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Microforming: Extrusion of micropins

Microforming: Extrusion of micropins. Jian Cao, Zhong Wang, Neil Krishnan and Anthony Swanson. Advanced Materials Processing Laboratory Northwestern University . Introduction. Meso-scale metallic parts : 100s of microns to 10 mm. Connector pins: 24 billion used annually for IC carriers.

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Microforming: Extrusion of micropins

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  1. Microforming: Extrusion of micropins Jian Cao, Zhong Wang, Neil Krishnan and Anthony Swanson Advanced Materials Processing Laboratory Northwestern University

  2. Introduction • Meso-scale metallic parts : 100s of microns to 10 mm. • Connector pins: 24 billion used annually for IC carriers. • Market Value of micro products: $45 billion in 2003*. • Growth Rate: 20%*. • Current manufacturing methods: machining, folding, swaging, stamping. * Geiger, M., Kleiner, M., Eckstein, R., Tiesler, N. and Engel, U., “Microforming”, Keynote Paper, Annals of the CIRP, 50-2 (2001), 445-462.

  3. Introduction • Machining: • Established process, complex geometries. • Low production rate makes it unsuitable for mass-production. • High material waste. • Folding: • Low process forces, rapid process. • Sheet material: cannot handle sheets that are extremely thin (100 microns). • Stamping: • Rapid process, complex 2D shapes. • Sheet material: restricts geometry of final product. • Swaging: • Requires several closely packed dies: challenging at smaller scales. • MEMS methods like Photolithography, LIGA, RIE: • Relatively slow, require clean rooms.

  4. Current Manufacturing Methods • Swiss turning machines • Large machines requiring 10ft x 6ft floor space. • High tolerances • Low production rates • Microformers • Use bulk deformation processes • Machines require 2.5ft x 2.5ft x 5ft • Tolerances not as good as turning. • Higher production rates

  5. Review of Literature • Geiger, M., Kleiner, M., Eckstein, R., Tiesler, N. and Engel, U., “Microforming”, Keynote Paper, Annals of the CIRP, 50-2 (2001), 445-462. • Applications, material behavior, processes, tool manufacturing. • Geiger, M., Messner, A., Engel, U., Kals, R.and Vollersten, F. “ Design of microforming processes – fundamentals, material data and friction behavior” Proceedings of the 9th International Cold Forging Congress, Solihull, UK-May – 1995, 155-163. • Tensile tests (0.2 to 2mm dia.) and upsetting tests(1 to 8.5mm OD) for CuZn15. • Decreasing grain size causes an increase in flow stress due to the decreasing share of surface grains. • The power law relation between flow stress and strain rate is valid for micro-dimensions. • Dry friction at this scale shows an influence of specimen size as well as of the average grain size. • The scattering of all data increases when scaling down specimen dimensions.

  6. Review of Literature • Engel, U. and Eckstein, R., “Microforming – from basic research to it’s realization”, Journal of Materials Processing Technology, 125-126 (2002), 35-44. • Double cup extrusion of CuZn15 specimens from 0.5 to 4 mm. • Forward rod – backward can extrusion of CuZn15 specimens from 0.5 to 4 mm with different grain size (4 m and 120 m).

  7. = parameter representing the ratio of the area of surface grains to the total area of the specimen cross-section w0 = specimen width s0 = specimen thickness L = grain size Thickness to grain size ratio Review of Literature • Raulea, L.V., Goijaerts, A.M., Govaert, L.E. and Baaijens, F.P.T., “Size effects in the processing of thin metal sheets”, Journal of Materials Processing Technology, 115 (2001), 44-48. • Uniaxial tension tests and bending experiments to investigate the effect grain size and specimen size for Aluminum. Tension Tests Bending Experiments

  8. Review of Literature • Michel, J.F. and Picart, P., “Size effects on the constitutive behavior for brass in sheet metal forming”, Journal of Materials Processing Technology, 141 (2003), 439-446. • Tensile tests and hydraulic bulge tests for brass. • New proposed model for flow stress curves Tensile Tests Hydraulic Bulge Tests (Flow stress independent of size effects) Proposed Model: (F = Corrective factor,  = sheet thickness)

  9. Review of Literature • Peng, X., Qin, Y. and Balendra, R., “Analysis of laser-heating methods for micro-parts stamping applications”, Journal of Materials Processing Technology, 150 (2004), 84-91. • FEM simulations and experiments for laser-heating assisted micro-stamping for 316SS and Cu. FE model of stamping Punch Force v/s displacement Stamping using tubular punch

  10. Micro-die fabricated from photochemically machinable glass. Microgear shaft made from Al-78Zn superplastic alloy. Pitch circle dia. = 200 m Review of Literature • Saotome, Y. and Iwazaki, H., “Superplastic backward microextrusion of microparts for micro-electro-mechanical systems”, Journal of Materials Processing Technology, 119 (2001), 307-311. • Microgear shafts of dia. 200 m. • Saotome, Y. and Okamoto, T., “An in-situ incremental forming system for three dimensional shell structures of foil materials”, Journal of Materials Processing Technology, 113 (2001), 636-640. Principle of incremental sheet metal forming SEM micrograph of deformed specimen (a car body)

  11. Preliminary Study: Extrusion of micropins • Extrusion : fast process ideal for mass production. • Established manufacturing process at macro-scale. • Key issues: • Forming force. • Surface interaction. • Workpiece-die failure. • Preliminary sample dies made by drilling. • Final Pin Dia.: 1.2mm, 0.8mm, 0.48mm. • Pins damaged during removal due to high force required to push pins out. • Improvements: Segmented dies

  12. Dimensions Big Pin Small Pin a 2 mm 0.8 mm 610 deg. C for 1 hr Grain size, ‘g’ = 87 microns 700 deg. C for 1 hr Grain size, ‘g’ = 211 microns b 1.2 mm 0.48 mm θ 30 deg. 30 deg. a θ A b Schematic of extruded pin with dimensions for the two cases Effect of grain size • Material : Brass C260 (Cu/Zn = 70/30). • Heat Treatment for different grain size. • Scale bar = 100 μm • Two pin sizes: • Base dia. = 2mm; Extruded dia. = 1.2mm • Base dia. = 0.8mm; Extruded dia. = 0.48mm • Location A marks the position where the deformed microstructure is observed.

  13. Effect of grain size • Microstructure of deformed pins. a = base diameter. g = grain size. a/g = no. of grains across sample width

  14. Effect of grain size: Tensile Tests • Material : Brass C260 (Cu/Zn = 70/30). • Three grain sizes: • 550 deg. C. for 1 hr: Grain size = 32 microns. • 610 deg. C. for 1 hr: Grain size = 87 microns. • 700 deg. C. for 1 hr: Grain size = 211 microns. • Three sample sizes • Dia. = 1.3mm, length = 15mm. • Dia. = 0.8mm, length = 7mm. • Dia. = 0.4mm, length = 5mm. • Two tests per sample for 1.3mm and 0.8mm. • One test per sample for 0.4mm.

  15. Effect of grain size: Tensile Tests • Sample dimensions do not show a pronounced effect on stress-strain curve

  16. Effect of grain size: Tensile Tests • Increasing grain size does cause a decrease in flow stress 32 micron 87 micron 211 micron

  17. Extrusion • Extrusion dies made using drilling and polishing. • Die mounted in a forming assembly consisting of a ram which is moved on supporting rods using linear bearings. • The forming assembly is placed inside a loading sub-stage to measure ram force and ram displacement. Forming assembly Loading sub-stage with forming assembly mounted.

  18. Extrusion 1 – Crossheads 2 – Support screws 3 – Frame 4 – Load cell 5 – LVDT 7 – Drive shaft 8 – Gear box 9 – Motor 10 – Sample clamps SEM Loading sub-stage manufactured by Ernest F. Fullam, INC., New York Load Capacity – 2000 lbs

  19. a Image captured using optical microscope θ b Extrusion • Two Extrusion dies • Drilled – (rough surface finish) • Drilled & Polished – (smooth surface finish)

  20. Extrusion • Ram force v/s ram displacement. • Smooth die.

  21. 211 211 87 87 32 32 32 32 87 87 211 211 32 32 87 87 211 211 Extrusion • Change in surface roughness with testing. • Smooth die. Surface roughness does not change appreciably during testing

  22. Extrusion • Ram force v/s ram displacement. • Rough die. First set of results for each case is lower than other tests

  23. 32 32 87 87 211 211 211 211 87 87 32 32 87 87 32 32 211 211 Extrusion • Change in surface roughness with testing. • Rough die. Surface roughness decreases during initial tests and then remains approximately the same

  24. a  b Extrusion: Estimation of friction coefficient • Modified die Three die sizes Same surface roughness Same extrusion ratio

  25. Extrusion: Estimation of friction coefficient • Estimate friction coefficient by comparing pin length and extrusion force from experiments with FEM simulations. Deformed mesh for FEM simulations of extrusion with different coefficients of friction. (ABAQUS/Explicit)

  26. Extrusion: Estimation of friction coefficient • Comparison of extrusion force from experiments with FEM simulations using a friction coefficient of 0.2.

  27. Extrusion: Estimation of friction coefficient • Friction coefficients obtained by matching the pin length and extrusion force from experiments and FEM

  28. Summary • Micro-extrusion has the potential of being an efficient and cost-effective method of fabrication for meso-scale parts such as connector pins. • Effects of material grain size need to be considered in this length scale (100s of microns to 10 mm). • In tensile test results for C260 brass, grain size has a more pronounced effect on the stress-strain response than sample dimensions. • The effects of grain size and surface roughness on the extrusion process are being investigated by capturing the force-displacement response. • The friction coefficient can be estimated by comparing the pin length and extrusion force profiles obtained in experiments and FEM simulations.

  29. Thank You

  30. Machined Pins

  31. Folded Pins

  32. Stamped Pins

  33. Swaging

  34. Extrusion • Comparison of rough and smooth die results.

  35. Extrusion • Final pin dimensions :

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