An Introduction to CNC Turning(light weight metal Bevis)
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How Does CNC Turning Work?
CNC turning relies on predefined toolpaths and code to control the movements of the cutting tool and achieve the desired part shape and dimensions. The basic CNC turning process involves the workpiece being securely clamped in a chuck or collet on the spindle of the lathe. As the spindle rotates, the cutting tool moves longitudinally along the axis of the workpiece, gradually removing material and forming the outside profile.
The movements of the cutting tool are controlled by G-code and M-code instructions that have been programmed into the CNC machine controller. G-code provides the coordinate data which guides the tool movements, while M-code controls auxiliary functions like coolant flow or spindle speed. Skilled CNC programmers determine the right toolpaths and code needed to machine each feature of the part based on its design specifications.
The programmed code functions as a set of step-by-step instructions that enable automated precision turning without continuous manual intervention by the operator. Modern CNC controls enable adjustments to the program as needed to optimize the machining process. Operators monitor the process and may make minor adjustments, but the CNC system allows for largely hands-off production once the part program is proven out.
Key Components of CNC Turning
CNC lathes contain the same basic components as manual lathes, but with the added CNC controls. Key components include:
- Headstock: The headstock contains the spindle which grips the workpiece and rotates it at high speeds during the machining process. The spindle is coupled to a motor which provides the drive power and speed control.
- Tailstock: The tailstock is located opposite the headstock and can hold tooling or fixtures for supporting the free end of the workpiece. It provides flexibility in machining longer workpieces.
- Tool turret: The turret or toolpost holds the cutting tools and can index different tools into the cutting position when needed. Having multiple tools mounted enables automated tool changes for different operations.
- Tool carousel: An automated tool carousel provides access to a larger selection of tooling stored off the machine, enabling automatic tool changes for more complex part programming.
- Axis slides: Precision ground slideways enable precise longitudinal and transverse motions of the cutting tool, allowing for the machining of contoured, asymmetrical turning features.
- Control panel: The CNC control panel allows the operator to input and adjust the part program, set up the machine, initiate production, and monitor the process.
- Chip conveyor: Shavings and chips are evacuated from the machining area through the chip conveyor. Maintaining cleanliness is critical for precision machining.
- Coolant system: Coolant is applied to the cutting area to control the temperature, flush away chips, and prolong tool life. Coolant flow is programmed into the CNC control.
Advantages of CNC Turning
There are several key advantages that make CNC turning widely used for high production manufacturing:
- Precision and Accuracy: The programmed tool movements and precision ground components of CNC lathes enable extremely tight tolerances down to +/- 0.0005 inches. Complex geometry and fine surface finishes can be achieved.
- Automation: Once programmed and set up, CNC turning enables 'hands-off' production with minimal operator involvement compared to manual turning. Automating repetitive tasks improves consistency.
- Quick Changeover: Changing over CNC programs and tools is fast and simple compared to manual changeovers. This allows economical production of small batches.
- Reduced Lead Times: CNC turning improves production rates and reduces completed part lead times. The non-stop production and unattended capability provide faster throughput.
- Improved Safety: Automating dangerous manual tasks results in a safer working environment for the operator. The protective machine enclosure also improves safety.
- Advanced Capabilities: Modern CNC lathes offer live tooling, multi-axis contouring, and other advanced features that greatly expand the range of achievable part geometries.
- Consistent Quality: Minimizing manual work improves part consistency. CNC automation provides repeatable precision and accuracy from the first part to the last.
Common CNC Turning Operations
A wide variety of turning operations can be performed on CNC lathes, including:
- Facing: Machining the face of the part square to the axis of rotation. Performed using a standard turning tool.
- OD Turning: Machining the external diameter of the part. Performed using standard turning inserts and tooling.
- Boring: Enlarging holes or internal diameters often using single point boring bars. Allows accurate sizing and finishing of pre-drilled holes.
- Grooving: Machining grooves or recess features in the outside or face of the part using form tools.
- Parting/Cutoff: Cutting off the finished part from the excess barstock using a blade tool.
- Threading: Single or multi-start thread cutting using qualified threading tooling.
- Drilling: Adding holes axially in the face or OD using live drilling tools. Holes can be spot drilled or pencil drilled.
- Tapping: Tapping drilled holes using live or rigid tapping methods.
- Milling: Addition of flats, slots, keyways, splines and other features, performed using live milling tools and multiaxis contouring.
Workholding for CNC Turning
Proper workholding is critical for precision and safety during CNC turning operations. Common workholding methods include:
- 3-Jaw Chucks: The most common method. The three movable jaws securely clamp the workpiece. High precision chucks provide maximum rigidity and accuracy.
- Collet Chucks: Provide tight concentric clamping of bar stock or pre-turned diameters when high precision is required. Available in a range of sizes and styles.
- 4-Jaw Chucks: Used when eccentric workpieces or non-round shapes must be machined. The four independent jaws are manually adjusted.
- Faceplates: Utilized for oddly-shaped work lacking a uniform diameter for chucking. Parts are fastened directly to the faceplate.
- Steady Rests: Support the free end of long slender workpieces to prevent deflection and vibration under cutting forces.
- Follower Rests: Also called traveling steady rests. They ride against the workpiece and move longitudinally with the tool to provide support near the cutting zone.
- Mandrels: Used for holding the ID of rings, bushings, sleeves and other tubular parts for machining the OD. Provide good concentricity.
Optimizing CNC Turning Operations
To consistently produce quality turned parts, CNC turning processes must be continuously monitored and optimized. Key optimization strategies include:
- Selecting the right tooling - Carbide insert material, tool geometry, edge preparation and coatings must match the application. Proper tool selection improves surface finish and tool life.
- Utilizing correct feeds and speeds - Following manufacturer's recommendations for the specific material, insert grade, depth of cut and operation. Optimizes cutting conditions.
- Employing proper chipbreaking techniques - Using chipbreaker inserts or programming intermittent cuts to break chips and evacuate them from the cutting zone. Critical for effective machining.
- Applying appropriate coolant - Using the proper flow rate and coolant nozzle placement to break chips and maintain a consistent process temperature.
- Minimizing vibration/chatter - Properly securing the workpiece, maintaining tight tolerances on tooling, and taking lighter cuts to prevent chatter which degrades surface finish.
- Adjusting in-process - Making minor program tweaks based on measurements of finished parts. Compensates for slight tool wear or machine performance drift.
By following precision machining best practices and leveraging the newest capabilities of CNC turning technology, manufacturers can improve productivity, part quality, and cost-effectiveness. CNC Milling CNC Machining