Effect of Peak Cavity Pressure on Unreinforced Polyamide Linear Shrinkage Rates
Elevating peak cavity pressure compresses unreinforced polyamide melt, suppressing specific volume and reducing post-moulding linear shrinkage rates.
Tool Steel Recutting
Meaning
The machining process of removing material from an existing mold plate or core block allows for the modification of part dimensions or the correction of molded-in defects. Performing tool steel recutting is a standard procedure when adjusting for polymer shrinkage variations that were under-predicted during the initial mold design. This modification involves milling, grinding, or using electrical discharge machining to enlarge the cavity or gate paths.
It must be planned carefully because tool steel can only be removed, not added, without expensive welding.
Dimensional Adjustment
Moulders often begin with steel-safe dimensions, meaning the mold cavity is cut slightly smaller than the target size so that the molded part is initially too small. After measuring the first-off samples, tool steel recutting is used to widen the cavity to the precise dimension required to meet the drawing specifications. This iterative process avoids the need to build a new mold and ensures that critical part tolerances are met.
This approach compensates for the discrepancy between the resin datasheet shrinkage value and the actual shrinkage observed in production.
Process Cost
Modifying the tool steel requires the mold to be disassembled and removed from the injection molding machine, which stops production and increases labor costs. This tool steel recutting must be executed by experienced toolmakers to prevent damaging the hardened surfaces of the mold. Mistakes during this stage can ruin the mold plate entirely.
Structural Limitation
Hardness of the tool steel dictates the type of machining methods that can be used for the modification. Pre-hardened steels allow for direct milling, whereas fully hardened tool steels require grinding or electrical discharge machining. Frequent recutting can weaken the structural integrity of the mold walls, making them susceptible to cracking under high injection pressures.
It is therefore necessary to verify the remaining wall thickness before any steel is removed.