The future development impetus for the ICE will focus on the reduction of CO2emissions. This is dependent upon fuel consumption, which in turn is determined by internal engine friction. The goal of form honing is a form-optimised cylinder bore under typical operating conditions. This technology can be sub-divided into two process variations: form honing light and form honing professional.
Form honing light simulates thermal distortion by creating different tapered shapes. Thermal expansion due to the higher taper in the top centre leads to a cylinder bore which must be honed to a smaller size at the top and a larger size at the bottom. Thus, the piston shirt has less contact with the bore, resulting in significantly less friction.
The conical shape is generated by feedback controlled stroke displacement with higher stock removal in the lower bore section, due to increased contact time with the abrasives. Electro-mechanical feeding changes the radial expansion position of the honing stones during the stroke movement according to the form and, subsequently, improves the previous conical shape.
These process components assure the reliability of round, non-cylindrical tapered bores within the standard cycle time. Form honing has already been integrated globally into mass production scenarios. The application of form honing light has shown that significant improvements in emissions reductions are possible.
Form honing professional not only optimises the local piston clearance but compensates for cylinder deviations from static and thermal distortions. This capability means that in running conditions, round and straight bores can be achieved. Ring tension is reduced, which results in adaptive friction and C02reductions.
The non-cylindrical shape deviations can be defined through CAE assessments or torque plate bracing and tempering. To implement form honing professional, innovative processing hardware is necessary. The hardware includes: special honing tools with independent actuated abrasives; a piezo feeding system; a shape adaptive control; and a spring-loaded finish-honing tool.
Shape data for the cylindrical deviations will be converted for every single cylinder of the engine using the form honing control. This process interaction between the feeding system, shape and the form honing tooling creates an optimal result, says Gehring.
Form honing professional has been implemented by customers for small batch scenarios. It is said that the process produces cylinder deviations and surface finish profiles with high reproducibility and economical processing times. In addition, the process delivers free shapes and surface profiles with high reproducibility to conditions that still conform to cycle time requirements.
