Standard Operating Procedure for Plastic Mold Changeover
Mold changeover is a critical transition process in injection molding. Traditional methods can take 30–60 minutes and are prone to human error. Implementing a standardized procedure reduces changeover time to 5–15 minutes, improves positioning accuracy to within ±0.02 mm, and significantly cuts downtime losses (which typically account for 15–20% of total production costs). This document outlines the standard workflow for safe and efficient mold changes.
I. Pre-Changeover Preparation
Adhere to the "Four Readiness" principle (Personnel, Tools, Mold, Equipment) to ensure a smooth transition:
Personnel Readiness: Assign two trained operators. The primary operator handles the machine and mold positioning, while the assistant manages tooling, connections, and safety monitoring. Both must wear safety helmets, steel-toe boots, and heat-resistant gloves.
Tooling Readiness: Verify the tool list, ensuring the availability of lifting equipment (crane, eye bolts), Grade 12.9 fasteners (per GB/T 3098.1—2010), torque wrenches (±5% accuracy), calipers (0.01mm precision), and cleaning supplies. Prepare the mold drawing and process parameter sheet.
Mold Readiness: Inspect the new mold for cleanliness and damage. Ensure ejector pins and guide pillars move freely. Check that the locating ring fits the machine's locating hole with a clearance of 0.01–0.03 mm. Record the status of the outgoing mold for maintenance tracking.
Equipment Readiness: Set the machine to Manual mode and reduce clamping force to the minimum. Clean the platens of debris. Inspect the T-slots and ensure the crane's brakes are functional. The lifting speed should be controlled between 0.2–0.5 m/s.
II. Core Mold Changeover Operations
Follow the "Safety First, Step-by-Step" protocol to prevent damage:
Shutdown Confirmation: Turn off heating, hydraulic, and electrical systems. Lock out the main power supply and display a "Mold Change in Progress" warning sign. Purge the barrel of residual material to prevent cross-contamination; this should be completed within 5 minutes.
Old Mold Removal: Disconnect cooling lines and hot runner cables, ensuring they are clearly labeled. Loosen the clamp bolts diagonally using a torque wrench (e.g., ≥45 N·m for M16 bolts). Attach lifting eye bolts (per GB/T 825) and use the crane to lift the mold horizontally, avoiding collisions with the machine.
Cleaning & Inspection: Wipe the moving and fixed platens to remove oil and debris. Clean the new mold's mounting surfaces. Verify the locating ring fits perfectly and that the surface roughness of the mounting face is Ra ≤ 0.2 μm.
New Mold Installation: Position the new mold so the locating ring seats correctly. Secure it initially with clamps, then tighten the bolts uniformly in a diagonal sequence to the specified torque (e.g., 45–55 N·m for M16 bolts). Large molds require 4–6 clamping points with spacing ≤ 500 mm. Reconnect all hoses and cables, double-checking labels to prevent leaks or electrical issues.
III. Trial Run & Parameter Setup
Validate the mold and machine compatibility to ensure stable production:
Parameter Reset: Power on the systems and set preheating temperatures (e.g., 40–60°C for PE molds). Once temperatures stabilize within ±5°C, cycle the mold slowly in Manual mode to check for smooth operation and proper ejector pin movement.
First Article Production: Input the process parameters (clamping force, injection pressure, etc.) and run the first article in Semi-Automatic mode. Observe the filling process for short shots or flash. The trial cycle time should be within 1.2 times the standard production cycle.
First Article Inspection: Measure critical dimensions using a CMM, ensuring tolerances are within ±0.02 mm. Check the appearance for defects; the parting line flash must be ≤ 0.05 mm for precision molds. Adjust parameters as needed until the part meets specifications.
IV. Post-Changeover & Documentation
Ensure process closure and maintain traceability:
Mold Storage: Clean the outgoing mold and apply rust inhibitor to cavities and guide pillars. Store it on a rack with clear labels (ID, production run, next maintenance date), maintaining a gap of ≥ 10 cm between molds to prevent damage.
Site Cleanup: Return all tools to the tool cabinet and clear the area of waste. Reinstall safety guards and remove the warning sign; this should take no longer than 10 minutes.
Documentation: Complete the "Mold Changeover Record Sheet," noting the changeover time (to the minute), mold ID, operators, issues encountered, and inspection results. Submit the record to production management within 1 hour.
V. Safety Precautions
Lifting Safety: Always use properly rated eye bolts and cranes. Fully seat the bolts in the threaded holes. Never exceed the weight limit. Personnel must stay at least 1 meter away from the suspended load.
Machine Access: If entry between the platens is required, the machine must be fully stopped and locked out. A second person must be present to monitor.
Clamping Protocol: Always tighten bolts diagonally. Uneven clamping causes mold shift or deformation. Recheck the torque after initial tightening.
Monitoring: During the trial run, operate the machine at low speed. Immediately stop if any abnormalities (noise, leaks, misalignment) are detected. Do not run the mold with faults.
