Meaning
Positional and operational consistency achieved by processing machinery executing identical command sequences over continuous operating cycles defines the machine baseline for product consistency. Measured on injection moulding presses, extrusion pullers, and handling robotics, repeat accuracy quantifies the deviation spread observed across mechanical motions, injection stroke cut-offs, clamp movements, and screw recovery positions. The metric governs machine capability under uniform operating conditions, stopping where external material variations, thermal drifts, or hydraulic oil viscosity shifts introduce independent process fluctuations.
Screw Positioning Mechanics
Digital encoders tracking screw stroke lengths during injection moulding require absolute physical reliability to maintain shot volume stability. Tight repeat accuracy ensures the screw stops within hundredths of a millimetre at the transition from velocity-controlled filling to pressure-controlled packing. If the physical cut-off point drifts across cycles, cavity filling percentages fluctuate independently of hydraulic pressure control.
This instability induces flash when the screw over-travels and sink marks when it stops short, demonstrating that mechanical positioning consistency dictates final part tolerance.
Hydraulic Valve Response
High-speed linear injection processes rely heavily on rapid response times from servo-electric drives or proportional hydraulic valves. Variations in valve spool movement directly undermine repeat accuracy, introducing shot-to-shot variance in peak cavity pressure. In thin-wall packaging applications running sub-second injection phases, a two-millisecond deviation in valve opening changes total delivered mass by critical percentages.
Machine wear in sliding guides, cylinder seals, and linear transducers gradually degrades repeat accuracy, necessitating physical recalibration and component rebuilding.
Tooling Protection Exposure
Automated part removal robotics require dependable physical indexing to enter delicate open moulds without striking tool steel surfaces. Robot repeat accuracy within a fraction of a millimetre prevents costly damage to expensive core pins, hot runner nozzle tips, and complex side-action slides. Where regrind resins produce fluctuating part shrinkage and irregular ejection force, high machine repeat accuracy ensures the robot end-of-arm tooling consistently grips the moulded component without cycling errors.
Mechanical rigidity across thousands of uninterrupted cycles preserves overall operational efficiency.
