What is CNC Turning?(types of rivits Earl)

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CNC turning is a machining process that uses computer numerical control (CNC) to automate the turning of cylindrical parts. Turning produces rotational, symmetrical parts by rotating a cutting tool against a workpiece that is held in a chuck on a spindle. By precisely controlling the movement and cutting parameters, complex geometric features like threads, tapers, grooves, and profiles can be machined with accuracy and repeatability.
CNC turning centers are commonly used to produce parts at high volumes and with minimal setup times compared to manual turning. The CNC control allows the exact duplication of parts that may previously have required extensive manual work by highly skilled operators. Modern CNC lathes can have multiple axes of motion and live tooling capabilities allowing a range of milling and drilling operations to be performed in the same setup.
How Does CNC Turning Work?
CNC turning uses programmable logic controls to automate the turning process. Rather than manually controlling the cutting tools, settings like feed rate, spindle speed, and cut depth are controlled by coded instructions programmed into the CNC machine. Here are the basic steps in CNC turning:
1. Design and Programming - An engineer drafts the part blueprint and creates the CNC program using CAD/CAM software. Postprocessors convert the tool paths into gcode that the CNC can interpret.
2. Setup - The operator secures the workpiece in a chuck or collet on the spindle. Tools are loaded into the tool turret. The CNC control is set to the correct program.
3. Machining - The CNC executes the program step-by-step, controlling the motion of the cutting tool, spindle, and axes to machine the part to specifications. The tool turret indexes to bring new tools into position when needed.
4. Inspection - The finished part is removed and inspected. Measurements are taken to verify critical dimensions are within tolerance compared to the blueprint.
5. Editing - If needed, the CNC program is edited to adjust the tool paths and cutting parameters until the part meets all quality standards.
CNC turning accomplishes in minutes what would take an hour or more by manual turning. The automated and precision movements result in mass production and consistency unattainable with manual work.
CNC Turning Machines
There are several types of CNC turning centers designed for different parts, volumes, and complexity:
- CNC Chucking Lathes - For high volume production. Parts are held in a 3-jaw or collet chuck. Live tooling provides milling capability.
- CNC Vertical Turning Lathes - For very large diameter parts. Rotates the part horizontally and the tools cut vertically.
- CNC Turret Lathes - Offer multiple tool positions for reduced setups. Allow longer uninterrupted cutting.
- CNC Multi-Spindle Lathes - For high production. Multiple work spindles allow simultaneous machining.
- CNC Swiss-Style Lathes - Specialized for small, complex parts. Use guide bushing for support and overlapping machining.
Other specialized CNC turning centers include gang tool lathes, sliding headstock lathes, and slant-bed CNC lathes. The variety of machines provide flexible options depending on the needs of the application.
Turning Operations Performed by CNC
Here are some of the common turning operations that CNC automation enhances versus manual machining:
- Facing - Machining the face of the part square to the axis of rotation. Performed by feeding a cutter perpendicular to the rotating workpiece.
- Turning - Machining the external diameter to size by feeding the cutter parallel to the rotating part. Produces the basic external profile.
- Boring - An internal turning operation that enlarges holes and bores. Requires a single point boring tool or boring head.
- Grooving - Cutting grooves of various widths and depths along the diameter of the part. Uses a specially shaped grooving tool.
- Parting - Cutting off completed parts from the source material by feeding a blade tool radially into the workpiece.
- Threading - Using a specially ground tool to cut external and internal screw threads. CNC precisely coordinates the feeds to create accurate thread forms.
- Drilling - Machining holes using rotating twist drills or indexable drills pressed into the rotating workpiece.
- Tapping - Cutting internal screw threads by coordinating the rotation and feed of a tap tool.
CNC brings speed, accuracy, and consistency to each of these fundamental turning processes to maximize productivity.
Benefits of CNC Turning
There are many advantages CNC turning offers over manual turning techniques:
- Higher Production Rates - CNC machines parts uninterrupted 24/7. More parts machined per hour than manual methods.
- Improved Consistency - Every part identically machined within microns. CNC repeatability eliminates human error.
- Reduced Setup Time - CNC allows quick changeover between parts. Minimizes downtime between production runs.
- Complex Geometries - Intricate contours, shapes, angles easily programmed. Less reliance on highly skilled operators.
- Automated Inspection - Probing cycles check dimensions and verify part quality. Reduces manual inspection time.
- Safer Operation - CNC eliminates risks associated with manual turning. Programmable control safer than hand feeding tools.
- Lower Labor Costs - One skilled programmer and setup tech can run multiple machines. Requires less manual labor.
- Increased Flexibility - Quick changeover to new parts. Easily edit programs to change dimensions. New designs manufactured faster.
From high volume production runs to fast prototyping of new designs, CNC turning centers provide manufacturers with improved efficiency and cost-savings over manual turning.
Programming CNC Turning
Creating CNC turning programs was traditionally done manually using G-code. Modern CAM software has simplified programming to the point where machinists only require basic knowledge of CNC. Here is an overview of CNC turning programming:
- Blueprint Analysis - Critical dimensions, features, and tolerances are identified. Stock material, workholding requirements and tooling needs determined.
- Tool Selection - Programmer chooses suitable tooling from vast libraries of pre-defined tools. Correct inserts specified for optimal tool life and surface finish.
- Machining Process - Turning operations like roughing, finishing and grooving are sequenced in the optimal order to machine the part efficiently.
- Tool Path Generation - CAM software calculates precise tool paths based on part geometry, stock material, tooling dimensions, and machining parameters.
- Post Processing - Tool paths converted to specific g-code for the make and model of CNC machine. Allowing machine-specific capabilities and flavors.
- Simulation - Program simulated visually to check for errors like incorrect orientations or collisions before attempting on machine.
- Program Editing - Program fine-tuned by editing cutting conditions, tweaking tool paths, and adjusting speeds and feeds to optimize cycle times.
- Program Verification - First part cycle verifies program on machine before starting production run. Confirms proper turning strategy and dimensions.
The combination CAM software and CNC now allows parts programmed by anyone with basic computer skills rather than master machinists. Setup technicians simply load the verified programs and run production.
Turning Inserts and Tooling
Proper tool selection helps maximize productivity in CNC turning. Carbide inserts with special geometries and coatings are engineered for optimal cutting performance and tool life. Here are some common types of turning inserts:
- Wiper Inserts - Special top geometries for finishing with excellent surface finish and smaller contact area.
- Chipbreaker Inserts - Complex chipbreaker geometries that excel in roughing and interrupted cuts.
- Insert Grades - Advanced substrate and coating combinations for specific materials. Higher speed machining potential.
- Insert Edge Preps - Edge treatments like chamfers or hones for stronger edges. Help depth of cut, tool life, and workpiece entry.
- Multifaceted Inserts - Inserts with more than one cutting corner to distribute wear and utilize fresh cutting edges.
- Grooving Inserts - Inserts ground with wider top geometry for grooving, parting and cutoff work.
- Threading Inserts - Ground with a 60° profile for cutting internal and external screw threads.
Carbide inserts allow high speed machining while maintaining precision and long tool life. Using the optimal insert for each operation is key to maximizing productivity in CNC turning.
In Summary
CNC turning automation has revolutionized the production of rotational parts. By utilizing programmable machine tools, turning has transitioned from an art mastered by machinists into a production method programmable by anyone. Tighter tolerances, faster cycle times, and increased complexity are now achievable compared to manual turning techniques. Continuous improvements in CNC technology, cutting tools, and programming make modern CNC turning a highly efficient manufacturing process for industries producing high precision, cylindrical parts. CNC Milling