Machine design 2
Joints
1
loads
•
•
•
•
mechanical  forces, moments…
thermal

chemical
changing in place/ time
…
static
cyclic
dynamic
2
materials
• metals
– ferrous/ non~
• cast iron
• steel
– carbon/ alloy
• plastics
• ceramics
• composite
•
•
•
•
•
•
•
•
•
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
Joint types 1.
• permanent
–
–
–
–
–
–
welded
soldered
brazed
glued
riveted
…
• detachable (fasteners)
– bolted
– pin/ cotter pin/ spline
–…
semi-detachable:
press fitted
7
melting
Tm
welding
base material melts
not melts
pressing
hot
100°C
brazing
glueing
cold
450°C
soldering
permanent
mech.
joints
detachable
w/wo parts
© bagyinszky
8
Joint types 2.
• joining by:
force
shape
material
9
Joint types 2.
• joining shaft & hub by:
force
friction
shape
positive,
no-slip
material
we/ so /gl
10
hybrids
Split/ groowed pin
bolt
11
Keys & pins
square par.
flat ~
tapered
Gib-head
round
Woodruff
pin
roll-pin
keyseat/ keyway
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…
roll pin
taper
groowed pin
other fasteners 1
loads:
bending
shearing
contact strs.
double shear
pin/ bolt
„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…
MIG, RSW…
butt weld filler material
corner weld
(fillet seam)
spot welding 19
strength calculations
• useful length / thickness (faults)
allowable stress:
σa = Reh 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
brazing
T < 450 °C
lead, tin, zinc…
• T > 450 °C
silver, brass…
0.05 -0.2 mm
adhesive forces
less strength
23
surface pretreatment
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!
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