Spiral Milling Welded Cast Iron

Hey metalheads,

Currently in the process of attempting to repair some cast iron details that were run incorrectly. I have to re cut some areas that contain a set of 16mm dowels as well as a set of 16mm taps. I found out very quickly that the nickel rod they use to weld CI produces and extremely hard weld. Seemingly my best bet (correct me if I'm wrong)is to use a spiraling process to remove the existing stock and weld, as well as come back in for a finishing pass to size. I'm use a solid carbide, .375" relieved endmill from helical. Any quick and dirty suggestions as to feed and speed? Right now I'm treating it like hardcut. Respond with any questions in addition to response if it'll help clarify. Thanks!

I'd use parameters for the hardest material in the cut; Helical's machining advisor tends to give good numbers. I always skim cut on any dimension or surface finish that matters.

The Ni-rod isn't hard it's the cast iron quenched at the weld edges. Take the tops off the weld about .005-.010" above the finished surface and then go back & work down to the surface. Don't be surprised if you have to hand work the toes of the weld down by hand some.

Good luck,
Matt

There are a couple of grades of Ni welding rod. 99% nickel rod should produce easily machinable deposits. But it sounds like your guys used 55% nickel rod, which makes deposits ranging from "challenging" or "difficult, hard". The more they fuse the base cast iron with the rod, the harder the deposits get.

If you have more of these to do, get your welders to use N99 rod. If they balk at the price, have a manager do the cost spreadsheet that takes your time, tool consumption, and scrap parts into consideration.

I prefer the ferro nickel alloy rods... deposits fast (reverse polarity), good wetting ability, machinable as any, and you can get an inch of bead laid in about 10 seconds and get it peened out. The pure nickel rods deposit way too slow, and even with low amperage, there is so much dwell time caused by waiting for a blob to transfer, that you end up putting more heat into the job. Plus pure nickel is hot short, the exact opposite property to what is desirable in a cast iron weld.

UTP used to make a rod called 85 FN which was the first one I fell in love with. Most other specialty rod companies have a crossover rod with similar analysis.

Preheat should always be used to lessen the quench effect in the HAZ. The more heat, the better, but 500 degrees is nice. If you have to burn oil out of the metal, you'll need to get it dull red anyways, otherwise porosity will appear.

Now as for tapping, I'd not try tapping in the HAZ. Rather, I'd rather machine a larger hole and fill it, so that tapping can take place 100% in the weld. In some situations, it makes sense to weld a low carbon slug in place to receive the new threads. It won't look the same, but for the most part, you can always see a difference between the weld and the parent metal.

You should have use a better rod, both stoody and al-state sell a good cast iron rod, both run $150/lb or so but is well worth it to avoid the fight you have now...Phil

I'm beginning to think no preheat was applied when they welded the casting up. The HAZ is wildly hardened. We should have plugged the holes in question. Instead our material handler had them weld the holes closed as far as they could get. it's a mess

You might find to grind down welds may be a little time-consuming but less costly than breaking mill cutters.