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Leonardo Times DECEMBER 2013ENGINEERING PRODUCTIVITY
An increase in productivity is required for the European aviation industry to remain competitive in a world with more compe-tition, shorter development timescales, products that are more complex and de-creasing numbers of technically skilled personnel. The development of aircraft electrical wiring harnesses at Fokker Elmo could benefit from an increase in produc-tivity.
WIRING HARNESS DESIGN & MANU-FACTURING
Aircraft wiring harnesses are designed in a 3D digital environment such as CATIA. Fig-ure 1 shows the digital wiring model for the Airbus A350. To efficiently manufac-ture wiring harnesses, flat tables are used as shown in Figure 2. A wiring harness is represented on these tables by means of 1:1 scale production drawings called formboards.
PAST
In the past, before the availability of 3D digital mock-ups, formboard drawings were created by manufacturing a proto-type wiring harness in the 3D physical mock-up of the airplane. This prototype harness was then physically flattened (by force) on a table and a drawing of photo of the contours was made as a blueprint for series production. As the prototype could fit in the physical mock-up, harnesses built with these drawings would fit in the air-craft as well.
PRESENT
At date, preparing a wiring harness design for manufacturing is a repetitive, time-consuming and mostly manual, experi-ence-based process. This is mainly due to the fact that several manual quality checks and adjustments are required to ensure that the 2D drawing matches the 3D digi-tal model such that the manufactured wiring harness (in a flat plane) can be in-stalled in the (3D) airplane without caus-ing damage or requircaus-ing excessive force from the installation operator. Creating a single drawing may take from a few hours up to several days. The formboard design process consists of the following steps: 1. Analysis. Check on quality and com-pleteness of the 3D design definition. 2. Flattening. Transformation of the 3D model to a flat plane.
3. Fitting. Rearrangement of the flat mod-el to fit the given dimensions of a table frame.
4. Dress-up. Addition of manufacturing instructions.
Considering the time currently required to create a high quality formboard, the productivity of the formboard designers could be improved by eliminating manual, repetitive development steps through au-tomation. Knowledge Based Engineering (KBE) is proposed as the design automa-tion technology to increase the process productivity.
KNOWLEDGE BASED ENGINEERING
Dr. ir. G. La Rocca (FPP chair, Faculty of Aerospace Engineering, TU Delft) defines KBE as: “a technology based on dedicated software tools called KBE systems that can capture and reuse product and process engineering knowledge” (La Rocca, 2011). A KBE system allows a user to develop ex-pert systems with geometry handling and data processing capabilities. As such it can be described as the merger of Artificial Intelligence (AI) and Computer Aided De-sign (CAD) technologies. The KBE system used at FPP is GDL by Genworks.
BUILDING BLOCKS
KBE applications can be constructed using flexible parametric building blocks called
Knowledge Based Engineering to support wiring harness
manufacturing design at Fokker Elmo
Increase in aircraft wiring complexity call for manufacturing design improvements
to reduce cost and lead-time. To achieve such improvements, a joint research project
was performed by the Flight Performance and Propulsion (FPP) group and Fokker
Elmo BV, the second largest aircraft wiring harness manufacturer in the world. The
project objective was to largely automate the creation of manufacturing drawings
using Knowledge Based Engineering techniques.
TEXT Tobie van den Berg, PhD candidate at Flight Performance and Propulsion
AUTOMATING WIRING FORMBOARD DESIGN
Figure 1. Wiring in the Airbus A350 digital mock-up. FLIGHT M AG A ZI N E
DECEMBER 2013 Leonardo Times
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3D design exchangeCAD analysisDesign Flattening Fitting Dress-up Production 1.
2. 3.
4.
5.
High Level Primitives (HLP). As opposed to (low-level) CAD primitives such as points, lines and solids, a HLP is a functional ele-ment or parametric building block, incor-porating and reusing relevant knowledge. HLPs have been defined and implement-ed for the main wiring harness compo-nents. Although the wiring harness is a single product, it needs to be represented in both the 3D design definition and the 2D production state. To allow this, wiring harness HLPs are defined featuring geom-etry attributes corresponding to multiple geometric states.
DEVELOPMENT
The research was performed by working for few days a week at Fokker Elmo and with support from the FPP spin-off com-pany KE-works, which specializes in devel-oping KBE applications. Expert knowledge on wiring harnesses and the formboard design process was provided by a team or ‘Task Force’ consisting of senior Fokker Elmo engineers from the design engi-neering and manufacturing engiengi-neering departments. Development of the KBE solutions was done by iteratively identify-ing key process steps and requirements, acquiring, formalizing, implementing (in a KBE application) and verifying knowl-edge in collaboration with the Task Force members. This resulted in three KBE ap-plications: a CAD import application to re-parameterize CATIA generated STEP files (step 1 in Figure 3), an application for anal-ysis and flattening and an application for fitting, dress-up and export of a drawing.
ANALYSIS & FLATTENING
The capabilities of current analysis and flattening tools are limited, requiring time-consuming, repetitive manual work. The automatic flattening provided by the CAD system electrical workbench is un-reliable and requires additional checks and adjustments. Procedures have been developed and implemented in a KBE ap-plication to automatically evaluate the 3D
wiring harness state for potential flexibil-ity violations with respect to the 2D manu-facturing state (step 2 in Figure 3). Flexibil-ity evaluations are performed by means of experiment-based rules, validated by years of industrial practice at Fokker Elmo. A new method for wiring harness flatten-ing was devised that aligns the 2D ge-ometry states of the wiring harness HLPs with respect to each other. This returns 2D models with deformations within allowed limits and the minimum amount of bun-dle twisting (step 3 in Figure 3).
FITTING & DRESS-UP
A flattened wiring harness model is cur-rently adjusted manually to make it fit within a standard formboard frame size. In the KBE implementation this translates to a search problem with multiple quality and manufacturing efficiency objectives such as minimize frame size, eliminate crossings and optimize for manufacturing ergonomics. To ensure that the fitted wir-ing harness state can be deformed to the 3D installation state, the flattened model is discretized into bendable sections for which bending limits are established. Both manual fitting by an engineer and automatic fitting using search methods are constrained by these limits, eliminat-ing the need for time-consumeliminat-ing checks and adjustments. From experimentations with different automatic fitting approach-es, the so-called alignment method, based on manual fitting heuristics, is selected and implemented. This method attempts to align branches of bundles with respect to each other according to a limited set of bending and flipping strategies (step 4 in Figure 3). A formboard frame is automati-cally selected, the layout is adjusted with respect to manufacturing ergonomics and production instructions are added (step 5 in Figure 3). Finally, the resulting drawing can be exported to a 1:1 scale PDF file.
THE POTENTIAL OF APPLYING KBE
The developed KBE applications were
tested using twenty-five 3D digital wir-ing harness models from a current com-mercial aircraft program at Fokker Elmo. Formboard design experts approved the quality of the output formboard draw-ings. The time spent on formboard design tasks was demonstrated to reduce from values in the order of hours to minutes. A conservative calculation indicates that in practice a five-fold productivity increase can be obtained.
The developed formboard KBE suite offers functionalities that are not present in con-ventional CAD systems. The applications can considerably reduce the amount of re-petitive work, while ensuring compliance to physical constraints and manufacturing guidelines.
FURTHER WORK
There are many opportunities to improve and extend the developed KBE applica-tions. Some of the topics that are of inter-est are different optimization techniques for fitting, flattening so-called closed-loop wiring harnesses, change identification and generating semi-3D formboard tool-ing (e.g. with 3D-printed moulds). Work has already started on some of these top-ics by students doing their Master thesis work.
ACKNOWLEDGEMENTS
This research was made possible by the expertise of and close cooperation with Fokker Elmo BV and support from KE-works. FOKKER E LMO B .V . References
1. G. La Rocca, Knowledge Based Engi-neering to support aircraft design and optimization, PhD thesis, TU Delft, 2011 2. T. van den Berg, Harnessing the po-tential of Knowledge Based Engineering in manufacturing design, PhD thesis, TU Delft, 2013, to be published
Figure 2. Manufacturing a wiring harness on a formboard at Fokker Elmo
Figure 3. A wiring harness going through the steps of the KBE supported formboard design workflow
