An Introduction to Turning Operations in CNC Machining (bending of metal Penelope)

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Turning is one of the most common machining processes performed on CNC machine tools. It involves rotating a cylindrical workpiece while a cutting tool is fed into it to remove material. This produces a precisely machined cylindrical shape. Turning operations are ideal for machining parts that have external cylindrical features such as diameters, shoulders, grooves, threads, tapers, etc. They enable fast material removal and good dimensional accuracy and surface finishes. Here is an overview of CNC turning.
What is Turning?
Turning, also known as cylindrical turning, is a machining process used to produce cylindrical parts by rotating the workpiece while a cutting tool removes material from its outer diameter (OD). The workpiece is usually clamped in a chuck and rotated while the cutter held in the tool post is fed towards it radially, cutting away material while creating the desired shape. This process utilizes a single point cutting tool for material removal. Turning produces cylindrical features like diameters, tapers, grooves, and threading. It is ideal for machining parts that are axisymmetric.
Types of Turning in CNC
There are several different types of turning operations that can be performed on CNC machine tools:
- Outer Diameter (OD) Turning - The most common turning operation. Produces diameters by feeding the cutter radially into the rotating workpiece.
- Facing - Machining the face of the workpiece by feeding the cutter into it axially. Performs facing cuts.
- Boring - Enlarging existing holes in the workpiece by feeding the cutter radially into them.
- Grooving/Parting - Cutting grooves and recesses by feeding the tool radially. Parting is a grooving operation that cuts through the entire workpiece.
- Threading - Machining threads by coordinating axial movement of the cutter with the workpiece rotation.
- Taper Turning - Producing tapered diameters by orienting the cutter at an angle to the workpiece axis.
- Profile Turning - Machining more complex contours and shapes by coordinating axial and radial cutter motions.
- Undercutting - Reaching into recesses and cutting overhangs by orienting the cutter at an angle.
Turning Methods
There are two main methods of CNC turning:
- External Turning - Turning of the external surfaces of a workpiece. The most common type of turning.
- Internal Turning - Also known as boring. Machining internal surfaces by reaching inside holes/openings in the workpiece. Requires a boring bar tool.
Both methods can utilize the same types of turning operations for different machining needs. External turning is more common but internal turning allows machining internal features like enlargeing holes.
Turning Process Overview
Here is a basic overview of the common steps in a CNC turning process:
1. The workpiece is loaded into a chuck or collet which clamps it tightly.
2. The chuck and workpiece are rotated by the spindle motor. Speed is determined by the material.
3. The cutting tool is loaded into the tool post and positioned near the workpiece.
4. Coolant is applied to the cutting area for lubrication and chip control.
5. The feed motion is initiated, moving the cutter to remove material from the rotating workpiece.
6. Cutting parameters like feed rate, depth of cut, and cut speed are optimized for the operation.
7. Multiple passes are made to achieve the desired dimensions and finish.
8. The tool path may combine linear and radial interpolating motions.
9. Finished parts are unloaded and new workpieces are loaded to repeat the process.
Benefits of CNC Turning
There are many advantages to using CNC machine tools for turning operations:
- High dimensional accuracy and repeatability. Tolerances within 0.001" are possible.
- Excellent surface finishes are achieved. Fine finishing cuts are possible.
- Low labor requirements. The CNC machine runs unattended once programmed.
- Fast material removal rates maximize productivity. Complex parts can be completed in one setup.
- Automation reduces human errors. Skilled operators are only needed for programming.
- Quick changeover between jobs. Fixtures allow rapid workholding setups.
- Flexibility to handle small and large batch sizes. Short and long production runs can utilize turning.
- Ability to machine a wide range of materials, from plastics to exotic alloys.
- Complete integration with other CNC operations like milling and drilling.
Turning is one of the most efficient and commonly used processes in CNC machining. Mastering turning operations unlocks huge productivity gains and part accuracy. Any manufacturer producing cylindrical components should consider implementing CNC turning. CNC Milling