Temperature Control of Injection Molds

The different thermal conductivity of metals can be used for temperature control of injection molds. In this way, heat can be removed from critical or difHcult to access areas. Mostly, copper elements (beryllium copper) are used and are integrated as a segment into the mold insert. 

Inductive heating is thus another possibility of temperature control in injection molds. It can always be considered for special requirements or when conventional options are not available or only in combination with significant increases in cycle time, such as in the variothermal process, which is frequently used for the manufacturing of micro components or microstructures. 

In the present study, we design an optical pattern of PC resin so that the light distribution characteristics within the plate from the side LED source light can be understood in a better manner. Then, molding experiments compare the effect of the replication of conventional injection molding with or without dynamic mold surface temperature control of LGP molding. 

To ensure consistency, the two critical areas for control specific to injection molding are shot size control and temperature control on the injection system, i.e., screw portion for the reciprocating screw machines, and both the screw and ram sections for the screw/ram machines. As mentioned previously, for temperature and cure control, the use of microprocessor controls has significantly improved the performance of injection molding machines, including control of the shot size. 

Table V illustrates the results obtained by the experimental technique which essentially simulates injection molding while satisfying the time-temperature conditions effective in the fabric laminate work. The large strength increases were reduced to only approximately 10% over the bare glass controls. The conclusion is that the high shear environment of injection molding which yields discontinuous fibers does not allow the same strength increases obtained in earlier experimental work.

Injection mold n. A mold used in the process of injection molding. The mold usually comprises two main sections held together by a hydraulic or mechanical clamping press that have sufficient strength and rigidity to contain the high pressure of molten plastic when it is injected. It is provided with channels for mold venting and for circulation of temperature-control media, and with means for product ejection. 

The process of injection molding can be controlled by monitoring four areas of the molding process, namely temperature, pressure, time, and distance. The four parameters are shown in Figure A.2. 

Control of the mold temperature is a key component for plastics quality. Table A.3 lists the typical mold temperatures for common plastics during injection molding (http //www.matweb.com/). The mold temperature can influence the quality of the plastic part. Warmer mold temperatures can help relieve stresses imposed on the plastic part during injection molding process and aid material flow of thin wall sections. The stresses imposed on the plastic part can cause warpage in the plastic part after it is removed from the mold. Cooler mold temperatures can help cool the plastic part faster and cause a reduction in cycle time. 

Nozzle designs with positive shut-off devices have been successfully used. The gas must be free to escape through the nozzle. Material freeze off in the nozzle or malfunction of the positive shut-off device could develop pressure to cause blow-back of the material through the feed zone and hopper or create hazardous conditions. In such cases, conventional free flow and reverse taper type fitted with a heater band for temperature control of the nozzle prevents nozzle drool or freeze off of the material and is used and in nylon processing. Sprue cutter is associated with the nozzle to help the process. A nozzle forms a seal between the injection system and the mold. 

Injection molding In this method molten plastic material is cooled under pressure in a mold, solidified and finally taken out of the mold. Injection molding is used to prepare articles with accurate dimension and weight, and desired surface finish (Carraher, 2008). Temperature, pressure, and injection speed are the main parameters which control the injection molding process. Decrease in tensile strength and Young s modulus of HDPE has been observed with increase in injection speed (Jiang et al., 2011). 

The temperature control of an injection mold has to fulfill two main tasks (Figure 2.77). In compliance with the required quality and part properties as a result of the amount and uniformity of temperature distribution in the mold, the injection mold continues to have the task to evenly dissipate the introduced heat in a very short time. Here, quality and efficiency often oppose each other. 

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