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Plastic Mold Steels


Processing Guidelines

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.

  • Milling
    High-speed steel cutters give excellent results and very smooth machined surfaces. The best results are obtained with cutter geometries incorporating a positive rake angle of 15-20 and a relief angle of less than 10.

    Carbide cutting tools (P40 grade) will yield excellent results if the effective, positive rake angle of the insert and holder is approximately 8-15, and the relief angle is less than 10. When negative rake carbide is used, inserting grades with greater toughness than P40 gives better results. In general, a positive rake configuration is superior to a negative rake configuration for milling NAK80

    Note: It is important that the inserts have a concave face with a sharp chip breaking edge. TiAln coatings work well.

  • Grinding
    NAK80 grinds easily. It is recommended that it be ground wet.
  • Drilling
    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 packing material.
  • Tapping
    NAK80 is a 40 HRc steel. The following is recommended to facilitate tapping:
  1. Use a new, sharp premium grade of tap, TiN coated and spiral pointed.
  2. Use a tapping oil or highly chlorinated sulfured oil. A mixture of 50% kerosene and 50% cutting oil also works well.
  • EDM
    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.
  • Polishing
    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.

  • Texturing
    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, homogenous steel.

    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.

  • Nitriding
    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 950F.

    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 NAK80.

    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 ". 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.




Recommended Reading

Unique Characteristics


Typical Chemistry

Mechanical Properties

Physical Properties

General Design Guidelines

Processing Guidelines

Welding Guidelines


  International Mold Steel, Inc. 
1155 Victory Place
Hebron, KY 41048 USA 
Tel: 859.342.6000
Fax: 859.342.6006
Sales E-mail: [email protected]
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