Page 47 - MetalForming April 2011

Tooling by Design
the weld-repaired sections must be annealed before machin- ing and then re-heat treated afterwards.
According to the referenced Key to Metals article, the resulting hardness of the weld deposit will be influenced by the following parameters:
• Preheat temperature, if used;
• Welding technique and welding sequence;
• Dilution of the weldmetal with base metal;
• Rate of cooling within the weld pool; and
• Tempering temperature of the welded tool after welding. Uniform hardness of the as-welded deposit can be
obtained if the temperature of the die section remains con- stant during welding. However, the temperature of the weld- ed section must not exceed the maximum drawing temper- ature for the particular class of tool steel being welded. Always follow the tool-steel manufacturer’s recommendation regarding these temperatures.
Use these guidelines when developing a welding proce- dure for repairing tools and dies:
Uniform hardness of the as-welded deposit can be obtained if the temperature of the die section remains constant during welding.
• Properly identify the tool steel being welded.
• Select a welding electrode to match the class of tool-steel and/or heat treatment.
• Establish the correct weld joint design, and prepare the joint properly for the repair.
• Preheat the workpiece.
• Deposit the repair weld in accordance with manufac- turer’s recommendations.
• Post-heat the repaired tool to temper the weld deposit or the repaired part.
Other tips:
When making large repairs to worn cutting edges or sur- faces, grind the damaged area sufficiently under-size to allow a uniform weld depth of at least 1⁄8 in. When repairing deeply damaged cutting edges that require multiple weld passes, it may be necessary to start at the bottom and grad- ually fill the damaged areas. To minimize weld shrinkage, warping (distortion) and cracking, peen the weldmetal while hot. Distortion also can be minimized by properly preheat- ing the die section prior to welding.
After repair welding, allow the die section to cool to room temperature, and then temper it by reheating to the recom- mended tempering temperature based on the type of tool steel and the welding electrode selected. To minimize the pos- sibility of weld-related service failures, employ a welder experienced with tool and die welding, and always follow the recommendations of the tool-steel and welding-electrode manufacturers. MF
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