Custom Rubber Molding Techniques

Rubber materials, such as EPDM, neoprene, nitrile, natural rubber, silicone, and others can be readily molded to create components with high precision. Gaskets, seals, grommets, tank diaphragms, valves, caps, and isolators are all examples of parts that can be molded.

Jefferson Molding Works is a leading manufacturer of molded rubber products with decades of experience. Here, we’ll take a closer look at three common molding techniques: injection molding, transfer molding, and compression molding. We’ll discuss how each of these processes works and some of their advantages.

Injection Molding

Often associated with plastics, injection molding can also be used with rubber materials. The material is processed into strips and conveyed into a closed mold with a screw feeder. Because of its viscosity, greater pressure is needed to inject rubber than most plastic materials.

Types of Parts Suitable for Injection Molding

Injection molding can be used for many types of parts, including those with highly complex geometries like holes, undercuts, thin walls, or intricate details. It can also be used for overmolding, in which rubber material is molded around or over another component made of a different material, like metal or plastic. Cycle times vary based on the size of the part and the curing time of the rubber material being molded.

Injection Molding Cost Considerations

The largest cost associated with injection molding is design and manufacturing of custom tooling, especially for intricate or complicated part designs. However, once molds and tooling are created they can be used for the entire production lifecycle.

In contrast to tool and mold making, part production is cost-efficient. This process is well-suited to high-volume production because it is largely automated, with machines running most of the steps from injection to part ejection. This reduces labor time and costs.

Because the same tooling is used for each part, there is minimal variation between parts throughout the production run, and little wasted material. This results in less finishing work and very little scrap.

Advantages of Injection Molding

The main benefits of injection molding include:

  • High-Speed Production. The injection molding process is quick, which means material is forced into the mold and cures rapidly for short cycle times.
  • Consistency and Precision. Injection molded parts have minimal variation because they are made with highly precise molds and high-pressure material injection to fill cavities completely.
  • Automation Capabilities. Injection, cure time, and ejection or removal are all controlled by machines, which move efficiently and continuously for rapid, high-volume, high-precision production.
  • Cost-Effectiveness. Because a high volume of parts can be made very quickly, the initial investment in tooling and material costs are spread out, making it cost-effective.

Transfer Molding

In transfer molding, rubber material is pre-weighed to measure the correct amount for each part. The material is then heated and placed in a transfer bowl, and poured into the closed mold. The mold is then held at a designated pressure and temperature for a prescribed amount of time as the material cures. This process can produce a smooth surface finish for a more polished-looking product.

Transfer molding is more labor-intensive than injection molding and is therefore well-suited to low- or medium-volume production and parts that are small or extremely detailed. It may not be as cost-effective as injection molding for high-volume production.

Compression Molding

In compression molding, the rubber material is pre-formed by weighing out the required amount and shaping it into an approximation of the finished shape and size. Then, it is placed in a mold, the mold is closed, and the piece cures under a constant pressure and temperature for a specified amount of time. Depending on the size and complexity of the component, results may not be as consistent as with other molding methods.

Because it is a more labor-intensive process than injection molding, compression molding may be more suitable for low-volume production or large quantities of relatively simple parts. It is also more difficult to control flashing with this method because the mold is closed after the material is added to it, making it easier for small amounts of material to escape. As a result, additional finishing may be required to remove flashing.

Custom Rubber Molding Techniques from Jefferson Rubber Works

Consider the following when choosing the best molding method for an application:

  • Part Geometry and Complexity. When selecting the ideal rubber molding method, it’s important to consider the size, shape, and intricacies of the design.
  • Production Volume. More labor-intensive methods, such as compression and transfer molding, may not be cost-effective for large production runs; however, simple shapes can be produced at scale with compression molding.
  • Material Properties. These include requirements for hardness, temperature resistance, and elasticity. Material options include EPDM, silicone, SBR, nitrile, NBR, natural rubber, neoprene, polyisoprene, butyl, and chlorobutyl.
  • Cost. Certain techniques will cost more due to the expenses associated with equipment, tooling, and labor.

Learn more about rubber molding from Jefferson Rubber Works on our website, or contact us today to get started on your next project.