Introduction to CNC Turning(how to strip chrome Lucien)
- source:WEINBERG CNC Machining
How CNC Turning Works
On a CNC lathe, the workpiece is securely clamped in a chuck or collet on the machine's rotating spindle. As the workpiece rotates, the cutting tool moves along the X and Z axes, engaging with the material and removing it to achieve the desired dimensions and features. The linear movements of the tool are precisely controlled by CNC programming code generated from CAD models or by manually writing G-code. This allows for the creation of complex forms, such as contours, tapers, grooves, and threads, with tight tolerances.
The cutting tool, typically made from carbide, high-speed steel, ceramic, diamond, or cubic boron nitride, is held rigidly in the tool post and can be indexed to present different edges to the workpiece. Multiple tools may be used in a sequence to machine various features of the part in a single setup. CNC turning centers have programmable coolant systems to flood the cutting area and evacuate chips and heat. The machine's rigid construction minimizes vibration and deflection, enabling stable cuts and fine surface finishes.
Benefits of CNC Turning
There are several key benefits that make CNC turning a ubiquitous manufacturing process:
- High precision and repeatability: CNC turning machines have positioning accuracy down to 0.0005 inches (0.0127mm) or better, allowing precise control of dimensions. Once the program is verified, the same part can be produced repeatedly within very tight tolerances.
- Complex geometries: The programmable nature of CNC turning allows the production of complex cylindrical forms and features that would be impossible or very difficult to produce manually. Concave and convex forms, oblique shapes, and asymmetric features can be machined with relative ease.
- Quick changeover: Changing over a CNC turning center to run a different part is as simple as loading a new CNC program. No manual setup is required, enabling flexible production of small lot sizes. Different workpiece sizes and features can be turned without adjustment of the machine.
- Automated operation: Once properly programmed, CNC turning machines can run largely unattended for extended periods. This allows parts to be produced efficiently with minimal operator intervention. One operator can effectively run multiple machines, maximizing productivity.
- Improved consistency: The computer control removes inconsistencies inherent in manual machining. CNC turning produces uniform quality parts regardless of operator skill. The automated parameters are repeatable over different batches and production runs.
- Reduced costs: The efficiency, consistency and minimization of skilled labor in CNC turning results in cost savings versus manual methods. Less scrap and tool wear also lowers overall costs and improves competitiveness. The rapid changeover facilitates economical small batch production.
CNC Turning Operations
There are several fundamental turning operations that are commonly performed on CNC lathes:
- Facing: A facing operation uses a square-shanked cutting tool to remove material from the face of a cylindrical workpiece and create a flat reference surface perpendicular to the axis of rotation. This establishes part length and provides a smooth surface for further operations.
- Turning: In longitudinal turning, the cutting tool moves parallel to the axis of the rotating workpiece to reduce the outer diameter and create the desired cylindrical form. Multiple passes are made at increasing depths to remove material efficiently.
- Boring: A boring tool with a rotating tip is fed into a stationary hole in the workpiece to enlarge the hole to specification. Precise hole size, straightness and surface finish can be achieved.
- Grooving: Using a specially shaped cutting tool, grooves of various widths and depths can be cut into the workpiece surface. Common groove types are straight, tapered, dovetail, concave and radius forms.
- Threading: Threading tools cut external and internal screw threads, producing strong and precise mating components. Single or multi-start threads can be machined helically around a workpiece.
- Parting/Cut off: A specially ground parting tool cuts entirely through the workpiece to sever a completed part from the raw material. Parting leaves a clean, square end surface.
- Drilling: Drilling operations can produce through holes or blind holes in the end or sides of the workpiece using rotating drill bits. Holes of various depths and diameters can be machined.
- Taper turning: By offsetting the tailstock, angled tapers can be turned on a workpiece. The taper angle is controlled by the degree of offset. Special form tools can also cut tapers.
- Profiling: Complex non-cylindrical contours, lobes, and radii can be generated through interpolation of the cutting tool movement in multiple axes simultaneously. 2D and 3D profiles are machined from CAD models.
Programming for CNC Turning
The programming required to produce parts on a CNC turning center can be done manually or with CAM software:
Manual programming involves coding G-code and M-code commands that specify the precise movements and actions of the machine. Variables for feed rate, depth of cut, tool offsets, spindle speed and other parameters are defined. The logical sequence of operations is written line-by-line. G-code is still commonly used by skilled machinists for simple turning jobs.
Computer-aided manufacturing (CAM) software allows the CNC program to be generated automatically based on a 3D model of the part. The desired operations are programmed interactively using the software without the need for G-code knowledge. CAM software optimizes toolpaths, manages cutter compensation, and simulates machining, providing sophisticated programming for 3D profiles. CAM programming is required for complex CNC turning jobs.
Whether programmed manually or with CAM, the CNC code is stored as a file on a machine control computer. The code is then run on the turning center to produce the physical part. The program can be modified and refined as needed to achieve the optimal turning sequence, parameters and finished results.
CNC Turning Capabilities
Modern CNC turning centers offer a wide range of capabilities that enable the production of precision parts suited to many industries and applications:
- Main and sub spindle allowing complete machining from bar stock in one setup
- Live tooling for milling, drilling and tapping without removing workpiece
- Y-axis to enable complex contours and off-centerline features
- B axis for producing contours at angles and 3D forms
- Backworking attachment for reaching internal features
- Single and multiple turrets for reduced tool changeover time
- Large through bores to accommodate long workpieces
- Powerful spindles reaching 10,000 RPM for cutting hard materials
- 12-foot bed lengths for machining larger components
- Automatic tool changer stores multiple tools for fast changeover
- High pressure coolant delivery up to 1000 PSI for chip control
- Automated feed systems to supply bar stock or pre-cut blanks
- Gantry loaders to automate loading/unloading of parts
In summary, CNC turning is a highly programmable machining process capable of efficiently producing precision cylindrical components. The combination of rotary workholding and computer numerically controlled tool motion allows complex geometries to be machined with minimal setup time. CNC turning offers advantages in accuracy, surface finish, repeatability, productivity and cost versus manual methods. Continued advances in machine tool design, cutting tools, programming options, automation, and capabilities are expanding the applications of CNC turning to meet the needs of modern manufacturing. CNC Milling