Detailed Explanation:
The correct answer is D. Mistake-proofing.
The team changed the physical design of the part so that it can be oriented correctly and assembly errors are prevented or greatly reduced. This is the classic concept of mistake-proofing (also known as poka-yoke)—designing a product or process so that an error either cannot occur or is immediately prevented from causing a defect.
Here, the 45° corner cut creates a clear physical feature that helps the automated assembly machine distinguish the correct orientation of the part. Instead of relying only on detection after an error occurs, the change makes incorrect assembly less likely in the first place. That is why this is mistake-proofing.
Why the other options are incorrect:
A. Quality function deployment (QFD)
QFD is a method used to translate customer needs into product or process design requirements. It is not primarily a method for preventing assembly orientation errors through physical design features.
B. Kaizen
Kaizen means continuous improvement through small, ongoing improvements. Although this situation does involve improvement, the specific method used here is more precisely identified as mistake-proofing, because the solution prevents the error by design.
C. Single-minute exchange of die (SMED)
SMED is a method used to reduce setup and changeover time. It is not related to preventing incorrect part orientation in assembly.
Why D is the best answer from a Quality Management Excellence perspective:
This question requires selecting the method that is most directly supported by the facts given. The observable evidence is:
the part was being assembled in the wrong orientation,
the team modified the part design,
the modification significantly reduced assembly errors.
The most accurate interpretation is that the team introduced an error-prevention feature into the design. Under Quality Management Excellence logic, that makes mistake-proofing the best answer because it directly addresses the cause of the defect at the source.
This also aligns with organizational excellence principles that favor:
prevention over correction,
built-in quality over inspection alone,
and process or design controls that reduce the chance of human or machine error.
So, while the activity may also reflect continuous improvement in a broad sense, the specific technique used is mistake-proofing.
