1、Geometrical Dimensioning and Tolerancing GD&T 形位允差&幾何允差,Reasonable Tolerance Zone,Process 之偏移量,長期而言，Process有1.5s偏移量(經驗值),Motorola公司之 6 Sigma,在6s 品質水準下每百萬件產品將有3.4個不合格點p(z4.5)+p(z-7.5)=0.0000034,製程平均數不變與移動 1.5的百萬分之缺點數比較,尺寸變異,形狀變形,方向變形,位置變形,GD&T 處理0.01mm 以上之變形量,GD&T 處理 0.01mm以上之變形量,Geometry Control Too
2、l,Feature Control Frame,Feature Control Frame,Basic Dimension,基準面的標示方式,利用點之組合定義基準面,利用點來定義基準面,Rocking Datum,Datum Selection Priority (For sheet metal parts),The largest surface. The longest cutting edge. The shorter cutting edge. The longest bending edge with lowest height. The 2nd long bending edge
3、with lower height. The highest bending edge with datum target.,Parts do not have center lines, Feature have Axis,形位控制工具,一個使用於形位控制框格的項目，其目的係說明那一種形位係可接受變異。尺寸( Size Tools ) ：例如直徑、球的直徑、厚度、寬度 形狀( Form Tools )：例如直線度、平面度等 方向( Orientation Tools ): 例如平行度、垂直度、方向度等 位置( Location Tools ) ：例如位置度、同軸度等,SYMBOLS,尺寸工具
4、( Size Tools ),Flatness,Flatness,In Examples 1 and 2 the problem may cause an acceptable surface to be rejected.,Problem: Often insufficient points are taken to evaluate the flatness error. As a result, an out of spec surface may be accepted.,Bottom line, inspecting flatness requires time and patien
5、ce.,Cylindricity,Straightness,Circularity,What the designer wants.,What the designer might get according to the print.,The standard is very clear on the limitations of size and form controls. They are individual controls. They do not relate features to one another.,Straightness with Circularity,方向工具
6、( Orientation Tools ),Angularity,The 2009 revision of the Standard gives us an Alternative Practice of using angularity for any of the orientation tolerances.,Stabilizing an Orientation Tolerance Zone,Parallelism,Position - Feature of Size,If You Use Position, Make Sure You Have a Feature of Size,Po
7、sition - Location of Irregular Feature,The figure shown below is a possible gage that might be used to inspect the position tolerance. The values shown are theoretical design values, which do not include gage tolerance and wear allowance.,Symmetry,(忽略特徵大小) RFS,Controlling Symmetrical Relationships w
8、ith Positional Tolerancing,Symmetry,Circular Runout,Total Runout,Does Runout Equal Concentricity?Sort Of.,The concentricity error cannot be greater than the measured runout. Runout is almost always easier to measure and controls the form of the feature as well as the concentricity. Concentricity ign
9、ores any form error. So, runout is almost always a better choice.,ASME Y14.41-2003,the ASME Y14.41-2003 standard on digital modeling recommends thatdirect tolerancing only be used to define the size of a feature 3.1.1, item(4).,Digital product data definition, reduced dimension drawings and paperles
10、s part definition will continue to grow in popularity. The sooner organizations embrace geometric tolerancing and use toleranced dimensionsprimarily for size, the sooner technology in this area will advance.,Features of size are unique because they: Contain opposed points Have a reproducible derived
11、 median point, axis or center plane Have limits (are not basic),You Better Know Who the Features of Size Are.,Many geometric tolerances, where applied to a feature of size, are controlling the features center point, axis or center plane. If you do not recognize the feature as a feature of size, you
12、might think the tolerance is being applied to the surface.,Sheet Metal Initial Tolerance Values (mm) Based Upon Manufacturing Process,Mating Position,(84.262-84.08)2 + (37.654-37.16)2,2X,= 1.052,(84.5-84.08)2 + (37.576-37.16)2,2X,= 1.18,1.,5.,張 永 裕Steve Chang Email : .twTel : 886-3-4526107 分機: 3534T
13、el :直撥 114-3534 ( 公司內部),Tolerance,For mm.,For inch,ASME Y14.5M-2009,Movable Datum Target,Movable Datum Target,All Over,Translation Modifier,Translation Modifier,3D Unilaterally Outside,3D Unilaterally Outside,Independency,On this shaft, the Independency symbol has been applied to the 100.1. This rem
14、oves the requirement for the feature to fit an envelope at 10.1. The size of this feature may be verified using micrometers. However, this overrides Rule #1. So, the form of the feature is not controlled by the limits of size. The straightness and circularity of the feature are controlled by the cir
15、cular runout tolerance. Care must be taken whenever the Independency symbol is applied to assure that the form of the feature is controlled by something other than the limits of size,Rule #1 requires that a feature not violate an envelope of perfect form at MMC. On this part, MMC of the hole is 5.95
16、. If an actual hole measures 5.95 at every cross section, the only way it could meet this requirement is if it is perfectly straight, circular and cylindrical. Of course, this “perfect“ hole cannot exist. But, if a hole is made close to 5.95 and had very good form, it would be acceptable. If two-point measurements are close to 6.05, the form error could be nearly 0.1 - the total size tolerance. This default rule helps assure that parts will assemble. However, this rule often becomes unreasonable as the length to diameter or width becomes large.,CF- Continuous Feature,
