What is CNC Turning?(cnc machining stainless steel Sara)
- source:WEINBERG CNC Machining
In CNC turning, the workpiece is rotated while a single-point cutting tool moves linearly to cut away material. The linear and rotary motions are controlled by CNC along multiple axes. CNC turning machines, called CNC lathes, can have multiple axes including X (radial), Z (longitudinal), C (axial rotation of workpiece) and Y (cross travel). The CNC lathe follows instructions from pre-programmed G-code to manipulate the tool and achieve the desired geometry.
CNC turning is capable of producing parts with excellent dimensional accuracy and complex geometries. Parts that can be produced via CNC turning include shafts, sleeves, pins, bushings and disks. It is ideal for high volume production and prototyping. CNC turning is widely used in automotive, aerospace, medical, and other precision machining industries.
How does CNC Turning work?
The CNC turning process starts with loading the raw material, usually a cylindrical bar or rod, into the CNC lathe chuck or collet. The chuck provides the axial rotation needed to turn the workpiece. The cutting tool is mounted on the tool turret or tool post where it can move in the X and Z axes. Tool types include boring bars, drills, inserts and cutters. The tool material depends on the workpiece material, usually a hard material like carbide.
Before machining, the dimensions of the workpiece are manually measured and entered into the CNC machine control which uses this to calculate coordinates. The operator then programs the cutting operations into the CNC machine using G-code. The program specifies the machining sequence, tool selection, spindle speed, feed rate, depth of cut and other parameters.
During machining, the CNC system positions the cutting tool and workpiece based on the G-code program. As the chuck rotates the workpiece, the tool follows the programmed paths to cut the material. Computer controls precisely synchronize the linear and rotary motions. Cutting fluid is pumped over the work area to cool and lubricate. Chips and dust are flushed away by the fluid.
As material is removed, the workpiece diameter gets smaller while its axial length remains unchanged. Cuts and movements in the X-Z plane create the outside contour based on the tool path. The Z-axis movements infeed the tool to rough out and finish the part. Precise movements in micron increments are possible for fine finishing. Some CNC lathes have live tooling which allows milling and drilling operations to be performed.
Once machining is complete, the finished part is unloaded. Post-processing like deburring or polishing may be done. The production of multiple identical parts is possible by repeating the programmed operations. Overall, CNC turning automates turning to accurately and repeatedly produce components at high speeds.
CNC Turning Process Steps
The main steps in the CNC turning process are:
1. Design - Part is designed in CAD software with dimensions, geometries, and tolerances specified.
2. Program - G-code program is written based on CAD design, tooling, and machining sequence.
3. Setup - Workpiece material is loaded, chucked, and indicated. Tooling is installed and offsets set.
4. Simulation - Optional simulation is done to visualize machining process and detect errors.
5. Machining - The machine is run and follows the G-code program to produce the part.
6. Inspection - Finished part is measured to ensure it meets specifications.
7. Adjustment - Any necessary offsets or program adjustments are made if part is out of tolerance.
8. Production - Multiple identical parts are machined by repeating the program.
CNC Turning Machines (Lathes)
CNC lathes are the machines used for CNC turning. The main components of CNC lathes are:
- Headstock - Holds the chuck and rotates the workpiece. Contains the main spindle powered by an electric motor. High spindle speeds up to 7500 RPM are possible. The spindle is precisely controlled by the CNC system.
- Tailstock - Holds dead centers or other tooling on the opposite end of the workpiece for support. Can be manually or CNC controlled.
- Tool turret/post - Holds multiple cutting tools and rotates to index each tool into position for machining. Some turrets have live tooling capabilities.
- Tool magazine - Stores tools not currently in use. Allows for automatic tool changing.
- Bed - Rigid base that connects the headstock and tailstock. Guides for the saddle and tool post slide along it.
- Saddle - Mounts on the bed and provides X-axis motion.
- Lead screw/drive system - Converts rotary motion into linear motion to move the saddle and tool post.
- Control panel - The user interface to program, operate, and monitor the machine. Modern systems use CNC controls with touchscreen displays.
- Enclosure - Covers the working area and protects the operator. Includes chip collection system and safety guards.
CNC lathes range from basic 3-axis machines to complex multi-axis turning centers with live tooling, Y-axis, part handling, and other capabilities. Larger machines can turn diameters over 100 inches. Swiss-style CNC lathes have sliding headstock and guide bushings for holding bar stock and machining small, complex parts.
CNC Turning Tools
A variety of single-point cutting tools are used in CNC turning including:
- Turning/Facing - For external turning and facing. Carbide inserts have an acute cutting edge and different geometries. High speed steel tools can also be used.
- Boring - Internal boring bars allow enlargement of holes or internal turning. Rigid supported bars with small inserts reach deep holes.
- Threading - Threading tools cut external and internal threads. May use inserts or high speed steel.
- Grooving/parting - For cutting grooves and parting off finished parts from the bar stock. Parting tools are thicker for rigidity.
- Forming - Used to create special profiles not possible with standard inserts. May involve moving around an axis during one pass.
- Drilling - Live tooling drills holes in front or back of part including through and blind holes. Requires C-axis capability.
Other toolholding systems like quick change tool posts speed up tool changing for high production. Cutting tools require proper handling and regular indexing/replacement to produce consistent parts. The right tooling helps maximize productivity and part accuracy.
CNC Turning Advantages and Disadvantages
CNC turning offers various benefits:
- High accuracy and repeatability - Precision machinable to tolerances within 0.001". Ideal for complex, tight tolerance parts.
- Excellent surface finishes - Fine finishes to 32 microinches are possible. Reduces secondary polishing operations.
- Low operator involvement - Automated after programming so one operator can run multiple machines.
- Fast production rates - CNC achieves much higher speeds than manual turning. Makes highly productive.
- Complex geometries - Capable of contouring, tapering, grooving, threading and other complex features.
- Quick changeover - Switching programs is fast allowing flexible production of small batches.
- Unattended operation - Can safely run overnight reducing labor costs. Useful for large production runs.
Potential disadvantages include:
- High initial costs - CNC lathes have large capital investment for purchase and installation.
- Programming expertise - G-code programming knowledge required to operate machines efficiently.
- Limited part sizes - Determined by machine bed length and swing over bed capacity.
- Rigid setup - Fixtures often needed to hold and locate parts, adding time and costs.
- Maintenance - Trained technicians needed to maintain and repair CNC equipment.
- Operator training - Developing skilled CNC machinists takes significant training investment.
Applications of CNC Turning
CNC turning is used across many industries to produce machined components including:
- Automotive - Engine valves, pistons, axle shafts, turbocharger housings, brake rotors, driveline components
- Aerospace - Wing spindles, engine combustion casings, landing gear parts, missile cones, fasteners
- Medical - Implants, prosthetics, surgical instruments, orthopedic joints/fixations
- Oil/gas - Valve bodies, couplings, drill tools, pipes
- Construction/agriculture - Gears, shafts, bearings, bushings, engine parts
- Industrial - Rollers, shafts, couplings, spindles, hydraulic cylinders, press plates
- Consumer - Appliance housings/components, power tool parts, musical instruments
Almost any part with cylindrical symmetry or rotary function can benefit from CNC turning. It offers precision machining for prototypes or high volume production. Continued improvements in CNC technology increase the applications possible with CNC turning.
The Future of CNC Turning
CNC turning will expand in capability and popularity as automation and smart manufacturing continue trending. Some future developments include:
- Multi-function machines - More live tooling, multi-axis, and multi-process abilities on one machine.
- Smart machines - With artificial intelligence, machine learning and advanced sensors to optimize processes.
- Additive hybrids - Combining with 3D printing for complex geometries and in-process metal deposition.
- Micro machining - Machining tiny, ultra-precise parts for electronics and medical uses.
- New materials - Cutting composites, alloys, ceramics and other exotic materials.
- Quick changeover - Faster, flexible changeovers from one part to the next.
- Green machining - More use of minimum quantity lubrication and vegetable/synthetic oils.
- Monitoring - Use of IoT and data to track machine performance and part quality.
- Robot assistants - Robots help load/unload parts and service the CNC machines.
- Operator aids - Augmented reality, smart glasses and other aids to improve programming and operation.
CNC turning will continue expanding its capabilities to machine an ever-wider range of part geometries, sizes and materials. With automation and smart capabilities, productivity and precision will keep improving. CNC turning has already changed manufacturing and will play an essential role in factories of the future. CNC Milling