SURFACE ROUGHNESS OF FORGED CRANKSHAFTS FOR MARINE ENGINES UNDER GRINDING WITH CUBIC-FORM BORON NITRIDE WHEELS

Abstract

The article is devoted to the problem of provision and control the surface roughness of forged crankshafts for marine engines. A set of monitoring measures is presented to assess the possibility of continuing the effective operation of the machine in a grinding system of the product of complex shape and accuracy, unique in terms of material consumption and labor intensity. The crankshafts have a length of up to 12 m and weigh up to 25 tons. The work was performed with grinding machine type DB12500, equipped with Sinumerik 840D control system, as well as measuring and eccentric processing systems. The grinding tool was a Molemab B126-100639 S.630090 disc type grinding wheel with especially hard abrasive tool material (c-BN). A considerable length of the working part of the grinding wheel around the periphery (over 6 m) is an important prerequisite for ensuring tool durability in the cycle of productive and high-quality external processing of specified functional surfaces of considered large crankshafts. Processing allowances were distributed between the preliminary and final grinding transitions with a slight increase (redundancy to ensure accuracy) for crank-pins, which were processed by the second plan. The microgeometric surface quality was controlled using a Surftest SJ-201P portable surface roughness meter, which avoided the obvious problems of stationary profilometry in the control of large-sized multiple-profile parts. The obtained roughness parameters after grinding (Ra ≤ 0.4 μm) were found highly satisfactory, allowing effective polishing afterwards up to the level of Ra 0.3 μm necessary for the main functional surfaces.

Keywords

• сrankshaft
• grinding
• wheel
• cubic-form boron nitride
• roughness
• profilometry