In many areas, tools like injection molding are used to produce parts such as compression springs. This method isn't limited to simple applications, it's also used in large-scale manufacturing. This article focuses on using injection molding to create plastic compression springs, which can replace traditional metal springs in some cases. Plastic springs weigh less than metal ones, making them a valid option if the weight is a significant factor in your design. You will learn about the technical details, from how to calculate deflection in plastic springs to understanding the key steps in the injection molding process. This information will help you apply this method in your spring manufacturing activities.

## Calculating Deflection in Plastic Compression Springs

Deflection in plastic compression springs refers to the measurable vertical displacement seen when the spring experiences applied pressure. The value of deflection is beneficial to discern the response of the spring to a specific force, a factor that informs the steps taken in designing and manufacture.

Utilize the formula D= F/k to compute deflection in a compression spring. Letters D, F, and k in this formula correspond to deflection, applied force on the spring, and spring constant respectively. The last mentioned, the spring constant, measures the stiffness of the spring and is typically denoted in units like pounds per inch or newtons per meter. To provide an illustration, a compression spring with a constant value of 10 pounds per inch, when subjected to a 20 pound-force, yields a deflection value of 2 inches.

Plastic springs exhibit a lower modulus of elasticity in comparison to metallic springs, resulting in higher deflection when subjected to identical force. Exploiting this difference in material properties, an engineering design incorporated a plastic spring that was lighter and flexible in fulfilling the requirements of a specific application. Hence, comprehensive knowledge of these properties facilitates tailoring spring designs to meet the demands of its intended use.

## Differences Between Traditional and Injection Molded Springs

• Material: Traditional springs consist of metals such as steel or alloy. Injection molded springs, in contrast, use plastic materials that are either thermosets or thermoplastics. In some applications where the spring encounters corrosive environments, a thermoplastic material like Polyvinyl Chloride (PVC) has high resistance to corrosion.
• Weight: Injection molded springs constructed with thermoplastics or thermosets weigh less than traditional metal springs. In sectors like aerospace, where the weight of components is crucial, the reliance on injection molded springs can lead to a decrease in overall weight.
• Resilience: In situations requiring springs to endure high levels of stress or heat, a metal spring would be the more suitable choice due to its high elastic limit and heat resistance. However, for uses involving moderate stress levels and operating temperatures, injection molded springs created from plastics might be an appropriate choice.
• Manufacturing Complexity: The process of injection molding allows for the production of springs with complex shapes, which might be difficult to achieve with other manufacturing methods. This capability permits the design of springs with detailed features that can serve to meet specific functional requirements.
• Cost: The initial outlay for injection molding could be more due to the expense of mold creation. Nevertheless, this mold can be used repeatedly, which makes it a cost-effective option for manufacturing large volumes. On the other hand, traditional methods might be more cost-effective for low-volume production due to lower setup costs.

## Requirements for the Injection Molding Process

• Injection Molding Machine: Choose a machine capable of molding springs of various sizes to match your production needs. Ensure the machine maintains a stable injection rate and pressure for uniform spring production.

• Mold and Material: Account for the application of the spring and the type of plastic material during mold design. Suitable materials for springs requiring strength and elasticity might be Polycarbonate (PC) or Acrylonitrile Butadiene Styrene (ABS). Include these material properties in the mold design process.

• Design Considerations: The spring design should factor in predicted loading conditions, environmental exposure, and production volume. For example, an environment with high vibration may require a spring with a greater coil count to ensure continued functionality and load-deflection characteristics.

• Process Parameters: Parameters, such as injection speed, pressure, temperature, and cooling time are crucial for creating high-quality springs. For instance, molds for thin-walled springs might require quicker injection speeds. However, a faster speed could raise the temperature, necessitating a longer cooling time to avoid possible warping or material degradation. Thus, managing these parameters effectively is vital for the production process.

## Conclusion

Through understanding the deflection calculations and the differences between traditional and injection molded springs, your design skillset has grown. Correct application of requirements for injection molding can save production costs. Learning to work with injection molded compression springs may initially seem complex, but with practice and guidance, it will become a regular part of your work. Being proficient with these springs is beneficial as they can improve the functionality and affordability of the products you design.