Wednesday, September 26, 2012
Multi shot molding improves product quality
Multi shot molding is a process in which a number of separate material shots are used to produce the final product. Movement of the molding tool and the molded part can allow two, three and even four-shot processes. Multi shot molding is also called in-mold assembly, because the resulting part consists of two or more pieces made of different materials that would normally be joined in a downstream assembly operation.Multi shot molding is widely used to make products that fit in the hand. In the medical device industry, these include small drug-delivery systems and various handheld metering and diagnostic devices. The medical industry has been slow to embrace multi shot molding, but appears to be gradually gearing up to this complex, costly, but highly capable process.China Composite Resin - Construction Structural Adhesive for Anchoring (Tube) ManufacturersProducts made by multi shot processes combine the characteristics and properties of two or more different materials.By eliminating assembly steps, multi shot molding eliminates the labor, machinery, adhesives and mechanical fasteners required for assembly. This simplifies production and lowers manufacturing costs. It also improves the lot-to-lot consistency of products. The in mold combination of two or more parts into one reduces the amount of quality related inspection of individual components. Less assembly and inspection translates into less component handling, which in turn lowers the risk of contamination. Multi shot molding also can eliminate downstream decoration operation. Text, logos and other graphic designs can be molded into products, producing more durable decorations than labels and stickers. The most important advantage is more important than its effect on product quality. Though multi shot molding can streamline the manufacturing process, reduce part costs, and improve product quality, it is not without significant limitations.A number of techniques are used for multi shot molding. The choice of a method is normally based on cost and part design. Common multi shot methods include over-molding, common core, rotary stripper plate, and core toggle or core back.China Composite Resin - Construction Structural Adhesive for Anchoring (Bucket) ManufacturersOver-molding involves two separate molds in two different machines. After plastic components are molded in one machine, they are brought to a second machine that adds a rubber layer or part to the components. A relatively low cost two shot alternative, over-molding is suitable for low-volume jobs that do not justify the purchase of expensive two-shot machines and molds.In common core process, parts stay on a common core throughout the manufacturing process. After the first shot, a platen or turntable rotates 180 degree to move parts to different mold cavities that create space for the second shot. When second shot material must completely envelop the first shot, molders change both core and cavity steel for the second shot. This can be done with a rotary stripper plate, which lifts first-shot material off its core steel, rotates 180 degree in most cases, and then sets the material on new core steel. New cavity steel is also waiting at the second location. The new core and cavity create the space for second-shot material to run in, around, and through the first shot.Another method involves no tool opening or rotation between the first and second shots, but slides inside the tool move to create space for the second shot. By eliminating rotation in the mold, this method lowers two shot costs and is unlike common core and rotary stripper plate techniques. But not all part geometries can be produced this way. China Carbon Laminate 50mm Width, 1.2mm Thickness ManufacturersSometimes, however, a molder can make design changes to initially unsuitable parts that will allow the use of core toggle.Multi shot tooling is more complex than conventional tooling because it includes rotating platens or other features that allow it to create multi piece parts in one mold. Multi shot tooling can usually cost at least twice compared to the conventional tooling. Even though multi shot molding eliminates assembly, manufacturers may find that it is less expensive to mold two low-cost conventional parts and assemble them using a high-speed automated cell. With its high up-front costs,China Carbon Laminate 100mm Width, 1.2mm Thickness Manufacturers multi shot molding is normally used in high-volume manufacturing operations that will provide an adequate return on investment. As a general rule, multi shot molding provides cost effectiveness when more than half a million units are made in a year. Multi shot molding has other limitations in addition to the higher initial cost. It requires proper gate location and proper cavity fill. Multi shot molding requires more maintenance compared to the conventional molding technique.