Abstract
Nowadays, moulding technology has become a remarkable manufacturing process in the intimate apparel industry. Polyurethane (PU) foam sheets are used to mould three-dimensional (3D) seamless bra cups of various softness and shapes, which eliminate bulky seams and reduce production costs. However, it has been challenging to accurately and effectively control the moulding process and bra cup thickness. In this study, the theoretical mechanism of heat transfer and the thermal conductivity of PU foams are first examined. Experimental studies are carried out to investigate the changes in foam materials at various moulding conditions (viz., temperatures, and lengths of dwell time) in terms of surface morphology and thickness by using electron and optical microscopy. Based on the theoretical and experimental investigations of the thermal conductivity of the foam materials, empirical equations of shrinkage ratio and thermal conduction of foam materials were established. A regression model to predict flexible PU foam shrinkage during the bra cup moulding process was formulated by using the Levenberg-Marquardt method of nonlinear least squares algorithm and verified for accuracy. This study therefore provides an effective approach that optimizes control of the bra cup moulding process and assures the ultimate quality and thickness of moulded foam cups.
Highlights
Due to the growing importance of the intimate apparel market, there has been an ever-increasing interest in the bra cup moulding process for making seamless bras
The data are further manipulated in a computer-aided design (CAD) system [1] and transferred to a computer numerical control (CNC)
Foam used for bra cup moulding is available in a diversity of hardness, thickness, and density as it is made from different chemical recipes that possess a wide range of physical, thermal, and mechanical properties which affect the degree of foam shrinkage after moulding [2]
Summary
Due to the growing importance of the intimate apparel market, there has been an ever-increasing interest in the bra cup moulding process for making seamless bras. In the bra cup moulding process, a pair of hot aluminum male and female moulds (~200 ◦ C) with conformed shapes is used to mould a piece of flat and flexible polyurethane (PU) foam sheet into a specified three-dimensional (3D). Polymers 2018, 10, 472 bra-making process is highly complex, time-consuming, and error-prone due to the large variations in foam properties, cup styles and sizes, and geometric features of graduated padding. To expedite control of the moulding process and to avoid costly trials and errors, previous studies [3,4] have identified the key material properties of PU foam materials that affect the cup shape after moulding, the level of breast support, as well as the tactile feel of the bra cup. Substantial variations in cup shape and thickness were consistently observed, and the control of the bra cup moulding process is still far from reliable
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