Cores and Cavities

Machining Core and cavity Slide and inserts Core pins, etc. Mold base... 

Reduce the significant tolerances of cores and cavities, and on the dimensions affecting the alignment (elements) of the mold. This can be very expensive but can (and should) be done with high quality mass production molds to ensure that all products are as close as possible to the ideal shape and that the mold components are interchangeable. 

Basic tooling construction. In general, the open-mold processes can be expected to have lower tooling costs than any of the closed-mold processes for parts of equivalent complexity because only one side of a mold has to be built. Other types of molding require both a male and female half (core and cavity) or two female halves (split cavity for hollow parts) however, open molds require either a male or a female section. This is illustrated in Fig. 8.8, which depicts a female mold which forms the outside of the part as in Fig. 8.8a and a male mold which forms the inside of the part as in Fig. 8.86. 

Cores and cavities are often polished and chrome plated to obtain a glossy surface appearance and in some instances to facilitate ejection. Chrome plating is also used vdth corrosive resin molding systems such as polyvinyl chloride. Stainless steel molds have also been used successfully and should not be overlooked. Cast beryllium-copper may be used for production cavities but should be flash-chromed to prevent surface staining with some resin systems, e.g., polycarbonate. 

The cores and cavities determine the configuration and surface appearance of the part. The cavity is the female section of the mold and determines the exterior portion of the part. The core is the male section of the mold and forms the inside portion of the part. 

Top and Bottom Gamp Plates. These are mounted directly to the press platen. They are used in multicavity molds to provide structural backing for the cores and cavities. 

Sleeve Plates. These are located between the core and cavity plate. It can eject the part itself or contain a number of separately mounted sleeves as required in multicavity molds. Sleeves often are used for circular parts with an undercut in the core section or where core pins prohibit use of ejection pins. The sleeve surrounds the core in a flash free fit. When activated on the opening stroke of the press, the sleeve moves forward beyond the core, stripping the part from the mold. This requires a taper match between the sleeve and core generally about 3-10 deg per side to eliminate wear. 

Sleeve Plates. Steel plates located between the core and cavity plate and used for sleeve ejection. The sleeve plate itself can perform the ejection or can contain a number of separately mounted individual sleeves as used in multicavity molds. 

When an injection mold fills, the incoming high-velocity melt stream is resisted by, and must displace, the air in the feed system and cavities. Molders often rely on incidental air gaps between the parting faces and between the assembled parts of the core and cavity to provide a leakage path for air, but this is no substitute for properly engineered venting which should be... 

Figure 9. Measured temperature variations of core and cavity for dynamic mold surface temperature control. (One heating/cooling cycle)...

Mold Design, Knowledge Management, Core and Cavity,... 

Due to the combination of conventional injection mold materials and the integration with RT core and cavity mold inserts produced as with DMLS technology, the thermal behavior (the cooling time) of the hybrid injection molds mostly can not be optimized using standard available flow simulation packages. 

The frame of the hybrid mold has been produced by use of standard 1730 steel. Both mold core and cavity are produced using the DMLS DS50 method. Based on conventional injection parameters for both amorphous and crystalline polymers, the mold has been analyzed by verified FE analyses. After mold design and FE model setup, all boundary conditions were implemented. The model was solved using steady state and transient solver control, by use of the Jacobin solution method and the quadric solver with Chebychev accelerator [5]. 

The primary attribute of CNS-V that makes it attractive to the mold industry is its high thennal conductivity (its high strength is easily provided by tool steels). With conductivity in excess of 4 times that of common tool steels, the alloy can be used in core and cavity plications to remove hot spots, reduce warpage in molded parts and reduee cycle time [3,4]. The overall effect is better productivity. 

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