To avoid the cost of tooling, many will search to find an “off-the-shelf” plastic extrusion that can fit a specific need. There are times, however, when the nature of the part and application make it necessary to design and develop an extruded profile shape that is manufactured for a specific purpose. The question we will answer here is, “what is involved in the process of making a custom plastic extrusion part?”
Where to Begin?
The process begins with either a sketch or drawing of the desired extrusion, or the portion of the assembly where it will be needed. This information helps communicate to our engineering team what function the extrusion will serve and the space/design constraints that are involved. For simple shapes, the process is pretty straightforward. However, when the design involves more complexity, we will schedule a conference with the appropriate parties during which we will hope to learn about the application, the purpose of the extrusion, the tolerances involved, the material specified, the potential obstacles to overcome, the part’s operating environment as well as any other information that will guide us during our review and design stage.
Following this exchange, we will begin the process of designing an extrusion that takes into consideration these design elements. Our work will have two goals. First, to design a part that will satisfy your application, which includes an analysis of the tolerances and fit required. Second, to design an extrusion that is optimized for the extrusion process. This is important because, in our experience, some extrusions are designed with little regard for producing parts from the extrusion process. Factors related to the tooling investment, the natural variability of both the materials and the process, as well as the complexity of the profile are all important inputs to getting the best outcome, which we define as an extrusion that is both cost-effective and consistently reliable.
Next, we will submit a drawing of the proposed extruded part. It will incorporate our best thinking into a profile shape that will satisfy the application’s needs and be optimized for the extrusion process. The part will include expected tolerances. Many times, we will also offer our thoughts on where the issues might be as we move forward. What does this mean? Well, having designed and manufactured thousands of extrusions over the years we know that the elements of certain profile shapes can provide challenges to the extrusion process. For example, the size of a radius or the potential for sink marks on a surface (see our articles on extrusion design). Typically, we design for these circumstances; however, it is important to inform expected outcomes to ensure we serve your needs. Once an agreement is reached on the initial design, we will issue a written quotation.
The Development Process
Upon receipt of a purchase order to proceed, we will begin the process of designing the tooling elements necessary to manufacture the extrusion. Once these designs are complete, the tooling pieces will be built using a variety of metalworking techniques. When all the elements are complete, the tooling will be assembled onto an extruder for the first trial.
Each new extrusion brings its own unique requirements. We are pushing molten plastic through this new tooling and releasing it into atmospheric pressure at temperatures in excess of 300 deg F – it is here that we evaluate the flow and dimensions. For complex profiles, each trial has its own goal with respect to what element of the shape we are trying to evaluate at that point. Some shapes will be developed in stages, each specific design element building on the next – for example, the hollow section followed by the side fin. After each trial, modifications are made to the tools to get us closer to the completed part; most of these modifications are planned as part of the development process. The typical profile requires several trials before samples are ready for the customer’s evaluation.
When the shape is completed, samples are sent to the customer for evaluation of the design. From there, we are ready to respond to the customer’s needs for additional samples or production. Once an extrusion is completed, the tooling should provide years of use.