Either use your stun ammo on them or charge your main attack to sun them. That'll kill their shield momentarily.

look here; http://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=813413469

I don't think you have stun ammo initially, but yes -- bash them real hard.

Thanks guys. Big help. I'm using an Xbox One controller , hold the "X" button knocks out the shield then the Mechs gonzo. Have no idea why I couldn't figure it out LOL burned out 😝😝

If you've unlocked the focus attack which is used by pressing Y+B, that will also knock an enemy's shield out.