Die Casting vs Aluminum Extrusion vs CNC Machining: Choosing a Manufacturing Route
Choose an aluminum manufacturing route by matching geometry, material requirements, order pattern and design maturity. Extrusion is a candidate for a repeated cross-section; die casting can form complex shapes in a die; CNC machining removes material to create specified features. A finished component may use more than one of these processes.
There is no universal production quantity at which one route becomes the best choice. Evaluate the complete part, including tooling, secondary operations, finishing and inspection.
How the three routes differ
In extrusion, material is pushed through a die to form a profile that is cut to length. Die casting introduces molten metal into a die and can produce shapes with changing cross-sections. These geometric differences are described by NADCA's comparison of die casting and extrusion.
CNC machining can create a part from stock or add features to a casting or extrusion. When requesting a quote, distinguish a fully machined route from machining performed as a secondary operation.
Route | Geometry to investigate | Questions for the quotation |
Aluminum extrusion | A profile repeated along its length | Which holes, ends or pockets need later operations? |
Die casting | A three-dimensional shape intended for repeat production | What tooling and design changes are required? |
CNC machining | Features made by removing material from accessible surfaces | What stock, setups and machining access are proposed? |
Combined route | A casting or profile with local machined features | Who controls the handoff and final inspection? |
Start with geometry and function
Mark the part's assembly interfaces and identify what must remain unchanged. Then ask a supplier to explain how the proposed process reaches those features.
For an extrusion proposal, discuss the profile, cut length and secondary work. For a casting proposal, ask for a design review covering the proposed die arrangement and any requested changes. For a machined proposal, ask about workholding, access to features and which surfaces establish the part's position during machining.
Do not accept a design change solely because it reduces one operation. Have the responsible engineer confirm its effect on assembly and function.
Compare the complete cost scope
Request separate assumptions for tooling, material, part production, secondary operations, finishing, inspection and packaging. Keep sample and production quantities distinct.
Tooling is an important part of die casting economics, and design affects process costs, as outlined in NADCA's process cost guidance. Your comparison should use current quotations for the actual design instead of a generic break-even number.
If the design is still changing, ask what a revision would affect: the die, fixtures, program, approved samples or delivery date. This discussion often matters as much as the first quoted unit price.
A practical decision sequence
Confirm the functional requirements and drawing revision.
List candidate routes without assuming they use identical alloys.
Request a feasibility review and written exceptions for each route.
Compare the full delivered-part scope at the same quantity assumptions.
Agree how samples will be evaluated before releasing production tooling or orders.
Illustrative example: an electronics enclosure
A long enclosure with the same cross-section could be reviewed as an extrusion with machined ends and holes. A differently shaped enclosure with features in several directions could be reviewed as a casting with selected machined interfaces. A design that is still evolving might also be quoted as a machined prototype.
These are routes to investigate, not a feasibility judgment for an unseen part. The final choice depends on the drawing, application and supplier review.
Frequently asked questions
Can extruded or die cast parts also need CNC machining?
Yes. Identify which features will be formed by the primary process and which will be machined. Agree the condition in which final dimensions are inspected.
Is CNC machining always the cheapest prototype route?
No. Ask for quotations and availability for the specific geometry, stock, finish and quantity. Avoid applying a single cost rule to every prototype.
Can I use the same alloy for every process?
Do not assume interchangeability. Have the material and manufacturing route reviewed together, including any required properties and finish.
Review the routes with ONTOPS
Explore die casting, aluminum extrusion and CNC machining. Send your drawings to ONTOPS and ask for a process proposal with clearly stated assumptions.
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