MOULD MAKING PETplanet Insider Vol. 23 No. 06/22 www.petpla.net 14 Additive manufacturing on food and beverage moulds Metal 3D printing technology The characteristics of beverage mould parts and the shortcomings of conventional water channels manufacturing technology led GDXL to adopt metal 3D printing technology to several mould development projects since 2020. All of which have demonstrated good operational results. Challenges and solutions Shrinkage, flow lines, ovality, slow cycle time and other quality problems led GDXL to investigate metal additive manufacturing for the manufacture of mould parts and, since 2020, to use the process for commercial scale production. When conventional machining is used to manufacture mould parts, water channels are, generally, made up of lines connected horizontally and vertically. Many areas on the parts cannot be processed with water channels because of technology limitations. This particularly affects movable mould parts that are susceptible to operational failure and, consequently, leads to problems such as uneven cooling, large flow pressure loss and cooling blind spots. This results in unsatisfactory moulding efficiency and quality problems. Beverage mould parts are generally small, which makes water channels difficult to process. Accuracy requirements are relatively high, especially for moving sliders, inclined roofs and other structures. 3D printing technology – additive manufacturing – is an ideal solution to resolve the problem of poor cooling critical parts and has a relatively good cost/benefit ratio. At present, steel alloy powder materials most frequently used for 3D printing mould parts include stainless steel, high-strength steel and tool steel types. GDXL uses steel alloy powder materials with hardness reaching HRC48-52 after heat treatment, with tensile strength above 1,700MPa and good rust resistance properties. Selective Laser Melting (SLM) powder bed fusion technology is one of the most widely used technologies for the production of industrial parts. It offers high printing density, no void bubbles or similar internal defects, and less shrinkage. GDXL uses leading SLM equipment to manufacture critical mould parts and integrates the process with vacuum heat treatment, fine machining and cutting. Application on preform mould: In the middle of 2020, a customer reported that their preform mould for making hot fill 38mm preform neck finish had an ovality issue: the key dimension was out of tolerance. Preliminary analysis found that the wall of the bottle neck was relatively thick; the poor cooling of the conventional machined water channel caused it to shrink and deform in an oval shape. The size was also out of tolerance. In order to solve the problem, GDXL suggested using 3D printing technology to process mould parts with conformal water channels. According to the theory of heat transfer, increasing the heat exchange area between the solid and the liquid zones can increase the heat transfer efficiency. The application of 3D printing, when compared with the conventional machined water channel, not only significantly increased the heat transfer area but also maintained a uniform distance from the moulding surface, and had no flow dead angle. Therefore, cooling rate and cooling uniformity could theoretically be improved. GDXL designed a neck ring part with a conformal water channel and used simulation analysis software to compare and verify the cooling effect of the neck ring part with the original design. It was found that the cooling rate and cooling uniformity were better. Four new neck rings with conformal water channel were made for trial at customer’s facility. After the trial, the customer reported that the ovality issue was reduced by about 45%, which met the quality requirements, and demoulding temperature had also been reduced, to a certain extent. Schematic diagram of the structure of conventionally machined neck ring parts Schematic diagram of neck ring parts with 3D printing conformal water channels Schematic diagram of surface temperature distribution of conventionally machined neck ring parts Schematic diagram of surface temperature distribution of neck ring parts with 3D printing conformal water channels MOULD MAKING
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