(1) define rule1 and rule2 before f, and (2) wrap the rhs of the definition with Evaluate to suppress the HoldAll attribute of SetDelayed:
f[x_, y_, z_] := Evaluate[(int1 + int2 + int3) /. rule1 /. rule2];
f[1, 2, 3]
14
kglr
- 400.5k
- 18
- 488
- 929