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Level 38

22 - MACHINING OPERATIONS AND MACHINE TOOLS


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Rotational and prismatic parts
Rotational parts are cylindrical or disk-shaped and are machined on a turning machine (e.g., a lathe); prismatic parts are block-shaped or flat and are generally produced on a milling machine, shaper, or planer.
Generating and turning
Generating refers to the creation of work geometry due to the feed trajectory of the cutting tool; examples include straight turning, taper turning, and profile milling. Forming involves the creation of work geometry due to the shape of the cutting tool; common examples include form turning and drilling.
Combined forming and generating
The two examples given in the text are thread cutting on a lathe and slot milling
Turning process
Turning is a machining process in which a single-point tool removes material from the surface of a rotating cylindrical workpiece, the tool being fed in a direction parallel to the axis of work rotation.
Threading and tapping
A threading operation is performed on a turning machine and produces an external thread, while tapping is normally performed on a drilling machine and produces an internal thread.
Boring and turning
Boring produces an internal cylindrical shape from an existing hole, while turning produces an external cylindrical shape.
What is meant by the designation 12 x 36 inch lathe?
A 12 x 36 lathe has a 12 inch swing (maximum work diameter that can be accommodated) and a 36 inch distance between centers (indicating the maximum work length that can be held between centers).
Work holding
Methods of holding the work in a lathe include: (1) Between centers - dog plate spins work held between centers. (2) Three jaw chuck - the usual lathe clamping method you know so well from school. (3) Collet - flexible parts inside a rigid hole grab and hold fast a part. (4) Face plate - 4 clamps grab a noncylindrical part.
Live and dead centers
A center holds the work during rotation at the tailstock end of the lathe. A live center is mounted in bearings and rotates with the work, while a dead center does not rotate - the work rotates about it.
Turret and engine lathe
A turret lathe has a toolholding turret in place of a tailstock; the tools in the turret can be brought to work to perform multiple cutting operations on the work without the need to change tools as in operating a conventional engine lathe.
Vertical turret lathe
VTLs are used to turn large diameter round parts that are too large to be held in a horizontal lathe.
Peripheral and face milling
In peripheral milling, cutting is accomplished by the peripheral teeth of the milling cutter and the tool axis is parallel to the work surface; in face milling, cutting is accomplished by the flat face of the cutter whose axis is perpendicular to the work surface.
Profile milling
Profile milling generally involves the milling of the outside periphery of a flat part.
Pocket milling
Pocket milling uses an end milling cutter to machine a shallow cavity (pocket) into a flat workpart.
Up and down milling
In up milling, the cutter speed direction is opposite the feed direction; in down milling, the direction of cutter rotation is the same as the feed direction.
Universal milling machine
The universal milling machine has a worktable that can be rotated about a vertical axis to present the part at any specified angle to the cutter spindle.
Machining center
A machining center is a CNC machine tool capable of performing multiple types of cutting operations involving rotating spindles (e.g., milling, drilling); the machine is typically equipped with automatic tool-changing, pallet shuttles to speed workpart changing, and automatic workpart positioning.
Turning center
A machining center is generally confined to rotating spindle operations (e.g., milling, drilling); while a turning center performs turning type operations, generally with single-point tools
Mill turn center
The mill-turn center has the capacity to position a rotational workpart at a specified angular location, permitting milling or drilling to be performed at a location on the periphery of the part.
Axes in vertical machining center
The four axes in a vertical machining center are the three linear axes: X, Y, Z; and the rotational axis: alpha.
Shaping and planning
In shaping, the work is stationary during the cut, and the speed motion is performed by the cutting tool; while in planing, the cutting tool is stationary, and the workpart is moved past the tool in the speed motion.
Internal and external broaching
Internal broaching is accomplished on the inside surface (hole) of a workpart; while external broaching is performed on one of the outside surfaces of the part
Sawing operations
The three forms of sawing are: (1) hacksawing, (2) bandsawing, and (3) circular sawing.
Blind hole
A blind hole does not exit the work; by comparison, a through hole exits the opposite side of the workpart.
Twist drill
The three parts of a common twist drill are the: 1) shank, 2) flutes, and 3) point
Gang drilling machine
A gang drilling machine consist of two or more common drilling machines mounted on a common base or table. Each machine is setup to perform a different operation on a part. The operator can move down the line performing each operation in succession.
Radial drill press
A radial drill has a long radial arm along which the drill head can be positioned to allow the drilling of large work parts. The radial arm can also be swiveled about the column to drill parts on either side of the worktable.