Process Engineering Basics of Process Planning for computer implementation

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Process EngineeringBasics of Process Planning
for computer implementation

• IE550 -- Manufacturing Systems
• Fall 2008
• Dr. R. A. Wysk

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Chapter 6 -- Process Engineering
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The Engineering Process
Design specifications
Inspection
Process capability
Process planning
Finished part
Processes
Stock Material
Need to understand the process capabilities.
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PROCESS CAPABILITIES

• Process certain way an operation is carried
  out, e.g. turning, drilling, milling.
• Tool physical object which is used to carrying
  out a process, e.g. twist drill, spade drill, gun
  drill.
• Machine tool machine on which process is carried
  out, e.g. lathe, drill press, milling machine,
  machining center.

Process capability The geometry and tolerance a
manufacturing process can produce, and its
limitations, . i.e. shape and size, dimensional
and geometric tolerances, material removal rate,
relative cost, other cutting constraints.
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LEVELS OF PROCESS CAPABILITIES

• Universal level
• Handbook and textbook level data. Aggregate
  characterization of what can be expected.
  General measures of the process capability such
  as shape and size. What the process can
  accomplish in an average shop on a typical
  machine tool.
• Shop level
• Specific to a particular manufacturing system.
  What is the best attainable capability in one
  specific shop, e.g. the turning capability of
  the student machine shop is far worse than that
  in the shop of a precision spindle manufacturer.
• Machine level
• Specific to a machine. Machines in the same shop
  has very different capability. A table top lathe
  can machine a small part, yet a large slant bed
  lathe may be able to handle a 20"x 10' part.

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PROCESS KNOWLEDGE COLLECTION

• Few scientific data available or published.
• Most process knowledge are gained during actual
  manufacturing practice.
• Practical manufacturing knowledge is still an art
  instead of a science.
• Certain information can be found in the
  textbooks, handbooks, machining data handbook,
  etc.
• Tolerance capability may be obtained from control
  charts, inspection reports, and on-line sensor
  data.

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EXPERIENCE-BASED PLANNING

• Relay on one's experience. Most frequently this
  is the way industry operates.
• Problems
• a. Experience requires a significant period of
  time to accumulate.
• b. Experience represents only approximate, not
  exact knowledge.
• c. Experience is not directly applicable to new
  processes or new systems.

Need to automate.
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MACHINIST HANDBOOKS

• Universal or shop level knowledge.
• e.g. Surface-finish chart - limiting extremes of
  process
• 8 in - use grinding, polishing, lapping
• Usually not with milling, however, finish
  milling may achieve the specification.
• The information is general. It does not mean
  every machine or shop can achieve that accuracy.
• Turning limit (6.3 - 0.4 m or 250 - 16
  inch)
• Diamond turning at Lawrence Livermore Lab
• (12.5 nm or 0.47 inch)

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SURFACE FINISH CHART
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(No Transcript)
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Dimensional accuracies for Process Planning
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HOLE MAKING KNOWLEDGE

• Following data is taken from a manufacturer's
  process planner's handbook.
• I. Dia lt 0.5"
• A. True position gt 0.010"
• 1. Tolerance gt 0.010"
• Drill the hole.
• 2. Tolerance lt 0.010"
• Drill and ream the hole.
• B. True position lt 0.010
• 1. Tolerance lt 0.010"
• Drill, then finish bore the hole.
• 2. Tolerance lt 0.002"
• Drill, semi-finish bore, then finish bore the
  hole.
• II. 0.05" lt dia lt 1.00"

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DECISION TABLES
To computerize the decision making, one simple
way is to use decision tables. If the conditions
set in an entry are satisfied, the actions in the
entry are executed. The stub contains the
condition or action statements. Entries
mark which conditions or actions are applicable.
Each entry contain one rule.
Entries
Stub
Conditions
Actions
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EXAMPLE DECISION TABLE

• Dia lt 0.5
• 0.5 lt Dia lt 1.0
• T.P lt 0.010
• T.P lt 0.010
• Tol gt 0.010
• 0.002 lt Tol lt 0.010
• Tol lt 0.002
• Drill
• Ream
• Semi-finish bore
• Finish bore

X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
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DECISION TREES
To computerize the decision making, one simple
way is to use decision trees. Decision tree is a
graph with a single root and branches emanating
from the root. Each branch has a condition
statement associate with it. Actions are written
at the terminal. Probabilities may be assigned
to the branches. In this case, the tree
represents probabilistic state transitions.
terminal
Branch
Root
The node may be "AND" nodes or "OR" nodes.
Node
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EXAMPLE DECISION TREE
Tol gt 0.010
Drill
Tol lt 0.010
T.P lt 0.010
Drill, then ream
Dia lt 0.5
T.P lt 0.010
0.5 lt Dia lt 1.0
0.002 lt Tol lt 0.010
Drill, then finish bore
Tol lt 0.002
Drill, semifinish bore, then finish bore
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PROCESS-CAPABILITY ANALYSIS
PROCESS BOUNDARY Data

• twist drilling (code 1)
• 111 hole
• ( ( if
• (shape ! 111 )
• ( length ! 12.0 diameter ! lt )
• ( diameter! 0.0625 gt )
• ( diameter! 2.000 lt )
• ( tlp ! diameter ! 0.5 0.007 gt )
• ( tln ! diameter ! 0.5 0.007 0.003 gt
  )
• ( straightness ! length ! diameter ! / 3.
  0.0005 0.002 gt )
• ( roundness ! 0.004 gt )
• ( parallelism ! length ! diameter ! / 3.
  0.001 0.003 gt )
• ( true ! 0.008 gt )
• ( sf ! 100 gt )
• )

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PROCESSES, TOOLS, AND MACHINES

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PROCESSES, TOOLS, AND MACHINES
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CUTTING EDGE AND FEED
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VOLUME PRODUCING CAPABILITIES
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VOLUME PRODUCING CAPABILITIES
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PROCESS TOLERANCE RANGE
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PROCESS TOLERANCE RANGE
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AUTOMOTIVE PARTS REQUIREMENTS

• Cylinder bore 13 - 25 in honed
• Main bearing bore 63 - 200 in
• Crankshaft bearing 3-13 in polished
• Brake drum 63-125 in turned
• Clutch pressure plate 25-100 in turned

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BASIC MACHINING CALCULATIONS
Machining time
Total amount of time to finish a workpiece. For
drilling, one pass turning, and milling
clearance or overhang distance.
For multipass turning
integer round up
For milling
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BASIC MACHINING CALCULATIONS
Machine control parameters are f, V, ap.
a. Feed and feedrate


V

inch
/
min
f


V

f
n
turning or drilling
f



V

f
n
N
V
milling
f
f



of
teech
in
milling
N

1
in
drilling


n

rpm
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BASIC MACHINING CALCULATIONS
Cutting speed


V
in
sfpm
surface speed





p
D
n
V

12
D Diameter
Depth of cut
D
0
D
i
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BASIC MACHINING CALCULATIONS
2
p
Metal removal rate
D
4
v
f
Drilling



2
p
D
2
2
p
(

D
)
MRR

v
D
o
i
4
f
4
f

3
D
V
Turning



2
2
p
(
D

D
)
v
o
i
MRR

v
f
4
f

6(
D

D
)
f
V
o
i
Milling





MRR

a
w
v
p
f
12
a
w
n
p

f
V
p
D
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BASIC MACHINING CALCULATIONS
Machining time
Total amount of time to finish a workpiece. For
drilling, one pass turning, and milling
clearance or overhang distance.
For multipass turning
integer round up
For milling
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CUTTING FORCE AND POWER
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MATERIAL REMOVAL RATE
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CONSTRAINTS
Spindle-speed constraint
workpiece tool
Feed constraint


f


f

f
min
max
Cutting-force constraint
Power constraint
Surface-finish constraint
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MODELS
Multiple pass model
i pass number
Additional constraint depth of cut
number of passes is a function of the depth of
cut.
Productivity model
s sale price/piece