View Full Version : machining aluminum castings

10-14-2004, 06:37 PM
I have some thin-walled (.063" thick) alum castings that I'm machining on a manual mill and a cnc (depending on the feature) and was wondering what techniques work well. I'm using small (.093"-.187") hss endmills at about 1000 rpm in order to hold the heat down. This makes for slow going. Is there a different type of cutting tool that might work better? I'm using an acid brush to apply Accu-lube to the cutter so it won't load up. Is there a better lube for this? TIA

10-14-2004, 08:42 PM
try varsol, ive found it prevents clogging or loading of cutters and improves surface finish.

10-14-2004, 08:54 PM
You could try hooking up a simple regulated air blast, it wont take much air to blow aluminum chips, also switch to carbide cutters, you may also be defeating the purpose using 1000rpm, that is very slow and may not throw the chips out of the way as well as a more appropriate rpm.You will find the carbide much better cutting.

10-14-2004, 09:03 PM
We machine cast alum. at work, high rpms, and flood the cutter with a synthetic oil/water based cutting fluid. Carbid definetly work good if you can afford them.

10-15-2004, 02:24 PM
Thanks to everyone for the replies. I don't have flood coolant on my CNC so I have to use a mister which doesn't get the job done. I find using a lube like oil or Accu-lube works best although it's tedious having to brush it on the tool. The endmill is in a trap cut and we've found over the years that carbide doesn't do this well. I think it's because carbide's flute can't be ground as sharp as hss/cobalt endmills. The lack of sharpness causes too much heat and the cast mat'l melts onto the tool(which is why I run slow rpms). Has anybody tried different styles of tool geometry? I was wondering if a router type bit (single straight flute) would have more room for chips? Anyone doing something out of the ordinary? TIA

10-15-2004, 03:12 PM
I'd be mad as hell if 1000 rpm in aluminum, with a 3/16 cutter was as fast as I could go :D

Although a new Trico Micro-lube dispenser is expensive, it works extremely well in aluminum. There's enough air coming out to move the chips, and enough lube is applied to keep the cutter from plugging up. Misting devices may not be as effective because they are not able to dispense as oily a fluid as the Trico unit can.

You should be able to run as fast as that mill will permit, depth of cut being no more than the radius of the cutter at one go.

11-04-2004, 08:13 AM
I know it sounds cheap, but I have never found anything to work better on AL than good ol WD-40. As fat as tooling, there are allot of advancements in indexable. Iscar and others have new inserts with polished faces and ground edges. I think the smallest diamater is about .500 though.

I used to run a .750 2 flute at 6000RPM and anywhere between 60-100IPM, .600 deep, with about a .200 curf (width of cut) in cast aluminum stepping down a wall. On the same part, ran a 2Inch face mill 6000RPM, 280+IPM with 4 or 6 flutes.

11-04-2004, 11:27 AM
Thanx for replying-I thought this thread had died. Years ago in machining class we used kerosene on alum. and it also worked great. I'm switched to a fairly heavy oil with sulphur in it that our punch press dept. uses and it doing ok. I'm using a 3/16" cobalt endmill to cut small windows in this casting. I couldn't figure out why I had to run such slow rpms but found out these castings have been hardened through a heat -treating operation so that might explain it. It's wearing out my tools pretty quickly. The speeds and feeds you mentioned sound like what I run on 2024 and 6061 alum. but couldn't possibly do that on these parts plus I have a pretty flaky set-up. I'm on a sine-bar clamped to a 3/4"piece of steel sticking about 8" above the vise and clamped to it with 3 clamps so I don't want too much in the way of tool pressure. Thanx again.

11-04-2004, 10:24 PM
The machinability of different aluminum casting alloys will vary widely. Raw castings often "gum" for lack of a better word, build-up on the edge of the tool, and make life miserable in general. What treatment (if any) are the castings recieving? Is the aluminum actually melting, or is the alloy too soft? When I did my own 356 castings, if I didn't heat treat them and artificially age, they would machine like the cheapest aluminum garbage you'd find in a hardware store. After treatment, the chip formation was vastly improved. The chips would come off in a brilliant shower and the finish was excellent.

I think the advise to speed things up and get adequate loading of the tool is sound. Carbide at high RPM and aggressive feed has always worked well for me.

11-05-2004, 07:12 AM
Here is a link to the inserts I was speaking of above. The polished face really helps on cast AL as it allows the chip to slide off real easy, with a great reduction of friction (which cuts down on the het that loads up the cutter). As far as sharp, these inserts have a ground edge, VERY sharp edge. And being that they are Iscar, the price is resonable.

This is the larger insert, but they do make it in a smalle .250 wide version also.