Mold coring, side

Obviously, Fig. 4.8A is bad design, since the change in thickness is far more than 100%. In Fig. 4.8B and 4.8C, however, either design is good, and the choice depends entirely on which better suits the desired product and, to some extent, on the appearance. In most cases, coring from the core side of the mold (the inside of the product) is preferable. The effect of coring will also help to keep the product on that side of the mold from which it will be ejected— usually, but not. necessarily, the core side of the product. 

The theory of stripping is quite simple. As the mold opens, and after the cavity has moved away from the core side, the ejection starts, caused by the stripper moving forward. In doing so, the plastic product is pushed over the hump in the core (Fig.4.52) this causes the plastic to expand so that the portion that is inside the groove in the core can slip out of the groove. 

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. 

Excessive variation in wall thickness is not the only cause of nonuniform cooling of the part. It can also result from a mold which is not adequately cooled. Ideally, the mold temperature would be maintained at a constant temperature across the molding surface. This ideal is virtually impossible to attain because the shape of the part usually limits the mold designer s freedom to place water lines where they can best perform their function. An example of this type of situation is a box configuration. The core side of the box corner receives heat from three directions (both sides and the top), whereas the core which forms the side of the box is heated only by the melt on that side. For there to be no temperature differential between those two parts of the core, the corner must receive more coolant than the side. This could require a very expensive cooling system which the budget cannot support. 

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. 

The term coring in injection molding refers to the addition of steel to the mold for the purpose of eliminating plastic material in that area. Usually, coring is necessary to create a pocket or opening in the part, or simply for the purpose of reducing an overly heavy wall section (see Fig. 11-64). For simplicity and economy in injection molds, cores should be parallel to the line of draw of the mold. Cores placed in any other direction usually create the need for some type of side action (either a cam or hydraulic cylinder) or manually loaded and unloaded loose cores [2]. 

Molds widi side cores (Figs. 11-98 through 11-101)... 

Figure 11-99. A schematic of a mold with side core action, a battery case molded of PP.

In the mold design, design of the mold with specific supplementary geometry, usually on the core side, is quite complicated by the inclusion of projection and depression [20]. Important factors of designing the mold include mold size, number of cavity, cavity layouts, runner systems, gating systems, shrinkage, and ejection system [21-23]. 

FIGURE 1.200 Cross section of a mold with core side and hood side... 

FIGURE 4.14 Overall mold assembly on the core side, including all movable slide functions... 

Even the flow properties of the plastic material in the mold are influenced by polishing quality and alignment. In the case of marks through slider movements, the flow behavior of the plastic material in the mold can be affected on the core side by the polishing roughness so that marks can be reduced or avoided. 

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. 

Tooling. The tools for RTM follow all of the rules for standard compression molding. Their cost is higher because consideration must be given for the construction of the pot in the core side of the mold. Multiple cavity layouts will also require more time for mold design and layout of the raw material feed system. 

Undercuts as depicted in case A in Figure 7 result in an expensive mold because side cores must be used. Design solutions without undercuts are shown in cases B and C in Figure 7. 

The detailed molding conditions are shown in Table 1. Fig. 3 shows the schonatics of the mold surface with the miao-feature and inducfitm-heating coil. Before filling, the mold tonperature of side surface had always been kept as 60 °C, meanwhile the temperature of the core side containing the miao-feature varied from 70 ° C -140 ° C. The experiment is paformed with 2 conditions, with and without vacuum. 

The tenqterature distribution of mold surface was also measured by infi ared radiation thermal imaging (IRTI) system [5]. Several interested locations at core side and cavity side were selected as shown in Figure 8, and the mold surface tenperature was detected once the mold was open. Temperature variations at these points are used to verify the simulation results, and the result comparisons are fisted fi om table 1 to table 4. The temperature results calculated by ANSYS are also included in these tables. From the conparison through these tables, we can see that both ANSYS and our simulation methodology can predict the surface temperature in core side and cavity side well qualitatively. 

An example of the contribution of polar interactions between an acrylic PSA and a substrate is shown in Fig. 6. By copolymerizing iso-octylacrylate and acrylic acid, using a monomer ratio of, respectively, 95/5 and 90/10, two otherwise identical PSAs were made. The PSAs were laminated to both sides of a foam core to make an attachment tape as used in the automotive industry for the application of body side moldings to a car. One side of the foam tape was laminated against an aluminum foil backing. The other side was laminated against an automotive paint-coated panel to make the final test sample. The test sample was allowed to... 

Blind holes in molded plastics are created by a core supported by only one side of the mold. The length of the core and depth of the hole are limited by the ability of the core to withstand the bending forces produced by the flowing plastic without excessive deflection. For this reason, the depth of a blind hole should not exceed three times its diameter or minimum cross-sectional dimension. For small blind holes with a minimum dimension below 1/4 in., the L/D ratio should be kept to two. With through holes the cores can be longer, since the opposite side of the mold cavity supports them (3). 

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