Rubber Mold Steels
The optimum cutting conditions for NAK80 vary by machine tools. Cutting tools
incorporating the recommended geometries will produce superb finish machined
surfaces, often completely eliminating grinding. NAK80 does not work harden.
NAK80 grinds easily. It is recommended that it be ground wet.
NAK80 drills easily. The cutting speed should be lowered as the drill diameter
increases. A smaller than standard twist angle and shorter length will reduce
the danger of broken tools. Peck cycles are recommended, as NAK80 is a chip
NAK80 is a 40 HRc steel. The following is recommended to facilitate tapping:
- Use a new, sharp premium grade of tap, TiN coated and spiral pointed.
- Use a tapping oil or highly chlorinated sulfured 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 NAK80 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 NAK80 is
much easier than with other steels.
NAK80 is Vacuum-Arc Re-melted steel of exceptional cleanliness and as such, it
polishes to a SPE/SPI #1 finish. Normal polishing techniques, with light
pressure, will yield excellent results. It is also recommended to use light
pressure during buffing.
NAK80 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 NAK80 is also advantageous, since carbon is a potent
alloying element and a major contributor to chemical segregation.
The uniform hardness of NAK80 assures even and uniformly textured patterns
regardless of work-piece 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.
NAK80 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 NAK80. 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.
Note: All clearance values are at molding temperature.
- Sharp Corners
Sharp or square corners serve as focal points for concentrating stresses that
build up in molds and dies during operating conditions. A .100" - .120" radius
to all corners is recommended, especially large box-type molds. To avoid these
stresses, the thickness of the material backing up a sharp corner should be
increased by 50% compared with softer steels.
- Thin Sections
Due to the toughness limitations of NAK80, it is suggested that other types of
steel be inserted at thin rising sections (4-to-1 ratio or more) and that a
radius be put on the base of rising sections from the initial design stages.
- Cavity Depth
Cavity depth should be limited to no more than 50 - 55% of the block thickness
in high-pressure injection molds.
- Cooling/Heater Water Lines
Do not locate cooling or heater lines directly below the corner of a mold
cavity. The ideal location for heating or cooling lines is located three (3)
times the hole diameter from the molding surface. 1.5 times the hole diameter
from the molding surface is the minimum. Example: a 1/4" diameter waterline
should be at least 3/8" away from mold surface and preferably ¾". The distance
between lines should be five (5) times the line diameter minimum.
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.