aluminium extruded heatsink converted into die cast part
how to convert an extruded heatsink to a die casting heatsink
Generally the extrusion process must be more suitable for some complicated heatsink part,especially when the heatsink has much thin and long fins. But for some extrusion heatsink part, the production cost can be higher than that of die casting part,because the heatsink part should be cut off from the whole profile bar,which is a labor intensive work with high rejection rate.
When we got the 3-d design of the small heatsink, the first thought was that it must be a challenge project for us. As the extrusion part can be extruded out without any taper. But as for die casting process, the draft angle is a necessary technical requirement. Thus we added draft angles to the extrusion part. And with customer's requirement, the draft angle should be controlled with 0.5-1 degree. Even the 3-d pattern adaptation was an immense job.
As the former extruded heatsink had concentrated long fins, the draft angles couldn't be located from one end to the other end of the heatsink. because the long dimension with long draft angle can be deviated from the former dimension a lot. Besides the two ends of the heatsink were designed to contact other parts. Thus the parting line should be located on the middle of the heatsink, then the draft angles were applied from the middle line to each end with an angle no more than 1 degree.
Such parting line location can guarantee the two ends have the same dimension and appearance. The adapted 3-d pattern was transferred between the customer and our engineer for several times before we worked out the final design. As customer's insisting, some draft angles for critical dimensions were reduced to 0.5 degree.
When the 3-d design for raw casting was confirmed, we started to prepare the die casting mold.In order to achieve such thin wall die casting heatsink, we paid a lot attention to the die casting mold. For a good die casting mold is critical for casting out qualified heatsink. We chose much tough and hard SK24 tooling steel for the mold cavity. By the way, it was a single cavity mold. We must say a single cavity mold must be our limitation. We were unable to carry out a multi-cavities mold for such complicated die casting heatsink part.
Frankly speaking, except the thin and concentrated fins, it was simple die casting mold for us with any slide core and embedded lump. The spark machining for the fin features in the mold cavity really took us much time. After the mold components were ready, the mold was assembled much carefully.
It totally took us 35 days to finish the mold, which is 10 days longer than that for a common die casting mold. However the long mold production proved it good. The first samples were inspected by three-coordinate measuring machine. The CMM report showed that the samples were qualified.
