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Investigation of the geometric and optical quality of polymer lenses in the injection molding process is costly and timeconsuming. So, reducing the cost of inspection while ensuring the optical quality of the lenses after production is considered in this study. The geometric quality of bi-convex and bi-concave spherical lenses is achieved by monitoring the pressure and temperature profile inside the mold cavity during injection. Regarding the priority of the effect of the geometric parameters, average volumetric shrinkage and warpage are the best parameters for consideration. The results show that the most important effective injection molding process parameters in lens molding are packing time, packing pressure, melt temperature and mold temperature. According to the experimental results, the average amounts of PV for the two surfaces of the bi-convex lens in the optimum level are 7.7 μ and 7.9 μ and for the bi-concave lens are 8.8 μ and 8.1 μ. In addition, the geometric quality of a lens is better when the trend of slope of the pressure graph is lowered to zero and should not be reduced suddenly for all three sensors locations.

In spite of product quality increase in the cold roll forming process by previous practical researches for defects prevention, there are some ill-considered defects such as over-bending, which diminished the product quality in the open section products of this process. This defect which happens by superfluous bending of sheet in the forming stand not only lead to defective products, but also trigger other defects such as edge wrinkling. Since in an elaborate process such as cold roll forming, forming parameters play an active role in defect prevention, the effect of some important parameters is investigated on the over-bending defect and product bending angle by doing 68 experimental tests and numerical simulations in the present study. The list of parameters which are investigated includes bend angle increment, flange width, strip thickness, radius of bend, strength of the materials, and inter-distance between successive stands. In addition, the reason behind the effect of each parameter on the accuracy of the bending angle is laid out. Results show that over-bending defect can be compensated or even eliminated by decreasing the bending angle in each stand, a technique called bending angle increment. Increasing the number of forming stands from two to five causes the over-bending to decrease from 6° to 0°. With bending angle increment being the most impactful factor, bending radius, flange width, and strip thickness have a decreasing impact on over-bending. This study also brings forward a reverse relationship between the strength of the material and the intensity of over-bending. The inter-distance between successive stands was found to have the least effect on over-bending. Results highlight the importance of pre-form rolls at the beginning of the roll forming line. Without the usage of pre-form rolls, the folding of strips on a 60° angle, cannot be done in one stand.

This study investigated the directional warpage on bi-convex and bi-concave spherical lenses by experimentally monitoring the changes in the pressure and temperature of mold cavity and comparing them with the simulation results. Warpage was investigated in the direction of the introduction of molten materials into the cavity of the mold, and when it was perpendicular to the direction of the fluid wave front. Packing conditions, including packing time and packing pressure, and mold temperatures are among the important factors influencing lens warpage and their geometric quality. In this research, these factors were investigated in a full factorial design of experiment. Also, simulation results are in good agreement with the experimental results obtained by the vision measuring machine apparatus. According to the results of this study, the least warpage values in bi-convex and bi-concave lenses in the direction of the fluid wave front were 180 and 200 microns, respectively; while these values were 172 and 198 microns when the lenses were perpendicular to the fluid wave front. The experimental values of these in the direction of the melt in the entrance of the mold for bi-convex and bi-concave lenses were 149 and 186 microns, respectively, while these values were 143 and 180 microns when the lenses were perpendicular to the flow front direction. In addition, the results of the pressure diagram inside the mold cavities indicated the correlation with the warpage, such that when the slope of the pressure graph was lower, the lens warpage was less too.