Heat treating, before or after welding (or both)

 

I’ve blathered about heat, post-weld heat treatment, heat sinking, and blown a lot of hot air in general. Mostly, the discussion has focused on weld characteristics and weldability. This blog will take a slightly different angle.

Heat treating can be used for a variety of reasons: strengthening, annealing, stress relieving, and wear resistance to name a few. But, when is the best time to heat treat your welded part?

Generally, the answer is after all other operations are complete. But there are always exceptions.

If your material (say 17-4PH stainless) welds well in a hardened condition and the final assembly is quite large, it may make more sense to harden your subcomponents prior to welding and finish machining. That large assembly may require a larger oven, commanding a higher price.

Some of the 400 series stainless steels will tolerate being welding in the hardened condition with excellent strength characteristics retained.

Many grades of (weldable) aluminum do quite well when welded in the hardened condition. That large aluminum case fabrication may not fit into a chamber for heat treatment at all, and may not require any additional strengthening of the weld anyhow.

If you’re working with a material that is not readily weldable in the hardened condition, H13 steel for example, you will want to seriously consider machining and welding it in the annealed state, with the heat treat and temper as one of the last steps in the process. That will ensure that the characteristics of your part are homogeneous and free from defects.

You know I like to toss in a caveat or two into each of these posts, so here’s something to consider.

Just because heat treating beforehand yields a defect-free weld, that does not mean that the weld will always have the same characteristics as the parent material. Contact us at 860.653-0111 to consult with an expert who can tell you what to expect in your welded assembly so you can make the best decision possible about heat treatment.

Laser welding aluminum – stay light by welding with light

Warning: This is a blog, not a how-to guide.  I won’t be giving away any secrets today.  If you want those, it’ll cost you $$$!

This is a hot topic.  Aluminum is a popular material due to its light weight, ease of machining, relatively low cost, and good wear and corrosion characteristics.  It is commonly GTAW and MIG welded – think bicycle frames, hand rails, and truck tool boxes.

Aluminum is rapidly replacing other materials (stainless steel, steel) in much smaller applications – battery cases, tiny enclosures, and handheld devices to name a few.  This requires welding techniques that are both cost effective and capable of precision heat input.

Aluminum can be challenging to weld due to high thermal conductivity and a low melting point.  In thin parts, heat can rapidly build up and turn a precision component into a puddle of goo.  A delicate touch is required.  Enter laser technology.

This blog wouldn’t be very interesting if there weren’t a plot twist.  Here it is – aluminum is highly reflective to laser energy.  It requires a particularly bright laser to get energy into the part without doing more harm than good (or reflecting back into your peepers).  How fortunate that new laser technology has evolved to fit the bill.  As little as a decade ago, laser welding aluminum was considered to be limited to very specific applications.

Ok, so if you’ve read any of my other blogs, you know I like to use examples.  So, here’s one from a battery case application:

A prototyping house, specializing in making stainless steel prismatic cans for the battery industry, was looking to make a new line of prototypes from aluminum to save weight and impress their customers.  Their old style stainless cans could be welded in a variety of ways, but these new aluminum cans required very precise heat input to keep distortion to a minimum and prevent overheating during the weld process. 

A high power NIR laser was chosen for the application, and in conjunction with form tools and proper heat sinking (see our blog on heat sinking), excellent welds were achieved and thousands of pre-production cases were fabricated in very short order.  Not only were the welds structurally sound, they were cosmetically excellent, and the process time was shorter than that for the stainless cans.

Not all aluminum alloys are weldable, so be sure to speak with an expert when you approach your next small-scale aluminum project. 

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