Explain This

Engineering explained! Taking interview question inspiration from everyday items is extremely common in mechanical engineering interviews. Not only do these questions test your technical awareness and ability to apply that knowledge practically, but they also serve as a chance to understand how inquisitive you are about the world around you and how engineering exists within it.

One of the most common forms of this question is handing or showing the interviewee a well-known object, such as a stapler, and asking how it is produced. Manufacturing methods are critical to know as an industry mechanical engineer, however, students understandably often have limited knowledge of this technical area. I would take a guess that you have used a 3D printer, laser cutter, maybe a mill or CNC, etc., but probably have never ordered mass produced custom parts often from overseas. This example of a stapler is intended to start probing you to think more about the items you see everyday and how they are produced so that come time for interviews, you will be well versed and able to critically think on the spot when answering similar questions.

Without going into the technical part names, a stapler has a few main components. It has underlying metal framing to give the device strength and rigidity as well as to isolate and deform the staple, a spring to push the stored staples towards the dispensing end, another spring to ensure the top arm recoils open after pressing a staple, plastic and rubber external parts to aid in aesthetics and ergonomics, a metal pins to act as a hinge, and mechanical fasteners to hold parts together.

The metal framing and base plate, which deflects the staples, are made by stamping, in which sheet metal is mechanically cut out by dies into shapes and can further be bent and shaped. The leaf spring, resembling a diving board, restores the stapler’s upper arm position after a stapling motion and is similarly produced by stamping. In particular, bending or rolling are leveraged to create the desired final waved shape. The compression spring, which pushes the staples to the dispensing end, is made by metal coiling, where wire is fed into metal rollers that create the wound geometry. The rivets, which are mechanical fasteners for the thin sheet metal parts, along with the hinge pin, are made by machining or metal forging. Externally, the plastic outer facing parts are made by injection molding in which melted plastic pellets are pressed into a mold and cooled into the hardened shape. Compression molding is a very similar process, however, it is used for rubber parts such as any grips on the stapler.

Several of these processes are very common for mass producing metal, plastic, and rubber parts in an inexpensive and scalable way. This example only scratches the surface, however, and I recommend that you Google search any manufacturing methods above that are unfamiliar to you. Start to look at everyday objects under this lens of identifying how they came to be, and doing so will surely prepare you well for mechanical engineering interview questions!