机械制造技术基础英文课件CHAPTER6 - 图文

6.2.3.2 machining accuracy influenced by forces

（1）influencedbythepositionvariationoftheforces

Oneofthefeaturesofthemachiningsystemstiffnessisthatthestiffness

varieswiththepositionvariationoftheforces,whichmakesthevariationofthediameterindifferentsection,andcausestheshapeerror.

（2）Influenced by the variation of the force size

Thenon-uniformofthematerialhardnessormetalremovalwillcausethevariationofthecuttingforce,whichwillmakethenon-uniformdeformationandleadtomachiningerror.Fig.6.20showsasituationwhenashortcylindricalstockwithellipseerrorwasmachinedonalathe.Ineachrotation,thebackengagementwillvaryfromthemaximumvalueap1totheminimumvalueap2，whilst,thecuttingforcewillalsovaryfromthemaximumFY1totheminimumFY2，fromtheformulaY=Fy/K,theyielddeformationofthecuttercausedbythevariationofthecuttingforceisY1andY2.

Fig.6.20 the copy of the stock shape error movie

According to the cutting theory,the cutting force is proportional to the back engagement under certain condition

FY1?CaP1;FY2?CaP2where：C?CFYfYFYKFY——constatnt N／mm；

——back engagement，mm ——normal cutting forces N

aP1FY1ap2FY2