Chapter 16 Machining Operations and Tools

Generating vs forming

Generating: part geometry determined by feed trajectory of cutting tool

• straight turning, taper turning, contour turning, plain milling, profile milling

Forming: part geometry created by shape of cutting tool

• form turning, drilling, broaching

Together:

• thread cutting on lathe

• slot milling

Turning

single point cutting tool removes mtl from rotating workpiece → cylindrical shape

• performed on lathe

• types:

  • facing

  • contour turning

  • chamfering

  • cut off

  • threading/boring/drilling

Engine lathe

• headstock

  • houses main spindle → holds workpiece using chuck, collet, faceplate

• tool post on carriage

• tailstock

  • workpiece support (holds both dead center and live center)

Methods of holding workpiece in lathe

1. holding work btwn 2 centers / dog & dogplate

   1. lathe centers used to support long length jobs → mounted in tail stock

   2. live center (rotates) vs dead (doesnt)

2. chuck

   1. 3: all 3 jaws move in/out simultaneously

   2. 4: all 4 jaws move independently/rectangular shape

3. collet

   1. round, square, hexagon

4. face plate

   1. face plate & angle plate

Turret lathe

tail stock replaced w/ turret that holds up to 6 tools

tool post replaced by 4 sided turret to index 4 tools

Chucking machine

uses chuck in spindle to hold workpiece

no tail stock, not mounted btwn 2 centers

cutting tool actions controlled automatically

Bar machine (like chuck)

collet replaces chuck, permitting long bar stock to be fed through headstock

automatic screw machine is the same but smaller → hi production of screws

Boring

boring performed on inside diameter of existing hole

• turning performed on outside

boring can be horizontal or vertical (orientation of axis of rotation)

Drilling

creates round hole in workpart

tool: drill or drill bit

machine: drill press

through vs blind hole

through: drill exits all the way through

blind: does not exit

Drilling order

1. center drill

2. drill

3. boring

4. reaming

Reaming tapping and counterboring

Countersinking, center drilling, spot facing

Drill press

upright drill press stands on floor

Work holding for drill presses

1. vise

   1. general purpose work holder with two jaws

   2. not accurate

2. fixture

   1. workholding device custom designed to workpart

3. drill jig

   1. similar to fixture but also provides means of guiding tool during drilling

Milling

machining operation in which work is fed past a rotating tool with multiple cutting edges

• axis of tool rotation perpin to feed

• types of milling:

  • peripheral: cutting axis parallel to surface

  • face: cutting axes perpindicular to surface'

    • can do sides or bottoms and pockets or contour

Climb cut/down vs conventional cut/up milling

• down milling: same direction → better finishing

• up milling: thin to thick & opp direction

  • preferred b/c of thin to thick

Planing vs shaping

both: both use single point cutting

planing: workpiece moves, large pieces (10 m)

• chip breakers needed, long chips are good, more problems b/c of vibrations, heat, high friction

shaping: tool moves, smaller pieces (1-2 m)

Broaching

multiple tooth cutting tool moved linear relative to work in direction of tool axis

• successive teeth smaller → larger

• started hole required

• good surface finish, close tolerances

• expensive bc tooling

• internal & external

Sawing

cuts narrow slit in work by a tool consisting of a series of narrowly spaced teeth

types:

• power hacksaw

  • steel

  • cuts 1 direction

• band saw

  • linear continuous motion of bandsaw blade

• circular saw

  • rotating saw blade provides continuous motion of tool past workpart

Types of saw teeth

gullet: pathway for wood chips

straight tooth: copper and brass

raker: steel and cast iron

wave: thin sheet or wall

Filing

material removal with find wide teeth

• small chips formed

• finishing and deburring

types:

• single: rows of parallel teeth

• double: 2 series of parallel teeth

• rasp: each tooth raised out of surface

  • removes more mtl in one pass

• curved: parallel curves

  • smooth and nice finish

Burs

types:

• high speed steel

• carbide

• rotary file

used for inside finishing

High speed machining

damper under machine needed bc of hi speed

chip breaker needed

DN ratio: bearing bore diameter multiplied by maximum spindle speed

• for hi speed: 500k to 1mil

How to avoid chatter

add stiffness or damping

operate at speeds avoiding cyclical forces w/ frequencies close to natural freq of machine tool

cutting fluid