Plastic Mold Steels
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.
- 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
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
- 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.
- 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
- 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
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.
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.