What are the most common design mistakes for assembly and disassembly?

Reducing fastener count is a key part of DFA. I didn’t see it mentioned here but looking at the fastener geometry also needs to be considered. If your using headed pins or screws they only go in one way, it requires more time to pick up and orient non-symmetrical parts. If your doing automated equipment the fasteners are typically fed head hanging which helps, but if your doing manual assembly the fastener needs to be manually oriented. Some fasteners tangle if they are supplied in bulk to an assembly line. IE springs. This takes more time to untangle and orient those fasteners. A symmetrical pin or fastener can be installed in either direction. Using fasteners designed not to tangle also solves a-lot of assembly issues.

Using too many parts and fasteners can increase the complexity, weight, and cost of the product, as well as the assembly time and effort. It can also have a negative impact on the environment, as more materials and energy are consumed and more waste is generated. One thing I’ve found helpful is to apply the design for assembly principles of part count reduction and standardization. By reducing the number of parts and fasteners, and using common and reusable components, I can simplify the assembly process, improve the product performance, and reduce the environmental footprint.

I remember a project where we designed a product that required manual assembly by workers. We assumed that the workers would have the same skills, abilities, and preferences as us, and we did not test the product with them. When we delivered the product to the assembly line, we discovered that some workers had difficulties in handling, aligning, and inserting the parts. Some workers also complained about the ergonomics and safety of the product. We realized that failing to consider human factors can lead to assembly errors, low productivity, and low satisfaction. A good design for assembly should take into account the human factors of the assembly workers, such as their physical, cognitive, and emotional characteristics.

Earlier in my career, I worked on a product that was designed for assembly in a controlled environment, such as a factory. We didn't consider the possibility that the product might need to be assembled or disassembled in a different environment, such as a field or a customer site. When we shipped the product to the customers, we received feedback that it was difficult to assemble or disassemble in some situations, such as in low light, or limited space. We realized that neglecting the assembly environment can lead to customer dissatisfaction and poor product performance. A good design for assembly should consider the possible variations and constraints of the assembly environment, such as lighting, temperature, humidity, noise, and space.

In my experience this is a major cost driver that many design engineers do not consider when designing a new product. In one of the mistakes listed above about fasteners, it recommends reducing fastener count. I have had long discussions with design engineers asking why eliminating one rivet or screw really matters ? The rivet only costs $0.02 each. It’s not the rivet , but the assembly equipment and labor required to install the rivet or screw. This is especially true if your building an automated assembly line. Small , tiny fasteners are an even bigger issue if your doing manual assembly.

Overlooking the assembly tools and equipment can result in suboptimal assembly processes and products. For example, using the wrong tools or equipment can cause damage to the parts, increase the assembly time and effort, or compromise the quality and reliability of the product. On the other hand, using the right tools or equipment can facilitate the assembly process, improve the product performance, and reduce the assembly cost. A good design for assembly should consider the type, size, availability, and compatibility of the assembly tools and equipment, such as the screwdrivers, wrenches, hammers, drills, clamps, fixtures, robots, and machines.

Besides the six common design mistakes for assembly and disassembly, other factors can affect the design for assembly, such as the product life cycle, the product function, the product quality, the product cost, the product innovation, and the product sustainability. A good design for assembly should consider these factors and balance them to achieve the optimal design solution. A good design for assembly is not only a technical challenge, but also a creative opportunity. By applying the design for assembly principles and avoiding common design mistakes, we can design products that are easy to assemble and disassemble, as well as functional, reliable, affordable, attractive, and eco-friendly.