Injection Molding – A Few Notes
Industrial design and engineering in the injection molding manufacturing industry has advanced beyond the methods that originally made the technology work over the last 25 years. The molds themselves have become more automated so that there is rarely a need for an inspection department to pull defective items off the line. Mold sensors can tell, before the mold is even opened, if the part is good or bad. The computer-controlled molding press has become the control center for the manufacturing cell, linking the chain of auxiliary equipment, materials handling, and other equipment together in the machine controller. Innovations have made the removal and exchange of molds easier, and all-electric equipment has gradually been replacing hydraulic equipment.
Multiple injection technology has undergone rapid development in the last few years. New variants of the processes, the plastics and material combinations have been developing regularly. These innovations have enabled new applications in automotive, medical, electronics, packaging, sports equipment and communications technology industries.
Bi-injection technology enables two components to be simultaneously or sequentially injected into the same cavity, quickly producing more complex products and different color combinations in one step.
There are several different techniques used in bi-injection molding. The core-back technique adds two components into one cavity, one after the other, by the shifting of a valve. Transfer techniques make use of robots to transform a preform into a second cavity or machine. Rotary techniques make use of axial or vertical rotation to transfer material. Sandwich techniques have been developed to laminate different plastics together to produce a skin-and-core structure.
Microinjection molding can produce very small components through a very high-precision injection molding process. The system uses a microinjection unit that allows manufacturers to mass produce miniaturized parts with consistent accuracy. Microinjection molding can produce elaborated and articulated parts that weigh less than a gram. These parts can be reproduced by the thousands, millions or even billions, with the same precision every time.
The microinjection system can also produce macro-scale geometries in objects that are, themselves, on a larger scale. For instance, a part measuring an inch long can have micro-sized features and walls a tenth of a millimeter thick. The ability to micro-mold two different materials on the same part, at the same time, in one mold cycle, greatly expands the utility of the process, especially in medical applications. A device 2.4 mm in diameter can have a soft material in the center surrounded by a hard structural material.
New materials are flowing into new molding machines and producing new kinds of parts. New processes are being monitored and controlled by new types of equipment. Recently, for instance, new kinds of resin materials have been formulated just for the medical market. The medical market is driving a lot of new material innovation.
For implantable devices, a biodegradable material, called Bionate, allows the manufacture of implants that do not have to be removed when their usefulness expires. Clear plastics have been developed to manufacture lens carriers that are transparent and neutrally refractive, so that customers can check the quality of lens after it is placed in the carrier. Stronger plastic materials for medical use, like Questra, are being molded into structural components. Injection molding manufacturers are also using materials that contain special fillers. Glass-filled plastics are being used to make laparoscopes and other medical optical tools. Filled plastics that are opaque to radiation are being used to shield bodies during radiation therapy.
The range of customized equipment in the injection molding industry has enormously broadened to meet the increasing technical demands of clients. Injection molding machines are getting smaller in order to make smaller medical products. “Part sizes are driving down machine sizes,” says one observer. One company even recently showed a “desktop” injection molding machine measuring 2.5 feet long by 1 foot wide.
With so much innovation in the methods and materials used by the molding industry, the possibilities and applications for manufacturers are nearly endless. From medical uses to technological and consumer goods, manufacturers will continue to be able to produce more complex and useful products.