Casted Materials in CNC Machining(4 axis cnc Dora)
- source:FANYA CNC Machining
Sand casting is a common approach for producing cast components by pouring molten metal into a mold cavity formed in sand. The sand is contained within a frame called a flask, and two mold halves are aligned to form the complete cavity Geometry like holes, slots and threads can be formed using removable sand cores. Pressure die casting forces the molten metal into steel dies under high pressure for good surface finish and dimensional accuracy. Investment casting uses wax patterns coated with ceramic slurry to form molds that are burned out before casting. This facilitates complex shapes but with higher cost.
Benefits of Casted Materials
Casting produces near net shape parts by forming metals directly into the desired geometry. This minimizes the need for extensive machining compared to other manufacturing methods. Casting also enables consolidate one-piece fabrication rather than having to weld or fasten multiple components together. Parts can be cast with hollow interiors to reduce weight. Specific alloy compositions can be created by adjusting the percentages of elements like carbon, silicon, manganese, sulfur and phosphorus during melting. This allows tailoring of properties like strength, hardness, corrosion resistance, machinability and wear resistance.
Cast Iron Characteristics
Cast iron contains over 2% carbon with silicon, manganese and phosphorus alloys. The higher carbon creates free graphite flakes that enable self-lubrication during machining. Gray cast iron is more brittle but very vibration dampening. Ductile cast iron has nodular graphite for better impact resistance. Cast iron grades are identified by class number, like Class 20, 30 and 40. Higher class numbers indicate higher strength. Most cast iron has relatively low cost, good machinability, high compressive strength and excellent vibration damping. However, it suffers from low tensile strength and elongation.
Cast Aluminum Properties
Cast aluminum alloys provide higher strength than pure aluminum but less than wrought alloys. Common casting alloys are A356 and A380, with silicon as the primary alloying element. These alloys offer good fluidity for casting complex geometries. Heat treatment can enhance properties by precipitation hardening of alloy precipitates. Cast aluminum is resistant to corrosion and has low density. Drawbacks are lower elongation and ductility compared to wrought alloys. Porosity defects may also occur during solidification.
Machining Casted Components
Premachining operations like thermal cutting or band sawing are often needed to remove gates, risers and flash. The as-cast surfaces tend to be rough with low dimensional accuracy. Facing and profiling may be required before finer machining. Adequate clamping is crucial to avoid distortion under cutting forces. Using fixtures helps locate off actual part surfaces rather than the imprecise as-cast surfaces. Soft jaws allow gripping onto casted parts without damage.
Roughing uses higher depths of cut and feed rates to efficiently remove material. Carbide tooling with specialized geometries is favored for interrupted cuts and varying hardness in the microstructure. Finishing uses lower parameters for attaining required surface finish and tolerances. Chip control is critical for clearing tough, stringy chips prone to workpiece scoring. Coolant should be applied for cooling and chip flushing.
CNC Programming Factors
The CNC program must accommodate the stock allowance present from the raw casting. Adaptive toolpaths like 3D profiling may be needed for removing irregular contours or convex radii. Scallop heights and cusps should be minimized on visible surfaces like hoods or panels. Drilling and boring should leave stock for finish reaming and tapping holes. Avoid sharp corners at transitions that can stress cast materials. Add fillets and chamfers where possible. For thin sections, reduce depth of cut and provide adequate chip clearance.
In summary, casted materials like iron and aluminum alloys offer useful properties that make them suitable for CNC machining. With proper fixturing, tooling selection, operating parameters and programming techniques, quality casted parts can be produced via CNC automation. Understanding the unique considerations for casted stock ensures an efficient process. CNC Milling CNC Machining