In early 2022, Van’s Aircraft started producing some of its metal aircraft parts using laser cutting processes. This article addresses questions and details around the process and the testing Van’s performed before making the decision to leverage the laser cutting process.
Q: Generally, what parts will Van’s manufacture using laser cutting? (skins, ribs, stiffeners, brackets, etc.)
Internal parts made from sheet material that have passed fatigue testing will be laser cut. Skins are all punched with vinyl protective coating on both sides. Only thinner sheet thicknesses are being laser cut. The parts that are laser cut only need to have the small burr removed along the edge of the part where the laser exited.
Q: Is it a common practice in the aircraft industry to employ laser cutting?
Historically, it has not been standard practice to laser cut aircraft components, but this was based on the technology commonly used 20 years ago when only CO2 lasers were available. Aircraft manufacturers, especially at the large commercial level, now use laser cutting as an approved manufacturing process. Modern high-wattage fiber lasers cut much faster and have a narrow-focused beam. A modern, high-quality fiber laser using the proper operating parameters leaves a very small heat-affected zone that has little if any effect on the fatigue life of a component.
Q: Has Van’s performed testing to ensure the metal does not anneal or suffer any other negative effects (strength, corrosion, etc.) in the area of the cut?
The amount of testing we performed has been a significant contributor to the time it has taken to increase our production rates. We knew we needed to increase part production, but we did not allow this pressure to rush us through the testing process. At Van’s, we have a commitment to testing, a principle that has resulted in the trust in our kit designs over the past 50 years. Our testing results showed little or no change in the fatigue life of the parts – between laser cut parts, punched parts, deburred parts, or parts with a machined edge – for the parts we’ve approved for laser cutting.
Q: What type of testing has been done?
There are several variables that we considered. These included the material type, thickness, reflectivity, coatings such as blue vinyl, and the effect of fabrication operations such as deburring and sandblasting. Variables specific to laser-cutting included laser brand type, laser design type, wattage, cut speeds, focus plane, blowout/refusing of material on the exit side of the cut, and even the cut pattern – i.e., the path of the laser – especially in areas where the laser starts or ends a cut.
Considering these variables, we focused our tests on three areas: stress concentrations related to imperfections on the cut edge (which also exist in punched and CNC edges), stress concentrations along edges and surfaces that are part of the component’s design (such as at notches and corners, which would be present regardless of the way the part was manufactured), and lastly, the effect on fastener holes.
Each set of tests included at least two groups of samples: A control or baseline group, consisting of samples fabricated using Van’s current manufacturing methods (punching or CNC milling, deburring aluminum, sand-blasting steel) and a group of laser-cut, but otherwise identical samples. To ensure a conservative approach, most tests also included a third group consisting of laser-cut samples but skipping some operations such as deburring. Occasionally, a fourth group consisted of punched/CNC parts with no deburring.
For each set of tests, these multiple groups of sample parts were all tested to failure, “head-to-head,” using identical loads. This provided a clear picture of how each manufacturing process impacts the fatigue life of our airplane parts.
Samples included the structural details where fatigue cracks can form: Some samples consisted of various kinds of industry-standard “dog bone” or ”hourglass” shapes, which tests the quality of cut edges and the impact of stress concentrations at corners and notches; Other samples included multiple configurations of riveted and bolted joints.
The validity of these tests was assured by: the recent calibration and certification of our structural test machine, the close agreement between the past few months’ data, fatigue test data that Van’s has accumulated since the late ‘90s (both in-house and using outside laboratories), the FAA’s extensive library of fatigue data and analysis methods for general aviation airplanes, and the fatigue analysis manuals and test reports published by industry and academia since the 1970s.
As of early 2022, testing is still ongoing. We have recently completed fatigue testing of steel samples so that we can soon begin laser-cutting steel parts. We are now working closely with laser cutters to fine-tune settings and cut patterns that we hope will allow thicker aluminum material to be laser-cut.