Category: Mold Repair

A Really Tiny Laser Welded Mold Repair

This plastic part had a problem with localized flashing at the parting line, making it difficult to assemble to its mating part. A tiny nick on the parting line of the mold cavity was the source of the problem. The welded repair needed to be very delicate so it could be re-finished by hand without needing to go back into the EDM machine for re-burning.

1. THE PLASTIC PART: This tiny flash was all it took to mess up the assembly.

2. THE DEFECT IN THE MOLD CAVITY: The cavity is P20 Hi- Hard mold steel and the ding is circled in blue and red. Also visible laying across the penny is a bit of welding wire 0.005″ in diameter (about the thickness of a human hair). Welding wire in this size is very difficult to handle; it’s so fine you can’t feel it with your fingers. I have a special technique for managing wire this small: I use microsurgical needle drivers left over from my days as a dentist to hang onto it…that’s what caused the nicks you can see along its length.

3. THE REPAIRED DEFECT: The challenge with these very tiny welds is not to burn away the corners of the cavity with the welding pulse, and to place the tiny, wiggly welding wire in the proper spot without blowing it out of position with the shielding gas. It takes a lot of practice to do this with confidence…I used up a good half of my 0.005″ wire stock just learning how to handle it, and I can’t have coffee before doing this class of repair welding.

4. THE INSERT ON THE BENCH READY FOR FINISHING: All that’s needed now is a couple of minutes with a ruby stone and the mold can go back together.

laser welding: mold repair: worn core pins

The cores have worn in the corners and are flashing during molding. The repair must not gouge the corners of the existing part, and must be built up enough for refinishing. The material is P20 mold steel.

laser welding: mold repair: machining mistake

The corner was gouged with a cutter during rough machining. The repair must completely fill this large defect, but the heat of welding cannot be allowed to distort the part and shouldn’t disrupt the copper plug that seals a waterline in this part.

The material is 420M stainless at 52 RC.

This is about as big a weld volume as can be conveniently handled by laser micro welding. Bigger weld areas are better handled with TIG, but at the risk that the part will distort.

It is possible to do the rough welding using TIG and manage areas of distortion afterward, with the laser welder.

1. TOP VIEW: Note the huge number of individual welds required to fill this defect. (Each hemispherical mark you see, is formed by a discrete weld deposit using a 0.015” diameter 420 M stainless welding wire under argon gas coverage).

2. SIDE VIEW: The weld is about 4 layers deep at its thickest.

3. AFTER MACHINING: some defects are still visible and will be corrected by spot weld placement.


5. FINAL FINISHING: At approximately 40X magnification, the defect is barely discernable, and is completely invisible to the naked eye.

laser welding: mold repair: changing engraving

The engraving was changed per customer request.

The surface geometry to enable re-machining the insert was not available, therefore the welding needed to be delicate, allowing it to be re-finished using only polishing stones. On the left side, a logo has already been welded and hand stoned to 600 stone finish.

1. The lettering is approximately 1/8” (3.2mm) tall. The welds stand proud of the surface less than 0.003” (0.1mm). The material is P20 mold steel.

2. A DETAIL SHOT: (From another insert with slightly larger letters)


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