Introduction to Turning in CNC Machining(cheapest metals Armand)
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CNC turning has many advantages over manual turning. It allows for precise control of cutting parameters like speed, feed rate, and depth of cut. CNC machines can also turn complex shapes that would be difficult or impossible to produce manually. Turning on a CNC lathe is a versatile process suitable for making parts with cylindrical features, grooves, threads, tapers, drilled holes, and more.
Types of Turning in CNC
There are several different types of turning operations that can be performed on CNC lathes:
- Outside Diameter (OD) Turning - The most common operation, OD turning is done on the external surface of a cylindrical part. The cutting tool shapes the rotating outside diameter as it moves linearly along the axis of the workpiece. This can produce straight diameters, tapers, grooves, threads, and profiles.
- Inside Diameter (ID) Turning - Also known as boring, ID turning tools cut along the internal surface of a cylindrical part. This is used to create holes, counterbores, tapers, and other inside features.
- Facing - A facing operation cuts off material from the face of a part using a turning tool oriented perpendicular to the axis. This produces flat surfaces and squares the ends of cylindrical blanks.
- Parting and Grooving - Parting tools are used to cut off a completed part from the remaining stock. Grooving tools can cut grooves and small diameters internally and externally.
- Threading - Thread turning tools contain the matching pitch and form to cut screw threads onto a part. Single point threading tools produce external and internal threads and worm gears.
- Drilling and Tapping - With appropriate live tooling, CNC lathes can perform drilling and tapping operations off-centerline from the main spindle. Live tools add substantial versatility to a basic turning machine.
- Form turning - Using specially shaped cutting tools, form turning machines complex irregular contours through interpolation of multiple axes. Hard turning is form turning of hardened components that normally would require grinding.
CNC Lathe Components
CNC lathes contain the same basic components as manual machines but with the addition of computerized controls. Major components of a CNC turning center include:
- Headstock - The headstock contains high precision spindle bearings and drive systems to rotate the work at high speeds. The spindle accepts chucks, collets, or centers to mount the workpiece.
- Tailstock - The tailstock slides on the bed and contains a Morse taper to hold tooling for the non-rotating end of the workpiece. It provides support for long parts.
- Tool turret - An indexable turret provides multiple tool positions for quick changes to minimize non-cutting time. Some CNC lathes have live tooling with rotating T or Y-axis capabilities.
- Guideways - Ball or roller linear guideways provide precise axis movement and cutting accuracy. Box way and V-flat ways are also used.
- Control panel - Manual controls aid in setup and job startup. Parameters can be entered and the job can be started and monitored from the control panel.
- Computer control - The CNC control guides axis motion and runs automatic cycles. It interprets part programs and CAD/CAM files.
- Chip management - Built-in chip conveyors, cutting fluid nozzles, and enclosures help manage swarf and minimize mess.
Turning Operations Performed on CNC Lathes
While basic turning processes are similar between manual and CNC machines, the programmable nature of CNC allows multiple operations to be performed in one setup. Common CNC turning operations include:
- Facing - Removing material from the end face of a part to create a flat reference surface.
- Rough turning - Taking deeper cuts to remove the bulk of material down to within a certain amount of the final dimensions.
- Finish turning - Using smaller cuts and higher speeds to achieve the final dimensions and surface finish. Multiple finish passes may be required to meet tolerance.
- Taper turning - Tapers are turned by offsetting the tool position or adjusting the angle of the tailstock. The CNC program coordinates the axes.
- Grooving - Using a specially shaped tool to cut internal and external grooves for seals, parting lines, threading, or decorative patterns.
- Parting-off - Cutting through the entire part to separate it from the remaining stock held in the chuck.
- Threading - Cutting external and internal screw threads using the coordinated movement of the X and Z axes during the pass.
- Drilling - With live tooling, holes can be machined off-centerline. The CNC program synchronizes the tool spindle and main spindle.
- Boring - An internal turning operation that enlarges and improves the accuracy of an existing hole.
- Tapping - Threading internal holes by coordinating the live tool spindle with the movement of the axes.
- Knurling - Using a special knurling tool to create criss-cross patterns or diamond-shaped patterns on the part surface. Often done for improved grip on handles and control knobs.
- Radius & form turning - Complex shapes defined in a CAD model can be turned through interpolation of multiple axes.
- Cut-off - Separating the finished part from the remaining bar stock by cutting through the entire part with a parting tool.
The wide range of operations possible on a CNC turning center allows complicated parts to be machined in one setup. Lathes with live tooling are capable of producing parts complete in a single chucking.
Setting Up Workholding for CNC Turning
Workholding is a critical step in any machining operation. The part must be held securely and avoid deflection during cutting. Typical workholding methods for CNC turning include:
- Three-jaw chucks - The most common type of lathe chuck has three jaws which close around the part. It is ideal for eccentric turning of rounds and flats.
- Four-jaw chucks - Used for irregular shaped parts or when higher precision is required. Having four jaws allows each one to be dialed in independently.
- Collet chucks - These hold the workpiece using hardened steel collets that provide rigidity and concentric accuracy. Each collet is size specific and good for standard round stock.
- Steady rests - Support the free end of long parts by using adjustable fingers that press against the workpiece. This provides rigidity and avoids chatter.
- Centers - Dead centers in the headstock and rotating live centers in the tailstock support the workpiece between them. Typically used for thinner long parts requiring rotational support.
- Mandrels - Used to hold small diameter parts or those with existing holes. The mandrel fits through the pre-bored hole for turning the outside.
- Faceplates - Large irregular shaped parts can be bolted directly onto a faceplate attached to the headstock spindle.
- Magnetic chucks - Electropermanent magnetic chucks help hold irregular shaped parts made of magnetic materials for milling and grinding.
- Vacuum chucks - Used for holding non-magnetic parts. The vacuum pressure clamps the workpiece down during machining.
Proper setup of workholding is the first step in any CNC turning job. The part must be held securely without vibration. Workholding accessories like centers, chucks, and rests enable versatility in the shapes and sizes that can be turned efficiently.
Cutting Tools Used in CNC Turning
There is a wide variety of turning tool inserts and toolholder styles used in CNC turning:
- Roughing tools - Form tool geometries designed to efficiently hog out material at higher feed rates. Uncoated carbide inserts with a stronger edge are common.
- Finishing tools - Insert shapes optimized for tighter tolerances, better surface finish, and lower cutting forces. More heat resistant coatings and sharper edges on finishing tool inserts.
- Threading tools - Carbide inserts shaped with the matching thread form ground into the cutting face. Available for unified, metric, ACME, and specialty thread forms.
- Grooving and cutoff tools - Narrow inserts shaped for cutting grooves or severing the part from the stock. Grooving inserts are available in many widths.
- Boring bars - Solid boring bars with replaceable carbide inserts for internal sizing and finishing. Available in many lengths.
- Drills and taps - For live tooling lathes, twist drills and taps can be used off-centerline. Carbide drills often used due to high spindle speeds.
- Toolholders - Wide range of toolholder sizes and styles for holding and presenting inserts to the workpiece. Provides correct clearance angles.
The programmable nature of CNC allows fast tool changes to reduce non-cutting time. Using the optimal tool for each operation results in maximized productivity and part quality. Continual improvements in carbide grades and coatings optimize tool life and performance.
Programming CNC Lathes
CNC turning centers are programmed using G-code, a standard numerical control programming language that controls axis motion, speeds, and other functions. Programs can be written manually, but most are generated using CAM software. Common G-codes for CNC lathes include:
- G00 - Rapid linear motion
- G01 - Linear interpolation motion
- G02 - Circular interpolation CW
- G03 - Circular interpolation CCW
- G04 - Dwell time pause
- G96 - Constant surface speed control
- G97 - Constant spindle speed mode
- G98 - Feed per minute mode
- G99 - Feed per revolution mode
In addition to G-codes, CNC lathe programs specify important parameters including:
- Feed rate (inches or mm per revolution)
- Spindle speed (RPM)
- Depth of cut
- Coolant (on/off, high pressure, through spindle, mist)
CAD/CAM software is the easiest way to generate optimized CNC turning programs directly from 3D part models. CAM simulates the machining process and outputs G-code customized for the particular CNC lathe. This simplifies programming and avoids manual coding errors.
Benefits of CNC Turning
There are many advantages to using CNC turning centers rather than manual lathes:
- Increased automation - CNC allows multiple operations in one setup with minimal operator involvement needed. Automated cycles boost productivity.
- Accuracy and repeatability - The precision controls of CNC turning produce parts within tighter tolerances. Programs can be stored and reused.
- Complex parts - CNC machines can turn complex geometries and curvatures that would require special manual setups or secondary operations.
- Quick changeovers - Programming and workholding setups allow fast changeovers between parts. Flexibility minimizes downtime.
- Advanced tooling - Powerful spindles allow higher speeds and feeds. Live tools enable features like off-center drilling and tapping.
- Intelligent controls - Advanced software features like look-ahead, adaptive control, and safe tool zones optimize the machining process.
- Operator safety - The hands-off nature of CNC turning improves the safety of operators by minimizing direct contact with the cutting.
- Training - While skilled setup is needed, basic CNC operation has a shorter learning curve than developing manual machining expertise.
For companies looking to improve productivity, part consistency, and manufacturing agility, investing in CNC turning is a strategic step. The precision and automation of CNC turning make it a key manufacturing process suitable for both high volume and flexible low volume production.
Conclusion
From manual beginnings, CNC turning has developed into an essential manufacturing process that combines automation, accuracy, and flexibility. Modern CNC lathes can turn a wide range of part sizes and geometries complete in a single setup. With intelligent programming and setup, CNC turning produces precision parts quickly and repeatably. For manufacturers machining cylindrical parts, implementing CNC turning offers advantages over manual turning methods. Ongoing advances in machine tool technology, cutting tools, programming, and workholding continue to extend the capabilities of CNC turning. CNC Milling CNC Machining