Casting Experts?

[MJuric]

Not related to CAD or anything else really but wondering if there are any casting experts here or know of any who are?

We have a product line that we get castings, all relatively similar shapes, but of varying sizes. Not very complex.

Because we do a significant number of these castings we have spread out our purchasing to 3-4 different foundries. The issue we are running into is that despite all the castings being specc'd with the same material we often times run into significantly different machining characteristics from foundry to foundry and some times even from the same foundry.

We recently had a batch of castings that essentially nuked two sets of tooling in short order that generally last a day a more typically. We called the foundry in and they took the castings back and did an analysis on them.

We just got the report back and two things. One, I know next to nothing about castings so the terminology and more importantly the actual effect of the differences was foreign to me so I simply didn't completely grasp it. Two, the report read a bit like "Ok, yeah there are things that aren't the same, even though they are from the exact same batch, and yeah one is at one extreme and the other is at the other extreme....but technically they aren't wrong as they are in spec. However, even though there's nothing wrong with these castings, we could change things and they would be significantly easier to machine.

In the perfect world I would like to send chunks of castings from all our vendors to someone and have them all analyzed as baselines. As we run into machining issues I would then like to get those tested as well....but to me that sounds really expensive.

However to start I would simply like to find someone smarter than me on the subject and talk to them about things we should look for and how to approach this issue to get it resolved. Even better would be a testing method which we can check incoming materials so we could discover "Difficult machining" material prior to them hitting the machine. I'd prefer these people be independent so I don't run into a "Well if you gave US the business you'd never have this issue" sort of thing.

Thanks

[Merovingien]

"Manufacturing" isn't the best place for this thread ?

[mattpeneguy]

What is your specification? Maybe see if they could meet a more stringent specification such as ASTM A148. That's a rabbit hole I don't have time to go all the way down right now. But, just ask one of them how much more money that would cost for these parts and see what they say?
Looking at it a little more closely, you may have to specify maximum and minimum values for things like carbon...This is complicated and you may need a metallurgist's input...

[MJuric]

What is your specification? Maybe see if they could meet a more stringent specification such as ASTM A148. That's a rabbit hole I don't have time to go all the way down right now. But, just ask one of them how much more money that would cost for these parts and see what they say?
Looking at it a little more closely, you may have to specify maximum and minimum values for things like carbon...This is complicated and you may need a metallurgist's input...

Oh, well, specifications is a completely different animal that I'm playing the role of Sisyphus on. As the drawings are now the foundries could probably ship us a teddy bear and be in spec.

Changing or tightening the spec is an option and for the most part necessary in order for us to have more control over our process, but what I really need to find out is what are the specs we should be looking at?

For instance the vendor that took the castings back saw a rather large, still in spec, difference in hardness. Something like 180-195 brinell on one casting to 240-255 on the other casting. These were supposedly from the same pour and processed together at the same time. They also found some microstructure differences but again "In spec" One of them machined well, the other nuked our tooling in short order.

It's even possible that one vendor is actually sending us something that may be out of spec and a lower grade material which is why it machines so nicely. It's also possible that that same vendor is delivering in spec product but with some different makeup, process etc that makes it machine better....which is what I need to find out.

[matt]

There might be some problem with batch processing instead of continuous processing that causes quenching/heat treat/anneal to result in different properties. If a batch takes a long time to create, but is heat treated as a batch, some parts may be already cooled before they are quenched, so you'd see some of them harden and others not. Or maybe the quench media is heating up over the course of a batch. I'm no casting expert, but I've had to trouble shoot processing errors based on results a fair bit.

[mattpeneguy]

What is your specification? Maybe see if they could meet a more stringent specification such as ASTM A148. That's a rabbit hole I don't have time to go all the way down right now. But, just ask one of them how much more money that would cost for these parts and see what they say?
Looking at it a little more closely, you may have to specify maximum and minimum values for things like carbon...This is complicated and you may need a metallurgist's input...

Oh, well, specifications is a completely different animal that I'm playing the role of Sisyphus on. As the drawings are now the foundries could probably ship us a teddy bear and be in spec.

Changing or tightening the spec is an option and for the most part necessary in order for us to have more control over our process, but what I really need to find out is what are the specs we should be looking at?

For instance the vendor that took the castings back saw a rather large, still in spec, difference in hardness. Something like 180-195 brinell on one casting to 240-255 on the other casting. These were supposedly from the same pour and processed together at the same time. They also found some microstructure differences but again "In spec" One of them machined well, the other nuked our tooling in short order.

It's even possible that one vendor is actually sending us something that may be out of spec and a lower grade material which is why it machines so nicely. It's also possible that that same vendor is delivering in spec product but with some different makeup, process etc that makes it machine better....which is what I need to find out.

I believe that A148 addresses some of this. Though, I couldn't find anything in that particular spec. It does reference other specs, though and that info may be in those...rabbit hole as I said.
I may be able to dig up one of our testing reports for a casting if that helps.

[Frederick_Law]

255 brinell is around Rc 25.
Get better tooling?
Change casting spec to include max hardness? Possibly increase cost. Hence invest in tooling instead?

[mattpeneguy]

255 brinell is around Rc 25.
Get better tooling?
Change casting spec to include max hardness? Possibly increase cost. Hence invest in tooling instead?

Now that does depend on how much machining that's needed, right? Of course if you are needing to do too much machining, maybe the mold needs to be adjusted, right?

[mike miller]

255 brinell is around Rc 25.
Get better tooling?
Change casting spec to include max hardness? Possibly increase cost. Hence invest in tooling instead?

Ease of machining is determined more by chemistry than hardness. *dodging flames* Of course hardness has an effect, but I'll take 25 Hrc over gummy any day!

Case in point;
12L14 has a similar hardness to 1020. Ask any machinist which one they want to use.
304 SS is softer than 17-4 H900. The former is a pain due to the sheer gummy-ness.

[Frederick_Law]

Maybe he got some "bubble gum steel" from China.
We need more info.
What kind of material?
You have problem with low hardness or high hardness?

[MJuric]

There might be some problem with batch processing instead of continuous processing that causes quenching/heat treat/anneal to result in different properties. If a batch takes a long time to create, but is heat treated as a batch, some parts may be already cooled before they are quenched, so you'd see some of them harden and others not. Or maybe the quench media is heating up over the course of a batch. I'm no casting expert, but I've had to trouble shoot processing errors based on results a fair bit.

I don't believe they are quenching them at all. In fact when they were here they said that if they took off the sand to fast that would effect hardness so they always leave all their castings in the sand for a full day to cool off.

These two were supposed to be poured at the same time from the same pour. Identical patterns, different results. I agree something has to be different in the process, no idea what.

[MJuric]

255 brinell is around Rc 25.
Get better tooling?
Change casting spec to include max hardness? Possibly increase cost. Hence invest in tooling instead?

Material call out "Supposedly" covers hardness but as I said we are ridiculously vague with our specs so limiting aspects of the specifications would be an option.

We regularly have tooling guys in here and we regularly test and move to newer better tooling if we see any gain.

The problem here is not the tooling but that one vendors part machines like butter while another vendors similar part rips inserts out of the cutter after a few faces.

[MJuric]

255 brinell is around Rc 25.
Get better tooling?
Change casting spec to include max hardness? Possibly increase cost. Hence invest in tooling instead?

Ease of machining is determined more by chemistry than hardness. *dodging flames* Of course hardness has an effect, but I'll take 25 Hrc over gummy any day!

Case in point;
12L14 has a similar hardness to 1020. Ask any machinist which one they want to use.
304 SS is softer than 17-4 H900. The former is a pain due to the sheer gummy-ness.

Yes exactly which is why I'm trying to get an understanding of what specs cause an increase and decrease in ease of machining in castings. I'm familiar with material toughness and what makes a material tough with materials like 1018, 12L14, Hastaloy, 8620 etc...kinda a clueless when it comes to castings. The report mentioned material grain, graphite, dendrites, innoculation....yeah no idea how that stuff effects toughness.

[MJuric]

Maybe he got some "bubble gum steel" from China.
We need more info.
What kind of material?
You have problem with low hardness or high hardness?

Currently all of our castings are spec'd as Grey Class 35....that's it, no hardness, no finish...nothing.

I'm not convinced it's a hardness problem at all. As mentioned in the other thread "Material toughness" is only marginally related to material hardness.

All I know at present is we have some castings that are spec'd as the same material that come in, look great, cut like butter, no problem. Then we have some castings come in that look much worse and we have serious problems cutting it.

I was just over three and we have a casting sitting over there that we took 1/2" off of and we stopped machining it because it was full of pockets of white powder. Maybe we got the wrong casting and someone was trying to smuggle cocaine to another country or something.

[Frederick_Law]

You got cavity and sand in the metal.
You can't machine sand. That's over Rc60.

[MJuric]

You got cavity and sand in the metal.
You can't machine sand. That's over Rc60.

that's what we've been asking the vendor and the answer has always been "That can't happen". It makes sense to me that if some amount of sand is getting into the outer layers of the casting that we'd be nuking tooling in short order because we are machining bits of sand.

It's like using a chain saw and running into the dirt on accident, blade is completely worthless in seconds.

Same case here. Tooling hits bits of sand and the inserts are nuked in short order and degrade even faster sometimes ending up in a catastrophic insert failure.

[Frederick_Law]

You might want to avoid this vendor if they can't/won't fix the problem.
Their mould is falling apart while pouring. Or even before.
You might want to x-ray or UT the casting for cavity.

[MJuric]

You might want to avoid this vendor if they can't/won't fix the problem.
Their mould is falling apart while pouring. Or even before.
You might want to x-ray or UT the casting for cavity.

We've had problems with porosity as well.

Unfortunately we've had similar problems with multiple vendors. Right now we have one vendor that I would call a good vendor. It's actually ridiculous that you can walk out and look over a room of castings and know which ones came from that vendor just by how they look. Better finish, better corners, consistent color and so on. If it were for avoiding the "All you're eggs in one basket" syndrome this vendor would be getting all our business.

[Frederick_Law]

We got similar "problem" with fab.
More like our problem. We "want" 2" plate flame cut and bend within 1/16 so we don't need to machine them.
Well we end up just rejecting most of the parts. Doesn't really help.
Soon we might run out of vendor .....

[MJuric]

We got similar "problem" with fab.
More like our problem. We "want" 2" plate flame cut and bend within 1/16 so we don't need to machine them.
Well we end up just rejecting most of the parts. Doesn't really help.
Soon we might run out of vendor .....

You want a 2" plate bent to with in .0625"?

[Frederick_Law]

Not me, the boss.
We just rejected another batch of frame cut because they can see the "bump" where the frame lead in.
Keep this up, I'll need to find another job.
Can't machine anything without material.

[DanPihlaja]

I assume we are dealing with sand castings here and not investment castings.

Sand castings are notorious for having extra material all over the bloody place.

Do your customer drawings for the castings have cast datums that you are supposed to use for machining purposes for the 1st operation?

If not, then I would suggest you get with your supplier and define some (assuming your customer allows it). Then make sure that gates and other areas that cause a lot of variation are not near these cast datums (again, assuming your customer allows it).

[zxys001]

as Fred mentioned,....it does sounds like a harder outer shell layer (skin) on the casting - sand ...apply moisturizing cream

[MJuric]

as Fred mentioned,....it does sounds like a harder outer shell layer (skin) on the casting - sand ...apply moisturizing cream

At present it looks like we've chosen "Avoid those vendors" which leaves us with only one for hundreds of castings which does not leave me with warm and fuzzies.

That being said we definitely need to tighten up our casting drawing specs in about every fashion, material call outs, hardness, gate location, casting datums etc etc etc. Right now our drawings are little more than "Well make it generally look like this"...and generally, not surprisingly, that's what we get.

[grhenning]

I've been involved with sand casting issues for years. Biggest issues have been from castings from China. However, there have been issues with castings the company I worked for has poured as well, which I think sometimes has to deal with if they are using purchased ingot or re-melted castings. From the manufacturing side: Hardness test, material analysis, tooling geometry design & coatings, feeds & speeds all play a roll. From the foundry side: pattern layout, gating & risers have also made a difference. Even fixturing (how the casting is being held during machining has made a difference.) The best information I've gathered is from experienced tool designers, foundry personnel, setup people & operators who pay attention to details.

[MJuric]

I've been involved with sand casting issues for years. Biggest issues have been from castings from China. However, there have been issues with castings the company I worked for has poured as well, which I think sometimes has to deal with if they are using purchased ingot or re-melted castings. From the manufacturing side: Hardness test, material analysis, tooling geometry design & coatings, feeds & speeds all play a roll. From the foundry side: pattern layout, gating & risers have also made a difference. Even fixturing (how the casting is being held during machining has made a difference.) The best information I've gathered is from experienced tool designers, foundry personnel, setup people & operators who pay attention to details.

We are pretty solid on the manufacturing/Fixturing side. What we don't have is "Casting Expertise". It's obvious, in manufacturing and even visibly, that castings from some vendors are not the same as other vendors despite the same material call out, specs etc.

I can walk into a room of our castings and pick out "Good Vendor" and "Not so good vendor" from 10 feet away by surface finish, casting color/discoloration, extra material/lack of material and so on. Chips coming off of one casting are significantly different than the other using the same tooling, speeds feeds etc. Tool life is significantly different as well.

This is also not an issue with "Just one" vendor but in fact we only have one out of half dozen we've used over the years that has NOT had similar issues. So "the one" apparently has some trick that makes their castings exceptional by comparison, at least for our application.

These are all sand castings, not investment casting.

[Wardaddy]

It's usual for Us to request laboratory cylinder for make test about chemical composition or brinell hardnees requirements.
We buy in some companies about the world like Brasil, China and Argentina too. Not always has issues about casting type, but if the casting it's a little bit more hardener the cost of the bits for milling is on the cost of the supplier.
But we usually uses DIN/EN GG25/GGG60L or GGG70L not another ones. Wich one did you buy on your components?