MATERI PROSES MANUFAKTUR Pengenalan Teori Permesinan [Compatibility Mode]
-
Upload
suardi-hasjum -
Category
Documents
-
view
98 -
download
3
description
Transcript of MATERI PROSES MANUFAKTUR Pengenalan Teori Permesinan [Compatibility Mode]
-
THEORY OF METAL MACHININGTHEORY OF METAL MACHINING
1. Overview of Machining Technology2. Theory of Chip Formation in Metal Machining3. Force Relationships and the Merchant
EquationEquation4. Power and Energy Relationships in Machining5. Cutting Temperatureg p
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
-
Material Removal ProcessesMaterial Removal Processes
A family of shaping operations, the common f t f hi h i l f t i l ffeature of which is removal of material from a starting workpart so the remaining part has the desired geometryg y
Machining material removal by a sharp cutting tool, e.g., turning, milling, drillingAb i i l l b Abrasive processes material removal by hard, abrasive particles, e.g., grinding
Nontraditional processes - various energyNontraditional processes various energy forms other than sharp cutting tool to remove material
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
-
Machining
Cutting action involves shear deformation of work material to form a chip
g
material to form a chip As chip is removed, new surface is exposed
Figure 21.2 (a) A cross-sectional view of the machining process, (b) tool with negative rake angle; compare with positive rake angle in (a).
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
-
Why Machining is ImportantWhy Machining is Important
Variety of work materials can be machined Most frequently used to cut metals
Variety of part shapes and special geometric features possible such as:features possible, such as: Screw threads Accurate round holes Very straight edges and surfaces
Good dimensional accuracy and surface finish
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
-
Disadvantages with MachiningDisadvantages with Machining
Wasteful of material Chips generated in machining are wasted
material, at least in the unit operation Time consuming Time consuming A machining operation generally takes more
time to shape a given part than alternative shaping processes, such as casting, powder metallurgy, or forming
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
-
Machining in Manufacturing SequenceMachining in Manufacturing Sequence
Generally performed after other manufacturing h ti f i d bprocesses, such as casting, forging, and bar
drawing Other processes create the general shapeOther processes create the general shape
of the starting workpart Machining provides the final shape,
di i fi i h d i l idimensions, finish, and special geometric details that other processes cannot create
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
-
Machining OperationsMachining Operations
Most important machining operations: Turning Drilling
Milli Milling Other machining operations: Shaping and planing Shaping and planing Broaching Sawingg
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
-
Turning
Single point cutting tool removes material from a t ti k i t f li d i l h
g
rotating workpiece to form a cylindrical shape
Fig re 21 3 Three most common machining processes (a) t rning
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
Figure 21.3 Three most common machining processes: (a) turning,
-
Drilling
Used to create a round hole, usually by means of a rotating tool (drill bit) with two cutting edges
g
a rotating tool (drill bit) with two cutting edges
Figure 21.3 (b) drilling,
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
-
Milling
Rotating multiple-cutting-edge tool is moved across work to cut a plane or straight surface
g
across work to cut a plane or straight surface Two forms: peripheral milling and face milling
Fig re 21 3 (c) peripheral milling and (d) face milling
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
Figure 21.3 (c) peripheral milling, and (d) face milling.
-
Cutting Tool ClassificationCutting Tool Classification
1. Single-Point Tools One dominant cutting edge Point is usually rounded to form a nose
radiusradius Turning uses single point tools
2. Multiple Cutting Edge Toolsp g g More than one cutting edge Motion relative to work achieved by rotating Drilling and milling use rotating multiple
cutting edge tools
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
-
Cutting Toolsg
Figure 21.4 (a) A single-point tool showing rake face, flank, and tool point; and (b) a helical milling cutter, representative of tools with multiple cutting edges.
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
-
Cutting Conditions in Machining
Three dimensions of a machining process:C tti d i ti Cutting speed v primary motion Feed f secondary motion Depth of cut d penetration of tool Depth of cut d penetration of tool
below original work surface For certain operations, material removal
rate can be computed as RMR = v f d
h tti d f f d dwhere v = cutting speed; f = feed; d = depth of cut
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
-
Top View
Side ViewEnd View
-
Relief AngleRelief AngleRelief angle semakin besar jika benda kerja semaking j j
lunak
Contoh; jika menggunakan pahat potong dari CarbidaContoh; jika menggunakan pahat potong dari Carbidamaka :
Hard and Tough material : 5 7 derajat
Medium/mild steel cast iron : 5 10 derajat Medium/mild steel, cast iron : 5 10 derajat
Ductile material : 8 14 derajatj
-
Relief AnglegRelief angle yang sangat besar
akan menyebabkan : akan menyebabkan :
Penyelesaian permukaan yang b ik baik, namun
Sisi potong lemah dan mudahpatah jika pemotongan berat
Relief angle yang sangat kecil akan menyebabkan : Umur pahat berkurang karena keausan pada sisi dibawah
sisi potong meningkat
-
Rake AngelRake AngelRake angle yang bergerak ke arah positiive akan
menyebabkan :
Umur pahat meningkatUmur pahat meningkat
Gaya dan temperatur pemotongan menurun
Rake angle yang bergerak ke arah negative akanmenyebabkan :
menguatkan sisi potong (side rake angle negative)
menguatkan nose (back rake angle negative)menguatkan nose (back rake angle negative)
-
End Cutting Edge AngleEnd Cutting Edge AngleMengurangi End cutting edge angle akan menghambatMengurangi End cutting edge angle akan menghambat
rambatan cratering (kawah)
-
Side Cutting and Lead AngleSide Cutting and Lead Angle
Lead angle meningkat maka akan meningkatkan umur Lead angle meningkat maka akan meningkatkan umurpahat menghambat rambatan cratering (kawah)
N jik l d l t l l b k k Namun, jika lead angle terlalu besar maka akanmenyebakan chatter (bunyi gemeretak)
-
Nose Radius Nose yang tajam dapat menurunkan umur pahat
Nose Radius Nose yang tajam dapat menurunkan umur pahat
Nose yang besar membuat laju pemakanan baiky g j pcepat dan penyelesaian permukaan yang baik
Nose yang terlalu besar akan menyebabkan chatter Nose yang terlalu besar akan menyebabkan chatter
-
Cutting Conditions for Turningg g
Figure 21.5 Speed, feed, and depth of cut in turning.
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
-
Roughing vs. FinishingRoughing vs. Finishing
In production, several roughing cuts are usually taken on the part followed by one or twotaken on the part, followed by one or two finishing cuts
Roughing - removes large amounts of material f t ti k tfrom starting workpart Creates shape close to desired geometry,
but leaves some material for finish cuttingg High feeds and depths, low speeds
Finishing - completes part geometryFi l di i t l d fi i h Final dimensions, tolerances, and finish Low feeds and depths, high cutting speeds
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
-
Machine ToolsMachine Tools
A power-driven machine that performs a hi i ti i l di i dimachining operation, including grinding
Functions in machining: Holds workpart Holds workpart Positions tool relative to work Provides power at speed, feed, and depth p p , , p
that have been set The term is also applied to machines that
f t l f i tiperform metal forming operations
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
-
Orthogonal Cutting ModelSimplified 2-D model of machining that describes
the mechanics of machining fairly accurately
O ogo a Cu g ode
the mechanics of machining fairly accurately
Figure 21.6 Orthogonal cutting: (a) as a three-dimensional process.
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
-
Sudut apakahd h tpada pahat
potong yang himempengaruhi
bentuk chips danh t ?umur pahat ?
-
Chip Thickness RatioChip Thickness Ratio
ottr =
where r = chip thickness ratio; to =
ct
othickness of the chip prior to chip formation; and tc = chip thickness after separationseparation
Chip thickness after cut always greater than before, so chip ratio always less than 1.0
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
-
Determining Shear Plane AngleDetermining Shear Plane Angle
Based on the geometric parameters of the th l d l th h l l orthogonal model, the shear plane angle can
be determined as:
cosr
sincostanr
r= 1
where r = chip ratio, and = rake angle
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
-
Shear Strain in Chip Formation
Figure 21.7 Shear strain during chip formation: (a) chip formation depicted as a series of parallel plates sliding relative to each other, (b) one of the plates isolated to show shear strain, and (c) shear strain
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
triangle used to derive strain equation.
-
Shear StrainShear Strain
Shear strain in machining can be computed from the following equation based on thefrom the following equation, based on the preceding parallel plate model:
= tan( - ) + cot ( ) where = shear strain, = shear plane angle, and = rake angle of cutting tool
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
-
Chip FormationC p o a o
Figure 21.8 More realistic view of chip formation, showing shear zone rather than shear plane. Also shown is the secondary shear
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
zone resulting from tool-chip friction.
-
Four Basic Types of Chip in MachiningFour Basic Types of Chip in Machining
1. Discontinuous chip2. Continuous chip3. Continuous chip with Built-up Edge (BUE)4 S t d hi4. Serrated chip
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
-
Discontinuous Chip
Brittle work materialsL tti d Low cutting speeds
Large feed and depth of cutof cut
High tool-chip friction
Figure 21.9 Four types of chip formation in metal cutting: (a) discontinuous
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
-
Continuous Chip
Ductile work materials
p
High cutting speeds Small feeds and
depths
Sharp cutting edge Low tool-chip friction
Fi 21 9 (b) iFigure 21.9 (b) continuous
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
-
Continuous with BUE
Ductile materials Low-to-medium cutting
speeds Tool chip friction Tool-chip friction
causes portions of chip to adhere to rake face
BUE forms, then breaks off, cyclically
Figure 21.9 (c) continuous with built-up edge
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
-
Serrated Chip
Semicontinuous -saw toothsaw-tooth appearance
Cyclical chip forms y pwith alternating high shear strain then low shear strainshear strain
Associated with difficult-to-machine metals at high cutting speeds Figure 21.9 (d) serrated.
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
-
Forces Acting on Chip
Friction force F and Normal force to friction NSh f F d N l f t h F
g
Shear force Fs and Normal force to shear Fn
Figure 21.10 Forces in metal cutting: (a) forces acting on the chip in orthogonal cutting
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
-
Resultant ForcesResultant Forces
Vector addition of F and N = resultant R Vector addition of Fs and Fn = resultant R' Forces acting on the chip must be in balance:
R' t b l i it d t R R' must be equal in magnitude to R R must be opposite in direction to R R must be collinear with R R must be collinear with R
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
-
Coefficient of FrictionCoefficient of Friction
Coefficient of friction between tool and chip:
NF=
Friction angle related to coefficient of friction as follows:
tan=
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
-
Shear StressShear Stress
Shear stress acting along the shear plane:
s
sAFS =
wtA o=where As = area of the shear plane
sinAo
s =
Shear stress = shear strength of work materialShear stress = shear strength of work material during cutting
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
-
Cutting Force and Thrust Force
F, N, Fs, and Fn cannot be directly measured Forces acting on the tool that can be measured:
g
Forces acting on the tool that can be measured: Cutting force Fc and Thrust force Ft
Figure 21 10 ForcesFigure 21.10 Forces in metal cutting: (b) forces acting on the tool that can betool that can be measured
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
-
Forces in Metal CuttingForces in Metal Cutting
Equations can be derived to relate the forces th t t b d t th f th tthat cannot be measured to the forces that can be measured:
F = F sin + Ft cosF Fc sin Ft cosN = Fc cos - Ft sinFs = Fc cos - Ft sins c tFn = Fc sin + Ft cos
Based on these calculated force, shear stress d ffi i t f f i ti b d t i dand coefficient of friction can be determined
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
-
The Merchant EquationThe Merchant Equation
Of all the possible angles at which shear d f ti th k t i l illdeformation can occur, the work material will select a shear plane angle that minimizes energy, given bygy g y
2245 +=
Derived by Eugene Merchant Based on orthogonal cutting, but validity
extends to 3 D machiningextends to 3-D machining
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
-
What the Merchant Equation Tells UsWhat the Merchant Equation Tells Us
45
T i h l l
2245 +=
To increase shear plane angle Increase the rake angle Reduce the friction angle (or coefficient of Reduce the friction angle (or coefficient of
friction)
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
-
Effect of Higher Shear Plane Angle Higher shear plane angle means smaller shear
plane which means lower shear force cutting
ec o g e S ea a e g e
plane which means lower shear force, cutting forces, power, and temperature
Figure 21.12 Effect of shear plane angle : (a) higher with a resulting lower shear plane area; (b) smaller with a corresponding larger shear plane area Note that the rake angle is larger in (a) which
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
larger shear plane area. Note that the rake angle is larger in (a), which tends to increase shear angle according to the Merchant equation
-
Power and Energy RelationshipsPower and Energy Relationships
A machining operation requires power The power to perform machining can be
computed from: P = F vPc = Fc v
where Pc = cutting power; Fc = cutting force; and v = cutting speed
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
-
Power and Energy RelationshipsPower and Energy Relationships
In U.S. customary units, power is traditional d h (di idi ft lb/ i bexpressed as horsepower (dividing ft-lb/min by
33,000)
00033,vFHP cc =
where HPc = cutting horsepower, hp
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
-
Power and Energy RelationshipsPower and Energy Relationships
Gross power to operate the machine tool Pg or HP i i bHPg is given by
orPP c HPHP corE
P cg = EHPc
g =
where E = mechanical efficiency of machine tool Typical E for machine tools 90%
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
-
Unit Power in MachiningUnit Power in Machining
Useful to convert power into power per unit l t f t l tvolume rate of metal cut
Called unit power, Pu or unit horsepower, HPu
orMR
cU R
PP =
MR
cu R
HPHP =
where RMR = material removal rate
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
-
Specific Energy in MachiningSpecific Energy in Machining
Unit power is also known as the specific energy U
wvtvF
RP
PUo
c
MR
cu ===
Units for specific energy are typically
oMR
Units for specific energy are typically N-m/mm3 or J/mm3 (in-lb/in3)
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
-
Cutting TemperatureCutting Temperature
Approximately 98% of the energy in machining i t d i t h tis converted into heat
This can cause temperatures to be very high at the tool-chipthe tool chip
The remaining energy (about 2%) is retained as elastic energy in the chip
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
-
Cutting Temperatures are ImportantCutting Temperatures are Important
High cutting temperatures 1. Reduce tool life2. Produce hot chips that pose safety hazards to
the machine operatorthe machine operator3. Can cause inaccuracies in part dimensions
due to thermal expansion of work material
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
-
Cutting Temperature
Analytical method derived by Nathan Cook from dimensional analysis usingfrom dimensional analysis using experimental data for various work materials
3330 333040 ..
=K
vtCUT o
where T = temperature rise at tool-chip interface; U = specific energy; v = cutting speed; t = chip thickness before cut; C =speed; to = chip thickness before cut; C = volumetric specific heat of work material; K = thermal diffusivity of work material
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e
-
Cutting TemperatureCutting Temperature
Experimental methods can be used to measure t t i hi itemperatures in machining Most frequently used technique is the
tool-chip thermocoupletool chip thermocouple Using this method, Ken Trigger determined the
speed-temperature relationship to be of the fform:
T = K vm
where T = measured tool chip interfacewhere T = measured tool-chip interface temperature, and v = cutting speed
2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e