Purpose

Multi-jet fusion (MJF) process is based on a polymeric powder bed that is heated and irradiated by infra-red lamps. The layer under construction is jetted with inks to provide the desired heat management conditions for selective melting. Depending on several process variables, manufactured parts can exhibit lifting of the borders of the top surface of the shape under construction. This phenomenon is related to the capillarity effect. As a result, the top surface of MJF-manufactured parts can present a peculiar convex shape. This study aims to propose a solution that instead induces the capillarity effect outside of the part under construction.

Design/methodology/approach

A specific design is developed to avoid the capillarity effect in MJF. It is based on an analytical model that was previously developed by the authors to estimate the shape and extent of the capillary on top surfaces of benchmark components. The proposed methodology is established by the predicted calculation of maximum values of capillarity rise and length, and safety factors. A fin-shaped geometry is designed to avoid the capillarity effect. An experimental campaign is implemented to verify the effectiveness of the proposed solution. Prototypes are manufactured by an HP MultiJet 4200 in the original design and the so-called finned-riser design, by adding a well-dimensioned appendage on the top surface to shift the capillarity effect outside the border of the part under construction. Measurements are done by a CAM2 ScanArm contactless measuring system to achieve the real shape of top surfaces. Geomagic Control X software by 3D systems is used to evaluate the quality of measured surfaces in comparison with the expected geometry of the top plane of the benchmark.

Findings

The investigated approach involves adding an auxiliary finned-shape appendage, which acts similarly to the risers in foundry technology, to the top surface of the part that is being produced by MJF technology. The procedure and rules for determining the dimensions of the fin are established based on physical considerations and process modelling. The method is then applied to a prototype part, which is designed to highlight the effectiveness of the finned-riser design for improving the dimensional accuracy of the top surfaces of products manufactured by the MJF process. Experimental measurements of top surfaces of the original benchmark are compared to the same ones in the case of the finned-riser benchmark. Reported results are satisfactory, and the capillary effect occurred in the fins outside the border edges of the part. Further developments are planned to extend the proposed design.

Originality/value

MJF technology is attracting large interest from manufacturers to produce mass customised products. The quality of manufactured parts could be affected by peculiar defects related to process parameters. The present work aims to show a method to avoid the capillarity effect. It is based on an original analytical model developed by the authors and implemented successfully in the case of a benchmark geometry.

中文翻译：

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鳍状冒口设计可避免多喷嘴融合技术中的毛细效应

目的

多喷射聚变（MJF）工艺基于聚合物粉末床，该粉末床由红外灯加热和辐照。用墨水喷射在建的层，以提供所需的热量管理条件以进行选择性熔化。取决于几个过程变量，制造的零件可能会呈现出正在构造的形状顶面边界的凸起。这种现象与毛细作用有关。结果，MJF制造的部件的顶表面可以呈现出特殊的凸形。这项研究旨在提出一种解决方案，该解决方案可在正在构造的零件外部引发毛细效应。

设计/方法/方法

为避免MJF中的毛细作用，开发了一种特殊的设计。它基于作者先前开发的分析模型，用于估计基准组件顶面上毛细管的形状和范围。通过对毛细血管上升和长度的最大值以及安全系数的预测计算来建立所提出的方法。鳍状的几何形状可避免毛细作用。实施了一项实验性活动以验证所提出解决方案的有效性。原型是通过HP MultiJet 4200的原始设计和所谓的翅片提升器设计制造的，方法是在顶表面上添加尺寸合适的附件，以将毛细作用转移到在建零件的边界之外。测量是通过CAM2 ScanArm非接触式测量系统完成的，以实现顶面的真实形状。3D系统的Geomagic Control X软件用于与基准基准的预期几何形状相比，评估被测表面的质量。

发现

研究的方法涉及在MJF技术生产的零件的顶部表面添加辅助的鳍状附件，该附件的形状类似于铸造技术中的冒口。确定翅片尺寸的过程和规则是基于物理考虑和过程建模而建立的。然后，将该方法应用于原型零件，该零件的设计旨在突出鳍状冒口设计对提高MJF工艺制造的产品顶面尺寸精度的有效性。将原始基准的顶表面的实验测量值与带翅片的基准的相同测量值进行比较。报告的结果令人满意，并且毛细管效应发生在零件边界边缘之外的散热片中。

创意/价值

MJF技术吸引了制造商的大量兴趣，以生产大量的定制产品。制造零件的质量可能会受到与工艺参数有关的特殊缺陷的影响。本工作旨在展示一种避免毛细作用的方法。它基于作者开发的原始分析模型，并在基准几何的情况下成功实施。