The sheet metal assembly is again seen during the production of products on a large scale because it is considered a cost-effective method for creating big structures. After all, the processing equipment is considered to be well-established, and there is no requirement of creating expensive large tools to make plastic parts.
However, as parts are made by an assembly of parts and not formed together, there exist tolerance concerns that one should consider. They could otherwise be avoided by a person using a one-shot process such as RIM, structural foam, or hard injection.
One needs to get a good hand with the process via which sheet metal parts are manufactured for understanding why and what this exactly is. There exists a mixed bag of processing technology from stamping, bending, and shearing to drawing. However, for designers working on large parts with relatively low quantities, most sheet metal parts tend to be cut or stamped with lasers and CNC presses and then formed on semi-automated brakes. It happens due to the tooling investment to make tools and to stamp dies that would never be amortized in relatively low quantities.
However, as these machines bend a step at a time, the tolerance considerations are not very similar compared to the parts with all the formed features. As design consultancies, companies tend to witness various parts originally designed to tackle the tolerances in manufacturing. But with the presence of many bends stacked up together, the parts ended up not fitting at all.
Things to remember while designing sheet metal parts
When you are designing sheet metal parts, you should always remember that the primary form is generally cut out of a flat sheet in a single setup, this typically means that all the features that stay in one single plane will tend to have the highest level of tolerance as bends would not have been successfully introduced. With designing parts that require to key together, it is a great idea to use all the features known to exist in a particular plane.
For instance, while a person is creating vertical divisions for a drive rack, it might be tempting for him to try positioning dividers with the same bolts that secure them in their respective place. However, there will be around two bends in between the bolt holes. As a result, the tolerance between them will be loose that leading to canted dividers.
By considering all the constraints of medium or low volume sheet metal assembly and manufacturing, one will balance his way to design parts that fit together irrespective of where a particular part tends to fall in the range of tolerance.