The Art and Science Behind Plastic Injection Mold Design: Precision Tooling for Precision Products

The Art and Science Behind Plastic Injection Mold Design: Precision Tooling for Precision Products

Designing custom injection molds for precision plastic parts is a complex process that involves many unique considerations. Throughout the entire design process, constant collaboration between SRC’s design engineers and the customer is critical to achieving a successful end product that meets all expectations in quality, performance, and price point.

Additionally, for ongoing projects we’ll often employ ongoing design improvements and optimization to enhance mold performance and extend its lifespan, further ensuring product quality while minimizing costs. Below, we take a closer look at the art, science, and manufacturing experience that goes into designing the perfect injection mold.

It All Starts with Product Design

Before we delve too far into designing the mold via 3D CAD modeling, we need a complete understanding of the product that will be manufactured. This obviously includes all critical design factors like part geometry, size, complexity, material requirements, as well as production volume.

However, our design experts will also consider the product’s end use, any extraneous factors that could affect service life or performance, along with cost and quality considerations. We can then use this information to further optimize the product and mold designs concurrently.

An Overview of the Injection Mold Design Process

Material Selection

The chosen materials can significantly affect the performance and thus the design of the mold. That’s why it’s important to decide on materials early in the process, testing multiple material options if necessary. SRC’s design team chooses the appropriate material for each mold based on numerous factors like manufacturing material, expected production volume, and the specific parameters of the molding process to be used.

Gate Design

Selecting the right gate type and location is essential for proper material flow freely and evenly into the mold cavity. Common gate types include sprue, runner, and gate at various locations on the mold. These options are considered alongside the unique features and complexity of the product design to arrive at the most optimal gate arrangement.

Runner System

Designing an efficient runner system is likewise crucial for uniform distributing material throughout the mold cavity and minimizing cycle time. This includes the layout and dimensions of runners, as well as the use of hot or cold runners to achieve the highest efficiency possible.

Cavity and Core Design

Developing precise cavity and core geometry is essential for producing accurate and high-quality injection molded parts. The design must consider factors such as draft angles, surface finishes, and cooling channels, as well as the unique physical properties of the plastic material to be used.

Draft Angles

Incorporating proper draft angles relative to part features helps facilitate ejection from the mold, preventing damage to both the part and the mold. Typically, a draft angle of at least 1 degree is needed to ensure consistent and reliable part injection.

Ejection System

Designing an effective ejection system, including ejector pins or sleeves, is crucial for removing the molded part from the mold without causing damage.

Cooling System

Efficient cooling is essential to maintain consistent cycle times, prevent warping, and ensure the overall quality of the molded plastic. Cooling channels are strategically placed to extract heat from the mold and facilitate even cooling.


Adequate venting is necessary to allow gasses to escape during the injection process. Insufficient venting can cause air to get trapped, resulting in defects like burns, bubbles, or voids in the final molded part.

Mold Steel Hardness

Selecting the appropriate hardness for mold steel is essential to withstand the wear and tear associated with repeated molding cycles. For example, we can use aluminum or softer mold steels for prototyping projects and low-volume runs. This saves money on the tooling process and allows for easier design modification.

Injection Molding Machine Compatibility

Of course, we also must make sure the mold design is compatible with the injection molding machines we will be employing for production. These considerations include clamp force, shot size, and other machine-specific parameters.

Testing and Design Validation

Perform thorough testing and validation of the mold design through prototyping and analysis to identify and address potential issues before mass production.

Quality American Injection Molding Services Since 1972

For more than half a century, SRC Plastics has remained one of Massachusetts’ leading injection molding companies for the food and beverage sector and beyond. We provide reliable American manufacturing services for virtually any molded plastic food products with a focus on better quality and better sustainability.