Meaning
High-precision dimensional standards define the tightest allowable variations for critical moulded components. Adhering to class 1 tolerances requires advanced tooling and stable resins. These limits are typically reserved for parts with interlocking geometries where fit is paramount.
Achieving such precision increases the cost of the mould and the complexity of the moulding cycle.
Tooling Accuracy
Machining the cavity and core to extremely fine limits is the first step in meeting these requirements. For class 1 tolerances, the steel must be ground and wire-cut with offsets that account for the predicted shrinkage of the plastic. This requires a deep understanding of how the specific resin behaves as it cools from a melt.
Material Selection
High-performance polymers with low and predictable shrinkage rates are necessary to hold these tight dimensions. Resins that vary significantly with moisture or temperature make it impossible to maintain class 1 tolerances across a long production run.
Process Control
Maintaining a stable environment inside the cavity is essential for preventing dimensional drift. Sensors monitor the melt pressure and temperature to ensure that each shot is identical to the last. When the process stays within the window for class 1 tolerances, the scrap rate remains low even for the most demanding parts.
Precise control of the mould temperature prevents the small variations that lead to out-of-tolerance parts. Automated sorting systems sometimes verify the dimensions of each part as it leaves the machine.
