Beat the Heat – How to Avoid HAZ on your Metal Projects

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Heat Wave. Deep Heat. Heat of the Night. While heat might be a good thing to sing about in a rock and roll song, it’s something to be avoided in most metalworking operations. That’s because, as with many things in life, too much of it can be a bad thing.

Heat leads to HAZ, an acronym for heat-affected zone. A metallurgist will explain in mind-numbing detail that HAZ is an area of metal that has experienced degradation of its internal microstructure after being exposed to high heat. This causes surface discoloration, as seen in the pretty rainbow pattern found in many welded or plasma-cut workpieces. It also weakens the metal, which can lead to cracking.

It’s for this reason that an aircraft engineer will tell you it must be avoided at all costs, as HAZ in turbine blades has been linked to engine failures during flight. HAZ’s negatives aren’t limited to flight-critical components, however. HAZ produces local hardening in some metals. It makes them more difficult to weld or bend, as well as more brittle (through a process known as hydrogen embrittlement) and less corrosion resistant.

Down with HAZ

Solution annealing can help. This is the process of heating a metal to a specific temperature and holding it there long enough for the crystalline structure within to reorient itself, although this is not always practical nor affordable, especially on larger workpieces. The bottom line? HAZ should be minimized on any mechanical or structural components whenever possible.

Okay, fine, you say. How? For starters, HAZ most often occurs during welding, although, as already mentioned, plasma and especially oxy-fuel cutting are also culprits. Simply put, the higher the temperature and the slower the speed, the greater the amount of HAZ. This is why laser cutting is the least HAZ-inducing of all thermal cutting processes. More on this in a moment.

If HAZ is entirely unacceptable, shearing is an option, albeit for square and rectangular shapes in thin-gage metals. Punching and nibbling work as well, although here again, the geometry and material thickness is limited. Abrasive water jet (AWJ) is an excellent choice, especially on very thick materials, but you’ll pay a price—AWJ is easily the slowest of the processes mentioned so far.

Beaming up

This brings us back to lasers. Despite the fact that the evil Auric Goldfinger tried to slice James Bond in two with an industrial laser while delivering the infamous line, “No, Mr. Bond, I expect you to die,” most are put to far less violent purposes. Lasers cut quickly and cleanly. They use a relatively small beam diameter that minimizes the amount of heat transferred to the adjoining areas. Of all the thermal cutting processes—plasma, oxy-fuel, and laser—it’s the latter that creates the least amount of HAZ, while also being the most accurate and, in many cases, the most cost-effective.

How the parts are laser-cut also plays a role in part quality. Look for a cutting service that uses high-purity nitrogen for the cleanest, most oxidation free surface possible. Just note that thicker materials may require the use of oxygen as an assist gas, which might mean some edge prep with a wire brush or chemical cleaner before painting, welding, or plating.

At SendCutSend, we use industrial lasers to slice and dice carbon steel, stainless steel, aluminum, copper and brass, titanium…the list goes on (no British Secret Service agents, however). Depending on the metal, thicknesses up to 1/2″ are available, with a maximum size of 46″ x 118″. Our projects range from signage to precision machine components, as well as parts that will later be welded, bent, formed, or assembled. And if you need painting, anodizing, or other types of finishing, we can help there, too. Just give us a call or upload a file.

As the immortal Glenn Frey once told us, the heat is on. It’s up to you to stay cool.

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