Traditional Machining - Manufacturing technique

Traditional Machining - Manufacturing technique

1. Traditional Manufacturing Processes Casting Forming Sheet metal processing Cutting Joining Powder- and Ceramics Processing Plastics processing Surface treatment

2. Cutting Sawing Shaping (or planing), Broaching, drilling, Grinding, Turning Milling Processes that involve removal of material from solid workpiece Important concept: PROCESS PLANNING Fixturing and Location Operations sequencing Setup planning Operations planning

3. Sawing A process to cut components, stock, etc. Process character : Precision: [very low,, very high]; MRR: low

4. Sawing

5. Shaping A process to plane the surface of a workpiece (or to reduce part thickness Process character : High MRR, medium Surface finish, dimension control

6. Broaching Precise process for mass-production of complex geometry parts (complicated hole-shapes) Process character : High MRR, Very good surface, dimension control, Expensive

7. Drilling, Reaming, Boring Processes to make holes Process character : High MRR, Cheap, Medium-high surface, dimension control

8. Drilling basics - softer materials  small point angle; hard, brittle material: larger point angle - Length/Diameter ratio is large  gun-drilling (L/D ratio ~ 300) - Very small diameter holes (e.g. < 0.5 mm): can’t drill (why?) - F drilled hole > F drill: vibrations, misalignments, … - Tight dimension control: drill  ream - Spade drills: large, deep holes - Coutersink / counterbore drills: multiple diameter hole  screws/bolts heads

9. Tapping Processes to make threads in holes Process character : low MRR, Cheap, good surface, dimension control Manual tap and die set Automated tapping

10. Grinding, Abrasive Machining Processes to finish and smooth surfaces Process character : very low MRR, very high surface, dimension control 1. To improve the surface finish of a manufactured part (a) Injection molding die: milling  manual grinding/electro-grinding. (b) Cylinders of engine: turning  grinding  honing  lapping 2. To improve the dimensional tolerance of a manufactured part (a) ball-bearings: forging  grinding [control: < 15 m m] (b) Knives: forged steel  hardened  grinding 3. To cut hard brittle materials (a) Semiconductor IC chips: slicing and dicing 4. To remove unwanted materials of a cutting process (a) Deburring parts made by drilling, milling

11. Abrasive tools and Machines

12. Turning Processes to cut cylindrical stock into revolved shapes Process character : high MRR, high surface, dimension control

13. Turning operations

14. Fixturing parts for turning

15. Milling Versatile process to cut arbitrary 3D shapes Process character : high MRR, high surface, dimension control [source: Kalpakjian & Schmid ] ] ]

16. Common vertical milling cutters Flat Ballnose Bullnose

17. Up and Down milling

18. Fixtures for Milling: Vise

19. Fixtures for Milling: Clamps

20. Process Analysis Fundamental understanding of the process  improve, control, optimize Method: Observation  modeling  verification Every process must be analyzed; [we only look at orthogonal 1-pt cutting ]

21. Geometry of the cutting tool

22. Modeling: Mechanism of cutting Old model: crack propagation Current model: shear

23. Tool wear: observations and models High stresses, High friction, High temp (1000  C)  tool damage Adhesion wear : fragments of the workpiece get welded to the tool surface at high temperatures; eventually, they break off, tearing small parts of the tool with them. Abrasion : hard particles, microscopic variations on the bottom surface of the chips rub against the tool surface Diffusion wear : at high temperatures, atoms from tool diffuse across to the chip; the rate of diffusion increases exponentially with temperature; this reduces the fracture strength of the crystals.

24. Tool wear, Tool failure, Tool life criteria Catastrophic failure (e.g. tool is broken completely) VB = 0.3 mm (uniform wear in Zone B), or VBmax = 0.6 mm (non-uniform flank wear) KT = 0.06 + 0.3f , (where f = feed in mm/revolution).

25. Built-up edge (BUE) Deposition, work hardening of a thin layer of the workpiece material on the surface of the tool. BUE  poor surface finish Likelihood of BUE decreases with (i) decrease in depth of cut, (ii) increase in rake angle, (iii) use of proper cutting fluid during machining.

26. Process modeling: empirical results Experimental chart showing relation of tool wear with f and V [source: Boothroyd]

27. Modeling: surface finish Relation of feed and surface finish

28. Analysis: Machining Economics How can we optimize the machining of a part ? Identify the objective, formulate a model, solve for optimality Typical objectives: maximum production rate , and/or minimum cost Are these objectives compatible (satisfied simultaneously) ? Formulating model: observations  hypothesis  theory  model

29. Analysis: Machining Economics.. Formulating model: observations  hypothesis  theory  model Observation: A given machine, tool, workpiece combination has finite max MRR Hypothesis: Total volume to cut is minimum  Maximum production rate Model objective: Find minimum volume stock for a given part -- Near-net shape stocks (use casting, forging, …) -- Minimum enclosing volumes of 3D shapes Models: - minimum enclosing cylinder for a rotational part - minimum enclosing rectangular box for a milled part Solving: -- requires some knowledge of computational geometry

30. Analysis: Machining Economics.. Model objective: Find optimum operations plan and tools for a given part Model: Process Planning - Machining volume, tool selection, operations sequencing Solving: - in general, difficult to optimize Example:   or or ??

31. Analysis: process parameters optimization Model objective: Find optimum feed, cutting speed to [maximize MRR]/[minimize cost]/… Feed: Higher feed  higher MRR Finish cutting: surface finish  feed  Given surface finish, we can find maximum allowed feed rate

32. Process parameters optimization: feed Rough cutting: MRR  cutting speed, V MRR  feed, f  cannot increase V and f arbitrarily ↑ V  ↑ MRR; surface finish ≠ f(V); energy per unit volume MRR ≠ f(V) Tool temperature  V, f ; Friction wear  V; Friction wear ≠ f For a given increase in MRR: ↑ V  lower tool life than ↑ f Optimum feed : maximum allowed for tool [given machine power, tool strength]

33. Process parameters optimization: Speed  provided upper limits, but not optimum Need a relation between tool life and cutting speed (other parameters being constant) Model objective: Given optimum feed, what is the optimum cutting speed Taylor’s model (empirically based): V t n = constant

34. Process parameters optimization: Speed One batch of large number, N b , of identical parts Replace tool by a new one whenever it is worn Total non-productive time = N b t l t l = time to (load the stock + position the tool + unload the part) N b be the total number of parts in the batch. Total machining time = N b t m t m = time to machine the part Total tool change time = N t t c t c = time to replace the worn tool with a new one N t = total number tools used to machine the entire batch. Cost of each tool = C t , Cost per unit time for machine and operator = M . Average cost per item:

35. Process parameters optimization: Speed Average cost per item: Let: total length of the tool path = L t = tool life  N t = (N b t m )/t  N t / N b = t m / t Taylor’s model Vt n = C’  t = C’ 1/n / V 1/n = C/V 1/n

36. Process parameters optimization: Speed Average cost per item:

37. Process parameters optimization: Speed Optimum speed (to minimize costs) Optimum speed (to minimize time) Average time to produce part:

38. Process parameters optimization: Speed Optimum speed (to minimize costs) Optimum speed (to minimize time) Average time to produce part: load/unload time machining time tool change time Substitute, differentiate, solve for V*

39. Process Planning The process plan specifies: operations tools , path plan and operation conditions setups sequences possible machine routings fixtures

40. Process Planning

41. Operation sequencing examples (Milling) step  hole or hole  step big-hole  step  small hole or small hole  step  big-hole or …

42. Traditional Manufacturing Processes Casting Forming Sheet metal processing Cutting Joining Powder- and Ceramics Processing Plastics processing Surface treatment

43. Joining Processes Types of Joints: 1. Joints that allow relative motion (kinematic joints) 2. Joints that disallow any relative motion (rigid joints) Uses of Joints: 1. To restrict some degrees of freedom of motion 2. If complex part shape is impossible/expensive to manufacture 3. To allow assembled product be disassembled for maintenance. 4. Transporting a disassembled product is sometimes easier/feasible

44. Joining Processes Fusion welding: joining metals by melting  solidification Solid state welding: joining metals without melting Brazing: joining metals with a lower mp metal Soldering: joining metals with solder (very low mp) Gluing: joining with glue Mechanical joining: screws, rivets etc.

45. Arc welding Oxy-acetylene welding Flame: 3000  C arc: 30,000  C manual robotic Gas shielded arc welding Argon MIG TIG Al Ti, Mg, Thin sections Fusion welding

46. Plasma arc welding Electron beam welding Laser beam welding Deep, narrow welds Aerospace, medical, automobile body panels Faster than TIW, slower than Laser Nd:YAG and CO 2 lasers, power ~ 100kW Fast, high quality, deep, narrow welds deep, narrow welds, expensive Fusion welding..

47. Solid state welding Diffusion welds between very clean, smooth pieces of metal, at 0.3~0.5T m Cold welding (roll bonding) coins, bimetal strips

48. Solid state welding.. Ultrasonic welding 25 m m Al wire on IC Chip Ultrasonic wire bonder Medical, Packaging, IC chips, Toys Materials: metal, plastic - clean, fast, cheap

49. Resistance welding Welding metal strips: clamp together, heat by current Spot welding Seam welding

50. Brazing Torch brazing Furnace brazing T m of Filler material < T m of the metals being joined Common Filler materials: copper-alloys, e.g. bronze Common applications: pipe joint seals, ship-construction Soldering Tin + Lead alloy, very low T m (~ 200C) Main application: electronic circuits

51. Gluing

52. Mechanical fasteners (a) Screws (b) Bolts, nuts and washers (c) Rivets (a) pneumatic carton stapler (b) Clips (c) A circlip in the gear drive of a kitchen mixer Plastic wire clips Wire  conductor: crimping Plastic snap-fasteners

53. Traditional Manufacturing Processes Casting Forming Sheet metal processing Cutting Joining Powder- and Ceramics Processing Plastics processing Surface treatment

54. Surface treatment, Coating, Painting Improving the hardness Improving the wear resistance Controlling friction, Reduction of adhesion, improving the lubrication, etc. Improving corrosion resistance Improving aesthetics Post-production processes Only affect the surface, not the bulk of the material

55. Mechanical hardening Shot peening precision auto gears [source: www.vacu-blast.co.uk] [source: www.uwinint.co.kr] Shot peening Laser peening

56. Case hardening Process Dopant Procedure Notes Applications Carburizing C Low-carbon steel part in oven at 870-950  C with excess CO 2 0.5 ~ 1.5mm case gets to 65 HRC; poor dimension control Gears, cams, shafts, bearings CarboNitriding C and N Low-carbon steel part in oven at 800-900  C with excess CO 2 and NH 3 0.07~0.5mm case, up to 62 HRC, lower distortion Nuts, bolts, gears Cyaniding C and N Low-carbon steel part in bath of cyanide salts with 30% NaCN 0.025~0.25mm case, up to 65 HRC nuts, bolts, gears, screws Nitriding N Low-carbon steel part in oven at 500-600  C with excess NH 3 0.1~0.6mm case, up to 1100 HV tools, gears, shafts Boronizing B Part heated in oven with Boron containing gas Very hard, wear resistant case, 0.025~0.075mm Tool and die steels

57. Vapor deposition Deposition of thin film (1~10 m m) of metal Sputtering : important process in IC Chip manufacture

58. Thermal spraying High velocity oxy-fuel spraying Thermal metal powder spray Plasma spray Tungsten Carbide / Cobalt Chromium Coating on roll for Paper Manufacturing Industry [source: www.fst.nl/process.htm]

59. Electroplating Deposit metal on cathode, sacrifice from anode Anodizing chrome-plated auto parts copper-plating Metal part on anode: oxide+coloring-dye deposited using electrolytic process

60. Painting Type of paints: Enamel : oil-based; smooth, glossy surface Lacquers : resin based; dry as solvent evaporates out; e.g. wood varnish Water-based paints : e.g. wall paints, home-interior paints Painting methods Dip coating : part is dipped into a container of paint, and pulled out. Spray coating :  most common industrial painting method Electrostatic spraying : charged paint particles sprayed to part using voltage Silk-screening : very important method in IC electronics mfg

61. Painting Electrostatic Spray Painting Spray Painting in BMW plant Silk screening

62. These notes covered processes: cutting, joining and surface treatment We studied one method of modeling a process , in order to optimize it We introduced the importance and difficulties of process planning . Summary Further reading: Chapters 24, 21, 30-32: Kalpajian & Schmid