Introduction to Turning Operations in CNC Machining(what is bead blasting Borg)

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Turning is one of the most common and important machining processes used in manufacturing. It involves rotating a cutting tool against the surface of a cylindrical workpiece to cut away material and shape the part. Turning operations are performed on a lathe, which holds the workpiece while it rotates at high speeds. The cutting tool is fed towards the workpiece to remove material.
Turning is an efficient method for machining rotational, symmetric parts like shafts, pins, axles, spindles, and more. It can produce parts with excellent dimensional accuracy and surface finishes. Turning is also versatile - it can perform a variety of operations like facing, boring, grooving, threading, tapering, knurling, and more. Understanding what turning is and how it works is essential for those involved in CNC machining and part production.
What is Turning?
Turning is a machining process where a cutting tool removes material from the outer diameter of a rotating cylindrical workpiece. The workpiece is held and rotated by the headstock while the cutting tool is fed towards it along the axis of rotation. As the tool makes contact with the workpiece, it cuts away material in the form of chips to create the desired shape.
The turning operation usually takes place on a machine called a lathe. Lathes have been around for thousands of years but modern CNC lathes allow for precise computer control of the cutting process. On a manual lathe, the operator controls the cutting by handwheels; on a CNC lathe, the movements are controlled by computer numerical control (CNC) commands.
How Does Turning Work?
During a basic turning operation, the workpiece rotates at a constant speed while the single point cutting tool moves at a constant rate against it. This produces a cylindrical cut with a specific diameter and surface finish. The depth of cut, feed rate, speed, and tool path can all be precisely controlled to shape the workpiece as required.
As the workpiece rotates, the cutting tool makes contact with the surface and shears away a chip of material. The shear plane is along the cutting edge of the tool which must be sharper than the material being cut. The material on the shear plane undergoes plastic deformation before being separated. High heat is generated in this process which must be properly cooled.
The feed rate determines how much material is removed per revolution while the depth of cut controls how deep the tool penetrates radially into the workpiece. These parameters along with cutting speed determine machining time, tool life, and final part quality. Suitable cutting parameters depend on the specific material, tool material, rigidity of setup, and surface finish requirements.
Types of Turning Operations
Many different operations can be performed on a CNC lathe to create all kinds of rotational parts. Common turning operations include:
- Facing: Machining the end face of a cylindrical workpiece flat and perpendicular to its axis. This is often the first operation.
- Straight Turning: Machining the outer diameter of a cylindrical workpiece to a required dimension. Also known as cylindrical turning.
- Taper Turning: Machining a tapered contour on the cylindrical workpiece. Done by offsetting the tool or tailstock.
- Grooving: Cutting a groove of a specific width and depth along the axis of the workpiece.
- Threading: Cutting threads externally or internally on workpieces using single point threading tools.
- Boring: Enlarging and smoothing existing holes in a workpiece along its axis. Requires boring bars.
- Parting/Cutoff: Separating a finished part from its parent stock using a specially shaped parting tool.
- Knurling: Creating crossed diagonal pattern lines on the workpiece to provide improved grip. Uses a knurling tool.
- Chamfering: Beveling sharp edges and creating chamfers on the workpiece.
- Drilling: Creating a round hole in the end face or side of the workpiece using a drill bit.
- Reaming: Finishing and sizing existing holes to high tolerances using a reamer tool.
These operations demonstrate the versatility of CNC turning centers. Complex parts can be produced by programming the appropriate sequence of turning operations.
Turning Methods
There are two main methods of turning - longitudinal turning and face turning.
Longitudinal turning, also known as cylindrical turning, is the most common type. It is used to reduce the outside diameter of a workpiece rotating between centers or a chuck. The cutting tool feeds parallel to the rotational axis to cut the outer cylindrical profile. Operations like straight turning, facing, and threading are done this way.
Face turning involves feeding the tool at right angles to the axis of rotation to cut surfaces on the end face of the workpiece. Operations like boring, grooving, and facing are performed this way. The workpiece must be held in a chuck for rigidity.
In practice, most turning operations involve a combination of longitudinal and face turning. The distinction is important for programming the CNC to move the tool along the correct axes. Proper turning method selection avoids collisions and improper cutting.
Turning Equipment
CNC turning centers come in various configurations but mainly consist of the following components:
- Headstock: Holds the revolving workpiece on its spindle nose and provides the rotational drive. Different workholding methods like chucks or collets can be used.
- Tailstock: Located opposite the headstock to support the free end of long workpieces. It can also hold tools like drills or reamers.
- Tool turret: Holds multiple cutting tools and indexes them into position for automatic tool changing. May be mounted transversely or longitudinally.
- Tool post: Holds a single cutting tool rigidly for straight turning operations. Can be manual or automatic.
- Channels: Guideways that allow the transverse movement of tool turret or tool post during cutting.
- Control panel: Computer control unit that stores machining programs and commands the movements and functions.
- Chip conveyor: Removes the debris and swarf produced during machining. Keeps the area clean.
Precision components made of durable materials provide the stiffness, accuracy, and repeatability needed for turning operations. The capabilities of the machining center depend on the specifications of these components.
Turning Operations Requirements
Performing turning operations on a CNC machining center requires:
- Rigid setup: The workpiece must be securely clamped with minimal overhang to prevent vibration or chatter during cutting.
- High spindle speeds: Turning uses higher rotational speeds compared to milling to get optimum cutting conditions. Speeds range from 100 to 2500 RPM.
- Proper feeds/speeds: Appropriate feed rates, depth of cuts, and cutting speeds prolong tool life and give better surface finishes.
- Suitable workpiece: The blank material must be cylindrical and dimensionally suitable for the features to be machined.
- Sharp tools: Turning tools like high-speed steel or carbide inserts must have sharp cutting edges and proper rake angles.
- Coolant: High pressure coolant directed at the cutting zone prevents overheating and removes chips.
Proper fixturing, tooling selection, feeds/speeds calculations, and cooling are critical factors for viable turning operations. The CNC program must generate toolpaths accordingly.
Benefits of Turning
Compared to other machining processes, turning offers several advantages:
- Excellent dimensional accuracy and surface finish quality. Tolerances up to 0.01 mm are possible.
- Ability to produce complex parts via turning operations like grooving, threading, drilling, boring etc.
- No burrs or sharp edges are present on the machined surfaces.
- Setup time is low compared to milling processes.
- Cutting tools have long tool life owing to mostly single point contact.
- Low forces are required to remove material. Power consumption is low.
- High material removal rates are possible up to 15 cubic inches per minute.
- Variety of materials can be machined including metals, plastics, composites etc.
- Automation using CNC turning centers reduces labor cost and idle times.
Turning's capabilities to manufacture precision round parts make it an indispensable manufacturing process.
Turning is a versatile machining process that rotates a workpiece against a cutting tool to produce cylindrical and facing cuts. It is applied primarily to shape parts that have a radial symmetry along a rotational axis. The numerous operations possible on modern CNC turning centers allow complex prototyping and mass production of precision parts for machinery, automotive, aerospace, and other industries. Understanding what turning is and how it works enables better utilization of this important machining technology. CNC Milling