  A precision mass investigation of the neutron-rich titanium isotopes
$^{51-55}$Ti was performed at TRIUMF's Ion Trap for Atomic and Nuclear science
(TITAN). The range of the measurements covers the $N=32$ shell closure and the
overall uncertainties of the $^{52-55}$Ti mass values were significantly
reduced. Our results confirm the existence of a weak shell effect at $N=32$,
establishing the abrupt onset of this shell closure. Our data were compared
with state-of-the-art \textit{ab-initio} shell model calculations which,
despite very successfully describing where the $N=32$ shell gap is strong,
overpredict its strength and extent in titanium and heavier isotones. These
measurements also represent the first scientific results of TITAN using the
newly commissioned Multiple-Reflection Time-of-Flight Mass Spectrometer
(MR-TOF-MS), substantiated by independent measurements from TITAN's Penning
trap mass spectrometer.
