Welding International 2003 17 (11) 899–904 Selected from Svarochnoe Proizvodstvo 2003 46 (6) 16–21; Reference SP/03/6/16; Translation 3230
A differentiated approach to the computer design of welded structures
LS DENISOV Association of Welders of Belarus, Minsk
S V MEDVEDEV Joint Institute of Problems of Informatics, Academy of Sciences of Belarus, Minsk
The welding production in the CIS countries is characterised by increased (by a factor of 1.5–2) metal requirement, the volume of deposited metal and the consumption of electric energy in the manufacture of welded structures in comparison with the parameters in European countries. Consequently, it is necessary to develop new approaches in the main stages of development, fabrication, inspection and monitoring of welded structures, namely: methods, models and algorithms of the computer design of welded structures and parallel formation of appropriate systems of the quality of welded joints and components as a whole. The processes of technical preparation of assembling and welding production are influenced by the universal means of the computer designs of technical systems. However, the specific features of the preparation of welding production are not sufficiently reflected in universal systems. Experts who are not experts in welding find it difficult, using universal packages, to develop rational welded structures from the viewpoint of the designer and the technologist at the same time. In addition, there are problems with ensuring the quality of fabrication and certification of the resultant products. It should be mentioned that there are only a few teams in the CIS countries, fully concerned with the problems of computerisation of the welding processes and related technologies. There have been individual efficient studies
but the requirements of practice result in the demand for computer integration of both objects and processes of designing welded structures, technologies, organisation of production and the formation of systems of quality inspection. In this article, special attention is given to the solution of the problem of the designer in a specific region in which engineering, constructional and other companies are concerned with the production of components represented largely by welded structures for general applications. It is required to propose a set of computer, design, technological and organisational methods, ensuring the development and fabrication of efficient welded structures with the required service life made of low carbon and low-alloy steels. The current approach to the organisation of welding production in different branches of industry should be differentiated, taking into account the distribution of welded structures into individual groups on the basis of the overall dimensions, weight and form of the welded joints.1 It is assumed that the main types of welded structures in a region and the most characteristic representatives of these structures have been determined in a previous stage (in order to simplify further considerations, Table 1 presents these types of welded structures). The authors of Ref. 2 proposed to examine the welding production in Belarus as some assembling–welding holding, governed
Table 1 P re d ic te d d istrib utio n o f we ld e d struc ture s in Be la rus in 2 0 0 2 , % S truc ture s
M e ta l wo rk ing ma c hine s
Tra c to r c o nstruc tio n
Ve hic le c o nstruc tio n
P ro d uc tio n o f e ngine e ring struc ture s
Agric ultura l e ngine e ring
C o nstruc tio na l, ro a d a nd c o mmuna l e ngine e ring
Ave ra ge d a ta fo r e ngine e ring c o mp a nie s
F la t Be a m F ra me C a sing La ttic e s C ylind ric a l Ma c hine c o mp o ne nts O the r
5.9 13.0 16.4 41.9 2.5 3.7 4.5 2.1
28.3 26.8 17.0 9.3 1.4 8.2 5.1 3.8
37.9 6.4 19.5 21.6 4.6 7.5 0.7 1.9
23.3 32.0 7.2 – 22.2 6.1 4.0 5.1
9.2 1.9 42.0 18.4 6.9 6.5 13.6 1.5
1.0 4.3 38.5 16.1 9.8 19.7 1.6 9.1
17.6 14.0 23.9 17.8 15.8 8.6 4.9 3.9
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Board of Chief Welders of Holding Companies
Metal working machines
Flat
Vehicle construction
Beam
RC of assembling–welding structural–technological design and audit of welded structures
Tractor construction
Frame
RC of computer design of technological processes and quality systems
RC of computer design analysis of technologically essential jigging
Casing RC of computer design of robotised processes for assembling, welding and inspection
Regional Centre of Computer Prediction of Structural–Technological Strength and Service Life of Welded Structures
Lattice
Production of engineering metal structures
Cylindrical
Machine components
Agricultural engineering
Others
Constructional, transport and communal engineering
1 The structure of the virtual assembling–welding holding.
by a board of directors, supporting the application of advanced computer technologies (Fig. 1). Belarus has a considerable scientific–technical and personal potential for the formulation and efficient solution of these problems. The majority of the companies of the regional assembling–welding holding are carrying out work in the introduction and application of information technologies in design, communication, circulation of documents, electronic purchasing, etc. The following scientific–procedural and organisational–technical problems form in development by means of computer systems in all stages of the life cycle of welded structures in parallel to the development of their design and technological variants. 1 The initial multivariant nature of the technological processes (TP), the systems of the question might components of the assembling–welding unit (AWU) and design of facilities; the TP of assembling–welding are variable with respect to a number of factors affecting the stress–strain state (SSS) of the welded joints (the position of the SSS and the technological sections in space, the sequence of main operations, the direction of production of welded joints, the principal diagram of the systems, the design of the principal system and ergonomic characteristics of the facilities, the possibilities of influencing production processes, the methods of determination and prevention of the formation, welding conditions, heat treatment conditions, etc). 2 The almost complete absence of standard types of structures of equipment and assembling–welding systems (AWS) with a constant structure, but variable dimensions, even in the conditions of the same plant. 3 The individual (unique) nature of the design of technology and facilities; the selection of facilities, stands,
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5
6
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and jigs from some database for a specific assembling– welding unit without only excessive additional work is often not possible. The absence of the methods of traditional design of objects and assembling–welding processes which may be efficiently transferred into algorithms and programmes. The absence in the universal packages of finiteelement analysis of reliable models of rapidly moving heat sources which include the welding arc. The currently available methods of calculation and engineering design of the stress–strain state of welded structures are not suitable for efficient operation of experts in the department of the chief welder has no access to unique computing resources (for example, supercomputers). The absence of the methods of introduction of international standards ISO 9000.3
If these difficulties are to be overcome by means of traditional interactive facilities of basic graphical systems, there will be no significant improvement of the technical– economic parameters of the design processes (in contrast to drawing and text documents). The low level of the development of technology has also prevented the improvement of the principles of technological design, proposed by N O Okerblom 4 in the 1960's. Computing technology generations change every 1.5–2 years, the technical possibilities of personal computers, graphic stations and supercomputers makes it possible to acquire new facilities for the principles of structural and technological design in the conditions of current production. With special reference to the robotised processes of resistance and arc welding in car industry, western
Differentiated approach to computer design companies have developed facilities for Computer Aided Production Engineering (CAPE), ensuring the construction of virtual production and autonomous programming of flexible equipment.5 The development of information technologies and means of computing technology has resulted in the formation of computer Continuous Acquisition and Life Cycle Support (CA LS) technologies of parallel development and maintenance of all stages of the life cycle of new components.6 To a certain degree, the CALS technologies can also be regarded as an independent confirmation of the principles of structural and technological design proposed by N O Okerblom. The authors of Ref. 7 proposed a method of combined synthesis of the AWU–AWA complex in the information field of description of design solutions of welded structures and assembling–welding equipment. The sequence of synthesis operations is determined by the TP which, with some assumptions, may be regarded as a set of operations on three–dimensional computer models of components, welded joints, welding tools (WTO), and also elements of basic assembling–welding equipment (AWE) and non-standard welding equipment (NSWE). The set of the objects of technological preparation, represented by the three-dimensional computer objects, and a set of design actions above them, ensuring the transformation of the described AWU on the level of the input into the set of the design and technological documents on the level of the output, which makes it possible to produce these objects was minimal losses, will be referred to as the technological welding–assembling system (TAWS). In the the framework of the processes of computer design of the TAWS the interface between the design
TAWS AWUin AWU TP
AWE
WTO
NSWE
AWE– AWA complex
AWA
AWUout 2 The interaction of objects and processes in the technological assembling–welding system.
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and technological tasks is removed, and the the design– technological development with the controlling opinion of the engineer–technologies in welding becomes dominant. Figure 2 shows the diagram of the TAWS objects and cyclic design processes, carried out with them. The objects and processes are ‘immersed’ into the programme– procedure shell, ensuring the efficient prediction of the strain–stress state of the AWU, the AWU–AWA complex, and also the reflection of the interaction of the internal SSS of the AWU with service loading. In a general case, a welded structure from the level of input into the TAWS (AWU in) to the level of output (AWU out) is subjected to the design procedures, reflecting division into technological sections (I), the preferential position of the technological sections or components in assembling– welding (II), the prediction of the probable accuracy of assembling–welding operations (III), the accessibility of welded joints for welding tools, the visibility of the welding zone for the welder (IV) and ergonomic and organisational characteristics of the assembling–welding processes of the AWU (V). Taking into account the cyclic nature of design procedures, the following stages of solving the problems of computer structural–technological design of welded structures have been proposed: – in the ideology of interactive–algorithmic synthesis to develop a solid-state model of the AWU with submodels of welded joints; – determine the sequence of assembling–tack welding– welding of components of technological sections, resulting in the formation of high-quality welded joints, and also the sequence and direction of producing welded joints; – produce the pattern of general residual stresses and strains of the AWU in welding in the free (without fixing) conditions; determine (if necessary) the strains (stresses) and other characteristics of the stress–strain state in the critical points or sections of of the components; – produce the basic scheme by taking into account the stress–strain state of the previous stage and the dimensional aims of the component or technological sections; – carry out interactive–algorithmic formation of the solidstate model of the variants of the technologically essential facilities; – evaluate the stress–strain state of the AWU of the attachment, component in the attachment, and also after extraction from the jigging; – loading the model of the AWU with the stress–strain state after assembling–welding in the AWE by the external service load; – evaluate the redistribution of internal stresses and the zone of critical concentration of these stresses; – if concentrators are too large and/or the number of concentrators is high, it is necessary to change the order of assembling, the order and direction of production of welded joints, the basic procedure, structural design, the type of drive and/or the force of the fixing elements,
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material and the rigidity of the body of equipment, the jig, the stand. The availability of the unique three-dimensional models of the AWU, TP, AWA, WT, AWE and NSWE makes it possible to carry out simultaneous (parallel) design, matching, connection and evaluation, and also the distribution on specific production platforms. For the design evaluation of the SSS of AWU, AWA and the prediction of the probable accuracy of production of AWU, it has been proposed to use simplified theories of welding strains and also approaches of the theory of stochastic similarity of technical objects and processes. 8 The criterion for selecting the optimum variant of the TP is the minimum of general residual strains of the AWU at the acceptable level of the stresses taking into account the design of equipment, labour content and cost of production, the order and sequence of their manufacture and the accessibility of welded joints for WT, and also the stress–strain state of the AWA–AWE complex. The design of the AWE in accordance with the AWU and TZ procedures for design is carried out by the INSVAR software with a reduction of the design time and the duration of preparation of drawings by a factor of 1.5– 4. 9 In Ref. 3,10 and 11, the authors proposed a concept of the system facilities for ensuring the quality of welding operations and production of welded joints, corresponding to the ISO 9000 international standards, and also presented examples of controlling quality. 10 Special attention has been given to the latest world strategy of quality and the new (2000) version of the ISO 9000. The principle and aim of the concept is the establishment and maintenance of high-quality welding operations on the basis of a factor–functional analysis of production, the determination of reason–consequence relationships ‘defect–reason’ with regulation of technological processes and continuous improvement of quality. The new tasks, ensuring the establishment, maintenance and improvement of quality in plants using the proposed concept, including methods of systematisation of the design elements of welding production, the establishment of homogeneous batches of products and controlling factors of quality, the methods and means of measuring quality, preventative charts for inspection, algorithms and computer programs of quality systems. According to the experimental results, the largest loss of quality takes place as a result of the unsatisfactory state and the negative effect of the following production factors: the qualification and motivation of the executor; the welding and welded material; welding equipment and technological jigging; preparation and assembling for welding; welding process and its control. In welding operations, these factors determine 85– 95% of all defects and, consequently, special attention must be concentrated on these problems. Analysis of the individual factors was carried out on the basis of characteristic features of these factors, using specific parameters. These parameters were determined
in plants by expert or experimental methods. Factor F contains some number of parameters P, evaluated on the basis of the number, nature and dimensions of defects, determined by this factor:
n Φ → Π i → ( Π Xi ...Τn X n ). i=1
∑
[1]
Each factor is characterised by its parameters whose optimisation with respect to the parameters X i makes it possible to determine the boundaries of permissible values. Movement outside these boundaries has a negative effect on the technological process and results in its destabilisation and the formation of defects in welded joints. In this case, it is necessary to determine the reasons causing deviations of the parameters (including the movement of the parameters outside the permissible range). For example, the high moisture content of the electrode coating forms as a result of a number of reasons: prior to application, electrodes were not baked; the welder has not used a hermetic box, etc. The destabilising parameter, situated outside the limits of the regulation range, is a reason for the formation of defects or deviation from the optimum conditions of the process. However, high-quality welded joints form as a result of not one but a large number of factors. In the examination of the quality of a welded joint K c it is recommended to use systems consisting of several controlling factors, determined for the specific range of welding with the known boundaries of the parameters:
Kc →
n
∑ Φ → (Φ a ...Φ a ). i
i =1
i i
n n
[2]
In this case, the value of K c was estimated on the basis of the number, nature and dimensions of defects. In subsequent stages, multifactor and parametric systems were transformed in a model for controlling the processes and production in the ISO 9000 quality systems. Consequently, the following equation can be used for the parametric models:
K co = F ( K cc , C c , Ye ) ,
[3]
where K co is the output level of quality; K cc is the calculated (annual) level for all parameters (X i... X n) and (ai... an); Cc are systematic and random deviations; Y e are the controlling effects. In production, usually 5–7 controlling factors are considered. These factors are determined in detail in order to determine the parameters, the level of defects and reasons for the formation of the defects. Having the statistics and the history of the quality of products, it is possible to value the level of quality and predict a quality for actual production conditions. 11 Figure 3 shows the algorithms for the introduction of a quality system. Initially, it is necessary to develop four important preparation blocks, ensuring the relationships and adaptation with the quality systems in accordance
Differentiated approach to computer design
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Board of Chief Welders of Holding Companies Regional centre
Systemisation of elements of CP Establishment of uniform sets of joints Introduction of qualitative quality parameters
Analysis of state of technical processes and quality
Factor analysis of production
Evaluation of stability of technical processes
Determination of dominant factors
Evaluation of the quality level
Determination of reasons for defects Detemination of reason–defect relationship
Development and confirmaion of standard documents For welding processes and inspection For evaluation of quality, etc. Development of systems
Development of quality systems ISO 9000, 9001, 9004, 19011 Process models Responsibility Planning System of quality control (requirements) Realisation of production
Determination of parameters (analysis and improvement) Inspection of documents, registration Optimisation of the prediction of quality Correcting and preventive measures 3 The algorithms for introducing the ISO 9000 quality systems into welding production.
with the ISO 9000 and fulfilment of the requirement of this standard for a number of sections (the model of the processes, parameters, measurements, analysis and improvement, processes in the individual stages of the life cycle, etc.). The further direction of investigations is based mainly on the development of essential procedures and program facilities of engineering analysis, modelling of welded structures and variants of production technologies in high-productivity supercomputers of the SKIF series. It is proposed to use both imported packages of finite element analysis in the operation system Linux and MPI, together with the development of own original modules. Conclusions 1 A prerequisite for the effective application of continuous computer technologies of the technical preparation of assembling–welding production is the differen-
tiation of produced welded structures on the basis of the design–technological features regardless of the dependence on the affiliation of companies and organisation of the particular region. 2 All the stages of the life cycle of welded structures can be modelled rationally using a single program platform of three-dimensional computer models of technological assembling–welding systems and a set of design actions in respect to the components of the welded structures. 3 Taking into account the restricted technological possibilities of the traditional means of computing technology, it is rational to consider the organisation of regional centres and design and analysis of welded structures within the framework of virtual assembling–welding teams having access to supercomputers on the Internet. 4 The systems of formation of the quality of welded joints, corresponding to the requirements of ISO 9000, should
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be developed together with the design of welded structures and production technologies. References 1 2
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Paton B E et al: 'Analysis of the structure and production of welded structures in the industry of the USSR'. Avt Svarka 1983 (11) 1–12. Kunkevich D P et al: 'Elements of continuous computer technologies in the preparation of production of welded structures'. In: 'Welding and allied technologies'. Publ BR NAK PM Minsk No.3 2000 35–38. Denisov L S: 'Procedure approaches to achieving and maintaining high quality of welding operations with the introduction of international standards ISO-9000'. In: 'Welding and allied technologies'. Publ BR NAK PM Minsk No.3 2000 85– 93. Okerblom N O: 'Structural and technological design of welded structures'. Publ Mashinostroenie Moscow–Leningrad 1964.
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Tikhomirov V G: 'Making virtual production real'. Informatsionnie Teknologii 1997 (1) 39–42. 6 Mitrofanov V G and Solomentsev Yu M: 'Problems of formation of computersing integrated productions'. Tekhnologiya Mashinostroeniya 2000 (4) 45–48. 7 Medvedev S V: 'Computer technologies of design assembling and welding equipment'. Publ Institute of Technical Cybernetics of the Academy of Sciences of Belarus Minsk 2000. 8 Medvedev S V: 'Computer prediction of residual strains in welded structures in technological design'. Svar Proiz 2001 (8) 10– 18. 9 Medvedev S V and Kunkevich D P: 'Experience with effective computer design of assembling–welding technological equipment'. Avt Svarka 2001(3) 41–44. 1 0 Denisov L S and Zankovets P V: 'Controlling the quality of welding operations'. Avt Svarka 1996 (12) 26–31. 11 Denisov L S and Zankovets P V: 'Technological level, expenditure and quality and achievement of competition capacity in welding production'. In: 'Welding and allied technologies'. Publ BR NAK PM Minsk No.1 1999 73–76.
