Variable Distance Adjustment for Conformal Cooling Channel Design in Rapid Tool K. M. All1 Department of Industrial and Systems Engineering, The Hong Kong Polytechnic University, Hung Horn, Kowloon 852, Hong Kong e-mail: akm_kenneth@yahoo.com.hk K. M. Yu EF603, Department of Industrial and Systems Engineering, The Hong Kong Polytechnic University, Hung Horn, Kowloon 852, Hong Kong e-mail: km.yu@polyu.edu.hk During thermoplastic injection moulding process, the gradual increase of the coolant temperature along the conformal cooling channel (CCC) inside the rapid tool reduces the rate of heat transfer from the polymeric melt to the cooling channel surface at the outlet portion. Injection moulded defects such as irregular warpage of the part between the coolant inlet and outlet cannot be avoided. Rapid tooling (RT) technology offers a speedy and automatic method for rapid tool design and fabrication integrated with complex internal structure such as CCC. This paper presents a novel adjustment method for cooling distance modification between the CCC and its mould cavity (or core) surface along the cooling channel. The proposed method can compensate the grad ual increase of the coolant temperature from the coolant inlet to the coolant outlet. More heat can be transferred from the mould surface near the coolant outlet to the proposed variable distance conformal cooling channel (VDCCC). In this study, the cooling channel distance modification relies on two adjustment attributes: (1) the adjustment direction and (2) the adjustment amount, between the mould cavity (or core) surface (terrain) and the cool ing channel axis (polyline) after the linearized approximation. A computer-aided melt flow analysis tool of moldflow plastics insight is employed in the case study in order to demonstrate the feasibility of the proposed method. The cooling performance of the proposed VDCCC design can be verified. [DOI: 10.1115/1.4026494] Keywords: conformal cooling channel, variable distance, adjustment method, rapid tooling, thermoplastic injection moulding Introduction Thermoplastic injection moulding (TIM) process [1-5] is one of the significant polymer processing technologies in the manufac- turing industry. Various daily consumer products are manufac- tured by this process. Better control of the cooling process and its parameters (e.g., coolant temperature, cooling channel diameter, or coolant flow rate) can improve the part quality and increase the productivity [6-8]. In mould cooling process, heat is transferred from the poly- meric melt to the boundary of the cooling channel by conduction 'Corresponding author. Contributed by the Manufacturing Engineering Division of ASME for publication in the J ournal of M anufacturing Science and E ngineering . Manuscript received December 29, 2010; final manuscript received January 7, 2014; published online May 21,2014. Assoc. Editor: Yong Huang. Journal of Manufacturing Science and Engineering Copyright© and is carried away by the coolant via convection along the tem- perature gradient. The amount of heat-in equals the amount of heat-out [9], The continuous heat removal process from the poly - meric melt into the cooling channel by conduction will raise the coolant temperature at the coolant inlet portion initially. As the coolant temperature increases along the cooling passageway, less heat can be removed near the outlet portion. Temperature differ- ence between the coolant outlet portion and the mould cavity (or core) surface will become smaller. Undesirable defect such as irregular warpage of the part between the coolant inlet and outlet is unavoidable. Literature Review To demonstrate the effect of conductive heat transfer in TIM process, the distance between the mould cavity surface and the boundary of the cooling channel is the decisive factor. It can be expressed by the rate of conductive heat transfer, tjcond according to Fourier’s law [10] (see below equation) ,dT ^cond — (1) dL where <7COnd (W) is the rate of conductive heat transfer, the rate of conductive heat transfer highly depends on various parameters, such as cooling channel diameter, size, or thermal conductivity of mould material (e.g., stainless steel). To achieve a uniform cool- ing in TIM, dT/dL is maintained constant (see below equation) —<7cond dT kA = ~dL~ constant (2) Nowadays, various research efforts have been focused on the design of the CCC in the injection mould or the rapid tool in TIM cooling process [11—16], CCC can be defined as a cooling passa- geway which follows the shape of the mould cavity (or core) sur- face. More effective cooling can be achieved between the mould surface and the CCC than the straight-line hole drilled one. How - ever, no existing research work can be found for studying coolant temperature compensation. Current research studies only focus on various cooling channel design methodology. Temperature and Distance Variations of Conductive Heat Transfer in CCC Without loss of generality, the distance, x between the CCC and the mould surface is constant in mould cooling design stage. Heat energy at any region on the mould surface can be transferred uniformly to the cooling channel surface at the same time. The coolant temperature from the coolant inlet to the coolant outlet along the CCC is increasing. Instantaneously, a temperature varia- tion is set up between the coolant inlet and the coolant outlet. The temperature change at the coolant inlet is larger than at the coolant outlet along the CCC pathway (see Fig. 1). Therefore, heat energy absorbed at the coolant outlet is smaller than at the coolant inlet as the coolant temperature at the coolant inlet is the lowest. The accumulative effect of heat energy increases the coolant tempera- ture at the coolant outlet. Little heat energy can be absorbed at the coolant outlet. To compensate the gradual increase of coolant temperature from the coolant inlet to the coolant outlet, an adjustment method is proposed for modifying distance between the existing CCC and its cavity (or core) surface with characteristic of VDCCC. VDCCC aims to achieve a comparatively more uniform and effec- tive cooling performances than existing CCC designs (see Fig. 2). Proposed Methodology In this study, a VDCCC is created and generated according to the earlier proposed contemporary CCC design. To simplify the proposed method, the CCC design is simplified from 3D to 2D in AUGUST 2014, Vol. 136 / 044501-1 114 by ASME