won’t affect the cosmetic appearance.”

Well, this back and forth usually goes on and on.  During the conversation, I mention that 303 is not ideal for welding.  There is a rapid and fierce push back about how all 300 series stainless steels are easy to weld. 

Reality check

Here’s the thing – 303 stainless steel is GREAT for machining.  Wonderfully easy to work with, readily available, and fairly inexpensive.  That said – it’s just not meant for welding, no matter how you slice it.  The stuff they add to make it free-machining, sulfur and phosphorus, don’t mix well with welding.  They evaporate with fervor – to put it mildly – during the laser weld process, leading to copious weld spatter and frequently cracking, not to mention porosity.  

The conversation will end with one of three outcomes: 

  1. Customer will have us work with the 303 parts, and add a ductile filler wire (such as 308L or Hastelloy W) to add some good material back into the “ugly” weld, and Mr. Customer will tolerate the resulting cosmetic blemishes.
  2. Customer remakes parts out of 304L and everything is hunky-dory.
  3. Customer hangs up in anger because his parts can’t be made exactly as he wants them from the material he already had purchased.

I’d like to say option 3 never happens, but unfortunately it’s a real situation that occurs regularly. So, the lesson to be taken from this – always check with your weld house BEFORE manufacturing parts.  Make sure that the material that you want welded is actually weldable, please.  I’ll speak more about weldable and non-weldable materials in other posts.