Backpressure Optimization in Foam Injection Molding: Method and Assessment of Sustainability

Abstract

Inspired by the Industry 4.0 trend towards greater user-friendliness and self-optimization of machines, we present a novel approach to reducing backpressure in foam injection molding. Our method builds on the compressibility of polymer-gas mixtures to detect undissolved gas phases during processing at insufficient backpressures. Identification of a characteristic behavior of the bulk modulus upon transition from homogeneous to heterogeneous polymer-gas mixtures facilitated the determination of the minimum pressure required during production to be determined, as verified by ultrasound measurements. Optimization of the pressure conditions inside the barrel by means of our approach saves resources, making the process more sustainable. Our method yielded a 45% increase in plasticizing capacity, reduced the torque needed by 24%, and required 46% less plasticizing work and lower pressures in the gas supply chain. The components produced exhibited both improved mechanical bending properties and lower densities. From an economic point of view, the main advantages of optimized backpressures are reduced wear and lower energy consumption. The methodology presented in this study has considerable potential in terms of sustainable production and offers the prospect of fully autonomous process optimization.

Cavity pressure profile study during foam injection molding and its effect on cell formation of polypropylene/chemical blowing agent foam

“…Figure 8 represents the respective cavity pressure profiles in relation to various back pressure values ranging from 5 to 15 MPa. Typically, higher back pressure increases the batching time that facilitates in efficient mixing of CBA into a molten polymer during the screw retraction phase of the injection molding cycle 13,49,50 . At low backpressure of 5 MPa, a very high residual pressure is observed in the cooling stage and its effect on morphology of cells can be clearly seen in Figure 8a.…”

“…Typically, higher back pressure increases the batching time that facilitates in efficient mixing of CBA into a molten polymer during the screw retraction phase of the injection molding cycle. 13,49,50 At low backpressure of 5 MPa, a very high residual pressure is observed in the cooling stage and its effect on morphology of cells can be clearly seen in Figure 8a. A highly irregular foamed microstructure (cell size range: 90 to 140 μm (Figure 8d)) was attained that can be well explained by the insufficient dissolution of CBA with polymer melt at low back pressure.…”

“…The result is a product that exhibits a foamed core and two compact unfoamed outer layers, typically resembling a sandwich structure constituting a composite lightweight material. 3,[12][13][14] For fabricating various foamed industrial components, FIM is considered a most versatile technique attributed to its flexibility and efficiency in producing parts with desired densities, high geometrical accuracy, dimensional stability and short manufacturing cycle with capacity to directly mold complex products. 5,12,15 Physical or chemical blowing agents (CBA) are usually employed in FIM process to create a cellular structure in the polymer matrix.…”

“…These nuclei steadily grow into macrocells through gas diffusion and finally the foam structure is stabilized by reducing the temperature lower than the glass transition temperature of the polymer. The result is a product that exhibits a foamed core and two compact unfoamed outer layers, typically resembling a sandwich structure constituting a composite lightweight material 3,12–14 . For fabricating various foamed industrial components, FIM is considered a most versatile technique attributed to its flexibility and efficiency in producing parts with desired densities, high geometrical accuracy, dimensional stability and short manufacturing cycle with capacity to directly mold complex products 5,12,15 …”