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interesting. That forging line should be sanded flat with a die grinder and flap wheel to help to prevent this from happening.
Grinding produces a damage layer in the remaining material that is more prone to crack initiation, so while the local stress riser is removed by grinding, a new weakness is produced. Its a "damned if you do, damned if you don't" situation.
Grinding produces a damage layer in the remaining material that is more prone to crack initiation, so while the local stress riser is removed by grinding, a new weakness is produced. Its a "damned if you do, damned if you don't" situation.
I said sanded with a flap wheel on a die grinder. Not grinding. Don't go into the main forging, just remove the riser. Properly done, it will certainly reduce the stress riser from what's shown in the pictures. This procedure is done on factory forged steel connecting rods all the time.
It's a flash line crack. Basically a forging defect. Removing the bit of flashing won't change anything.
And grinding or sanding is the same thing. You're removing material with abrasion. Whether its a sanding disk, grinding wheel, or carbide burr. The only difference is the size of the chips coming off the part.
I said sanded with a flap wheel on a die grinder. Not grinding. Don't go into the main forging, just remove the riser. Properly done, it will certainly reduce the stress riser from what's shown in the pictures. This procedure is done on factory forged steel connecting rods all the time.
Any degree of sanding that removes that much material will produce a more crack-prone material microstructure. It would have to be taken to a fine polish to get rid of the undesirable microstructure. People may perform such flapper wheel sanding operations all the time, but that doesn't mean no harm is done to the microstructure. Perhaps in the case you describe, the harm to the material microstructure is not has bad as having the stress riser present. This may be the case for the control arm too. Or it might not.
LGTD, I wouldn't call that a flash line crack in the sense of forging. However its possible that the microstructure in that region is less optimal due to it perhaps being a last-to-solidify region that would contain more insoluble or lower melting point elements.
It's not a forged piece, there is no weld. The entire piece is cast as it looks and both bores are machined to properly fit the bushing and ball joint. The line that is the cause of this issue is a parting line, it's essentially excess material that was squeezed out between the mold halves. You can tell it's a cast piece the same way you would a crankshaft, by looking at how thin the parting line is. Forged pieces usually have a parting line that's about 0.5-1" in width, while cast parts are thinner like this (usually 1/16-1/8").
Forging is a very vague term and is often misused in marketing material. It is probably cast and ran though a forging press while still hot and finally annealed in an oven. That's pretty typical for lots of mass produced aluminum parts.
Found a number of cracks in my rear suspension arms. I’ve owned the car since new. It was my daily driver up to 2013. Has been sitting in the garage mostly since then.
Jan 15, 2019, 07:26 AM
