Extruded heat sinks — and when you should not pay for a die

Usually not, and this is where most money gets wasted. A die is a one-time cost that has to be spread over every piece you will ever order from it, so at 50 or 100 pieces it dominates the price completely. The alternative almost nobody offers you: take a stock 6063 profile whose fin section is close enough, cut it to your length, and machine everything else — mounting pattern, pockets, counterbores, tapped holes, cut-outs at the ends. You get your footprint without owning a die, from 1 piece. A die starts to pay when the volume is there and no stock section is close, and we will say which case you are in before you spend anything.

About 1.20 mm is the normal floor in 6063, and the fin aspect ratio lands near 12:1 — so a 1.20 mm fin runs to roughly 14.00 mm tall. Specialised high-ratio presses push further, at a price. The reason for the limit is that molten-soft aluminium has to be pushed through a narrow slot in the die and then survive being pulled out; thin, deep slots run cold, wear fast and produce fins that wave. If your design needs 0.30 or 0.50 mm fins, extrusion is the wrong process and no supplier can fix that with a better die — that geometry belongs to skiving or bonded fin.

Because the profile has to come out of the die and off the press without binding, so each fin carries draft, typically one to two degrees per side. The fin is therefore always thicker at the root than at the tip. That happens to suit the physics — the root carries the whole heat flow of the fin while the tip carries almost none — but it is a manufacturing requirement first. It also means a drawing calling for parallel-sided fins cannot be extruded as drawn, whatever the thickness.

6063 for nearly every heat sink. It extrudes freely, holds fine detail in the die, takes a clean anodised finish and conducts about 201 W/m·K. 6061-T6 is the structural choice — stronger, but it extrudes less freely, needs thicker walls, and conducts about 167 W/m·K, roughly 17 percent less. Pick 6061 only when the heat sink is also carrying load or being threaded and stressed. 7075-T6 at about 130 W/m·K has no thermal case at all and is not extruded into fin profiles. Aluminium 1050 conducts best of the four at about 229 W/m·K but is too soft to hold a mounting thread.

That is the single most common heat sink job here and it needs no die at all. We take the stock section, cut it to your length, face the base flat, add the mounting pattern, counterbores and tapped holes, machine any cut-outs where a connector or capacitor has to pass, and finish it. The result is a part in your dimensions built on a section somebody else already paid to develop. If the old profile has been discontinued and you only have the part in your hand, we measure it and reproduce it — including rebuilding the extrusion-look section as a machined part when quantities are low.

Four things, all following from one fact: a die produces exactly one cross-section, constant along the whole length. So it cannot give you fin fields that step between heights on one base; it cannot open a gap in the field so a mounting screw passes through; it cannot put fins on both faces of one base; and it cannot make a wave or corrugated fin, since the section would have to change along the length. Every one of those is routine on a cut fin field, which is why the two processes end up complementary rather than competing.

Yes — clear, black or coloured anodising, and black does help slightly, but less than most people expect. The gain is in radiation, which matters in still air and becomes almost irrelevant once a fan is moving air across the fins. In natural convection black anodising is worth having; in forced convection specify it for appearance and corrosion, not for thermal performance. If any face has to stay electrically conductive, chromate conversion coating keeps conductivity where anodising does not.