Mold parts Side coring

Lines left on a molded part by poor mating and fit of side action cores. 

For fully automatic cycles, molds for such a part may be constructed with cam-actuated or hydraulically actuated side cores which serve the same purpose as the previously described mandrel. In each cycle, after the mold is closed and prior to injection of material, the side core is automatically actuated into place. Following the cycle, the side core is retracted automatically prior to mold opening and part ejection (Fig. 6.26). 

Note in this illustration that there is a hole in the side of the part. The core that makes that hole would interfere with the ejection of the part from the mold. Therefore, that core is placed in a removable section which has to be replaced after every cycle. This procedure is too time consuming for high-speed production, and mechanical devices, such as air cylinders and cams, which are activated by the relative motion between the two mold halves, are used to achieve higher production rates. These mechanisms are referred to as slides or side actions and they can also be used to operate the halves of a split cavity when it is used for injection molding. 

On the wall opposite the one with the side hole in Fig. 8.9a, there is an indentation on the core side of the wall that does not protrude all the way through the wall of the part. That indent, known as an undercut, would also interfere with ejection of the part from the core. However, when the undercut is shallow, its edges are adequately radiused and the material is sufficiently flexible, an undercut can be stripped from the mold once the cavity has been removed. If the undercut is too deep to be stripped, removable core inserts or a collapsing core will be required. Undercuts can be placed in the cavity as well however, a split cavity, slides, or removable core inserts will be required if the undercut is too deep to be stripped. Cavity undercuts can be deeper than core undercuts by the amoimt of the shrinkage since the part shrinks away from the cavity wall. Removable core inserts add a considerable amount of time to the molding cycle split cavities or slides add substantial cost to the mold and collapsing cores are, generally, expensive to tool when they are feasible at all. 

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. 

Injection molding is capable of accommodating the broadest range of materials. Nearly all the thermoplastics can be injection molded and, with special equipment, even many thermoset materials can be used. The mold capabilities of the process are also a major asset. Moldmakers have succeeded in constructing incredibly complex molds using side actions to create holes perpendicular to the parting line, split cavities for imusual shapes, and cores which collapse to permit withdrawal from undercuts. 

In mold design, the core is (1) a channel in a mold for circulation of heat transfer media or (2) a part of a complex mold that molds undercut parts. In the latter case the cores are usually withdrawn to one side before the main sections of the mold open (also called a core pin). Cores are usually withdrawn before the main sections of the mold are opened. A core drill is a device for making cooling channels in the mold. 

AND MATING WITH CORE FORMS UNDERCUT WITHOUT NEED FOR SIDE CORE. IT DOES, HOWEVER, LEAVE SMALL W/A/DOW OR OPENING IN MOLDED PART. 

Production blow molds are always made from several parts. Figure 1.150 illustrates a typical blow mold for a packaging product. Movable mold sections can also be used to relieve deep undercuts or to compress specific areas of the product (i.e., to create articles without weld lines). Figure 1.151 shows a blow mold for a fuel tank, with various side cores to compress some areas and to release undercuts in the product for ejection. Materials used for extrusion blow molds ... 

At the end of the production chain is the assembly of all of these parts. As a rule, the molds consist of the following shell side, core side, slide parts, hot runners. 

---