Introduction to CNC Turning(chrome plating removal Eileen)

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Computer numerical control (CNC) turning is a machining process used to create rotational, symmetrical parts by removing material from a cylindrical workpiece. The workpiece is rotated while a single point cutting tool moves linearly, cutting away material to produce the desired shape. CNC turning is an extremely versatile and precise manufacturing process ideal for producing parts like shafts, bushes, cylinders, and discs in large volumes.
How Does CNC Turning Work?
CNC turning operations are performed on a lathe that has computer numerical control. This means the movement of the cutting tool and rotation of the workpiece are controlled by programmed commands that are input into the CNC machine. The basic CNC turning process involves the following steps:
1. The workpiece, usually a cylindrical bar of material like metal or plastic, is loaded into the CNC lathe chuck which clamps it into position. The chuck can rotate at variable spindle speeds.
2. The cutting tool, typically made of hardened steel or a carbide tip, is mounted onto a tool post attached to the CNC carriage. The linear movements of the carriage allow the tool to be fed towards or away from the rotating workpiece.
3. The machine operator inputs the CNC program code into the control panel. This program contains commands controlling the motions of the cutting tool, the spindle speed and feed rates, and other machining parameters.
4. When the cycle starts, the workpiece rotates and the cutting tool moves according to the CNC program. The tool progressively cuts away excess material as it moves across the workpiece from end to end, producing the desired shape.
5. Coolant is pumped over the work area to reduce heat and flush away metal chips. The machine repeats the cutting motions in multiple passes to achieve the specified dimensions.
6. When complete, the finished part is removed and a new workpiece is loaded for the next cycle. The CNC program can be repeated as needed to produce multiple identical parts.
Benefits of CNC Turning
There are many advantages to using CNC turning over manual lathe machining:
- High degree of accuracy and repeatability. CNC automation ensures each part is machined to precise tolerances as programmed.
- Ability to produce complex shapes and contours through interpolation and multi-axis control. Parts don't have to be completely symmetrical.
- Fast production rates. CNC turning produces parts rapidly compared to manual methods.
- Minimal human intervention needed once cycle starts. The machine can run untended once properly set up.
- Quick changeover between jobs. Changing CNC programs is faster than manual setups.
- Consistent high quality. automated CNC process removes human errors and variability.
- Lower production costs. Reduced cycle times maximize productivity for higher profits.
- Safer working conditions. CNC enclosure protects operator from rotating parts and cutting fluids.
Common CNC Turning Operations
While basic cylindrical facing and straight cutting are the most common CNC turning operations, the versatility of CNC allows many other possible machining capabilities:
- Tapered surfaces - By adjusting the tool angle or rotating the workpiece at an angle, tapered diameters can be cut.
- Grooving/undercutting - Narrow grooves and undercuts can be machined for parts like o-rings, sealing surfaces, retaining rings, etc.
- Threading - The CNC machine can cut external and internal threads for bolts, fasteners, and threaded holes.
- Boring - Internal boring bars are used to enlarge and taper inside diameters to high accuracy.
- Drilling/tapping - Live tooling attachments can drill and tap holes in the sides of parts.
- Knurling - Special knurling tools impress a diamond pattern on the workpiece for better grip.
- Face, shoulder and peel cutting - These operations cut surfaces perpendicular to the part axis.
- Form turning - Complex shapes are possible through interpolation and multiple axis control.
- Parting/cutoff - Grooves are cut to separate finished parts from the raw stock remnant.
CNC Turning Equipment
CNC turning centers utilize advanced technologies and composite machine construction for precision and efficiency. Common components found on CNC lathes include:
- Automatic tool changer - Allows quick tool changes to reduce cycle times.
- 12-24 station turret - Holds multiple preset tools for access without re-loading.
- Live tooling - Combines rotating, positioning, and milling capability in one turret spot.
- Y-axis off-center machining - Adds side milling and drilling capability.
- B-axis milling - Adds angle milling capability with a tilting tool turret.
- Built-in motor spindle - Reaches higher RPMs for faster material removal.
- Linear guideways - Use ball bearings instead of friction slides for smoother motion.
- Rigid one-piece bed - Provides vibration dampening for heavy cuts and high torque.
- High pressure coolant - Flushes away more chips and heat for better finishes.
- Automated gantry part loader - Allows a lathe to run untended for hours of lights-out production.
- CNC control - Converts CAM program files into motion commands. Displays critical machine metrics.
Workholding for CNC Turning
Proper workholding is critical for accurate and efficient CNC turning. Common workholding methods include:
- 3-Jaw Chuck - The most basic gripping device with internal or external jaws to hold cylindrical work.
- 4-Jaw Independent Chuck - Each jaw can move independently for gripping non-cylindrical shapes. Requires manual indication to center the workpiece.
- Collet Chucks - Precision engineered collets provide tight concentric clamping and fast job changes. Limited to gripping round bars.
- Hydraulic Chucks - Powerful hydraulic actuation provides strong clamping forces for high rigidity and heavy cuts.
- Vacuum Chucks - Utilize negative air pressure for secure holding without distortion of softer materials like plastic.
- Fixture Plates - Custom plates with locators can accurately hold oddly shaped workpieces. Allows batch production.
- Steady Rests - Support the free end of long slender workpieces to prevent deflection and vibration under cutting forces.
- Follower Rests - A trailing support that prevents thin tubing and pipes from buckling under machining stresses.
- Mandrels - Used to grip internal bores or expand delicate thin-walled parts for external turning operations.
The CNC turning process continues to evolve with advancing technologies that allow ever more complex parts to be manufactured with greater precision and efficiency. CNC turning makes production of high-quality rotationally symmetric parts fast, consistent, and cost-effective compared to manual lathe machining. It is an essential manufacturing process for modern industry. CNC Milling