Blog Investment Casting vs. CNC vs. 3D Printing: The Best Way To Make Pump Impellers

When it comes to pump impeller manufacturing, manufacturers evaluate several production methods including CNC machining, investment casting, and 3D metal printing. Each has its strengths, but when it comes to balancing cost, design flexibility, and performance, investment casting consistently emerges as the best choice.

In this article, we’ll explore:

• How the investment casting process works
• Why it’s ideal for pump impeller production
• The limitations of CNC machining
• The role of 3D metal printing in impeller manufacturing

What is Investment Casting?

Investment casting, also known as lost-wax casting, is a precision manufacturing method that has been used for centuries and perfected in modern industries like aerospace, process equipment, automotive, and energy. It’s particularly effective for producing complex, high-strength parts such as pump impellers.

How Investment Casting Works:

Wax Pattern Creation

• A wax replica of the impeller is produced with an allowance for thermal contraction (i.e. shrinking).
• Patterns are typically made of wax using a metal injection die.

1. Mounting Pattern
   • Multiple replicas can be assembled into a “tree” for batch casting.
2. Shell Building
   • The wax is dipped in ceramic slurry and coated with fine sand.
   • Repeated layers form a strong ceramic shell.
3. Wax Removal
   • The ceramic-coated wax is heated, melting out the wax and leaving a hollow mold.
4. Metal Pouring
   • Molten metal is poured into the mold.
   • Once cooled, the ceramic shell is broken away.
5. Finishing
   • The impeller is cleaned, trimmed, and polished.

This process results in a near-net-shape component with excellent dimensional accuracy and minimal waste.

Why Investment Casting is Ideal for Pump Impellers

Pump impellers feature intricate geometries such as curved vanes, thinner walls, and flow-optimized channels.  These can be difficult and costly to machine from solid metal. Investment casting overcomes these challenges.

Key Benefits:

• Design Flexibility
  • Complex, curved impeller blades are cast directly into shape.
  • No limitations from machining tool paths.
• Material Efficiency
  • Only the necessary alloy is used.
  • CNC machining wastes up to 70–80% of the billet.
• Cost Savings at Scale
  • Once tooling is made, casting offers lower per-part costs than CNC.
  • Reduced machining time and tool wear.
• Smooth Surface Finish
  • Cast impellers have inherently smooth flow surfaces.
  • Improves hydraulic efficiency and reduces polishing needs.
• Consistency & Repeatability
  • Casting ensures uniformity across production runs.
  • Every impeller performs reliably within design parameters.

CNC Machining: Benefits and Limitations

CNC machining is highly precise but not always efficient for pump impellers.

Where CNC Falls Short:

• Material Waste – Large portions of expensive alloys are cut away and scrapped.
• Complexity – 5-axis machining is slow and costly for curved impellers.
• Tool Wear – Cutting tough alloys increases maintenance costs.
• Low Scalability – Each impeller can take hours, if not days to machine.

When CNC Still Works:

• Prototypes or one-off impellers (if 3D Metal Printing is not an option)
• Extremely small production runs
• Parts requiring ultra-tight tolerances beyond casting capability

3D Metal Printing for Pump Impellers

Additive manufacturing (metal 3D printing) is revolutionizing pump impeller design. While not yet cost-effective for high-volume production, it shines in prototyping and custom applications.

Advantages:

• Unmatched Design Freedom – Internal channels and lattice structures are possible.
• Rapid Prototyping – New designs can be tested in days, not weeks.
• No Tooling Required – Perfect for low-volume or experimental impellers.

Limitations:

• High Cost Per Part – Printing remains expensive for large runs.
• Surface Finish – Parts often require polishing to achieve smooth flow surfaces.
• Size Restrictions – Large impellers may exceed build chamber limits.

Best Uses Today:

• Prototype impellers
• Custom or one-off pump designs
• Experimental, high-performance geometries

Quick Comparison: Investment Casting vs CNC vs 3D Printing

Feature	Investment Casting	CNC Machining	3D Metal Printing
Complexity of Design	Excellent	Limited	Excellent
Material Efficiency	High	Low	High
Cost (High Volume)	Low	High	Very High
Cost (Low Volume)	Medium	Medium	High
Surface Finish	Smooth	Smooth	Rough (requires finishing)
Scalability	High	Low	Low
Best Use Case	Production impellers	Custom & prototypes	Prototypes & R&D

Conclusion

When selecting a manufacturing method for pump impellers, consider your design requirements, production volume, and budget.

• Investment Casting is the gold standard for medium to high-volume, complex impellers.
• CNC Machining is best for prototypes and custom, small-batch production.
• 3D Metal Printing is ideal for rapid prototyping and advanced designs.

For most manufacturers, investment casting offers the perfect balance of cost-efficiency, performance, and scalability, making it the top choice for pump impeller production today.

To learn more about investment casting or 3D metal printing, contact MetalTek today. We would love to hear more about your needs and determine if we can help.

Investment casting and 3D metal printing is used at MetalTek’s Wisconsin Investcast Division.