An Overview of Turning Operations on CNC Lathes(prototype to manufacturing Tiffany)

  • Time:
  • Click:6
  • source:YESCOM CNC Machining
Turning is one of the most common machining processes performed on computer numerical control (CNC) lathes. It involves rotating a part while a single-point cutting tool is fed linearly against it to cut away material. Turning produces cylindrical shapes and can be used to reduce diameters, face surfaces, and produce various geometric features through the movement of the cutting tool. In this article, we will provide an overview of turning operations on CNC lathes, including the basics of the process, types of turning, tooling considerations, and programming methods.
The Turning Process
The turning process utilizes a rotating cylindrical workpiece, known as the work, that is held firmly in the chuck of a lathe. As the chuck rotates, a cutting tool is fed towards the work linearly to remove material. The cutting tool only engages a small portion of the work at a time, taking successive cuts to reduce the diameter or face the end of the workpiece. Chips are formed as the tool shears away the material and are evacuated by chip breakers and cutting fluid. Precise movements of the tool allow for cutting of external diameters, tapers, grooves, shoulders, and other geometric features. The tool moves in two axes – longitudinally parallel to the workpiece axis of rotation, and radially perpendicular to it.
Types of Turning Operations
There are several basic types of turning operations that can be performed on CNC lathes:
- Facing: Machining the end face of a cylindrical part. The tool feeds at 90 degrees into the end of the rotating workpiece to flatten and surface the end of the part.
- OD (Outside Diameter) Turning: Reducing the outer diameter of a cylindrical part. The tool feeds parallel to the work axis to take radial cuts that remove material and reduce the OD.
- ID (Inside Diameter) Turning: Machining the inner diameter of a tubular or bored component. The tool feeds into the ID at an angle to enlarge or finish machine an existing hole. A boring bar is typically used.
- Taper Turning: Producing a tapered diameter by feeding the tool at an angle to the rotating workpiece. The depth of cut changes gradually to form the tapered profile.
- Grooving: Cutting a groove along the OD or face of the part. Performed with a specially shaped cutting tool.
- Threading: Cutting screw threads along the OD or ID. Requires coordinated longitudinal and radial movements to produce the thread form.
- Profiling: Machining complex angular or curvilinear shapes by moving the tool in two or more axes under CNC program control.
Turning Tooling
A variety of single-point cutting tools can be used for turning operations. The most common are:
- Round Insert Tools: Use indexable round inserts for versatility in OD turning, facing, and boring. Carbide inserts with sharp cutting edges provide good tool life.
- Cutoff Tools: Used for parting off finished parts. Designed for rigidity and strength when separating parts from barstock.
- Threading Tools: Ground tools for cutting thread forms. May have 60 degree carbide inserts or ground HSS/cobalt tooling. Multiple insert edges for repeated threading.
- Boring Bars: Long overhang tools for internal turning. May have replaceable carbide inserts or HSS boring bars. Available in many styles and sizes.
- Form Tools: Shaped HSS or carbide tools for turning profiles and specialized shapes not possible with standard inserts.
Proper selection of tool geometry, coating, and grade is necessary to optimize turning performance for a given material. The toolholder style also impacts rigidity, access, and cutting forces.
CNC Turning Programming
Creating CNC turning programs requires defining the machining operations, cutting conditions, and toolpaths. While manual programming is possible using G-code, most CNC turning programming is now done with CAM software. Common steps in CNC turning programming include:
- Define the raw material size in the CAD/CAM system
- Specify the required turned geometry, either from a CAD model or by interactive feature definition
- Select suitable tooling and enter correct tool geometry data
- Set machining parameters such as feed rate, spindle speed, and depth of cut
- Generate toolpaths including facing, OD/ID turning, drilling, grooving, and threading moves
- Add tool change positions and other non-cutting moves
- Set feed rates for different operations and transitions
- Simulate program to verify toolpaths and avoid errors
- Post-process to convert code to the machine-specific format
- Output code to send to the CNC lathe controller
For complex turned parts with many features, CAM software automates the programming process significantly compared to manual G-code programming. However, an experienced CNC machinist can still optimize the toolpaths and parameters to gain maximum efficiency and part quality.
Turning is an essential capability of CNC lathes that allows high production machining of precision round parts. Using programmable machine motions and advanced tooling, modern CNC turning centers can hold extremely tight tolerances and create complex geometries. With the right combination of process planning, tooling, programming, and machining parameters, outstanding turned part quality and efficiency can be achieved. Continued advances in CNC technology are also expanding the flexibility, automation, and intelligence of computer controlled turning. CNC Milling CNC Machining