What is a Turning? An Overview of Turning Operations in CNC Machining(strong lightweight metal Kevin)

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Turning is one of the most common and important machining processes used in manufacturing. It involves rotating a workpiece while a cutting tool removes material to produce cylindrical parts. Turning operations can create various outside diameters, shoulders, tapers, grooves, and other features on parts. Understanding what turning is and how it works is key for anyone involved in CNC machining or manufacturing.
Definition of Turning
Turning, also known as lathe turning, is a machining process in which a cutting tool removes material from the external or outer diameter of a rotating cylindrical workpiece. The workpiece is held and rotated by a spindle while the cutting tool feeds into it axially, radially, or at an angle to cut away material. This produces the desired shape and features on the workpiece.
Turning can be used to machine various cylindrical and conical parts like shafts, sleeves, rods, pins, axles, spindles, and many others. It is ideal for high production runs and achieving tight tolerances and fine surface finishes. Turning is done on specialized machine tools called lathes. It is one of the most efficient methods for machining cylindrical parts and is commonly used across many industries like automotive, aerospace, oil and gas, and more.
How Does Turning Work?
The turning process relies on the rotation of the workpiece and the axial movement of the cutting tool to gradually remove material. Here are the basic steps involved:
1. The workpiece is held securely by a chuck or collet on the spindle of the lathe. The spindle rotates the workpiece at a defined speed.
2. The cutting tool is held rigidly in the tool post and positioned at the desired angle and depth near the surface of the rotating workpiece. Common tool angles are perpendicular or at an angle less than 90 degrees.
3. The cutting edges of the tool remove material from the workpiece as it rotates. The tool feeds slowly in a linear motion along the axis of the workpiece as it cuts.
4. The depth of cut, feed rate, and cutting speed are precisely controlled to remove material evenly and produce the required shape and finish. Coolant is often used to keep the tool from overheating.
5. The process continues with multiple passes of incremental depth of cut until the final dimensions are achieved. Then a finishing pass is made to get the desired surface roughness.
So in summary, turning uses the rotation of the workpiece and linear axial movement of the cutter to shape the outside surfaces of cylindrical and conical parts. By precisely controlling the feeds, speeds, and depth of cuts, high dimensional accuracy and fine surface finishes can be obtained.
Types of Turning Operations
There are several common turning operations that allow machining different features on a workpiece:
Facing - Machining the ends of the workpiece flat and perpendicular to create a reference surface.
O.D Turning - Machining the external diameter of a cylindrical workpiece to size. Also known as external turning.
Boring - Enlarging the inside diameter of holes in a workpiece using a boring bar.
Taper Turning - Machining an external tapered surface on the workpiece. Done using the compound rest set at an angle.
Grooving - Cutting grooves or recess into the surface of the workpiece. Useful for splines, threads, and grooves.
Profiling - Shaping the outside contour of a workpiece by moving the tool at an angle to the axis of rotation.
Parting/Cutoff - Separating a part from the stock by cutting through it completely. Uses a specialized parting tool.
Form Turning - Using a shaped tool to machine complex profiles in a single pass.
Threading - Machining threads using the lathe threading dials. Can produce external and internal threads.
Knurling - Creating decorative patterns or crossed lines on the workpiece to provide better grip. Uses a knurling tool.
Undercutting - Forming a recess perpendicular to the axis to create an overhang on the workpiece.
The wide variety of turning operations allows complex geometries with different features to be machined on lathes. The process can be optimized and automated using CNC turning centers.
Benefits of Turning
Here are some of the main benefits and advantages of turning in manufacturing:
- High production rates possible for cylindrical parts. Turning is very fast and efficient.
- Excellent dimensional accuracy and control. Tolerances up to 0.001 inches or better are achievable.
- Fine surface finishes. Surface roughness of 10 Ra microinches or less is possible.
- Versatile ability to produce various cylindrical geometries and features.
- Low force and stress on the workpiece compared to milling. Less chance of warping.
- Only requires a single rotating cutting edge. Makes setup faster and easier compared to milling.
- Ideal for machining harder materials like hardened steels and titanium alloys.
- Lower costs for cylindrical parts compared to other processes like grinding.
- CNC automation allows fast changeovers between jobs. Minimal operator involvement needed.
- Environmentally cleaner compared to grinding which needs cutting fluids and produces more waste.
Turning has key advantages in roundness, surface finish, speed, cost, and flexibility that make it a staple machining method for high-production manufacturing. Mastering turning is an essential skill for engineers, machinists, and technologists.
Turning Tools and Equipment
Turning requires some unique cutting tools and machine tools:
- Lathe - The fundamental machine tool used for turning operations. CNC lathes automate the process.
- Cutting tools - Made of hard materials like high-speed steel, carbide, ceramic, diamond, and cubic boron nitride. Ground to precise angles and geometries.
- Tool holder - Holds and clamps the cutting tool rigidly. Provides proper orientation of the tool.
- Chuck - Holds the workpiece firmly and centers it precisely on the spindle axis. HYDROSHY power chucks are common.
- Collet - Accurately holds and centers bar stock or smaller parts for turning. Available in different sizes.
- Tool post - Supports and positions the tool holder and cutting tool for proper alignment with the workpiece.
- Coolant system - Provides coolant to the cutting area to cool the tool and part, wash away chips, and prolong tool life.
- Steady rest - Supports long slender workpieces at intermediate points while turning. Prevents workpiece deflection.
- Follower rest - Holds long tubular workpieces at the free end during turning operations. Reduces chatter and vibration.
- Faceplate - Large flat circular plate mounted to the spindle. Used for holding irregular shaped workpieces.
- Drive center - Fits precisely into the spindle nose and rotates the workpiece. Keeps the workpiece aligned.
Precision machined turning tools, tool holders, and work holding devices are essential for successful turning operations. The optimal setup depends on the particular application.
Turning Techniques and Best Practices
These techniques will help maximize quality and productivity in turning applications:
- Select suitable tool materials and geometries to match the workpiece material and features required. Carbide inserts with chipbreakers work well for most steels.
- Use proper cutting speed, feed, and depth of cut based on tool/workpiece materials, desired finish, rigidity, and machine power. Start light, then increase.
- Use sharp, undamaged tools. Replace or re-grind tools as soon as cutting edges deteriorate. Use multiple tools for roughing and finishing.
- Apply proper cutting fluids or coolants to help cutting and extend tool life. Use flood coolant or mist systems.
- Use steady rests and follower rests to support long slender workpieces so they don't deflect during turning.
- Take light finish passes to achieve fine surface finish and accuracies. Clean the workpiece between passes.
- Leave enough material for finishing passes. Rough to within 0.020-0.025 inches of final size for finishing allowance.
- Handle finished parts carefully to avoid damaging the surfaces. Avoid hard impacts that can distort dimensions.
- Perform in-process inspection of key dimensions at regular intervals. Make corrections promptly.
With the right techniques, tools, and parameters, turning can produce incredibly accurate and high quality machined components essential to products across many industries.
Applications of Turning
Turning is used extensively across manufacturing sectors anytime cylindrical parts are needed:
Automotive - Engine crankshafts, camshafts, gears, drive shafts, axles, wheel hubs
Aerospace - Aircraft engine turbines, hydraulic actuators, rocket motor casings, nozzles
Medical - Bone screws, replacement joints, surgical instruments, dental implants
Automation - Robot arms, conveyor rollers, linear shafts, lead screws, fasteners
Hardware - Bolts, screws, nuts, valves, fittings, plumbing parts, hose connectors
Oil/Gas - Pump housings, valves, compression fittings, couplings, drill bits
Transportation - Train wheels, axles, couplers, transit system rollers, off-road vehicle gearbox components
Appliances - Washing machine drums, blender blades, mixer shafts, fan motors
The versatility of turning means it produces mission-critical components across virtually every modern industry. Mastering turning unlocks enormous manufacturing capabilities.
The Future of Turning
While a mature process, turning continues progressing in capability and efficiency:
- Harder tool materials like cubic boron nitride and ceramics allow faster speeds and feeds to increase productivity.
- Advanced chipbreaking tool geometries provide better chip control and surface finishes.
- Multi-axis CNC turning centers can machine complex parts in a single setup without secondary processing.
- More powerful and responsive CNC systems allow on-the-fly adjustments to optimize cycle times.
- In-process metrology and adaptive control systems help maintain tight tolerances automatically.
- Smart multi-sensor capabilities improve process monitoring and control.
- Minimum quantity lubrication technology reduces fluid use and waste.
- Automation with robots, gantry loaders, and pallet systems streamline high-volume production.
While turning has been around for centuries, modern advancements are unlocking new potential. The capabilities of computer-controlled precision turning will continue expanding.
Turning is a versatile, efficient, and important machining process that has stood the test of time. It produces cylindrical and conical parts by rotating a workpiece while precisely controlling the movement and cutting parameters of the tool. Turning can generate very accurate dimensions, fine surface finishes, and complex geometries. Understanding the principles and techniques of turning helps manufacturing professionals maximize the value from CNC turning equipment. With continued innovations and smarter machine tools, turning will remain a go-to manufacturing process for the foreseeable future across many industries and applications. CNC Milling