Ratchet & Clank 3: Up Your Arsenal

To obtain all 40 Titanium bolts, you need certain gadgets that you may not have on the earlier levels. So I suggest to go for this towards the end of the game or on your Challenge mode playthrough. The Map-O-Matic gadget that you get on Metropolis is helpful in finding the Titanium bolts since it highlights secret areas in green that often have the bolts.

Here is a list of how many are on each planet (planets that aren't listed don't have any Titanium bolts on them):

Planet Florana - 2 Titanium Bolts
Starship Pheonix - 7 Titanium Bolts
Planet Marcadia - 3 Titanium Bolts
Annihilation Nation - 2 Titanium Bolts
Planet Aquatos - 5 Titanium Bolts
Planet Tyhrranosis - 2 Titanium Bolt
Planet Daxx - 2 Titanium Bolts
Obani Gemini - 2 Titanium Bolts
Holostar Studios - 3 Titanium Bolts
Zeldrin Starport - 2 Titanium Bolts
Planet Metropolis - 3 Titanium Bolt
Crash Site - 1 Titanium Bolt
Planet Aridia - 2 Titanium Bolts
Qwark's Hideout - 1 Titanium Bolt
Planet Koros - 2 Titanium Bolts
Command Center - 1 Titanium Bolt

Here's a great written guide on the Ratchet & Clank wiki that could help:
http://ratchet.wikia.com/wiki/Ratchet_%26_Clank:_Up_Your_Ars...

Also, here's a video guide thanks to TheCODBrothers / TheLegendaryPaul