Introduction to CNC Turning(strong but lightweight materials Regina)
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What is CNC Turning?
CNC turning refers to turning operations performed on a computer numerical control (CNC) lathe. Like all CNC machining processes, turning is performed by programing the cutting motions into a computer, which then controls the machine tool. On a CNC lathe, the stock material (usually a cylindrical bar) rotates while a cutter is fed horizontally or vertically into the workpiece to remove material. By precisely controlling the cutting tool’s movements in multiple axes, complex geometric features like tapers, grooves, threads and contours can be machined with a high level of dimensional accuracy and repeatability.
CNC Turning Equipment
The main piece of equipment needed for CNC turning is a CNC lathe. CNC lathes come in a variety of sizes and configurations, but fundamentally they consist of a spindle, servo motors for axis movement, cutting tools mounted on tool posts or turrets, programmable logic controllers (PLC), and a computer numerical control system.
The main components of a CNC lathe include:
- Headstock: Holds the part and contains the spindle which rotates the workpiece. The spindle is powered by an electric motor and a gearbox that provides different spindle speed ranges.
- Tailstock: Located opposite the headstock and used to hold long workpieces with a live center. The tailstock can move longitudinally and be locked into position.
- Tool turret/tool post: Holds the cutting tools and indexes them into position for machining operations. Tool turrets provide quick tool changes.
- CNC control: Controls the motion of the machine. Accepts programming input and converts it into electrical signals to drive servos and perform the programmed actions.
- Coolant system: Provides coolant to cutting area to reduce heat and improve tool life. May include pumps, filters, and nozzles.
- Chuck: A workholding device mounted in the spindle. Chucks have adjustable jaws to grip different sized workpieces.
- Ball/lead screws: Convert rotary motion from the servomotors into linear motion to move the turret/tool post and tailstock.
- Guideways: Provide linear motion for slides and components. High precision guideways are essential for accurate machining.
- Chip management: Systems for efficient chip/swarf removal from the machine. May include conveyors, augers, and chip collectors.
Tooling for CNC Turning
CNC turning relies on replaceable single point cutting tools to shape materials. There are various tooling considerations, including:
- Tool material: Carbide, cubic boron nitride, diamond, and high-speed steel are commonly used. The material affects tool life and surface finish.
- Tool geometry: Turning tools have a precisely ground cutting edge angle, nose radius, and rake angles designed for specific operations.
- Tool inserts/holders: Inserts provide the cutting edges and are secured in tool holders which mount in the turret. Many styles of interchangeable inserts are available.
- Boring bars: Used for internal boring operations. May be solid carbide or have replaceable inserts.
- Threading tools: Used to machine external and internal threads. May use interchangeable inserts or solid dies.
- Grooving/parting tools: For cutting grooves, slots, and parting off finished parts. Carbide or ceramic are common insert materials.
- Tooling coatings: Special coatings like titanium aluminum nitride, titanium carbon nitride, and diamond-like carbon improve tool life, friction, and reduce heat.
CNC Turning Operations
Some of the common operations that can be performed on a CNC turning center include:
- Facing: Machining the face of the part to create a flat reference surface. Performed using a facing tool or roughing endmill.
- OD (Outside Diameter) turning: Roughing and finishing cuts to reduce the outer diameter to size. OD turning uses replaceable insert tooling.
- Boring: Enlarging internal diameters to size. Boring bars and boring heads are used for boring operations.
- ID (Internal Diameter) turning: Machines internal surfaces using boring bars inserted through the spindle. Also known as internal turning.
- Taper turning: Produces external and internal tapered surfaces using the machine’s live tooling axes.
- Grooving: Cutting grooves of various widths along the diameter of a part.
- Cut-off/parting: Using a parting tool to cut off a finished part from the bar stock remnant.
- Threading: Single or multi-point threading tools are used to machine external and internal threads.
- Drilling: Live tooling can drill center holes or perform spot drilling operations.
- Tapping: Threads holes using tap holders mounted in the turret.
- Knurling: Using special knurling tools to imprint diamond, straight, or cross patterns on the part diameter.
- Chamfering: Beveling sharp corners and removing burrs with chamfering tools.
- Form turning: Complex shapes can be generated through interpolation turning with CNC control.
Advantages of CNC Turning
There are many benefits that make CNC turning a popular production process:
- Precision and accuracy: CNC machines offer extremely precise dimensional control and repeatability down to a few microns. Machining errors are essentially eliminated.
- Complexity: Intricate component geometries can be produced that would be impossible or prohibitively expensive with manual methods.
- Automation: CNC turning minimizes human input. Once programmed, CNC lathes can run 24/7 with minimal supervision. This boosts productivity and consistency.
- Speed: CNC turning is much faster than manual turning, providing high throughput. Cycle times are shorter with CNC.
- Setup time reductions: CNC tool changes and turret indexing reduces setups between operations. Jobs spend more time cutting and less time between operations.
- Tool life: The optimized tool paths of CNC turning extend cutting tool life leading to reduced consumable costs.
- Surface finishes: Excellent surface finishes are achievable on CNC lathes due to precision cutting parameters and rigid setups.
- Labor savings: One CNC operator can run multiple machines leading to substantial reductions in labor costs. Less skilled labor is required versus manual machining.
- Flexibility: Quick changeovers between jobs allows economical small lot production. CNC lathes can produce a wide variety of parts.
- Safer: CNC eliminates exposure to cutting tools during manual turning. The operator simply supervises the process.
Limitations of CNC Turning
With all its benefits, CNC turning does have some limitations:
- High initial investment: CNC lathes have a much higher upfront cost than manual lathes. However, they provide a faster return-on-investment.
- Programming: While easier to program than milling, programming knowledge is still required for generating CNC turning programs. New operators require training.
- Not for one-offs: For very low production volumes, manual turning may be more cost effective than CNC setup and programming.
- Size limitations: The maximum workpiece size is constrained by the lathe's center height and through-hole capacity. Larger CNC lathes are more expensive.
- Live tooling limits: CNC lathes with full contouring capability and driven tooling can be substantially more expensive than more basic CNC turning centers.
- Maintenance: CNC machines require maintenance like any other precision equipment. Components must be kept clean and properly lubricated.
Common Applications of CNC Turning
Due to its versatility and precision, CNC turning is used across many industries to produce a wide array of components:
- Automotive: Engine valves, pistons, axles, turbocharger shafts, brake rotors, pulleys, and steering components.
- Aerospace: Turbine blades, landing gear parts, missile and rocket components, fasteners, fittings, and bushings.
- Medical and dental: Bone screws, hip and knee replacements, surgical instruments, dental implants, and prosthetics.
- Firearms: Rifle barrels, magazines, bolts, cylinders, and supressors.
- Oil and gas: Valve bodies, downhole tools, wellhead parts, hydraulic components, and pipe fittings.
- Construction/mining: Buckets, sheaves, sprockets, grader blades, drill bits, wear parts, and excavator links.
- Fluid power: Hydraulic cylinders, manifolds, valves, pumps, compressors, and actuators.
- Hardware: Nuts, bolts, shafts, fasteners, bushings, pins, and plumbing fittings.
Conclusion
In conclusion, CNC turning is an essential manufacturing process for machining precision round metal components. When performed on modern CNC lathes, turning provides unparalleled accuracy, surface finishes, and repeatability. CNC turning excels at producing high-volume production runs efficiently and economically. With its advantages in precision, automation and flexibility, CNC turning will continue growing as a go-to manufacturing process across many industries. CNC Milling
