Rubber Mold Steels
The optimum cutting conditions for NAK55 vary by machine tools. Cutting tools
incorporating the recommended geometries will produce superb finish machined
surfaces, often completely eliminating grinding. NAK55 does not work harden.
- Use a new, sharp, premium grade of tap, TiN coated and spiral pointed.
- Use a tapping oil or highly chlorinated sulfurized oil. A mixture of 50%
kerosene and 50% cutting oil also works well.
Copper or graphite electrodes are suitable, or the steel may be used as an
electrode when burning mating halves together to achieve a fit.
The recast layer for NAK55 is soft (approximately 32 HRc). Other low alloy
grades such as P20, or more highly alloyed steels such as S7 and H13, have
recast layers equivalent to their high, as-quenched hardness. Because the EDM
white layer must be removed, the subsequent stoning or grinding of NAK55 is
much easier than with other steels.
NAK55 may develop a striped pattern with a low amperage finishing burn.
NAK55 is a Vacuum-Arc Remelted steel of exceptional cleanliness and as such,
it polishes beautifully.
Normal polishing techniques will yield excellent results. All stoning
operations should be done with reciprocating tools.
Note: No rotary stoning.
NAK55 steel contains uniformly dispersed manganese sulfides. These sulfides
reduce friction between the steel and the stones and actually improve
polishability. However, if a circular motion is used, the sulfides can be
lifted up from the surface creating the appearance of pits.
Therefore, it is
important to use a reciprocating stoning technique and light pressure during
Due to the sulfide content of NAK55, do not exceed 3000 grit Diamond Compound.
NAK55 is an ideal steel for photo etching or texturing. Vacuum-Arc Remelted
processing employs a continuous ingot casting procedure that nearly eliminates
chemical segregation of the alloying elements. This results in a clean,
The low carbon content of NAK55 is also advantageous, since carbon is a potent
alloying element and a major contributor to chemical segregation.
The uniform hardness of NAK55 assures even and uniformly textured patterns
regardless of workpiece size or depth of cavity. Furthermore, the ability to
easily restore a uniform hardness to welded areas is a tremendous advantage
for texturing in comparison to other steels.
NAK55 contains 1% aluminum and responds very well to nitriding. There are many
forms of nitriding and each has advantages. However, for molding die
applications, ion-nitriding, in particular, is very suitable for NAK55. When
employing standard gas nitriding do not exceed 950°F.
The ion-nitriding process is done in a controlled atmosphere. It is clean,
with minimal distortion, and can be done at temperatures that do not damage
Nitriding increases wear resistance and creates a hard surface ideal for
slides or dies that mold abrasive or mineral-filled thermoplastics. The
nitrided surface has a hardness over 60 HRc, improved corrosion resistance,
and can be polished to a finer finish than possible at base metal hardness.
Old logo milled out.
Cavity preheated 600-750°F.
Welded with NAK weld rod.
Post-heated at 950°F for one (1) hour
Cavity and weld ground down.
Cavity face polished.
Now engraved over welded area!
Design change capability (5th engineering change on this tool)
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.