Choosing an aluminum material for a precision-machined part isn’t just about picking an alloy grade — it starts with choosing between two fundamentally different production routes: casting a near-net-shape blank and finish-machining it with CNC, or machining directly from a solid aluminum billet (bar, plate, or block). This decision affects the entire cost structure, lead time, and the product’s final mechanical properties.
Two basic production routes: cast-and-finish-machine, or machine directly from solid billet
The first route: pressure die-casting (or gravity casting) to create a near-net-shape blank, then CNC machining the surfaces that need tight tolerances — suits products with complex geometry, high production volume, and where not every surface needs high precision. Upfront mold cost is high, but per-unit cost drops quickly as volume grows.
The second route: machining directly from a solid aluminum billet (often called “machining from billet”) — suits low production volume, relatively simpler geometry, or cases needing uniform mechanical properties throughout the part without the internal porosity risk found in castings. No mold investment is needed, but machining time per part is longer and the scrap rate is significantly higher.
Selection criteria: four factors to weigh simultaneously
01. Expected production volume
This is usually the first deciding factor. At high volume, the casting route is almost always more economical thanks to mold cost being spread across many units. At low volume or for prototypes, machining directly from billet is typically faster and more economical since it doesn’t require waiting for a mold.
02. Geometric complexity
Parts with complex geometry, many ribs, or internal cavities hard to reach with a CNC cutting tool typically suit the casting route better. Conversely, relatively simple shapes, mostly flat surfaces and drilled holes, can be machined directly from billet without taking much time.
03. Mechanical property and reliability requirements
For parts subject to dynamic loading, fatigue, or requiring high mechanical reliability, wrought billet material is typically favored since it carries no casting-porosity risk affecting fatigue strength. For ordinary static-load parts, cast material usually meets requirements adequately.
04. Budget and project timeline
If the project has a limited budget for the initial development stage or needs a quick prototype to validate the design, machining directly from billet avoids mold cost and lead time, though per-unit cost will be higher if the product later moves to mass production.
Common wrought aluminum alloys for machining directly from billet
Unlike casting alloys (such as ADC12 and A380 covered in previous articles), aluminum material used for machining directly from billet belongs to the wrought aluminum alloy family, with an entirely different designation system.
| Alloy grade | Notable characteristics | Common applications |
|---|---|---|
| 6061 | Good balance of strength, machinability, and corrosion resistance; can be heat-treated for higher strength | Structural frames, mechanical brackets, general CNC-machined components |
| 7075 | Very high mechanical strength after heat treatment, but lower corrosion resistance than 6061 | Aerospace components, high-load precision-machined parts |
| 2024 | Good fatigue strength, commonly used in cyclic-load applications | Dynamic load-bearing structures, some aerospace components |
| 5052 | Very good corrosion resistance, easy to form, moderate strength | Housings exposed to moisture, marine applications |
The fundamental difference from casting alloys is that these grades aren’t optimized for fluidity (since they’re not used for casting), but for mechanical properties after rolling or extrusion and for machinability.
Applications by industry: which route to choose when
In the industrial equipment and automation sector, parts requiring high precision but not extremely large volumes are typically well suited to machining directly from billet, especially during new product development.
In the automotive and motorcycle industry, with high production volumes and many complex-shaped parts (engine housings, brackets), the casting-then-finish-machining route for critical assembly surfaces is typically the more economical choice.
In aerospace and high-load equipment, where mechanical reliability is prioritized absolutely over cost, machining directly from billet using alloy grades such as 7075 or 2024 is typically a mandatory requirement, regardless of production volume.
Frequently asked questions
Can casting and CNC machining both be used for the same part?
Yes — this is actually the most common model in practice: casting creates the near-final shape, then CNC machining finishes assembly surfaces or tight-tolerance features. The question of “casting or machining from billet” is really a question of the ratio between the two steps, not an absolute choice of one over the other.
Is billet material more expensive than casting alloy?
By weight, billet material (rolled or extruded aluminum) is typically priced higher than raw casting alloy, but that’s only part of the total cost — you also need to add mold cost (for casting) or machining cost and scrap rate (for machining from billet) to compare actual total cost.
If future production volume is uncertain, which route should be started with?
It’s best to start with machining directly from billet for the prototype and initial small-volume stage, while designing the drawing with future conversion to casting in mind if volume grows later — avoiding a complete redesign when switching production routes.
Contact Daiwa for advice on choosing the right material and production route
If you’re deciding between casting-then-finish-machining or machining directly from solid aluminum billet for a new product, Daiwa’s technical team can advise based on your drawing, expected volume, and specific mechanical property requirements.