Human error is a fact of life. No amount of training, procedures, or supervision can eliminate it entirely. However, steps can be taken to reduce the likelihood of it having a negative impact on one’s business.
That is what Donnelly Custom Manufacturing Company set out to do two years ago. An injection molder of aircraft seats and components, as well as other plastic parts, the company prides itself on best-in-class processes, continuous improvement, and commitment to quality.
However, even with Lean and Six Sigma practices in place, quality improvement can plateau. What’s holding progress back? A significant driver is the inevitable human error.
In the business of short-run molding, where Donnelly operates, complexity is a way of life. And complex operations mean prepackaged continuous-improvement tools are not always the answer. So the company took lessons learned from its work with Training Within Industry—a Lean technique used to prepare supervisors to rapidly and consistently train employees to solve problems—and developed a program that would train employees on the concept of mistake proofing.
Mistake proofing is already a part of Lean practices. However, most applications focus on taking mistakes out in the design phase and are process-centric more than people-centric. At Donnelly, mistake proofing addresses the human side of continuous improvement. It teaches employees throughout the company preventative measures designed to decrease the defects caused by errors.
In one instance, Donnelly found that nine events over one year caused the company to fail to meet the quality goals set by a customer. Upon further analysis, Donnelly discovered most of them were due to simple human error. Lean doesn’t eliminate these, but people-focused mistake proofing can. Applying mistake proofing resulted in a reduction of reject incidents due to human error by 75% year over year and reduced overall parts-per-million defect measures by two-thirds.
The practice first teaches all employees why mistakes happen, using scientific research of human behavior. Employees are then shown how to analyze jobs to reduce error, thereby improving quality and increasing output. This develops and prepares people to become both problem identifiers and problem solvers. As a group, employees break down a job to identify the specific mistake(s) and causes, brainstorm possible improvements, evaluate and select the best solution, and apply the countermeasure.
One simple way to look at the process is to consider a railroad crossing. Planners had to determine the best solution at each crossing to avoid mistakes made by drivers that lead to accidents. Results ranged from building a bridge to installing a gate to simply posting a sign and warning light (depending on risk, cost, and effectiveness of each option). Even though people know to yield at a railroad crossing, human error in decision making or action is inevitable and therefore requires the mistake-proofing process.
In the aerospace industry, Donnelly took to the task of addressing missing inserts in molded parts for B/E Aerospace, a leading supplier of commercial aircraft seating and other interior products and services worldwide. One troublesome part requires 24 pegs of two different sizes to be welded on. Before the sonic welder takes over, the operator needs to place the correctly sized peg into each hole. Mistakes consisted of putting the wrong peg into a hole or forgetting the peg altogether.
Using the mistake-proofing process, a team got together, analyzed the errors, and identified many possible solutions. It is a low-volume part, so further automation was not a viable option. The team decided to create a holder for the 24 inserts so the right numbers of long and short pegs were available to the operator for each part as well as a color-coded template. This template fit directly on top of the part, and holes with numbers, colors, and the designations “long” and “short” appeared over each opening that needed a peg.
Now the operator can insert the right pegs into the corresponding holes in sequence, from one to 24—eliminating the errors of skipping an insert or inputting the wrong size. This solution has proved an effective countermeasure, resulting in zero defects since implementation.
These practices are suitable for nearly any low- to mid-volume manufacturer looking to take Lean to the next level. Mistake proofing can teach an organization to look at challenges not as problems but as opportunities for innovation.
Sam Wagner, Director of Advanced Manufacturing, Donnelly Custom Manufacturing, wrote this article for Aerospace Engineering.