New fixtures for car body assembly operations in the vehicle industry
Research Project SMARTFLEX
The paper summarizes part of the results of the project SMARTFLEX (co-funded by the Italian Ministry of Research and Education) - Smart, reconfigurable, flexible production systems: research of enabling technologies for flexibility, reconfigurability and intelligence of production systems for the vehicle industry.
The project involves Comau Robotics and FIAT (Centro Ricerche FIAT and FIAT Group Automobiles) with the goal to create conditions for breakthrough innovation in the car body assembly process in terms of autonomy and adaptivity to achieve higher flexibility and re-configurability. The overall objective is an assembly line processing numerous car bodies also with remarkably different geometry.
The results presented in the paper deal with the technology of fixturing of car body steel components for the welding. The fixtures in use have mechanical clamps with yaws from both sides of the pack of sheets to join. Resistive spot welding is used and the spots are given in two rounds, a first one to lock the sheets and a second one to complete the joining. The new fixtures have a mix of different grasping and locking units assembled modularly on a common base frame. The project develops either the new modules and the tools for fixturing planning and design. A major industrial result is in the use of clamps leaving one side of the sheet pack free and fully accessible, in particular and in perspective for remote laser welding.
The assembly processes in automobile manufacturing are the sum of multiple elementary operations.
Each operation corresponds to a function of the process that must be followed. Today this happens using "devices", or "machines", more or less available on the market (robots, tools, stamps, shifting devices).
The improvement of these devices is the innovation key and the main topic of the current industrial research.
Beyond this current vision focusing on the single instruments, the approach of SMARFLEX is the deep re-engineering of the whole automotive assembly process: Starting from the elementary functionalities to provide (part shifting, reference, blocking, joining, measure, control), new devices are introduced which, today, are not in use in the automotive field and require basic research.
The projection of this vision in the fixturing for joining pushes the design of new fixing methods "compact and re-shaping". The procedure adopted is to add features to the current clamping systems maintaining or improving the available performance and at the same time elevating the flexibility level and clamping adaptability. All solutions considered: keep the clamping safe and precise, cut down the global manufacturing cost, do not hinder the joining process and, furthermore, they make it easier, reduce the obstruction impact on process timing.
An innovation of the clamping system is suggested by the exploration of radically different solutions compared to the traditional directions of development:
- use of magnetic forces
- "intelligent" blocks, self adapting to the tolerances of the process and/or to the parts
- active fixtures collaborating with the manufacturing units
The use of magnetism as grasping principle for the handling and transportation of magnetic sheets and components is known but, currently, hardly any study on positioning and clamping during the assembling operations, relying on electromagnetism, is coming to industrial results.
Between the adaptable blockings, instead, the development aims are: increased workpiece accessibility, increased fixture-workpiece system rigidity, decreased need for specific supports, increased productivity. Obviously the fixture releasing phase, after the expected joining cycles operations, has been considered.
The final result of the project is a reconfigurable fixture for car body assembly with a mix of mechanical yaws and magnetic clamps distributed over mobile supports for their quick online repositioning and the adaptation of the fixture to parts with totally different geometries and fixturing requirements. A prototype of this fixtures has been built and is under testing.
Rezia Molfino, Matteo Zoppi, PMAR University of Genova
Manuel Lai, Antonella Turi, Amit Eytan, CRF Centro Ricerche Fiat
Fulvio Rusinà, COMAU Robotics