激光束焊接在航空工业的知识模型

ORIGINAL ARTICLEKnowledge modelling for laser beam welding in the aircraft industryXiaofeng Sun &Essam Shehab &Jörn MehnenReceived:11January 2012/Accepted:27June 2012/Published online:11July 2012#Springer-Verlag London Limited 2012Abstract This paper presents a knowledge model of the laser beam welding (LBW)in the aircraft industry,which is developed through the utilisation of integration definition for function modelling and concept mapping.The devel-oped knowledge model has been captured in the form of rules and recommendations,which is commonly used as guidelines in this field,and represented with unified model-ling language.The LBW component development com-prises four key stages,namely,structure design,process planning,fixture fabrication and component fabrication.This has been achieved through the adoption of a three-phase qualitative research methodology:data collection and analysis,knowledge model development and validation.The captured knowledge in the form of rules and recom-mendations has developed an understanding of the LBW in the aircraft industry and improved the structure design and process planning from joint type selection,structure dimen-sion definition and process parameter optimisation,etc.A prototype handbook has been developed based on skin –stringer connection of aircraft fuselage to guide designers and engineers directly in developing laser beam-welded fuselage panels.The procedure of knowledge modelling for the LBW as well as the methods and tools adopted can be applied to other processes.The developed knowledge model has been validated through a case study.Keywords Laser beam welding .Aircraft industry .Structure design .Process planning .Knowledge modelling1IntroductionAlthough the application of composites has been increasing dramatically recently,reaching 50and 53%of the structure mass for B787and A350,respectively,light metals,such as aluminium and titanium,still account for over 30%of the structure mass [16].The development of the third generation of Al-Li alloys and Al-Mg-Sc alloys illustrates that metal technology in the aircraft industry will keep developing [12].Thus,a study of technologies and manufacturing processes which focuses on these light metals still has great potential.The laser beam welding (LBW)process has been develop-ing rapidly in recent decades as it is possible to manufacture joints of most light metals and their combinations for its high power intensity [21].It is a trend of the development of the metal fuselage in the aircraft industry as it is capable of inte-grating and simplifying the structure [20],as well as reducing the weight and cost [23],which meet the main concerns of the aircraft industry.Furthermore,the high production rate and automation of LBW can easily solve the shortage of the tradi-tional riveting process which is intensive in process time [7].Structure design and process planning are always guided or restricted by rules and recommendations in the aircraft industry to reduce mistakes induced by individuals.Thus,it will contribute to the application of the LBW process in this field if knowledge of the process is captured in the form of rules and recommendations and utilised to guide structure design and process planning.However,such rules and recommendations for the LBW process are still lacking in the aircraft industry today.2Literature reviewKnowledge modelling is a process to create knowledge,which is a key procedure within knowledge managementX.SunShanghai Aircraft Manufacturing Co.,Ltd.,Shanghai 200436,ChinaE.Shehab (*):J.MehnenManufacturing and Materials Department,Cranfield University,Bedford MK430AL,UKe-mail:e.shehab@Int J Adv Manuf Technol (2013)66:763–774DOI 10.1007/s00170-012-4364-0and is necessary for a company to innovate products and processes.Davenport and Prusak [6]believe that knowledge modelling contributes to a developed understanding of the knowledge,including knowledge source,the input and out-put,the flow of knowledge and other variables.Mohammad et al.[15]has developed two different frameworks for capturing tacit and explicit knowledge,which are concise and cost efficient and could be used by most large organ-isations.A knowledge web-based system is developed to support collaboration in a global engineering environment [19],which is capable of distributing the product life cycle information and knowledge effectively.For material pro-cessing,Rentzsch et al.[18]recommend knowledge map-ping to locate knowledge about the impact of process stages to the product attributions.With this method,the impact of every process stage on every product attribute can be cap-tured and visualised systematically.Hunter et al.[11]sug-gest a knowledge template that defines the common entities and inference processes in the fixture design process for machining,which is able to be reused to other types of fixtures uses like assembly or welding.Wang et al.[24]proposes a rough set-based knowledge modelling method for the aluminium alloy pulsed gas tungsten arc welding process to obtain the knowledge and make it easily under-stood and revised,which is regarded as the basis of the intelligent control of the welding process.LBW is a fusion welding process which is capable of joining two or more pieces of material by the interaction of the laser beam and the material surface (American Welding Society (AWS)[2]).There are two distinctly different modes of LBW which are commonly referred to as conduc-tion mode welding and keyhole mode welding.According to the different energy sources,LBW can be classified as single beam welding,dual beam welding and laser-X hybrid welding (X is a different welding method)as illustrated in Fig.1.For a T butt joint,dual beam welding is preferred for lower distortion resulting from symmetric welding.Single beam welding for this configuration easily causes residual stress and distortion [8].Laser-X hybrid weldingcombinesFig.1Laser beam welding methods (AWS 2010)Fig.2A typical structure of a skin –stringer connectionthe advantages of both welding technologies because it introduces a secondary energy source to the weld pool area.Schubert et al.[21]state that LBW is capable of manu-facturing joints of most light metals and their combinations,such as aluminium,magnesium and titanium,because of its high energy density.Brenner et al.[4]compare LBW with riveting and found that the LBW process illustrates signifi-cant advantages,such as weight reduction of the aircraft fuselage panel,operation cost saving and corrosion resis-tance improvement.Other advantages,such as improvement of production rate and simplicity of fixture are also remark-able.Rendigs and Knower [17]found in their research that the LBW speed can reach 8to 10m/min while the compa-rable riveting process is only 0.15to 0.25m/min.It is two times of the automatic riveting speed [14].Recent research by Li et al.[13]confirm that the LBW process gains more advantages from high power density and welding speed,such as a small heat affected zone,low distortion,high joint strength and high production rate,compared with traditionalwelding process,such as gas metal arc welding.Walz [23]proposes a solution to reduce the influence of high capital cost of a LBW system by sharing the system to other processes,such as laser cutting,surface hardening and trim-ming.Because LBW is an accurate process,close fitting,well clamping and exact positioning are required;otherwise,the accurate beam/joint alignment cannot be achieved and the workpiece cannot be welded properly.It is found that a stable LBW process depends on defining and controlling the processing parameters which influence process stability for high-quality welds at high welding speeds [5].The laser power [25],welding speed [1]and focal position [5]have been studied and identified to be the most important process parameters for the LBW process as they are related to a hidden parameter called energy density which is a key factor of penetration welding and will influence the weld formation.All these three parameters are found to have great influence on tensile strength of the welds [1,5,25].Anawa et al.[3]develop a mathematical model to describe the influence of theseTable 1Sample of questions and their responses Sample of questionsResponseQ1.For chemical-milled skin,what tolerance is usually given in the design stage?Are there any rules?To investigate the design tolerance and rules of chemical-milled skins Q2.How to verify that the whole LBW procedure is under control?What are the vehicles?To investigate the method of process control Q3.How to locate and clamp the skin?How to define the fixture tolerance?To investigate the method and tool for skin locating and clamping,as well as the fixture toleranceJointWelding speedFocal opticsLaser PowerProtection gasFiller metalMaterialProcess control StructureProcess SpecificationMaterial controlEquipment ProcedureProcess parameters ProcessFacility controlDesign factorsProcess factorsProduct Resource Personnel Fixture GeometryDimensionToleranceWeldbilitypreparationFig.3A concept map of design and process factors for laser beam weldingparameters on the fusion zone area and to predict its value, which is capable of optimising the process parameters.The utilisation of protection gas[25],filler metal[9,26]and joint preparation[5,10]have also been studied and found effective to the final weld.LBW is a possible solution that contributes to weight reduc-tion of fuselage panels and has been studied by many research-ers.However,most of these research studies are about weld properties of a certain material based on experiments.There are only a few research studies about knowledge modelling of the LBW process and even fewer about knowledge modelling of the LBW process in this field in the form of rules and recommen-dations,aiming to guide structure design and process planning. 3Research methodologyThe approach adopted in this paper to build the knowl-edge model for the LBW process in the aircraft industry is based on a literature review and investigation in prac-tice.A qualitative methodology was adopted in this paper,using the primary tools of interviews,question-naire and literature review to collect data and information and using concept mapping,rules and recommendations, integration definition for function modelling(IDEF0)and unified modelling language to build the knowledge mod-el.The research methodology comprises three major phases:data collection and analysis,knowledge model development and validation.Data collection and analysis is essential for knowledge model development as the final results will be greatly influenced by the efficiency of data and information. Thus,a questionnaire,a number of semi-structured inter-views and a comprehensive literature review have been conducted in this phase to collect enough efficient data and information.The semi-structured interviews were conducted with specialists from an aerospace company in China to collect information from industry.Based on this,concept mapping has been utilised to analyse and categorise the collected information.In the second phase,process mapping with IDEF0and concept mapping are used to further analyse the LBW process in the aircraft industry,based on the collected data in the previous phase.An IDEF0map was built for the LBW structure development procedure to structure the col-lected information and identify the considerations of this procedure.Then the knowledge about these considerations can be identified,captured and represented,so as to develop the knowledge model.The skin–stringer connection of an aircraft's low fuselage panel(see Fig.2)has been chosen as the case to be studied in the third phase because it is a typical structure in the aircraft industry.The proposed knowl-edge model is applied to this specific component for validation.FinalSDRR: Structure Design Rules and RecommendationsPPRR: Process Planning Rules and RecommendationsQC: Quality ControlFig.4Top-level route map oflaser beam welding componentdevelopmentFig.5Develop laser beam welding component4Data collection and analysisThe semi-structured questionnaire was designed to capture data on fuselage panel structure design (including geometry,dimension and tolerance),LBW process planning and fix-ture design.Eleven experts and engineers from a leading aircraft manufacturing company in China were interviewed in this stage,including three structure designers,two man-ufacturing engineers,two fixture/tooling designers and four LBW process researchers.Seventeen questions were designed.Table 1illustrates three examples of questions and their responses.The question “For chemical-milled skin,what tolerance is usually given in the design stage?Are there any rules?”was designed to investigate the design tolerance of chemical-milled skins,whilst the question “How to verify that the whole LBW procedure is under control?”was asked to investigate the LBW procedure is followed.It is widely accepted in the manufacturing industry that the data and information of each production can be divided into three domains:product,process and resource.This is defined in the structure of ISO 10303-214(ISO/TC184/SC4)and other standards.It is obvious that the LBW process in the aircraft industry should follow this basic principle.In this paper,product information includes design factors induced in the design stage,such as structure dimensionC7: material specification C4: current manufacturing capability O1: material choice O2: structure model O3: technique requirement O4: quality control plan O 5: work order O6: procedure O7: work instruction O8: NC code O9: fixture design O10: fixture O11: final product O12: best practice or lessons learntFig.6Decomposed map for develop laser beam welding componentC2: strength requirementC3: rules and recommendationsC4: current manufacturing capability Fig.7Design structure for the laser beam weldingand tolerance,whilst process and resource information means process factors induced in the process planning stage,such as procedure,process parameters and fixture (see Fig.3).The LBW process capabilities are greatly influenced by these factors.Based on the collected information from the questionnaire,semi-structured interviews and literature review,all the LBW process-related information is classified as design factors and process factors,i.e.two aspects.Furthermore,the design fac-tors are further categorised as material and structure aspects,while the process factors are categorised as procedure,processparameter,fixture design and process control,i.e.four aspects.A concept map including all of this information has been built to show the inter-relationships of these aspects,as illustrated in Fig.3.This provides a foundation for the knowledge modeldevelopment.C3: rules and recommendationsC4: current manufacturing capability C5: other regulations of the company Fig.9Plan process for the laser beam welding componentRRSSDRRProductGeometryDimension Telorance PPRRProcessProcedure Laser powerFocal positionWelding speedFiller metalShielding gas Joint preparationResource FixtureFig.10Categorisation of captured knowledge about laser beam welding5Knowledge model development5.1Laser beam welding component development procedure The top-level route map of the LBW component development procedure in the aircraft industry is illustrated in Fig.4.The whole procedure was broken down into four key stages,namely,structure design,process planning,fixture fabrication and component fabrication.The design and process planning is guided and assessed by certain rules and recommendations to ensure the design and process quality,while the fixture and component fabrication are assessed by quality control require-ments.Rules and recommendations play an important role in this procedure as it is possible to make the design and process suitable for LBW at the conceptual design stage so as to reduce the cost of rework after releasing the design and process.IDEF0was utilised to build a process map of LBW component development procedure for its advantages inprocess knowledge modelling as shown in Fig.5.The main inputs of LBW component development include upstream design inputs (including surface geometry,frame plane and stringer axis)and raw materials,whilst the outputs include final product as well as best practice or lessons learnt.The procedure is controlled by geometry restriction,strength requirement,structure design rules and recommendations (SDRRs)and process planning rules and recommendations (PPRRs),current manufacturing capability,other regula-tions of the company,material specification and process specification.Personnel (including structure designers,pro-cess engineers,fixture designers and welding operators),tools (including computers and design software etc.),Inter-net/intranet and facilities (fixture fabrication equipment,LBW equipment etc.)are the main mechanics of this procedure.This procedure contains several stages according to the top-level route map.Thus,a decomposed IDEF0map was developed to further analyse this procedure as illustrated in Fig.6.As “fabricate fixture/tooling ”and “fabricate LBW component ”are both controlled by the outputs of the “plan process for LBW component ”,they are not considered as key stages influencing the LBW process capabilities.Most of the LBW process variables are defined and prepared in the design and planning stages.Thus,the identified LBW considerations have been focused on structure design and process planning.5.1.1Structure design considerationsThe design structure for the LBW component was decom-posed into “design skin structure ”,“design stringer struc-ture ”and “design weld seam ”as illustrated in Fig.7.Additionally,the joint type as well as the structure for skin and stringer should be selected before the design isconducted.Fig.11Example of rules and recommendations for productdomainFig.12Example of rules and recommendations for resource domainOne of the main considerations for LBW structure design is the material,including what material to choose and how to ensure the quality of the material.The weldability of materials is the first influencing factor of material choice because it determines the weldability of the component directly.Material with better weldability as well as high strength and toughness is preferred for laser beam-welded component.To ensure the quality of material,a material specification defining the trademarks of materials as well as suppliers is specified during this stage to give the process planning a guideline or regulation for material preparation.The joint structure should adequately fulfil its service requirements,and the configuration and size should bepractical for LBW.The dimension of the skin is limited by the LBW equipment and the process margin.If there is no special requirement,the standard extruded “L ”profile (see Fig.8)with simple section geometry is preferred and a profile structure with various thicknesses should be avoided.For any developed aircraft,it is necessary to demonstrate that safety and airworthiness will be given throughout the whole lifetime of the structure.Thus,proper technique requirements should be established;the most important one is process specification,containing all the information and requirements for a stable process.Weld defects criteria should also be established so that the welding results can be assessed.However,the requirements should also bepracticalFig.13Example of rules and recommendations for processdomainFig.14Schematicrepresentation of laser beam welding in the aircraft industryfor the current LBW process capabilities.High technique requirements will not provide extra safety but will increase the operation cost and make the process uneconomic.5.1.2Process planning considerationsFigure 9illustrates the decomposed IDEF0map for the plan process of LBW component.This action is decomposed into “plan LBW process ”,“plan skin fabrication process ”and “plan stringer fabrication process ”.The fabrication processes of skin and stringer are out of scope of this paper and restricted by the LBW process;thus,they will not be discussed in this paper.The main considerations are identified and classified into two aspects:process and resource.It is necessary to develop and establish a reliable and validated procedure to make sure that the whole fabrication process is under control and stable because it is a focus of airworthiness.The influence from each stage of the proce-dure should be considered in order to improve the results.Furthermore,the procedure should be validated within the industry environment as different conditions may affect the results.High-quality laser welds are obtained only after opti-misation of the key process parameters.So the process param-eters should be optimised through performance testing andverification experiment,and the optimised parameters should be defined in the process specifications.Resource is always a strong support of a process;no process can be completed successfully without resource.It can be categorised as material,equipment,fixture and personnel in the aircraft industry.The considera-tions include the quality of material,the accuracy and capability of the equipment,the efficiency of the fixture and the certification of operators.Taking fixture as an example,the workpiece should be located and clamped with a specific fixture to ensure good fit-up of parts and minimise gap to achieve the required laser beam/joint alignment tolerances.When designing the fixture/tooling for LBW,the accessibility of the laser beam to the joint as well as the shielding gas should also be considered.5.2Knowledge captureBased on the identified structure design and process planning considerations in Section 5.1,knowledge about these consid-erations is captured as rules and recommendations.The whole structure of the rules and recommendations set includes two aspects,SDRR and PPRR as shown in Fig.10.Introduction Terms and definitions include include include includeincludeincludeAdvantages and disadvantages LBW handbookApplicationsStructure designmanualProcess planningmanualJoint type recommendationProcess selection recommendation Fixture design recommendationEffect of welding speed Effect of laser power Fig.15Content of prototype of LBW handbook for aircraft fuselage panel developmentFig.16Refinement of the stringer structure for laser beam weldingRules check whether the structure designing and process planning are respecting the considerations.They are made up of a condition (“IF ”)and an action or statement (“THEN ”).Recommendations suggest the suitable structure design and process planning solutions from experience,experiments and/or literature.Three examples of rules and recommendations for aluminium LBW process in the aircraft industry are shown in Figs.11,12,and 13,regarding to structure design,process and fixture,respectively.5.3Knowledge representationBased on the product,process and resource (PPR)model and identified considerations,a further developed schematic dia-gram was built to represent the LBW process in the aircraft industry as shown in Fig.14.Before conducting LBW fabri-cation,component design for LBW,including joint type se-lection,skin and stringer structure design and weld definition and process planning,including LBW process definition,the process parameter optimisation and resource preparation must be identified.All of these aspects can be guided by the developed rules and recommendations.A prototype of the LBW handbook for the aircraft fuselage panel was developed to illustrate the implemen-tation of the knowledge.Figure 15presents the content of the handbook,including an introduction of the principle,advantages and disadvantages as well as the applications in the aircraft industry to develop an understanding of the LBW process in the aircraft industry.The structure design and process planning manual guide designers and engi-neers on how to design a structure suitable for LBW,how to design a fixture to achieve accurate locating and clamping as well as good fit-up and how to optimise process parameters to gain a sound as-welded geometry.Each rule or recommendation is described and explained in detail,based on which,a complete understanding of the rule can be gained and the aim of sharing the knowl-edge can be achieved.6Validation of the developed knowledge modelIn order to demonstrate the potential weight reduction,a fuselage panel from a commercial aircraft was chosen for the case study.The panel was originally designed for rivet-ing with a “Z ”-type stringer and the dimension is 1,731×2,786×530mm.The material for the skin is Al-Li alloy 2198while the material for the stringer is Al-Li alloy 2099,both having good weldability.CATIA V5R18is used for structure design and weight calculation.Following the rules and recommendations for structure design,the stringer is modified from “Z ”type to “L ”type (see Fig.16).The weight of a low fuselage panel before and after design optimisation is shown in Table 2.The calculated weight reduction is 8.89%.This result corresponds with the data obtained from the literature,namely 5%[4]to 10%[22]of weight reduction.Experiments were carried out in Commercial Aircraft Corporation of China to validate the effect of laser power (P )on as-welded geometry.The experiments for testing the effect of P to weld depth (H ),weld width (W )and the angle of weld profile (γ)were on condition that welding speed (V w )03.8m/min and feeding speed (V f )02.7m/min and the structure of these specimens is illustrated in Fig.17with dimensions of 200×100mm.The micrographs of weld geometry in different laser power are shown in Fig.18,which prove that the weld depth and width increase withTable 2The weight of a low fuselage panel before and after design optimisation StateDimensionMaterialMass (kg)Before 1,731×2,786×530mm Al-Li alloy 2198(skin)59.153Al-Li alloy 2099(stringer)After 1,731×2,786×530mm Al-Li alloy 2198(skin)53.893Al-Li alloy 2099(stringer)Fig.17Schematic diagram of specimen structureP=1.9KWP=1.6KWP=1.7KW P=1.8KW 1mmDepthFig.18Effect of laser power to weld profilethe laser power.When the power is low,the welding mode is likely to be conduction welding and the weld pools at both sides of the T butt joint are separate.With the increase of laser power,the two pools become united and the weld angle decreases which results in a concave weld profile.The experiments carried out for testing deflection were on condition that V f 02.7m/min and the dimension of speci-mens is 600×150mm.The deflection include deformation (δ)and angular distortion (φ).Figure 19illustrates the effect of linear heat input (E ′)to deflection,which proves that both δand φincrease with the E ′.The deflection is thought to be mainly caused by solidification shrinkage,which increases with the E ′.As E ′increases with the P at the same time,thus,if P increases,the deformation increases.7Conclusions and future researchThis paper has described the knowledge modelling for the LBW process in the aircraft industry,which is a necessity for expanding its application.A set of rules and recommen-dations as well as a prototype handbook was developed to guide the designers and engineers for structure design,pro-cess parameter optimisation and fixture design.Some key rules were selected and validated through case studies and experiments.The results of this research can be summarised as follows:1.Structure design rules and recommendations guidestructure designers to make design suitable for LBW;2.Process planning rules and recommendations guidemanufacturing engineers to optimise process parameters to achieve the required as-welded geometry;3.Fixture design rules and recommendations give basicguidelines to the fixture designers to make their design suitable for LBW;4.The prototype handbook has contributed to the under-standing of the LBW process in the aircraft industry and detailed the application of rules and recommendations.This research focused on LBW of skin –stringer connec-tions on a fuselage panel because it is the major source of weight reduction and is a simple repeating and time con-suming job which is extremely suited to LBW.The rules and recommendations for skin and stringer structure design canonly be applied to the aircraft industry,which is the limita-tion of these rules.Furthermore,only the effect of process parameters on as-welded geometry was studied for process planning;the effects of these parameters to defects as well as the interactions of these parameters were not covered,which also limits the contribution of these rules and recommenda-tions.Thus,the effect of process parameters on defects,such as pores and hot cracking,is a possible topic for further research,while the interactions of process parameters is another one.Both studies of these two topics are capable of enhancing the rules and recommendations.The knowl-edge of LBW process can be enriched if a quality control system or handbook of LBW process in the aircraft industry can be developed.The development of an advisor system which is compatible with the structure design and fixture design software can further implement these rules and recommendations.Acknowledgments This work was supported by the Commercial Aircraft Corporation of China (COMAC).The authors would like to thank Dr Hongbing Liu and other interviewees of COMAC for taking part in the questionnaire and semi-structured interviews,as well as Dr Xiaohong Zhan of COMAC and Mr Suder Wojciech of Cranfield University for validation of the developed rules and recommendations.References1.Al-Kazzaz 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