Modeling and simulation of residual stresses during glass bulb pressing process

Abstract

The residual stresses accumulated in the forming process have great effects on the product quality of the glass bulb. Based on the characteristics analysis of glass bulb forming, a mathematical model has been established for calculating residual stresses of glass pressing process. The material is assumed as thermorheologically simple thermoviscoelastic material, and the flow-induced stress is neglected. The consequences of equilibrium and compatibility equations are discussed in detail, and the boundary conditions are specified for various stages of the forming process. The numerical solution is based on the theory of thin layers, combined with finite difference method in the time and layer difference in the thickness direction. The presented model and solution method could easily be extended to general pressing process of glass, and applied to problems relative to glass pressing, providing extensive reference values.glass bulb, residual stresses, mathematical modeling, numerical simulation, theory of thin layers With the rapid development of electronic products such as TV sets and computers, the need for glass bulb as upper products of color picture tubes also increases greatly. A glass bulb consists of a panel and a cone, which are both pressed in a special press table.In forming, molten glass is pressed into a relatively cold mold, in which complicated and transient flow occurs. Glass melt with high temperature in the core flows toward the mold wall in the glass/air interface of front ceaselessly, which is called as fountain flow. After pressing, the melt is pressurized by pressure of the plunge until the plunger is removed. Because of the mold and air cooling, the layers that come into contact with the mold surface in pressing solidify immediately. And the part will solidify from surface toward core after pressing. The specific volume of glass varies with the changes of temperature. The solidification and shrinkage layer by layer of glass result in a buildup of self-equilibrating residual stresses. Because glass exhibits time-dependent (viscoelastic) thermomechanical behavior, the local stresses "relax" continually

A review of research in numerical simulation for the glass-pressing process

“…Zhou and colleagues have performed comprehensive studies for the glass-pressing process, which covers the whole forming process including glass flow, heat transfer, mould cooling, residual stresses, shrinkage, mould deformation, etc. [23,45,46,[66][67][68][69][70]74]. Their achievements bring a clearer and more systematic insight to this process, and are of practical value to the modern glass industry.…”

Simulation Strategy of the Final Dimension in the Glass Pressing Process

“…However, for the analysis of part contraction and mold deformation, the history and distribution of the temperature and pressure of the part during the whole forming process, together with the cycle‐averaged steady temperature distribution of the mold, are essential inputs. Therefore, a complete simulation of the forming cycle is a precondition for predicting the final dimension, which has already been performed by the author's group 13–19 …”

“…Therefore, a complete simulation of the forming cycle is a precondition for predicting the final dimension, which has already been performed by the author's group. [13][14][15][16][17][18][19] For the pressing stage, a three-dimensional (3D) finite element method is used to perform the simulation of the fluid and heat flow, which uses an equal-order velocitypressure interpolation method. 13,14 The model of the mold temperature is established by cycle-average analysis,…”

“…Daudeville and Carre 12 used Narayanaswamy's model to describe the thermomechanical behavior of glass, including both stress relaxation (to take into account the viscous aspect of glass) and structural relaxation (to take into account the structural state of glass). In recent years, the author's research group performed a wide range of studies for the whole glass pressing process, including glass pressing, 13,14 mold cooling, 15 integrated simulation of the glass and mold, 16 part cooling, 17,18 residual stresses, 19 and so on.…”

Finite Element Simulation on the Roller Pressure during the Rolling of Glass

“…The traditional glass rolling formation craft and the mold design mainly depends upon designer's intuition, the experience and the experimental mold engineer's technique level [2]. In this kind of production process the method of trial-and-error which is based on experience causes the fact that the product development cycle is long, the cost is high and it is difficult to guarantee the quality of the products.…”