Tool Repair by Welding

When tool and die steels wear or become unexpectedly damaged in service, metalformers may be able to weld-repair the worn or damaged areas. Welding not only can prove to be a structurally sound and economical repair method, but also can allow a metalformer to return damaged punch and die components back into service quickly.

To achieve desirable results, let’s review some important principles of tool and die welding. These principles were culled from a technical article titled, Welding of Tool Steels, which appears on the Key to Metals website (www.keytometals.com).

The article describes four basic types of die steels that can be repaired by welding: water-hardening, oil-hardening, air-hardening and hot-working steels. Successfully welding these materials depends on the use of a properly developed welding procedure and welding sequence, and careful selection of the welding electrode.

Selecting the appropriate electrode or filler metal, the stamper attempts to match the heat treatment of the die steel being repaired, since electrodes may not als be available to match the composition of the tool steel or the specific heat treatment of each tool or die component. Welding-electrode manufacturers provide information concerning each of their electrodes by specifying the types of tool or die steels for which they are designed, including the properties of the weldmetal deposited. Further assistance can be obtained by consulting with representatives of the electrode manufacturer.

The electrode selected for a particular tool and die repair must result in weld deposits of sufficient hardness in the as-welded condition. If the repaired tools lend themselves to grinding or EDM machining, treatment other than tempering is not required. However, if traditional machining is required, the weld-repaired sections must be annealed before machining 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.