Mold material for plastics injection

In this lesson I will show how to choose the mold material for plastics injection. As you know, injection mold mass production much so durability of the material is very important. If we choose material not good, we will lose much money for repair mold when mass production.

I. Mold material for plastics injection must follow.

+Abrasion Resistance.
Consider how long a mold will last or if parts will accurately maintain their dimensions depending on production quantity.
+Polishing.
Consider how much a mold should be polished for the desired part finish.
+Machinability.
Use a solid material that can process mold or parts good.
+Heat Treatability.
Use a material that can be processed evenly by heat treatment.
+Durability.
Use a material that is durable against pulling stress, compression stress, or bend stress during the molding process.
+Heat Conductivity.
Use a material whose temperature can be easily controlled while cooling the mold.
+Delivery / Cost.
Use a low-cost material that is easy to get in the market as well as delivered securely and immediately.

II. Mold material for plastics injection.

The different parts of a mold have different function so they require different materials. Some parts need hardness, abrasion resistance, working in high temperature,… but some parts do not need. We can choose the material by the function of the parts.

+ Sliding parts such as guide bush, guide pin, return pin, ejector pin,… that require high hardness, does not has scratch in using so we need to use carbon tool steels (JIS symbol: SK3 – SK7).
+ The parts do not require strength and hardness such as ejector plate, spacer block, support pillar,… we can use Rolled steel (JIS symbol: SS400).
+ The parts assembly with injection machine, mold such as fix plate, moving plate, support plate, locating ring, or sprue bush,… We can use carbon steel (JIS symbol: S25C – S55C) that can quenching & tempering
+ A part need hardness and abrasion resistance, working in high temperature such as: core insert and cavity insert,… we can use Alloy Tool Steels (JIS symbol: SKD, SKS)
The table below shows the steels that are used as a mold plate material.