Wire EDM Question
Posted: Wed Apr 28, 2021 7:01 am
A question for the wire EDM experts -
There was excessive play in the Walschaerts valve gear on full-sized Alaska Railroad #557. We are replacing all the bushings and any pins that have excessive wear. There is also play in the reverse link. The overhaul crew believes it can be corrected by building up the surfaces of the link block and having it ground back to the 64-5/16" radius for the proper clearance. We have a local firm that can do the build up, but not the grinding. We have a good heat treater. However, the firm that does the spray welding says that if the part is built up by spray welding that it can't be heat treated without the possibility of the new surface delaminating.
The attached drawing is from 1942 (during wartime material shortages) with the part made from an obscure grade of carbon steel which was case hardened and ground all over. We also have a later drawing of the same part using another obscure grade of carbon steel. A note on the later drawing originally specified case hardening, but this was stricken through and changed to flame hardened. The dimensions of the later part is identical except for a change in the oil grooves. That makes me wonder if would be more practical to make a new part from a modern, hardenable grade of steel with all of the machining done except for the radii, having it heat treated, and then finishing the radii with a wire EDM.
The comments I have seen here over the years have lead me to believe that wire EDM is a viable replacement for grinding in this type of application.
My questions are -
If we built up the surface by spray welding, is wire EDM an appropriate and cost effective process, in lieu of grinding, to finish the radii?
Or would it be more practical and cost effective to make a new part from a modern, heat treatable alloy, heat treat it, and use wire edm to machine the radii on the hardened part?
There was excessive play in the Walschaerts valve gear on full-sized Alaska Railroad #557. We are replacing all the bushings and any pins that have excessive wear. There is also play in the reverse link. The overhaul crew believes it can be corrected by building up the surfaces of the link block and having it ground back to the 64-5/16" radius for the proper clearance. We have a local firm that can do the build up, but not the grinding. We have a good heat treater. However, the firm that does the spray welding says that if the part is built up by spray welding that it can't be heat treated without the possibility of the new surface delaminating.
The attached drawing is from 1942 (during wartime material shortages) with the part made from an obscure grade of carbon steel which was case hardened and ground all over. We also have a later drawing of the same part using another obscure grade of carbon steel. A note on the later drawing originally specified case hardening, but this was stricken through and changed to flame hardened. The dimensions of the later part is identical except for a change in the oil grooves. That makes me wonder if would be more practical to make a new part from a modern, hardenable grade of steel with all of the machining done except for the radii, having it heat treated, and then finishing the radii with a wire EDM.
The comments I have seen here over the years have lead me to believe that wire EDM is a viable replacement for grinding in this type of application.
My questions are -
If we built up the surface by spray welding, is wire EDM an appropriate and cost effective process, in lieu of grinding, to finish the radii?
Or would it be more practical and cost effective to make a new part from a modern, heat treatable alloy, heat treat it, and use wire edm to machine the radii on the hardened part?