It is hard to tell because the pictures are not crisp enough. But looking at the fact that the fins are so close together and they have no draft and they have a shiny and dull side, I would guess it is a bonded fin process.
The aspect ratio on the fins is too big for it to be cast, though the texture on the surface is like that of some cast parts.
I have seen heat-sinks that are extruded (probably not this one), some have the fins bonded into the base. It is hard to tell from the pictures, can you try using a macro setting to get a clear picture of the fin root?
If that’s not clear enough I could try to make a makeshift stand for it maybe? but with the limited depth of field (I think that’s the term) with the CD lens, you can only see a very specific distance each time…
Back on topic:
If the fins were bonded on, how would that explain one side being smooth and the other not?
What’s messing you up is the rough side vs the smooth side, and this may be due to a completely different process issue, relating to how the fins are made (not how they are attached to the body).
How they are made: I am speculating that they are made by a sputtering type process, where the metal is melted and sprayed (as a liquid) onto a flat plate. The back is as smooth as the plate, the front is rough. This is very very fast when forming thin plates and gives a different strength profile compared to rolled-out plates of metal. The rough surface somewhat enhances the heat radiation since it has a greater surface area.
You need the small curve to cover the slot in the mold that the fins fit in to, so the base ‘slab’ can be poured over it all. If it was straight, it would either need to fit very closely or you’d have to allow some metal to dribble down into the fin cavity. Speculation again, though.
Yes, depth of field is the term. To increase the depth of field, you use a smaller aperture (on a camera, F16 versus F5.6). So, try putting a metal plate with a 1mm (more or less - experiment!) hole in it in front of (against) the lens. You will need more light for an equivalent brightness, but the tradeoff is a greater depth of field. 0.1 mm would not be too small, but lighting some objects may be tricky.
It’s from a PC so sputtering process is out, too expensive. Not bonded, too expensive.
The base part is an aluminum extrusion to the outside profile. The gaps between fins are formed in one of 2 ways most likely.
there is a gang saw with many saw blades, with spacers in between, on a horizontal shaft that is mounted on a horizontal mill type machine. The roughness would be a function of shoving the parts thru at a high rate. Since aluminum recycles readily, it’s better to have a fast process with lots of scrap then a slow process with little scrap. Remember, must be cheep but effective.
(this is the fun option) I have seen heatsinks that are formed by a knife that cuts into a solid block of of aluminum in progressive cuts. Just like whittling a fire starter. But this gives slightly curved fins with the root with a sharp angle (not flat).
Looking at the pictures again, I go with the knife (shaving) option. Shiny side is the “cut” side. Dull side is the “ripped” side. The fins are set even, vertical, straight, as a separate operation. This is a low waste and fast process. It has to be a big fun machine to watch. AAvid, and other engineered extrusion heatsink companies do not use this process.
Since you are into building cool optical tools, may I suggest building one which will let you view it through a polarized filter illuminated with polarized light. I believe this referred to as polarized microscopy.
I haven’t build one myself, but I suggest it because the shiny side in the second photo seems to have circular striations. To me that looks like it is due to cooling on a casting. There are also a distinctive dark mark at the root which looks like a surface abrasion due to forceful clamping or extraction of some supporting surface.
If you look at the base of the fins you can see a nice round radius all the way throughout the gap between fins. The heatsink the OP posted about has a very particular shape at the base of each fin where one side is radiused while the other side has a sharp corner. This is a very important detail about how the part was made, because those sharp corners could not have come out of a casting (easily).
produces parts that clearly meet what I’d expect from skiving, and do not look like the original part, at least not to me.
The rough side, and what looks like flakes of oxidized scale on the “Single fin - dull side”, leave me in the cast camp. I still don’t know how they cast it unless they cast the individual fins and bonded them to the base plate. It kind of looks like that in the movie, but of course that is what I’m looking for, and at times, there is enough blurryness to see the Mona Lisa. I’ll ask some of the experts at work for other opinions.
The closeup on the psychopath website shows a similar rough texture, so I’m convinced. I’d like to change my vote to skived as well. My new riddle is whether the texture is a feature, or a side effect of the process. Do they stamp the billet between each skive pass to increase surface area, or where does it come from?
From Wikipedia, not the best source, but it does mention the roughness:
Skiving or Skivetek is also used for the manufacturing of heat sinks for PC cooling products. A PC cooler created with the use of skiving has the benefit that the heat sink base and the heat sink fins are created from one piece of material (copper or aluminum). This provides optimal dissipation and transfer of the heat from the base to the fins. Additionally, the skiving process also increases the roughness of the heat-sink’s fins. Unlike the underside of a heat-sink which needs to be smooth for maximum surface area contact with the heat-source that it cools, the fins benefit from this roughness because it increases the fins’ surface area which serves to provide more area on which to release heat into the ambient environment.
I’ll venture that the rough texture is simply a byproduct of the planing process. Machining is not so much “cutting” metal as it is plowing and crushing the material ahead of the cutter such that it yields. The upper surface is more deformed than the lower as it is on the inside of the curve and also cannot be burnished by the cutting tool. (I have an old 3rd edition of Materials and Processes in Manufacturing by DeGarmo that has some interesting closeup photos.)
I just looked at a long, continuous chip that came from drilling a hole in Aluminum. The lower surface is very shiny. The upper surface is a dull, matte finish. It is not as pronounced as the heatsink, but definitely noticeable. And that’s just a thin chip.