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Everything You Need To Know About Injection Mold Design

Injection molding design is the process that helps mold makers to create a product. First, however, certain basic concepts should be considered when designing an injection mold. These include tolerance control, sprues, parting lines, ejector pin marks, and flow paths.

Flow Path

A flow path is one of the most important factors in injection mold design & manufacturing. It combines the material, the injection parameters, and the mold cavity structure. It is the path that the molten plastic flows along inside the mold cavity.

Injection molding is the process of filling a mold with molten plastic. Flow lines are formed by circular ripples, indicating the material flow’s direction. Flow paths are created by altering the mold’s cavities, adjusting the material thickness, or adding or removing stabilizers.

To design a flow path, you must determine the optimum flow length. To do this, you will need to know the density of the material and the melt temperature. Then, you will need to create a fuzzy logic model. This type of simulation predicts the flow length based on the change in injection parameters.

Tolerance Control

Using the proper method to control tolerances in injection mold design can make a big difference. Optimizing tolerances can lead to a more cost-effective product and improve end-user satisfaction.

The proper way to control tolerances is to maintain a certain degree of accuracy. This can be achieved through statistical analysis and process controls. It is also helpful to consider tolerances early in the design stage.

Tolerances are critical when producing parts, especially when they are assembled. This is especially true in products with multiple injection molded parts. A failure of one of these parts can lead to a failure of an assembly. Luckily, the consequences of these failures are usually low.

Parting Lines

Getting a parting line right is crucial to the quality of your finished product. A clean parting line can help reduce the chance of error and make the production process more efficient. But how do you choose the best parting line?

Parting lines are lines that mark the part’s path through the mold. They can be placed anywhere in a mold. However, the line usually follows the outside contour of the part.

The line’s shape and location will influence the final product’s aesthetics, strength, and functionality. For instance, a part made of a specialty material may require a different molding process than a standard part.


Runners and gates are an important part of injection molding. They help convey melted plastic from an injection unit to cavities. This system also assists in cooling the part.

These components’ size and design depend on the product being produced. For example, the part’s thickness will affect the runner’s size and design. The runner can also influence the efficiency of the molding process. For example, the runner may be designed to provide a greater draft. This can help simplify the removal of the part from the runner.

Runners and gates are usually used for spot-level injection molding. They are rarely used in large-scale production applications.

Ejector Pin Marks

During the injection molding, ejector pin marks are formed on the molded part. These marks can have a negative aesthetic impact on the final product. However, they can be prevented if the proper design is followed.

Ejector pins are small pieces of metal or plastic that exert a force on a molded part to break it from the mold. They are usually placed on the B-side half of the mold.

Ejector pins should be arranged to exert a consistent force over the entire part. This will minimize the number of marks made by the ejector pin. They should also be designed to minimize the impact of ejection.

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