• Dossier on subcontracting Technical article

    Subcontracting: Decorative Sheet Metal Work, Facade, Cladding, Railings, etc.

Submitted by benoit.cantin on Thu 17/06/2021 - 16:37
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  • The building industry uses a lot of custom-made sheet metal parts:

    • either for decorative items, such as façades, railings, cladding, casing, etc.

    • or parts for fitting or covering, including:

    - window sills, caps, corners, covers, etc. - covering parts or mounting brackets for lifts, freight elevators, stairs, etc.

    In the building industry, these kind of products are often produced in small quantities and are custom-made, in accordance with their end-use and the building itself. Lead times are also often important criteria when choosing a subcontractor.

    Construction parts can be quite simple or very elaborate (sheet metal or decorative trims). The production technology is fairly widespread, but the difficulties lie in the behaviour of the material, particularly when it distorts.

    This article focuses on cutting technologies for the building industry, as well as the distortion of materials, which is an important element to consider for decorative parts.

  • 1- The Cutting of Parts

    Shearing Machines
    Rectangular parts can be made with a simple shearing machine, especially if the part does not have any interior openings.

    Punching Machine, Combined Laser-Punching Machine and Combined Shearing-Punching Machine

    Punching is ideal for parts that have:

    • interior openings, bosses, or other distortions, tapping and even small folds. Indeed, some punching machines with adapted tools are designed to make little bends, such as lugs.

    • There is a limit to the contours that can be achieved with a punching machine. The part’s design has to be simpler than for a laser cutting machine, with few or no sharp curves. Bends would require nibbling, which is more time consuming and less aesthetically pleasing than laser cutting.

    Decorative sheet metal
    Decorative sheet - Copyright LPS

    Machines that combine two technologies, such as laser cutting/punching, are only worthwhile if the part warrants it, because the cost per hour is higher than a ‘single’ machine. A combined machine combines the advantages of both.

    Punching creates little "spikes" that may need to be deburred, which would require an additional operation.

    Laser, Plasma, Oxycut, and Waterjet Cutting
    Laser cutters are probably among the most used machines, especially for cutting decorative parts. Indeed, these parts are designed freely, and the machine can accommodate all kinds of shapes. The quality of finish is also very good, while maintaining decent cutting speeds. Deburring may be necessary though in some cases. Depending on the material and the technology, the machine can cut through a thickness of up to 50mm.

    There are other cutting technologies available too, such as plasma, oxycut or waterjet. They allow to cut through thicker materials and, for waterjet cutting, through almost any type of material (ferrous, composite, plastic, etc.).
     

  • 2- Flattening Sheets to "Treat" Distorted Parts!

    No matter the machine, cutting parts distorts them. This phenomenon is amplified for very elaborate parts, i.e., with lots of interior openings, or a small width.

    Planeuse : pièce de décoration pour le bâtiment
    Decorative piece for the building industry - Copyright LPS

    Michael Boulier, LPS, gives an example: "Railings are increasingly made with laser cutting rather than profiles. The small width of the parts means that there is a lot of distortion. The same applies to decorative sheets, such as those that can be seen on some buildings with elaborate patterns and lots of openings. This weakens the material and causes it to distort more!”

    Metals that have been distorted by punching or laser cutting can be straightened using a leveller. This machine uses staggered rollers to knead the metal in order to release internal tensions and flatten it. The cycle time is variable and mainly depends on the handling of the machine.

    Michael Boulier, LPS, adds "that the parts have to be clean, or to have been deburred, before carrying out the flattening operation.”

    Conclusion
    This article aims to detail the different techniques and steps involved in manufacturing parts for the construction and building industry. Special measures sometimes need to be taken, particularly when it comes to decorative, cladding and finishing parts. For some, therefore, flattening is a key step. Unlike other means of production, such as cutting or folding, which are frequently used, subcontractor do not often use levelling machines. They may therefore have to subcontract this operation, which can result in longer lead times. Identifying the steps required to manufacture these parts at the start of the project will enable the prime contractor and subcontractor to define realistic specifications, including the delivery date.