Investment Casting vs Machining Invar 36: Which Process Fits Your Part
Most Invar parts discussed on this site are machined from solid bar or plate, but investment casting is a real alternative for certain geometries and volumes, and it changes the cost and lead time picture in ways worth understanding before you commit to a process on the drawing.
Why casting enters the conversation
Invar 36 bar and plate are expensive and available in limited stock sizes, covered in why Invar 36 parts are costly. For a complex part with a shape far from a simple block or cylinder, machining from solid stock means removing a large fraction of that expensive material as chips. Investment casting produces a near-net shape closer to the finished geometry, which can reduce both material waste and the machining time needed to reach final dimensions, particularly on parts with internal cavities, complex external contours or thin ribs that would be difficult and slow to machine from solid.
How the process works for Invar
Investment casting, also called lost-wax casting, produces a wax or similar pattern of the part, builds a ceramic shell around it, then melts out the pattern and pours molten Invar into the resulting cavity. The casting comes out close to final shape but still requires machining on any feature that needs a precision tolerance, flatness or surface finish beyond what casting alone achieves. In practice, a cast Invar part usually still goes through targeted machining, stress relief and finishing on its critical features, following much the same logic covered in stress relief for Invar machined parts, just starting from a cast blank instead of solid bar or plate.
What casting changes and what it does not
What it changes: material utilization on complex shapes, the practicality of internal cavities or undercuts that would be difficult to machine, and potentially overall cost and lead time for the right geometry and volume.
What it does not change: the need for stress relief and careful finishing on features that require tight tolerance, flatness or surface finish. Casting produces a rough or semi-finished shape, not a finished precision part, and the same principles covered in Invar machining tolerances still apply to whatever features are machined after casting.
Tooling cost and volume
Investment casting requires tooling, a die to produce the wax pattern, which represents a real upfront cost that only pays back across enough parts. For a one-off or small prototype quantity, this tooling cost usually makes machining from solid the more practical choice even if it wastes more material, a tradeoff also discussed from the machining side in prototype vs production Invar machining. Casting becomes attractive once volume is high enough, and geometry complex enough, that the tooling investment pays for itself in reduced machining time and material cost across the run.
Dimensional considerations specific to casting
Cast parts can carry their own residual stress from the solidification and cooling process, distinct from but analogous to the machining-induced stress covered in why Invar work hardens. A casting supplier experienced with Invar should account for this in how the part is designed, gated and cooled, and the part still benefits from the same measured-at-controlled-temperature inspection approach used for machined Invar parts, covered in Invar machining tolerances.
Porosity, a common casting consideration in many alloys, is another factor to discuss with a casting supplier specifically experienced in Invar, since it can affect both mechanical properties and, on some applications, vacuum compatibility, a topic covered from the machined-part side in Invar for cryogenic and vacuum applications.
When to choose casting over machining from solid
- Complex geometry with internal features, undercuts or contours that would be slow or impractical to machine from solid
- Moderate to high volume, enough to justify tooling cost
- Parts where near-net shape significantly reduces expensive material waste
When to stick with machining from solid
- Prototype or low quantity, where tooling cost outweighs any machining time saved
- Simple geometry, block or cylindrical shapes that machine efficiently from standard stock anyway
- Programs requiring the material traceability and process history more commonly associated with wrought bar and plate, a consideration covered in Invar material certification
Getting a quote for either process
If your part’s geometry and volume make casting worth evaluating, describe both in detail on your RFQ so a shop can weigh in on which process actually saves you money, rather than defaulting to whichever process happens to be their specialty.
Send your drawing through our RFQ form, and we match you with shops that can advise honestly on machining from solid versus casting for your specific part.
Frequently asked questions
Is a cast Invar 36 part as dimensionally stable as a machined one?
A cast part still needs the same stress relief and finishing attention as a machined one for its final critical surfaces, since casting does not eliminate the need to machine and stabilize the features that actually need to hold tolerance. The casting mainly changes how the rough shape is produced, not the finishing requirements.
Is investment casting cheaper than machining from solid for Invar parts?
It depends heavily on geometry and quantity. For complex shapes in moderate to high volume, casting can reduce machining time and material waste significantly. For simple shapes or low quantities, the tooling cost of casting often makes machining from solid the cheaper option.
Need a quote for this part?
Send the drawing. We match you with up to 3 shops that machine Invar and reply within 24 business hours.
Get matched with an Invar shop