What is a Turning?(stainless melting point Tiffany)

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A turning is a machining process in which a cutting tool is used to remove material from a rotating workpiece to generate a specific geometric shape. The turning process is typically performed on a lathe or turning machine, which rotates the workpiece at high speeds while the cutter is fed linearly against it to cut away material.
Turning is one of the most common and fundamental machining processes, used to produce cylindrical and conical shapes. It is an essential process in manufacturing cylindrical parts like shafts, bearings, gears, and more. Understanding the basics of turning is important for anyone involved in manufacturing or CNC machining.
How Does Turning Work?
The turning process utilizes a rotating cylindrical workpiece, called the work, and a non-rotating cutting tool that is fed linearly against the work. The cutting tool, often called the tool bit, is held rigidly in a tool post and can be fed towards or away from the work axis by manual or automated controls.
As the workpiece rotates, the tool bit cuts away a layer of material in a continuous spiral around the work. The linear and rotational movement combines to form the helical cutting path. By precisely controlling the depth of cut and position of the tool bit, intricate features like grooves, tapers, threads and profiles can be generated on the workpiece surface.
The excess material removed from the workpiece is called swarf or chips. Effective chip control is critical for an efficient turning process. The swarf must be removed quickly from the cutting area to prevent recutting and built-up edge on the tool bit. Proper chip control improves surface finish, tool life, and dimensional accuracy.
Types of Turning Operations
There are several fundamental types of turning operations, each designed to generate a specific geometry on the cylindrical workpiece:
- Facing - Machining the end surface of the workpiece by feeding the tool perpendicular to the work axis. This generates a flat surface.
- Turning - Machining the external cylindrical surface of the workpiece by feeding the tool parallel to the work axis. This reduces the diameter and generates the desired cylindrical form.
- Boring - Machining the internal cylindrical surface of the workpiece, enlarging the diameter, by feeding the tool parallel to the work axis inside a drilled hole.
- Parting or Cut-off - Machining a deep, narrow groove around the workpiece to cut it off, using a specially shaped tool bit.
- Grooving - Machining a groove around the circumference of the workpiece using a specially shaped tool bit. Grooves provide space for tool clearance, parting, threading, and aesthetics.
- Threading - Generating helical threads by coordinating the rotation of the workpiece and linear feedrate to move the tool bit in a precise helical path. Many different thread forms can be machined.
- Taper turning - Machining a uniformly tapered surface by offsetting the tool bit from parallel with the work axis to generate the required angle. The workpiece diameter decreases along its length.
- Form turning - Complex rotational forms and profiles can be generated by precisely controlling the position of the tool bit as the workpiece rotates. CNC control makes form turning highly accurate and repeatable.
Turning Machines and Equipment
Turning operations are performed on a lathe, the most basic type of turning machine. Engine lathes are generally horizontal spindle machines with manual controls, while CNC lathes have vertically oriented spindles and utilize computerized controls. CNC machines provide a higher degree of automation and precision.
The main components of a basic turning machine include:
- Headstock - Houses the main spindle, drive motor, and change gears. The spindle supports and rotates the workpiece. Variable speed control allows optimum cutting speeds.
- Tailstock - Located opposite the headstock and holds the tail center to support the free end of the workpiece. Can be slid horizontally to accommodate varying workpiece lengths.
- Tool post - Holds and secures the cutting tool rigidly in position. May be operated manually or with power feeds for automation.
- Carriage - The base that sits atop the bed and can be moved transversely by hand or with automated feeds. Allows moving the tool bit perpendicular and parallel to the work axis.
- Bed - Provides the foundation for the machine. Includes guideways that allow smooth movement of the carriage and tailstock.
- Lead screw - Rotating screw that moves the carriage and cross slide via nut drives. Coordinates with spindle rotation for feeds and threading.
- Chuck - A workholding device mounted in the headstock spindle. Typically has adjustable jaws for securing different workpieces.
- Centers - Pointed conical tips in the headstock and tailstock to securely hold each end of the workpiece. Provide precise alignment and rotation.
In addition to the standard features, CNC lathes utilize programmable controls and axes drives to automate the turning process. The computer control precisely coordinates the cutting tool motion and other machine functions like spindle speed and feedrate.
Turning Tools and Tool Geometry
Selecting the appropriate cutting tool is critical for effective turning operations. Turning tools come in various standard shapes and sizes and include unique geometries optimized for particular operations. Common tool bit geometries include:
- Round nose - General all-purpose turning tool for roughing and light finishing cuts. Produces strong cutting edge but relatively broad surface finish.
- Flat nose - Squared-off tool nose creates stronger tip for facing, turning high-feedrate cuts and reaching into corners.
- Diamond shape - Sharp pointed nose for turning grooves, parting, and threading. Tip angles down to 35-40 degrees provide narrow insertions.
- Knife shape - Form ground with angled nose and side relief ideal for cutting off workpieces.
- Threading - Ground with a 60 degree tip angle specifically for forming threads. Side and back relief provide necessary clearance.
- Boring - Round tipped bars insertable into pre-bored holes. Available in multiple diameters.
Carbide inserts with precision ground geometries are also commonly used in turning operations. They allow combining optimal tool geometry with incredibly hard cutting surfaces. Indexable carbide inserts are cost-effective, providing multiple cutting edges on one insert.
Geometry aspects like rake angle, side relief angles, nose radius, and inclination angle all influence cutting performance. CNC tool libraries store the ideal tool geometry data for various workpiece materials and operations. Selecting the correct tool geometry improves productivity, tool life, and machined surface finish.
Turning Process Parameters
There are several important turning process parameters that must be selected appropriately to generate the desired workpiece geometry efficiently. These include:
- Cutting speed - The speed at which the work surface moves past the cutting tool, typically measured in feet or meters per minute. Influences tool wear, chatter, surface finish, and more. Higher with carbide tools.
- Feed rate - The linear rate at which the tool bit moves across the work, typically measured in inches or mm per revolution. Affects productivity and surface finish.
- Depth of cut - Thickness of the chip or layer of material removed by the cutting tool in one pass. Limited by rigidity of the setup.
- Cutting fluid - Coolant or lubricant used to keep tool-work interface cool, flush away chips, and prevent buildup on tool. Essential for most operations besides parting.
Optimal settings depend on workpiece material, tool material, rigidity of setup, surface finish requirements, and more. Following handbook recommendations for each operation maximizes productivity and minimizes tool wear.
Turning Applications and Advantages
Turning is an extremely versatile machining process used across virtually every industry. It generates common geometries like cylinders, cones, and spheres with a high level of precision and efficiency. Typical applications include:
- Automotive - Crankshafts, pistons, axles, gears, and bearings
- Aerospace - Bushings, fittings, valves, and compressor parts
- Medical - Implants, surgical tools, needles, and syringe barrels
- Construction/Mining - Shafts, couplings, sheaves, rollers, and augers
- Fluid Handling - Valves, fittings, nozzles, pump housings, and plumbing parts
The key benefits of turning include:
- High dimensional accuracy and repeatability. Tolerances within 0.001 inches are attainable
- Excellent surface finish quality. Low surface roughness down to 8-16 microinches is possible.
- Versatile machining abilities. Complex geometries and threads can be generated.
- Fast material removal rate compared to other machining processes
- Applicable to nearly all machinable materials including metals, plastics and composites.
- Lower setup costs compared to milling. Simple tooling requires little adjustment.
- Minimal toxic cutting fluids required for most applications
By following proper procedures and selecting appropriate parameters, turning can produce precisely dimensioned parts with fine surface finishes. It is one of the most cost-effective and widely utilized manufacturing processes. CNC Milling CNC Machining