A weld cylinder having a single piston arrangement is provided. The
cylinder has a movable retract piston assembly with the piston arranged
within the retract piston assembly. The piston supports a rod that is
movable between home, intermediate, work, and advanced work positions.
The rod moves rapidly from the home position to the intermediate position
however, the rod moves more slowly from the intermediate position to the
work position to reduce the impact force. A cushion chamber slowly
exhausts through a hole in the cushion valve while an isolator is in an
open position. Once the cushion valve opens in response to a weld-forward
pressure on the cushion valve, the cushion chamber exhausts rapidly so
that weld force increases rapidly to minimize increases in cycle time.