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An automated welding operation planning system
for block assembly in shipbuilding
Kyu-Kab Cho*, Jung-Guy Sun, Jung-Soo Oh
Abstract
The block assembly process is one of the most important manufacturing processes for shipbuilding. Since block is composed of several steel plates and steel sections with predetermined shapes according to ship design, the welding operation planning to construct a block is a critical activity for shipbuilding, but this activity has traditionally been experience based. Thus, it is required to develop an automated welding operation planning system to assemble blocks. This paper describes the development of an automated welding operation planning system for block assembly in shipbuilding. Based on the information about parts, topological relationship between parts and assembly sequences for block, the developed system performs the determination of welding postures, welding methods, welding equipment and welding materials. The developed system implemented successfully for real blocks constructed in shipyard.
Keywords: Block assembly; Expert system; Operation planning; Welding process
1. Introduction
Shipbuilding is traditionally a labor-intensive assembly industry that employs the welding process as a basic production technology. In shipbuilding, there are several types of manufacturing process planning for cutting and bending, assembly, out- fitting, and erection. Among these process planning activities, the assembly process planning is by far the most important, since the construction process for a hull block comprises approximately 48~50% of the total shipbuilding process [1,2]. The main operation for block assembly is the welding operation. The welding operation planning problems in block assembly are very difficult to solve because all blocks are different in size, type, and constituting sub-assemblies that depend on the types of ships. Also, since this activity has traditionally been experienced-based, welding operation planning in shipbuilding has been performed manually. Thus, it is very important to develop an automated welding
operation planning system for shipbuilding. There is relatively very little literature available on automated welding operation planning systems for shipbuilding [3,4].
This paper deals with the development of an automated welding operation planning system for block assembly in shipbuilding. The rule-based expert system for welding operations has been developed using Smart Elements as an expert system tool. The developed system is demonstrated and verified by using actual blocks in the shipyard.
2. Development of an automated welding operation planning system
2.1. System framework
The automated welding operation planning system developed in this paper consists of four modules: welding postures module, welding methods module, welding equipment module, and welding materials module. The framework of this system is shown in Fig. 1.
2.2. Determination of welding postures
This module determines the posture of the welding operator. Welding posture is reasoned by considering connection types and positional direction between two connected parts, direction information of assembly base part, existence of turnover, and assembly level.
Connection types are classified into butt type (B) and fillet type (T), as shown in Fig. 2. The four types of welding postures, down posture (D), overhead posture (O), horizontal posture (H), and vertical posture (V), are considered in this paper, as shown in Fig. 2 [5,6]. The most stable and easiest welding posture is the down welding posture, and the most difficult one is the overhead welding posture. The welding operator determines an efficient welding posture according to the working conditions.
For relationship of connection between two parts that are welded, one part is considered as the base and the other is connected to the base. The part that is considered as a base is represented as PartFrom and the other that is connected to the base is represented as PartTo.
The levels of block assembly to assemble steel plates and sections into the final block are classified into subassembly (SA) level, unit block assembly (UBA) level, and final block assembly (FBA) level.Subassembly levels may be divided into small subassembly (SSA) levels and intermediate subassembly (ISA) levels according to the size and weight of the subassembly as shown in Fig. 3.
For determining welding postures, the block assembly levels are classified into two groups. The first group is the small subassembly level; the second group consists of the intermediate subassembly, the unit block assembly, and the final block assembly levels. The reason for this grouping is that there is no turnover process in the small subassembly
level, but the assembly levels belonging to the second group may have turnover processes. Turnover processes cause the change of welding postures that are determined before the turnover process.
2.2.1. Determining welding postures in the first group level
The following are examples of rules to determine the welding posture for a small subassembly level. The connection types of welding joints between two parts used in this rule are: Butt type (0) and T type (1).
(1) IF (Part Level=Small Assembly)
(Connection Type=1)
(Direction of Assembly Base=Connection Direction)
(PartFrom=not Assembly Base Part)
(PartTo=not Assembly Base Part)
THEN (Welding Posture=H)
(2) IF (Part Level=Small Assembly)
(Connection Type=1)
(Direction of Assembly Base Part=not Connection Direction)
(PartFrom=not Assembly Base Part)
(PartTo=not Assembly Base Part)
THEN (Welding Posture=V)
An example of a small subassembly is shown in Fig. 4. In this case, there are Tve parts, and the assembly base parts are A and B. The relationships between the parts are listed in Table 1 and the results of the determination of welding postures for this example are shown in Table 2.
2.2.2. Determining welding postures in the second group levels
In the second group levels, information for determining welding postures is the same as for the small subassembly level. Welding postures are determined between the assembly base part and other parts that are connected to the assembly base part in a similar way to the small subassembly. Other welding postures are determined between parts that are not an assembly base part. If turnover processes exist, the direction of the assembly base part is changed at an angle of 180° and the welding posture is also changed. An example of the rules for the second group levels are as follows:
(1) IF (Part Level＝not Small Assembly)
(Connection Type is 0)
(Direction of Assembly Base Part＝Connection Direction)
(PartFrom＝not Assembly Base Part)
(PartTo＝not Assembly Base Part)
THEN (Welding Posture＝H)
(2) IF (Part Level＝not Small Assembly)
(Connection Type＝0)
(Direction of Assembly Base Part＝not Connection Direction)
(PartFrom＝not Assembly Base Part)
(PartTo＝not Assembly Base Part)
THEN (Welding Posture＝V)
2.3. Determination of welding methods
This module determines the welding methods based on welding postures by rule-based reasoning. Welding methods used in this paper are summarized in Table 3, according to the connection types of welding joints and welding processes [7].
In general, there are several welding techniques such as braze welding, forge welding, gas welding, resistance welding, induction welding, arc welding, and special welding. Considering the features of shipbuilding, the welding process used in the shipyard is the arc welding process. Arc welding is a process in which coalescence is obtained by heat produced from an electric arc between the work and an electrode [8].
Arc welding is classified into several types, according to the welding mechanisms such as shield metal arc welding (SMAW), flux cored arc welding (FCAW), submerged arc welding (SAW), and electrogas arc welding (EGW). SMAW is one of the oldest, simplest, and most versatile joining processes. Currently, about 50% of most industrial and maintenance welding is performed by this process, but this process is used approximately less than 5% at most large shipyards. In FCAW, an electrode that is tubular in shape is used, and if necessary, the welding area is shielded by carbon dioxide. In SAW, the weld arc is shielded by granular flux, consisting of lime, silica, manganese oxide, calcium fluoride, and other materials. The flux is fed into the weld zone by gravity flow through a nozzle. EGW is used primarily for welding the edges of sections vertically in one pass, with the pieces placed edge to edge (butt type) [9].
To build the knowledge base for the determination of welding methods, knowledge is aquired from welding handbooks and experts. Input information of this module is geometrical information that is provided from CAD system and the welding posture determined by welding posture determination module. The knowledge is represented by rules. The examples of the rule for the determination of welding methods are as follows:
(1) IF (Connection Type=0)
(Groove=none)
(Welding Posture=O)
(6≤Thickness≤50)
THEN (Welding Method=SMAW-MANUAL BUTT)
(2) IF (Connection Type=1)
(Leg Length≥4.5mm)
(Welding Posture=O, H, V)
THEN (Welding Method=FCAW-FILLET)
2.4. Determination of welding equipment
This module selects the appropriate welding equipment by rule-based reasoning based on information about welding postures and welding methods. Table 4 shows the relationship between welding methods and welding equipment. After determining welding methods, welding equipment is automatically selected by using the information contained in Table 4.
2.5. Determination of welding materials
This module determines the most proper welding materials by rule-based reasoning, based on information about welding postures, methods, and equipment. In general, steels used for block assembly are mild steels and high tensile steels. Mild steel is a rolled plate, the tensile strength of which is less than 50 kg f/mm2. High tensile steel is a low-carbon alloy steel, the tensile strength of which is more than 50 kg f/mm2 with a yield strength of more than 30 kg f/mm2. Mild steel has four grades: A, B, D, and E. High tensile steel has three grades: AH, DH, and EH [9]. The following are examples of rules to determine welding materials.
(1) IF (Welding Posture=D)
(Welding Methods=FCAW FILLET)
(Welding Equipment=LN-7 or LN-9)
(Steel Grade=(Mild Steel A,B,D,E) Highten-sile Steel AH,DH)
THEN (Welding Material=MX-200H)
(2) (Welding Posture=D)
(Welding Methods=SAW Bothside BUTT)
(Welding Equipment=SW-41)
(Steel Grade=Mild Steel A,B,D,E)
THEN (Welding Material=L-8xs-707EF H-14XS705EF L-8XNSH52)
3. System implementation and discussions
In order to demonstrate and to verify the automated welding operation planning system for block assembly, a block located at the upper deck part of crude oil carrier is examined. Fig. 5 shows the structure of an example block and Fig. 6 represents its hierarchical structure. An example final block shown in Fig. 5 has two unit blocks, one intermediate subassembly, 15 small subassemblies, and 169 component parts. The final welding operation planning for the unit block assembly level is shown in Fig. 7. The results are verified by an expert process planner and implemented by using actual blocks in an assembly shop.
4. Conclusion
An automatic welding operation planning system consisting of four modules (welding postures, welding methods, welding equipment, and welding materials) is developed by using Smart Elements as an expert system tool. The developed system is verified by using actual block and implemented in a block assembly shop.
Acknowledgements
This work is supported by the research grant from Hyundai Heavy Industries Co., Ltd.
References
[1] H. Nakayama, Expert process planning system of CIM for shipbuilding, Proceedings of International Conference on Computer Applications in Shipbuilding, 1994, pp. 12.55－12.66.
[2] Ship and Ocean Foundation, Research Report on Shipbuilding CIMS Pilot Model Development, Japan, 1991.
[3] H.B. Cary, Summary of computer programs for welding engineering, Welding Journal 70 (1) (1991) 40－46.
[4] D.M. Barborak, D.W. Dickinson, R.B. Madigan, PC-based expert system and their applications to welding, Welding Journal 70 (1) (1991) 29－38.
[5] J. Weber et al., Welding expert focus on the future, Welding Journal 69(7) (1990) 37－46.
[6] K.K. Cho et al., An automatic process planning system for block assembly in shipbuilding, Annals of the CIRP 45 (1) (1996) 41－44.
[7] J. Gustafsson, M. Heinakari, Experiences with CIM in shipbuilding, Welding Journal 70 (3) (1991) 27－35.
[8] B.H. Amstead et al., Manufacturing Processes, 8th ed., Wiley, New York, 1987, pp. 156D157.
[9] S. Kalpakjian, Manufacturing Engineering and Technology, 3rd, Addison-Wesley, Reading, MA, 1995, pp.862－870.
自動(dòng)焊接操作系統(tǒng)
Kyu-Kab Cho*, Jung-Guy Sun, Jung-Soo Oh
摘要：
船舶建造的分組裝配作業(yè)加工是其最重要的制造法。因?yàn)閴K由若干鋼板塊和型鋼同預(yù)定形狀按照船舶設(shè)計(jì)組成的，所以對(duì)船舶建造來說焊接操作計(jì)劃構(gòu)造塊是一項(xiàng)關(guān)鍵任務(wù)，但是這個(gè)是以傳統(tǒng)經(jīng)驗(yàn)為基礎(chǔ)的，因此，有必要研制一種自動(dòng)焊接操作計(jì)劃系統(tǒng)來組裝塊。這篇論文描述了船舶建造分組裝配作業(yè)的自動(dòng)焊接操作計(jì)劃系統(tǒng)的發(fā)展。根據(jù)零件和裝配次序的拓?fù)潢P(guān)系介紹部分，系統(tǒng)完成確定焊接位置，焊接方法，焊接設(shè)備和焊接材料。系統(tǒng)成功地實(shí)現(xiàn)了船舶建造塊的構(gòu)造。
關(guān)鍵詞：分組裝配作業(yè)；專家系統(tǒng)；操作計(jì)劃；焊接過程
⒈ 簡(jiǎn)介
船舶建造是傳統(tǒng)的勞動(dòng)強(qiáng)度大的組裝工業(yè)，焊接是其基本生產(chǎn)技術(shù)。在船舶建造中,存在幾種類型切割,裝配制造法。在這些工藝設(shè)計(jì)活動(dòng)之中,裝配工藝計(jì)劃是最重要的,因?yàn)榇w結(jié)構(gòu)加工大約包含了船舶建造加工總數(shù)的40%-50%。焊接操作是分組裝配作業(yè)的主要操作。焊接操作規(guī)劃問題在裝配過程中是很難解決的，因?yàn)椴考拇笮? 類型,以及組成的取決于船的類型的亞部件是不同。同樣地，因?yàn)檫@些活動(dòng)是以傳統(tǒng)經(jīng)驗(yàn)為基礎(chǔ)的，所以，焊接操作在船舶建造中是人工執(zhí)行的。因此，在船舶建造中，研制自動(dòng)焊接操作計(jì)劃系統(tǒng)是非常重要的。對(duì)船舶建造，幾乎沒有自動(dòng)焊接操作計(jì)劃系統(tǒng)的文獻(xiàn)可以利用。這篇論文涉及船舶建造分組裝配作業(yè)的自動(dòng)焊接操作計(jì)劃系統(tǒng)的研制。這種基于規(guī)則的將靈敏元件當(dāng)做專家系統(tǒng)工具的焊接操作專家系統(tǒng)已經(jīng)被研制出來了。這個(gè)系統(tǒng)通過造船廠的實(shí)際的部件已經(jīng)被證明和復(fù)核。
⒉ 自動(dòng)焊接操作系統(tǒng)的發(fā)展
2.1. 系統(tǒng)框架
在此論文里自動(dòng)焊接操作計(jì)劃系統(tǒng)由焊接位置模數(shù)、焊接方法模數(shù)、焊接設(shè)備模數(shù)，并且焊接材料模數(shù)組成四模數(shù)。這個(gè)系統(tǒng)的框架將在圖1中展示。
2.2. 焊接位置的確定
模數(shù)決定焊工的焊接位置?？紤]到兩連接零件連接類型和位置，方向部件的方向信息，翻轉(zhuǎn)的存在以及裝配等級(jí)等因素，焊接位置是受影響的。連接類型被分為對(duì)接和角接類型，如圖２所示。這篇論文考慮了四種焊接位置:向下焊接，水平焊接，垂直焊接和仰焊接，如圖２所示。最穩(wěn)定的和輕松的焊接位置是下向焊位置，最困難的是仰焊位置。根據(jù)工作條件焊工決定采用一種有效的焊接位置。兩焊接部的連接的關(guān)系，一個(gè)部分被認(rèn)為是基體，而另一個(gè)被認(rèn)為是連接在這個(gè)基體上。被認(rèn)為是基體的部分被當(dāng)做partfrom而連接到基體的部分被當(dāng)做PartTo。裝配鋼板和型鋼變成最后的部件的分組裝配作業(yè)水平被分為組件水平（SA），單元塊組裝水平（UBA）和最后的分組裝配作業(yè)水平（FBA）。根據(jù)組件的尺寸和重量組件水平可以被分成小組件水平（SSA）和中間的組件水平（ISA）如圖３所示。因?yàn)闆Q定焊接位置,分組裝配作業(yè)水平被分為組。第一個(gè)組是小部件水平；第二組由中間部件組成，為單元塊組裝和最后的分組裝配作業(yè)水平。這樣分組的理由是看是否有翻轉(zhuǎn)的加工小部件，但是裝配水平屬于第二組的也許也有翻轉(zhuǎn)加工。翻轉(zhuǎn)加工之前的決定產(chǎn)生致使焊接位置發(fā)生變化。
2.2.1. 決定焊接位置的第一組水平
以下用來決定焊接位置的規(guī)則適合于小部件水平。用于此規(guī)則焊接接頭的連接類型是：對(duì)接式（0）和T類型（1）。
(1) IF (Part Level=Small Assembly)
(Connection Type=1)
(Direction of Assembly Base=Connection Direction)
(PartFrom=not Assembly Base Part)
(PartTo=not Assembly Base Part)
THEN (Welding Posture=H)
(2) IF (Part Level=SmallAssembly)
(Connection Type=1)
(Direction of Assembly Base Part=not Connection Direction)
(PartFrom=not Assembly Base Part)
(PartTo=not Assembly Base Part)
THEN (Welding Posture=V)
小部件的例子在圖４中列出。這里有五部分，部件基體部分是A和B。這些部分之間的關(guān)系在表格1中列出，這些例子確定焊接位置的結(jié)果將在表格２中列出。
2.2.2. 決定焊接位置的第二組類水平
在第二組類水平, 決定焊接位置的情況同小部件水平是一樣的。其他的焊接位置取決于非部件基體間的部件。如果存在翻轉(zhuǎn)加工，部件基體的方向是以180o的角度變化，焊接位置也同樣地變化。
適合于第二組類水平的例子規(guī)則的如下：
(1) IF (Part Level=not SmallAssembly)
(Connection Type is 0)
(Direction of Assembly Base Part=Connection Direction)
(PartFrom=not Assembly Base Part)
(PartTo=not Assembly Base Part)
THEN (Welding Posture=H)
(2) IF (Part Level=not SmallAssembly)
(Connection Type=0)
(Direction of Assembly Base Part=not Connection Direction)
(PartFrom=not Assembly Base Part)
(PartTo=not Assembly Base Part)
THEN (Welding Posture=V)
2.3. 焊接方法的確定
按規(guī)則根據(jù)焊接位置此模數(shù)決定焊接方法。根據(jù)焊接接頭的連接類型和焊接過程[7]，此論文中使用的焊接方法被歸納于表格３中。通常,有若干焊接技術(shù)比如釬焊、壓力焊、氣保焊、電阻焊接、感應(yīng)焊接、電弧焊以及特種焊接?？紤]船舶建造的特色，被用于這造船廠的焊接方法是電弧焊接法。電弧焊是由工件和電極間電弧產(chǎn)生的熱而獲得的接合法。電弧焊根據(jù)焊接機(jī)構(gòu)被分為若干類型，例如保護(hù)金屬極電弧焊（SMAW），藥芯焊絲電弧焊（FCAW），埋弧焊（SAW）和氣體保護(hù)電弧焊（EGW）。保護(hù)金屬極電弧焊是其中最老的，最簡(jiǎn)單的，最靈活多變的焊接方法。目前大約50％的工業(yè)焊接采用這種方法，但是在大多數(shù)造船廠中這種加工方法的使用大約小于5%。在藥芯焊絲電弧焊，在外形上管狀電極是使用的，必要時(shí)，焊縫橫截面面積被二氧化碳保護(hù)。在埋弧焊，焊接電弧被由石灰、硅石、氧化錳、氟化鈣及其他材料組成的顆粒狀熔劑遮擋。焊劑是靠重力流過焊縫進(jìn)入焊接區(qū)的。氣體保護(hù)焊主要適合于焊接型鋼的邊緣，（對(duì)接式）[9]。
建立這一知識(shí)庫(kù)適合于焊接方法的確定。知識(shí)庫(kù)數(shù)據(jù)是從焊接手冊(cè)和專家取得。此模數(shù)的輸入信息是由CAD系統(tǒng)和焊接位置提供的幾何信息，焊接位置由焊接位置確定模數(shù)確定。數(shù)據(jù)由準(zhǔn)則代替。確定焊接方法的準(zhǔn)則例子如下：
(1) IF (Connection Type=0)
(Groove=none)
(Welding Posture=O)
(6≤Thickness t ≤50)
THEN (Welding Method=SMAW-MANUAL-BUTT)
(2) IF (Connection Type=1)
(Leg Length≥4.5mm)
(Welding Posture=O, H, V)
THEN (Welding Method=FCAW-FILLET)
2.4. 焊接設(shè)備的確定
此模數(shù)按規(guī)則，根據(jù)有關(guān)焊接位置和焊接方法的信息選擇適當(dāng)?shù)暮附釉O(shè)備。表格４顯示焊接方法和焊接設(shè)備之間的關(guān)系。利用表格4列舉的情況，在確定焊接方法后，焊接設(shè)備被自動(dòng)地選擇。
2.5. 焊接材料的確定
根據(jù)焊接位置、方法和設(shè)備的有關(guān)情況，此模數(shù)按規(guī)則確定最適當(dāng)?shù)暮附硬牧?。通常、被用來作分組裝配作業(yè)的鋼材是低碳鋼和高強(qiáng)度鋼。低碳鋼是軋制鋼板，其抗拉強(qiáng)度小于50 kg f / mm2。高強(qiáng)度鋼是低碳合金鋼、其抗拉的強(qiáng)度大于50 kg f / mm2，屈服強(qiáng)度超過30 kg f / mm2。低碳鋼有四個(gè)等級(jí)：A, B, D，和E.高強(qiáng)度鋼有三個(gè)等級(jí)：AH, DH, 和 EH [ 9]。下面是確定焊接材料的例子。
(1) IF (Welding Posture＝D)
(Welding Methods＝FCAW FILLET)
(Welding Equipment＝LN-7 or LN-9)
(Steel Grade＝(Mild Steel A,B,D,E) Hightensile-Steel AH,DH)
THEN (Welding Material＝MX-200H)
(2) IF (Welding Posture=D)
(Welding Methods=SAW Bothside BUTT)
(Welding Equipment=SW-41)
(Steel Grade=Mild Steel A,B,D,E)
THEN (Welding Material=L-8xs-707EF H-14XS705EF L-8XNSH52)
⒊ 系統(tǒng)實(shí)現(xiàn)和討論
為了證明和檢驗(yàn)用作于分組裝配作業(yè)的自動(dòng)焊接操作計(jì)劃系統(tǒng)，位于原油運(yùn)輸船上甲板一部分的部件被試驗(yàn)。圖５顯示樣本部件的結(jié)構(gòu)，圖６表示它的分級(jí)結(jié)構(gòu)。圖５樣本最后的部件列出有雙機(jī)組部件,中間的部件、15小部件，和 169組合零件。用于單元組件裝配的最終焊道操作在圖７中列出。利用在裝配車間實(shí)際部件的實(shí)現(xiàn)和專家實(shí)施，結(jié)果被證實(shí)。
⒋ 結(jié)論
由四模數(shù)組成（焊接位置、焊接方法、焊接設(shè)備、和焊接材料）的自動(dòng)焊操作系統(tǒng)的研制是利用將靈敏元件當(dāng)做專家系統(tǒng)工具來實(shí)現(xiàn)的。利用實(shí)際的部件和其在分段裝配車間的實(shí)現(xiàn)該系統(tǒng)被證實(shí)。
感謝
此研究科研經(jīng)費(fèi)由hyundai重工業(yè)有限公司提供。
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