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Plastic Mold Steels NAK55 Welding Guidelines Welding of NAK55 should be performed employing only NAK-W Welding Rods. NAK-W Welding Rods are copper-coated for either TIG or Heli-Arc welding. Employ only recognized, safe shop welding practices. General The die or mold should be free of all oil, rust, scale residue, or any other potential contaminates before attempting to weld. All cracks and surface treatments should be completely removed before attempting to weld. Sharp corners should be rounded to a minimum radius of .120". To repair a crack, remove sufficient stock to eliminate the crack and insure only sound material remains. Dress the corners where stock was removed to eliminate any square corners by rounding to a minimum radius of .120". Preheating Prior to making a welding repair, preheat the piece to be repaired by slowly heating in a furnace or with a gas burner to between 600° and 750°F. Heating from the bottom is recommended if a gas burner is used. Uniform temperatures within the recommended range should be maintained during the entire period of time required to complete the repair. Ideally, the entire mold should be heated in a furnace to achieve uniform temperatures. This is easy to do for small molds, but may not be practical, or possible, for large molds. Localized preheating is the only option for large molds, and attention must be paid to the following: Preheating temperature must be achieved to at least 2" away in all directions from area to be welded. Use an oxygen-propane gas burner with a low flame temperature. Heat the mold carefully and gradually, maintaining a distance of 18" between the flame and the mold surface. Apply a temperature choke or a surface contact thermometer to accurately measure the preheating temperature. Re-heat as necessary during welding to maintain the above 600°F range.   Technique Use DC normal polarity Use lowest possible amperage for the job Use backhand welding - weld away Use smallest diameter rod possible Weld small beads Peen weld as necessary Upon completion of welding, proceed immediately to post-weld heating procedure   Post-Weld Heating It is imperative that the following procedure be carefully followed to assure the welded section is completely restored to a uniform hardness: The weld-repaired piece should be heated to between 860°F-940°F and held at this range for a minimum of one (1) hour to re-age. This re-aging process should be conducted immediately after welding. Heating with a furnace is highly recommended, however a gas burner may be used as a last resort. If a gas burner is used, heating from the bottom is recommended, however the entire welded area, and as much as 2" surrounding the weld, must be kept in the post heat temperature range for a minimum of one (1) hour. Cool slowly to room temperature. Note: Post-weld heating should be performed after every three layers of weld buildup in order to alleviate welding stress and avoid over-aging of adjacent parent metal. Conditions Rod diameter Electrode diameter Current/Amps .0470" .0470" 40~70 .0630" .0630" 70~150 .0946" .0946" 150~250 All technical and engineering data and suggested procedures, specifications and applications contained in this publication are for general information only. Daido Steel, International Mold Steel and/or their distributors disclaim any and all express or implied warranties of merchantability, suitability for any particular purpose or use, or freedom from infringement of any patent, trademark or copyright. NAK80® is a registered trademark of International Mold Steel, Inc. and Daido Steel Limited.

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