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Title: The Basics of CNC Turning and Milling for Manufacturing Custom Metal Parts
Introduction:
Computer numerical control (CNC) machining is an essential manufacturing process used to produce custom metal parts and components. The two most common CNC machining techniques are turning and milling. Understanding the basics of CNC turning and milling is important for engineers and designers when specifying machined parts as well as for manufacturing managers when planning production. This article will provide an overview of CNC turning and milling processes, equipment, and applications.
What is CNC Turning?
CNC turning, also known as CNC lathe machining, is a process in which a computer-controlled machine tool called a CNC lathe removes material from a rotating workpiece to cut and shape it into a desired form. The workpiece is securely clamped in a chuck and rotated at high speeds while the cutting tool moves linearly against it to cut away material.
CNC lathes have programmable controls which allow the machining of intricate and complex part geometries. The CNC control precisely positions the cutting tool as per the programmed instructions to ensure accuracy and consistency. Parts machined using CNC turning include axles, shafts, pins, bushings, and much more. It is ideal for producing rotationally symmetric parts in high volumes.
Types of CNC Turning
There are two main types of CNC turning:
- Chuck turning: The workpiece is held and rotated in a chuck. Different cutting tools can access the part from multiple directions. This allows for more complex part geometries.
- Bar feeding: The raw material is fed into the machine as a long bar. As material is removed, the bar keeps feeding through. This is efficient for high volume production of simple rotational parts.
CNC Turning Machines and Equipment
The most important element of a CNC turning machine is the programmable computer control. Other key components include:
- Headstock: Holds the chuck and rotates the workpiece. Different speed settings allow optimal cutting at various stages.
- Turret: Holds multiple cutting tools and indexes them into position for machining different areas of the part.
- Tool post: Holds a single cutter for detailed cuts. The tool can be precisely positioned.
- Tailstock: Situated opposite the headstock, it can hold the end of the workpiece for support during machining.
- Coolant system: Delivers coolant to lubricate and cool the machining. This improves cutting tool life.
- Automatic tool changer: Allows new tools to be swapped in without operator intervention.
- Chip conveyor: Clears away material waste.
Applications of CNC Turning
The precision, repeatability, and automation capabilities of CNC turning make it indispensable for high-volume production across many industries including:
- Automotive: Engine valves, pistons, axles, gears are common automotive parts produced by CNC turning.
- Aerospace: Aircraft structural components and engine parts are machined using CNC lathes.
- Medical: Surgical instruments, implants, prosthetics are manufactured using CNC turning.
- Oil & gas: Valves, fittings, pumps for pipelines are turned on CNC lathes.
For lower quantities, CNC turning is ideal for machining custom parts and prototypes. The automated programming minimizes setup times for quick turnarounds.
Overview of CNC Milling
CNC milling is a subtractive manufacturing process where rotary cutting tools remove material from a stationary workpiece to produce the desired 2D or 3D form. Like turning, milling operations are controlled by pre-programmed CNC instructions.
CNC milling utilizes multi-point rotary cutters called endmills which can precisely cut in multiple directions. This enables the machining of angled slots, holes, contours, pockets, flat surfaces and complex 3D shapes. Parts made through CNC milling include mold dies, tooling components, engine parts, turbines, and much more.
Types of CNC Milling
Common CNC milling machine configurations include:
- Vertical machining centers (VMCs): The spindle holding the endmill is vertically oriented and the table moves the workpiece in X and Y axes.
- Horizontal machining centers (HMCs): The cutter spindle is horizontally placed while the worktable moves in the X, Y, and Z axes to position the workpiece.
- Gantry mills: The cutter head is suspended from a gantry that moves over a stationary table. Very heavy/large parts can be machined.
- CNC routers: Similar to VMCs but optimized for woodworking. Mostly used for signs, furniture, etc.
CNC Milling Components
CNC milling machines consist of the following components:
- Mill head: Consists of the spindle and drive motor. The spindle exchanges tools from the magazine.
- Tool magazine: Holds the tool inventory including endmills, drills, reamers for automatic exchanges.
- Worktable: The part is placed here to be machined. Multiple workholding options are used.
- Column: Supports the head and allows Z-axis movement.
- Control panel: Facilitates the programming, operation, and control of the machine.
- Coolant system: Circulates coolant to reduce heat in the cutting zone.
Applications of CNC Milling
Like turning, CNC milling is suitable for both high-volume production and low-quantity machining. Here are some common applications:
- Aerospace: Structural airframe components, wings, turbine blades are milled from metals like aluminum and titanium.
- Mold & die: Complex mold tooling with conformal cooling channels are manufactured through CNC milling.
- Automotive: Engine blocks, transmission cases, wheel hubs are prototyped and mass-produced using CNC mills.
- Medical: Dental crowns, prosthetics, implants rely on precisely CNC milled parts.
- Consumer products: CNC milling is used to make parts for appliances, computers, phones, and more.
Choosing Between CNC Turning and Milling
When selecting between CNC turning and milling for a machined part, consider factors like:
- Geometry: Turning is ideal for cylindrical shapes while milling can produce highly complex parts.
- Setup time: Turning usually has faster setups than milling for simple geometries.
- Volume: Turning suits high-volume production well. Milling offers more flexibility for mixed quantities.
- Equipment cost: Turning machines are generally less expensive than CNC mills.
- Materials: Turning uses single point cutting appropriate for most metals while endmills offer versatility across many materials.
An experienced manufacturing engineer can recommend the best process based on these considerations. Using a combination of turning and milling often produces optimal results.
Conclusion
CNC turning and milling are essential machining technologies for manufacturing precision metal components. Turning produces cylindrical and rotationally symmetric parts of high complexity. Milling offers multidirectional cutting suitable for low or high volumes of intricate parts. With programmable automation and precision, CNC turning and milling provide manufacturers consistent quality and fast turnaround for custom components across many industries. CNC Milling CNC Machining