Chapter 4 Mechanical Methods

8/3/2019 Chapter 4 Mechanical Methods

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Chapter 4 IT 208 1

Mechanical Methods of

Material Removal

Chapter 4


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Chapter 4 IT 208 2

Competencies

Identify the unique characteristicsassociated with powered mechanical

methods of material removal Calculate the optimum feeds and

speeds for milling, drilling and turning

List and define the two types of millingmachine configurations

List the 3 major functions of cutting


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Chapter 4 IT 208 3


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Chapter 4 IT 208 4

POWERED MECHANICAL METHOD

OF MATERIAL REMOVAL

Two most versatile Lathe to make cylindrical, conical, spherical, treaded shapes Vertical mill prismatic parts with contours with various shapes

Lathe Components

Bed- supports all other major components Carriage- slides along the ways and consists of an assembly cross-slide, tool post, and apron.

Headstock- fixed to the bed and has motors, pulleys, and v-belts thatsupply power to the spindle (hollow) (work holding device attached tothe spindle)

Tailstock- can slide along the ways and can be clamped down.

Supports the part on the rear end with Live or Dead center6. Feed rod and lead screw- used to provide power to the carriage tofeed it along or across the work piece.


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Chapter 4 IT 208 5

MATERIAL REMOVAL

4 Considerations that determine how fast to run a

lathe:

Workpiece material Tool diameter Diameter of the work piece Depth of cut


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Chapter 4 IT 208 6

MATERIAL REMOVAL

Cutting fluids- provide 3 major functions

Lubrication

Cooling Chip removal


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Chapter 4 IT 208 7

MATERIAL REMOVAL

Milling- A process that is capable of producing a

variety of configurations using a multitooth tool,

turns the tool and holds the workpiece toprovide the cutting action

Types of Milling Machines

Horizontal- the spindle is placed horizontal(used for heavier cutting)

Vertical- the spindle is placed vertical (themost common type of milling machine)


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Chapter 4 IT 208 8

MATERIAL REMOVALShaping and Planning - Cutting blades rotate while the

material is passed through them.

Routing - Uses specially shaped cutting tool to remove

material in a defined geometry.Broaching - Specific file geometry is used to duplicate the

profile of the broach inside a hole.

Drilling and Boring

Drilling - Stock is held stationary and the drill is rotated

Boring - Cutting tool is stationary and the material rotated


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Chapter 4 IT 208 9

MATERIAL REMOVAL

Reaming and Honing

Reamer- Similar to a drill, but has straight cutting edges andis used for finishing a hole to very close tolerances.

Hones - Small grindstone used to move material andsmooth out the final surface.


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Chapter 4 IT 208 10

MATERIAL REMOVALSawing

Advantages: Quick and cheap method of material removal Disadvantages: Leaves rough surface on both sides of the

cut.

Saw Set Making the kerf wider than the blade backingso that the blade will not bind in the kerf.

Blade selection: Harder the material, the finer and closerthe teeth. Steel 14-30 t.p.i., Aluminum 8-12 t.p.i.

Circular Saws, Jig Saws, Hack Saws, Band, Saws,Chain Saws.

Abrasive Saws- used to cut (grind) extremely hardmaterials cannot be used to cut soft materials because it willload the blade.


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Chapter 4 IT 208 11

MATERIAL REMOVAL

Shearing and Punching

Shearing- Process of slitting flat stock up to inthickness

Punching- Shearing any shaped hole in flat stock.Grinding Removal of material by abrasion.

Dressing a wheel is a process of using a diamond toremove the outer layer of a wheel, so that it becomes round

(true) and the ends square.

Grit Size refers to the size of grit that will pass through thenumber of openings per linear inch in a sieve. (i.e. 100 grit

sand paper)


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Chapter 4 IT 208 12

MATERIAL REMOVAL

Cutting Tool Shapes (see fig. 4-50) Side, back, and end rake angles are determined by the

materials being cut and the type of cut being made. Hard

materials require very little side or back rake angle.

High Speed Steel (HSS) best choice for roughingpurposes. They are inexpensive, can be easily

resharpened, and are not extremely brittle. The HSS tools

will take considerable shock. Their drawback is that they

dull faster, especially in the cutting of harder metals.


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Chapter 4 IT 208 13

MATERIAL REMOVAL

Carbide Carbide tips will cut harder steels, but theyare brittle and should not be used for roughing

purposes. Carbide-tipped tools can produce closer

tolerances and better finishes than the HSS tools. Ceramic tools - are not affected by heat, and can be

operated at extremely high revolutions per minute.

However, these tools are similar to glass in brittleness.

Ceramic tools are generally used only for the final,

very light cut on very hard steels.


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Chapter 4 IT 208 14

MATERIAL REMOVALFeeds & Speeds

Cutting Speed is the velocity of the surface of aworkpiece as it passes the cutting tool.

Speed (SFPM) given in surface feet per minute (SFPM). Spindle Speed is the rotational speed in revolutions per

minute at which the lathe, milling machine, saw, grinder, ordrill press is running.

Feed - the rate of advance of the cutting tool per revolution. Depth of Cut is the distance to which the cutting tool

enters the workpiece.


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Chapter 4 IT 208 15

MATERIAL REMOVAL

Determining Optimum production

where N = spindle speed (rpm), CS = recommended SFPM,and D = diameter (ft)

Using recommended Cutting Speeds and Feeds Table

4.2 p.105

D

C

N

S

T


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Chapter 4 IT 208 16

Problem

A 4-in.-diameter piece of mild, low-carbon steel

is to be turned on a lathe using a carbide

cutting tool. What is the optimum speed ofthe lathe? From table 2, Cs = 550 sfpm

rpm

inft

N 21.525

)121*4(

550!!

T


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Chapter 4 IT 208 17

Problem

A 0.5-in.-diameter hole is to be drilled in a piece

of 316 stainless steel with a HSS drill. At what

rpm should the drill press be set? From table2, Cs= 100 sfpm

rpm

inftinD

CN

S9.763

)121*5(.

100!!

TT

rpmD

CN

S 7645.

82.3*10082.3*!!


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Chapter 4 IT 208 18

Problem

A lathe has a maximum speed of 1500 rpm.

Could it be run at this maximum rpm using a

carbide-tipped tool to cut a 2

-in.

-diameter pieceof aluminum?

rpmN 22922

82.3*1200!!

Yes, Cs = 1200 sfpm, Maximum

recommended speed is 2292

RPM

Chapter 4 Mechanical Methods

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