Introduction to CNC Turning(cnc machining tools Karen)
- source:BREDA CNC Machining
CNC turning has become one of the most common and important machining processes used in manufacturing industries today. Compared to manual turning, CNC offers improved efficiency, accuracy, and capability to produce complex parts. This article will provide an overview of CNC turning, including the basic principles, primary components, machining operations, and benefits.
How CNC Turning Works
CNC turning uses programmable logic controls to operate a lathe. The basic components involved in CNC turning are the CNC controller, servo drives, servo motors, and cutting tools. The CNC controller interprets instructions from CAD/CAM software and converts them into commands for the servo drives and motors. The servo drives control the axis motors to position the cutting tool and workpiece for machining operations. Common CNC controlled axes on a lathe include X (cross slide), Z (vertical slide), C (chuck) and Y (turret indexing).
The main machining operations performed on CNC turning centers are facing, boring, grooving, threading, tapering, drilling, and cutting-off. The turret holds multiple tools and can automatically index to the required tool for a specific operation in the program sequence. The part is machined by precisely controlling the movements between the rotating workpiece and moving cutting tool. Typical CNC turning cycles include roughing, finishing, threading, grooving, drilling, and cut-off. More advanced multi-axis CNC lathes allow complex contours and shapes to be machined.
Benefits of CNC Turning
There are many advantages to using CNC turning centers instead of manual lathes:
- Increased Automation - The automated nature of CNC turning minimizes the need for operator intervention once the machine is setup and running. The CNC program guides all of the machining operations.
- Improved Consistency - CNC automation ensures high repeatability and consistency in the manufacturing process. The same program can be reused for production runs of parts.
- Greater Accuracy - CNC machines provide more precise control over feeds, speeds, and positioning. This results in better tolerances and surface finishes on turned parts. Precision is further enhanced with the use of servo and stepper motors.
- Faster Machining - CNC turning centers can operate at much faster feeds and speeds compared to manual machines. Cycle times are reduced through automated tool changes and movements.
- Complex Capabilities - The programmable nature of CNC allows the production of complex 3D shapes and precision machined profiles not feasible on manual lathes. Multi-axis CNC lathes add further complexity capabilities.
- Safer Operation - The automated operation of CNC turning centers results in improved workplace safety by minimizing the need for operators to directly interface with the machine during cutting. The risk of accidents is greatly reduced.
- Less Skilled Labor - With the automation and programming doing most of the work, less skilled labor is required to oversee and operate CNC turning machines compared to manual lathes.
- Increased Uptime - CNC turning centers typically have lower setup times between jobs. Faster changeovers and tooling setups mean increased uptime and productivity for the machine shop.
CNC Turning Operations
The most common operations that can be performed on CNC turning centers include:
Facing - Machining the face of the raw material down to a desired length prior to turning outer diameters. This establishes the final part length dimension.
Rough Turning - Roughing passes remove the bulk of material using deeper depths of cut and faster feeds to hog out material efficiently. This process leaves a small amount of excess stock for the finishing operation.
Finish Turning - The finishing operation uses lighter finishing cuts to achieve the final dimensions, surface finish, and tolerances specified on the engineering drawing. Finishing cuts utilize slower feed rates.
Boring - An internal boring bar machines holes to accurate diameters and cylindrical form. Concentricity of bored holes is critical for assembling parts onto shafts and pins.
Drilling - Drilling operations on CNC lathes allow holes to be machined into the sides or face of the part using drill bits held in tool holders. Canned drilling cycles automate the repetitive pecking motion.
Grooving - Cutting grooves in the OD (outer diameter) or face is performed using a grooving or cutoff tool. Grooving is an efficient method for breaking edges, parting off, and cutting lubrication channels.
Threading - Threads can be cut on the OD or ID (inner diameter) using specialized thread cutting tools. Single point or multi-point insert threading tools are programmed to cut common or custom thread forms.
Taper Turning - A tapered form can be machined using the programmable offsets and geometry calculations of the CNC controller. This interpolates the lateral movements between the tool and workpiece to create the taper angle.
Cut-Off - The cutoff operation cuts the finished part off the excess barstock material, parting at a predetermined length position. This can be done in one operation or as a separate step.
CNC Turning Methods
While basic CNC turning relies on rotating the workpiece while the cutter moves linearly, there are also more advanced methods that improve capabilities:
- Eccentric Turning - The workpiece center is programmatically offset from true center in the chuck. This allows complex cam and eccentric profiles to be machined with a single point cutting tool.
- Multi-Axis Turning - Additional axes of motion added to the linear and rotary movements provide angled approaches and contouring capability. Multi-axis CNC lathes have improved complexity and functionality.
- Turn-Mill Machining - CNC lathes with live milling tools, B-axis, and C-axis allow milling operations to be performed on the workpiece without unclamping. This provides flexibility for mills, slots, flats, square profiles, and complex prismatic shapes to be done in one setup.
Programming CNC Turning
Manual programming of CNC turning involves writing machine code (G-code) to define the operations. However, most CNC turning is programmed using CAD/CAM software. This provides an interactive graphical interface for defining the part geometry, toolpaths, and post-processing the code for the machine. The basic steps in CAM programming for CNC turning include:
1. Import Part Geometry - The 3D model geometry is imported into the CAM system. This can come from the original CAD file or may require remodeling the blueprint design.
2. Select Material - The workpiece material, diameter and length dimensions are specified. The material database provides the required tooling and cutting data.
3. Define Operations - The necessary operations (facing, roughing, finishing, grooving, etc) are selected and tooling is assigned. Machining parameters and cutting conditions are set.
4. Generate Toolpaths - The CAM software calculates the toolpaths required to machine the features for the operations selected. The toolpaths can be graphically simulated to verify clearance and performance.
5. Post-Process - The toolpaths are translated into the specific machine code syntax required by the CNC turning machine through post-processing. Any required codes for workholding, tool changes, coolant, etc are added.
6. Transfer Program - The verified CNC program is then transferred to the machine control via networking or transfer media. The program is now ready to be loaded into the CNC control and run to make the part.
Setup is required prior to running the program to ensure the part is properly clamped, tooling is loaded, work coordinates are set, and other prerequisites for machining are complete. The program then runs semi-automatically, prompting the operator as needed for tool changes and measurements.
CNC turning has evolved into an essential manufacturing process enabling the automated production of cylindrical components. While early CNC lathes were limited to basic turning, modern CNC lathes can handle multiple axes, live tooling, and multi-tasking capabilities. The programmable nature of CNC turning makes it a versatile machining center for everything from high volume automotive parts to low volume aerospace components. Implementing CNC turning improves consistency and productivity for precision turned parts. CNC Milling CNC Machining