When planning for the processing of rubber seal products or plastic seal products and mechanical components, there are several factors that must be considered to satisfy customer requirements. Although the conventional wisdom is to bring larger volume projects to China for the low prices, American manufacturing innovation and good old fashioned productivity have created many opportunities to produce products domestically – and do it competitively.
The first consideration is the material requirement or specification for the part being considered. The physical requirements for the application will largely determine the material selection, which, in turn, will create the pathways for processing options. As a general rule, thermoset rubber materials have superior physical characteristics over thermoplastics. Theroset rubber materials have traditionally been processed with compression and transfer molding methods, which are quite labor intensive. In the last several years, however, great advances in injection molding technology of thermoset rubber materials have been made domestically. The materials are modified chemically to improve their flow properties, which then allow them to be molded in much the same way that plastics are. They still require secondary finishing to remove flash, but the productive processing rate could make a strong competitive base to work from. If the material is to be thermoplastic, domestic manufacturing is generally more competitive than comparable
The next consideration is the geometry of the part, and the type of tooling necessary to meet geometric, size, and tolerance requirements. There is a limit to the layout of cavities for all processes of molding, so considering spacing and symmetry, the broad rule of thumb is the smaller the geometry, the higher number of cavities. The total volume of the cavities, however, cannot exceed 4 X the projected area of the hydraulic ram tonnage of the press, or the press will not be capable of closing the mold. Generally speaking, thermosetting rubber materials will have a longer cycle time to vulcanization than plastics will to set up, so the productive rate multiplied by the # of cavities will begin to set the stage for the most economical approach to production.
When these parameters begin to be fleshed out, one of the important considerations is what kind of repeatability can be achieved in meeting customer requirements. The more capital intensive the process (generally speaking), the more repeatable the process. Processes that require human interaction will by their very nature vary with the nature of the human element. Advances in controls that include large quantities of sensors create conditions that are optimized by machines, so that any variables are minimized, and so that the process can be stopped at any time if the variables begin to drift away from optimized limits. The result of this approach normally includes a higher yield, better dimensional consistency, and more consistent results overall.
American innovation is on the forefront of advances in capital equipment, primarily in electronic sensors and controls that create higher and higher degrees of control. There is much to be gained by utilizing a more capital intensive approach to production, but the cost of capital can be considerable. While there is still a strong argument for the old fashioned approach in many cases, engineers and designers are wise to keep up with advances in production, and design their rubber and plastic seal products and mechanical components accordingly.
