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

(Mohr, H-M-H)

Stress distribution uniforn/linear

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

8

welding

glueing

mech.

joints

brazing

soldering

melting

pressing

hot

cold

Tm

100°C 450°C

base material melts

permanent

detachable

© bagyinszky

w/wo parts

not melts

Joint types 2.

• joining by:

force shape material

9

Joint types 2.

• joining shaft & hub by:

force shape material

10

friction positive, we/ so /gl

no-slip

hybrids

11

bolt

Split/ groowed pin

Keys & pins

12

square par.

flat ~

tapered

Gib-head

round

Woodruff

pin

roll-pin

keyseat/ keyway

keyways - stresses

13

milling cutters

shearing

crushing

sliding, stress concentration

14evolvent/ kerb-splines

poligon

splined shaft

shaft-hub joints by friction

press fitconic rings

+ locknutclamp

fit by other means…

roll pin

groowed pintaper

other fasteners 1

pin/ bolt

double shear

loads:bending

shearing

contact strs.

„bearing” stress p = F/vdcrushing

other fasteners 2(threaded joints next time…)

18

pin: fastening, locating

cotter pin

(elastic)

retaining rings

welding

19

same material (cohesive forces)

melting and/or pressing

weldeability (rigidness, oxidation)

heat sources: flame, arc, current, beam…

butt weld

corner weld

(fillet seam)

filler materialMIG, RSW…

spot welding

strength calculations

• useful length / thickness (faults)

20

allowable stress:

σa = Reh φ /n

φ factor of weakening 0,5~0,9

n safety factor

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

solderingT < 450 °C

lead, tin, zinc…

brazing•T > 450 °C

silver, brass…

23

adhesive forces

less strength

surface pretreatment

0.05 -0.2 mm

rivets

24

shearing

rupture of plates

crushing

solid tubular, blind

adhesive bonding (glueing)

25

physical bond:

solvent, contact, hot-melt…

chemical bond:

hardening polymers

(epoxy resins…)

adhesives – pros & cons

•quick, easy

•no heat

•insulates

•repairs

•pretreatment

•limited strength

•limited temps

•….

26

honeycomb structure

Thank you for kindly attention!

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