This document summarizes the assembly process for a ceramic microwave resonator cavity using a shrink fit technique. Key steps include heating the aluminum housing to expand it, inserting the ceramic puck using an alignment fixture, and allowing the assembly to cool which causes the housing to contract around the puck, holding it firmly in place through compression. Finite element analysis confirms the ceramic is held safely in compression while the housing experiences some permanent plastic deformation within its yield strength to form an interference fit.

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.