A comparison of seven filling to packing switchover methods for injection molding

Abstract

The effectiveness of seven methods for controlling switchover from the filling to packing stage were investigated, including: (1) screw position, (2) injection time, (3) machine pressure, (4) nozzle pressure, (5) runner pressure near the sprue, (6) cavity pressure near the gate, and (7) cavity temperature at the end of flow. The activation threshold for each of the seven switchover methods was iteratively determined so as to produce similar part weights relative to a standard process. A design of experiments was implemented for each of the seven switchover methods that perturbs the process settings by an amount equal to six standard deviations of the standard process so as to replicate the expected long‐term process variation. The results suggest that conventional switchover methods (e.g., screw position) had lower short‐term variation, but other methods were more robust with respect to rejecting long‐term process variation. The merits of different dimensional measurements for quality control are also discussed relative to the society of the plastics industry (SPI) standard tolerances. POLYM. ENG. SCI., 50:2031–2043, 2010. © 2010 Society of Plastics Engineers

A Proposed Technique to Acquire Cavity Pressure Using a Surface Strain Sensor During Injection-Compression Molding

“…To achieve and maintain high quality of the molded parts, considerable researches have been reported on process monitoring and control of injection molding over the last two decades [2][3][4][5][6][7][8][9]. Among the process variables in injection molding, which mainly include melt pressure (in the nozzle [2,3], runner [2], and cavity [2][3][4][5][6][7][8][9]) and melt temperature (in the nozzle, runner [1], and cavity [2,7]), the cavity pressure is widely recognized to be especially critical to the process control and final part qualities. Specifically, the cavity pressure is found to be a reliable indicator for the shrinkage, warpage, weight, and thickness of the molded part.…”

“…To implement the measurement of pressure, a variety of pressure sensors based on piezoelectric [2,9] and piezoresistive materials, load cells, strain gages [20], and optical fiber [21] have been developed. The wired piezoelectric pressure sensor is widely employed in the process monitoring and control during injection molding and extrusion.…”

Filling-To-Packing Switchover Mode Based on Cavity Temperature for Injection Molding

“…Kazmer [22] compared seven switchover modes; the results indicated that the machine controlled switchover modes (by screw position, injection time, and machine pressure) had a lower short-term variation in the quality of the molded parts, the other switchover modes (by nozzle pressure, runner pressure near the sprue, cavity pressure near the gate, and cavity temperature at the end of flow) were more robust with respect to rejecting long-term process variation.…”

Correlation between runner pressure and cavity pressure within injection mold

“…For example, the process parameters are corrected by monitoring the cavity pressure in order to reduce shrinkage and warpage resulting from residual stress inside the plastic parts [1][2][3]. There are many methods of monitoring the physical quantities inside a cavity during the process, including measuring the melt flow front [4][5][6][7][8][9], mold heat flux [10,11], mold temperature [11][12][13][14][15], cavity pressure/ temperature [1,2,[14][15][16][17][18][19][20][21][22][23], and dimensions and properties of the molded part [3,[24][25][26][27]. The sensor types include the frequently used contact type, noncontact type [28][29][30][31], and even a wireless type of sensor [32][33][34][35][36].…”