Introduction to CNC Turning(ai cnc machining Noah)
- source:YESCOM CNC Machining
In CNC turning, the cutting tool moves perpendicular to the axis of rotation of the rotating workpiece. The tool follows a programmed path generated from CAD models and CAM software. By precisely controlling the movements and cutting parameters, intricate features like grooves, tapers and threads can be machined on the outside diameter (OD) or inside diameter (ID) of the part.
CNC turning is done on a lathe, either a horizontal or vertical spindle type. Common CNC lathes include 2-axis, 3-axis, multi-spindle, multi-turret, and twin spindle/twin turret models. The axes of movement correspond to the X (radial) and Z (longitudinal) directions. More advanced CNC lathes also have a Y-axis allowing off-center milling capability. The workpiece is held tightly in a chuck or collet while a turret houses the tooling used for the cutting operations.
Here are some key advantages of CNC turning:
- Automation - Once programmed, the machine runs unattended increasing productivity. Complex parts can be produced efficiently.
- Accuracy and Repeatability - CNC machining ensures each part meets tight tolerances. The same program can be run repeatedly producing identical parts.
- Complex Geometries - Intricate features like threads, tapers and eccentrics can be produced using CNC interpolation. Difficult geometries are no problem for CNC.
- Quick Changeover - Changing programs and tools on a CNC lathe can be done rapidly reducing downtime between production runs.
- Safer Operation - The automation of CNC turning reduces operator fatigue and the risks associated with manually turning parts. The operator simply loads/unloads parts and measures finished components.
The CNC Turning Process
CNC turning involves three main stages:
1. Programming - The desired part geometry is modeled in CAD software. The CAD model is then converted into a CAM program which will control the cutting tool movements, coordinates and speeds. Post-processing generates the G-code file the CNC lathe will run.
2. Setup - The raw material, usually a rod, bar or casting, is securely clamped in the chuck. The turret is loaded with the required cutting tools for the operations. The tools are set at the correct height and offsets are entered into the program. A trial run with no cutting may be done to confirm positions.
3. Production - The CNC program is loaded and the cycle start button pressed. As the workpiece rotates, the cutting tools follow the programmed contours to machine the desired features. Multiple tools may be used to complete roughing, finishing and grooving passes. Parts are completed unloaded and new stock loaded to repeat the process.
During production, the operator oversees the process, measures sample parts, changes tools and ensures adequate coolant levels & chip removal.
CNC Turning Operations
Here are some common CNC turning operations:
- Facing - A square faced finish is machined on the end of a part using a CNC facing operation. This prepares the surface for other turning operations.
- Roughing - Roughing passes remove the bulk of material using feed rates optimal for tool life and surface finish. This process defines the final dimensions with allowances left for finish machining.
- Boring - The boring operation using single point boring bars or boring heads to achieve tight tolerance internal diameters. Boring bars can machine straight or tapered holes.
- Drilling - Deep drill holes are produced using specialized CNC drilling cycles. Peck drilling, chip breaking and coolant flow are programmable parameters.
- Grooving - Turning tools equipped with inserts having a sharp corner radius cut grooves, undercuts and parting lines. Grooving operations provide scalloped finish for functional or decorative purposes.
- Profiling - The profiling process machines complex outlines specified in the CAM software. Multi-point turning tool inserts machine the contours with continuous cutting motion.
- Finishing - Light finishing cuts are taken to remove any remaining material left from roughing. Finishing produces the final dimensions and surface finish quality required.
CNC Turning Tools
CNC lathes utilize a wide selection of cutting tools to perform the machining operations. Tooling includes:
- Roughing Tool - Rough turning tools feature inserts with large radius cutting edges permitting heavy depth of cuts. Common indexable insert geometries are 80?? rhombic, 55?? rhombic and triangle.
- Finishing Tool - Finishing inserts have sharper cutting edges and enhanced edge preparations ideal for light passes and good surface finish. Popular indexable geometries include 80?? diamond, 55?? diamond and triangle inserts.
- Boring Bar - Single or multi-bladed boring bars have replaceable carbide or PCD inserts to accurately bore internal diameters. Rigidity and vibration resistance are key factors.
- Drill - For deep hole drilling, fluted high-strength twist drills with through coolant capability drill precision holes. Variable helix geometry improves chip extraction.
- Grooving Tool - Grooving tools have inserts with sharp corners that intersect at 90?? angles. Chipbreakers and internal coolant prevent chip packing in grooves.
- Threading Tool - 60?? triangular inserts having specially ground chipbreaking profiles cut internal and external threads. Multiple flank insert designs optimize hand of cut.
- Form Tool - Carbide form tools ground to custom shapes machine special profiles not possible with standard insert tooling.
- Knurling Tool - Using rolling dies, knurling tools impress cross-hatched patterns or straight serrations onto parts, providing an improved grip.
CNC Turning Materials
CNC lathes are capable of effectively machining a wide range of engineering materials. Typical workpiece materials include:
- Aluminum - Popular for parts requiring good corrosion resistance, lightweight, and high thermal and electrical conductivity. Readily machines and good for high production.
- Stainless Steel - Austenitic and ferritic stainless steels offer excellent corrosion resistance needed for medical, marine and food industry applications where sanitation is critical. Also used for high strength structural parts. More difficult to machine but doable with proper tooling and techniques.
- Titanium - With its high strength-to-weight ratio and biocompatibility, titanium is indispensable for aerospace and medical industries. Difficult to machine material requiring rigid setups and specialized tooling. Typical depth of cuts are light.
- Brass - Brass is valued for its aesthetic appearance and corrosion resistance. Leaded free-cutting brasses offer improved machinability ratings. Used for valves, fittings and instrumentation.
- Carbon & Alloy Steel - Most commonly CNC turned material because of good mechanical properties and ease of machining. Widely utilized for shafts, gears, cylinders, couplings and other automotive and industrial components.
- Tool Steel - Tool steels have excellent wear resistance characteristics needed for tooling applications like extrusion and injection molding. Tough on tooling during CNC turning requiring proper insert grade selection.
- Nickel Alloys - Nickel alloys like Inconel are capable of retaining strength and toughness at extreme temperatures making them popular for aerospace engines and power generation turbines. Notoriously challenging to machine material placing heavy demands on cutting tools.
- Plastics - Turning is ideal for producing plastic parts to close tolerances like bushings, insulators and pump impellers. Proper tool geometry, low speeds and depths of cut are used when machining thermoplastics and thermosets.
In summary, CNC turning is a versatile manufacturing process allowing precision metal and plastic parts to be machined efficiently on computer controlled lathes. With the capability to produce geometric complexity and part repeatability, CNC turning will continue as a dominant precision machining method for high-value components. CNC Milling CNC Machining