A variable search technique was investigated for use with a melt modulation system with multiple control valves. The method was developed in order to obtain an optimum solution which determines the positions of all valves. It was shown that not all valve angles in the system had to be determined, as only certain significant valves needed to be fine tuned during the searching process. It was also shown that the valve position and location were greatly dependent on the cavity and runner configurations. Once the valve control variable search method had been established, a series of family mold models was created and analyzed using MoldFlow. Instead of using the default runner from the software, a modification of the 3D models was made in order to embed melt modulation valves. The result showed that within a limited number of trials, an optimum solution can be obtained. The number of searching trials can also be reduced by applying different search gains and changing certain appropriate initial values.
To develop the control over mold filling during polymer melt manipulation, an alternative way of driving rotary plug valves, which were placed on mold runners, was investigated in this study. During the present investigation, the pneumatic stepping motor concept was explored by designing, fabricating, and testing a specific motor for a target injection molding base application. In order to improve the actuator performance, which is used to drive the valves, a stepping motor driven by a sequence of digital solenoid valves utilizing pressurized air was designed to enhance torque capacity and reduce energy consumption, while maintaining a fixed position for a long period of time. Similar to electromagnetic stepping motors, this pneumatic stepping motor can be driven by a simple switching circuit, which only moves one step for each driving signal without a fading rotation. This mechanism yields an effective system for speed and position control. Although the speed of pressurized air switching is limited by the response time of air solenoid valves that cause a lower rotation output speed, the holding torque and efficiency of this actuator was found to be relatively higher. By using a set of circular pistons aligned so as to actuate on axial wobble gear, the motor produced a very unique motion between the gear and rotor, causing the beneficial characteristics. In this study, the performance of the new motor was tested and compared to a similar size of electromagnetic stepping motor, as well. Thus, this study provides fundamental concepts to develop a suitable actuator for control valves in injection molding at low cost.
New melt modulation system with multiple control valves was successfully developed to facilitate melt control in cold runner based injection molding. The entire valve mechanism and port geometry were significantly improved. The new valve gave better control characteristic and can be made inexpensively. Valve driving mechanism was also redesigned to be more compact and easy to be installed in a limited mold space. It allows four control valves to be placed in the same mold in which only two original valves were able to fit. The four valve melt modulation performed on a runner system that the effect of melt flow from each valve was influenced by all other valves. The interaction between four valves caused complicated behavior and also a difficulty to establish valve control parameters. A reciprocal search method was utilized and able to determine valve control variables within a reasonable number of trials. Experimentation was done on a potential case study that included both family molding and weld line positioning problems. As a part of the outcome, a simple gain modification was developed and able to find an optimum solution. The technique was carried out in both traditional fixed angle and new developed Bang-Bang control methods. The results shows that melt modulation system with multiple control valves was able to effectively control melt behavior and enhanced filling process.
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