134 Chapter 11 material and increases the cost. Several companies are today working on methods of increas- ing the strength and reducing the weight and mass of steel in order to make it more competi- tive with low-weight aluminum applications. The Nanosteel Company is one such company who offers advanced steel solutions that begin to achieve similar weight as aluminum but still retaining the high strength of steel (Nanosteel, 2014). Aluminum enclosures can either be of stamped or die-cast methods. Aluminum offers lower weight than steel but can require additional material thickness in order to meet strength require- ments, especially in stamped pieces.
The other method that can be used with aluminum is in the form of die casting. This can be either through high-pressure die casting (HPDC) which offers the best strength, porosity, and surface quality but can be very expensive to tool. Sand casting tends to be less expensive to tool but the part quality is often so low that additional finishing steps may be required. Plaster casting offers the best of both worlds, it is relatively low cost to tool and offers finishes nearly as good as the HPDC methods. The biggest challenges with plaster casting are the porosity of the flow which can create weak spots in the final product.
That makes plaster casting, at least for large pieces, most beneficial as a prototype solution. HPDC aluminum offers the benefit of being able to design a part with many features inte- grated into the cast itself, from mounting features to air flow channels, to structural ribs, and supports. This in addition to its low weight makes it an ideal solution for many lithium-ion battery solutions. If the system design is based on one or more of these types of metals, then it is also important to evaluate the need for coatings. There are several reasons that you may want to use a coating and even several types of coatings.
One reason to add a coating is to prevent grounding and shorting of the electronics and battery cells, in other words, to add an isolation function to the battery system. This may be available in one of several materials and types. One common usage is to use an isolating film that has an adhesive on one side. This can then be installed directly to the metal to provide the level of isolation needed. Another method for coatings is to provide either a liquid coating or a powder coating. These two methods are more often used to provide environmental protection rather than isolation. When using metal enclosures, the design must be evaluated for strength.
It is often necessary to include structural reinforcements in the enclosure. This may take the form of either addi- tional metal components that are bolted or welded into plate, or for cast enclosures it may take the form of adding ribbing into the design. Determining which and how much reinforce- ment should be added should be managed through finite element analysis structural, shock and vibration management. Special care must be taken when dissimilar materials are used together as some dissimilar metals, when used together, can create unwanted chemical reaction and cause one of the metals to corrode. This is called galvanic corrosion and is especially important in electrical