Process of creating a plastic injection mold

Creating an injection mold is a complex process that involves multiple stages, each requiring precision and expertise. Here’s an overview of the typical procedures for making an injection mold:

1. Concept and Design

Product Design: Begin with the design of the part to be molded. This includes considering the material, shape, dimensions, tolerances, and other specifications. CAD (Computer-Aided Design) software is commonly used.

Mold Design: The next step is to design the mold itself. The design includes decisions on the number of cavities, type of mold (e.g., two-plate, three-plate, hot runner), cooling channels, ejection systems, and gating.

2. Material Selection

Mold Material: Choose the appropriate materials for the mold based on the required durability, production volume, and the material being injected. Common mold materials include hardened steel, pre-hardened steel, aluminum, and copper alloys.

Surface Finish Considerations: Depending on the desired finish of the part, additional materials or coatings may be selected to ensure the mold can achieve the required surface polish or texture.

3. Mold Flow Analysis

Simulation: Use mold flow analysis software to simulate the injection molding process. This helps identify potential issues like air traps, weld lines, and material flow problems, and allows for optimizing the mold design before manufacturing.

4. Mold Fabrication

CNC Machining: The core and cavity of the mold are typically machined using CNC (Computer Numerical Control) milling machines. This process involves cutting the steel or aluminum blocks to the precise shapes needed.

EDM (Electrical Discharge Machining): For complex shapes or intricate details that cannot be easily machined, EDM is used. This process involves shaping the mold using electrical discharges to erode the material.

Surface Finishing: After the main machining, the mold surfaces are polished or textured according to the SPI Mold Finish Standards. This can involve hand polishing, grit blasting, or chemical etching.

5. Heat Treatment (if needed)

Hardening: The mold components, particularly those made from steel, may undergo heat treatment to harden them. This increases the durability of the mold, allowing it to withstand the pressures and wear of injection molding.

Stress Relief: Heat treatment can also be used to relieve internal stresses in the mold material, which helps prevent warping or distortion during use.

6. Assembly

Fitting and Assembly: The various components of the mold, including the core, cavity, ejector pins, slides, and cooling systems, are assembled. Precision fitting is critical to ensure the mold operates correctly.

Alignment: Proper alignment of the mold halves (core and cavity) is checked to ensure that they close perfectly without gaps or misalignment.

7. Testing and Tuning

Trial Runs (Sampling): The mold is tested by running it in an injection molding machine with the intended material. This step is known as mold sampling or trial runs.

Tuning: Adjustments are made based on the trial results. This may involve altering the mold design, adjusting cooling times, or tweaking other parameters to ensure the final parts meet all specifications.

8. Final Inspection and Approval

Dimensional Inspection: The mold is inspected to ensure it meets the specified dimensions and tolerances. This often involves the use of precision measuring equipment like CMM (Coordinate Measuring Machines).

Functional Testing: The mold is tested to confirm it functions as expected, including checking the ejection system, cooling efficiency, and part quality.