Modern Machine Shop

AUG 2018

Modern Machine Shop is focused on all aspects of metalworking technology - Providing the new product technologies; process solutions; supplier listings; business management; networking; and event information that companies need to be competitive.

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ADDITIVE INSIG MMS AUGUST 2018 42 Understanding Industrial 3D Pr AUTHO | Timothy Simps Professor of Engineering Design & Manufac Pennsylvania State Univer Realize your vision From quick prototypes to serial production, we got you covered . ExOne Binder Jetting ¨ Visit ExOne at IMTS in Chicago, IL from September 10 - 15, 2018 Booth 432308 (West Hall) The results we obtained surprised us, and I wanted to share some of the highlights with you now that our full paper is available in the Journal of Manufacturing Processes For this study, we designed and fabricated a standard block-type support structure in Inconel 718, varying the height to enable us to study differences in cutting forces and milling behav- ior. The machining specimens and test setup are shown in Figure 1. The average wall thickness of the supports is 0.11 mm, and the spacing between walls is 0.8 mm—typical dimensions for this type of support-structure geometry. So, what happens when you try to machine away these thin-walled support structures? Well, we found that they do not uproot or cleanly shear when milled, nor do they break away from the base material as they are intended to do. Instead, the supports maintain their structure, and the thin-walls tend to collapse (see Figure 2a). In the tall supports, trapped powder was revealed inside the support structures as milling depth increased. Despite using high-pressure air to blow out as much of the powder as we could before machining, at cutting depths below 2 mm, powder was still trapped inside (see Figure 2b). As the thin walls are machined, they form localized chips. The chips formed from the sup- port structures were nearly uniform in width (the depth of cut), but their lengths varied based on the position of the tool path relative to the thin-walled region being cut. Examples of chips can be seen in Figure 2c alongside chips from cutting the fully dense material in Figure 2d. So, supports can be machined, but cutting-force analysis revealed that the specific cutting energy to mill the supports is only 12 percent of what is needed to mill the fully dense material based on swept volume (43-percent difference if material volume is considered). We were surprised that this value was so low, and the machining community will need to reevaluate recommended speeds and feeds for milling different alloys used in support structures.

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