Airplane wings require hundreds, and sometimes thousands, of holes to be drilled in complex, fragile surfaces with high accuracy, posing two challenges for manufacturers:
- Developing a method of securing parts during drilling that doesn’t cause damage
- Providing an ergonomic work environment, customizable to each worker, that allows them to drill thousands of holes per day without injury
At Spirit AeroSystems in Tulsa, Oklahoma, these challenges were especially pronounced on the drilling stations for the wedge and cove-angle components of the Boeing 787 aircraft wing. Using input from operators and Bosch Rexroth aluminum structural framing, Spirit AeroSystems developed an ergonomic workstation that significantly improved quality, reduced worker injuries, and improved throughput.
The wedge structure is a composite piece of the airplane wing’s leading edge, and there are 10 variations of the part. Each wedge requires around 300 manually drilled holes and the typical production rate is six wedges per day – 1,500 to 2,000 holes per day – no small task for any operator.
“In the automotive industry, probably 90% of drilling is automated, with only about 10% of drilling operations being done manually. In the aerospace industry, the situation is almost the exact opposite,” says Brian Lewis, continuous improvement specialist at Spirit AeroSystems.
The original assembly workstation layout used a standard, flat table to hold the wedge during drilling. But the wedge is contoured, making it extremely challenging for the operator to drill hundreds of holes in precise locations. The part tended to rock back-and-forth on its curved edge, so the operator often had to hold the part with one hand while drilling with the other hand. The lack of control from one-handed drilling, coupled with the odd position of the part, often led to drill-starts where the hole is started in the wrong spot, marking the part and in some cases, producing an out-of-spec, elongated hole.
Additionally, drilling hundreds of holes per day – even on flat, stable parts – requires thoughtful workspace design to ensure good ergonomics. Wedge line operator James Wright was plagued by the effects of poor workstation ergonomics. So, he proposed a rotating fixture – inspired by a rotisserie – that would allow the part to be positioned at any angle and height, depending on the current operator’s preferences. What started as a napkin sketch was taken to Lewis, who accepted the task of making this concept a reality.
Having worked with Bosch Rexroth aluminum framing to build tables, workbenches, and holding fixtures for other areas of the factory, Lewis immediately enlisted the help of Spirit AeroSystems Design Engineer Matt Sheets and Jay Rogers of Pacific Integrated Handling (PIH), in Tacoma, Washington, to help design a wedge fixturing system. PIH is a distributor with more than 20 years’ experience applying Bosch Rexroth aluminum framing to specialized tooling and fixtures.
Based on Wright’s sketch, the team designed the wedge fixture with aluminum framing for structural support, along with a counterbalance system to ease rotation of the wedge – an incredibly heavy part. The fixture is infinitely adjustable in height, and the ability to rotate the wedge allows each operator to set the workpiece at a comfortable drilling angle. To accommodate variations in wedge designs, one wedge end is supported by a Bosch Rexroth size 25 ball rail, allowing the width of the fixture to be adjusted to the wedge’s length.
A workstation design that once required five people to complete five units per day, now has three people completing six to seven units per day. Put another way, on an 8-hour shift, man-hours per part fell about 54%, from 8 hours per part to less than 4 hours. And the company has been able to reallocate resources from the wedge area to other operating stations. Since the fixture was put in use, rework in this area has been reduced by 80%.
Possibly the most important outcome of this new fixture is the improved ergonomics. With the previous workstation design, operators experienced back problems from bending over or leaning in to drill holes, and soreness in the upper body was a common complaint.
“The improvement in ergonomics was immediate,” Wright says. “This fixture, and the ability to adjust it to my specific needs, has really made a difference in my physical well-being. Other areas are looking to replace their old, ‘dinosaur’ tooling and fixtures – typically made of steel – with lighter, more cost- effective, and more ergonomic designs made from Bosch Rexroth aluminum framing.”
Cove-angle carousel fixture
A cove angle is also a part of the Boeing 787 wing – a structural member used in the front slats to produce lift. Like the wedge, there are 10 variations to the cove angle, and each variation requires drilling 168 holes. Cove angles require operators to drill a pilot hole and then a second hole to the specified size.
In the original cove angle workstation, operators drilled one part at a time on a typical, flat workbench. This was inefficient, since no real work was occurring every time the operator had to offload one part and load the next. Damage from drill-starts and out-of-round holes resulted in high rework and scrap rates.
The solution to these issues – a rotating carousel fixture – drew inspiration from a fixture that Sprit AeroSystems had implemented on a smaller scale in the Boeing 737 program – essentially the same part but made from aluminum rather than composite.
Cove angles are approximately 12ft long x 2" wide, making them ideal for loading onto a carousel, supported by Bosch Rexroth aluminum framing that holds five parts at a time. The carousel rotates and locks into place while the operator drills each part and moves in and out, to be closer to or farther away from operators to meet ergonomic preferences.
A monitor mounted to the structural framing displays work instruction and layout of each part. With feedback from a linear encoder, the monitor can be moved down the fixture along the part’s length. As the monitor moves, the drawing displayed corresponds to its position along the part, providing instructions specific to that exact spot on the part. After finishing one part, the operator rotates the carousel and works back along the length of the fixture on the next part.
Although inspired by a B737 program solution, the much larger cove-angle carousel fixture was especially challenging to design and manufacture. One difficulty was making a fixture that could rotate while maintaining enough stiffness to support the pressure from drilling.
Spirit AeroSystems completely outsourced the design and manufacturing to PIH, and the PIH team worked with designers and operators at Spirit AeroSystems to provide a turnkey solution that met the operators’ requirements for ergonomics and simplicity, while meeting Spirit’s cost and timeframe goals.
Since the fixture’s implementation, productivity in the cove angle area has increased by 50%, and like the wedge area, ergonomics vastly improved. The cove angle fixture’s ability to handle five parts at a time also reduced floor space and improved part-flow through the line.
Both the wedge and cove angle fixtures greatly improved ergonomics for the operators, improving productivity and quality. The return on investment (ROI) for these projects was well within the three-year timeframe set by management, based on increased throughput and reduced quality costs. Not only did these projects exceed the company’s ROI target, worker compensation issues also decreased. As a bonus, upper management at Spirit AeroSystems was impressed with the amount of input and level of engagement the operators demonstrated in the design and realization of these two fixturing projects.