Introduction to Turning(what are the lightest metals Moses)

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Turning is a machining process used to create cylindrical parts by rotating a workpiece while a cutting tool is fed linearly against it. The turning process removes material from the outside diameter of the workpiece to reduce it to a desired dimension while the workpiece spins at a constant rotational speed. Turning can produce parts with excellent dimensional accuracy and surface finishes. It is one of the most common and versatile manufacturing processes used in the metalworking industry today.
In this article, we will provide an overview of turning, including key terminology, types of turning operations, and the steps involved in the turning process. We will also discuss the advantages of turning and applications where turning excels as a manufacturing technique.
Key Terminology
Here are some key terms used in turning:
- Workpiece - The raw material that will be machined into the desired part shape. Common workpiece materials are metals like steel, aluminum, brass, and plastics.
- Chuck - A device that clamps and centers the workpiece in the lathe to allow rotation. Chucks have adjustable jaws to secure different sized workpieces.
- Lathe - The machine tool used for turning operations. The lathe rotates the workpiece at a constant speed while the cutter tool is fed against it to cut away material.
- Cutting tool - Usually a single point cutting tool made of hard materials like high speed steel, carbide, ceramic, diamond, or cubic boron nitride. The pointy tip removes material from the workpiece.
- Tool post - Holds and positions the cutting tool rigidly on the lathe carriage. Allows quick tool changes.
- Feed rate - The speed at which the cutting tool advances against the workpiece, typically in mm/revolution.
- Depth of cut - Radial distance below the workpiece surface that the tool penetrates, determining how much material is removed.
- RPM - Revolutions per minute of the workpiece. Higher RPMs allow faster material removal but may decrease precision.
Types of Turning Operations
There are several basic types of turning operations:
- Facing - Machining the end face of a cylindrical workpiece flat and perpendicular to the axis of rotation. Used to create a smooth surface to mount parts against each other.
- Straight (external) turning - Machining the external surface of a cylindrical workpiece to reduce its diameter to precise dimensions. The most common operation.
- Taper turning - Producing a tapered diameter by angling the cutting tool at an angle to the workpiece axis as it feeds. Used to create tapered shafts, fasteners, and mounts.
- Groove cutting - Cutting grooves or circumferential channels along the surface of the workpiece. Useful for Oil retention and part assembly.
- Undercutting - Turning a groove or relief below a surface to allow room for a tool or part to fit. Important for machinable fits.
- Parting/Cut off - Using a specially shaped tool to cut workpieces from bar stock or cut workpieces into shorter sections.
- Boring - Enlarging and smoothing internal diameters by feeding the tool radially into a bored hole. Achieves precise internal dimensions.
- Threading - Using a specially ground cutter or single point tool to cut external or internal screw threads for assembling parts.
The Turning Process
Here are the typical steps used to complete a basic external turning operation:
1. The workpiece material, usually a cylinder called the blank, is securely clamped in a chuck attached to the lathe headstock.
2. The chuck and blank are rotated at an appropriate constant RPM for the material size, type, and desired finish.
3. The cutting tool is selected based on the desired operation, material, finish, and dimensional tolerances. It is secured rigidly on the tool post at the proper height.
4. Coolant may be applied to the cutting area to reduce heat, flush away chips, and prolong tool life.
5. The cutting tool is fed towards the rotating blank and begins to remove material from the outside diameter as the carriage moves longitudinally.
6. The depth of cut, feed rate, and cutting speed are adjusted as needed during the operation. Multiple roughing passes may remove substantial material before final finish passes.
7. Measurements are taken periodically to check dimensional accuracy as the workpiece diameter is reduced. The tool is fed incrementally outward after each pass.
8. When dimensions are within tolerance, the desired surface finish is achieved on the last pass. The tool is retracted and the machine stopped.
9. The finished part is removed from the chuck for cleaning and further processing. Turning parameters and measurements may be adjusted before repeating the process on the next workpiece.
Advantages of Turning
Here are some of the primary advantages of turning:
- Excellent dimensional accuracy and surface finishes are possible, with tolerances down to 0.001 inches or less.
- A wide range of materials can be machined including all common metals, plastics, woods, composites, and glass.
- Relatively fast metal removal rates compared to other techniques. Both roughing and finishing can be performed.
- Set up is simple relative to milling operations. No complex workholding is required.
- Generates mostly cylindrical shapes but also spheres, discs, helical screw threads, and grooves.
- No subtractive cutting forces generated so even slender parts are rigidly supported when clamped. Vibration is minimal.
- Continuous production possible by automating the process with CNC turning centers.
Applications of Turning
Turning is ideal for manufacturing:
- Shafts - Engine crankshafts, transmission gears, drive shafts, axles, lead screws.
- Fasteners - Bolts, screws, nuts, rivets. External threads are rolled or cut by turning.
- Bushings and sleeves - Replaceable bearings used on shafts and housings. Require precision boring and turning.
- Pistons - Engine pistons are machined all over by turning, boring, and drilling. Good surface finish allows effective sealing and sliding.
- Rollers and wheels - Produced by turning an elongated cylinder and then slicing discs. Railroad and industrial wheels are commonly turned.
- Pulleys - Used to drive belts and cables on machinery. Have precisely turned grooves to guide the belts.
- Cylinders and tubing - Many fluid cylinders and plumbing components like valves and couplings are manufactured by turning processes.
- Spheres and hemispheres - Produced by a specialized form of turning called spin casting which shapes the material with centrifugal force.
In summary, turning is a versatile machining process capable of excellent tolerances, surface finishes, and repeatable cylindrical geometries on metal and plastic workpieces. It is widely used across many industries to manufacture common components like shafts, pulleys, pistons, cylinders, bearings, rollers, and threaded fasteners economically and precisely. With the addition of automated CNC turning machines, turning has become an even more valuable production method suitable for medium to high volume component manufacturing. CNC Milling CNC Machining