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| HOME >> Special Purpose Machines / Plant Construction >> Prefabricated stud-frame houses | Tuesday, January 6, 2009 | |||||||
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COST-EFFECTIVE PRODUCTION OF INDIVIDUALLY DESIGNED, PREFABRICATED STUD-FRAME HOUSES  Innovative production technology for production of prefabricated stud-frame houses
Since its founding in 1979, the Bad Wurzach-based company LISSMAC Maschinenbau und Diamantwerkzeuge GmbH has continued to grow. It currently produces several thousands of construction machines, series machines as well as individually manufactured special-purpose machines. For more than 20 years, the company has also been producing complete plants with different levels of automation for industrial-scale construction. Its extensive know-how on automated production of brick walls provides an excellent basis for equipping complete factories producing prefabricated timber-frame houses. Such a factory was recently put into operation in Semyonov, which lies close to the Russian city of Nizhny Novgorod on the River Volga.
Prefabricated stud-frame houses generally consist of a series of upright wooden studs sheathed by various types of boards. The cavities are filled with insulating material. The light-weight building materials allow industrial-scale prefabrication of wall, ceiling and roof elements with a high level of automation. They can also be easily handled in the production hall and efficiently transported. A standard single-family house can be erected on top of a cellar or a floor slab in two to three days so that it can be locked up and is weatherproof. Work on the interior construction and fittings can be started immediately.
Production of solid structural timber and glued laminated timber The factory buys sawn timber from the saw mill and then dries it to a residual moisture content of approx. 12 ±2 percent. The moisture content of the individual timbers is checked during subsequent stack separation. The wood is then rough-planed to ensure dimensional accuracy of the cross-section. Planing facilitates the identification of any imperfections that compromise the strength, such as branchiness, cracks, wanes, blue stains, etc. These imperfections are visually identified, marked and automatically cut out with a cutoff saw. This results in timbers with a length of 0.30 to 3.00 metres. These timbers with different lengths are bundled and then finger-jointed, coated with glue and pressed into an endless strand. The cutoff saw at the end of the press cuts these endless strands into final lengths of 9.00 to 12.00 metres. After curing, the individual solid structural timbers are singled out and fed into a four-side planer. Glued laminated timber (glulam) is used for roof purlins and can also be ordered for visible ceiling beams. Glulam is produced in the same way as the finger-jointed timbers up to the intermediate storage stage. These structural timbers are singled out of the intermediate store and likewise planed, then coated with glue on the flat face and pressed together. After the glued beams have cured in the press, they are fed into a four-side planer, then chamfered and automatically stacked. The plant engineering systems supplied by MINDA Industrieanlagen GmbH end at intermediate storage of the solid structural timbers and the glue laminated timber. This is followed by the production engineering equipment supplied, assembled and installed by LISSMAC Maschinenbau und Diamantwerkzeuge GmbH. Finishing of the structural timbers Two speed-cut machines process the structural timbers used to produce wall, ceiling and roof elements as well as special elements such as gables, dormers and jamb walls. This means that each wooden part, whether it is to be used as a chord, stud, ceiling beam or rafter, is automatically cut to the specified length and then milled, drilled, marked and labelled according to the geometric CAD data of the house design. Generally, LISSMAC-specific CAM software provides the data for the automated machines in the factory. The production control computer sends the complete dataset automatically to the respective machines, i.e. to the speed-cut machines in this case. Board cutting Seamless manufacturing of the wall, ceiling and roof elements requires the availability of the corresponding waterproof chipboards, cement-fibre boards, plywood sheets, gypsum fibreboards and gypsum plasterboards. LISSMAC has installed an electronically controlled board saw for this. Sawing in bundles is more cost-effective. The sawing centre receives the dimensions from the LISSMAC production control computer, which processes the CAD data for each individual machine. All boards used for sheathing the interior and exterior wall elements as well as the ceiling and roof elements are accurately cut to the planned dimensions by the sawing centre. Production of wall elements The line for manufacturing prefabricated wall elements can process wall elements varying between 900 and 12,000 millimetres in length and between 2,500 and 3,000 millimetres in width. Interior walls are 105 millimetres thick and exterior walls, in this factory, are 231 millimetres. Naturally, thicker exterior walls are possible for other climatic zones. Manufacturing starts with the semi-automatic insertion of accurately positioned, presized structural wall timbers into the framing station.
The first table is used to cover the interior side of the stud frames with gypsum plasterboard. Pneumatic stops automatically secure the incoming frame element. Workers then span a vapour barrier film over the entire surface of the frame and tack it down. A board handling unit, which is guided by an overhead carrier system and has a vacuum cup suspension device, moves the presized gypsum plasterboards into the desired X, Y and Z directions onto the film, then aligns and anchors the board. The openings for windows and doors remain open. The frame is transported to the second wall assembly table. Pneumatic stops on the second wall table secure the incoming frame when it reaches the programmed position. This ensures that the automatically inserted staples joining the gypsum plasterboards to the studs and chords in the frame are positioned correctly according to the assembly plan. LISSMAC functional bridge LISSMAC has developed the illustrated multifunctional bridge for automatic stapling.
Insulation and exterior panelling The chain conveyor moves the prepared wall element to a pair of tilting tables known as a butterfly turning table. The electrical sockets are installed on the first tilting table. When this is complete, the tilting table turns the wall element onto the neighbouring tilting table, which is installed parallel to the first. The conduits for the electrical cables are installed in the wall element on the second tilting table. Some of the thermal insulation material is inserted at the same time. The chain conveyor then transports the wall element to the next assembly table where the remaining thermal insulation material is inserted manually. The element is transported to the next table where it is secured by pneumatic stops. The workers position the boards for the outer panelling using a second, identical board handling unit. Gypsum plasterboards are used once again for interior walls. After the boards have been aligned and tacked, the integrated chain conveyor transports the wall element to the next work table, which is equipped with the second LISSMAC functional bridge. It staples the panelling boards onto the wooden frame and cuts any predetermined openings in the boards. The chain conveyor then transports the wall element to the last work table in the production line, where the windows are inserted with a special lifter. A tilting transverse transfer table accepts the finished interior wall elements, sets them upright and transports them vertically into the wall store. The wall storage area is spacious enough to allow certain remaining work to be carried out, such as fitting the doors. The transverse transfer table transports exterior walls horizontally to one of the two work tables on which the preparatory work for adding additional thermal insulation as well as the base render coat is carried out. The house is externally rendered at the building site. After the additional thermal insulation boards have been adhesively bonded to the exterior panelling boards, the unit is transported vertically into one of the three spray booths, where the base render coat is applied, a mesh is pressed in and the entire exterior surface is smoothed over with a thin layer of plaster. After a few finishing steps have been completed, the exterior walls are transported to the wall store. Production of special, ceiling and roof elements Special elements are produced manually along the longitudinal wall of the production hall next to the spray booths. These include gable and jamb walls with stud frames. The special elements are manufactured on tiltable work tables. This side of the hall also accommodates the areas for manufacturing ceiling and roof elements.
Comprehensive know-how for industrial manufacture of prefabricated houses Prefabricated housing elements with a timber-framed structure have been produced industrially in Semyonov since July 2008. The factory is configured for the production of four standardised prefabricated houses per day in two shifts. With 250 working days, this amounts to 1000 houses per year. After only a short start-up phase, it became clear that the market required not only standard houses, but also individually designed prefabricated houses. The production technology, particularly the plant engineering equipment downstream of the finishing section for the solid structural timbers, is configured so that individually designed houses can be also manufactured with a high degree of automation. The CAM solution developed by LISSMAC Maschinenbau und Diamantwerkzeuge GmbH is particularly important because it enables CAD data from different suppliers to be processed so that the machines receive the appropriate programmes from one production control computer. The LISSMAC CAM solution is the key factor in work preparation for coordinated and efficient manufacturing of individual prefabricated housing elements, and forms the basis for high levels of flexibility and automation, which is particularly desirable for operators of such production facilities. In addition to the technical and organisational requirements for the construction of high-quality prefabricated houses, LISSMAC also offers comprehensive support in training specialist personnel. This includes training of the operating personnel as well as the process engineers who design such prefabricated houses. Thus LISSMAC not only supplies production-ready manufacturing facilities, but also provides the operator with all the know-how for manufacturing prefabricated houses according to the buyer's requirements and in the required quality. LISSMAC will also act as a general contractor for such investments on request.
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