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Optimization of bag forming machine c20

Eller, Tom (2011) Optimization of bag forming machine c20.

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Abstract:This report covers the main design decisions made during the re-engineering of bag forming machine C20. Machine C20 is situated in the conversion department of the plant and has several operational shortfalls, causing long downtimes and high waste rates. First, the current setup of machine C20 was analysed with specific reference to these operational shortfalls. It was found that a difference in tension between the main film and the strip films was causing problems in the final product. Furthermore, the machine produces bad seals when it is stopped and restarted by machine operators. These operators didn’t seem to work very structured either: they hardly ever notice a reel running out and don’t have a systematic set up plan to do job changeovers on C20. Finally, there were several alignment problems to be solved. The re-engineering of machine C20 can be split up in four different parts: the unwind system for the main reel, the unwind system for the strip reels, the folding frame and some smaller, remaining projects. For the unwind system of the main reel, a tensioning system, a line guide and safety chucks were implemented. The tensioning system consists of a pneumatic system with a dancer roller and brakes and makes sure that the tension in the film remains constant. The line guide controls the horizontal position of the film in the machine, tracking a printed line and actuating the position of the main reel. The safety chucks enable machine operators to quickly change the reel. The advantage of a safety chuck is that the driving mechanism of the shaft does not need to be removed when the core holding shaft is exchanged. Total costs for this subsystem are estimated at R 70.500, in which workshop hours and materials are the biggest expense. For the unwind system of the strip reels, a braking mechanism was selected with total costs as main criterion. An AC motor with variable speed drive was selected to deliver the braking moment, an arm with a rotational potentiometer measures the current reel diameter and gives the necessary feedback. With this system, the tension is controlled at the same tension as the main film. The strip unwinds will be mounted on the sides of the unwind station, under a angle with the main reel. To guide the strip films to the correct location on the main film, an adjustable ‘fold-in’-mechanism will be incorporated in the frame. Total costs for this subsystem are estimated at R 62.800, again with workshop hours and materials as the biggest expense. The folding frame was redesigned to incorporate the gusset folder. In the old situation, the folding mechanism consisted of two separate stations: at the first station, the plastic film was folded in half using a so-called A-frame folder, the second station created a gusset into the folded side of the film. Disadvantage of having two separate stations is the difficult alignment procedure when setting up the machine. The new design incorporates both folders into one frame and has a spring loaded mechanism to avoid tearing the film. Total manufacturing costs are estimated at R 25.000. Finally, the flying knife attachment was reconsidered to enhance operator friendliness and bigger pneumatic pistons were selected for the nip rollers. A systematic set up procedure was developed to reduce waste during product changeovers. During machine set up, operators wasted hundreds of meters of high quality, printed plastic film. After the first test with the new set up plan, only 3 meters of material was wasted, which is a promising result. The total re-engineering costs are estimated at R 162.200.
Item Type:Internship Report (Master)
Faculty:ET: Engineering Technology
Subject:52 mechanical engineering
Programme:Mechanical Engineering MSc (60439)
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