Introduction to Casted Materials in CNC Machining(edm machining process Dale)
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Types of Casted Materials for CNC Machining
The most common casted materials used in CNC machining include:
- Aluminum - An excellent material for casted parts due to its lightweight nature, corrosion resistance, strength, and machinability. Aluminum alloys like 360, 380, and 413 are commonly used.
- Iron - Cast iron provides good damping properties, resistance to wear, and machinability. Grey cast iron and ductile iron are the most popular.
- Steel - Carbon steels and alloy steels can be cast into strong, durable parts. Common grades are 4140, 4340, 8620.
- Brass - Has excellent machinability and corrosion resistance. Leaded brass alloys like C260 or C360 are often casted.
- Bronze - Provides high strength, corrosion resistance, and biofouling resistance. Silicon bronzes and aluminum bronzes are typical.
- Magnesium - The lightest structural metal, often cast for parts requiring low density. AZ91 is a common magnesium alloy.
- Zinc - Offers excellent corrosion protection at low cost, but limited strength. Zamak alloys with aluminum and copper are popular.
Advantages of Casted Parts for CNC Machining
There are several notable benefits of using casted parts in CNC machining:
- Complex shapes - Casting enables intricate, organic shapes that would be impossible with subtractive methods. Hollow and enclosed voids are also possible.
- Dimensional accuracy - Modern casting methods can achieve tight tolerances, reducing secondary machining. Static castings average 50-100 microns accuracy.
- Material versatility - Many materials can be cast, including ferrous and non-ferrous metals, polymers, ceramics, and even composites.
- Cost effective - Casting has low material waste and labor when producing high volumes. Per-part cost is very low compared to CNC machining.
- Rapid prototyping - Casting allows quick turnaround of prototype parts before full-scale production. Lead times range from days to weeks.
Limitations of Casted Parts for CNC Machining
Despite the advantages, casting does have some limitations to consider:
- Lower strength - Cast parts have lower strength than wrought metals due to porosity from shrinkage. They require added stock for machining.
- Dimensional accuracy - Tolerance range is wider compared to other processes like CNC machining or injection molding.
- Surface finish - As-cast surfaces are rough with a grainy texture. Machining is needed for cosmetic surfaces.
- Limitations on properties - Mechanical properties can vary throughout a cast part due to rapid cooling.
- Potential for defects - Casting is prone to defects like pores, inclusions, and cracks. Careful process control is needed.
- Alloys limited - Only certain alloys are suitable for casting, restricting material options compared to wrought alloys.
CNC Machining Operations on Casted Parts
Once a part is casted, it often requires additional CNC machining to achieve the final dimensions, surface, and geometries required. Common CNC operations on casted parts include:
- Facing - Machining flat reference surfaces parallel to the part axis. This removes unevenness from the casting process.
- Drilling - Creating holes for fasteners, pins, bushings, and other inserts needed in the final part.
- Boring - Enlarging and smoothing pre-cast holes to specific diameters and finishes.
- Turning - Using single point tools to cut external diameters and contours to precise dimensions.
- Milling - Milling removes bulk material using multi-tooth cutters to leave a clean surface texture.
- Tapping - Forming internal screw threads in holes using taps. This allows assembly with bolts or other threaded parts.
- Broaching - Cutting special internal shapes like splines, keyways, and involute gears via broaching tools.
Best Practices for Machining Casted Parts
Follow these guidelines when CNC machining casted parts:
- Allow extra stock - Add 1-3 mm over final dimensions to account for variability in the casting.
- Use rigid setups - Cast parts can distort if fixturing is insufficient. Clamp on solid mounting features.
- Rough in stages - Take light initial roughing cuts to expose underlying surfaces. Avoid deep cuts.
- Check dimensions early - Periodically verify critical features to avoid compounding errors.
- Use ceramic inserts - Hardened ceramics handle interrupted cuts on rough surfaces with less wear.
- Slow feeds/speeds - Reduce feed rates and spindle speeds compared to wrought materials.
- High coolant flow - Flush away chips and heat buildup from friction when machining cast metals.
Conclusion
Casting provides an efficient way to produce complex, near net-shape components that would be costly or impossible to manufacture otherwise. When combined with CNC machining, casted parts can achieve the tight dimensional tolerances, surface finishes, and geometries needed for many critical applications. With an understanding of the casting process and effective machining techniques, manufacturers can leverage the advantages of casted materials in their CNC production workflows. CNC Milling CNC Machining