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How to choose plastic injection mold steel?

A complete set of injection mold have a variety of parts, each part of the mold pays different role and the steel to use are different as well. Choosing the proper mold steel can ensure high quality mold, efficiency and lowest cost.
Plastic injection mold steel
There are some basic principles to follow when you choose steel for injection mold.

Machining Properties
Most of the mold making jobs are done by machining, ease of machining can shorten the manufacturing time. Also good machining properties can extend the life of cutting tools, improve cutting performance, reduce surface roughness to get high precision parts.

Hardness and wear resistance
Surface roughness, dimensional accuracy of plastic parts and injection mold life heavily rely on the surface hardness and wear resistance of mold steel. Therefore, plastic injection molding surface of the mold requires sufficient hardness, the hardness after quenching should be not less than 55 H RC.

Strength and toughness
During plastic injection molding process, the mold plates stand hundreds of thousands of clamping pressure, especially big-sized and complicated structure injection molds, the mold steel used must have high strength and good toughness to performance well.

Polishing properties
To get high glossy plastic parts, the mold cavities required a high glossy surface, the mold steel should not have holes, impurities and other defects after polishing, steel S136, H13 etc has very good polishing properties.

Heat treatment
The mold steel often needs heat treatment process to achieve the necessary hardness, so the steel requires good heat treatment properties. Plastic injection mold cavities has complex design usually, it gets more difficult to process after quenching, or sometimes it just simply can not be processed. So choose proper mold steel that has less deformation after heat treatment to ease manufacturing.

Good corrosion resistance
Some plastics and additives will produce corrosive gases during injection molding, mold steel selected should resist to corrosion. For example, the PVC materials, mold steel have to be S136.

You can also employ nickel, chromium and other methods to improve the corrosion resistance of mold cavities.
very good information thank you.
- - - -> by: Farag Gad

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