Extruded Heat Sink by Aavid

Extruded Heat Sinks: The Metal Version of Play Dough

Thermal Design

Extruded heat sinks are one of the most popular types of heat sinks. They’re easy to make in bulk, economical, and have fewer secondary operations before a final product than other heat sink technologies. That’s why the extrusion process is so widely used in other industries like window frames and door jams, pipes and tubing, and food like pasta and french fries.  Extrusion is straightforward and in the thermal management industry, it’s easy for us to take advantage of this technology.

Extrusions and Extruded Heat Sinks: How They’re Made

I remember playing with Play Dough as a kid. Especially when I put a giant handful into what looked like a garlic press and pulled the lever down. The pressure I put on the dough squeezed out dough with this crazy shape I chose in the front, making a long strand with that same shape cross section.

Extrusion of Play Doh Courtesy of Fun Skool India
Play Doh Extruder Image Courtesy of Fun Skool India

 

This childhood activity is similar to the process we use for extruded heat sinks. We use aluminum instead of dough; a manual level is replaced by a multi-ton hydraulic press (way more pressure than any arm could make, child or adult); and an extrusion die takes the place of the plastic bit with crazy shapes.

Extrusion - Schematic of Process and Machine - Courtesy of the Aluminum Extruders Council
Courtesy of the Aluminum Extruders Council

 

Under Pressure

In the aluminum extrusion process, the metal in a billet form is heated up to the point where it’s soft enough where it can squeeze through the extrusion die, but not so soft where it’s molten and would just drip out. The hydraulic press pushes a ram into the billet which forces the aluminum through the heavily engineered extrusion die. This die is the cross section the long extrusion will have.

Aluminum Extruded Heat Sink Die Example Courtesy of Aluminum Extrusion World
Aluminum Extruded Heat Sink Die Example Courtesy of Aluminum Extrusion World

 

Engineers carefully design extrusion dies so they produce the required shape, but can still withstand the pressure of the aluminum billet being pressed against it without breaking. This is especially true for heat sink dies since there are lots of fingers for the fin gaps which could break off from the die. Too much aluminum pressing on long thin fingers will easily snap them on and destroy the die.

Food Extrusion Dies to Illustrate Extruded Heat Sink Basics
Extrusions my child-self would have been more interested in. Courtesy of Hamill Machine Company

 

The Home Stretch

After the aluminum is extruded out, it’s pulled along the run out table where it is straightened and allowed to cool. When first manufactured, these bars can be upwards of hundreds of feet long. For ease of shipping and manufacturing purposes, the giant lengths  are then cut into more manageable lengths, typically around 8 feet.

From Raw Bar to Extruded Heat Sinks

From here, these aluminum extrusions are then cut to length for the application they will be used in. Any sort of machining, holes or other features are machined into the extrusion to customize it as necessary. This is also when finishing, like anodizing or painting, occur to finish off the heat sink.

Extruded Heat Sinks with Chromate Finish by Aavid