Introduction to CNC Turning(cnc milled Frederica)
- source:MAJA CNC Machining
How CNC Turning Works
On a CNC turning center, the workpiece is held in the chuck of the main spindle. The spindle rotates, turning the part at the desired speed for optimal cutting. The cutting tool is held stationary in the tool turret, which positions the tool at precise locations and angles. As the workpiece turns, the cutter machines away material to achieve the desired dimensions and finish.
The motion of the tool and spindle are controlled by G-code programs. G-code tells the machine how fast to turn the spindle, how far to move the cutter, and the toolpaths to follow to create the feature. Precision ground ballscrews translate the rotary motion of servo motors into linear motion to position the cutter. Encoder feedback ensures accurate positioning.
CNC turning operations include:
- Facing: Machining the face of the part to length.
- Turning: Machining the outside diameter of the part to size.
- Boring: Enlarging holes or machining internal diameters.
- Grooving: Cutting grooves or undercuts.
- Threading: Cutting external or internal threads.
- Drilling: Drilling center holes.
- Taper turning: Machining angled diameters.
- Form turning: Turning complex profiles.
The CNC control allows many parts to be turned automatically, without operator intervention. Repeatable precision tolerances of 0.0005 inches or better can be held on most CNC lathes.
CNC Turning Machine Components
CNC turning centers come in several common configurations:
- Vertical Turning Lathes (VTLs): The spindle is oriented vertically, allowing large diameter parts to swing over the bed. VTLs excel at facing, turning, and boring.
- Horizontal Turning Centers: The spindle is horizontal, ideal for shaft-type workpieces. Used for high production turning.
- Chucker Lathes: Compact turning centers with a sliding headstock, suitable for smaller turned parts.
- Multi-Axis Turning Centers: Turning centers with additional axes like Y-axis, milling capability, and sub-spindle for complex parts.
Other components of a CNC turning center include:
- Spindle: Rotates the workpiece at desired cutting speeds, driven by a spindle motor. High torque spindles accelerate quickly.
- Chuck: Holds and centers the workpiece in the spindle, usually a hydraulic or pneumatic chuck. Collet chucks provide high accuracy.
- Tailstock: Supports long workpieces from the end, with live center, drill chuck, or tooling for second operations.
- Tool turret: Holds and indexes turning tools for quick changes. May have live tooling for milling, drilling, and tapping.
- Coolant system: Delivers coolant to the cut to maximize tool life, finish, and effective chip removal.
- Guideways: Precision surfaces that allow smooth, accurate motion of slides and turrets.
- Ballscrews: Translate rotary servo motor motion into linear axis movement to position slides.
- Control: The CNC system processes G-code and provides interactive menus. Controls motion, spindle speed, tool changes, and more.
Advantages of CNC Turning
CNC turning offers many benefits over manual turning:
- Automated Unattended Operation: CNC turning centers can run untended for hours, improving productivity.
- Speed and Efficiency: CNC machines parts much faster than manual operation. Quick tool changes, rapids, and high-speed contouring minimize cycle times.
- Repeatability: Every part is machined identically with precision G-code programs. Greatly reduces scrap and rework.
- Complex Geometry: Intricate profiles, grooves, tapers, and threads can be turned easily with CNC. Difficult or impossible manually.
- Multi-Axis Capability: Adding a Y-axis or sub-spindle allows complex parts to be completed in one setup.
- Flexibility: Changeovers between jobs take minutes. Add live tools for milling, drilling, and tapping without changing setups.
- Higher Accuracy: Far superior to manual turning with reliable G-code programming and stiffness. Hold tolerances under 0.001" routinely.
- Safer Operation: Removes operator contact with rotating workpiece. Controlled feeds and speeds prevent tool crashes.
- Skilled Labor Savings: One programmer can supervise several CNC machines, replacing multiple manual machinists.
When to use CNC Turning
CNC turning excels at producing large quantities of rotationally symmetric parts. Common applications include:
- Automotive: Shafts, bushings, pulleys, injector bodies, valve spools
- Aerospace: Nose cones, turbine blades, landing gear components, fasteners
- Medical: Bone screws, hip implants, surgical tools
- Firearms: Receivers, barrels, cylinders, bolts
- Industrial Machinery: Gears, rollers, axles, couplers, spindles, pistons
- Piping: Fittings, unions, valves, plugs, nozzles
- Hardware: Handles, knobs, fasteners, couplings
For complex shapes, multi-axis CNC lathes with live tooling offer milling, drilling, and tapping to completely machine the part in one setup. Live tooling adds flexibility to tackle more demanding geometries.
Programming CNC Turning
Programming for CNC turning involves using CAD/CAM software to convert the part design into G-code. Key steps include:
1. Import CAD model: The solid model provides precise geometry to program against.
2. Analyze blueprints: All dimensions, tolerances, and specifications for the part must be understood.
3. Choose workholding: Determine how to hold the blank - chuck, collet, faceplate, between centers, etc.
4. Select tooling: Match cutting tools to required operations - roughing, finishing, grooving, threading, etc.
5. Program toolpaths: Define machining operations like facing, turning, boring. Input machining parameters including feed, speed, depth of cut.
6. Simulation: Verify toolpaths avoid collisions and machine the part correctly.
7. Post process: Convert toolpaths into G-code for the machine control.
8. Setup and run: Set up workholding, tools, part zero, offsets. Prove out program on machine.
9. Inspect: Check critical dimensions. Adapt program if needed to fine tune accuracy.
10. Optimize: Refine program to reduce cycle time. Streamline toolpaths, choose faster feeds/speeds.
With the proper machining knowledge and CAM programming software, developing efficient CNC turning programs is straightforward. Simulation ensures programs run safely and as intended before ever setting up on the machine.
CNC Turning Tooling Fundamentals
Proper selection of cutting tools is critical to successful CNC turning operations. Key tooling considerations:
- Material: Carbide, ceramic, cubic boron nitride (CBN), and diamond cutting materials each have advantages depending on the workpiece material.
- Coatings: Coatings like titanium aluminum nitride and titanium carbon nitride prolong tool life and allow higher speeds and feeds.
- Insert geometries: Different insert shapes excel at specific turning operations like facing, turning, profiling.
- Approach/lead angles: Proper lead angles provide sharp cutting edges and good chip formation.
- Insert radius: Smaller radius inserts offer stronger edges for interrupted cuts, while larger radii provide finer finishes.
- Chipbreaker: Different chipbreaker patterns help break chips for effective chip removal. Important for stringy materials like stainless steel.
- Coolant: Through spindle or high pressure coolant maximizes heat removal and chip control.
A variety of toolholders fit the turret or tailstock to present the cutter at the optimal orientation. Common toolholders include ISO, CAT, BT, HSK, and CAPTO systems.
With automated precision, fast cycle times, and complex machining capabilities, CNC turning is an indispensable manufacturing process. Continued advancements in CNC technology, cutting tools, and programming enable turned parts to be made better, faster, and more cost-effectively than ever. CNC turning will continue as a primary method for producing the cylindrical components that keep industry turning for years to come. CNC Milling CNC Machining