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Process Engineering Basics of Process Planning for computer implementation

IE550 -- Manufacturing Systems Fall 2008 Dr. R. A. Wysk. Process Engineering Basics of Process Planning for computer implementation. Chapter 6 -- Process Engineering. The Engineering Process. Design specifications. Inspection. Process capability. Process planning.

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Process Engineering Basics of Process Planning for computer implementation

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  1. IE550 -- Manufacturing Systems Fall 2008 Dr. R. A. Wysk Process EngineeringBasics of Process Planning for computer implementation

  2. Chapter 6 -- Process Engineering

  3. The Engineering Process Design specifications Inspection Process capability Process planning Finished part Processes Stock Material Need to understand the process capabilities.

  4. 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 CAPABILITIES 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.

  5. 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. LEVELS OF PROCESS CAPABILITIES

  6. 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. PROCESS KNOWLEDGE COLLECTION

  7. 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. EXPERIENCE-BASED PLANNING Need to automate.

  8. 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) MACHINIST HANDBOOKS

  9. SURFACE FINISH CHART

  10. Dimensional accuracies for Process Planning

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

  12. 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

  13. Dia < 0.5 0.5 < Dia < 1.0 T.P < 0.010 T.P < 0.010 Tol > 0.010 0.002 < Tol < 0.010 Tol < 0.002 Drill Ream Semi-finish bore Finish bore EXAMPLE DECISION TABLE X X X X X X X X X X X X X X X X X X X X X X X

  14. 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

  15. EXAMPLE DECISION TREE Tol > 0.010 Drill Tol < 0.010 T.P < 0.010 Drill, then ream Dia < 0.5 T.P < 0.010 0.5 < Dia < 1.0 0.002 < Tol < 0.010 Drill, then finish bore Tol < 0.002 Drill, semifinish bore, then finish bore

  16. ; ; twist drilling (code 1) ; 111: hole ( ( if (shape ! 111 = ) ( length ! 12.0 diameter ! * <= ) ( diameter! 0.0625 >= ) ( diameter! 2.000 <= ) ( tlp ! diameter ! 0.5 ** 0.007 * >= ) ( tln ! diameter ! 0.5 ** 0.007 * 0.003 + >= ) ( straightness ! length ! diameter ! / 3. ** 0.0005 * 0.002 + >= ) ( roundness ! 0.004 >= ) ( parallelism ! length ! diameter ! / 3. ** 0.001 * 0.003 + >= ) ( true ! 0.008 >= ) ( sf ! 100 >= ) ) PROCESS-CAPABILITY ANALYSIS PROCESS BOUNDARY Data

  17. PROCESSES, TOOLS, AND MACHINES

  18. PROCESSES, TOOLS, AND MACHINES

  19. CUTTING EDGE AND FEED

  20. VOLUME PRODUCING CAPABILITIES

  21. VOLUME PRODUCING CAPABILITIES

  22. PROCESS TOLERANCE RANGE

  23. PROCESS TOLERANCE RANGE

  24. 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 AUTOMOTIVE PARTS REQUIREMENTS

  25. 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

  26. 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

  27. BASIC MACHINING CALCULATIONS Cutting speed V in sfpm surface speed p D n V = 12 D: Diameter Depth of cut D 0 D i

  28. BASIC MACHINING CALCULATIONS 2 p D Metal removal rate 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

  29. 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

  30. CUTTING FORCE AND POWER

  31. MATERIAL REMOVAL RATE

  32. CONSTRAINTS Spindle-speed constraint: workpiece tool Feed constraint: f £ f £ f min max Cutting-force constraint: Power constraint: Surface-finish constraint:

  33. 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

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