How to Manufacture Precision Molds

Customized Mold Manufacturer

Table of Contents

Manufacturing precision molds is an extremely complex and systematic engineering project that integrates materials science, precision machining, heat treatment technology, and extensive experience.

Core Process of Precision Mold Manufacturing

The manufacturing of precision molds follows a rigorous process where each step is interlinked and crucial.

Phase I: Design & Programming (Foundation & Core)

  1. Product Analysis (DFM – Design for Manufacturability):
    • Purpose: To analyze the manufacturability of the product jointly with the client before mold design.
    • Content: Evaluate whether the product structure is reasonable? Is the draft angle sufficient? Is the wall thickness uniform? How should the parting line be set? How can the gating system, cooling system, and ejection system be laid out most efficiently?
    • Output: Finalize the product’s 3D model and the mold design scheme.
  2. Mold Design:
    • Parting Surface Design: Determine the interface between the moving half and the fixed half of the mold – this is the most critical structure.
    • Mold Flow Analysis (CAE): Use software (e.g., Moldflow) to simulate the filling, packing, and cooling processes of plastic within the mold cavity. This is essential for precision molds, allowing prediction and resolution of issues like air traps, weld lines, and warpage before production, and optimizing gate and cooling channel design.
    • Structural Design:
      • Cavity & Core: The parts that form the external and internal surfaces of the product; the heart of the mold.
      • Gating System: Includes the sprue, runners, and gates, responsible for directing the molten plastic into the cavity.
      • Cooling System: Designs uniform and efficient cooling channels to ensure the mold cools quickly and evenly, reducing cycle time and improving product quality.
      • Ejection System: Designs ejector pins, sleeve ejectors, etc., to eject the cooled part from the mold.
      • Venting System: Creates tiny channels at the end of the melt flow to vent air, preventing short shots or burning.
      • Guiding & Positioning System: Ensures precise alignment when the moving and fixed halves close.
    • Drafting: Generate detailed 2D engineering drawings, annotating all dimensions, tolerances, and surface finish requirements.
  3. CNC Programming:
    • Generate toolpaths for CNC machines using CAM software based on the 3D model.
    • Programming Strategy: Plans the tools, cutting parameters, and tool paths for roughing, semi-finishing, and finishing operations to ensure efficient material removal and achieve high surface quality.

Phase II: Precision Machining (Turning Design into Reality)

  1. Rough Machining:
    • Equipment: Large CNC milling machines, lathes.
    • Purpose: To rapidly remove the bulk of the material, achieving the preliminary shape of the mold.
    • Key Point: Leave sufficient allowance for finish machining.
  2. Heat Treatment:
    • Purpose: To increase the hardness and wear resistance of the mold steel, ensuring mold longevity.
    • Process: Primarily involves Quenching and Tempering. Precision molds typically use Vacuum Heat Treatment to prevent surface oxidation and decarburization.
  3. Finish Machining:
    • Precision CNC Milling/Turning:
      • Uses high-precision, high-stability CNC equipment (e.g., 5-axis machining centers).
      • Employs small-diameter tools for fine detailing, achieving high-precision surfaces and minute features.
    • Electrical Discharge Machining (EDM):
      • Application Scenario: For deep slots, narrow gaps, sharp corners, and complex geometries inaccessible to CNC cutters.
      • Principle: Uses controlled pulsed sparks between an electrode and the workpiece to erode material through high temperatures.
      • Types: Mirror EDM can be used to achieve excellent surface finishes.
    • Slow-Feed Wire Cutting (Slow-Feed Wire EDM):
      • Application Scenario: For machining high-precision through-holes with straight walls, irregular shaped holes, inserts, etc.
      • Characteristics: Extremely high accuracy (can reach ±0.002mm), good surface finish.
  4. Surface Treatment & Polishing:
    • Manual Polishing: Performed by experienced polishers using various grades of oil stones, sandpaper, and diamond paste. This is a critical step determining the mold’s surface quality (smoothness, texture), directly impacting the product’s appearance.
    • Technical Standard: Often denoted by “#” for finish levels, e.g., #1000, #3000, up to mirror finish (A1 grade).
    • Other Surface Treatments: Such as Electroplating (hard chrome for wear resistance and release), Nitriding (increases surface hardness), etc.

Phase III: Assembly, Trial & Acceptance

  1. Mold Assembly:
    • Carefully assemble all machined components (core, cavity, sliders, lifters, ejector pins, etc.).
    • Key Point: Check fit and clearances to ensure smooth movement and precise mold closure.
  2. Trial Production (T1, T2…):
    • Conduct test production on an actual injection molding machine.
    • Purpose:
      • Verify mold functions correctly (ejection, core pulling, etc.).
      • Check if the first article parts’ dimensions and appearance meet design requirements.
      • Identify and document issues like sink marks, flash, short shots, warpage, etc.
    • Mold Modification: Make fine adjustments and corrections to the mold based on trial results. Multiple trial runs (T1, T2, T3…) may be needed to achieve perfection.
  3. Final Acceptance & Delivery:
    • The client approves the final sample parts.
    • Deliver the complete mold, spare parts, and final design documentation.