An Introduction to CNC Turning(tight tolerance machining Malcolm)

  • Time:
  • Click:9
CNC (Computer Numerical Control) turning is a machining process used to produce rotational, axisymmetric parts. In CNC turning, the workpiece is rotated while a single point cutting tool removes material to create the desired shape. CNC turning is an efficient and precise machining process that is commonly used to produce parts for industries like aerospace, automotive, medical, and more. In this article, we will provide an overview of CNC turning, including the equipment, process, applications, advantages, and more.
CNC Turning Equipment
CNC turning centers contain the following key components:
- Machine bed and base - Provides a rigid frame to support the other components. Usually made from cast iron or welded steel.
- Headstock - Holds the rotating spindle which grips the workpiece. Contains high precision bearings and the spindle motor.
- Tailstock - Can hold the end of the workpiece for initial facing and center drilling. It can be positioned along the bed via a hand wheel or servo motor.
- Tool turret - Holds the cutting tools and can index them into the cutting position automatically. Tool holders are mounted to the turret.
- CNC control system - Controls the machine axes and spindle. Executes the machining program.
- Axis slides - Allows linear motion of the turret and tailstock via servo or stepper motors. The X-axis controls cross travel, the Z-axis controls longitudinal feed.
- Chuck - Grips and centers the workpiece in the spindle. Different types include 3-jaw, 4-jaw, and collet chucks.
- Chip conveyor - Removes swarf and chips from the machining area.
- Coolant system - Provides coolant to the cutting area to reduce heat and clear chips.
- Safety enclosures - Protect the operator from flying chips and coolant. Newer machines have full enclosures.
The precision and capabilities of a CNC turning center depend greatly on the construction and components used. More expensive machines provide greater rigidity, faster spindles, quicker tool changes, and better motion control.
CNC Turning Process
The basic CNC turning process involves these key steps:
1. The raw material, usually a diameter bar stock, is center drilled and loaded into the chuck or collet. The max diameter is limited by the swing over bed capacity.
2. The chuck self-centers the workpiece along the spindle axis. A steady rest may support long slender parts.
3. The turret indexes the correct tool into the cut position. Common tools are the turning tool, grooving tool, drill, tap, boring bar, etc.
4. The machine executes the programmed cutting motions - facing, turning, boring, grooving, drilling, threading, etc.
5. Inserted cutting tools with carbide inserts are commonly used due to their durability and lower cost per part.
6. The tool feed rates, spindle speeds, depth of cuts are set based on the material, tool material, and other parameters. Proper speeds and feeds maximize tool life.
7. Cutting fluid is applied to the cutting zone to cool, lubricate, and flush away chips. Flood coolant or mist systems are used.
8. The turret indexes to the next tool to complete the next operation until the part is fully machined.
9. For mass production, the machine uses a parts catcher, conveyor, or robot to automate the part handling.
10. The finished parts are then cleaned and inspected to ensure they meet specifications. Secondary operations like deburring may also be required.
When properly programmed, setup, and run, CNC turning produces parts with accuracy up to 0.005mm (0.0002") or better. The automated cycles improve consistency and allow minimally attended production.
CNC Turning Applications
Due to its capabilities, CNC turning is used across many industries to produce a variety of part types including:
- Automotive - Engine valves, pistons, brake rotors, drums, hubs, axle shafts
- Aerospace - Bushings, nozzle bodies, fittings, engine mounts
- Medical - Bone screws, surgical tools, implants, prosthetics
- Firearms - Receivers, barrels, cylinders, suppressors
- Industrial - Shafts, rollers, turbines, couplings
- Consumer - Appliance housings, fittings, knobs, wheels
Ideal turned parts have rotational symmetry, decent production volumes, and precision requirements. The turns centers can be found in job shops, OEM factories, and other manufacturing facilities. Advances in turning technology allow more complex parts to be machined entirely on the CNC lathe.
Benefits of CNC Turning
Some of the key benefits of CNC turning include:
- Precision and accuracy - Modern CNCs can easily hold tolerances of 0.005mm or 0.0002" for precision turning applications. The rigid machine construction provides precision.
- Automation - The tools are changed automatically allowing faster cycle times and unattended operation. Parts can be automated via conveyors or robots.
- Repeatability - CNC machines perform the same way repeatedly maximizing consistency in production. Minimal part variation.
- Flexibility - Quick change tooling and programmable control allows fast changeovers between parts. Complex programming reduces setups.
- Productivity - CNC turning produces completed parts in one operation. Minimal handling reduces labor. Automatic cycles also improve efficiency.
- Intricate features - Complex internal and external features like threads, tapers, grooves, profiles can be added via programming. No secondary operations.
- Cost effective - CNC turning is ideal for medium to high production volumes. The automated processing lowers the cost per part.
- Safer operation - The enclosures and automation improve working conditions for the operator. Less manual labor needed.
With so many benefits, it is easy to understand why CNC turning has become one of the most commonly used manufacturing processes. Continual improvements in equipment, tooling, programming, and automation will further increase the applications and productivity of CNC turning.
In Summary
We have provided an overview of CNC turning including the key equipment components, machining process steps, applications, and advantages of this important manufacturing process. The combination of fast material removal rates, excellent accuracy and repeatability, and efficient automation make CNC turning ideal for producing precision parts for many industries. Continued advances and innovations will further cement CNC turning as a critical manufacturing process for years to come. We hope this article helped explain this technology and how it is impacting manufacturing across the globe. Please reach out with any additional CNC turning questions. CNC Milling