WO1996015022A1

WO1996015022A1 - A method and a device for building ship hull elements

Info

Publication number: WO1996015022A1
Application number: PCT/NO1995/000212
Authority: WO
Inventors: Einar Pedersen; Harald Ask
Original assignee: Tts Automation A/S
Priority date: 1994-11-09
Filing date: 1995-11-09
Publication date: 1996-05-23
Also published as: AU3884095A; NO944272D0

Abstract

A method for building structural members for ship hulls uses a movable gantry (1) for moving webs (17), intercostals (15) and stiffeners (19) from storage cassettes (20, 21, 22) to their respective positions on a supporting surface (16), where the elements are tack welded together. The webs (17) or intercostals (15) have slots (18) for the stiffeners (19), and during the assembly the stiffeners (19) are threaded through the slots (18) in the first web or intercostal. After tack welding the stiffeners thus mounted, the remaining webs or intercostals are threaded onto the stiffeners (19). These operations are made possible by the gantry having a manipulator unit (4) supported in a trolley (3) on the bridge (2) of the gantry, the manipulator unit having clamps (10) and supporting magnets (12) for the structural member elements (15, 17, 19), the gantry employing frequency regulated electrical gear motors and hydraulic proportional techniques to obtain the very precise movements necessary for the positioning and threading operations.

Description

A Method and a Device for building ship hull elements

The present invention relates to a method for building structural members for ship hulls, in particular, but not exclusively so-called eggboxes, wherein a lattice-like structure comprising a plurality of substantially parallel first type web or intercoastal plate elements and a plu¬ rality of stiffeners arranged transversely of and extending through slots therefor in said first type plate elements, the plate elements and stiffeners being tack welded together before final welding.

Such structural members, which may be used e.g. in the double bottom of tankers, have usually been made using an overhead crane to move the various elements into their approximate posision, considerable manual labour being necessary in order to accomplish the final positioning of the elements. This work is both time consuming and hazar- dous due to the considerable mass of the elements to be moved manually in place and the necessity of having to perform some of the work in cramped areas. Furthermore, since all the elements have to be lowered into position from above by means of the crane, undesirable sub-divisions of some elements and rather large dimensional tolerances in the elements themselves and e.g. cut-outs for crossing parts have to be accepted, thus necessitating considerable additional welding to fill larger welding joints or the welding of additional strips to close gaps too wide to be welded directly.

The object of the present invention is to avoid the above- mentioned drawbacks and deficiencies, thus providing a method that will allow quick accurate, safe and ecconomical building structural elements like eggboxes for ship hulls.

This is obtained according to the invention through a method as recited in the introductory paragraph, said method being characterized by the steps of: a) placing an initial one of said first type plate elements on a supporting surface and securing the plate element in a predetermined position, b) placing at least one of said stiffeners on said support and threading one end of each stiffener through the respec¬ tive one of said slots in said first type plate element and tack welding the stiffeners in a position parallel to each other, c) bringing the next of said first type plate elements in position on the supporting surface with said slots in the element aligned with the other end of the stiffeners, d) threading said next plate element onto the stiffeners while moving the plate element along the supporting surface to its predetermined position with respect to the preceding first type plate element and tack welding it in place, e) repeating steps c) and d) as necessary.

Further advantageous features of the invention are recited in the dependent claims.

The invention also relates to a device for use in performing the method according to the invention. This device is characterized by the features recited in claim 10.

In order for the invention to be better understood, a detailed description will be given with reference to the appended drawings, where:

Fig. 1 shows a side view of a gantry according to the invention,

Fig. 2 shows a perspective view of part of the gantry in Fig. 1,

Fig. 3 shows a perspective view of a structural member in the course of being built by the use of one method according to the invention,

Figs. 4 - 7 illustrate a first embodiment of the method according to the invention,

Figs. 8 - 11 illustrate a second embodiment of the method according to the invention,

Figs. 12 - 14 illustrate a third embodiment of the method according to the invention,

Fig. 15 is a partial side view on a larger scale of the area XV encircled in Fig. 3,

Figs. 16 - 19 illustrate a fourth embodiment of the method according to the invention, and

Figs. 20 and 21 illustrate a fifth embodiment of the method according to the invention.

In Fig. 1, a special gantry, generally designated 1, is shown. The gantry comprises a very stiff bridge 2, along which a trolley 3 can be driven. A manipulator unit 4 is ridgidly connected to the trolley 3 and depends therefrom. The manipulator unit 4 may be lowered and raised, Fig. 1 showing the trolley 3 in two different positions with the manipulator unit 4 in the raised and lowered position, respectively. The crane bridge 2 and trolley 3 are equipped with frequency regulated electric gear motors to ensure exact speed regulation and positioning, the gantry being movable along tracks 5, 6.

The manipulator unit 4 is shown schematically in perspective view in Fig. 2. The unit comprises a rotatable underframe

7, which is supported in a plurality of hydraulic cylinders

8 from the trolley 3 through a rotatable connection 9. The underframe 7 is provided with two clamps 10, which may be raised and lowered with respect to the underframe 7 by means of hydraulic cylinders 11. Furthermore, the underframe 7 is equipped with supporting magnets 12, which are horizontally movable through hydraulic means with respect to respective supporting brackets 13, the brackets in turn being verti¬ cally movable by means of telescopic cylinders 14.

Fig. 2 shows and intercostal plate 15 being suspended from the clamps 10. The clamps contain grips operated by hydraulic cylinders to ensure a preclamping force prior to lifting the plate for safety reasons. When lifting is started, the clamp grips will be mechanically self-locking. Furthermore, in the upper part of each clamp housing a special suspension unit is mounted. This unit allows a certain angular deviation so that the element held by the clamp may be manipulated during the mounting operation, as will be explained later. The supporting magnets 12, by pushing or pulling horizontally, may tilt the plate 15 with respect to the vertical position to facilitate mounting of the plate. Both the clamps 10 and magnets 12 may be operated independently of each other to provide maximum movement flexibility.

Fig. 3 illustrates one each of the elements commonly making up a so-called eggbox in their mutual relationship. The supporting surface 16 may be a welding floor or, alterna¬ tively, a ship panel which is to form part of the eggbox structure. On this supporting surface 16 a web 17 is erected, and an intercostal 15 extends transversely of the web. The intercostal has slots 18 for stiffeners 19, one of which is illustrated. It will be understood that an eggbox contains a plurality of ecah of these elements, although in some eggboxes one of the elements may not be present, as will become apparent from the following description of various embodiments of the method according to the inven¬ tion. What may be labelled the standard method for building the eggboxes on a welding floor is illustrated in Fig. 4 - 7. These figures all show the welding floor 16, the gantry 1 with the bridge 2, trolley 3 and running tracks 5, 6. The structural elements to go into the eggbox are brought to the building area in cassetes 20, 21, 22 and placed in easy reach of the manipulator unit 4 of the gantry 1. A mounting fixture 23 is arranged on the welding floor 16 for purposes to be explained below. The mounting fixture contains electromagnets that may be turned on to firmly hold an egg¬ box element placed adjacent to the fixture.

In the first step of the standard method, a web 17 is picked by the gantry from the web cassette 21 and placed on the welding floor against the mounting fixture 23, the electro¬ magnets of which are switched on to firmly hold the web in the vertical position, as shown also in Fig. 3. The next step is illustrated in Fig. 5, where an intercostal is brought from the cassette 22 and is placed in a predeter- mined position against and transversely of the web 17 held by the mounting fixture. The intercostal is tack welded to the web 17 in the position shown.

Next, the stiffeners 19 are picked from the cassette 20 one by one and threaded through the respective slots 18 in the intercostal 15. This threading operation, which requires a high degree of accuracy due to the small clearance available between the vertical web of the stiffeners 19 and the corresponding part of the slots 18, is nevertheless possible due to the unusual manoeuverability of the gantry 1, its trolley 3 and the various functions of the manipulator unit

4, said functions employing proportional techniques.

Through this extraordinary manoeuverability it is also possible to ascertain that the stiffeners 19 are positioned parallel to each other and to the initial web 17.

With the stiffeners 19 in position, the remaining intercos- tals 15 are picked up one by one and threaded onto the stiffeners, whereupon they are tack welded in the appropri¬ ate position. Once all the intercostals have been mounted in this way, a new web 17 is placed against the free ends of the intercostals and tack welded, whereupon a new intercos¬ tal is arranged as shown in Fig. 7, ready to receive the next set of stiffeners. Intercostals, webs and stiffeners are installed in this manner until the eggbox is completed.

An alternative working procedure is used for instance when the web are longer than the width of the working area

(delimited by horisontal dotted lines) . In this procedure, which is illustrated in Figs. 8 - 11, the web cassette 21 is placed alongside the supporting surface 16 but still within the reach of the gantry 1. Also the mounting fixture 23 is now placed in the direction of the movement of the gantry so as to be parallel to the web cassette 21.

As shown in Fig. 8, a first web 17 is placed against the mounting fixture 23 and held firmly by its magnets. In this case, the webs 17 have the slots 18 for the stiffeners, and the stiffeners 19 are threaded through these slots in the first web 17 and tack welded as explained in connection with

Fig. 6. However, the stiffeners are grouped in sets of three so as to leave room for the intercostals 15, the first set of which is mounted as shown in Fig. 10. Next, the second web 17 is threaded onto the stiffeners 19 and moved up against the free ends of the first set of intercostals.

After tacvk welding, the nex6t set of intercostals 15 are brought in place and secured, whereupon the third web is threaded onto the stiffeners, and so on.

Another alternative working procedure is illustrated in Fig. 12 - 14. Here, as shown in Fig. 12, the webs 17 are positioned on the welding floor 16 and stayed as required. Next, the intercostals are threaded down onto the webs in ready made slots and tack welded as required. The result is shown in Fig. 13. Finally, the stiffeners 19 are threaded through slots 18 in the webs 17 to complete the eggbox. It will be understood that during the threading of the stiffe¬ ners, the manipulator unit of the gantry will have to change its grip along the stiffeners, finally using only one of the clamps 10.

In the operations described above, where a web 17 or inter¬ costal 15 is threaded onto several stiffeners 19 more or less simultaneously, various techniques can be used to ease this operation. One such technique is to rotate the underframe 7 of the manipulator unit 4 slightly above its vertical axis in order to create a small angle between the web or intercostal plate and a vertical plane perpendicular to the stiffeners. When moving the slightly angled plate towards the free ends of the stiffeners, the stiffeners will be engaged in their respective slots 18 in the plate, one at a time, which is much easier to accomplish than having the stiffeners hit all the slots simultaneously.

In another method the slot 18 is made as shown in Figure 15. The horizontal part 24 of the slot for accommodating the flange 25 of the stiffener is made with a substantial clearance to the flange 25, while the vertical part of the slot provides very little clearance to the vertical web 26 of the stiffener. Furthermore, the transition area between the horizontal and vertical parts of the slot is chamfered such as at 27. Before approaching the plate 15, 17 to the stiffeners 19, the plate is tilted somewhat forward, for instance by pulling the magnets 12 towards their brackets 13 (Figure 2) . Consequently, the flanges 25 of the stiffeners will enter the wide horizontal part 24 of the slots momen¬ tarily before the webs 16 of the stiffeners have to find their position in the slot when the plate is moved towards the stiffeners. During this movement, the chamfered portions 27 of the slots 18 will guide the webs 26 of the stiffeners into their respective parts of the slots 18, thus permitting the free ends of the stiffeners 19 to align themselves properly with respect to the slots 18.

The methods described above for making eggboxes have used a welding floor as the supporting surface 16. It will be understood, however, that essentially the same methods can be used with a ship panel as the supporting surface. In such cases the eggbox elements would be tack-welded also to the panel. It will be understood that in such cases the mounting fixture 23 can be dispensed with.

When having the benefit of a ship panel as the working surface, two further methods may be used, as illustrated respectively in Figures 16 - 19 and Figures 20 - 21.

In the first of these methods, an initial web 17 is placed on the panel 28 and tack-welded. Brackets may be used as necessary to secure the web in place. This initial step is shown in Figure 16. Subsequently, the stiffeners 19 are threaded in place in slots in the web, as illustrated in Figures 17 and 18. Next, as shown in figure 19, the remaining webs are threaded onto the stiffeners. In this case, no intercostals are necessary.

The final method to be described is also one where inter¬ costals are not used. Here, as illustrated in Figure 20, the webs are all positioned and secured before the stiff¬ eners, as suggested in Figure 21, are threaded in place. If, during positioning of the webs, they have not been mounted with sufficient accuracy to ensure that the corre¬ sponding slots for the stiffeners are not exactly aligned, the stiffeners may initially be threaded up against the second web, whereupon the position of this web is adjusted to align its slots 18 with the stiffeners. Then the webs are moved up against the next web, which is adjusted as necessary. Such adjustment may also have to be performed on the last web. It will be understood that the gantry 1 and its equipment must be controllable with very high precision and that all movable or rotatable connections must be free of lost motion and elasticity in order to permit, in particular, the threading operations forming a part of the methods described above. Not only is it necessary to position the elements to be threaded with great precision, it is also necessary to excert a certain horizontal force on the elements in order to overcome frictional forces during threading. Consequently, the vertically movable suspensions 8, 11 and 14 associated with the manipulator unit 4 will have to be essentially rigid when fixed in position.

Claims

C l a i s :

1. A method for building structural members for ship hulls, in particular, but not exclusively, so-called egg¬ boxes, wherein a lattice-like structure comprising a plurality of substantially parallel first type web or intercostal plate elements (15, 17) and a plurality of stiffeners (19) arranged transversely of and extending through slots (18) therefor in said first type plate elements (15, 17) , the plate elements and stiffeners being tack welded together before final welding, c h a r a c t e r i z e d by the steps of: a) placing an initial one of said first type plate elements (15, 17) on a supporting surface (16) and securing the plate element (15, 17) in a predetermined position, b) placing at least some of said stiffeners (19) on said support and threading one end of each stiffener through the respective one of said slots (18) in said first type plate element and tack welding the stiffeners in a position parallel to each other, c) bringing the next of said first type plate elements (15, 17) in position on the supporting surface (16) with said slots (18) in the element aligned with the other end of the stiffeners (19) , d) threading said next plate element (15, 17) onto the stiffeners (19) while moving the plate element along the supporting surface (16) to its predetermined position with respect to the preceding first type plate element (15, 17) and tack welding it in place, e) repeating steps c) and d) as necessary.

2. A method according to claim 1, c h a r a c t e¬ r i z e d by the step, performed before step a) of: f) placing and securing a second type web or intercostal plate element (17, 15) on said supporting surface (16) to form an abutment and support for said first type web or intercostal plate elements (15, 17) .

3. A method according to claim 1, c h a r a c t e¬ r i z e d by the steps, performed between steps b) and c) , of : g) placing and securing a second type of web or intercostal plate elements (15, 17) between some of and parallel to the stiffeners (19) , h) repeating step g) before each step c) .

4. A method for building structural members for ship hulls, in particular, but not exclusively, so-called egg¬ boxes, wherein a lattice-like structure comprising a plurality of substantially parallel first type web or intercostal plate elements (15, 17) and a plurality of stiffeners (19) arranged transversely of and extending through slots (18) therefor in said first type plate elements (15, 17) , the plate elements and stiffeners being tack welded together before final welding, c h a r a c t e r i z e d by the steps of: i) placing said first type web or intercostal plate elements (17) on a supporting surface (16) and securing the plate elements (17) in predetermined, spaced positions so that said slots (18) in the plate elements (17) are aligned with respect to each other transversely of the plate elements, and j) threading the stiffeners (19) through said aligned slots (18) .

5. A method according to claim 4, c h a r a c t e¬ r i z e d by the step, performed before step j) of: k) placing and securing a second type of web or intercostal plate elements (15) in spaced relationship transversely of said first type elements (17) .

6. A method according to any one of the preceding claims, c h a r a c t e r i z e d in that a welding surface is 6/15022

12 used as said supporting surface (16) .

7. A method according to an one of claims 1 - 5, c h a r a c t e r i z e d in that a ship panel is used as said supporting surface (16) .

8. A method according to claims 1 or 2, c h a r a c t e¬ r i z e d in that an electromagnetic fixture (23) is used to secure said initial first type or said second type plate element (15, 17) on the supporting surface (16) .

9. A method according to any one of the preceding claims, c h a r a c t e r i z e d in that said webs (17) , intercostals (15) and stiffeners (19) are moved from storage cassettes (20, 21, 22) to their respective positions in the structural member by means of a movable gantry (1) having a manipulator unit (4) able to grip, raise, lower, swing and tilt said webs (17) , intercostals (15) and stiffeners (19) .

10. A mobile gantry (l) for use in building structural members for ship hulls, said structural members comprising a lattice-like structure including elements like webs (17) , intercostals (15) and stiffeners (19) , said gantry (19) comprising a bridge (2) and a trolley (3) drivable along the bridge, a manipulating unit (4) comprising an underframe (7) rotatably supported from the trolley (3) , the underframe (7) having independently and vertically movable clamps (10) for gripping said elements (15, 17, 19) , c h a r a c t e¬ r i z e d in that said clamps (10) are rigidly supported in the underframe (7) to permit vertical movement only, and that the underframe (7) is provided with supporting magnets (12) for said elements (15, 17, 19), said magnets (12) being independently movable both vertically and horizontally with respect to the underframe (7) .