How to get around sanding casting iron before machining?

[orlorob]

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

 

[ornerynorsk]

You might be better off making your first op a machining of the reference surface.

 

[griffengm]

Is a double disc grinder an option? These are used where parallel faces need to be generated for machining. I believe I've also seen rotary tables built to carry the casting under a grinding wheel on a more or less continuous basis.
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

 

[orlorob]

Every surface is rough, as cast. The castings are delivered on the large side of the finished tolerance. The sanding merely being performed to get me parallel reference surfaces for work-holding in the mill.

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

 

[vzeos]

orlorob,

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.

 

[Tigerdawg]

Is the casting an odd shape with no opposite sides parallel (except for draft) even as cast? I would think you could make a jig where you could clamp the piece in your milling machine to mill your reference flats.

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.

 

[DAVIDSTECKER]

I you are not too far into the casting run you should look into a different type of casting process.
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.

 

[mrainey]

A look at the casting would be a big help.

Manufacturing Freeware and Shareware

http://mrainey.freeservers.com

 

[griffengm]

Orlorob,
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

 

[sbi]

GO BACK to the foundry and tell them what you want and were
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

 

[WhiteTiger]

Job specific fixturing is possible for any rough casting. All you really need is the temporary services of a good process engineer to design a cost effective fixture, imo.

 

[aamoroso]

Sounds to me like you should be able to throw them in a vice and face mill them. Possibly more than one at a time depending on part size. Determine a percentage of clean up you need (say 50% clean up lets you flip it and sit flat). Sanding them is going to be more expensive then popping them into a vice and milling (unless you don't have an available mill).



Fill what's empty. Empty what's full. And scratch where it itches.

 

[Mo1]

Rob,
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

 

[unclesyd]

You need to do a search on Fettling on Google.


We used either a Wheelabrator or Pangborn system to desand the casting with the initial machining being accomplished with a Blanchard Grinder.