Про характер зміни подачі при виході інструмента з тіла заготовки в процесі свердління наскрізних отворів

Abstract

На основі міцнісних характеристик свердла, яке розглянуто як консольно-закріплений стержень, з урахуванням приведеної жорсткості механізму подач вертикально-свердлильного верстата отримано різні закономірності зміни подачі при виході інструмента із тіла заготовки в процесі свердління наскрізних отворів залежно від діаметра свердла у вигляді системи рівнянь, виходячи із певних обмежень, а саме: пластичної міцності матеріалу інструменту; стійкості на поздовжній згин; міцності на кручення; міцності механізму подач вертикально-свердлильних верстатів.

The paper deals with the investigation of feed variations regularities in the tool exit from the work piece body in the process of through holes drilling. It is stressed that the labor input of drilling depending on the production mode including single part, small batch, batch and high volume manufacturing, are respectively from 6 – 7% to 20 – 30% the total value of the machining labor input. As a result of detailed and profound analysis of home bibliography dealing with the through holes drilling process it was found that at present time there is no unanimous opinion on the feed variations character on the stage of tool exit from the work piece body. The paper proposes to examine the drill as a console mounted rod (shank) which is hinged tilting with its free end. The rod feed is determined basing on certain restrictions: plastic strength of tool material; longitudinal bending resistance; torsion strength; strength of vertical drilling machine feed mechanism. The dependences are determined to found the ratios of the drilling axial force value and the force at which the Vickers hardness of the machining material. The dependences are also developed to calculate the feed value on the assumption of the condition of the strength ensuring of the tool material used. The design parameters of drills of different manufacturers that are regulated by Ukraine, Russian Federation, Sweden, Germany and the USA standards are analyzed. The formulae are found to calculate the length of the mounted drill console for different helical drills types and series. More accurate mathematical model is found to determine the feed value with the given assumptions considering the drill rod console length and as an example it is illustrated by different materials of corresponding graphs. The diagram of the feed variation depending on the drill diameter while drilling the holes in the steel with σв=750 MPa is given for the high speed steel Р9Ф5 taper-shank drills (tungsten content is about 9%, vanadium – 5%, carbon – 1%, chromium – 3,5 – 4%, molybdenum – 1%). The dependences to calculate the ranges of drills for which a feed is determined considering some or other restrictions are found. It is stated that depending on the drill diameter and the vertical drilling machine rigidity spindle as well as the parts deformation value of feeling, the character of feed change in the tool exit from the work piece body while holes drilling can cause the feed increase, decrease or can not change it at all.