Cold Plate Manufacturing Cost

Cold Plate Manufacturing Cost

Factors for cold plate manufacturing cost

Prices for cold plate can vary quite a bit; understanding why can help you reduce your costs and still get the performance you need to properly cool your application. The two biggest cost driving factorin cold plate manufacturing are thermal performance requirements and the annual demand, which generally thermal engineers and the manufacturing engineers have little or no control over. But you can cut costs by understanding how flatness, hardness, roughness, surface topography, mounting features, and liquid connections specifications affect the cost of a liquid cold plate. By involving your cold plate manufacturers early in the your custom cold plate design process, you will be able to identify the manufacturing cost driving factors and select the most cost effective design.

Most liquid cold plates are made of aluminum, while some new technologies use copper. Although copper has better thermal conductivity than aluminum, aluminum is used more often because it is cheaper, lighter, and easier to use.  It is very difficult and expensive for machining copper. Aluminum is usually the best material if it meets thermal performance specifications

The most popular aluminum cold plate technologies are pressured tubed, vacuum-brazed, friction welding. Pressured tubed cold plates are usually copper or stainless steel tubes pressed into a channeled aluminum plate. They are cost-effective and provide good overall thermal removal for low and medium watt densities. Vacuum-brazed cold plates consist of two metal plates bonded together with internal fin. They are available in all sizes and have extremely high performance, making them ery suitable for applications of heat loads concentration. Friction welded cold plates make the water channel design more free, sealing reliability better, at the same time can be used hard anode surface treatment. With both pressured tubed, friction welded and vacuum-brazed cold plate technologies, the labor time is limited. Therefore, for moderate volumes, we are a China cold plate manufacturers , the labor cost is lower than that in European and American countries, and the Chinese cold plate technology is mature, the production time is short, so the cost is lower, so our company exports a lot of cold plates to European and American countries every year.

The biggest cost driving factors for aluminum cold plates, after those mentioned above, are machining time and the additional processing steps. Cold plate manufacturers usually have a cost associated with machining time. This includes the depreciation costs of the machine, power supplies, consumables, and maintenance. Therefore, the longer the liquid cold plate sits in the machine, the more costly it is. Moreover, each additional processing step continues to increase the cost.

 

Extrusions and Castings

To minimize machining time and reduce cost, it is best to use extrusion and casting as much as possible. An extrusion is produced by pushing metal through a die to produce an object with a fixed cross section. Dies for a new extrusions are relatively cheap, Also, any channels or features must be straight.

Liquid cold plate manufacturer can also use a combination of extrusions and machining to reduce costs. An extrusion can be made for some features and then some more complicated features, for which extruding is not an option, can be machined. Another option for prototyping processing is to machine the cold plate for lower quantities and then, once the cold plate design is proven and fixed, make the die for the extrusion. This will help reduce extrusion costs, If you you design the plate with the extruded features in mind.

Another option is to cast cold plate. However, there are several disadvantages to castings. First, the thermal performance are slightly degraded. The degrade may be up to 10%. Second, there are limits to the tolerances that can be achieved. For example,  extrusion can easily maintain a tolerance of ±0.005 inch/inch, while a sand casting is more likely going to maintain ±0.03 inch/inch. A sand cast die typically costs is effective for hundreds of cold plates. Dies for higher technology applications are made by an investment cast process and It can cost up to 10 times as much as sand casting. Also, casting and machining can be used together. For example, if the casting cold plate is not flat enough, the secondary operation to get the cold plate to the required flatness specification will be necessary. It is important to note that sand castings are not an option for vacuum brazing cold plates as the melting point of most alloys is below the vacuum brazing temperature. Their use is strictly limited to the tubed cold plates. It is recommended to obtain quotes on the two production processes and weighing the pros and cons is recommended.

In general, the minimum purchase for extrusion or casting is high, so you need the right application to justify using these processes. Both extrusion and casting offer significant overall cost savings .However, they are hard to change, so if you expect changes in the future, it might make sense to choose other alternative production methods.

 

 

 

Surface Roughness

One requirement that can add significant cost without impact on performance is surface roughness (finish). Roughness on cold plates is an uneven, ridges, or projections on the surface that result in an unevenness on the thermal transfer surface. Contrary to some opinions, roughness has relatively little impact on thermal performance of cold plates. In most applications, the surface contact between the cold plate and the component is less than 10% and the air gap is more than 90%...

Most applications use a thermal interface material (TIM) between components or plates and the cold plates to help to minimize the gaps. The TIM should be as thin as possible, as the TIM's relatively high thermal resistance greatly overshadows any electrical conductivity improvements from having a smoother surface. Increasing the clamping force of a component or plate to the cold plate can also help to offset the higher roughness, but this may increase the stress on the plate or component. Clamping stress can also increase the influence of  influence as the cold plate and component or plate heat up.

Surface Flatness

Surface flatness has greater impact on the thermal performance of the cold plate than surface roughness,because if the cold plate is not flat, the contact area will be greatly reduced. Standard flatness specification is 0.001 inch/inch (0.003 cm/cm). Therefore, within an inch of the measuring point, the lowest point of the cold plate will not be more than 0.001 inch (0.003 cm) lower than the highest point. If your specification requires flatness better than 0.001 in/in (0.003 cm/cm), one way to save money is to specify the local flatness rather than a tight flatness across the whole base plate. For example, if you want to mount multiple insulated gate bipolar transistors (Igbt) on a cold plate and each IGBT needs to be 0.001 inch/inch (0.003 cm/cm) across the whole plate, specify the local flatness for a single IGBT rather than requiring the whole base plate to be very flat.

The flattening process of a cold plate usually involves a hydraulic press. To improve the flatness, the skim cut can be used. After skim cutting, the machine tool will determines the lowest point of your cold plate and skims off as little metal as possible at the lowest point and as much metal as possible at the higher area to achieve a flat surface. While it is very easy to to skim cutting a block of aluminum, It is more difficult to skim cutting a vacuum brazed cold plate or the tubed side of a tubed cold plate. The cooling surfaces of vacuum brazed cold plates and tubes in tubed cold plates are usually thinner to optimize thermal performance. If the cooling plate is not flat the skim cut could be too deep and the walls will be thinned, potentially becoming too weak to withstand pressure or even rupture. Alternatively, you can start with a thicker cold plate to eliminate the possibility of leakage, but you will sacrifice some performance.

Surface Topography

Minimizing surface topography is particularly important in keeping costs down, especially in circuit board applications. Complex surface topography usually requires starting with a thick block of aluminum and then machining off  unwanted aluminum. This leads to high raw materials costs and excessive machining time. If topography cannot be eliminated, bundling components with similar heights on the plate can reduce the machining requirements.

Hardness

Cast, extruded, or vacuum brazed cold plates are very soft after processing and usually having only a T0 hardness. Because soft aluminum is very difficult to process and handle, the cold plate must be hardened. To change the hardness from T0 to T4, the cold plate must be heat-treated. The heat treatment process involves bringing the cooling plate up to 1000°F (538°C), placing it at that temperature at the thickest temperature about 1 hour/inch thick, and then cooling it to thermally very quickly. One way to cool a cold plate down is to drop it directly out of the furnace and into a water bath. To bring the cold plate from T4 to T6, the cold plate must be artificially aged. This is accomplished by placing the cold plates at 300°F-400°F (149°C-204°C) for 8-16 hours.  The T6 provides a very hard cold plates with high tensile strength, typical for military and aerospace applications. T4 is hard enough for most applications, and specifying T6 will only add unnecessary costs.

Mounting and Holes

Another cost increase in cold plate manufacturing is the addition of holes. One of the main reasons that increased cost of the hole is that holes cannot be made in the fluid path. Therefore, for the tubed cold plate, the bend in the tube needs to be made to accommodate the hole, and each bend will adds cost. For the vacuum brazed cold plate, an island must be built in the fluid path, which also means electrical discharge machining (EDM) the internal fin. This can add quite a bit of processing time and therefore cost.

There are several types of holes for cold plate. One type is through hole, which passes from one side of the cooling plate to the other. The second type is tapped holes, which have screw threads. Because aluminum material is relatively soft, the life of tapped holes  is limited if the components or plates are frequently replaced. With tapped holes, helicoils are often used. A helicoil is a sturdy steel insert that adds strength to the threads for applications where there is likely to be frequent component change out. Through holes are created by a single drilling process, whereas tapped holes require an additional tool to be installed on the same machine. Helicoils require a tapped hole in order to be installed, and the helicoil installation itself is done outside of the machining center. All in all, the through holes are the least expensive and helicoils are the most expensive.

Tight tolerance of the location and spacing of holes can also add costs. the reasonable tolerance specification is ±0.005 inch (±0.013 cm). As with flatness, specifying local tolerances may reduce cost. With big liquid cold plates where holes can be relatively far away from each other, the tolerance will becomes harder to maintain. One reason is that the farther the head, the greater the machine's tolerance. Another reason is that there may be thermal gradients in the machine workshop, which can expand or contract the cold plate. Through holes are the easiest to specify a tighter tolerance for because production of a through hole is accomplished with a single tool operation, while tapped holes are not as easy to tolerance because producing them involves two tools.

Helicoils are the most difficult to tolerance because the process requires a tapped hole and the helicoil itself has a tolerance. All the tolerances add up, making the cold plate harder and more expensive to manufacture. Avoiding to making small tapped holes will also help to reduce cost. Hole sizes of 4-40 or smaller become hard to tap as the taps can break while drilling. To minimize this problem, the machine must run very slowly. A method to counter tight tolerances requirements on a cold plate is to increase the size of the mounting holes in the component or board.

Design and Manufacturing Partnerships

Working with a cold plate manufacturer early stages in a cold plate's design or having the flexibility to print designs, will maximize cost savings. Although the two biggest cost drivers in liquid cold plate manufacturing are thermal performance requirements and annual demand, there are many other factors over which thermal engineers and/or component engineers have some control. Making sure that each specification has its own reasons, as each specification may drive up cost, will help to reduce costs. It's important to determine when flatness, roughness, hardness, surface topography, mounting features and holes, and liquid connections specifications are required. In addition, it's important to recognize that there are many options in not only the design, but also the manufacturing processes in use, which can save  a lot of money in manufacturing.

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