Incremental method forms rapid panels and rings

Tom Shelley reports on new methods for rapidly manufacturing parts from sheet and rings A new machine can form single metal panels under NC instruction without the need for a press tool. Developed as a research project at a leading UK university, it has been used to produce finished parts in 20 minutes. The base technology is now being extended to profiled ring rolling. Incremental forming has been developed out of spinning. Early studies on mandrel free spinning led to research at the University of Cambridge Institute for Manufacturing in 1990 to 1992 by Colin Andrew and Nick Powell on the incremental forming of flanged sheet components. The technique was developed in Japan principally by Matsubarra, and there are now a number of groups around the world looking at it. The Amino corporation of Japan has developed a dedicated incremental forming machine which is said to be very expensive and equipped with limited sensing. One group in Germany has this machine, but all other research groups looking at incremental sheet forming are using conventional CNC machines with modified work piece holders. The team at Cambridge, led by Dr Julian Alllwood, has built what it considers to be the first dedicated research machine for the process, with what Dr Allwood describes as, "Excellent force sensing, plus space for stereo vision and space for a second tool to be added later." The machine works by pushing a tool with a hemispherical tip into a metal sheet, and then making it follow a computer generated path. Built for £5 less than its budget cost of £10,000, the development machine is so far able to form 2mm aluminium, 1.66 mm mild steel or 1mm stainless steel sheet. The hemisphere tool is 5, 10 or 15mm across and is made from Rockwell C58 hard tool steel. The hemisphere is lubricated and free to rotate, but not rotated under power. The tool is moved in X, Y and Z co-ordinates by lead screws. Dr Allwood said that he chose lead screw drives, because he did not expect to achieve sufficient precision from pneumatic or hydraulic actuators, even with position feedback. An aluminium bowl 150mm across takes 20 minutes to make. The machine is still being developed. The next stage is to be the addition of a second tool underneath and Dr Allwood said he was additionally working on sensing, and that "The technology of 3D vision is nearly ready for use for online feedback." Conventional stereoscopic vision based control is apparently unsuitable because of problems caused by metal surface reflectance and insufficient computation speed. This has led onto the development of a related manufacturing ring rolling process. "Ring rolling is already an incremental process, with a mandrel inside and a roller outside, patented back in 1856", explained Dr Allwood. The new development involves additional axial movement of the mandrel and use of a narrow or shaped roller to create profiles. Half of all hot rolled rings are apparently made in batches of three or less. The project is being undertaken in conjunction with the Technical University of Aachen, which is rolling wax rings, and the Turkish company ORS (Ortadogu Rulman Sanayi) Bearings based near Ankara, which rolls exceptionally large numbers of steel rings. Unlike the incremental sheet metal forming project, which is based mainly on traditional engineering "Suck it and see", the ring rolling project involves extensive computer modelling. Dr Allwood was encountered at a University of Cambridge 'Horizon' seminar, "Towards a sustainable Earth." Members of the Institute of Manufacturing have for some time been promoting technologies aimed at small scale, low cost manufacturing at distributed locations in order to do away with the transportation, storage and logistics costs associated with present day mass manufacturing at centralised locations. He expressed concern at the seminar with the fact that 10% of world energy is consumed by the movement of freight from one place to another. The incremental forming process is intended to be one of a basket of technologies for very versatile machines that would, it is hoped, allow almost any part to be made locally in response to CAM data downloaded via the Internet. One of its biggest potential advantages would be in the faster availability of motor vehicle parts for even the most obscure foreign-made vehicles for body repair shops. Two executives from Scania showed a strong interest in the technology at the meeting, expressing an interest in the possible rapid production of vehicle body parts for truck prototypes. University of Cambridge Institute for Manufacturing ORS Bearings Pointers * Process allows the forming of single sheets of metal without the need of a press tool * It is much slower than pressing but much faster than the time required to make a press tool * The process is being followed by new improvements to the traditional incremental forming process used to make steel rings