Your aluminium prototype works. Should production still use machining?

Start with how the shape is made

The bracket has mounting holes and locating faces. Machining a prototype proved that this particular part could be assembled. It did not prove that a cast or extruded version would meet the same requirements.

Machining removes material from stock. Casting forms molten metal in a mould; extrusion pushes material through a die to produce a continuous cross-section. Here, the casting option is die casting. Other casting processes need their own assessment rather than a single generic casting price.

An extruded profile does not emerge with every cross-hole already present. Hydro describes extrusion dies designed around the required profile.[1] If the bracket can share a consistent cross-section, cutting an extrusion to length and machining selected features may be worth quoting. The illustration separates the shape-forming step from the work still needed.

Draw in the operations that remain

A die-cast outline may still need machining on locating faces and holes, along with trimming, finishing and inspection. Compare routes on the basis of the required finished part. Otherwise, a near-net shape is being priced against a completed component.

Suppose the outer contour can change, but the mating face and hole positions cannot. Marking that distinction gives suppliers room to propose a production design. Requiring every prototype feature to remain identical may remove the benefit of another route before it is assessed.

Material needs the same attention. A proposed casting alloy or extrusion specification may differ from the alloy and temper used for the machined prototype. Engineering must assess the implications for load, corrosion, finishing and service conditions. Matching the dimensions alone does not establish interchangeability.

Divide tooling cost by an order scenario, not a sales forecast

Separate initial expenditure from repeat-order expenditure. Tooling, fixtures, initial samples and approval work may sit in the first group. Material, forming, machining, finishing, inspection and packing belong wherever the supplier actually charges them. Do not add an item again if the unit price already includes it.

Then compare the committed order, a repeat-order scenario and a design-change scenario. Dividing tooling by an optimistic lifetime sales forecast can make a route appear economical using units you may never buy. Batch prices and inventory obligations may also change with quantity, so a single unit rate should not silently carry across every scenario.

Armillotta’s machining-time study considers several influences beyond complexity.[2] It does not establish a universal point at which aluminium casting becomes cheaper. The relevant numbers must come from quotes for your drawing and order scenarios.

Keep design decisions and purchasing preparation moving together

If the mounting position may move, one option is to machine the immediate requirement while asking suppliers to review a casting design and an extrusion profile. You can prepare alternatives before authorising production tooling.

A successful machined prototype cannot automatically approve a changed production route. Different material, wall sections, machining datums or other design changes call for evaluation of the functions they affect. Including that work in the plan makes the initial-cost comparison more realistic.

Send suppliers a drawing that distinguishes fixed functional requirements from features open to proposals. State committed and forecast quantities separately, with timing, finish and inspection needs. Ask them to identify assumptions and additional qualification work in their response.

Choose a route you can explain

For this bracket, the first decision is which requirements can be frozen, and when. Develop an extrusion option if a common cross-section is feasible, and a casting option if suitable design changes are acceptable. Compare both with continued machining on the same finished-part basis.

Continuing with machining can be a considered result. You may have learned what demand or design change would justify another review. If tooling is the better option, the reason should include approval work and future changes as well as repeat unit cost.