What is a Turning? An Introduction to Turning Operations in CNC Machining(milling and turning Basil)

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Turning is one of the most common machining processes used in manufacturing today. It involves rotating a cylindrical workpiece while cutting tools remove material to shape the outside diameter and faces of the workpiece. Turning operations are typically performed on lathes or turning centers, which are machines that hold the workpiece while it rotates at high speeds. The cutting tools move across the workpiece to cut away excess material.
Turning has been used for thousands of years to create cylindrical objects, but the modern CNC (computer numerical control) lathe allows for precision, automation and complexity far beyond what was possible with traditional manual lathes. CNC turning centers are able to produce parts with fine surface finishes, tight tolerances and complex geometries thanks to precise computer control of the machining process.
In this article, we’ll provide an in-depth look at CNC turning operations, including:
- What is a CNC lathe and how does it work?
- Common types of turning operations
- Cutting tools used in turning
- Workholding methods
- Typical applications and industries
- Advantages of CNC turning
Understanding the turning process is key for anyone involved in manufacturing, from machine operators to production managers and product designers. Let’s get started!
What is a CNC Lathe and How Does It Work?
A CNC lathe (sometimes called a CNC turning center) is a machine that rotates the workpiece while precisely controlling the cutting tools. It consists of a bed, headstock, carriage, cutting tools, and control panel. The key components include:
- Bed: Provides a sturdy platform for the entire machine and moves the carriage
- Headstock: Rotates the workpiece at high speeds with extreme precision
- Spindle: Attaches the workpiece to the headstock and rotates it
- Carriage: Holds the cutting tools and moves them towards the workpiece
- Cross slide: Moves the cutting tool perpendicular to the workpiece axis
- Cutting tools: Removes material from the rotating workpiece
- Control panel: Allows the operator to program the movements of the machine
The basic turning process consists of clamping the workpiece securely in the headstock chuck, starting rotation of the workpiece, then moving the cutting tools across the face or diameter of the workpiece to cut away excess material. Feed rates and cutting speeds are set based on the material, tooling, and final specifications.
Modern CNC turning centers include programmable automation of the turning process. Operators upload the machining program, which provides instructions for all the cutting operations. The CNC system then moves the tools and workpiece precisely based on the programmed parameters while the machine is running to create the desired part geometry. This automation provides excellent accuracy and repeatability for high-volume production.
Common Types of Turning Operations
There are several basic turning operations that can be performed on a CNC lathe:
- Facing: Machining the end face of the workpiece flat and perpendicular to the cylindrical surface. This is often the first operation.
- Straight (external) turning: Machining the external cylindrical surfaces parallel to the rotational axis. This reduces the diameter and achieves the final workpiece shape. Internal turning tools can also be used to machine inside diameters.
- Taper turning: Machining external or internal tapers using turning tools tilted at an angle to the workpiece axis.
- Grooving: Machining grooves or recessing into the surface of the workpiece.
- Parting/cutoff: Cutting through the entire workpiece to cut off a completed part.
- Boring: Enlarging or smoothing internal diameters using boring bars or other internal turning tools.
- Threading: Cutting threads externally or internally using turning tools with specially shaped inserts.
- Drilling/tapping: Rotating a rotating drill or tap on the turret to create holes or threads in the side of the workpiece.
More complex operations like contouring, profiling and forming are also possible on CNC turning centers to create complex 3D geometries. Multi-axis CNC lathes can accomplish even more by manipulating the workpiece orientation.
Cutting Tools for Turning Operations
A wide variety of cutting tools are used for the various turning operations. Common tool types include:
- Turning Inserts: Indexable inserts with geometries for light roughing to very fine finishing. Carbide inserts with specialty coatings work best for most steels.
- Boring Bars: Rigid steel or carbide bars that hold removable boring heads to enlarge internal diameters.
- Threading Tools: Special V-shaped inserts for cutting external and internal threads.
- Form Tools: Steel tools ground to specific shapes for turning contours, grooves, and special profiles.
- Drills/Taps: Standard rotating tools to create holes and threads on a CNC lathe turret.
The most important factors in choosing cutting tools are the workpiece material, operations being performed, tolerances required, cutting speeds/feeds, and tool rigidity. Tool holders also play a key role in providing rigid clamping while minimizing deflection.
Workholding Methods in Turning
Since the workpiece rotates at high speed, it must be securely clamped during the machining process. Common CNC lathe workholding methods include:
- Chucks: Mechanical or hydraulic three-jaw chucks grip the outside of workpieces very rigidly. Popular for smaller parts.
- Collets: Accurate sleeves with an interior profile that match the workpiece shape. Available for round, square and hex shapes.
- Faceplates: Large round plates that can be bolted or welded to one end of the workpiece. Allow holding of very large diameters.
- Centers: Live centers in the tailstock or fixture plates can support the free end of long workpieces.
- Mandrels: Straight or tapered mandrels insert through the center of tubular parts to provide support.
- Fixtures: Custom fixtures can be designed and built to hold complex-shaped workpieces.
The workholding method must withstand the forces exerted during turning operations without allowing vibration or deflection. This ensures precision machining and good surface finishes.
Typical Applications and Industries
Turning is so widely used because it can create machined parts for nearly every industry. Typical applications include:
- Automotive: Engine cylinders, transmission cases, axles, driveshafts
- Aerospace: Structural cylinders, landing gear, turbine engine parts
- Medical: Implants, surgical tools, injection molded parts
- Firearms: Rifled gun barrels, receivers, bolts
- Robotics: Joints, actuators, roller screws
- Fluid handling: Valves, fittings, fluid motors, pumps
- Oil/gas: Downhole tools, drill collars, wellhead parts
Materials commonly machined on CNC lathes range from aluminum and brass to hardened tool steels and titanium alloys. The versatility of modern CNC turning centers allows them to efficiently produce parts from prototype through high-volume production runs.
Advantages of CNC Turning
There are many good reasons why CNC turning is one of the most popular manufacturing processes:
- High degree of precision and repeatability
- Excellent surface finish quality
- Ability to machine complex geometries
- Low operator involvement once setup
- Fast production rates with CNC automation
- Minimal scrap and rework rates
- Ability to turn very hard materials
- Turning averages lower production costs than milling
With cutting-edge CNC controls and software, today’s turning centers can hold extremely tight tolerances for precision parts. The combination of powerful rigid machine tools with smart programming enables untended production of parts around the clock.
In summary, turning is an essential manufacturing process that involves rotating a cylindrical workpiece while precisely controlling cutting tools to remove excess material. Modern CNC turning centers can produce precision parts in large volumes with automated efficiency. With so many important applications across industries, CNC lathes will continue improving and innovating for years to come. CNC Milling CNC Machining