Latest Developments in Industrial Hybrid Machine Tools that Combine Additive and Subtractive Operations

Abstract

Hybrid machine tools combining additive and subtractive processes have arisen as a solution to increasing manufacture requirements, boosting the potentials of both technologies, while compensating and minimizing their limitations. Nevertheless, the idea of hybrid machines is relatively new and there is a notable lack of knowledge about the implications arisen from their in-practice use. Therefore, the main goal of the present paper is to fill the existing gap, giving an insight into the current advancements and pending tasks of hybrid machines both from an academic and industrial perspective. To that end, the technical-economical potentials and challenges emerging from their use are identified and critically discussed. In addition, the current situation and future perspectives of hybrid machines from the point of view of process planning, monitoring, and inspection are analyzed. On the one hand, it is found that hybrid machines enable a more efficient use of the resources available, as well as the production of previously unattainable complex parts. On the other hand, it is concluded that there are still some technological challenges derived from the interaction of additive and subtractive processes to be overcome (e.g., process planning, decision planning, use of cutting fluids, and need for a post-processing) before a full implantation of hybrid machines is fulfilled.

State of the Art in Directed Energy Deposition: From Additive Manufacturing to Materials Design

“…Hybrid manufacturing is still a relatively new technology and requires a lot more research for acceptance into the market. Therefore, the most important steps to be taken in the direction of improvement of such machines would be process optimization strategies along with developments in software integration [165]. Other secondary processes that complement the performance of DED parts (to name a few) are: Inter-pass rolling [166] and Ultrasonic Vibration Assisted LENS™ [167], both used for grain size refinement to enhance the mechanical properties of the parts.…”

Hybrid manufacturing of titanium Ti-6Al-4V combining laser metal deposition and cryogenic milling

“…Cortina et al consider the remains of organic cutting fluids one of the major challenges in hybrid manufacturing, since they can lead to pores during subsequent material buildup and cause damage to the LMD system by contaminating the optical lenses [44]. For this reason, an extensive intermediate cleaning procedure would be required after milling with cooling lubricants in order to achieve sufficient cleanliness of the machined surfaces.…”

“…Especially for higher concentrations of cooling lubricants, laser cleaning was the only way to achieve acceptable surface conditions for further LMD, even though porosity could not be fully avoided [36]. These results, together with the analysis of the surface cleanliness level, strongly suggest that the use of conventional cutting fluids negatively affects the deposition of new material [44] and is therefore not suitable for hybrid manufacturing without a qualified cleaning process. Conversely, both dry and cryogenic intermediate machining can lead to a good bonding of the subsequent layer even without an additional cleaning step, provided that appropriate parameters for additive manufacturing are used on the milled surfaces.…”

Review: The Impact of Metal Additive Manufacturing on the Aerospace Industry

“…However, the benefits of a hybrid AM/SM approach could outweigh the disadvantages, provided that these combined techniques are streamlined into an integrated system. So far, researchers have worked towards developing a unified hybrid system that incorporates individual AM and SM capabilities within a single machine architecture, as detailed in various works [150][151][152][153][154]. The single hybrid machineries described in these studies are focused on merging and optimizing DED AM techniques to fabricate the metal parts, with multi-axis CNC machining used for the post-processing phase.…”