 In nearly every motor you will find piston rods, which transfer the piston stroke to the crankshaft. Frequently, separated piston rods are employed which, in the past, had to be produced in multi-level processes with a high standard of production accuracy. Through the use of piezo-electric force sensors, it is possible today to produce piston rods in a much more simplified production process. Here, the piston rods are systematically cracked at a predetermined breaking point and then fitted together later. In using this procedure, not only production costs decrease, but the piston rods also exhibit better behavior in relation to shear forces.
Procedure
Most piston rods have two bearing shells, which were always handled in separate processes and had to be intricately fine-tuned to enable proper mounting. This fine-tuning required a very high level of production precision and therefore represented a substantial cost factor. In order to reduce these costs, the piston rods are now produced as one-piece precision forging parts and then cracked at a defined position. The fracture faces created, fit together exactly and do not need any additional handling. Compared to conventional faces, micro gearing allows for high level of component strength against shear forces; the fracture faces are almost invisible after assembly.
Basic Conditions
Fracture splitting is interconnected with specific basic conditions in order to produce high quality cracked components. The deciding factor is the material itself. This should have no flow zone in order to minimize elastic deformations in the fracture area. Preferably, steels with higher carbon content are used since they are more brittle and therefore offer better fracture properties. The required fracture grooves are sintered or burned into the components by laser.
Process Monitoring
The actual cracking process is done using a pin. It pushes into the predetermined fracture grooves and ultimately produces the defined crack. This process only takes a few milliseconds.
The process and the quality of the fracture face created can be determined and controlled by measuring the load-time distribution of the fracture process. The force increases linearly to a maximum until cracking. The force decreases at the fracturing point and then increases to a maximum until the fracturing of the second web of the piston rod. The maximum value of this force and its chronological sequence are the characteristics of an exact fracture.
The use of rigid and extremely fast responding piezo-electric force sensors makes for exact and loss-free detection of fracture forces directly in power flow. The data is displayed in an HBM process monitoring module MP85, analyzed and saved. Here the initial operation of the whole chain is automated through the TEDS-functions (transducer electronic data sheets) of the charge amplifier and the process monitoring module and is therefore insusceptible to errors.
Summary
Sensor controlled process monitoring enables continuous control of the production process in fracture splitting and protects from production errors and excessive tool wear. Finally, it makes an improved planning and service range possible and, with recording and documentation options, turns cracking technology into a more transparent, cost effective and quality assured procedure.
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