Last updated: 2026-09-05 · 5 min read

Mold Runoff and Final Acceptance — What Steps Must Be Completed Before the Mold Leaves the Factory and Ships to Your Plant?

Mold runoff is the last series of shots before the mold ships — typically 50–200 consecutive shots verifying dimensional accuracy, surface finish, cycle time, ejector function, cooling uniformity and hot runner balance. The runoff produces the final sample set the customer measures and approves. Once accepted, the mold is crated, shipped and the warranty begins. Any defect found after the mold leaves becomes the customer’s problem.

Key Facts

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  • Seven-step procedure: dry cycle and function check (30 min), short shot study (1 hr), process optimization (2–4 hrs), first-article CMM check (2–4 hrs), stability run 50–200 shots (2–8 hrs), hot runner balance check, final documentation and sample packaging.
  • Seven documents delivered: CMM report (PDF + native data), process parameter sheet, steel and heat treatment records, electrode/EDM log, 2D mold drawing, spare parts list with physical kit, runoff video (50+ consecutive shots).
  • Timeline: single-cavity mold 1–2 days; multi-cavity with hot runner and sliders 2–3 days. If mold modifications needed, add 1–3 days for correction and re-trial.

    • Parting line — The line where the two mold halves (A-side and B-side) meet. Parting line location affects: gate placement, ejector pin marks, witness lines, and cosmetic appearance. A well-designed parting line minimizes visible witness marks. The related guide covers adjacent topics.

    What Is the Step-by-Step Runoff Procedure and What Does Each Step Verify?

    1. Dry cycle and function check (30 minutes). Run the mold without melt to verify ejector stroke, slider movement, core pull sequence and interlock function. Check that all ejector pins return fully, all sliders open and close without binding, and all safety interlocks engage correctly.
    2. First shots — short shot study (1 hour). Inject at progressively higher pressures to map the fill pattern and confirm gate location, weld line position and air trap location match mold flow prediction. Identifies last-minute venting or gate issues before full runoff.
    3. Process optimization (2–4 hours). Establish the stable process window: melt temperature, injection speed, packing pressure, cooling time and mold temperature. Record all parameters on the process sheet. Goal: a process that produces good parts consistently — not just one good shot.
    4. Dimensional check — first article (2–4 hours). Measure the first 5 shots on the CMM against the drawing. Check all critical dimensions, wall thickness, boss position and hole location. If any dimension is out of tolerance, adjust the process or modify the mold before continuing.
    5. Stability run — 50–200 consecutive shots (2–8 hours). Run at established parameters without interruption. Measure first and last shot on CMM to verify no process drift. Check weight of every 10th shot — variation within ±1%.
    6. Hot runner balance check (if applicable). Verify all cavities fill at the same time and to the same pressure. Check manifold temperature uniformity (±2°C) and nozzle tip condition. An unbalanced hot runner produces cavity-to-cavity variation that process adjustment cannot fix.
    7. Final documentation and sample packaging. Record process parameter sheet, photograph the mold running, measure and tag 10–20 sample parts, record video of 50+ consecutive shots. Package samples in labeled bags with mold ID, shot number and date.

    What Documents Should the Customer Receive with the Mold?

    Document Contents Format
    CMM report Full dimensional data for first and last shot, with deviation from nominal PDF + native data file (Excel or CSV)
    Process parameter sheet All machine settings: melt temp, mold temp, injection speed, packing pressure, cooling time, cycle time PDF, one per cavity if multi-cavity
    Steel and heat treatment records Mill test reports for cavity and core steel, heat treatment certificates with hardness values PDF, organized by insert
    Electrode and EDM log Record of all EDM electrodes used, with electrode ID and the cavity feature it produced PDF or spreadsheet
    Mold drawing (2D) Assembly drawing with all insert IDs, ejector layout, cooling channel layout and BOM PDF + DWG or DXF
    Spare parts list All wearable components (ejector pins, springs, O-rings, heater bands) with part numbers and quantities PDF + physical spare parts kit
    Runoff video Video of 50+ consecutive shots showing mold open/close, injection, ejection and part drop MP4 on USB drive or cloud link

    Cycle time — The total time for one injection molding cycle: injection + packing + cooling + mold open/close + ejection.
    Typical range: 15–60 seconds. Cycle time determines production rate and cost per part — reducing cycle by 5 seconds saves 10–15% annual production cost. The related guide covers adjacent topics.

    Mold runoff: 50–200 consecutive shots verifying dimensional accuracy, process stability, hot runner balance and ejector function. Seven documents delivered with the mold: CMM report, process sheet, steel records, EDM log, mold drawing, spare parts list and runoff video. The mold does not leave the factory with known defects.

  • Key parameter identified — critical variable confirmed against spec.
  • Tolerance within achievable range — commercial ±0.15mm or tighter as needed.
  • Material matched to application — resin grade selected for end-use environment.
  • Process window validated at T1 — parameters locked after first trial.
  • Inspection method defined — CMM, visual, or functional test specified.

    • Frequently Asked Questions

    Should the customer attend the runoff in person?

    For critical molds — multi-cavity tools, automotive programs or molds with tolerances below ±0.05 mm — attending in person is strongly recommended. The customer’s engineer can review CMM data in real time, request re-measurement of specific features and observe the mold’s running behavior.

    For simpler molds, the documentation package (CMM report, process sheet, video and samples) is sufficient for remote acceptance.

    What happens if a dimension is out of tolerance during the runoff?

    The mold must be corrected before it ships. If the part is too large, steel can be removed from the cavity (safe, fast). If the part is too small, steel must be added by welding and re-machining (slower, more expensive).

    The mold is not released for shipment until all critical dimensions are within tolerance and the customer has signed off on the corrected samples.

    How long does a complete mold runoff take?

    A single-cavity mold with straightforward geometry takes 1–2 days. A multi-cavity mold with hot runner, sliders and core pulls takes 2–3 days. The timeline includes process optimization (2–4 hrs), dimensional check (2–4 hrs), stability run (2–8 hrs) and documentation (2–4 hrs).

    If mold modifications are required, add 1–3 days for correction and re-trial.

    Key Takeaways

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  • Runoff: 50–200 consecutive shots — dimensional accuracy, process stability, hot runner balance, ejector function.
  • Seven steps: dry cycle, short shot, process optimization, CMM check, stability run, hot runner balance, documentation.
  • Seven documents: CMM report, process sheet, steel records, EDM log, mold drawing, spare parts, runoff video.
  • Mold does not ship with known defects — out-of-tolerance must be corrected and re-trialed first.

    • The mold runoff is the last opportunity to catch defects before the mold is crated and shipped.
    Once the mold leaves the factory, correction requires return shipment (expensive, slow) or on-site modification at your plant — which may lack the equipment to re-cut steel.

    Sources: Society of Plastics Engineers (SPE) — Mold Making Standards · ASTM International — Mold Acceptance Standards · HASCO — Mold Delivery and Acceptance Guide · DME — Mold Runoff Procedures · ENGEL — Mold Commissioning Guide

    — Arthur, Tooling Engineer at aCatMould