Assembly and welding of structures
From aluminum alloys
In the manufacture of units, sections and hulls of aluminum alloys, riveting, welding and glue-welded joints are used to connect parts.
Riveted structures are used in two cases:
– in the manufacture of structures from non-weldable alloys;
– in the manufacture of thin-sheet structures (thickness less than 3 mm).
The assembly of riveted structures made of light alloys is carried out in the following ways:
– By marking with the use of universal tools and devices;
– By assembly holes in the parts with the connection of parts with spring clamps;
– Assembly in fixtures that ensure the mutual arrangement of parts.
The assembly of riveted structures is carried out in the following sequence:
1. Installation of parts or assemblies in the assembly position.
2. Installation of a means of temporary fastening of parts to each other – spring clamps, assembly bolts, clamps.
3. Drilling and, if necessary, countersinking holes for rivets.
4. Removal of temporary fasteners, disassembly of the structure, cleaning of surfaces.
5. Anti-corrosion coating of mating surfaces.
6. Installing gaskets, applying sealant.
7. Final assembly for riveting with assembly quality control.
8. Riveting of connections.
In shipbuilding, impact and press riveting is used (Fig. 12.13).
Impact riveting is performed with a pneumatic hammer. Press riveting is performed on riveting presses and can be single and group (up to 36 rivets per press stroke). Press riveting is more productive than impact riveting, and the absence of noise and vibration improves the working conditions of riveters.
Fig.12.13. Riveting scheme
a) – impact riveting; 1 – pneumatic hammer, 2 – rivet, 3 – support;
b) press group riveting.
In the manufacture of welded structures from aluminum alloys, it is necessary to take into account the features of their welding and increased deformations compared to steel.
According to the degree of weldability, aluminum alloys can be divided into 3 groups:
1) – weldable ,
2) – weldable, but requiring heat treatment after welding;
3) – non- weldable .
Weldable alloys include all non-hardenable alloys. The second and third groups include thermally hardened alloys.
Welding of aluminum alloys is carried out in an inert gas environment – argon Ar. The following types of welding are used:
– automatic welding with a consumable and non-consumable electrode (Fig. 12.14) in the lower position;
– semi-automatic consumable electrode welding in any spatial position;
– manual electric arc welding with a non-consumable electrode in any spatial position.
Rice. 12.14. Schemes of argon-arc welding.
a – non-consumable electrode; b – consumable electrode;
1 – tungsten electrode; 2 – filler material;
3 and 6 – welding arc; 4 and 7 – argon flow; 5 – electrode wire.
High demands are placed on the accuracy of assembly and welding. To reduce welding deformations, welding of structures made of aluminum alloys must be carried out in rigid equipment.
In general terms, the technological processes of assembly and welding of aluminum structures are the same as for steel structures.
The assembly of nodes and welding of nodes – panels, T-beams, frame set nodes is carried out on assembly panels, which are made of thick plywood or metal sheets, using the necessary fixtures and conductors.
There are mechanized equipment for the manufacture of structures from aluminum alloys, which includes devices for preventing and eliminating welding deformations. On fig. 12.15. shows a device for eliminating welding deformations by rolling the near-weld zone.
Rice. 12.15. Structural diagram of a device for rolling welded seams with rollers.
1 – rolling beam; 2 – carriage; 3 – engine; 4 – movable beam;
5 – guide bushings; 6 – columns; 7 – cross; 8 – pressure rollers;
9 – screw; 10 – disc springs; 11 – welding panel; 12 – plate;
13 – bracket.
On fig. 12.16 shows a section for assembly and automatic welding of aluminum alloy flat panels.
Fig.12.16. Section for the production of flat sections from aluminum alloys
Assembling the hulls of light alloy ships can be done in two ways – in the slipway-conductor and up the keel on the slipway-bed.
When assembling a vessel in a slipway – conductor, first of all, the conductor itself is made (Fig. 12.17), checking its shape and dimensions according to the plasma data. The dimensions of the bonds of the slipway-conductor are determined by calculation, taking into account the expected welding deformations and stresses.
The assembly of the hull in a slipway – conductor begins with the installation of outer skin sheets and is carried out in the direction from the diametrical plane to the sides and from the middle to the extremities. The body parts are connected using electric tacks. The hull structures are attached to the conductor with the help of clamping bars. Apply semi-automatic welding in an argon environment.
Fig.1.17. Assembling the hull in a slipway – conductor
1 – the base of the slipway-conductor; 2 – patterns; 3 – clamping bars
The assembly of the hull up with the keel is performed on the slipway – bed, starting from the assembly of the deck flooring. Then, longitudinal stiffeners, bulkheads, a vertical keel, frame frames (see Fig. 12.18) are installed on the deck flooring, and so on the whole set.
Frame frames are pre-assembled on shields or in universal conductors. According to the plasma data, the contours of the assembled nodes are applied to the shields, along which fixing elements are installed, in the simplest case, wooden blocks.
On the finished frame (see Fig. 12.19), sheets of the keel belt are installed and welded, and behind it, sheets of the right and left sides are successively.
Upon completion of the assembly and welding of the hull, it is turned over, the joints and grooves of the deck flooring are welded, the superstructure or deckhouse is installed and outfitting work is performed.
The hulls of vessels made of aluminum alloys up to 25 m long are recommended to be assembled in a slipway-conductor or on a slipway-bed as a whole. With body length up to 35-45 m in the same equipment with two blocks, with a length up to 50-60 m – in three blocks. When assembling the vessel with the keel up, the finished hull blocks are turned over, and then assembled and welded along the assembly joints.
Rice. 12.18. Frame frame of the hull.
The slipway – conductor is an expensive equipment. The use of slipways – conductors is economically justified in the construction of a large series of ships. For single and small-scale construction of ships, it is preferable to use the assembly up with a keel on a slipway bed.
Rice. 12.19. Assembling the hull of the catamaran keel up
Glue-welded joints are used for thin-sheet structures and are obtained by contact spot welding on glue, the diagram of which is shown in Fig. 12.20. In contact spot welding on glue, parts 1 and 2, between which a layer of glue 3 is applied, are supplied through electrodes 4 with electric current from transformer 5 , and during welding the parts are compressed by forces P.
It is advisable to assemble joints for welding, especially profiles with sheets, along the assembly holes, connecting the parts with the help of spring clips. After welding, the assembly holes are riveted.
The use of glue-welded joints instead of riveted ones reduces labor intensity of work several times and improves working conditions.
Fig.12.20. Scheme of resistance spot welding on glue
Features of joining aluminum alloy structures with a steel hull
The trend of modern shipbuilding is a relative increase in the mass of superstructures (cuttings) and a decrease in the mass of the hull, which leads to a decrease in the stability of the vessel. The use of aluminum alloys for the manufacture of superstructures solves this problem.
If the ship’s hull is made of steel, and the superstructure is made of aluminum alloy (Fig. 12.21), a special design solution is required for their connection.
Rice. 12. 21. Aluminum alloy superstructure block
Conventional welding technology is not applicable due to the large differences in required temperatures for each of the metals. In addition, there is a risk of corrosion in the presence of an electrolyte (sea water). Aluminum in sea water is subject to corrosion in this case, and the steel is protected.
Traditional practice involved separating the two metals with a rubber or plastic spacer and connecting the superstructure (cabin) to the hull with riveting. The riveting is associated with difficult conditions and a large amount of manual labor, in addition, there is contact of metals through the rivet itself, which also leads to corrosion.
The assembly for welding structures made of aluminum alloys with steel structures consists in the fact that a bimetal part is exposed between adjacent elements of structures made of aluminum alloy and steel.
Bimetal can be obtained as a result of simultaneous pressing and rolling of two sheet blanks – steel and aluminum. Rolled bimetal is supplied in 10x600x600mm plates. To obtain strips of the required width (30 mm), the plates are cut into strips on a guillotine and used to connect steel and aluminum structures.
The steel part is welded to the bimetal steel layer by semi-automatic carbon dioxide welding, and the aluminum part is welded to the aluminum layer by manual TIG welding or semi-automatic consumable electrode welding in argon.
On fig. 12.22. shows the junction of the wall of the superstructure (cabin) made of aluminum alloy with the coaming on the deck of a steel ship.
Fig. 12.22 Scheme of welding on bimetallic strips
1. Shipbuilding technology. Textbook edited by A.D. Garmashev. “Profession”, St. Petersburg, 2003-341 p.
2. Aleksandrov V.L., Perelygin A.V., Sokolov V.F. Shipbuilding enterprise in the market conditions. Shipbuilding. St. Petersburg, 2003-427p.
3. Dobrolensky V.P., Dogadin A.V. Nikitin E.I., Roganov A.S. etc. Plaza works. Manufacture of body parts. Sectional and stack assembly. KTS – 4. St. Petersburg, ed. center SPbGMTU, 1997-72 p.
4. Nikitin V.A. Technological equipment for assembly and welding of ship sections. TsTSS, St. Petersburg, ed. center of TsTSS, 2015-236 p.
5. Nikitin V.A. Design of cold and hot pipe bending machines. TsTSS, St. Petersburg, ed. center of TsTSS, 2011-196 p.
6. Gorbach V.D., Vasiliev A.A., Levshakov V.N., Nissenbaum R.S. Technological design of hull processing shops of shipbuilding enterprises. FSUE TSNIITS, ed. Center TsNIITS, 2005-148 p.
7. Aleksandrov V.L., Smirnov V.A., Sokolov V.F. Assembler of metal ship hulls. St. Petersburg, Shipbuilding, 1998-430 p.