Should I Laser or TIG My Mold?

Hardness study gives guidance to best direction on tool materials and takes the guess work away 

By Dave Martin 

Welding. Some fear it, some embrace it, but most have never seen quantifiable results. It either works or it doesn’t.  

The TIG welding machine is a highly controlled, digital machine operated by a master welder, while the LASER welding process comprises a 120-amp output with a workstation air ride table that allows precise control over the placement of the weld. It is important to note that many welds – LASER or TIG – result in a bad outcome due to such factors as:

• No one knowing what the parent material is

• An unqualified technician

• Poor welding materials

• Older machines that have only nuclear heat setting modes. “Gas and Blast!".  

Proper storage of welding rods is also very important, as it helps to maintain their integrity by preventing corrosion and maintain their original properties.  

Once these variables have been controlled, a true comparison of the technologies can be made with some minor exceptions. TIG welding always produces a much larger heat affected zone right next to the bead, which never has the same integrity as the parent steel and shrinks causing heat sink areas and discoloring. While the LASER weld does have a heat affected zone it is miniscule and almost undetectable. Penetration of the LASER is also very shallow but firmly attaches. The LASER takes much longer when large areas of build up are required and is a more expensive technology to procure. 

In our hardness study, we took popular mold materials and verified "parent hardness" right from the mill, then, using the suggested welding rod, we applied a bead of material using the steel addition technologies of TIG and LASER. We then re-measured the hardness at the top of the crown of weld, followed by grinding the crown down flat to the parent surface in order to see what the net hardness level was before and after each weld was applied. 

The table below shows Rockwell scale b and C outcomes of the parent material, readings at the top of the ungrounded bead and readings after grinding. It dispels the myth that a weld is softer on high hardness materials and generally tells us that either technology yields great hardness on high hardness materials. The softer Mold materials, such as high density copper heat transfer materials (for example, AMPCO 940) and aluminum are best LASER welded.  

In conclusion, a well trained welder with good materials and a state-of-the-art machine can weld with equal success hardened tool steels, except that TIG produces heat sink and discoloring. LASER is better for textured surfaces and all softer materials of less than P-20 hardness. LASER also requires less clean up time in intricate areas and applies all localized heat that does not affect the areas surrounding the weld.

Dave Martin is President of Accu-Mold, Inc., located in Portage, MI.  Accu-Mold is a full-service mold manufacturing company that also offers both Laser and TIG welding services, among its other specialties.  To find out more about welding services or request additional mold and die material trials, call 269-323-0388 or email Accu-Mold at laser@accu-moldinc.com.  Website: www.accu-moldinc.com.

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