Delft University of Technology
Faculty Mechanical, Maritime and Materials Engineering Transport Technology
A.A.W.J. Verdult Automated truck frame assembly. A feasibility study. Masters thesis, Report 2006.TL.7078, Transport Engineering and Logistics.
The current production line for the assembly of truck frames at DAF is twenty years old. Its assembly process is done manually. Problems with noise levels, spinning bolts during tightening of the nuts and ergonomics made the management of DAF decide to start a research project. This study investigates the technical and financial feasibility of a new, more automated frame assembly line.
The start of the study was the examination of the frame variety. Truck ladder frames are made up of cross members enclosed by two side members. The 1836 different side member pairs give a good idea of the large variety of frames. To make 41.200 truck frames annually, DAF needs, for the assembly work and quality checks at the line, twelve workers in two shifts. The total production time is split in a mounting time percentage, which varies between 60% and 70%, and percentages for handling, unpacking and administration.
To solve the ergonomic problems and avoid the high labour costs, an exploration is done to the possibilities of an automated production line. Twelve ideas were evaluated and judged. Two of the best options are worked out further: two concepts for the handling of side- and cross members and two
possibilities for the tightening process.
Handling, Concept 1
Automated guided vehicles (AGV's), side member handling Autonomous carriers (Roboloop), cross member handling Handling, Concept 2
A crane system, positioning of the side members Moving pallets (Montaflex®), cross member handling Tightening, Fully automatic
Supplying and tightening of bolts and nuts Tightening, Semi automatic
Automatic tightening of bolts and nuts, all other work is done manually
All options have great advantages: a halved throughput time, an improved quality level and less ergonomic problems. There are difficulties though, that need to be solved. Concept 1 uses AGV's that need to be adapted for the positioning accuracy requirement and the Montaflex® system in concept 2 has problems with its maximum speed. A complex bolt- and nut supply unit and a minimum of twelve robots are needed for a fully automated tightening process. The semi automatic option needs only two robots but has a slight problem with spinning bolts. The costs for all options are estimated and compared to he savings on labour costs of seven workers. Concept 1, together with a semi automatic tightening process meets the technical and financial requirements best. Both options together will cost about 3,5 million euro.
With two workers for the pre-assembly work on the side members, two workers for the bolts and nuts and one supervisor/operator, this results in an automation degree of 57% and a Return on Investment (ROI) of 41 %. The direct costs for the assembly of frames change from € 52,2 to € 24,9 which is a reduction of 52%. A system like in concept 1 will be challenging and innovative but the financial and technical benefits make it highly recommendable.
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