I don't think you need more wall assuming it is in 1/4" range. That part should run fine. We're missing some important information regarding the cold shut in the last attempt. What was the pour temp...compared to previous runs? ....and remind me, what was the cross sectional area of each the runner, gate, and choke diameter at bottom of sprue? Realizing that you're limited in total melt/shot size, and your previous comments about minimizing mold weight and lbs of sand, how deep is the cope, and more to the point, how much sprue height do you have above the highest feature (the sump) in the cope? You might consider adding a sprue extension to provide a little more head. Everything may be just fine but could be the last bit of the mold fills very slowly due to this. Subject to the answers in the first sentence, it may require no change except a can packed full of sand for more sprue height. Best, Kelly
Thickness in that bit full of holes is only just over 1/8". I think I may still have some pattern registration issues (I had a really disastrous attempt before this and did some tune-up) - it's supposed to be a hair over 4mm (~5/32") thick but it looks thinner than that. I'll drill some holes in it this evening and measure properly. The horizontal sections are definitely thinner than designed since I dropped the cope pattern a little too much, I think I will shim it up half a mm or so. I am already pouring with an extension on top, which reaches to about 150mm (6") above the highest feature. After I realised I had the recommended pour temp wrong in my head, I dropped it somewhat. The most recent pics, the furnace was shut off at roughly 750 C (1382 F). EDIT: can't tell you cross-sectional areas off the top of my head, will ask the computer later!
I don't know anything bout your alloy but aluminum in general can be poured hotter than 1382F. That just looks like viscous slow flowing metal. And if you didn't measure it with an insertion device and are relying on furnace shutoff you are much colder than 1,382F. Unless you held the furnace at 1,382F for several minutes the recently melted metal in the crucible is still warming. You may have been only pouring at less than 1,300F when you include the time it took to get the crucible over the sprue and pour. Try it 100F higher. I pour my trivets at 1,500-1,550F to get small pieces to fill and have had success at 1,650F but surface finish suffers. Your corner bosses may do just as well with a small hole in the middle, smaller than your dowel size so it can be accurately drilled. A lot of the shrinkage will go into the hole. Or you could make a larger hole and press in a sleeve to get the dowel size you want.
Sorry, writing shorthand. I shut the furnace off when the pyrometer (admittedly made of cheap parts and uncalibrated) that I had immersed in the melt reads the temperature I'm after. The supplier's page about LM4 says it mustn't be overheated, but doesn't say what temperature would count as "over"! http://www.nortal.co.uk/LM4/ Can't make those dowel holes go through, that would be a source of an oil leak. I suppose I could press in a blind sleeve, but that's another operation for my long-suffering tame machinist.
I didn't suggest putting the dowel holes through, just a little blind hole. A dish, if you will, centered where the dowel will go. But I see I didn't say that. For a blind sleeve make a big blind hole then machine and sleeve it. I read their product description after I posted and also see that they say chills at heavy sections is essential. They don't say what heavy is either. but you may need to place a chill at each boss. They also say "moderately thin" so it might be appropriate to look for an alternative alloy which is described as suitable for thin castings if you can't get it with higher temperature and additional gate distribution. Looks to me that you are making great progress, albeit learning that casting is more than making a cavity to match the intended shape and pouring liquid metal into it. I'm in the steep part of the learning curve too.
Apologies again, you didn't say through-hole. Just the way I interpreted it. The two troublesome ones do now have a dish (second pic in the post above, though I appreciate that the pic is probably a little difficult to make sense of) and seem to be happy. The dishes aren't very neat as they're just hacked into the pattern and kinda touched up with glue and filler, but they seemed to mould up okay. I did consider making some chills for those spots... if they start shrinking again when I raise the pour temp, I guess I'll have to go that way. I have emailed the supplier to see if they'll give me a number on what "overheated" is!
Though it certainly can be done, I think that is a bit sporty for green sand home enthusiast, and as you can attest, will produce a lot of misruns. Should be fine. I think the discussion above sums up the situation. If you were going to have a more consistent chance at success with the part as is, I think you'd need enough metal to support the runner system I mentioned earlier and at least that way the part could be fed at a higher average temp. Trying to fill thin sections with big surface area, in the later stages of fill, with a suboptimal feed system is stacking the deck against you. Think you have one hand tied behind your back. Seems ok as long as you get right to it and don't lose too much heat on the way to the mold. Best, Kelly
Right. That's it. I'm done. Not totally 100% of perfect as there are still a couple of small defects near one of the corner bosses, but I believe it to be usable without welding. Thank goodness for that. This was achieved by none, some, or all of the following: - Further pattern registration tweaks - Runner now U-shaped with 4 gates - I cut a larger sprue (now 28mm), at a slight angle to make the troublesome bit get first shot at filling - Extra coat of paint on the troublesome area of the pattern - Shut down the furnace when the melt reached just a hair over 800. - Blind luck - Said the correct magic incantation - Poked the wire vents from the outside down to the pattern so there are no wires to tidy up (well, just one where I poked down to a vertical surface) Satisfyingly this was the best mould-up & pull I've done of this so far, so I'm glad it came out without any holes in. Hand-rubbed bosses for blind bolt holes: Sprue: This one will be going to see the machinist!
It all seems so easy when it works! It didn't take all that much more temperature. I think that was your key ingredient. Now if you turn the boss troughs into blind dimples...
Looks great. You are definitely making progress. Once you get the feel for the gating and risering thing, then it gets much easier, especially with thin parts
Funkster, are you going to heat treat that in any way? Looks to be fairly simple machining but a T5 or close approximation is fairly easily attained and will improve machinability, stability, and strength which could be of some benefit to sealing surfaces in the long run. Best, Kelly
I hadn't given it a lot of thought, but maybe I should - anything I can do to make the machinist's life easier will be appreciated. However, the only device I have available for heat treating is the oven in my kitchen, with max temp of 240 C. Is this likely to be suitable?
~T5 for A356 only requires precipitation not solution (quench) treatment. 230C for 7-9hrs (some say 5 will do) for A356 would do it (isn't LM4 roughly equivalent?). If using a kitchen oven, I would preheat, then place the part on a rack, place a piece of sheet metal between (but not touching) the part and heating element so it does not have a direct view of the heating element. The reason for the latter if to provide a more uniform heat to the part and prevent the radiant heat from the element creating a localized hot spot. For T6 solution treatment in my resistive furnace this was/is a must for me because it's much closer to melt temp and localized melting will occur. At 230C I sort of doubt it's necessary but just thought I'd toss is out there. I've found T5 to make a significant improvement to as cast strength and machinability and it is very easy to achieve. T6 isn't worth the risk unless you really want or need the mechanical properties. If you do nothing it'll probably be ok too but it tends to be a little gummy and load up cutters. Cutting fluid helps but without some temper it's more difficult to achieve a nice machined finish and typically have lesser durability on features like threads. Best, Kelly
Always some but concern but if it is well supported on a flat surface and shielded from grossly uneven heating I think it's probably a nonevent for that temp, especially if it was left to cool in the sand as cast until near or below that temp. It's probably much less concern than what it sees shaking it out hotter. When you try to solution treat at T6 things can get much more challenging because the ally just has very little strength near 1000F. Best, Kelly
T5 sounds like it's worth the effort, then... I'll stick it in the oven next time I'm at home for a whole day (I'm assuming it needs to be done all in one go). It was indeed left to cool in the sand before shakeout, I doubt it was much over 100 C by the time I got my (gloved) hands on it. My oven is a fan oven so I doubt hotspots will be an issue, but still putting a baffle between the part and the element sounds fairly straightforward. Thank you for the info!
See post #66 here for heat treating aluminum to T6: http://www.alloyavenue.com/vb/showt...le-racing-cylinder/page7&highlight=motorcycle If he can heat treat these thin motorcycle fins, then you should be able to heat treat your oil pan. Its a two-step process, and as long as you have close temperature control on your oven, you will be ok. I did not have close temperature control on my kiln, and so ruined some nice parts, but live and learn as they say. I have some AL heat treating info, I will try to dig it out and post it.
