Graded Freeform Machining of Cylinder Bores using Form Honing

Gerhard Konrad Flores

doi:10.4271/2015-01-1725

The use of form honing contributes to energy efficiency of modern internal combustion engines, especially to the reduction of CO₂. Until now the production of internal combustion engines has required cylindrical bores with high shape and surface quality. This machined macro form is not maintained for the function of the engine due to mechanical and thermal influences. During operation they cause complex distortion mechanisms which significantly deviate from the desired cylinder form.

Therefore Gehring developed a form honing process that does not produce the cylindrical bore form as its goal, but gives instead the expected cylindrical deformations having the quasi cylindrical bore geometries under specific operational conditions. Furthermore the current development of form honing considers the friction of the piston skirt of the cylinder operation temperature with specific clearance in the lower part of the bore. This is possible without impairment of the NVH behavior of the engine.

The freeform for compensation of cylinder distortions and the local clearance for reducing friction at the piston skirt, can be applied in a complex form or used separately. Correlating to the high degree of freedom of form honing, all the functional advantages of freeform of cylinders bores can be achieved.

The principle of form honing, the process components, the serial production capability, the increased quality concepts and the achieved machining and functional results are described below. Consequently, form honing is an innovative contributor to the sustainability of the internal combustion engine. This paper describes the production process, which is available for the serial production of internal combustion engines. The test results of the fired engines are not the knowledge of Gehring Technologies GmbH.

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Graded Freeform Machining of Cylinder Bores using Form Honing 2015-01-1725

SAE MOBILUS