What is a Turning?(fillet vs chamfer Cyril)
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Turning is one of the most common and important machining processes used in manufacturing. It produces cylindrical parts that have an axis of symmetry, such as shafts, bearings, gears, axles, disks, pulleys, and more. Understanding what turning is and how it works is key for those involved in manufacturing and CNC machining.
How Turning Works
During a turning operation, the cutting tool is fed towards the rotating workpiece which cuts away material. As material is removed by the cutting tool, the diameter of the workpiece is reduced, creating the outside diameter of the part being machined. The cutting tool can be fed in a straight line to produce a cylindrical shape or moved in more complex patterns to create contoured geometries.
The workpiece is held tightly and rotated by the chuck of the lathe, while the cutting tool is rigidly clamped to the tool post. The relative motion between the rotating work and the translating tool removes the desired material. The speed and feed rates can be precisely controlled to achieve the required finish and tolerances.
Types of Turning Operations
There are several basic types of turning operations:
- Facing - Machining the end surface of the workpiece to create a flat reference surface perpendicular to the axis of rotation. This establishes part length.
- Straight Turning - Machining the outside diameter of a cylindrical workpiece using a cutting tool fed parallel to the axis of rotation. This reduces the diameter to the required dimension.
- Taper Turning - Machining a tapered diameter by feeding the tool at an angle to the axis of rotation. The angle and length of the taper is precisely controlled.
- Contour Turning - Complex profiles or contours are machined by precisely controlling the transverse and axial motion of the cutting tool during rotation.
- Grooving/Parting - Narrow, straight cuts made into the workpiece to cut off a section, or “part off” a completed part.
- Boring - Enlarging or finishing the inside diameter of a bored hole using a boring bar. Provides precise hole size and finish.
- Threading - Using a turning tool to cut screw threads into a workpiece. Single or multi-start threads can be produced.
- Knurling - Pressing a knurling tool against the revolving part to produce a textured crosshatch pattern on the work surface. Often used for improved gripping.
- Drilling/Boring - Holes can be drilled or enlarged for pins, bushings, or finishing bores. Done using drill bits or boring bars.
- Forming - Using form tools or CNC to machine complex profiles not possible with basic tool shapes.
Turning Machines and Equipment
Turning operations are performed on a type of lathe called a turning machine. These machines have a headstock, carriage assembly, and tailstock to precisely control the rotation and feed motions required for turning:
- Headstock - The headstock houses the high-speed spindle which grips the workpiece and rotates it at a set speed. Powerful, variable speed motors provide accurate spindle speeds.
- Tailstock - The tailstock is located on the opposite end of the bed from the headstock. It provides support for long workpieces using a center point and can hold drill bits or boring bars.
- Carriage - The carriage houses the cross slide and compound slide which hold and move the cutting tool during operation. Power feeds move the tool along X and Z axes.
- Tool Post - A rigid, robust tool post is mounted to the compound slide to hold the turning tool in position as it cuts. Quick change style posts allow fast tool changes.
- Chuck - A high-precision chuck is mounted to the spindle to grip the workpiece. It centers the work and provides clamping force while rotating.
- Tooling - Turning requires single point cutting tools made of hard materials like carbide. Indexable inserts provide efficient cutting ability and economy.
- Controls - CNC turning machines have computer numerical controls which automate motion and spindle speeds. Settings are input using programs.
- Coolant - High pressure coolant nozzles apply lubricating fluids to the cutting area to minimize heat, improve surface finish, and evacuate chips.
Common Turning Materials
Turning can machine parts from almost any material, but is most commonly used for machining metals and plastics. The most common turning materials include:
- Aluminum - Parts including housings, fittings, and shafts. Turns quickly with a polished finish.
- Steel - A versatile material used for strong, durable turned parts. Low carbon steel turns easily while alloy steels require high cutting forces.
- Stainless Steel - Corrosion resistant parts can be turned but require high power and sharp tooling due to work hardening. Creates challenges for turning.
- Brass - Excellent turnability and finish. Used for decorative and mechanical components. Prone to work hardening during machining.
- Titanium - Very strong and durable, but difficult to cut and machine. Requires high pressure coolant and frequent tool changes.
- Plastics - Softer thermoplastics like Acrylic, Polystyrene, and PVC can be readily turned to precise dimensions. No coolant required.
- Wood - Turning soft materials like wood is an ancient craft. Modern CNC can produce complex shapes not possible manually.
Benefits of Turning
There are many benefits that make turning one of the most utilized manufacturing processes:
- Excellent dimensional accuracy and surface finishes
- Ability to produce parts from round stock material efficiently
- Generate complex geometries and special profiles
- No part shape restrictions due to axis of symmetry
- Wide range of materials can be machined, including metals, plastics, and composites
- No heat treatment or finishing required after most turning operations
- Quickly machine complex parts with CNC automation
- Minimal setup allows fast changeovers between jobs
- Performs well for medium and high volume production
- Ideal for round parts including shafts, rollers, knobs, and cylinders
Turning continues to expand as a vital process for precision machining operations. Understanding the fundamentals of how turning works provides key insight into this essential manufacturing method. With increased automation and cutting tool development, turning will remain an indispensable part of modern machining for creating rotational parts. CNC Milling CNC Machining