Multiple cavity

Injection molds are constmcted of metal precision-machined with internal cooling, multiple cavities, and multifaces, and with devices for extraction... 

Is a multiple-cavity tooling approach possible to reduce piece costs Yes Yes. Depends on size and configuration, although rapid cycle time may eliminate the need. Not necessarily. Secondary operations may be too costly and material flow too difficult... 

When we injection mold small plastic items, it is standard practice to mold several identical parts simultaneously in a mold containing multiple cavities. In order to insure product uniformity, we must design runners that distribute the molten polymer evenly to each cavity. 

Generalized Bom models do not suffer from the multiple cavity problem, which is a particular advantage of that methodology. However, initial studies have suggested that... 

Lastly, let us mention that the integral equation method applies mutatis mutandis to the case of multiple cavities (i.e. to the case when C has several connected components). This situation is encountered when studying chemical reactions in solution. 

Blow mold usually consists of two halves, each containing cavities which, when the mold is closed, define the exterior shape of the BM (Chapter 17). Multiple cavity molds are used. Because the process produces a hollow article, there are no cores to define the inner shape. Mold details and actions will vary considerably according to the geometry of the product and the BM process in use. Even though the following review concentrates on EBM, the information can also be applied to IBM. The two halves that meet on a plane are known as the parting line. The plane is chosen so that neither cavity half presents an... 

The female molded product has the greatest wall thickness with the thinnest bottoms. The reverse occurs when using a male mold. During the forming, the part of the hot sheet that touches any part of the mold will start to cool resulting in a thicker wall with possible frozen stresses. With multiple cavities the female mold permits the cavities to be spaced closer together. Costwise the lower cost is a male mold. 

Three general types of molds are used for CM. In the positive mold (Figure 14.3a) all the material is trapped in the mold cavity. The pressure applied compresses the material into the smallest possible volume. Any variation in the weight of the charge will result in a variation in part thickness. In multicavity molds, if one cavity has more material than the others, it will receive proportionately greater pressure. Multiple cavities, therefore, can result in density variations between parts if loading is not done with some degree of precision control.1 278 284... 

The principal types are two-plate, three-plate, and stack molds. Others include the family mold that has multiple cavities of different shapes in one mold.3, 324 A further distinction concerns the feed system that can be either the cold or hot type. These classifications overlap. Three-plate molds will usually have a cold runner feed system, and a stack mold will have a hot runner system. Two-plate molds can have either feed system. 

For complex items or a mold with multiple cavities and if optical perfection is required, counterflow injection molding or the similar SCO RIM1 process will help to eliminate flow lines. 

When compared with compression molding, transfer molding provides better product consistency, shorter cycle times, and better bonding of rubber to metal [55]. However, considerable amount of material is lost as scrap in the transfer pad, sprues, and flash. The basic three-plate multiple cavity mold is more complex and expensive than a comparable compression mold but is suited better for intricate parts or securing inserts [56]. 

Sprue. (1) The main feed channel that runs from the outer face of an injection mold to the gate in a single-cavity mold or to the runners of a multiple-cavity mold. The hquid polymer is forced through this orifice from a nozzle till the mold is filled to capacity. Some polymer remains in the sprue after the mold is closed, leaving a projecting piece that must be removed after the product is ejected. The viscosity of the polymer must be low enough to permit it to pass through the sprue readily. 

Fig. 8.109 Photograph of dies, several of which feature multiple cavities, and of corresponding punches (courtesy Kiiian, Kdin, Germany).

At the beginning of industrialization, various designs of mechanical punch-and-die presses with single or multiple cavities, including stone presses with indexed die tables, were used, particularly for the manufacture of high-quality bricks that required dimensional precision for their application (e.g., refractory bricks). Among the earliest machines of this type was the Couffmhal press (Fig. 6.10-14, Section 6.10.2). Later, hydraulic presses were also used. 

The differences between prototype and production molds are mainly durability and the addition of cooling to a production mold to decrease cycle times. Often a production mold is a multiple cavity tool that produces many replicates of the same part at once. Production molds usually are made from aluminum, steel, or other durable materials with good heat transfer characteristics. Tool steel is usually used for long run items. 

Injection blow molded bottles are generally blown on the same machine as the one that makes the preforms. It is a multistation machine, where the first station does the injection molding, the second station blows the bottle, and the third station ejects the finished bottle from the machine. The process is often arranged on a horizontal table, as shown in Fig. 12.10. Multiple cavity preform molds and bottle molds can be used in the process. However, the cavitation (the number of cavities) is limited by the size of the rotary table. 

The basic types of mold, regardless of whether they are compression, injection, transfer, or even blow molds, are usually classified by the type and number of cavities they have. For example, Figure 2.1 illustrates three mold types (a) single-cavity, (b) dedicated multiple-cavity, and (c) family multiple-cavity. 

FIGURE 2.1 Three basic types of molds, (a) single-cavity (b) dedicated multiple-cavity (c) family multiple-cavity. 

In multiple-cavity molds, series and parallel cooling circuits are used. Series cooling enters and cools one cavity, then moves to the next until all the cavities are cooled. The temperature of the water increases as it moves through the mold, and this results in non-uniform cooling. Parallel cooling, on the other hand, enters and exists all cavities simultaneously, thereby cooling all cavities at a uniform rate. Parallel cooling is thus the preferred method but it is not always possible due to limitations. 

Unbalanced cavity layout in multiple cavity mold Nonuniform cooling not properly appKed Poor or no venting... 

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