Injection mould design

Injection Mould Design: Key Principles, Specifications & Best Practices

Injection mould design is one of the most critical stages in the plastic part manufacturing process. A well-designed mould ensures product quality, dimensional accuracy, repeatability, and cost efficiency. Whether you’re developing a simple consumer item or a complex automotive component, a robust mould design is essential to achieving consistent, defect-free production.

In this blog, we’ll explore the fundamentals of injection mould design, important specifications, design considerations, and answer frequently asked questions to help guide your next tooling project.

What is Injection Mould Design?

Injection mould design refers to the engineering and structuring of moulds used in plastic injection moulding. The mould is a custom-fabricated tool that shapes molten plastic into a solid form when injected under pressure.

A typical injection mould includes core and cavity plates, cooling channels, runners, gates, and ejector systems. The design of these elements directly impacts cycle time, part quality, cooling efficiency, and mould life.

Types of Injection Moulds

Understanding the different types of moulds is crucial when initiating a tooling project:

1. Two-Plate Mould

The most common type, ideal for simpler parts. The mould splits into two halves — one fixed and one moving.

2. Three-Plate Mould

Features an extra plate to allow easier ejection and more flexible gate placement, typically used for more complex or multi-gated parts.

3. Hot Runner Mould

Uses heated channels to maintain molten plastic within the runner system, reducing waste and improving cycle time.

4. Cold Runner Mould

Allows the plastic in the runner to cool and solidify with each cycle. It's cost-effective but creates more waste.

Specifications of a High-Performance Injection Mould

Here are key technical specifications and design elements that define a reliable injection mould:

Key Considerations in Injection Mould Design

Designing a mould involves a balance between function, durability, and manufacturability. Below are the essential design factors:

1. Part Geometry

Understanding the shape and complexity of the part is critical. Sharp corners and uneven wall thicknesses should be avoided to reduce stress concentrations and improve flow.

2. Wall Thickness

Uniform wall thickness ensures consistent cooling and reduces defects like warping or sink marks. Aim for walls between 1 mm to 4 mm, depending on the part size and material.

3. Draft Angles

Include draft (typically 1° to 3°) to facilitate easy part ejection from the mould without damaging the part.

4. Cooling Channel Design

Efficient cooling is essential for reducing cycle time and improving part consistency. Use optimized baffle and channel placements to evenly cool the mould.

5. Material Selection

Choose the right material for the mould components based on the expected production volume, cycle time, and type of plastic being moulded.

6. Venting

Proper venting prevents trapped air and gas burns. Vents should be strategically placed in low-pressure areas.

Common Challenges in Mould Design

Even experienced designers encounter issues. Here are some common problems and how to avoid them:

• Short Shots: Caused by inadequate venting or poor runner design.
• Flash: Results from excessive injection pressure or worn parting lines.
• Warping: Uneven cooling or inconsistent wall thickness.
• Sink Marks: Thick sections that cool slower than surrounding areas.

Early collaboration between the product designer and toolmaker is key to solving these issues before production begins.

FAQs About Injection Mould Design

Q1. How long does it take to design and build an injection mould?

A: The design phase typically takes 1–3 weeks, while mould fabrication can take 4–8 weeks depending on complexity and revisions.

Q2. What’s the difference between prototype and production moulds?

A: Prototype moulds are usually made from aluminum and built quickly for low-volume testing, while production moulds use hardened steel for durability and mass production.

Q3. Can a single mould produce multiple parts?

A: Yes, multi-cavity moulds are designed to produce multiple identical parts per cycle, while family moulds can create different parts in the same mould.

Q4. How do I choose between a hot runner and cold runner mould?

A: Choose hot runners for high-volume, waste-reduction, and better flow control. Cold runners are simpler and more cost-effective for lower-volume applications.

Q5. What software is used for mould design?

A: Common tools include SolidWorks, Siemens NX, AutoCAD, CATIA, and Moldflow for simulation and analysis.

Final Thoughts

Injection mould design is the foundation of any successful plastic injection moulding project. A well-designed mould can improve product quality, reduce production costs, and extend tool life dramatically.

Investing time in mould design, simulation, and collaboration with skilled toolmakers pays off in the long run. Whether you're building a single prototype or launching mass production, understanding the principles of mould design helps you make smarter decisions for your product and business.