Joint design for welding: the pros and cons of groove joints

After you’ve selected the right material for your welding project, the next important consideration is joint design. We’ll be taking a look at the different types of joints and briefly discussing the pros and cons of each, especially in relation to laser and electron beam (EB) welding. Let’s start with one of the strongest joints, the groove joint, and what makes it so “groovy”:

First, a quick definition: Groove joints or square groove joints are a type of butt joint, with two flat pieces parallel to each other and butted together with a 100% weld joining the two pieces. Here’s an example:

Pros

  • High strength: Provides complete fusion, low stress, and 100% penetration.
  • Easy to machine
  • Good distortion control: Welds shrink evenly and are less likely to distort.
  • Easy to inspect

Cons

  • Geometry limited applications
  • Not suitable for applications with delicate items behind the weld, such as electronics
  • Not self-aligning – fixturing or a backer may be required
  • Sensitive to faying surface conditions

Additional considerations:

Fit up is important for groove joints, especially for laser and EB welding. Due to the energy density of these types of welding, the beam falls through large gaps.

Each type of joint has its advantages and disadvantages, but the biggest advantage of the butt joint and square groove joint is its strength. It can withstand stress better than any other type of weld joint. Pretty groovy, right?

Have questions about joint design for laser welding or EB welding? Ask one of our experts, or leave a comment in the space below.

Weld contamination part 2 – aluminum oxide

Aluminum oxide contamination is no big deal for that rusty yard art project, but can wreak havoc on critical applications like an axle shaft. (Spider by John Lucas, Jr.)

I’ve talked about weld contaminants in a previous post, but a recent conversation convinced me that it was a topic that warranted revisiting.

Aluminum oxide (AlO), in particular, is a nasty contaminant that is oft overlooked.

What exactly is AlO? Quite simply, it’s one of the most common abrasives used. It is present in most sandpaper, grinding disks, cutoff wheels, and even your favorite abrasive pads.

Why use AlO, and why is it so common? That, as well, is simple. It’s cheap, and it works. It’s a fantastic abrasive with low heat retention, making it ideally suited for all kinds of grinding processes.

Why is AlO a problem for welding? Ask a dozen welders, and you’ll get a dozen answers to this one.

Ultimately, the extent of the problem will be based on your part characteristics. If you’re welding up some rusty yard art with a stick welder, you’re probably not going to care that you just cut that shovel head and leaf spring with an AlO cutoff wheel. The residual contaminants from the parent material are going to contaminate the weld far more than the few embedded AlO particles.

Now, on the other hand, that alloy steel dragster axle shaft you’re about to have electron beam welded is going to care a whole lot about even the smallest defect. You might think that a couple of seemingly inconsequential grains of AlO abrasive couldn’t possible make the difference between a mid 5 second run and hitting the wall at breakneck speeds. That would be a dangerous assumption.

AlO melts at nearly 4,000 degrees (F), while steel melts at under 3,000 degrees (F). That means that those particles have the potential to sit buried in the resolidified weld as brittle little points of failure. No amount of post-weld heat treatment will reduce how brittle they are.

Now, let’s assume that we DO get the weld hot enough to melt the AlO particles. That should be OK, right? Not really. AlO is, as implied in the title, Aluminum and Oxygen, both of which will be liberated with sufficient heat. Neither of which you want in your steel.

As welders, we take extreme care to prevent the introduction of oxygen into our weldments. There are entire classes dedicated to this. For this blog, let’s just say oxygen is bad, mmm kay?

Aluminum is also something not desirable in steel. It forms brittle intermetallics that may or may not show up as weld defects. They WILL present in the form of unexpected strength and toughness characteristics.

One other way AlO can get you is by evaporating, but not dissolving into the parent material, causing porosity. Again, for your steel garden statue, no problem. For that axle, the results could be anywhere from embarrassing to straight-up dangerous.

What is the alternative? There are lots, but if abrasives are in your plan, consider Silicon Carbide as your final abrasive.

For more details, contact us at 860.653-0111 to reach out to an expert to go over some great options for your next artistic or high speed venture. You can also leave a question or comment in the space below.

Material selection for laser and EB welding – do’s and don’ts

One of the most important factors in a successful laser or electron beam (EB) welding project is choosing the right materials up front.  The right material can make the difference between a project that runs smoothly and gets delivered on time, and a project that takes longer, costs more, and causes a lot of aggravation. While we could probably write a book on this topic, here are a few do’s and don’ts to get started. 

DO check with us first to make sure the material you’re choosing can be easily welded.  This may seem obvious, but some customers ignore this at their peril.  As an example, many years ago I worked on a project involving parts going on the space station. The customer was so adamant about using a particular material that he ordered $80,000 worth of it… and then realized after purchasing and final machining that the material couldn’t be welded.  We eventually figured out how to make it work, but it took 10 times the effort and 10 times the cost.  The bottom line – make sure the designer and the welding engineer collaborate before making your final material choices.

DO pick good weldable alloys: 

  • Stainless steel is one of the most popular materials for laser and electron beam (EB) welding. But avoid stainless steels containing sulphur and phosphor. Their low melting points make them key culprits for cracking and porosity problems. Customers like 303 stainless because of its ease of machining, but the outcome with welding is not always ideal. Talk to your welding engineer BEFORE deciding on 303.

Stainless steels ending in F for free machining, such as 316 F and 430 F, should definitely be avoided.  Again, the sulphur and phosphor that are added to make them free machining are terrible for welding.  (We like to say the “F” stands for failure!) 

  • Low carbon stainless steels such as 304 L are also a good choice for laser welding and EB welding.

  • Aluminum alloys can also be laser and EB welded. Cleanliness is very important with aluminum, since oxidation can lead to weld failure. If you need a high strength alloy, certain aluminums are precipitation hardenable, which means they can be brought up to full strength after welding with heat treating. Some aluminums will require filler material.

  • Titanium is a popular material for many aerospace applications. Like aluminum, cleanliness is key for welding titanium. Titanium ranges from commercially pure grades to a number of titanium alloys containing things like tin with a low melting point. These titanium alloys are not unweldable, but you may need to incorporate certain joint designs in order to make them weldable.  Again… check with your welding engineer first.

DO preheat high carbon materials. The more carbon in steel, the harder it becomes to weld and the more prone it is to cracking. And I don’t mean little cracks – I mean big cracks with complete weld failure. To minimize the possibility of cracking, high carbon steels should be preheated prior to welding.

DON’T weld in the hardened condition (usually).  The success rate of welding hardened material is generally lower when compared with annealed material.  If possible, do your welding in the annealed condition and harden after welding.

Many factors go into choosing a material including cost, strength, design criteria, post-weld testing, etc.  But to repeat – make sure the material you’re considering is actually weldable BEFORE you make your final choice. 

Contact us at 860.653-0111 to discuss your next project.

10 advantages of electron beam welding

Since we started this blog a few months ago, we’ve written about a lot of topics related to laser welding, which hopefully you’ve found useful. Now we’d like to turn your attention to another type of welding that’s a favorite of ours – electron beam welding.

Electron beam (EB) welding is an excellent choice for joining advanced materials used in industries such as aerospace, semiconductors, and medical devices.  Here are 10 advantages of EB welding. (I could come up with more, but 10 is a nice round number, isn’t it?)

  1. No gas contamination: Because EB welding is done in vacuum, there’s no atmospheric gas contamination.  This results in the cleanest, highest-quality weld possible. For parts that require post-weld testing such as x-raying, EB welding is your best option.
  2. Less distortion and shrinkage:  EB welding is a very controlled process with minimal shrinkage. The EB spot size is under .003”,  which results in a very narrow weld and a very narrow heat affected zone. This minimal heat input results in less distortion and shrinkage. This is a major advantage for customers, since it allows finished parts to be welded without additional, post-weld processing.
  3. Excellent for refractory materials such as titanium, niobium, and tantalum. Since EB welding is done in a vacuum chamber, it prevents the exposure to oxygen that can cause these welds to fail. This is particularly an issue with welding titanium –  if the welds are exposed to oxygen, it can cause a serious failure called alpha casing.
  4. Will not damage heat-vulnerable materials:  Because of the low heat input of EB welding, temperature-sensitive parts can be located in proximity to the weld region.
  5. Ability to weld dissimilar metals:  This is another area where EB really shines. EB is a robust process for joining copper to stainless steel, and copper to nickel-based alloys including Inconels and Hastelloys, which would not be practical with other processes.
  6. Flexible process: I’ve welded materials less than .001” thick and up to 4” thick with the same machine.  It’s versatile enough to handle very deep to very shallow welds.
  7. Good for high volume, high quality welds:  EB welding technology has made leaps and bounds in productivity and accuracy in the recent past. Antechambers eliminate the pump down time from the equation, and seam tracking eliminates operator expertise. EB is now a very robust process.
  8. Automation:  EB welding has used CNC automation since the 1960s. In fact, some of the CNC EB machines that were built in the 1960s are still running today.  EB welding has proven longevity and is a very stable, repeatable process.
  9. Reflective materials: Because the delivery system of the energy in EB welding is electrons, not photons, EB can easily weld highly reflective materials like copper, platinum, and Hastelloys. Most laser beams would bounce right off these materials.
  10. Highly efficient:  EB welding is about 90 percent efficient – meaning 90 percent of the input power is reaching the part. That’s more important to us as welders rather than you the customer, but it’s another reason to love EB welding.

As you can see, there are many EB welding advantages that can provide solutions for your most challenging welding projects.  We’ll discuss these topics in more detail in future posts.  In the meantime, if you have a question or comment, feel free to leave it in the space below.  

And, as always, be sure to talk to a welding expert for the best recommendations on your particular project.