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Plastic Mold Steels


Processing Guidelines

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.

  • 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 1520 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 a 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 NAK55.

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

  • Grinding
    NAK55 grinds easily. It is recommended that it be ground wet.
  • Drilling
    NAK55 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 NAK55 is a chip packing material.
  • Tapping
    NAK55 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 sulfurized 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 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.
  • Polishing
    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 buffing.

    Due to the sulfide content of NAK55, do not exceed 3000 grit Diamond Compound.

  • Texturing
    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, homogenous steel.

    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.
  • Nitriding
    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 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 NAK55.

    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 600-750F.
Welded with NAK weld rod.
Post-heated at 950F 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.



Recommended Reading

Unique Characteristics


Typical Chemistry

Mechanical Properties

Physical Properties

General Design Guidelines

Processing Guidelines

Welding Guidelines

Technical Center


  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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