Development of a test cellfor automatic assembly and tack welding of components for jet engine exhaust cases

Abstract

The assembly and tack welding of jet engine turbine exhaust cases (TEC) is a complex and time consuming operation currently performed manually at Volvo Aero Norway. The assembly tolerances are very tight with a maximum alignment offset of 0.7 mm. The company wants to investigate the possibility ofa complete or partial automation of this process.

A test cell developed for studying the possibility of automating the assembly and tack welding operations of TEC components is presented. The test cell assembles TEC components using a control algorithm that combines high accuracy sensor measurements with an iterative stepwise alignment process performed bya robot. This test cell has been physically implemented and used for verifying the developed methodology.

The equipment used in the test cell is specified in the thesis. The test cell consists of two industrial robots, fixtures and a high accuracy laser sensor. The laser sensor is mounted on the tool flange of one robot; the other robot is fitted with a specially designed gripper for performing the adjustment operation. A modular fixture system has also been developed focusing on flexibility and simplicity. A developed control algorithm that coordinates the different operations performed by the elements of the test cell is presented.This control algorithm is implemented using the Python programming language; the implementation is described in detail.

The test cell assembly operation is based on the alignment of certain points on the components such that the offset is within tolerances. The iterative stepwise alignment process is described, including an operation for orienting the sensor for minimizing the offset measurement error. Once the points are aligned, the test cell simulates the tack welding operation.

Multiple tests have been performed in order to verify the test cell’s capability of aligning the components within tolerances. These tests have shown positive results for assessment of the automation of the current process.

To conclude, this thesis describes the developed test cell in detail. This includes the equipment used, the developed control algorithm, as well as multiple tests which confirm the test cell’s capability of aligningthe TEC components within tolerances. A valid methodology for robotic tack welding is also presented. Different studies for further development of the automation are finally proposed.