Lightweight automotive bodies take priority
The DEPRAG screwdriving function module sets flowform screws even in confined spaces
Lightweight construction takes priority! The energy-efficient car of the future has an extremely light bodywork structure made from various materials. Conventional assembly is being replaced by alternative technologies. One of these joining techniques is that of flowform fastening. Technical journalist Trixy Schmidt talked to Jürgen Hierold, Sales Manager at screwdriving specialists DEPRAG SCHULZ GMBH u. CO, based in Amberg, Germany, to discover more about the advantages of this joining technique for the lightweight structures now used in the production of vehicle bodies.
Trixy Schmidt: Lightweight vehicles are coming up in the fast lane because it is only such vehicles that meet the demands imposed by government policy and by consumers as regards energy consumption and CO2 emissions. What does that mean for car body construction?
Jürgen Hierold: Today’s car body structures combine materials such as steel, aluminium and magnesium alloys. So traditional assembly methods, such as the conventional resistance welding method, are being replaced by alternative joining techniques. Rivets are a possibility if the fastening point is accessible on both sides. If the design prevents this method from being used, screw fastenings made with flowform screws come to the fore as the solution to the problem. Flowform screws create a very high-strength fastening and form a process-reliable joint for different types of sheet metal.
Trixy Schmidt: In flowform fastening technology special screws - available on the market from several respected suppliers - are set in a six step process. But how does the technology actually work?
Jürgen Hierold: The flowform screw is positioned onto the aluminium or steel sheet, which has not been pre-drilled, and the screwdriving process begins. The screw - applied with a high down-force and also rotating at a very high speed - develops a high level of frictional heat, the material begins to flow and a kind of crater forms. In the next step the tip of the screw penetrates the material compound, thus forming a through-funnel. Enough material forms through this funnel shape to allow several thread turns to be applied. This produces a machine thread which can also accept a completely “normal” screw in the event that a repair is required later on. Once the thread has been formed, the screw is tightened to preliminary torque values for the head setting, and the fastening is then tightened to the pre-configured torque and angle parameters.
