How to select mold materials, harden VS soften steels in mold building?
In the plastic mold manufacturing, selecting the tooling steel is very important to project success. Harden and soft tooling(or named as Pre-harden) represent two different production conditions. Each type of steel is chosen based on the specific requirements of the application such as the type of plastic materials, expected production volume, required surface finishing, and the need for heat or corrosion resistance. This article aims to clarify the manners of mold building steel to make informed decisions aligned with their project requirements and objectives.
Pre-hardened Mold Steels
1. P20 (DIN 1.2311/1.2738)**: Widely used for medium to large-sized, general-purpose plastic injection molds for automotive parts, household appliances, and consumer goods.
2. 718/718H (DIN 1.2738): Suitable for high precision and high surface finish molds requiring good machinability and polishing. Commonly used in the electronics and packaging sectors.
3. NAK80 (DIN 1.2312): Known for its excellent polishing and dimensional stability, ideal for molds producing precise and mirror surfaces, often found in medical and optical applications.
4. S136 (DIN 1.2083): A corrosion-resistant steel used in molds that require high wear resistance and contact with aggressive plastics or water, prevalent in the production of clear and transparent items.
Hardened Mold Steels
1. H13 (DIN 1.2343/1.2344): A heat-resistant steel utilized for hot runner systems and molds subjected to high thermal stresses, typically in the automotive, aerospace, and die casting industries.
2. D2 (DIN 1.2379): Though primarily a cold work tool steel, D2 can be used for wear-resistant mold components demanding extreme hardness, seen in applications like extrusion dies.
3. SKD61 (JIS standard, similar to DIN 1.2343): Used for high-temperature applications due to its toughness and wear resistance, popular in the production of complex molds for automotive and precision components.
4. 420SS (DIN 1.2083): Stainless steel with high hardenability, suitable for molds handling corrosive plastics or those requiring high polish and long service life, common in the packaging and medical device manufacturing.
Comparative Analysis:
When considering the cost, lifespan, and product quality in the context of plastic molds, both hardened and non-hardened molds have their unique characteristics. Here is a brief analysis::
Cost:
Hardened Molds: The cost of hardened molds is typically higher due to the additional processes involved in the heat treatment and machining process times. However, the higher initial investment can often be justified by the longer lifespan and improved production quality these molds provide.
Non-Hardened Molds: Non-hardened molds tend to have a lower initial cost as they do not require hardening processes. However, they may require more frequent maintenance and replacement, leading to higher long-term costs.
Mold Life:
Hardened Molds: Hardened molds are designed to withstand higher pressures, temperatures, and abrasion, resulting in a significantly longer lifespan. They can often last for tens of thousands to hundreds of thousands of production cycles.
Non-Hardened Molds: Non-hardened molds, on the other hand, have a shorter lifespan due to their lower resistance to wear and tear. They may require replacement after several thousand production cycles, depending on the application.
Production Quality:
Hardened Molds: Hardened molds provide improved dimensional stability and surface finish, resulting in higher-quality products. The harder steel surface also resists scratching and abrasion, maintaining the mold's precision over a longer period.
Non-Hardened Molds: Non-hardened molds may not achieve the same level of dimensional stability and surface finish as hardened molds. However, they can still produce acceptable quality products for many applications, especially when the requirements are not as stringent.
In summary, the choice between hardened and non-hardened plastic molds depends on the specific requirements of the application, including cost, lifespan, and production quality. It is essential to carefully evaluate these factors to determine the most suitable mold type for your needs.
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