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

Abstract

Hybrid manufacturing, which, e.g., combines additive manufacturing with conventional machining processes, can be a way of overcoming limitations currently encountered in additive manufacturing. Cryogenic milling might be a viable option for hard-tocut materials, as it leaves a contamination-free surface and can increase surface quality and tool life compared to conventional cooling concepts. In this study, the influence of cryogenic milling with carbon dioxide on titanium Ti-6Al-4V specimens manufactured with laser metal deposition (LMD) was investigated regarding tool wear and surface integrity in comparison to dry machining and machining with cooling lubricants. Moreover, additional layers of material were deposited on top of conventionally and cryogenically machined surfaces by means of LMD. The interface zone was then examined for defects. The milling process was closely monitored by means of thermal and high-speed imaging. Optical and tactile surface analysis provided evidence that lower roughness values and improved surface qualities could be obtained with cryogenic machining in comparison to dry machining. Moreover, significantly less tool wear was observed when a cryogenic cooling medium was applied. Although the utilization of conventional cooling lubricants resulted in satisfying surface qualities, substantial residual contamination on the milled surface was detected by means of fluorescence analysis. These contaminants are suspected to cause defects when the next layer of material is deposited. This is supported by the fact that pores were found in the weld bead applied on top of the milled specimens by means of LMD. Conversely, cryogenic machining resulted in very clean surfaces due to the residue-free evaporation of the coolant. Hence, a good metallurgical bonding between the weld bead and the milled substrate could be achieved. The results indicate the great potential of cryogenic milling in hybrid manufacturing, especially in terms of intermediate machining, as it provides residue-free surfaces for subsequent material deposition without an additional cleaning step and can significantly prolongate tool life.

Tribological Behavior and Analysis on Surface Roughness of CNC Milled Dual Heat Treated Al6061 Composites

“…In particular, the better profile of tool selection is an important outcome observed here by Benattia Bloul et al [13]. Paper [14] has discussed the laser metal deposition method of additive manufacturing in milling surface in top and side of the Ti-6Al-4V specimen.…”

Machining of Additive Manufactured Metal Alloys

“…In case of close-loop control, metrology and sensing devices are mandatory. The concept of hybridization between AM and machining was exploited in [25] where layers of Ti6Al4V were deposited through Laser Metal Deposition on substrates of the same material that were previously additive manufactured and then milled using dry, flood and cryogenic cooling with carbon dioxide. Cryogenic milling allowed for a better deposition thanks to the attainment of clean machined surfaces without organic residues that provide good metallurgical bonding with the subsequent deposits.…”

The State of the Art in Machining Additively Manufactured Titanium Alloy Ti-6Al-4V

“…However, during the additive and subtractive hybrid manufacturing (ASHM) process, the laser source leads to a build-up of temperature, and the whole workpiece is heated. It results in a temperature field which is different from local heating, and the machining response (such as machining force, surface integrity, and tool wear) is impacted during successive machining processes [ 193 , 194 ]. Li et al [ 180 ] investigated the influence of temperature build-up on the machinability of DMD-produced Ti-6Al-4V during the ASHM process.…”