Kinematic Restraint Fixturing Mechanics for Injection Molded Thermoplastics Metrology
Kinematic restraint fixturing isolates molded thermoplastic part geometry by arresting six spatial degrees of freedom without introducing bending strain.
Six Point Location
Meaning
Geometric principles define the minimum number of contact points required to fully constrain a rigid body in three dimensional space. A standard six point location system uses three points to define a plane and two points to set an axis while a final point fixes the position. This method ensures that all six degrees of freedom are restricted without inducing stress.
It remains the standard approach in jig design for precision manufacturing.
Fixture Stability
Correct placement of the pins ensures that the part does not move during machining. The six point location strategy prevents the part from sliding or rotating under the force of a cutting tool. It provides a repeatable setup for high volume production runs.
Degree Restriction
Each point of contact removes one possibility of movement for the workpiece. The primary plane is established by the first three points to stop the part from tipping. Following this, the next two points create a line that prevents the part from spinning.
A sixth point acts as a stop to lock the part in its final position. This six point location approach avoids the problems of a part wobbling or being crushed by too many clamps. If more points are used, the system becomes overconstrained and the part may not sit flat.
Engineers must select these points based on the most stable surfaces of the raw casting. The design remains kinematic only when the contact is maintained at exactly six points.
Constraint Logic
Following this rule allows for the most accurate translation from a design model to a physical part. The six point location ensures that every part in a batch is measured from the same starting position.