As systems integrator Johann A. Krause Maschinenfabrik (Bremen, Germany) was putting together an automated assembly line for car engines, one station quickly emerged as a potential trouble spot: the station where centering sleeves are pressed into the cylinder block.
The sleeves are automatically fed into a loading plate and readied for press-fitting. When the press die is positioned, the centering sleeve is picked up and pressed through the loading plate into the cylinder block. If the sleeve is missing or installed at an angle, the cylinder head cannot be mounted. At best, such an error will cause the line to stop while the problem was fixed. At worst, the block will be ruined.
To minimize this type of error, Krause insert a PS20 servoelectric press from Bosch Rexroth Corp. Electric Drives and Controls Div. (Hoffman Estates, IL) to insert the sleeves. The press is equipped with sensors that enable the controller to monitor and control the force, speed and distance of the pressing operation. The travel sensor is a digital angle encoder with a resolution of 0.01 millimeter. Force is measured by strain gauges integrated into the housing of the press spindle.
Engineers can define the ratio of insertion force to distance traveled for each engine model and sleeve. When a preprogrammed switching point is reached, the speed of the ram can be reduced or stopped altogether. Assemblies that fall outside the target parameters are detected immediately. The ram then stops or backs off, and an error message is displayed to the operator. For analysis and quality assurance, the controller can display and print curves for each press-fit operation.
In addition to being precise and reliable, the servoelectric press is quieter than a pneumatic press, and because it consumes electricity only during a pressing operation, more energy efficient as well.
At other stations on the line, servoelectric presses are used to install sealing rings and bearings. All totaled, the line consists of 41 assembly stations and is 300 meters long. Each station is allowed a maximum cycle time of 40 seconds.
For more information on servoelectric presses, visit www.boschrexroth-us.com or call 800-REXROTH.