Die wear

Wear grooves appear on the surface of the die forming section or dimensions gradually increase, causing extruded product dimensions to continuously go out of tolerance — pipe outer diameter too large, wall thickness too thin, or profile cross-section shape deviating from design values. The die wear rate is directly related to filler content and hardness; formulations containing glass fiber or highly filled CaCO₃ can make ordinary steel dies go out of dimensional tolerance within a few weeks. Die wear is progressive and often gradually degrades product quality unnoticed.

1. Material/formulation factors: Abrasion of the die orifice by fillers (such as calcium carbonate, glass fiber). 2. Mold/tooling factors: Production volume reaches the die life limit. 3. Mold/tooling factors: Insufficient die material hardness or surface treatment failure. 4. Cooling and sizing factors: The cooling rate and uniformity of extruded products determine crystallinity, internal stress level, and dimensional stability. Uneven cooling causes pipe ovality, profile deformation, and internal stress concentration; the cooling water circuit layout and water temperature control must be optimized.

1. Process parameter optimization and adjustment: Select highly wear-resistant tool steel (such as nitrided steel, cemented carbide). 2. Mold/tooling improvement and maintenance: Perform surface nitriding, chrome plating, or PVD coating treatment on the die. 3. Equipment inspection and system maintenance: Select fillers with smaller particle size and spherical shape. 4. Material/formulation optimization: Establish die service life records for regular inspection and replacement. 6. Preventive management: Establish standardized process parameter cards and quality control limits for each mold/product, and regularly conduct process capability index (CPK) evaluations. For recurring problems, use fishbone diagrams or 5Why analysis to trace the root cause, and solidify countermeasures as PFMEA control points. Establish a regular equipment maintenance system and implement life management for key tooling such as dies/spinnerets/calender rolls/coating heads.

This problem is a typical manifestation of die wear in extrusion molding. The core of the solution lies in eliminating the root cause of the defect through systematic optimization of process parameters (temperature, speed, pressure) and precision correction of the die/sizing system. It is recommended to start with parameter adjustment and gradually go deeper into the equipment and tooling levels.