45 x 180 mm Aluminium Extrusion vs Casting: Which One to Specify

Process engineers and buyers mid-decision—keep a part as die-cast aluminium or move it to a constant-section extrusion—need tooling numbers, break-even logic and a worked example. The physical product on this page is the 45 × 180 mm ten-slot 6063-T5 section (GP-SP-45180-10S-RJ). GrownParts manufactures in China and exports from Shanghai or Ningbo; we do not operate a mill in Rajkot.

We extrude in China (Shanghai / Ningbo loading), cut dies in-house, and machine. Die cost for a comparable industrial section is typically in the 1,500–4,000 USD band with 7–12 days die lead time—orders of magnitude below many casting tools. Use this page when the question is process selection; use sibling pages when the question is ESD, EU docs, wind, or dock QC.

Decision rule: does the cross-section change along the length?

If the part is a prism—same envelope from end to end, features added by machining—extrusion is the default. Beams, rails, guides, conveyor side plates, frame posts, heat-sink bases with a uniform fin logic: these map cleanly onto a 45 × 180 (or a dedicated die). If the part needs local thickness changes, integral bosses in mid-span, undercuts that cannot be pulled through a die, or sealed internal cavities, stay with casting or switch to fabrication. The argument is geometric before it is commercial.

Tooling cost and calendar: extrusion die vs casting die

Send the current fully machined casting cost with the drawing. The comparison only works when both sides include machining—extrusion usually needs more of it than a near-net casting. First-article on a CMM for machined features is part of our RJ inspection path.

Volume break-even—and when casting still wins

At low and medium volumes, die cost dominates: extrusion wins early. At very high volumes with a true near-net shape and minimal CNC, casting can undercut extrusion piece price even after tool amortisation. Plot your annual metres (or pieces × cut length) against: die amortisation + extrusion + finish + CNC time. If more than ~30–40% of the casting mass is machined away today, extrusion + CNC is usually cheaper and more stable dimensionally for prismatic parts.

• Keep casting when geometry is non-prismatic or when casting already finishes critical faces as-cast within tolerance.
• Move to extrusion when the section is constant, slots/T-nuts replace drilled patterns, or you need 8–12% elongation ductility that ADC12 does not give.
• Hybrid is common: extrude the rail (45 × 180 class), cast or machine the end brackets.

6063-T5 vs ADC12 — properties that change the design

6063-T5 on this section: ductile, weldable/joinable with care, anodises cleanly, ~6.20 kg/m for 45 × 180 with ten slots, about 400 cm⁴ strong-axis stiffness. ADC12 (and similar casting alloys): higher as-cast strength in some tempers, brittle relative to 6063, poorer anodising cosmetics, excellent for complex bosses. Elongation on 6063-T5 in the 8–12% class means crash and overload behaviour differs—do not copy a casting rib pattern one-for-one without checking local buckling of thin extrusion walls.

Worked example: specifying the 45 × 180 ten-slot

Envelope 45 × 180 mm; grooves ~10 × 10.2 mm, 10 mm mouth, 45 mm pitch, outermost pair 135 mm apart; EN 755-9 wall ±0.15 mm; straightness 1.5 mm/m; twist 2°; cut ±0.5 mm; mill or AA15/AA20; FOB/CIF/EXW; lead time 7–12 days new die + 5–8 days run plus machining. Applications that fit: constant-section beams, rails, guides, conveyor side plates, heat-sink bases, frame members previously cast only because “we have a casting vendor.”

Cross-links when the decision is already “extrude” but the buyer intent differs: importer arrival QC for India inbound lots; EU document pack when the rail feeds an EN 1090 job.

Acceptance when a casting becomes an extrusion

RFQ for a process decision (not a catalogue click)

After you choose extrusion: next documents

When the conversion is approved, the next documents are a die drawing, a machining allowance map, and a first-article plan. Local mill presence is not claimed—capability and decision criteria are. If the converted rail later ships into EU work or Indian ports, see the Maghreb / EU document page or the Mumbai inspection page for packing and certificates.

Typical process supply: die cost in the 1,500–4,000 USD class; die lead time 7–12 days; production run 5–8 days plus machining; MOQ 150 m or trial length; FAI on CMM; timber cradles for raw lengths, plywood case for machined parts; about 600 t/month with in-house die shop and machining.

Process FAQ