Introduction to CNC Turning(torsion snap joint example Eden)

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Computer Numerical Control (CNC) turning is a machining process used to create rotational parts by removing material from a workpiece. The workpiece is held in a chuck or collet and rotated as cutting tools remove material. CNC turning is an automated process controlled by a computer program that dictates the tool movements and cutting parameters. This article will provide an overview of CNC turning, including the equipment, tooling, operations, applications, advantages and disadvantages.
CNC Turning Equipment
The key components of a CNC turning center include the machine base, bed, headstock, tailstock, chuck, tool turret, cutting tools, axes drives, spindle, controller and enclosure. The sturdy base and bed provide structural support and absorb cutting forces. The headstock contains the spindle, chuck and drive motor. It holds and rotates the workpiece. The tailstock provides additional workpiece support on the opposite end. The turret holds multiple cutting tools and indexes them into position for machining operations. Linear motion guideways precisely position the turret and tailstock. The cutting tools perform facing, turning, boring and other operations. The axes drives move the turret and tailstock under CNC program control. The spindle rotates the workpiece during cutting. The CNC controller stores machining programs and sends commands to control all machine movements and functions. The enclosure provides chip containment and operator safety.
CNC Turning Operations
Common CNC turning operations include:
- Facing: A facing tool levels and squares the face of the workpiece to create a uniform starting surface.
- Rough Turning: Rough turning uses coarse feeds and depths of cut to quickly remove the bulk of material. Carbide insert tooling is commonly used.
- Finish Turning: Finish turning uses fine feeds and shallow depths of cut to achieve the final dimensions and surface finish. Ceramic or diamond inserts are often used.
- Boring: A single point boring bar or multi-point boring head cuts internal diameters to precise sizes. Boring establishes hole location and straightness.
- Grooving: Grooving tools cut internal and external grooves for seals, parting lines and other features. Grooves may be radial or axial.
- Parting: Parting tools cut workpieces from the bar stock remnant using a broad, thin blade. Parting establishes the final part length.
- Threading: Threading tools cut internal and external screw threads. Single or multi-point inserts are used depending on the thread type.
- Drilling: Drilling tools can produce holes by interpolate drilling or with a live tooling spindle. Holes may be blind or through.
- Tapping: Tapping tools cut internal threads to match a screw’s external threads. Precise synchronization is required between the spindle and tap.
- Knurling: Knurling tools imprint a diamond pattern on the workpiece to provide a better grip for handles and fasteners. The patterns increase surface contact and friction.
- Form turning: Form tools cut complex profiles not possible with standard inserts. The profiles are often for special contours, radii and chamfers.
CNC Turning Workholding
Rotational workpieces are held in a collet, chuck or fixture during CNC turning:
- Collets: Collets are high precision grippers sized to hold a specific workpiece diameter. They provide excellent concentricity and traction.
- Chucks: Chucks have movable jaws that close to grip the outer diameter of a workpiece. Different jaw types accommodate various sizes and shapes.
- Fixtures: Fixtures hold irregular shaped workpieces or multiple parts. Fixtures locate each part relative to the rotational axis. They may use clamps, vises or adhesives.
- Centers: A center in the headstock tailstock supports long workpieces at both ends. The centers apply compressive force along the axis of rotation.
CNC turning requires properly securing the workpiece to avoid vibration, deflection and inaccurate dimensions. The holding method must withstand cutting forces and high spindle speeds.
CNC Turning Applications
CNC turning produces parts for many industries including:
- Automotive: Engine valves, pistons, turbochargers, axles, hubs, pulleys and driveshafts are common automotive applications. Precise dimensional control and excellent surface finishes are required.
- Aerospace: Aircraft contain structural forgings, fittings, hydraulic components, fasteners and actuators made by CNC turning. Exotic materials like titanium and Inconel are often machined.
- Medical: Surgical instruments, implants, prosthetics and dental components have complex turned features. Bio-compatible metals and plastics are used to tight tolerances.
- Firearms: Barrels, cylinders, bolts and bushings are examples of firearm components produced on CNC lathes. Turning provides the necessary precision and concentricity.
- Industrial: Pumps, compressors, hydraulics, valves and process equipment for factories rely on CNC turned parts. Wear resistance and dimensional accuracy are important.
Advantages of CNC Turning
The primary benefits of CNC turning include:
- High Productivity: CNC automation provides faster cycle times than manual turning. Multiple tools operating simultaneously further improve throughput.
- Precision: CNC machines offer accuracies up to 0.0005 inches for producing precision turned components.
- Repeatability: Turning programs allow identical parts to be quickly replicated. CNC precision minimizes variations.
- Low Labor: One machine operator oversees multiple CNC machines. Less manual skill is required versus manual lathes.
- Flexibility: Quick change tooling and programming adjustments accommodate various workpiece materials, features and batches.
- Complexity: CNC turning can produce complex geometric features, contours and 3D shapes not possible manually.
- Surface Finish: Advanced tooling, rigid setups and fine tolerances allow exceptional surface finishes down to 4 microinches.
Disadvantages of CNC Turning
Potential drawbacks associated with CNC turning include:
- High Initial Cost: CNC lathes carry a higher capital equipment investment than manual machines. However, automation reduces labor expenses over time.
- Programming: While easier than CNC milling, programming knowledge is still required for turning operations and machine setup.
- Setup Time: CNC jobs may require significant preparation including programming, fixturing and tooling adjustments. Quick change tooling can help reduce changeover times.
- Maintenance: CNC equipment requires maintenance like any other machine. Staff should be trained in basic upkeep and preventive procedures.
- Size Limitations: Although large turning centers are available, CNC lathes have greater size restrictions than manual machines. Maximum swing diameters range 10-100 inches typically.
With capabilities superior to manual methods, CNC turning is an essential manufacturing process for mass producing precision round parts. Continued advancements in machine tools, cutting tools, automation and computing power will drive further improvements in the efficiency and capabilities of CNC turning. CNC Milling CNC Machining