Post on 06-Apr-2018
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Mechanical Methods of
Material Removal
Chapter 4
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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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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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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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MATERIAL REMOVAL
Cutting fluids- provide 3 major functions
Lubrication
Cooling Chip removal
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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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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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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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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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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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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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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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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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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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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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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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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