Overmolded parts

A false belief of many injection molders is that one can achieve this goal of defect-free parts by monitoring the machine parameters. The machine parameters alone do not guarantee the quality of parts, since in the end these are just setting parameters, which do not enable to make any conclusions about, for example, the shrinkage behaviour of a molded part. In the same way, unfilled or overmolded parts can only be detected and sorted out reliably using the machine parameters. 

If the viscosities in muiti-cavity molds differ, the individuai cavities are filled differently, which ieads to unfilled parts on the one hand, and to overmolded parts on the other. 

TPEs are often employed to produce a resUient and soft ergonomic layer over a hard structural part. This could be done in a number of ways [213]. TPEs can also be overmolded onto an engineering material through insert molding or multiple-shot injection molding. 

The "catalytic" molded plastic part is then inserted, either manually or automatically, into either (a) a second mold (tool) base or (b) a second cavity within the same mold (tool) base. The second molding cycle injects a non-catalytic (or "non-plateable") resin which overmolds (encapsulates) the non-raised background areas of the first shot plastic part. This second shot cycle completes the molding process. The finished (ejected) plastic substrate, as shown in Figure 6, contains predefined patterned areas of exposed "first shot catalytic" resin and areas of "second shot-non catalytic" resin. 

Also molded are unreinforced or RP to metal hybrids. Plastic-metal hybrids are replacing all-steel structures in automotive front end modules at an accelerated rate. Technical approaches to hybrids are multiplying as more resin suppliers develop alternatives to the overmolding method first established by Bayer. Tier One automotive part suppliers, while tight-lipped on their plans, are also working on proprietary hybrid concepts. 

TPV market is primarily in automotive sealing where TPVs are displacing EPDM in less demanding (e.g., static) molded window seals. However, compression set remains an issue in more demanding (e.g., dynamic) applications such as door seals. TPVs are also increasingly used in overmolding on engineering plastics to achieve soft-touch tactile feel to the molded parts. 

Superior overmolding adhesion to rigid nylon parts (nylon-nylon compatibility) Low-temperature performance to —40 °C... 

Hence, from above properties, the PA/acrylate mbber TPV is particularly suited to various automotive under-the-hood applications where high heat and fluid resistance is needed such as in automotive boots (CVJ, rack, and pinion), noise/ vibration dampening components, dynamic seals, dust covers, underbody/e-coat plugs, grommets, clean air-intake ducts, transmission oil cooler hose, and so on. The nonautomotive applications take advantage of its better overmolding adhesion to nylons to make soft-touch, nylon parts such as power tool handles, overmolded clips, fasteners, and connectors. 

Either relocating the gate to the thickest section or avoiding gating to the thinnest wall area of the substrate may resolve the problem. Mold parts should be fully supported and substrate may need to be changed to resolve. Flow chart 5.2.13 shows a schematic approach to the problem of overmold breaks/impinges through hollow substrate. 

Two-shot injection molding. Two-shot or overmolding refers to a process wherein either different colors or different materials are molded into one part. In this process, the first material or color is injected, then the mold is rotated, and the second shot is injected as depicted in Fig. 1.67. An alternative method is to use a retractable core." In this case, the first material is injected and cooled to solidify, and then the core is retracted to allow injection of the second material as shown in Fig. 1.68. Bonding is accomplished through either strictly mechanical means or by adhesion between the two components through diffusion of the chains. This can result in parts with two combined materials without the need for an additional adhesive bonding step." In the case in which direct adhesion of the materials is desired, proper selection of compatible materials is required. Table... 

Eilms (0.2 to 1 mm) and sheets (2 to 5 mm) are coextruded. Coextruded sheets consisting of multilayers are thermoformed and inserted into an injection mold. This process is also referred to as overmolding. It is well established for automotive interiors. There are a number of promising developments for exterior applications. It is applicable for simple geometry parts with large surface area. See Figures 2 (1) and 3 (7). 

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