Die Casting vs Injection Molding -Key Differences

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.

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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

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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

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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

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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.

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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.

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KastMfg Manufacturing Co., Ltd. Email: yaoqingpu1983@gmail.com | Phone: +86 138 1403 4409 No.6, Rungu Road, Nanjing, China