Don’t look now, but you’re surrounded by sheet metal enclosures. The case to the computer in front of you is an enclosure. So is the sheet metal shell around the X-ray scanner at the airport. Enclosures are any sheet metal part or assembly designed to house other components. It tends to be a catch-all term for covers, boxes, shields, chassis, and other, more specific, part types.
Despite the wide variety of applications for enclosures, there are a few things that they have in common. For example, there are exterior issues, whether cosmetic or some form of marking or artwork. These, and other, specific features have implications when prototyping and manufacturing.
Maintaining a first class surface finish with pristine high-gloss powder is a challenge for quick turn prototyping. Often, facilities don’t use clean rooms or white glove processing. Choosing the right finishes can help achieve predictable and pleasing aesthetics. Powder coating and anodizing are the most common surface finish processes. Each provides a functional and attractive finish that is durable and cost effective.
When selecting a powder coat, keep in mind that a textured finish will hide blemishes such as scratches and fingerprints. On the other hand, if you are planning to silkscreen artwork onto the surface, a rough texture may affect the quality of the finished product. A semi-gloss, fine-textured powder coat, such as Cardinal Black C241-BK109 is a great compromise. It provides an attractive but durable finish and takes silkscreen images well.
The shape of a formed section of a part—known as the profile—is one aspect of geometry that has huge effect on manufacturing. It’s very common to see broad sweeping profiles that are comfortable to handle and attractive to the end user. But that pleasing shape costs more and increases lead times. Processing time during forming and welding goes up dramatically when broad corners are required that can’t be formed with a single hit. Bump forming requires 10 hits per inch of arc length. Rolling—using a 3-roller press to curve sheet metal—requires a significant time commitment. If your prototype is a proof of concept or will be used for destructive testing, opting for simpler single-hit bends is more cost effective.
Functional Additions to Sheet Metal Enclosures
Enclosures often require punch form features to serve various aesthetic and utilitarian functions. Louvers and hole-cluster patterns permit airflow and prevent accidental intrusion when handling. Embossments can serve as feet. They can also space features or stiffen a part, similar to a rib. Most manufacturers will have some of the tooling to create these forms in stock. If you’re flexible and accept the in-house tooling, it could save you substantial cost and lead time.
Most prototype manufacturers don’t have the tooling or equipment to create and test for watertight welds. While this may be significant at time of production there are some tricks to avoid this costly requirement. Consider using an RTV sealant to help create the watertight seal once you receive parts. These sealants are easy to work with and require little time to cure. Alternatively, you can request that your welds don’t go through a grinding process. It may not look as attractive, but you’ll reduce the chance of pinholes while cleaning the welds.
Mating Surfaces in Enclosures
Enclosures are often part of assemblies that include covers or other components. Because of this, they must be able to mate together. This presents some challenges when designing around sheet metals. A typical issue is loose tolerances. Here are two design considerations that will help you navigate the challenges of hole position and mating faces:
- Use floating hardware or slotted holes to give you more allowance to soak up the variance inherent in sheet metal tolerances.
- Design around your mating surface. If you want to create a single plane from multiple formed features you’ll be up against numerous tolerance challenges. Tolerances stack very quickly when measuring across bends. That affects the final hole pattern and flatness of your mating surface. To get around this, design the mating surface as a single surface.
Enclosures are a staple in the sheet metal world. They take many forms and represent a vast range of geometries. Being mindful of design aspects these parts share can help to ensure your prototyping efforts are cost effective and efficient.
Related Design Tips
For more helpful sheet metal design tips, download our Design for Manufacturing (DFM) Guide.