Forming for the final frontier

Westworld Consulting meets John Hammond, AMRO Fabricating Corporation's vice-president, sales and marketing and discovers how the California-based manufacturer is leading the way in space manufacturing and bringing its expertise to bear in the aerospace sector.
Manufacturing for the space sector is a complex business, it pushes the limits of any manufacturer's forming and machining capabilities because it requires complex components built to the highest tolerances. AMRO Fabricating has become a leader and expert in the forming of complex structures, known as Isogrid and Orthogrid patterns, which are used to ensure that spacecraft and now aircraft are stronger and lighter than ever before.

Originally developed by General Dynamics in the late 1950s, Isogrid structures typically consist of a skin that incorporates a repeating pattern of triangular stiffening ribs. This structure is usually machined from a single piece of material, like aluminium-lithium alloy, leaving stiffened ribs that display exceptional strength-to-weight and stiffness-to-weight characteristics. The repeating pattern is made up of equatorial triangles and this exploits the simple principle that triangular structures are extremely strong and distribute load evenly and efficiently. Any damage to the structure means that load is transferred to the surrounding area. Isogrid is able to withstand both compressive and bending loads, making it ideal for space and aerospace applications.

Orthogrid has similar benefits to Isogrid, however it differs in terms of its structural pattern – the stiffening ribs use a square or rectangular waffle pattern rather than triangular. This produces a structure that is lighter than Isogrid but the trade-off is a lower stiffness profile that is generally less forgiving.

Isogrid and Orthogrid patterns have long been used in space programmes, where they have been integrated into fuel tanks, boosters, inter-stage adapters and crew modules. Pattern selection is primarily based on the loads that the structure will encounter. Examples of real world application include the Space Shuttle's external fuel tank and NASA's Orion Crew Module - these use Orthogrid patterns, whilst the Atlas V and Delta IV rockets use Isogrid.

<Refining and developing>

Founded in 1977, AMRO first entered the Isogrid arena during the mid-1980s when it was selected and trained by McDonnell Douglas (MD) to become their go-to source for Isogrid panels. Until that time MD had formed all of its Isogrid panels in-house, but it realised that it would need additional support to form the payload fairings for the Titan IV heavy launch vehicle. AMRO was already an approved supplier to MD and AMRO's equipment and existing skills made them natural partners.

Since that time AMRO has been continuously refining and developing its Isogrid and Orthogrid manufacturing processes through a range of different space programmes, developing proprietary tooling and methodologies that have enabled it to become the leading forming expert in North America - producing parts that no others can.

“AMRO has complete turnkey machining, forming, heat-ageing and inspection equipment and undertakes all of its work in-house,” states John Hammond, vice-president, sales and marketing for AMRO. “This translates to better process control, quality and on time deliveries. Forming is a craft/art form and the design drives the process limitations. We have seen many configurations and we generally know what can and cannot be achieved. However, development is mandatory to drive out all the manufacturing risk. We are always pushing the limits of the forming and machining process and we like to work closely with the engineering community to arrive at a producible product.

“Through many years of development and experience, we have grown our forming capabilities to allow product designs to be more monolithic and complex. As an example, we have reduced parts counts in assemblies since we are able to form large thick sections to exact tolerances. This reduces product weight, cost and schedule. These advantages are significant with launch vehicles and spacecraft.”

Advances in machining equipment and AMRO's proprietary tooling, coupled with over 40 years' experience, have had a big impact on their manufacturing process.

“Parts are now designed with Geometric Dimensioning and Tolerancing (GD&T). Modern, repeatable and reliable machines are necessary to produce these very complex structures and meet the demands of today's designs - most profile tolerances are extremely tight. Additionally thermal compensation creeps into the equation and this must also be normalised.”

As specialists in lightweight metallic structures, AMRO has many high profile clients including Boeing, Lockheed Martin, NASA, SpaceX and ULA – which has meant involvement in programmes like Titan IV, Delta III, Delta IV, Atlas V, Orion, Ares I, SLS, Space Shuttle and Falcon 9.

Early engagement with the engineering community and true passion for space exploration has been key to AMRO's popularity with its customers and its success with complex forming and machining of lightweight metallics.
Such a customer-focused philosophy has also been applied to AMRO's other core competencies, which includes Major Assembly Tooling and Ground Support Equipment (GSE) for the aerospace industry – where AMRO is a preferred supplier and an excellence award holder for Boeing having produced major tooling for 787 and 777.

<Aerospace sector adoption>

Aircraft manufacturers are now realising the benefits of Isogrid and Orthogrid and incorporating patterns into aircraft design, which is an inevitable transfer of the technology. Airbus is one such example - on the A350, rib 1, Airbus introduced an aluminium-lithium isogrid pattern for the side-of-body rib, centre wing box. What would otherwise have been a complex series of spar caps and stiffeners fastened together is now a single, lightweight, machine formed isogrid part. Using Isogrid not only reduces weight, but also reduces assembly time for Airbus.

This migration and use of Isogrid and Orthogrid patterns on commercial aircraft presents significant opportunities for companies like AMRO who have a long history and extensive experience in producing these kinds of structures. As a business that operates internationally and serves customers on both sides of the Atlantic, Isogrid and Orthogrid for the aerospace sector is a natural progression for AMRO.

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