Flow-Pressed Heat Sinks
Square, rectangular, or round pin-fin and high-fin or cross-cut heat sinks made of aluminum or copper for small installation spaces. (...)
Impact Extrusion of Heat Sinks: Process, Benefits and Limits
Impact extrusion is a bulk forming process in which a slug is pressed between a punch and a die until the material flows under high pressure. The material fills the cavities of the tool and forms the base plate and pins or fins as one continuous part. In cold impact extrusion, also called cold forging, this happens without preheating, preferably with highly formable materials such as pure aluminum or copper.
Learn more in a conversationWhat is impact extrusion?
Under DIN 8583, impact extrusion is a compressive forming process. It belongs to the group of forming by pushing through a die (DIN 8583-6), together with extrusion and tapering. Unlike extrusion, which turns a heated billet into long profile lengths, impact extrusion produces individual parts in a closed tool.
A punch pushes the slug into the die. Inside the die, the material is under compressive stress from all sides, so it can be formed heavily without cracking and fills the bores and cavities of the tool. The result is pins, webs or cups that are one piece with the rest of the part.
Impact extrusion methods by material flow
The methods are distinguished by the direction in which the material flows relative to the punch movement. By part geometry, a further distinction is made between solid, hollow and cup extrusion. For pin fin heat sinks, the tool design determines whether the pins are formed in the direction of the punch stroke or against it.
Forward impact extrusion: The material flows in the direction of the punch movement, for example through openings in the die. Typical parts are shafts, bolts and studs.
Backward impact extrusion: The material flows against the punch movement, usually through the gap between punch and die. This produces cups, sleeves and thin-walled housings.
Lateral impact extrusion: The material flows at right angles to the punch movement into side cavities, for example for flanges, collars or lateral projections.
Combined impact extrusion: Several flow directions occur in the same stroke, for example a cup with a stud extruded forward at the same time.
Cold, warm and hot impact extrusion
In cold impact extrusion (cold forging), the slug is formed without preheating. The process achieves good dimensional accuracy and clean surfaces, and strain hardening increases the strength of the finished part. It requires a highly formable material. Pure aluminum and copper meet this requirement particularly well, which is why cold forging is common for heat sinks made from these materials.
In warm and hot impact extrusion, the slug is preheated. This lowers the flow stress and therefore the required press force. These variants are mainly used for steel and alloys that are difficult to form, when cold forming would require excessive forces or the material could crack.
How an impact-extruded heat sink is made
The individual steps depend on material, geometry and quantity. A typical sequence for pin fin heat sinks looks like this:
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Preparing the slug: Slugs are sawn or punched from bar or plate stock and soft-annealed if required.
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Lubrication: A lubricant on the surface reduces friction and prevents the material from sticking to the tool.
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Pressing: The punch pushes the slug into the die. The material flows into the bores or cavities and forms pins or fins that are one piece with the base plate.
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Ejection: An ejector releases the part from the tool.
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Secondary machining: Depending on the requirements, the mounting surface is face-milled, holes and threads are added, the pins are trimmed to a uniform height and the surface is finished, for example by anodizing.
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Pressing in functional elements: Heat pipes or copper inserts in the base plate spread heat from hotspots across the entire pin structure.
Benefits and limits of impact-extruded heat sinks
Benefits
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Pins and base plate are one piece. There is no joint or adhesive layer and therefore no additional contact resistance in the heat path.
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Pure aluminum such as EN AW-1050A can be processed. It conducts heat at around 230 W/(m·K), while the extrusion alloys EN AW-6060 and EN AW-6063 reach about 200 W/(m·K).
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The microstructure is dense and free of pores, and the grain flow follows the contour. Die castings, by contrast, can contain gas pores and shrinkage cavities.
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Round or square pins let air flow through the structure from several directions. This suits cross and diagonal airflow and installation positions with changing flow direction.
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Material utilization is high because the part is formed close to its final shape instead of being machined from solid stock.
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Cycle times in series production are short: the entire cooling structure is created during pressing and is not produced fin by fin.
Limits
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Pin height and slenderness are limited. The longer the flow path, the higher the required press force and the load on the tool.
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The spacing between pins cannot be reduced at will, because the webs of the die between the bores need a minimum thickness.
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Very thin base plates are difficult to achieve, as the press force rises sharply as the remaining base thickness decreases.
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Each geometry needs its own tool. Tooling costs are comparatively low but only pay off in series production. For prototypes and very small quantities, machining is often more economical.
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Mounting surfaces, holes, threads and tight tolerances usually require secondary machining.
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High-strength aluminum alloys are considerably harder to cold forge than pure aluminum.
Impact extrusion, extrusion, machining or bonded fins?
The right process depends on geometry, power density, installation space and quantity. An overview of the four common routes to an air-cooled heat sink:
Impact extrusion (PinFin)
Base plate and pins are formed as one piece. The pins can be arranged across the surface in both directions, round or square. Materials are pure aluminum or copper alloys. Strong choice for compact heat sinks in series production.
Extrusion (ExtruFin)
A heated aluminum billet is pressed through a die. The result is a profile with a constant cross-section, and the fins run only in the extrusion direction. Typical alloys are EN AW-6060 and EN AW-6063. Economical for long heat sinks and standard profiles.
Machining
Pins, fins and channels are milled from solid stock. There are no tooling costs and design freedom is high, but material removal and machining time per part are considerable. Well suited to prototypes and small batches.
Bonded fins (BondFin)
Individual fins are brazed, bonded or welded to the base plate. This allows very tall, thin and closely spaced fins as well as large dimensions. The joint is part of the heat path and is designed accordingly.
PinFin: cold-forged heat sinks from COOLTEC
PinFin heat sinks from COOLTEC are manufactured by impact extrusion. The vertical pins are round or square, so air can flow through the structure from several directions.
Materials: pure aluminum such as EN AW-1050A with 99.5% aluminum content, or copper alloys
Low tooling costs allow many variants and adapted designs
Compact geometries for limited installation space
Optionally with pressed-in heat pipes and copper inserts as heat spreaders
Typical applications: LED lighting, control electronics, power electronics and industrial automation
Not sure whether impact extrusion, extrusion or machining is the best fit for your geometry and quantity? Our engineering team reviews your requirements and supports you with the design.
View PinFin heat sinks
Frequently asked questions about impact extrusion
Under DIN 8583-6, both processes belong to forming by pushing through a die. In extrusion, a heated billet is pressed through a die to produce long profiles with a constant cross-section. In impact extrusion, a single slug is formed in a closed tool, often cold. This produces individual parts with features in several directions, such as pin arrays across a surface.
Cold impact extrusion is impact extrusion without preheating the slug. It provides good dimensional accuracy and clean surfaces, and strain hardening increases strength. It is mainly suited to highly formable materials such as pure aluminum, copper and low-carbon steels.
Pure aluminum such as EN AW-1050A and copper alloys have proven themselves. Pure aluminum is very easy to cold form and, at around 230 W/(m·K), conducts heat better than typical extrusion alloys at about 200 W/(m·K). Copper conducts heat even better but is heavier and more expensive.
That depends on geometry, material and tooling effort. Because each geometry needs its own tool, impact extrusion pays off mainly in series production. For prototypes and very small quantities, machining is often cheaper. Our engineering team is happy to advise you on the right manufacturing route.
Pins and base plate are one piece, so there is no contact resistance at a joint. Add to that the dense microstructure and highly conductive materials such as pure aluminum. The pin structure increases the surface area and accepts airflow from several directions.
A cold-forged heat sink for your application?
Send us your installation space, power dissipation and planned quantity. Our engineering team checks whether impact extrusion is the right process and supports you with design and selection.
