1. Cover-Gear Box assembly

2. Terms used
Cover (plastic)
Gear Box (aluminum)

3. Aim of the study
Check the good alignment of the cover on the gear box permitting to insert the 4 screws that seal the both parts together.
Sometimes on the line it is impossible to assemble the 2 parts because the 4 holes are not aligned. The cover hide the gear box hole  the screw can’t enter.
Good part
Bad part
There is a gap between the blue circle (cover) and the red one (screw on the gear box)

4. Assembly process
First the gear box is placed on the tool fixture by 3 pins matching in 3 holes on the gearbox. This operation doesn’t have any influence on the measurement required…
The operator place the cover by hand on the gear box using 2 pins and a surface as a stopper.
Surface
Pins
There is a seal on the Cover surface but not used in the simulation

5. Assembly process
Then when the cover seal touch the gear box stopper surface, the 4 screws go down and are assembled at the same time.
Pin 1
Mounting Points
Pin 2

6. My modeling First move (gear box to tool)  no influence
Second move (cover to gear box) I used a Step plane move aligning first the sealing surface as 1st locator. The others points used are in the model.
The hole-pin floats have been switched on.
I put a iterative logic condition in order to simulate the fact that if ever at the first shot the 4 mounting points are not aligned it is possible to remove the cover in order to find a correct positioning. That what happens in reality : the screwdriver will make the cover move on the gear box thanks to the hole pin floating until a assembly position would be found.
The measurement I made is a circle interference between half circle of the cover mounting points and the 4mm screw I supposed already in the gear box. The min limit is 0 as I don’t want any interference between the screw and the cover hole.

7. My modeling
All the tolerances are in the model.  true position of the various mounting points  size tolerance of the holes/pin  flatness of the surface
Do you see any incoherence in the model ?
Does it match with the process description I made to you ?
Any advice/improvement we could do ? Thanks !