Beginner’s Guide to Injection Mould Design
What is Injection Moulding?
Injection Moulding is a manufacturing process used to produce plastic parts by injecting molten plastic into a metal mould, where it cools and solidifies into the final shape.
Why Learn Injection Mould Design?
- It’s used in automotive, electronics, toys, packaging, and medical industries.
- Helps in designing cost-effective and mass-producible plastic products.
- Essential for mechanical/product designers and engineers.
Keychain / Keyring / Key Holder
Why Start with a Keychain?
- Very simple shape
- No complex features or moving parts
- Good practice for text, holes, and basic mould principles
Design Practice:
Feature Purpose Beginner Tip
Parting Line Where the mould splits Usually along the mid-plane
Draft Angle Allows part to come out Use 1°–2° on vertical walls
of the mould
Text For logos or names Use engraved text – easier to mould
Hole/Ring Loop For attaching to keyring Keep hole diameter ≥ 2 mm
Gate Location Entry point for plastic Place on edge or back to avoid visible marks
Ejector Pins Push part out after cooling Put on flat, hidden areas
Materials for Keychains:
- ABS – Strong and glossy
- PP (Polypropylene) – Flexible and tough
- TPE/TPU – Rubber-like feel
- Recycled plastics – Eco-friendly option
Project 2: USB Cable Organizer
- Teaches symmetry, snap fits, and optional undercuts
- Mix soft + rigid plastic for dual-material learning
Design Tips:
- Practice living hinges if using soft plastics
- Include clips or loops for holding cables
- Add flex zones to improve usability
Project 3: Plastic Spoon or Spatula
- Learn about flow behavior, cooling, and warping
Design Focus:
- Maintain uniform wall thickness
- Add cooling channels near thick areas
- Keep shape symmetrical to avoid warping
Project 4: Stackable Storage Box
- Teaches part alignment, draft angles, and nesting
Design Elements:
- Use ribs to strengthen without thickening walls
- Design stacking grooves/lips carefully
- Increase draft angle slightly on inner walls
Project 5: Simple Phone Stand
- Helps understand stable geometry and part strength
Design Practice:
- Add gussets or ribs to support thin areas
- Experiment with surface finishes
- Try multi-part design (e.g., stand + holder)
Project 6: Pen Body or Cap
- Great for practicing circular parts and tolerances
Key Concepts:
- Tight fit between cap and pen body
- Use vents to avoid trapped air
- Try pin or submarine gates for clean appearance
Core Concepts to Master
Draft Angles
- 1°–3° on vertical walls to help with ejection
Wall Thickness
- Keep uniform: 1 mm – 3 mm
- Prevents warp, sink, short shots
Ribs & Bosses
- Ribs: ≤ 60% thickness of wall
- Bosses: for screws, supported with ribs
Undercuts
Block straight ejection; fix with:
- Side cores
- Lifters
- Avoiding the undercut
Mould Components Overview | ||
Component | Purpose | Notes |
Core | Forms inner features | Usually on moving/ejector side |
Cavity | Forms outer shape | On fixed side |
Sprue | Delivers molten plastic from machine | Only in cold runner moulds |
Runner | Channels plastic to part cavities | Keep flow balanced |
Gate | Entry point to part | Choose based on part shape |
Ejector Pins | Push part out after cooling | Place behind strong areas |
Cooling Channels | Reduce cycle time, control warping | Add near thick zones |
Vents | Let trapped air escape | Tiny gaps (0.01–0.05 mm) |
Beginner Software to Use | ||
Software | What It Offers | Easy for Beginners? |
Fusion 360 | Free for hobbyists, 3D + mould design | Yes |
SolidWorks | Powerful tools, industry standard | Medium |
Autodesk Moldflow | Mould flow simulation | Advanced |
FreeCAD | Open-source basic CAD | Yes |
Learn More From:
YouTube Channels
- NYC CNC – CAD + manufacturing basics
- EngineerExplains – Part design tutorials
Websites
- Protolabs Design Tips
- Creative Mechanisms Blog
Books
- Injection Molding Handbook – Rosato & Rosato
- Plastic Part Design for Injection Molding – Robert Malloy