Choose the route from the finished part, not the raw blank
Investment casting, forging and CNC machining from billet can all be the correct starting route. The useful comparison is total finished cost and risk: tooling, material utilization, machining time, mechanical-property needs, annual volume, inspection and the geometry that must ultimately be delivered.
When investment casting often has an advantage
Investment casting becomes attractive when complex near-net geometry, flow passages, compound external shapes or several features can be consolidated into one casting. The value is strongest when the casting meaningfully reduces machining or assembly while still meeting the required material and inspection route.
When forging is a better starting form
Forging can be preferred when directional grain flow, high structural loading or a comparatively simple shape makes forged properties more important than geometric complexity. The trade-off is that undercuts, internal features and highly detailed near-net geometry are more constrained, and substantial finish machining may still be required.
When CNC from billet is the smartest choice
Machining from bar, plate or billet avoids casting or forging tooling and can be the fastest route for prototypes, low volumes and geometry that is readily accessible to cutting tools. It becomes less attractive as material removal, cycle time or inaccessible internal geometry grows.
Compare the whole route
A low-cost raw casting is not automatically the lowest-cost finished part if it requires excessive machining or inspection. Likewise, a billet route that looks expensive per kilogram can win when tooling would dominate a small program. Compare drawing-to-delivery cost, not blank-to-blank price.
RFQ takeaway
For a route comparison, send the final drawing / model, material requirement, annual volume, target batch size, critical mechanical properties, inspection requirements and expected program life. Those inputs are enough to screen the three routes without forcing a process choice too early.