HeatSink Material

[circa-]

I am in a milling class at school and because im advanced i got free time and im planing on makeing a heatsink maybe a waterblock. What material should i use? Pure metals or alloys?
what about pure alluminum????? if you know of a GREAT alloy please reply!!!

thanks

 

[Talonz]

Pure aluminum will probably be best for machining. Your only other real choice is copper, which you might have some trouble with because it's much harder.

 

[zer0signal667]

I am in a milling class at school and because im advanced i got free time and im planing on makeing a heatsink maybe a waterblock. What material should i use? Pure metals or alloys?
what about pure alluminum????? if you know of a GREAT alloy please reply!!!

thanks

Your best bet is going to be pure aluminum or copper, they both have their advantages. Copper has a larger thermal conductivity, which makes it ideal for heat transfer. However, aluminum is more easily machined and a good deal cheaper.

By the way, I've never seen a heatsink made by a milling operation. Cheap Al heatsinks are generally extruded or slitted, and copper ones are generally made by a process called skivving which is sort of like peeling away slices of metal.

 

[zer0signal667]

Pure aluminum will probably be best for machining. Your only other real choice is copper, which you might have some trouble with because it's much harder.

Being a materials engineer, I have to point this out...
Copper is not more difficult to machine because it is harder, it is an effect of microstructural properties and the way it deforms. Basically, it feels "sticky" to a mill/tool. It tends to need more cooling/lubricant to cut, and takes a bit longer.

 

[Talonz]

Being a materials engineer, I have to point this out...
Copper is not more difficult to machine because it is harder, it is an effect of microstructural properties and the way it deforms. Basically, it feels "sticky" to a mill/tool. It tends to need more cooling/lubricant to cut, and takes a bit longer.

Funny that you say that. I'm taking an intro materials engineering course right now, but we haven't gotten to that stuff yet

 

[Mad Machinist]

Being a materials engineer, I have to point this out...
Copper is not more difficult to machine because it is harder, it is an effect of microstructural properties and the way it deforms. Basically, it feels "sticky" to a mill/tool. It tends to need more cooling/lubricant to cut, and takes a bit longer.

Sticky is DEFINITELY the word........how would bronze do from a thermal conductivity standpoint.......????? Very easy to machine. Or you could mill from machineable of wax, and then try your hand at investment casting......I think a silver waterblock would work quite well

 

[circa-]

ok well i can do it two ways... mill it out in foam then pour aluminum into it so when it hardens its the shape or i can mill it on the big mill im going of the specs of current heatsink which sucks.... im also taking the clip from it since the mill is might fast it shouldnt take more then 30 minutes ( from expierence on little projects sort of like this)

i will experiment on designs they should be posted within a couple weeks.... and if some work better then others.

thanks for the input!

 

[fugu]

if you're going to mill a heatsink, my suggestion would be to mill out a lot of holes in a solid block to make a swiss-cheeze kind of grid, rather than trying to mill thin fins. there was a hsf unit a while back called "the core" that did something along those lines

 

[Ice Czar]

Thermal Conductivity
Material...............(cal/sec)/cm^2 C/cm)...............(W/m K)...................(W/cm-K)
Silver....................1.01.........................................406........................4.173
Copper..................0.99.........................................385........................3.937
Aluminum..............0.50.........................................205........................2.165

General Heat Transfer Guide

 

[circa-]

problem with silver is $

if i was to use silver i would mill in foam then pour metal onto it to make the heatsink that way i dont waste money compared to milling the metal which would take alot of metal off

donate me some silver spoons and forks so i can melt them down

 

[zer0signal667]

What kind of foam are you going to cast molten metal into?

An Al casting will probably turn out looking nasty or incomplete (casting thin sections can be difficult).

Bronze and brass have crappy thermal conductivity compared to copper.

 

[circa-]

its just a really light foam if casting doesnt work...fisrt ill try with Aluminium to see if it looks and turns out good then ill try the silver.

otherwise i will have to buy a big chunk of silver >.<

 

[Ice Czar]

for silver > lost wax

 

[Mad Machinist]

Actually you can use styrofoam as a pattern for a casting.....make your part in foam....cover it in plaster.......burn out the foam....then pour in the metal..... and I wasn't suggesting you machine silver...probably be worse than copper.....
silver for casting or .040 thick sheet isn't terribly expensive, I've bought and used it for more than one application.

 

[circa-]

i am likeing the plaster idea. Sounds more reliable then anything else right now. If i break a bit at school they make you pay for them >.<

 

[zer0signal667]

for silver > lost wax

Ah yes, a good method for a proficient foundry worker

I still maintain that the casting will turn out very badly from a caster with little to no experience (I'm assuming.) Aluminum oxidizes very readily at those temps, so you'll probably end up with chunks of oxide in there. It also has a large shrinkage percentage upon solidification, so to avoid porosity you'll need controlled cooling and a riser to supply more liquid to the main casting. With the fins you'll want to form, controlled cooling will be near impossible- the fins will freeze and shrink unevenly and you'll end up with a very porous casting.

I'm no foundryman, but I do have some experience in aluminum casting. I'll tell you from my experiences that it's much harder than it looks to obtain a sounf (solid) casting and even to make it look good. With such highly complex designs as heatsink fins, I wish you the best of luck. I won't say "Don't try it" because it's a good way to learn and have fun.

 

[Ice Czar]

all very correct
assuming fins

when I considered that process I was going for the basic shape and then micromachining
(Cathar's jet impingment) but now I have delusions of Phase Change Spray Cooling
but again would start with lost wax, but every time I scrabble enough money together
I spend it on something else