Mold parts Finish insert

Where applicable an undercut insert in the mold can remain as an insert in the finished part. Such inserts can be held in place by the undercut. If possible, they should be made from the same material used in forming the part so there will be no difference in thermal expansion and contraction. 

Finish insert (neck insert). In blow molding bottles, a removable part of the mold that aids in forming a specific neck finish of the bottle. 

As a closed-mold process, both surfaces of compression-molded parts can be finished. Draft for long-fiber compression-molded parts should be 3° per side, but less can be used for depths under 6 in—down to 1° per side in extreme cases. Molded-in holes are feasible in the plane of the parting line as are bosses, corrugated sections, molded-in labels, and raised lettering. Molded-in holes within a two-diameter distance from the outside edge of the part will need to be drilled as a secondary operation. The solid material thickness between two holes should not be less than one diameter (the largest). Core pulls, slides, split molds (for external undercuts), and metal inserts are recommended only for the SMC and BMC varieties. 

Ribs (B) and metal inserts (E, H) are not recommended for preforms, but they can be used with the other versions. The minimum inside radius (IR) is 0.125 in for preform-molded parts and 0.062 in for SMC-and BMC-molded parts. Long-fiber compression-molded parts can be trimmed in the mold. For Class A finishes in SMC parts, the inside radius at the base of a rib should be 0.020 in otherwise it should not be less than 0.060 in. The thickness at the base of the rib (B) can be equal to the nominal wall thickness (W), however, it must not exceed 0.75W under Class A surfaces. The height of the rib (C) should be 2 to 3 times the nominal wall thickness (W) and the draft should not be less than 1° per side except for ribs imder Class A surfaces (which can handle the cost premium) where it can go down to 0.5° per side. These same rib design rules apply to boss wall thicknesses for these parts. In-mold coating can be used for high-class finishes. 

Molded parts with very complex internal contours, for example with multiple internal undercuts, can t be produced using the conventional injection moiding because the needed compiex cores can t be puiied out. If the cores are made from a iow-meiting metai aiioy - preferably by a die- casting process - and are inserted into the moid, they can be melted out of the finished moided part e.g. using electric induction heating or an oil bath. 

In the vacuum injection process (Vacuum Assisted Resin Injection [VARlj), which is the most simple resin injection process, molds with a fixed and a flexible mold half and molds with two fixed mold halves are used (Figure 1.227). The textile semifinished part is inserted into the cavity, the mold is closed, and a vacuum is applied. The vacuum ensures that the mold stays closed and the reinforced structure is compacted. After opening the inlet, the structure is impregnated by infusing the matrix into the fiber material. After curing, the finished component can be removed from the mold. 

Gel coats are typicaHy used to provide a part with a finished surface directly from the mold. Various inserts, stiffeners, and mechanical attachments can be incorporated in the mol ding step, thereby further reducing secondary operations. Final edge trimming is accompHshed with a variety of tools such as... 

A special attribute of these processes is the abiHty to pre-position reinforcement, inserts, and core materials for stiffening ribs. Gel coatings can be apphed to the mold surface to eliminate post-mold finishing. Because both surfaces of the part are formed in a mold to close tolerances, accurate assemblies are possible, which is a requirement for many automotive or tmck body appHcations. 

This term is used both to describe designs that are etched or engraved in the mold surface and the process of inserting a printed film into the mold, to be produced as an integral component of the finished product. Etched surfaces can be drawn both parallel and perpendicular to a parting line of molds or postforming in an extrusion line.. However, be alert with molds to the fact that parallel to the parting line additional draft is required. A wide selection of patterns is available and new ones can be readily created. 

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. 

Adding vacuum chambers to compression molding equipment in recent years has reduced the number of defects caused by trapped air or water in the molding compound, resulting in higher-quality finished parts. Another relatively new improvement has been the addition of various forms of automation to the process. For example, robots are used both to install inserts and remove finished parts. 

As commented, PVC plastisols are suspensions of emulsion PVC in a plasticizer. Formulations contain components such as pigments and thermal stabilizers, but plasticizers are by far the major component. PVC plastisols are rotomolded to obtain hollow soft articles, mainly in the toy industry. It could be deduced that mechanical properties of these parts are not important, but the finishing operations such as insertion of eyes and hair in dolls heads or mechanisms in arms and bodies, or final assembly, imply big loads apphed to the part, and consequently, the mechanical properties have to be developed to the full. Moreover, the molds used in these apphcations have very intricate shapes, pronounced ribs and comers, and aesthetics and details reproduction is very important in these parts. These complex shapes may involve high tensions in the moldings and corrrphcate the demolding process. To obtain a good thickness distribntion in snch a mold, variables involved in the process have to be at the optimnm. 

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