Plastic Injection Molding Questions: 17 Top FAQs

Aluminum seldom makes sense if a mold is fabricated in China (which we cover later). Steel is the most common injection mold material, but choosing the right injection mold steel material is similar to selecting the foundation for a building: it dictates the mold's durability, performance, and ultimately, the quality of your parts. As engineers, we understand the critical nature of this decision.

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Let's delve into the three most common types of hard steel and pre-hardened steel utilized in injection molding:

Hard Steels:

1. / / H13: This trio offers a workhorse option. After hardening, they achieve a Rockwell C hardness of 49-53 HRC, making them suitable for ordinary hardening molds. Their versatility allows for applications across various projects.

ESR: This steel takes the performance of the previous group a notch higher. It boasts the same hardness range (49-53 HRC) after hardening but excels in applications demanding both durability and a highly polished finish.

S136 / S136SUP / : Don't be fooled by the 'steel steel' reference ' these are actually high-performance stainless steels. Their strength lies in corrosion resistance, making them ideal for molds processing materials like POM and PVC, which can be corrosive to standard steels. Additionally, they hold their own when it comes to achieving a polished finish.

Lifespan: Mold tooling made from hard steels like 1.#, #, and # will usually last for around 300k-500K shots, but can reach 1 Million if the mold structure is simple.

Pre-Hardened Steels:

S50C / S55C: These steels offer a cost-effective option for mold bases, providing adequate strength and machinability. However, their lower hardness limits their suitability for high-wear applications.

718 / 718H: Renowned for their toughness and ability to achieve a good surface finish with standard polishing techniques, 718 and 718H are popular choices for mold cavities and inserts. Their well-rounded properties make them a versatile option for various applications.

738 / 738H: Offering superior rigidity compared to 718 grades, 738 and 738H excel in core and insert applications. While their polishing capabilities are considered 'ordinary,' their rigidity often outweighs this limitation for specific applications.

A Note on P20: It's important to clarify the perception of P20 steel in China. While technically encompassing a series that might include materials like 718 or 738, the term 'P20' in China often refers to a lower-grade steel with potentially less desirable properties compared to the 718/738 series.

NAK80 / XPM: The champion of pre-hardened steels, NAK80 boasts a hardness of 37-43 HRC. This, coupled with its excellent polishing capabilities, makes it the go-to choice for molds requiring high-precision parts from materials like PC, PA+GF, and PC+GF.

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Remember, this is just a starting point. Selecting the optimal steel grade requires careful consideration of factors like part complexity, plastic-type, production volume, and budget. Consulting with experienced mold makers and material suppliers is crucial to ensure you make the best choice for your specific project.

Lifespan: For pre-hardened materials the mold life is usually 100K-300K shots.
In particular:

• 278#; 718#; p20#: 100k-200K;
• NAK80; XPM: 200-300K

Watch these videos on how to test steel's properties which may help you to select the types you require.

Both the 718H and P20 are plastic mold steels, but it is quite certain that the 718H.718 is an improved p20 steel, and the corresponding US steel is P20 +Ni.Although 718 USES the same as P20, but 718 has better hardenability and superior performance, it can produce large size, high-grade plastic mold forming parts.

Delivered Hardness'

pre-hardened to HB330-380

Comparable Standard:

WNr.1.

Characteristics:

• No hardening risks
• No hardening costs
• Time saving
• Lower tool costs
• Modifications easily carried out
• Can be subsequently nitrided to increase surface wear resistance and locally flame hardened to reduce surface damage
• Good polishing and photo-etching properties
• Good machinability
• High purity and good homogeneity
• Uniform hardness

Application:

• Injection moulds for thermoplastics
• Extrusion moulds for thermoplastics
• Blow moulds
• Forming tools
• Structural components, shafts

Contact us to discuss your requirements of 718h steel. Our experienced sales team can help you identify the options that best suit your needs.