perform shrink fit calculations for a ceramic dielectric microwave cavity resonator

1. Ceramic microwave resonator
cavity shrink fit assembly
4/9/18 rev A
Don Blanchet
3B Associates
dwb3298@verizon.net
Photo Courtesy of:
Advanced Microwave Technologies

2. Component Assembly
 Aluminum housing
 Cylindrical Ceramic resonator puck
 Heat housing in fixture
 Insert puck using alignment fixture
 Cool to room temperature
 Shrink fit established
– Puck in compression
– Housing in radial tension

3. HOUSING ID Expansion
 Δ𝑙 = 𝛼𝐿Δ𝑇 = 2.3𝑒 − 05 𝑥 1 𝑥 50
 50C rise = .00115 inch
 100C rise = .00230 inch
 200C rise = .00460 inch
 250C rise = .00575 inch
Aluminum Melting point 593 C

4. Assembly measurements example
for randomly selected parts :
 Housing ID = 0.998 at room temp
 Puck OD = 1.001 at room temp
 Heat housing to 225 C in fixture
 Hot housing ID = 1.0026
 Part clearance = (1.0026-1.001)/2 = .0008
gap-allows slip fit hot assembly
 Shrink interference begins at 195C
 Cooling Delta to room temp 195-25 = -175C
forms the interference fit

5. Main Questions ?
 Does the residual tensile stress in the
aluminum housing exceed the yield
point ?
 Is the residual compressive stress in
the dielectric ceramic puck safely
below the compressive fracture
strength ?

6. Linear FEA Results puck
in compression
80,000psi/25,550 = 3.1
FACTOR OF SAFETY

7. Linear housing in tension
aluminum yield strength exceeded
–permanent deformation
Max applied stress = 93,440 psi
Yield strength = 60,000 psi
2014-T6

8. Maximum permanent deformation after cooling = .003 inch
Exaggerated deformation shown 50X

9. Conclusions
 Ceramic dielectric puck does not
fracture.
 A shrink fit is established with .003
inch of permanent plastic deformation
in the aluminum housing.
 These calculations must be performed
for each pair of parts to be assembled.