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.
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.
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 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.
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?
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.
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.
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.
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.
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.
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.
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.
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.
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 …
