Die Casting vs Injection Molding - Key Differences
Die casting vs injection molding: compare materials, strength, tolerances, tooling cost, and production volumes to decide when metal die casting wins.
Mike Yao
Technical Director, Die Casting Engineering
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Die casting and injection molding look similar on the surface -both inject material under pressure into a precision steel mold -but they produce fundamentally different parts. One processes metal, the other processes plastic. This guide clarifies the differences and helps engineers and product designers choose the right manufacturing method.
The Core Difference
| Die Casting | Injection Molding | |
|---|---|---|
| Material | Non-ferrous metals: aluminum, zinc, magnesium | Thermoplastics (ABS, nylon, PP, PC) or thermosets |
| Process | Molten metal injected at 10-75 MPa into steel die | Molten plastic injected at 35-140 MPa into steel mold |
| Result | Metal component | Plastic component |
Detailed Comparison
| Parameter | Die Casting (Al A380) | Injection Molding (ABS) |
|---|---|---|
| Tensile strength | 317 MPa | 40-90 MPa |
| Hardness | 80 HRB | Rockwell R108 |
| Max service temperature | 150-175°C | 80-200°C |
| Thermal conductivity | 96 W/m·K | 0.17 W/m·K |
| Electrical conductivity | Yes (metal) | No (insulator unless filled) |
| EMI shielding | Inherent | Requires metallic coating |
| Wall thickness (min) | 1.2 mm | 0.5 mm |
| Dimensional tolerance | +/-0.05-0.1 mm | +/-0.1-0.3 mm |
| Surface finish (as-formed) | Ra 1.6-3.2 μm | Ra 0.8-1.6 μm |
| Tooling cost | $5,000-80,000 | $3,000-50,000 |
| Unit cost at 100,000 pcs | Lower (denser but stronger) | Lower (lighter material) |
| Density | 2.74 g/cm3 (aluminum) | 1.0-1.4 g/cm3 |
When to Choose Die Casting
- Structural strength required -die cast aluminum is 6-x stronger than ABS
- Thermal management -heat sink applications need metal's conductivity
- EMI/RFI shielding -die cast magnesium and aluminum are inherently shielding
- Elevated temperature service -above 100°C, most thermoplastics lose strength
- Pressure-tight enclosures -metal die castings can seal gas and fluid systems
- Long service life -metal does not creep, UV-degrade, or absorb moisture
- Rigidity without thickness -thinner metal walls can provide more rigidity than thicker plastic
When to Choose Injection Molding
- Weight is the absolute priority -plastic parts are 50-70% lighter than equivalent aluminum parts
- Electrical insulation required -circuit housings, connector bodies, switch covers
- Complex internal geometry -plastic's lower viscosity allows finer internal features, living hinges, and snap fits
- Color-through parts -pigment can be mixed directly into the plastic
- Very high volumes with simple geometry -cycle times as short as 5-30 seconds
- Low tooling budget -aluminum injection molds can be made for $3,000-8,000
Hybrid Approach -Die Cast Metal + Injection Molded Plastic
Many modern products use both: a die cast aluminum or magnesium structural frame (provides strength, heat dissipation, and EMI shielding) combined with injection-molded plastic panels (provides complex geometry, color, and weight savings). Power tools, laptops, automotive interiors, and consumer electronics routinely use this hybrid architecture.
FAQ
Can I switch a part from plastic to die casting?
Yes, but the design typically needs modification. Metal requires different wall thickness rules, draft angles, and gate locations. KastMfg provides free DFM review when converting parts from plastic to die casting.
Which is more expensive -die casting or injection molding?
It depends on material, volume, and part complexity. Tooling costs are broadly similar. Per-unit material cost is higher for metals. However, for structural applications, die cast parts often eliminate fasteners, inserts, and assembly steps that add cost to equivalent plastic assemblies.
Related Comparisons and Guides
- What is die casting — process fundamentals
- Die casting vs sand casting — another common comparison
- Die casting vs forging — strength and cost trade-offs
- Aluminum die casting — alloys and capability
Related
KastMfg Manufacturing Co., Ltd. Email: casting@kastdiecast.com | Phone: +86 138 1403 4409 No.6, Rungu Road, Nanjing, China
About The Author
Mike Yao on die casting vs injection molding
Technical Director, Die Casting Engineering
Technical Director at KastMfg with 20+ years in high-pressure die casting, leading engineering and program management across aluminum, zinc, and magnesium programs for automotive, EV, electronics, and medical OEMs worldwide.
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