How to get around sanding casting iron before machining?
How to get around sanding casting iron before machining?
(OP)
Hello -
We've got a job for 5,000+ iron hinges, which we're machining from ductile iron castings.
We've been belt sanding them, one at a time, to get a flat surface before the machining starts. This sanding is incredibly time consuming and costly.
I'm not a machinist, but I understand we've got to have flat surfaces for work-holding before we can run high-volume production.
Any ideas on how this belt sanding process could be eliminated or minimized?
Thanks,
Rob
We've got a job for 5,000+ iron hinges, which we're machining from ductile iron castings.
We've been belt sanding them, one at a time, to get a flat surface before the machining starts. This sanding is incredibly time consuming and costly.
I'm not a machinist, but I understand we've got to have flat surfaces for work-holding before we can run high-volume production.
Any ideas on how this belt sanding process could be eliminated or minimized?
Thanks,
Rob





RE: How to get around sanding casting iron before machining?
RE: How to get around sanding casting iron before machining?
You do not mention whether the belt is trying to achieve a specified surface finish as well as removing sand. If this is the case your options may be a little more limited.
Griffy
RE: How to get around sanding casting iron before machining?
I'm not familiar with a double disc grinder. We have a grinder but are using the belt sander. I've been talking this over more with people over here - the consensus is that since there isn't a single good surface to start with, we have to have a person hold it on the sander until we have two flat surfaces.
I'm still to any ideas to the contrary.
-r
RE: How to get around sanding casting iron before machining?
I don’t think you need to grind off the scale. Maybe things are different today, but when I studied machine shop practice many years ago, we were taught to deal with cast iron scale by making the first cut deep enough to keep the cutting edges beneath the scale and in contact with the cast iron. This will remove the scale and help preserve your cutting edges. Your castings should have enough material allowance to allow you to do this.
RE: How to get around sanding casting iron before machining?
You mentioned the parts are cast at the high end of the finished tolerence. It sounds like either the mold maker or the part designer screwed up and did not allow sufficient material for machining.
Does the part print call out finished surfaces? If not, are the tolerances sufficiently loose where a machined reference is not needed? Is the part cast iron for aesthitic reasons? If so the machined surfaces may actually detract from the customer's intentions. As engineers we generaly want each part identical, but they may be going for a 'rustic, blacksmithed' look.
RE: How to get around sanding casting iron before machining?
If your doing Green sand then look into No-Bake.
If your doing No-Bake try Resin Shell.
If your doing Resin Shell then try Investment casting or closed die.
If you have not done so you may need to make special fixtures that allow you more mis-alignment than a vise and stop rod.
I had to listen to the machists at another place I worked at every time they had to run some gearbox housings. It just blew there minds not having an exact starting point.
RE: How to get around sanding casting iron before machining?
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RE: How to get around sanding casting iron before machining?
How big are these parts? It they are <100mm the approach may be quite different than something larger.
In any case you are only making datum points from which to stage the next operation. This might be as simple as spot facing three points on one surface and proceding from there. Assuming that you are putting holes in these eventually the points for the holes would be good for locator spotting.
BTW, the double disc grinder has two grinding wheels that face each other. The part moves between them and two parallel faces are created simultaneously. My exposure to them was to face ends of roud pins and to create parallel faces on castings.
Griffy
RE: How to get around sanding casting iron before machining?
say a AFS 120 finnish on what side, they have the equepment to sand and grind much faster than you do!
All foundry work off a surface finnish that is related to the machine finnish scale used in a machine shop
SBI
Central Ne.,USA
RE: How to get around sanding casting iron before machining?
RE: How to get around sanding casting iron before machining?
Fill what's empty. Empty what's full. And scratch where it itches.
RE: How to get around sanding casting iron before machining?
As it was said by some of the responders, you should be able to start machining a casting. However, the process to do that is as follow:
- select the best surface on your casting
- plan to machine the opposite surface first
- clamp your part on the table mounting it on 3-point system (have 3 support spread as maximum as possible in a triangle pattern between the table and the casting surface (the best side, remember!).
- machine the top deep enough (I suggest a coated carbide tool) to remove the cast layer. run a final finish pass (small depth of cut).
- stop and turn the part over
- clamp the part (you do not need the 3-point system now)
- machine the rough surface.
You have 2 parallel surfaces to work with.
Good Luck
Mo
RE: How to get around sanding casting iron before machining?
We used either a Wheelabrator or Pangborn system to desand the casting with the initial machining being accomplished with a Blanchard Grinder.