Imagine for a moment a world without plastics… From the time we get up in the morning until we go to bed at night plastics are an integral part of our daily lives. From shampoo bottles and tooth brushes, to our cars, cell phones, and other electronic devices, it is nearly impossible to go through the average day of any American without interacting with products manufactured from plastics. On any given day on a global scale, millions of gallons of water are made safe to drink, our food supplies are protected from spoilage and dangerous pathogens, countless lives are saved in hospital emergency rooms, and millions more are transported safely from point A to point B all facilitated by products made from plastics. Indeed, without plastic, many of the things we take for granted everyday would be impossible.
With annual shipments exceeding $300 billion dollars, plastics manufacturing is one of the largest manufacturing sectors in our nation today. Of the various processing techniques, injection molding is one of the most common and economical methods of converting raw plastic into finished goods. Usually, in the long run, there are considerable, efficiency, quality and cost saving advantages associated with injection molding as a method of manufacture. While the initial cost for setting up a part for injection molding can be high due to tooling costs, the cost per part is often a fraction of what it would cost in comparison to manufacturing the same product by another method due to the efficiencies gained in the injection molding process.
The injection molding machine is at the core of the injection molding process. Generally speaking, an injection molding machine consists of two major components; these components include a clamp unit where the mold is mounted or “hung”, and an injection unit where the raw material is heated and mixed prior to being injected into the mold. Processing begins by inputting values and tolerances in the machines control system, such as: times, pressures, temperatures, and speeds. Processing knowledge and experience are critical in determining the proper parameters for quality and efficiency.
Before production begins, the mold is clamped into the machine and the necessary auxiliaries are hooked up, i.e. temperature controllers, hydraulic cores, etc. The mold is then inspected and dry cycled, to ensure proper set-up and function. After test shots are run to verify quality, production is ready to begin.
THE PRODUCTION PROCESS
At the beginning of each cycle, the clamp unit closes the mold and builds tonnage; keeping the mold locked during the injection stage. It is essential that a machine with the proper tonnage be selected in comparison to the size of the mold and the injection pressures used; otherwise, the mold can be blown apart from the extreme pressures produced during the injection stage. When the clamp is closed, the screw in the injection unit pushes forward and shoots the molten material into the mold. Once in the mold, continual pressure is applied to pack and hold the material while it solidifies. While the material in the mold is cooling, the screw rotates and retracts drawing more material into the barrel in preparation for the next shot. After the part has cooled, the clamp unit opens, ejects the finished parts, and the cycle begins again. The entire process or “cycle,” is generally automated and can range from roughly 5 seconds to over a minute, depending on the part size and type of material being used in the process. It is not uncommon for higher cavitation molds to produce thousands of parts in a single hour.