Edited by Lawrence Kren & Victoria Reitz
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Two electromechanical presses (top) place parts such as impellers (bottom) in automotive water pumps. |
A pump manufacturer in Mississauga, Ont., was in a bind when a supplier couldn't deliver a test assembly. The Innovative Cooling Dynamics (ICD) unit of Tesma, which manufactures water pumps for the auto industry, used asynchronous in-line assembly with testing after each operation. As a replacement, the supplier suggested an electromechanical press (EMAP) built by Promess Inc., of Brighton, Mich., which simultaneously assembles and handles necessary quality-control information.
ICD uses Promess EMAPs for four critical operations. They press bearings into pump housings, hubs onto pump shafts, seals into pump housings, and impellers onto pump shafts. The new equipment eliminates separate testing stations from the line, saving 20 to 25% in floor space, and reducing overall system costs. While the older system delivered a CpK of 1.4 with a 75micron standard deviation, the new processes have a CpK of 1.75 with a 40-micron standard deviation.
EMAP systems use an encoder-equipped servomotor to drive a ball-screw ram that can be equipped with a variety of sensors. The EMAP simultaneously monitors and controls the ram's force and position. EMAPs also carry out signature analysis and closedloop external sensing.
Signature analysis plots the force required to assemble components against the distance traveled to produce a unique assembly "signature." Setting upper and lower limits for this signature assures production of good assemblies without the need for any other inspections.
The exact shape of the signature also provides information about individual parts being assembled, which can be used as control inputs for other processes. For example, parts that are too soft or too hard produce distinct changes in signatures, as do parts with out-of-tolerance assembly details such as misplaced holes or incorrect shaft diameters.
The EMAP system also records six additional external sensing commands. This lets the system compensate for deflection, part creeping, and temperature, and calculate an overall tolerance from a separate reference surface.