How the “lower spar” is manufactured at voestalpine BÖHLER Aerospace

On average, the journey from the first production steps to installation of the finished component in the aircraft takes two years. We follow a “lower spar”—a piece connecting the aircraft wings and engine—on a small part of this journey: its production at voestalpine BÖHLER Aerospace.

Of all the companies in the High Performance Metals Division, voestalpine BÖHLER Aerospace is the one that has dedicated itself almost entirely to serving the aerospace sector. It produces highly stress-resistant drop forge parts for this demanding customer segment. One of these parts is the “lower spar,” a safety-critical component located in the pylon (center wing box), which connects the aircraft wing to the engine. At voestalpine BÖHLER Aerospace, the lower spar goes through countless production steps on its journey from bar-shaped pre-material to almost ready-to-install aircraft part.

Step 1: pre-materials warehouse and the tool and die workshop

The lower spar production chain starts in the pre-materials warehouse and the tool and die workshop. It is here that the pre-material—bar stock made from stainless chrome steel—is received from the supplier and carefully inspected. This step is essential, as parts for the aerospace industry are exceptionally safety-critical and must precisely meet the set standards and specifications at all times. The bar stock is subsequently marked and stored in the fully automated high-bay warehouse. Process cranes automatically transport the material to the connected sawing machines. Here it is sawn into smaller forged bars, which are prepared, marked, and passed on to the next step—press forging.

Goran B. prepares the input material for the start of the Lower Spar production.

Step 2: press forging

During press forging, the bars pass through a total of 17 production stages. In each stage, the piece comes a step closer to its final form, with the key processes ensuring its metallurgical properties are retained: from preforming on the new, state-of-the-art hydraulic high-speed forging press, prepressing on the screw press, to final pressing in which the material reaches its target contours. Lastly, in a two-stage heat treatment process using special furnaces, the part is given its final mechanical properties as specified by the customer. During stringent output controls and quality checks, the entire product—forged part plus documentation—is then once again meticulously controlled by trained specialists. After that, the lower spar is ready for the next stage in its journey.

Stefan Z. checks whether the Lower Spar is on the right path to its final shape.

Step 3: testing

Once the lower spar has completed its journey through the press forging stages, it is subjected to three major, and particularly sensitive, processing steps. Firstly, the part is manually processed, polished, and any burring removed. This step is called final cleaning, and is essential to guarantee that there are no flaws in the surface of the part. During the main testing procedure, fluorescent magnetic powder is then used to check the part for any cracks and to ensure the surface is flawless. The part also undergoes hardness testing, to verify the quality of the heat treatment process, which followed the forging. Employees working in test engineering need to have undergone extensive, globally standardized training before being permitted to carry out the tests. After final approval, the lower spar heads to its final stage—finishing.

In Stefanie S.’s case, the component has to pass the hardness test before its further journey.

Step 4: finishing

Once the forged lower spar reaches the finishing stage, jet cutting is used to remove a test piece, designed for this purpose, which is then taken for external testing. After that, the part is given its final marking in strict accordance with the customer specifications. Then the part undergoes optical measurement to check that the dimensions of the forged part are precisely as required. The surface of the lower spar is then machined to ensure its flatness falls within the narrow tolerance limits. After machining, tactile measurements are taken to (largely automatically) check its dimensions once again, and the processing of the forged part is verified. Once all these steps have been completed, the lower spar is delivered to the customer for finishing, before being later installed in the aircraft.

Dieter M. accompanies the Lower Spar during the last steps before delivery.

#voestalpineanbord—about the Group’s focus on aerospace

voestalpine has been an established supplier to the aerospace industry for around 100 years. The Group manufactures extremely complex, highly stressed, safety-critical components for renowned customers worldwide so that virtually every aircraft flies with a piece of voestalpine. After the severe turbulence during the COVID-19 pandemic, the company with its focus on aerospace is providing insights into the very special (aero)dynamics of this business area.