Hongtao Ding, PhD
Assistant Professor University of Iowa
2015 SME Outstanding Young Manufacturing Engineer SME Member Since 2013
SME SPEAKS GUEST EDITORIAL
Remanufacturing by 3D Printing of Metals? A Great Potential but Big Challenge
D
o you have expensive equipment that needs to be fi xed? Are you looking for a cost-saving repair method? Remanufacturing offers great potential for restoring non-
functional, discarded or traded-in products to like-new condition. The key idea in remanufacturing is “like-new,” and recondition- ing is the most important step when it comes to ensuring like-new condition. Welding has traditionally been used to restore the shape and functionality of damaged engineering components. However, since the welding process cannot rebuild three-dimensional (3D) features, it is not ideal for damaged 3D structures. In addition, it usually creates a nonuniform subsurface microstructure from the fi ller materials and base material. These undesired microstructures cause poor bonding between the fi ller material and the damaged part, leading to the loss of original product identity. After the geometric features of a damaged part are rebuilt,
post-processes are often required to achieve desirable dimen- sional tolerances, hardness and surface roughness, and to ensure like-new performance. Heat treatment is normally used in industry to increase hardness and wear resistance by introducing solid-state phase transformation in the material. However, there are major problems with these bulk-material hardening methods: (1) the severe thermal distortion induced to the whole structure; (2) the lack of versatility for parts to be rebuilt with complex and delicate geometric features; and (3) poor energy effi ciency. Heat treatment is usually followed by hard machining to semifi nish the hardened part to desirable dimensional tolerances and to elimi- nate distortions. Grinding is then applied to achieve the required surface roughness as the last step. However, the equipment used for these post-processes, such as CNC machining centers and grinders, is the same as that used in the production of new parts in manufacturing plants. This poses a serious challenge for remanufacturing a small batch of parts because setting up
machining centers and grinders for damaged parts with complex geometric features and toolpaths can be very costly. Even if geometrical reconditioning is achieved, surface integrity and ma- terial properties are diffi cult to restore to original standards with processes from new parts production.
Remanufacturing Using a 3D Printer? Recent progress in life-cycle engineering has shown that ac- curate 3D printing/additive manufacturing technologies have made 3D feature rebuilding economically viable. Furthermore, it has been demonstrated that remanufacturing cuts down the cost of waste disposal because it builds on the nondamaged portion, which is close to its fi nal form, and thus requires only a fraction of the mate- rial processing. Consequently, remanufacturing by accurate additive processes will enable industries to save energy and material. Laser metal deposition (LMD) is one of the most promising 3D print- ing technologies for creating 3D solid forms from damaged parts. During the LMD process, metal parts are fabricated directly from a computer-aided design solid model by using a metal powder in- jected into a molten pool created by a focused, high-powered laser beam. This technique is equivalent to several trademarked tech- niques such as laser direct deposition and direct metal deposition. Post-processes are still required after 3D printing the dam- aged part to achieve the desirable dimensional tolerances, hardness and surface roughness and to ensure like-new perfor- mance. The dimensional accuracy and porosity of parts made by LMD have been studied extensively. However, data on their metallurgical and mechanical properties are very sparse and disorganized, as these coupled attributes are highly process and material dependent. The essential feature of the LMD technique is that, as a result of layer overlap during the build-up of a part, the deposited material undergoes consecutive thermal cycles
November 2015 |
AdvancedManufacturing.org 19
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