Introduction to Casted Materials in CNC Machining(low alloy steel Walter)

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CNC (computer numerical control) machining is a manufacturing process that uses computer-controlled tools to shape raw material into finished parts and products. One of the key advantages of CNC machining is its ability to create complex geometries out of various materials, including casted materials. Casted materials refer to parts that have been formed by pouring molten metal into a mold cavity to create the desired shape. Common casted materials used in CNC machining include aluminum, brass, iron, and steel alloys.
Casted parts are widely used across many industries because casting allows for high-volume production of complex, net-shape components at a relatively low cost compared to other manufacturing methods. However, casted parts often require additional CNC machining to achieve final dimensional accuracy, surface finishes, and other critical features that cannot be easily cast. The casted near-net shape significantly reduces the amount of CNC machining required compared to machining a part from scratch. This article will provide an overview of working with casted materials in CNC machining operations.
Benefits of CNC Machining Casted Parts
There are several benefits to using CNC machining on pre-casted parts:
- Cost Savings: Because the overall shape and significant material removal has already been accomplished through the casting process, CNC machining casted parts requires less programming time, cutting tools, and machining time compared to raw bar or billet stock. This translates to lower overall manufacturing costs.
- Improved Quality: While castings provide close tolerances and an excellent finish on most surfaces, critical dimensions and finishes can be fine-tuned on a CNC machine. Machining can hold much tighter positional tolerances and create better surface finishes than most casting processes.
- Flexibility: CNC machines can add holes, slots, threads, chamfers, and other features to a casting that may not be feasible in the casting process alone. This allows castings to be customized and modified to meet different application requirements.
- Strength: The grain structure of a casting is optimized through controlled solidification in the mold cavity. Machining operations maintain the integrity of the casting grain structure leading to optimal strength characteristics.
Considerations for CNC Machining Casted Parts
There are also some unique considerations when CNC machining parts that have been pre-casted:
- Allowances - Casting tolerances, draft angles, and shrinkage allowances must be taken into account when designing CNC machining operations. The machinist has to know how much excess material needs to be removed.
- Fixturing - Castings may have irregular surfaces that require creative fixturing techniques. Additional setups may be required to access all necessary surfaces. Soft jaws and cast-specific fixtures help grip complex shapes.
- Machinability - The metal alloy, grain structure, hardness, and presence of impurities affect how easily it machines. This impacts feed rates, speeds, tool selection, and more. Cast iron machining is very different from cast aluminum, for example.
- Stresses - Internal stresses from the casting process can cause distortions during machining if processes are not optimized. Care must be taken to avoid releasing these stresses through drastic material removal.
- Features - Holes, bosses, flanges, and other features designed into the casting may need to be accounted for during programming and machining. They cannot always simply be machined over.
Best Practices for CNC Machining Castings
Here are some recommended best practices when CNC machining pre-casted parts:
- Perform in-process inspection of the casting before programming to identify potential issues and strategize the machining approach.
- Use fixtures and clamps that distribute clamping forces evenly to avoid distortion from stress release.
- Rough mill shallow depths of cut and leave an adequate amount of leftover material to account for inaccuracies in the casting surface.
- When possible, flip the part over and perform finishing operations from the bottom up so the machine is always cutting into a solid, stable base.
- Utilize coated carbide, ceramic, CBN, and other tools optimized for casted materials to handle interrupted cuts and abrasive alloys.
- Select tool paths, speeds, and feeds suited for cast materials. Conventional machining data may not apply.
- Use specifically designed CAD/CAM software strategies for casted parts that account for excess stock conditions.
With the right techniques, CNC machining casted blanks can improve quality, reduce costs, and enable more complex geometries compared to using wrought metals alone. Understanding the unique considerations of castings unlocks their advantages while mitigating their challenges through optimized fixturing, tooling selection, programming, and machining methods. CNC machining will continue growing as a solution for taking casted components to the next level across all industries. CNC Milling