Underjetting

Underjetting is a term used in fluid-jetting processes to describe a condition in which the jet's energy or momentum is insufficient to achieve the intended operation. It is one of several jetting defects and contrasts with excessive or over-jetting, where jetting exceeds the design target.

Applications include inkjet printing, spray coating, metallurgical deposition, and water-jet cutting. In these contexts, underjetting can manifest as incomplete droplet formation, reduced reach or penetration, inadequate spread on a substrate, or insufficient cutting or cleaning action.

Causes include low driving pressure or nozzle pressure; high liquid viscosity; elevated surface tension; low temperature; nozzle wear or partial clogging; deteriorated pumping or actuation; improper nozzle-to-surface distance; and incorrect fluid properties. These factors can prevent the jet from imparting enough momentum or energy to achieve the desired effect.

Detection and mitigation involve measuring jet velocity with high-speed imaging or flow sensors; adjusting pressure and flow rate; heating the fluid or adding additives to reduce viscosity; selecting different nozzle geometries; cleaning or replacing worn nozzles; and ensuring proper alignment and standoff distance. Process control strategies often focus on maintaining stable operating conditions and fluid properties to prevent underjetting from occurring.

In practice, the term is most common in industrial contexts and is typically considered alongside other jetting defects when optimizing manufacturing and printing processes. See also jetting, atomization, spray technology, and nozzle design.