In this article, we will provide an overview of CNC turning, looking at the key components of a CNC lathe, the turning process, tooling options, and programming considerations. Whether you are new to CNC machining or looking to get a refresher on this essential process, this guide will provide the key information you need to understand CNC turning.
Components of a CNC Lathe
CNC lathes consist of a bed, headstock, carriage, and tailstock. The bed provides the foundation for the machine and consists of guideways that allow the carriage and tailstock to move parallel to the axis of rotation. The headstock contains the main spindle, drive motor, and speed reduction unit. It spins the workpiece at a set speed for the turning operation.
The carriage houses the tool post and tool holder. It moves back and forth along the bed, enabling the cutting tool to traverse across the workpiece. The tailstock is mounted opposite the headstock and can hold live centers or other tools needed for turning operations. It slides along the bed to position these tools as needed.
Lathes designed specifically for CNC integration will also include servo motors, ballscrews, linear guideways, and a computerized control system. These components work together to precisely control the motion and position of the cutting tool during turning operations.
The Turning Process
During a basic turning operation, the workpiece is held and rotated by the headstock while the cutting tool feeds into it, shearing away material to create the desired dimensions and surface finish. The depth of cut, feed rate, speed, and tool path all contribute to the specifics of the turning process.
Workholding is a key consideration for turning operations. The workpiece must be securely clamped to avoid vibrations and maintain precision. Common workholding methods include chucks, collets, centers, faceplates, mandrels, and between centers turning. The setup used depends on the size, shape, tolerances, and features of the part being machined.
The depth of cut refers to how much material is removed radially in one pass of the tool. Light cuts ranging from 0.001" to 0.010" are often used for finishing passes, while roughing may involve depths up to 0.200" depending on the operation. The total depth is achieved through multiple progressive roughing and finishing cuts.
The feed rate determines how quickly the tool advances into the workpiece. It is measured in units per revolution, typically inches or millimeters. Correct feed rates maintain good chip loads on the tool without causing deflection, chatter, or overload. They depend on the operation, tool material, workpiece material, and depth of cut.
Cutting speed is the surface speed at which the workpiece material moves past the cutting tool, specified in surface feet per minute (SFM) or surface meters per minute (SMM). The optimal speed depends on the tooling, workpiece, and features being machined. Speeds generally range from 50 to 400 SFM for roughing and 100 to 1000 SFM for finishing.
The tool path refers to the programmed route that the tool follows as it machines the workpiece. Turning tool paths are typically straight axial movements parallel to the axis of rotation, but can also involve contours, tapers, grooves, undercuts, and profiling operations.
Cutting Tools for Turning
Single-point cutting tools perform the actual cutting action in turning operations. They feature geometries and materials tailored to specific types of turning tasks. Common tool materials include high-speed steel, cobalt steel, cast alloys, carbides, ceramics, diamonds, and cubic boron nitride.
Turning tools consist of a cutting insert brazed or clamped onto a tool holder. Many different insert shapes exist, such as triangular, diamond, round, and square. Typical angles include rake angles from -5 to -45 degrees and relief angles of 5 to 15 degrees. Multi-radii inserts can combine different edge profiles.
Boring bars allow internal turning of bores and holes. Threading tools cut screw threads, taps, or dies. Grooving and parting tools produce grooves, undercuts, and narrow slots. Facing tools machine surfaces perpendicular to the spindle axis. Form tools contain the inverse profile shape needed to machine complex contours.
Applying appropriate tools, speeds, feeds, and depths for the material and operation helps optimize turning results. Tool holders enable fast insert changes and consistent positioning. Selecting suitable tools is an important programming consideration for CNC turning.
CNC Programming for Turning
Effective programming is essential for CNC turning operations. While manual programming is possible, most CNC turning now utilizes CAM software to generate G-code programs through postprocessors. Common programming steps include:
Defining the workpiece geometry - The programmer models the stock shape and dimensions in the CAM system. This establishes the programming coordinate system and boundaries.
Specifying tooling - Tool libraries contain parameters for inserts, holders, and tool geometries. The programmer selects suitable tooling for each operation.
Programming tool paths - The desired tools paths, depths of cut, feeds, speeds, and other parameters are defined. The program strategies can utilize canned cycles for common turning operations.
Simulating and verifying the program - The program is run virtually to catch any errors. Collision detection checks for potential issues.
Postprocessing into G-code - The CAM software converts the programmed tool paths into G-code that the CNC machine understands. Postprocessors output code based on the specific machine.
Loading the program - The G-code file is loaded into the CNC control of the turning machine and prepared for execution.
Inspecting initial parts - The first pieces are inspected to confirm the program produces the workpiece accurately and efficiently before full production runs.
Programming for CNC turning takes advantage of the precise control and automation possible with computer numerical control. This makes modern turning fast, accurate, and consistent.
Turning is a versatile machining process that produces cylindrical parts to meet a wide range of manufacturing needs. Performing turning operations on CNC lathes provides advantages including automation, precision, control, and optimization. Key aspects of CNC turning include the machine components, cutting tools, speeds and feeds, program strategies, and verification.
With a properly prepared CNC program, skilled turning machine operation, appropriate workholding, and the right cutting tools, CNC turning can produce precision parts rapidly and accurately. Understanding the fundamentals of the turning process, tooling considerations, and programming techniques allows manufacturers to leverage CNC turning to its fullest potential. This enables fabricating high-quality turned components at competitive costs to meet modern manufacturing demands. CNC Milling