Warpage prediction of optical media

Abstract

A numerical simulation of the warpage of injectioncompression molded optical media such as CD's and DVD's due to asymmetric cooling is developed. A thermal viscoelastic constitutive model is employed to calculate the thermally induced stress. The stress is not symmetric with respect to the mid-plane of the disk because of the differential mold temperatures employed. Before demolding, the out-of-plane deformation is constrained by the mold walls. After ejection, the disk is quenched in the air, and is free to deform, causing warpage to develop in the disk. A finite element analysis code is developed using axisymmetric plate elements to simulate the warpage of the disk after demolding. The complete finite element formulation is described. Simulation results of warpage for CD-R moldings are compared with experimental observations under different processing conditions such as melt temperature, mold temperature, and packing pressure using an optical grade of polycarbonate. Good agreement of the simulation results and experimental observations is obtained. The comparison of the simulation and experiment reveals that the processing conditions have complicated effects on the warpage, and mold temperature has the greatest effect on the warpage in the current study.

Effect of processing conditions on warpage of film insert molded parts

“…The results showed bellshaped curves with summit values at 250 o C. The tendency can be explained by the counter effects of melt temperature on warpage variation. One is the increase of warpage and shrinkage due to increasing melt temperature and thermal expansion [10,11] and the other is the decrease of warpage due to reduced shrinkage resulted from more closely packed molecular chain structure that is induced by the increase in gate freezing time as the melt temperature is increased [19]. It is indicated that the former effect is superior to the latter when melt temperature is elevated from 230 o C to 250 o C, and vice versa when melt temperature is elevated from 250 o C to 270 o C.…”

“…Severe warpage can occur due to asymmetric residual stress distribution in the FIM part generated by the non-uniform temperature distribution. Many studies have been carried out to investigate the effect of processing conditions on the warpage of injection molded parts without any inserted film [6][7][8][9][10][11][12][13][14][15][16][17]. Huang and Tai [18] investigated the effective parameters in the warpage problem of an injection molded part.…”

Shrinkage and Warpage

“…However, there are other causes of nonuniform shrinkage including orientation and residual stress. For further information, the interested mold designer is referred to the research literature [18][19][20][21][22][23][24][25].…”

Thermoviscoelastic Behavior of Film‐Insert‐Molded Parts Prepared under Various Processing Conditions

“…[25,26] In the present study, the integral method was used to measure the residual stresses because it was appropriate to evaluate the residual stress variation in thickness direction during the incremental hole-drilling measurement. [11,[27][28][29] The elastic strain, " rr , measured by the rosette at the periphery of the hole is related to the principal stresses by the following equation:…”

“…Heat transfer perpendicular to the cavity wall can be retarded because the film is attached on one side of the cavity wall and two different polymers are used as the film and substrate. [5] Many studies have been carried out to investigate the effects of processing conditions on the warpage and residual stress distribution of injection molded parts without any inserted film; [6][7][8][9][10][11][12][13][14][15][16][17] however, investigations of the FIM process have rarely been reported. It is essential to understand the residual stress distribution and to predict the viscoelastic deformation of the molded part for the practical application of FIM to industrial end-user products.…”