The Main Differences Between Extrusion and Injection Molding
Both extrusion and injection molding are common plastic parts production processes. However, there are significant differences between the two methods pertaining to the process fundamentals, compatibility, strength, and precision. All these factors combine to affect the overall cost and time of the process, which in turn affects the overall costs and capabilities of both methods.
The basics of both processes are the same. Plastic is heated to deform and take the shape of a certain dye, but this is where the similarities between injection molding and extrusion end. The remaining processes are entirely different and require different approaches.
Compatible Plastics
Injection molding produces almost all thermoplastics and most thermoset plastics. This enables the production of permanent and recyclable components like nylon and acrylic. Extrusion only supports thermoplastics like PVC.
Melt Strength
The melt strength is an important parameter when it comes to plastic-related processes. By comparison, the melt strength for injection molding is lower than that of extrusion because the product is ready by the time it exists in the mold cavity.
Extrusion is different because the product doesn’t get cured and may even require some subsequent processing like thermoforming depending on the application. Therefore, the melt strength requirements for extrusion are quite high when compared to that for injection molding.
Costs
There is a significant difference between injection molding and extrusion when it comes to cost. Injection molding is generally more expensive and most of it is because of the mold costs. The mold needs to be either machined or 3D printed depending on the design’s complexity. Furthermore, the material also plays a significant part in determining the cost of injection mold. The better the material, the longer will the mold last but that will come at a cost.
The extrusion process, on the other hand, is much simpler and handles 2D shapes without any intricacies. As a result, the operating costs of the process are lower but remain unaffected by economies of scale. Moreover, the overall setup costs for extrusion can be quite high considering the restriction on complex designs.
End-Use Application
Both injection molding and extrusion work well with plastics. However, injection molding is more suitable for complex closed 3D shapes, like vehicle interior room components. These plastic components have a complex initial dye which significantly increases the capital costs but remains operational for many cycles.
Contrarily, extrusion is an ideal choice for continuous objects or repeatable parts with the same cross-section. For instance, PVC frames, pipes, and other similar objects with continuous cross-sections will almost always rely on extrusion for production.
