China: Analysis of 3D Printed Bolts

Chinese researchers have been investigating more precise ways to create bolts, detailing their findings in the recently published ‘Characterization of 3D printed bolts based on digital image correlation and infrared thermography.’

Recognizing the benefits of 3D printing for many industries, the authors, Xiaowei Feng and Fei Xue, list the ‘plethora of advantages,’ from the potential of decreasing the need for assembly lines to less time required for development and production, and the ability to customize more complex geometries that may not have been feasible previously.

While very little research has been performed concerned bolt printing, Feng and Xue were motivated to begin this study due to the amount of progress made with metal 3D printing—especially in applications like aerospace and medicine.

“Today, some important engineering materials such as steel, aluminum and titanium, may be 3D printed as full dense metal parts with outstanding properties,” explained the researchers.

“For instance, 3D printed Ti and Ti6Al4V parts have already been proven to have significant economic advantages and are currently being used for commercial applications in aerospace and biomedical fields; Sc-modified Al alloy by powder bed fusion (PBF) provides significant strength and ductility without hot tearing; Magnesium alloy infiltrated 3D-printed CoCr scaffolds is nearly fully dense and with excellent mechanical properties.”

(a) 3D scanning system arrangement and interpretation. (b) Scanned digital bolt and corresponding PT bolt.

For this study, the researchers scanned a model of a rock bolt using a MetraSCAN 750 handheld 3D scanner, and then it was 3D printed using an iSLM 150 SLM 3D printer, which was produced by ZRapid Tech in Suzhou City, Jiangsu Province, China.

(a) Schematic drawing representing the SLM printing method. (b) Images of the PT bolt and the bolts 3D printed with AL, DS, and SS. Note that a, b, and c represent the rib spacing, bolt radius at pitch, and nominal bolt radius, respectively.

Bolts were 3D printed from three different materials: SS (316 L), AL (AlSi10Mg), and DS (18Ni300), noting that PT bolt is a 20MnSi steel. All are reasonably cost-effective, with mechanical properties that are more suitable than the PT bolt.

(a) Basic mechanism for DIC and schematic diagram for 2D-DIC and 3D-DIC. (b) Prepared speckle patterns on specimens.

Feng and Xue noted that in terms of maximum temperature, the test was ‘comparatively larger’ for both the DS bolt and the SS bolt.

“Note that even though a sudden increase in the maximum temperature is a common feature of all the 3D printed bolts, the temperature before the sudden increase is relatively low, as seen in the respective curves,” stated the researchers.

“If the printing material is AL, a printed bolt cannot achieve desirable mechanical properties. None of the 3D printed bolts exhibited a yield process during tensile tests.”

IRT testing showed that for the bolt surfaces ‘captured maximum temperature’ on the bolt surface displayed a steadily increasing trend while the load was increasing—all except for the AL bolt.

Schematic illustration of ROI-1, ROI-2, ROI-3 and the coordinate system.

“On the whole, 3D printing is a useful tool to assist relevant studies regarding bolting technology. 3D printed AL bolt is not suitable for replicating the actual mechanical properties of PT bolt. A 3D printed DS bolt and a 3D printed SS bolt can be utilized to mimic a PT bolt, both of these bolts not only have an appropriate stiffness but also have a high bearing strength,” concluded the authors.

“In the future, 3D printed bolts can be used in laboratory research on any scale and can even be applied in engineering fields under certain circumstances as long as the digital source file is obtained and stored. The products can have exactly the same geometric profile and higher strength.”

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