Welcome Friend!
This time we are going to be doing some experiments to discover how easy it is (or difficult)
to heat treat aluminium castings, at home in your kitchen, and whether it's worth bothering
with.
[intro music]
If you caught the last video you will have
seen me cast and make some pipe clamps.
I did a T5 heat treatment of those pipe clamps, but it was only recently that I learned that
you could do such things at home in a standard kitchen oven.
I was really surprised at how simple a T5 heat treatment is, so in this video I want
to go into the details of how it's done, and to look into the tangle differences between
a heat treated part vs one that hasn't been heat treated.
Now I have got Martin, from Olfoundryman, to thank for this idea, and all I'm doing
here is pouring a bunch of scrap aluminium into bean can shaped round stock, essentially.
Which I can try different machining operations on, some of it will be heat treated others
wont.
Quenching of cast parts isn't really essential, and in fact it does introduce some distortion,
but when I dug into it, it does seem there is consensus in the literature that, straight
off the bat, it can increase the yield strength of the part.
Bean cans [crack].
I'm going to put on of them in the oven for about 6 hours at about 160 degrees-ish, and
the other one I am not going to do that with, and then we will compare to see how they machine,
how hard they are, that kind of thing.
Both of them were quenched straight after they were poured, as soon as they were, sort
of seemed solid enough, to do that without falling all apart.
So we will see.
[scrabbling]
Well it looks pretty solid down there...
[more scrabbling]
We have put some WD40 on the surface, we're getting straight in there, this is un-heat
treated.
We're cutting at 840rpm, depth of cut is almost a millimetre, but then it's a varying surface.
So we're straight in there, we'll give it a blitz.
[lathe noise]
Seemingly successful!
Well it turned just fine.
Chips: pretty nice little chips really.
Yep, little tight curls.
1050 RPM, quite a fast feed.
[lathe noise]
Those chips are looking really good.
You can see the difference in finish where the WD' was there...
It seems like a really nice surface.
Certainly no visible porosity.
Lets go to some edge turning.
Same speed, super aggressive feed, depth of cut 1.5 to 2mm.
[lathe struggling noise]
Lathe's struggling a bit with that.
It was asking a lot for this size of machine.
Lets go to say half that depth of cut - so 1mm, with some WD'.
[lathe noise]
OK, well I have to say, I think the turning with both of those, is quite nice.
It's a nice quality finish.
I think we were coming quite close to the surface here...
Lets just try knocking that off...
So at this stage in the proceedings, I have tried with WD40, without WD40, and I am wondering,
"where is this gummyness that everyone talks about?"
To conclude this non-heat treated experiment I went ahead and did a finishing pass of 0.2
mm.
OK, well, I wouldn't call that necessarily gummy turning or...
I just see no problem with that whatsoever.
So we will see how that compares to the heat treated one, but this non-heat treated one
turned at 1050 rpm seems to be pretty good, and the surface finish just seems quite excellent
to me.
The face here was 1mm depth of cut, this edge had a finishing pass of point two millimetre,
but to be honest it was just as good a finish at the millimetre depth of cut.
It would be interesting to see how super sharp high speed steel would finish it compared
to the carbide inserts I've been using.
Lets move on and look at the heat treating process.
In our kitchen we have a standard fan oven, and I'm running it at 180degrees C, and those
parts were in there for approximately five hours.
Lets take a step back and talk theory for a moment...
The main purpose of heat treating is to improve the mechanical properties, the strength and
so on of the part, but also its machinability.
That's what we have been testing so far, on the lathe.
What we are doing is a rough approximation of T5 heat treating, which people also call
artificial ageing - ageing being what seems to happen if you put something in the oven
for five hours.
Now if you pause the video and check out this table you will see that just water quenching
will improve the strength of a part, but water quenching followed by this artificial ageing
process really improves the strength quite a lot - the yield strength going all the way
up from 117 to 186.
You will notice on the bottom row of the T5 heat treatments, an even more effective regime
which uses a lower temperature, but for a much longer time.
But unless you can get away with monopolising the oven for 28 yours then that's out of the
question.
Lets try machining our heat treated test part.
For this rough cutting of the bottom we are using the same kind of speed and feed.
Considering we munched and monstered that off, that's a really nice finish.
Lets try a 0.2mm finishing pass...
[lathe noises] Ok that's a very nice finish.
Lets go for an aggressive first barrage on this edge turning.
Approximately 1.5mill depth of cut.
That was great.
Lets try a 0.2mm finishing cut.
Same speed and feed.
That's very shiny.
So I can feel the difference - this one's a bit more, kind of, catchy, on this cloth.
Where as this one - it just skids over.
I can feel that, with the finger nail as well.
I thought when I turned this that it couldn't get much better, but I was obviously wrong...
OK, I did a slightly different test as well, with this BIG block here.
That was just with the power hacksaw.
So that was the piece I cut off it.
I think that would definitely classify as what people call 'gummy'.
I have since heat treated this whole block, so I though if I tried tacking a slice off,
another one, and see how it cuts.
And check out the difference.
This blade is probably due a replacement actually.
So this was actually setup to run with coolant to begin with, and it has got a pump and everything,
and the coolant went off this little protrusion here.
I'm running it at half speed, so 30 Hz the inverter is running off, and I just find it
much more pleasant to run it at that speed.
It doesn't heat up the material or the blade very much, and so cooling is not necessary
which saves a lot of mess.
And although it's all setup with a tray and everything to catch the coolant and drain
it down and recirculate it in the pump, it just creates a really sludgy mess.
That's amplified in a workshop like this where I'm doing woodworking and things as well,
and any dust in the air really sticks to those kind of wet gunky surfaces.
All in all I love it as a method of cutting.
As long as you're not in a super rush.
You notice I don't need any hearing protection, it's just a kind of, it's almost like a gentle
calming lapping of the waves.
Well hacksaw test is very interesting, have a look at this!
I guess you would just call it 'gummy', there's bits that have just got tared and pulled over.
Un-heat treated test here: the same kind of deal.
Compare that to the heat treated cut!
And there's still little signs of that kind of thing here and there, but in general, MUCH
cleaner cutting.
Lets just take one last glance at the chips that came off the lathe.
So these are the heat treated ones - really tight curls, nice small chips - just what
you want.
Here's the non-heat treated ones, and certainly not terrible.
Good in fact, I would say, but not quite as nice as the others.
Well there it is friends.
Should you heat treat your parts?
You tell me, you have seen the machining differences.
I haven't experimentally gone into the strength differences but I'm almost certain they will
tally nicely with the literature as well.
Considering how easy it is to shove some parts in your kitchen oven, I'm not quite sure why
you wouldn't do it?
All this assumes you are using an alloy that's amenable to heat treatment for your castings,
and I certainly recommend you do.
Scrap alloy wheels are a fantastic resource in this respect.
Ok, I'm off to cast the rest of my pipe clamps, stay safe and see you next time.