How to Choose the Right Steel for Plastic Injection Molds
Choosing the right steel is one of the most critical decisions in injection mold manufacturing. The type of mold steel directly affects mold durability, production efficiency, part quality, and overall tooling cost.
Many product developers focus heavily on part design and material selection but overlook the importance of mold steel. In reality, using the wrong steel can lead to premature mold wear, unstable production, and expensive repairs.
At CNMOULDING, a Shanghai-based mold manufacturer established in 1997, we have manufactured hundreds of injection molds for customers worldwide. Through years of experience in automotive, medical, and consumer product industries, we have learned that proper mold steel selection is essential for reliable long-term production.
In this guide, we explain the most common injection mold steels, how to choose the right material, and how proper steel selection can reduce tooling cost and improve mold life.
Why Mold Steel Selection Matters
Injection molds operate under extreme conditions during production. Molten plastic is injected into the mold cavity at high temperature and pressure, and this cycle may repeat hundreds of thousands or even millions of times.
If the mold steel is not suitable for the application, several problems may occur:
mold wear after short production cycles
surface damage affecting part appearance
corrosion caused by certain plastic materials
frequent mold maintenance and downtime
For manufacturers producing high-volume parts, these issues can significantly increase production cost.
Selecting the right mold steel ensures that the mold maintains dimensional accuracy and consistent product quality throughout its service life.
Common Injection Mold Steels Used in Manufacturing
Several types of steel are commonly used in injection mold manufacturing. Each steel has different mechanical properties and is suitable for different production conditions.
P20 Mold Steel
P20 is one of the most widely used mold steels for plastic injection molds.
Key Characteristics
good machinability
moderate hardness
cost-effective for medium production volumes
Typical Applications
P20 is commonly used for:
consumer products
household appliance components
medium-volume production molds
Because of its balanced performance and relatively low cost, P20 is often selected for standard injection molds.
However, for very high production volumes or abrasive materials, harder steels may be required.
H13 Mold Steel
H13 is a high-strength tool steel known for its excellent resistance to wear and high temperatures.
Key Characteristics
high hardness and durability
strong resistance to thermal fatigue
suitable for high-pressure molding processes
Typical Applications
H13 is commonly used for molds producing parts made from abrasive materials, such as plastics containing glass fiber reinforcement.
These materials can cause rapid wear on softer mold steels, making H13 a more reliable choice.
S136 Stainless Mold Steel
S136 is a corrosion-resistant mold steel often used for high-precision applications.
Key Characteristics
excellent corrosion resistance
superior polishing capability
high dimensional stability
Typical Applications
S136 is commonly used for:
medical device components
optical parts
transparent plastic products
Its excellent polishing performance allows manufacturers to achieve mirror-like mold surfaces required for high cosmetic standards.
Real Case Study: Automotive Connector Mold
A European automotive customer contacted our Shanghai engineering team to develop an injection mold for a PA66 + 30% glass fiber connector housing.
Project Requirements
Material: PA66 GF30
Production volume: 400,000 parts per year
Tolerance requirement: high precision
Initial Steel Selection Problem
The customer initially planned to manufacture the mold using P20 steel to reduce tooling cost.
However, PA66 reinforced with glass fiber is highly abrasive. During production, the glass fibers can gradually wear down the mold cavity surface.
Based on our engineering experience, using P20 steel in this case would likely cause mold wear after approximately 50,000–70,000 cycles, requiring frequent maintenance.
Engineering Recommendation
After evaluating the production requirements, our engineering team recommended upgrading the mold steel to H13 hardened tool steel.
Although the tooling cost increased slightly, H13 provides significantly higher wear resistance for glass-filled materials.
Final Results
After switching to H13 steel:
mold life exceeded 400,000 cycles
mold maintenance frequency was greatly reduced
production stability improved significantly
In the long term, the customer actually reduced total manufacturing cost by avoiding frequent mold repairs.
This example shows that proper steel selection can save both time and money during production.
How to Choose the Right Mold Steel
Selecting the best steel for an injection mold requires evaluating several key factors.
Production Volume
Higher production volumes require more durable mold steels.
For example:
prototype molds → aluminum or P20
medium production → P20 or NAK80
high-volume production → H13 or hardened steel
Plastic Material Type
Some plastics are more abrasive or corrosive than others.
Examples include:
glass fiber reinforced plastics
flame-retardant materials
PVC or corrosive resins
These materials require more durable or corrosion-resistant mold steels.
Surface Finish Requirements
Products with high cosmetic standards often require mold steels with superior polishing capabilities.
For example:
optical lenses
medical housings
transparent plastic components
These applications typically require steels such as S136 stainless mold steel.
Tooling Budget
While premium mold steels provide longer mold life, they also increase initial tooling cost.
The key is balancing tooling investment with production requirements.
An experienced mold manufacturer can help determine the most cost-effective solution.
Why Work With an Experienced Mold Manufacturer
Choosing the right mold steel requires deep understanding of both material behavior and mold manufacturing processes.
At CNMOULDING (Shanghai), our engineering team evaluates every project based on:
product geometry
plastic material selection
production volume
mold life expectations
Our factory has been manufacturing injection molds since 1997, providing both mold manufacturing and plastic injection molding services for customers worldwide.
We operate under strict quality systems including:
ISO9001 quality management certification
ISO13485 certification for medical device manufacturing
These standards ensure consistent product quality and reliable manufacturing processes.
Start Your Injection Mold Project
If you are developing a new plastic product and need professional advice on injection mold steel selection, our engineering team can help evaluate your design and recommend the most suitable solution.
Contact our Shanghai engineering team today to discuss your project and receive expert support for your mold manufacturing and injection molding production needs.
