Machining Die Cast Parts
Castings brings a degree of difficulty to the machining process.
With cast parts, you need to take the tolerances into account, and can't depend on the features being perfectly flat or perfectly smooth. Porosity inside heavier sections of die cast parts can be an issue, so you won't want to cut into them too deeply.
The design of the casting is critical for providing good flow and fill characteristics for the die casting, and providing you with useful locating features and sufficient machine stock. If there's not enough machine stock designed in, you'll be scrapping parts after you've invested machining time into them.
There seems to be a lot of 'matrix buying out there' when you start new project. Where are the datums? Where is the parting line? Which dimensions will be affected by PL (Parting Line), flatness?
Another aspect is having quality-built fixtures to hold castings during machining. It is well worth the few dollars up front to have dedicated quality-built fixtures.
Machining process of die cast parts must be considered well before any order for the tooling is released. A careful evaluation of machined requirements can lead to redesign for net shape die-casting or near-net shape with reduced number of operations.
- Complete date: 3D CAD models and 2D drawings, quantity and all specs.
- Tolerances with focus on GD&T, flatness, porosity and cosmetics.
- Die Cast and Machining Datums.
- Machining stock regardless final tolerances and porosity specs.
- Surface treatment, such as Powder Coating (PC), Black Anodize and how this will impact tolerances.
- cast/machine/PC and masking or cast/PC (no masking) and machine.
- Black Anodize with tolerances under 0.001" hardly feasible to accomplish and different appearance compared with AL 6061 T6.
- Dimensional and cosmetic Inspection criteria.
- Parting Line and moving mold components affecting dimensional tolerances.
- Gate location and size in relation of porosity specs.