机械精度设计与检测技术 (15).pdf

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1、TOLERANCE PRINCIPLESCHAPTER 5Tolerance PrinciplesUp to now,we have already studied dimensional tolerancesand geometrical tolerances separately.AccordingtoISO,therelationsbetweendimensionaltolerances and geometrical tolerances are defined in variedtolerance principles.Independency PrincipleIndependen

2、cy principle:According to ISO,by default,dimensional tolerances and geometrical tolerances on adrawingareindependentlyappliedunlessspecifiedrelationships are shown between them.It means,normally,the dimensional tolerances and thegeometrical tolerances have no relation between each other.Dynamic Tole

3、rancing DiagramInordertodiscussclearlytherelationshipbetweendimensionaltolerancesandgeometricaltolerances,adynamic tolerancing diagram can be drawn.The red area shows the allowable tolerance zone in whichboth thedimensional error and straightness error arequalified.100 0-0 0.02020.0110100 0.0202Dime

4、nsional errorStraightness error0 0.0101Allowable tolerance zoneDynamic tolerancing diagramUnderstanding the Independency Principle20 0.10.320.119.9Flatness tolerance is 0.3?!Above 20.120.10.320.019.9Physical occupying areaFlatness tolerance is 0.3mm,but height size tolerance is only 0.1mm.Is this re

5、quest reasonable?According to independency principle,there are no relation between dimensional tolerances and geometrical tolerances.So this drawing has no problem!Using Independency PrincipleIf a special relationship is required between dimensionaltolerancesandgeometricaltolerances,thespecialrelati

6、onship must be specified on the drawing.If there is no specific relationship indicated on the drawing,the principle of independence is used.Considering Interdependence RelationshipHowever,in some situations,dimensional tolerances andgeometric tolerances may be related to each other.Such requirements are“Maximum material requirement”,“Least material requirement”,“Envelope requirement”,and“Reciprocity requirement”.The benefit of such requirements is that an additional orbonus tolerance zone is allowed.We will discuss these requirements in detail in the followingsections.