Mold deformation

A common hypothesis in injection molding simulation is to assume an infinitely rigid mold. However, in reality, the high cavity pressure can lead to mold deflection due to mold compliance. Experimental investigations (Leo and CuveUiez 1996 Delaunay et al. 2000b) have shown that the mold elastic deformation can play a significant role in the pressure-time history. 

Recall Eq. 3.21 in Sect. 3.1.1, where the term 0/z/0f is set to zero for rigid walls. This term should be included if we want to consider the effect of mold deflection. We write it as 

In the case of mold deformation, the cavity thickness his a function of the local pressure. Baaijens (1991) simply chose dh/dP = 0.4 pm/MPa and showed that a small amount of mold compliance can have a significant influence on the cavity pressure history, and neglect of the mold elasticity will lead to under-prediction of the cavity pressure. Pantani et al. (2001) assume the following relationship  

Equation 3.43 indicates that the effect of mold deformation corresponds to an increase in material compressibility. 

In the post-filling stage, when the gate freezes, the left-hand-side term in (3.42) is negligible, we then have 

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In all these isostatic pressing methods, the pressure is applied uniformly to the surface of the green body because the rubber mold deforms to follow the compaction of the powder. In addition there is little or no wall friction between the powder and the rubber mold. As a result, the force balance given by A t = 0 for (ylindrical coordinates gives, for the radial component. 

Because mold deformations are intended to occur in the linear-elastic range, an overlap between loads and deformations is permissible in principle. Linear-elastic means that the deformation changes linearly (i.e., along a straight line), as the force exerted upon a component increases. When the load is removed, deformation will return to zero. The component behaves like a spring. The modulus of elasticity is a measure of linearity for this response. The higher the modulus of elasticity, the less deformation will be experienced by a stressed component. 

An overlap between loads and mold deformations is permissible, because they occur within the elastic range. 

The term bh/dt is included to account for the mold deformation, or to allow the model to be applied to compression molding. One has bh/bt = 0 when the walls... 

A problem known as the core shift is closely related to the mold deformation problem. A core is the part of a mold that shapes the inside of a molded product. Core shift is the spatial deviation of the position of the core caused by non-uniform pressure distribution over the surface of the core during the filling and packing stages. Prediction of the core shift in injection molding has been attempted by some researchers, e.g., Bakharev et al. (2004). 

Of course, as a result of the need for styrene monomer for the production of SBR, much information was developed and the annual sales of polystyrene and its plastic derivatives grew to 2.5 million tons in the year 1985. However, in spite of its ease of fabrication by injection molding and its low cost, it was brittle and moldings deformed below the temperature of boiling water. 

SBS Star-block copolymer / PS blend with 80% PS, injection molded, deformed [14] ... 

Keywords Slab continuous casting. Mold, Deformation of copperplates. Cooling structure. 

More complex shapes can be made by cold isostatic pressing (CIP). CIP uses deformable mbber molds of the required shape to contain the powder. The appHcation of isostatic pressure to the mold suspended in a pressure transfer media, such as oil, compacts the powder. CIP is not as easily automated as uniaxial pressing, but has found wide appHcation in the preparation of more complex shapes such as spark plug insulators (26). 

Creep. The creep characteristic of plastic foams must be considered when they are used in stmctural appHcations. Creep is the change in dimensions of a material when it is maintained under a constant stress. Data on the deformation of polystyrene foam under various static loads have been compiled (158). There are two types of creep in this material short-term and long-term. Short-term creep exists in foams at all stress levels however, a threshold stress level exists below which there is no detectable long-term creep. The minimum load required to cause long-term creep in molded polystyrene foam varies with density ranging from 50 kPa (7.3 psi) for foam density 16 kg/m (1 lb /ft ) to 455 kPa (66 psi) at foam density 160 kg/m (10... 

Ash Fusibility. A molded cone of ash is heated in a mildly reducing atmosphere and observed using an optical pyrometer during heating. The initial deformation temperature is reached when the cone tip becomes rounded the softening temperature is evidenced when the height of the cone is equal to twice its width the hemispherical temperature occurs when the cone becomes a hemispherical lump and the fluid temperature is reached when no lump remains (D1857) (18). 

Thermal Properties. Thermal properties include heat-deflection temperature (HDT), specific heat, continuous use temperature, thermal conductivity, coefficient of thermal expansion, and flammability ratings. Heat-deflection temperature is a measure of the minimum temperature that results in a specified deformation of a plastic beam under loads of 1.82 or 0.46 N/mm (264 or 67 psi, respectively). Eor an unreinforced plastic, this is typically ca 20°C below the glass-transition temperature, T, at which the molecular mobility is altered. Sometimes confused with HDT is the UL Thermal Index, which Underwriters Laboratories estabflshed as a safe continuous operation temperature for apparatus made of plastics (37). Typically, UL temperature indexes are significantly lower than HDTs. Specific heat and thermal conductivity relate to insulating properties. The coefficient of thermal expansion is an important component of mold shrinkage and must be considered when designing composite stmctures. 

Form,/. form shape, cut, size mold tuyere design profile Soap) frame, -anderung, /. change of form deformation, strain, formknderungsfahig, a. capable of deformation plastic ductile. 

To constitute the We number, characteristic values such as the drop diameter, d, and particularly the interfacial tension, w, must be experimentally determined. However, the We number can also be obtained by deduction from mathematical analysis of droplet deforma-tional properties assuming a realistic model of the system. For a shear flow that is still dominant in the case of injection molding, Cox [25] derived an expression that for Newtonian fluids at not too high deformation has been proven to be valid ... 

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