Machine design 2

Joints

1

loads

• • • •

mechanical thermal



forces, moments…



chemical changing in place/ …

static cyclic dynamic

time

2

• metals – ferrous/ non~ • cast iron • steel – carbon/ alloy • plastics • ceramics • composite materials • density • conductivity • … • elasticity • plasticity • ductility • brittleness • toughness (impact) • creep 3

loads & stresses Stress distribution uniforn/linear (Mohr, H-M-H) 4

general purpose machine elements

static elements

• joints • frames • springs

(mechanical) drive systems

• bearings • shafts • couplings & clutches • drives

vessel systems

• pipes • valves • tanks • (technical fluids) 5

function of joints: join elements together:)

• Kinematic –allowing special freedoms of movement • Fixing or orientating no movement at all 6

• permanent – welded – soldered – brazed – glued – riveted – … Joint types 1.

• detachable (fasteners) – bolted – pin/ cotter pin/ spline – … semi-detachable: press fitted 7

melting 100 °C base material melts T m hot glueing welding pressing brazing soldering cold not melts 450 °C permanent mech.

joints detachable w/wo parts © bagyinszky 8

• joining by: force Joint types 2.

shape material 9

Joint types 2.

• joining shaft & hub by: force shape material friction positive, no-slip we/ so /gl 10

bolt hybrids Split/ groowed pin 11

Keys & pins keyseat/ keyway square par.

flat ~ tapered Gib-head round Woodruff pin roll-pin 12

keyways - stresses milling cutters shearing crushing 13

sliding, stress concentration splined shaft poligon evolvent/ kerb-splines 14

shaft-hub joints by friction press fit conic rings clamp + locknut

fit by other means… taper roll pin groowed pin

other fasteners 1 pin/ bolt loads: bending shearing contact strs .

double shear „bearing” stress p = F/vd crushing

other fasteners 2 (threaded joints next time…) pin: fastening, locating (elastic) retaining rings cotter pin 18

welding same material (cohesive forces) melting and/or pressing weldeability (rigidness, oxidation) heat sources: flame, arc, current, beam… butt weld MIG, RSW… filler material corner weld (fillet seam) spot welding 19

strength calculations • useful length / thickness (faults) allowable stress: σ a = R eh φ /n φ factor of weakening 0,5~0,9 n safety factor 20

design rules for welding     21

welding – pros & cons  • (almost) the same strength • no pretreatment • non-series, repair • can be automated • ….

 • residual stresses • oxidation • hidden failures • ….

22

molten filler metal

soldering

T < 450 °C lead, tin, zinc…

brazing

• T > 450 °C silver, brass … 0.05 -0.2 mm adhesive forces less strength

rivets shearing rupture of plates crushing solid  tubular, blind 24

adhesive bonding (glueing) physical bond: solvent, contact, hot melt… chemical bond: hardening polymers (epoxy resins…) 25

adhesives – pros & cons   • quick, easy • no heat • insulates • repairs • pretreatment • limited strength • limited temps • ….

honeycomb structure 26

Thank you for kindly attention!

27