Ch. 21
Through Hole vs. Blind Hole
(a) Through hole - drill exits opposite side of work and (b) blind hole - drill does not exit opposite side
Forms of milling
Peripheral and face
Broaching
Advantages: Good surface finish Close tolerances Variety of work shapes possible Cutting tool called a broach Owing to complicated and often custom‑shaped geometry, tooling is expensive
Types of Face Milling
Convention, partial, end, profile, pocket, surface contouring
High Speed Machining (HSM)
Cutting at speeds significantly higher than those used in conventional machining operations Persistent trend throughout history of machining is higher and higher cutting speeds At present there is a renewed interest in HSM due to potential for faster production rates, shorter lead times, and reduced costs
Boring
Difference between boring and turning: Boring is performed on the inside diameter of an existing hole Turning is performed on the outside diameter of an existing cylinder In effect, boring is internal turning operation Boring machines Horizontal or vertical - refers to the orientation of the axis of rotation of machine spindle
Drilling
Difference between boring and turning: Boring is performed on the inside diameter of an existing hole Turning is performed on the outside diameter of an existing cylinder In effect, boring is internal turning operation Boring machines Horizontal or vertical - refers to the orientation of the axis of rotation of machine spindle
Turning Operations
Facing, taper turning, contour turning, form turning, chamfering, cutoff,threading, boring, drilling
Principal Operations for Machining Gear Teeth
Form milling - use of a form milling cutter Gear hobbing - also milling but using a special cutter called a hob Gear shaping - two forms Single point tool to gradually shape each gear tooth spacing Cutter has general shape of the gear but with cutting teeth on one side Gear broaching - for internal and external gears
Machining Center
Highly automated machine tool that can perform multiple machining operations under CNC control in one setup with minimal human attention Typical operations are milling and drilling Three, four, or five axes Other features: Automatic tool‑changing Pallet shuttles Automatic workpart positioning
Milling
Machining operation in which work is fed past a rotating tool with multiple cutting edges Axis of tool rotation is perpendicular to feed Cutting tool called a milling cutter / END MILL Cutting edges called teeth Machine tool called a milling machine Interrupted cutting operation Basic milling operation creates a planar surface Other geometries possible
Machining
Material removal process in which a sharp cutting tool is used to mechanically cut away material so that the desired part geometry remains Most common application: metal parts Most versatile of all manufacturing processes for producing a variety of part shapes and geometric features with high precision and accuracy
Cutting Screw Threads
Methods for producing external threads Single-point threading Threading die Thread chasing using self-opening threading dies Thread milling Methods for producing internal threads Tapping - using a solid tap Collapsible taps - cutting teeth retract for quick removal from hole
Operations related to Drilling
Reaming, tapping, counterboring, counter sinking, center drilling, spot facing
Part Geometry
Relative motions between tool and workpart Generating - part geometry determined by feed trajectory of cutting tool Shape of the cutting tool Forming - part geometry is created by the shape of the cutting tool
Classifications of machined parts
Rotational - (a) cylindrical or disk‑like shape Nonrotational - (b) block‑like and plate‑like
Turning
Single point cutting tool removes material from a rotating workpiece to generate a cylindrical shape Performed on a machine tool called a lathe Variations of turning performed on a lathe Facing Contour turning Chamfering Cutoff Threading