May 2023 Volume 5

FORGING RESEARCH

time and a complex indexing arrangement during operation, and consequently led to long deposition times that are likely impractical for application in industry. Furthermore, the amount of operator time would significantly erode the anticipated economic payoff.

Fig. 3: The sequence of axial toolpaths leading to a net cladding deposit that can be machined to the B208 contour by EDM is a 5-stage sequence. Initial deposits were on die teeth, followed by deposits in the root sections (in two stages), the next stage covered the flanks, and the final stage added material a second time to teeth tips. Technical Objective The goal of this project was to complete the EDM, characterize the surface and microstructure, and conduct in-plant performance trials. Accomplishments The final outcomes of this project were that: • The tool with axial deposition was found to contain lack of-fusion defects at a level that prevented the EDM from successfully defining the tool surface. • A new set of tool paths intended to be consistent with prior successful production-level deposition at Lincoln Electric was defined in collaboration with Presrite and CWRU. A second end- of-life tool was obtained, characterized, skim cut, and clad. That die also revealed a level of voidage (presumably lack of-fusion) that prevented EDM. This aspect of the project was then stopped. • Two teams of students were then directed at bringing a system on-line at CWRU to allow low-cost wire-feed arc-based freeform welding in an on-campus environment. We envision allowing student use both in curricular and co-curricular settings to allow first-hand experience with rebuilding surfaces relevant to rejuvenation of tools in a creative and open-ended setting that permits experimentation and iteration. Results Two views of the cladded B208 using axial toolpaths is shown in Fig. 4. Several features are evident. The first is the strikingly small volume of material that was required to be removed from the original tool in order to completely remove any microstructural evidence of accumulated damage. Secondly, the multi-stage deposit approach was successful at getting into tight spaces such as the root regions in between the teeth in the die. One characteristic of the decision to use axial toolpaths is that there is a very high density of starts and stops – measured in the hundreds. This required a substantial amount of programming

Fig. 4: A B208 die fabricated from 718 that was skim cut using wire EDM at Presrite and then cladded using a laser hot-wire system at Lincoln Electric Automation using axial tool paths. The starts and stops also produced undesired relief on the top and bottom surfaces of the die. However, in neither case was the relief to a depth that would prevent the working surface from being completely revealed by the EDM.After standard 718 heat treatment using ASM International Materials Handbook data, the tool was partially EDMed at Presrite. The residual stress problem observed in the earlier experiments did not occur. However, examination of the as-cut surfaces of the parts that were removed revealed a line indicating a lack of fusion. This is shown in Fig. 5. The lack of fusion is ascribed to the lack of opportunity to optimize deposition parameters, the axial approach is a new one so there was a limited database to assist in choosing the parameters. Also, due to the extra time consumed in indexing, cooling time was longer than normal introducing another uncertainty.

Fig. 5: Three images of the material removed from the cladding by EDM. Above left is an image looking at the same orientation of the two contours in Fig. 2. The deposit is of appropriate thickness, and EDMed well. Look in the transverse view of the same piece (upper right) shows a line of lack of fusion. This is seen more clearly in the image at the lower right.

Consideration was given to radiographically inspecting the cladded die with the goal of identifying the location, quantity and depth of the defects contained.

FIA MAGAZINE | MAY 2023 87