شبيه سازي ارتعاشات چتر در فرايند سوراخ كاري

چكيده انگليسي :

Simulation of Chatter Vibration in Drilling Process Mojtaba Darvishi m darvishi@me iut ac ir Date of Submission 2011 05 22 Department of Mechanical Engineering Isfahan University of Technology Isfahan 84156 83111 IranDegree M Sc Language FarsiSupervisor Javad Zarkoob Zarkoob@cc iut ac ir Hassan Nahvi hnahvi@cc iut ac irAbstractMachining operation is one of the most important methods in part manufacturing and creating final outline ofthe part In this method by CNC machines and using various chipping operations such as turning milling boring grinding and etc additional materials are removed from raw material and the final shape is created Machining is usually one of the most common and may be the most complicated cutting process In order toproduce high quality surfaces in batch production with great amount of chipping and to create high qualitysurfaces at high speed a phenomenon called chatter encounter Other problems caused by chatter include thedecrease of machine tool lifetime and the work safety Chatter is an unstable self excited vibration occurring dueto different factors such as waves created by the tool vibration owing to previous period and amplified due tothe phase difference with the waves created in current period of machining Studying the chatter theory indrilling operation and analyzing the parameters influencing the system stability a model can be offered tocontrol the chatter vibrations during drilling operations In drilling and other machining processes we want torecognize the areas or circumstances in which the tool vibration becomes unstable and to avoid trapping inthese areas and situations which lead to the tool vibration instability Moreover we intend to identify the areasin which the highest chipping rate exists without instability For this purpose stability diagram method is one ofthe most credible methods and assessment criteria that show the border of stable and unstable regions inmachining In the current research the chatter vibrations in drilling process are simulated using MATLABsoftware and with regards to the modeling performed stability lobes are diagrammed In order to determinestability areas several methods can be used one of them is simulating the vibrations in the time domain Bysimulating the tool vibration we can determine its stability or instability and even specify drilled surfacequality and dimensional accuracy of the created hole Hence by using simulation in the time domain prior todrilling we can assess the vibration stability and the hole tolerances and determine whenever the vibration is notstable and hole shape or size is not acceptable This can be done by choosing appropriate cutting circumstancesand therefore without wasting money or spoiling the tool or workpiece favorable quality can be obtained Inorder to simulate in the time domain estimation of shear forces is critical increasing the force model accuracyresulted in more accurate results For this purpose a variety of models for estimation of shear forces in thedrilling operation has been presented that each of them had some limitations In the offered models the problemencountered was that just variations of rake angle have been considered in the shear pressure distributionequation However in addition to the rake angle oblique angle cutting width and helix angle of the drill alongwith the cutter lip have also effects in the shear pressure and their values are not constant Therefore in thisthesis a force model was proposed that considers all of these effects resulting greater application compared withthe other models In current model variations of geometrical parameters along the cutter lip have beenconsidered Another important factor in simulation of the tool vibration is the vibration model itself In drillingprocess determination of the vibration model needs more carefulness because the tool impact with theworkpiece is intensive and based on the material and various factors of the drill and the workpiece the vibrationmodel wou

درويشي، مجتبي

شبيه سازي ارتعاشات چتر در فرايند سوراخ كاري

نمودارهاي پايداري , شبيه سازي دربازه زمان , مدل نيرويي