Introduction to CNC Turning(cnc tips Natividad)

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CNC (Computer Numerical Control) turning is a machining process used to produce cylindrical parts on a CNC lathe. The workpiece is rotated at high speeds while a single point cutting tool removes material to cut the desired shape. CNC turning is an efficient and accurate process that can produce complex geometries with tight tolerances. This article will provide an overview of CNC turning operations, including turning methods, tooling, and equipment.
Types of Turning Operations
There are several common turning operations that can be performed on a CNC lathe:
- Facing - machining the end surfaces of a cylindrical workpiece. This produces a flat reference surface perpendicular to the axis of rotation.
- OD Turning - machining the external diameter of a cylindrical workpiece. The cutting tool moves radially across the rotating workpiece to reduce the diameter to the desired dimension.
- ID Turning - machining the internal diameter of a cylindrical workpiece. The cutting tool moves radially into the center of the workpiece to enlarge the diameter to specification.
- Taper Turning - machining a tapered diameter on the external or internal surface of a workpiece. This requires coordinated movement of the cutting tool and tailstock to produce the taper.
- Grooving - machining grooves or undercuts on the OD or ID of the workpiece. This is done with specially shaped cutting tools.
- Threading - machining screw threads on the OD or ID of a workpiece by synchronizing the tool movement with the rotation.
- Boring - accurately sizing and finishing pre-bored holes to achieve high dimensional accuracy and surface finish.
- Parting/Cut Off - severing a finished part from the bar stock it was machined from. A specially shaped blade makes the cut.
CNC Turning Methods
There are two primary turning methods:
- Conventional Turning - uses a single point cutting tool held statically at a fixed angle relative to the workpiece. For facing and OD turning, the tool moves perpendicular to the axis of rotation. For ID turning, the tool moves parallel to the axis.
- Turning with Live Tooling - uses a cutting tool mounted in a motorized "live" toolholder, allowing it to rotate and mill the workpiece. This enables more complex geometries, grooves, slots, and threads to be machined without unclamping the workpiece.
Cutting Tools for CNC Turning
A variety of interchangeable cutting tool inserts can be used for the different turning operations:
- Roughing - formed inserts with a sharp cutting edge for heavy material removal. Carbide grades withstand high temperatures.
- Finishing - sharper edged inserts often with a precision ground radius to produce fine surface finishes. Coated carbides or ceramic inserts are common.
- Threading - Ground inserts with a 60 degree profile for OD threading. Carbide or CBN inserts for strength and wear resistance.
- Grooving/Parting - Inserts with a thin width to machine narrow grooves. Carbide or ceramic materials with titanium-aluminum-nitride (TiAlN) coatings.
- Boring - Fine-grained uncoated carbide inserts shaped for boring accuracy. Ceramic or CBN inserts optionally used.
Tool holding is done via ISO standard tool holders. These rigid holders provide precision clamping and accurate positioning of inserts. Common tool holder styles used are SCLCR/L, SCLCL/L, SDJCR/L, and SVVBN.
CNC Lathe Machine Configurations
CNC lathes come in a variety of sizes and configurations:
- Horizontal Spindle - The most common orientation, with the workpiece rotating horizontally in front of the operator. The cutting tools are mounted vertically on the tool turret.
- Vertical Spindle - The workpiece rotates vertically, allowing chips to fall away from the work area. The tools are positioned horizontally around the workpiece.
- Twin Spindle - Has two spindles allowing simultaneous machining of both ends of a part. This improves production rates considerably.
- Chuck and Bar Feed - Uses a 12 foot bar feeder to automatically load bar stock into the lathe chuck for production turning of small parts. Minimizes manual handling.
- Flat Bed - An open bed way CNC lathe capable of handling very large workpieces not easily accommodated on a standard CNC lathe.
- Multitasking - CNC turning centers that combine turning functionality with milling, drilling, and other processes for complete machining in one setup.
CNC Turning Process Planning
Effective CNC turning requires advanced process planning before any machining is done. Key elements include:
- Design Analysis - Reviewing the print and solid model to determine all required turning features and necessary operations.
- Fixturing - Selecting/designing fixtures, chucks, collets that will hold the workpiece securely through all operations.
- Tool Selection - Choosing the best tool inserts based on the material, dimensions, tolerances, and surface finish requirements.
- Feeds/Speeds - Calculating the optimal spindle speeds and feed rates based on tooling, depth of cut, material, etc. This balances cycle time with tool life.
- Program Generation - Writing the CNC program code (G-code) that controls all aspects of the machining sequence. CAD/CAM systems are typically used.
In summary, CNC turning is a versatile machining process capable of producing a wide variety of precision cylindrical components. The combination of advanced CNC machine tools, carbide cutting tools, and CAD/CAM programming enables the production of complex parts with accuracy and repeatability. With continued innovations in cutting tools and equipment, CNC turning will remain a essential manufacturing process for high-value components. CNC Milling