Introduction to CNC Turning(how to paint over chrome without sanding Ives)
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CNC turning has largely replaced manual lathe turning in modern manufacturing due to its precision, consistency and ability to efficiently mass-produce complex parts. This article provides an overview of CNC turning, including key components of CNC turning machines, the turning process, tooling, applications, advantages and disadvantages.
How CNC Turning Works
CNC turning relies on preset computer instructions to control the movements of the cutting tool and spindle. Here are the key components that allow CNC turning machines to shape parts:
- Spindle: The spindle holds and rotates the workpiece at high speeds, usually between 1,000-6,000 RPM, although high speed spindles can reach much higher RPMs. The spindle is powered by a motor and integrated into the machine’s computer numeric control system.
- Chucks: Chucks are mounted to the spindle and grip the workpiece to hold it in place during the turning process. There are several types of chucks including 3-jaw chucks, 4-jaw chucks and collet chucks. Vacuum chucks may also be used to hold non-round workpieces.
- Cutting Tool: The cutting tool, also called a turning tool bit, is held by the tool post and fed towards the rotating workpiece to remove material. Turning tools come in various shapes like square, round and pointed to perform different types of turning operations.
- Tool Post: The tool post, sometimes called a turret, holds and positions the cutting tools during operations. CNC turning centers will have an automatic tool changer that allows them to change tools as required by the program.
- Machine Bed: The machine bed provides a rigid frame to locate the spindle, tailstock and slide assemblies. High rigidity is required to resist cutting forces and vibrations during turning.
- Tailstock: The tailstock holds long workpieces in place via a center to support the free end. It can be adjusted and moved along the bed as required.
- Coolant System: Coolant systems deliver cutting fluids to the tool/workpiece interface to cool and lubricate the cutting zone, remove chips and improve surface finishes.
The basic CNC turning process involves these steps:
1. The operator mounts the raw material workpiece onto the chuck which is then tightened to secure the piece.
2. The appropriate cutting tools are loaded into the tool post at the programmed positions.
3. The operator initiates the CNC program which then takes control of the machine.
4. As the workpiece rotates, the cutting tools are automatically fed towards it along programmed paths to cut the material.
5. Coolant is applied to the cutting area for lubrication, chip removal and cooling.
6. The program controls the tools to perform various straight and contour turning operations, as well as drilling and boring, until the part is complete.
7. Once finished, the part is unload from the chuck and new raw material can be loaded to repeat the process.
CNC Turning Tools
A wide selection of cutting tools are available for CNC turning operations, with each being optimized for different materials and applications. Here are some of the most common types:
- Turning Inserts: Indexable turning inserts feature replaceable cutting tips, allowing for quick changeovers between parts. Insert shapes include triangles, squares, circles etc. with a range of coatings.
- Boring Bars: Boring bars have small cutting inserts and are used to bore holes or enlarge existing holes. Rigidity is important to avoid vibration and produce accurate holes.
- Threading Tools: Thread turning tools can cut external and internal threads. They may have interchangeable inserts or replaceable dies.
- Grooving Tools: Grooving tools cut grooves, tapers and angles. Off-center turning can produce curved grooves.
- Drill Bits: Twist and gun drill bits create straight holes in turned parts. Deep hole drilling machines are required for holes with high length-to-diameter ratios.
- Forming Tools: Form tools have shaped profiles that can create complex contours by feeding laterally against a rotating workpiece.
- Knurling Tools: Knurling tools imprint diagonal patterns onto the surface to improve grip and aesthetics. Roller and straight knurls are common types.
In general, turning inserts with durable and heat-resistant coatings like titanium aluminum nitride or cubic boron nitride work best for most steels. Ceramic inserts last even longer, providing a cost-effective solution for high production runs.
CNC Turning Applications
Thanks to their accuracy, repeatability and efficiency, CNC lathes are ubiquitous in manufacturing. Here are some of the most common applications of CNC turning:
- Automotive: CNC turning machines produce a variety of engine components (crankshafts, camshafts, pistons), drive train parts, wheels, brake rotors and more for vehicles.
- Aerospace: Aircraft rely on precisely turned parts including hydraulics, fasteners, casings and tubing made from aluminum and stainless steel.
- Medical: Turned medical parts include IV components, orthopedic implants, dental implant fixtures, catheters and drug delivery devices.
- Marine: Propellers, drive shafts and engine components for boats and ships are turned from metals like stainless steel.
- Oil and gas: The energy industry depends on turned parts like valves, fittings, pumps, compressor parts and drill bits.
- Military/Defense: CNC turning produces missile and rocket casings, grenades, barrels for firearms and other defense components requiring high precision.
In general, any parts with cylindrical features can be efficiently produced using CNC turning centers.
Advantages of CNC Turning
Here are some of the main benefits that CNC turning offers over manual turning:
- Higher productivity: CNC turning machines can produce parts much faster than manual lathes. The computer control also allows for unattended operation once the process is dialed in.
- Consistency: CNC turning produces uniform parts batch after batch. The computer numeric control ensures each part meets the exact same specifications.
- Accuracy and precision: Modern CNC lathes can hold extremely tight tolerances down to ±0.001 inches for high precision parts.
- Complex geometries: CNC turning can produce parts with complex profiles that would be difficult or impossible to create on manual lathes.
- Reduced setup time: CNC setups are faster thanks to the ability to save tooling setups and load programs for recurring jobs.
- Flexibility: Quick change tooling and programming allow CNC lathes to switch between different parts with ease.
- Safer: CNC eliminates exposure to some hazardous direct contact with machinery during turning operations.
- Reduced training: While still requiring skilled programmers, CNCs reduce the manual skill level required for turning operations.
- 24/7 operation: CNC lathes can run lights out, allowing manufacturers to take advantage of untended production.
Of course, initial CNC machine prices can be higher than manual lathes. However, setup and labor savings over time usually far outweigh the initial costs for manufacturers that rely on turning work.
Disadvantages of CNC Turning
- Higher initial investment: CNC lathes have higher upfront costs compared to manual lathes. However, lower labor costs over time usually justify the investment.
- Advanced programming and setup: While reducing the skill required at the machine, CNC turning does require more advanced programming and setup skills compared to manual turning.
- Potential for downtime: Software glitches, tool breakage/wear and collisions can lead to CNC downtime and production delays if not properly monitored.
- Maintenance: CNC turning machines require maintenance of key components like ball screws, way surfaces, spindles and coolant systems.
- Equipment expertise: Manufacturers need staff members knowledgeable in CNC equipment maintenance and repairs or need to outsource to machine tool service firms.
- Limitations on object size: Although turning diameters can be very large, CNC lathe size limits the length of parts that can be produced. Additional tailstock support is needed for longer parts.
While requiring a higher initial capital investment, manufacturers focused on turning applications can usually achieve a quick return-on-investment by taking advantage of the significant time and labor savings of CNC turning.
Conclusion
With the ability to produce precision turned parts at high volumes, CNC turning machines are a transformative manufacturing technology. By automating turning operations under computer numerical control, CNC lathes provide consistency, accuracy and efficiency impossible to achieve manually. Manufacturers across many industries have adopted CNC turning as a superior alternative to manual turning. With advancements in controls, cutting tools, spindle design and automation, CNC turned parts will continue improving in quality while reducing production costs. CNC Milling CNC Machining