Siemens PLM Software Blog

What’s so difficult about fasteners when it comes to designing an airframe? You just drill some holes, grab some hardware and bolt the parts together, right? It seems as if it should not require that much thought or discussion.  Well, it’s not nearly that simple says Steve Peck, director of product & market strategy, aerostructures, for the Specialized Engineering Software business segment of Siemens PLM Software.

For example, consider the Boeing 747. The 747-400 has six million parts, half of which are fasteners. See the 747 Fun Facts page.

Keeping track of the enormous number of fasteners in the typical airframe is no small task. From the initial engineering specification of the fasteners to  procurement, installation, inspection and field repairs, there are challenges every step of the way. Think about the design-to-manufacturing process. Typically, designs and specifications can change rapidly, so how do you keep up with an evolving need for different lengths and types of bolts, nuts, collars and washers? Ultimately, the question is how do you keep your program on schedule?

Steve has spent the last decade working with major OEMs and Tier 1 suppliers and during that time he has seen a variety of data that reveals just how problematic and pervasive fastener management can be for aerospace manufacturers. By examining the postmortem analysis of engineering change orders (ECOs) data from a number of programs, Steve found that nearly 40 percent of engineering errors and manufacturing non-conformance were related to fasteners or the holes that they were intended to fill.  The most common issues were:

• Inaccurate Bills of Materials
• Incorrect fastener call outs
• Inadequate edge margins
• Misaligned holes in mating parts
• Assembly interferences
• Material/finish incompatibility
• Incorrect holes provided by suppliers

The root cause of these problems can often be traced to the engineering definition and/or the manufacturing consumption of the data. With hundreds of thousands, if not millions, of fasteners in an airframe, it is hardly surprising to see these issues at the top of the list.

Fasteners account for about half of the parts in an aircraft. Pictured are several hundred fasteners of various sizes and patterns in a wing-to-fuselage attachment joint.

Steve relates a telling comment from an industry veteran at a Tier 1 supplier: “He told me, ‘It’s not the big parts that will get you, it’s the holes that you drill and the bolts that secure them that will inevitably have you on the shop floor engineering a fix late at night.’”

Many companies have implemented a variety of tools and processes in an attempt to minimize the frequency of these costly problems. One of the most effective solutions for improving the fastener management process has been the Syncrofit™ portfolio of software for airframe assembly from Siemens PLM Software. Syncrofit transforms the CAD system into a specialized development platform for airframe assembly design and manufacturing.

In part two of this blog, we’ll examine the variety of ways manufacturers are addressing these  issues as well as how Syncrofit is helping OEMs and Tier 1 suppliers transform the way they are managing their fasteners.

In the meantime, don’t underestimate just how important it is to implement processes that control your fasteners from concept to first flight and beyond. The not-so-humble airframe fastener demands respect!

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Tags: airframe assembly, airframe fastener, ECOs, engineering change orders, fastener management, syncrofit