University of Nevada Las Vegas

MEG426/626 Manufacturing Processes

Department of Mechanical Engineering

Fall Semester 2000

 

Drilling and Related Operations

 

 

Drilling is a machining operation used to create a round hole in a workpart.

Tool: drill or drill bit.

Machine: drill press or drilling machine.

Difference from Boring:

Drilling: create round hole;

Boring: enlarge an exist hole.

 

Twist drill:

Spiral flutes,

Helix angle: the angle of the spiral flute, usually 300,

Web: the thickness of the drill between the flutes,

Point angle: 1180, Chisel edge.

 

 

Cutting Conditions in Drilling

v = p D N

where v = cutting speed, in./min (mm/min); D = drill diameter, in. (mm); and N = spindle revolution.

 

fr = N f

where fr = feed rate, in./min (mm/min); f = feed, in./rev. (mm/rev.)

 

Tm = (t + A)/fr for a through hole

Tm = d /fr for a blind hole

where Tm = drilling time, min; t = work thickness, in. (mm); fr = feed rate, in./min (mm/min); A = the distance the drill must feed into the work before reaching full diameter; and D = hole depth.

A = 0.5 D tan (90 - q /2)

where q = drill point angle.

MRR = (p D2 fr)/4

 

Operations Related to Drilling

 

  1. Reaming: to slightly enlarge a hole for a better tolerance and surface finish on its diameter.

    2. Tool: reamer, straight flutes.

  2. Tapping: to provide internal screw threads on an existing hole.

    3. Tool: tap.

  3. Counterboring: to provide a stepped hole, mostly for seating a bolt head.

  4. Countersinking: to provide a stepped hole with cone shape.

e) Centering: to drill a hole to establish its location for subsequent drilling.

f) Spotfacing: to provide a flat machined surface on the workpart in a localized area.

 

Drill Presses:

 

Milling

Mill is a machining operation in which a workpart is fed past a rotating cylindrical tool with multiple cutting edges.

Milling is an interrupted cutting operation.

 

Types of Milling Operations

Peripheral Milling: the axis of the tool is parallel to the surface being machined, also called plain milling.

Slab milling: the cutter width extends beyond the workpiece on both sides.

Slot milling: the cutter width is less than the workpiece width, creating slot in the work.

Side milling: the cutter machines the side of the workpiece.

Straddle milling: the same as side milling, only cutting takes place on both sides of the work.

 

Face Milling: the axis of the tool is perpendicular to the surface being milled, and machining is performed by cutting edges on both the end and outside periphery of the cutter.

Conventional face milling:

Partial face milling: the cutter overhangs the work on only one side.

End milling: the cutter diameter is less than the work width, so a slot is cut into the part.

Profile milling: a form of end milling in which the outside periphery of a flat part is cut.

Pocket milling: another form of end milling, used to mill shallow pockets into flat parts.

Surface contouring: a ball-nose cutter is fed back and forth across the work to create a three-dimensional surface form.

 

Milling Cutters

 

Plain milling cutters,

Face milling cutters,

End milling cutters.

 

Cutting Conditions in Milling

 

v = p D N

where v = cutting speed, in./min (mm/min); D = cutter diameter, in. (mm); and N = spindle revolution.

fr = N nt f

where fr = feed rate, in./min (mm/min); N = spindle speed, rev./min; nt = number of teeth on the cutter; and f = feed per cutter tooth, in./tooth (mm/tooth).

 

MRR = w d fr

Where w = width of cut; d = depth of cut; and fr = feed rate.

Created by Dr. Wang