Enclosure Manufacturer Compares Missile Skin Scans with CAD Designs

To meet the exacting requirements of a supplier to the U.S. military, Buckeye Shapeform adopted laser-scanning technology that watches for any deviations from the design.

Buckeye Shapeform, based in Columbus, Ohio, has long experience with creating a wide variety of enclosures — everything from electronics housings to lidded tins for scented candles. Recently, the company embarked on a project that required an even higher level of precision: creating housings for tube-launched, optically tracked, wireless-guided (TOW) missiles.

This wasn’t the company’s first foray into crafting missile housings, called skins. But it was the first time the customer had such tight requirements. The skin must mate precisely to the many other components of the missile, and as such it has more than 400 unique critical features. In addition, the skin is not the same thickness throughout; it ranges from four-hundredths to three-eighths of an inch thick at different points.

“They have GD&T [geometric dimensioning and tolerancing] tolerances that were difficult to do with standard measurements or a CMM [coordinate measuring machine],” explained Kevin Kretschmer, engineering manager for Buckeye Shapeform. Although any aerospace project is typically very specific about dimensions and tolerances, Kretschmer noted, missiles call for maximum attention to detail: “They want to make sure this thing explodes when it’s supposed to.”

Before taking on the demanding project, Buckeye Shapeform implemented a new system to verify that all the critical features of the skin are placed correctly. The first part of this system is a Nikon ALTERA CMM with a laser attachment, which performs both coordinate measuring and laser scanning. “We invested in it just for this project, specifically for the tolerances that were required,” said Kretschmer.

At regular intervals, a completed missile skin is taken from the production line and measured with the ALTERA, which collects both CMM and laser-scanning data in its CAMIO software. This information yields a 3D digital prototype of that particular unit, which is compared with the CAD model of the product design in PolyWorks, a 3D metrology platform. Features that perfectly match the original specifications are displayed in green; mismatches are shown in red so the Buckeye Shapeform team can quickly identify them and adjust manufacturing as needed.

The most time-consuming part of the process is setting up the software with the customer’s specifications, said Kretschmer. “The comparison is automatic, but it’s up to the operator to apply the correct GD&T to each specific hole or whatever it may be,” he noted. “[The missile skin] is just a tube with holes in it, but it’s complicated.” Once that task is complete, the rest goes quickly; PolyWorks populates the report for the customer in about 5 minutes, Kretschmer reported.

According to Buckeye Shapeform, conducting these quality checks with scanning data is much quicker and more accurate than manual measuring. “We were the first ones to digitally compare this part,” Kretschmer pointed out. “It’s been made for a long time, but nobody’s ever checked it to the level that we are.”

A Modern Process for the Future — and Past

The “complicated tube” — the metal shell that will encapsulate the payload portion of the missile — is made through a sophisticated process that begins with a design sent by the customer. The Buckeye Shapeform team determines how it will be produced, then uses Solid Edge to design all the tooling it will need. To create a seamless end result that has multiple wall thicknesses but no welds, the company relies on a reverse deep draw process. Metal is pulled (drawn) through a ring to form a cylinder, which is then drawn again in reverse.

During this sequence, various sections the material are ironed to make them thinner. The ability to vary wall thicknesses within the same cylinder is “what sets us apart,” said Kretschmer. “A lot of companies can extrude a tube, but they can’t do that.” Next, the cylinder will move on to be narrowed and expanded to the necessary diameters, have openings machined into it, and be scanned for quality verification.

Buckeye Shapeform has begun shipping the first of its TOW missile skins, and plans to continue building them for some time. There are multiple versions of this product, and the company will continue to use these manufacture and verification processes for all of them, Kretschmer predicts.

Although it’s notable for enabling the missile project, the 3D scanning technology holds promise for other areas of Buckeye Shapeform’s business as well — including its own tools. “The scanner gives us capabilities for reverse-engineering tools we don’t have CAD data on,” Kretschmer explained. The company can collect data about decades-old presses, for example, or tooling that has been modified over the years or was purchased from other companies without documentation.

“It’s been quite a learning curve for us, [but] we’ve learned a lot, and we are starting to it apply to other products,” said Kretschmer, including sheet metal stamping for electronics enclosures.