本帖最后由 ValleyViews 于 2015-7-12 17:24 编辑
是从一个必威APP精装版下载上看到的。该帖作者是想说明PTZ标注的优点。
Here’s the job I was working on a long time ago – a massive granite beam held in place with M20 tie-rods in an anchor plate. The clearance holes in the beam were Ø30mm, so lots of room. 很久前我所经历的一个案例---一根岩石梁用数根M20拉杆固定在锚接板上面。石梁上的通孔孔径为30毫米,所以间隙空间较富裕。
So I did the drawing using classical tolerancing, which should have been fine. A ±0.01mm tolerance should be more than needed to clear in case the holes weren’t perfectly straight. 当初我绘制图纸时采用的公差标注是比较传统的,想当然地认为应该是没问题的。我当初已经用了正负0.01毫米公差,这应该是超出实际需要了,不就是为了保证万无一失吗。
This is how the tie-rods looked in the manufactured plate – not straightand there’s no way this will fit in the granite beam. The shop apologized and remade the plates with straighter tapped holes and it worked. They only had to remake 2 plates. Of couse the schedule took a hit. 这是按原来的图纸加工后的平板,装上拉杆后可以看到的情景---明显的不直程度,大到无法装进岩石梁里面去。加工车间表示歉意并再给我做孔更直些的板件。自然进度有点受影响。
Here’sthe thing in this case, and many others – there are some serious disadvantages with classical dimensioning. * There’s no way to say how straight the holes should be 由此可以看到传统的尺寸标注在这一案例中体现的负面影响: So I redid the drawings using GD&T, as below. This is a 3-D systemthat ensures there only one way to measure and verify the part. In this case, it allowed me the following benefits:
I could loosen up the unnecessary tolerance to 0.030 from 0.010, saving manufacturing cost I could tighten up the tolerance where needed, by specifying a PTZ (Projected Tolerance Zone ‘P’) on the axis of the tapped hole. This saves money and time, as the requirement is unambiguous and the part will be delivered correctly the first time.
我后来从新绘图(见下图)。通过这一案例,有以下三点总结: 1.将不必要的公差0.01放松到了0.03,节约了加工成本; 2.指定了投射公差带这一必要的限制; 3.技术要求明确,加工方交货及时,我方节约了时间与金钱。
See the red axis boundary indicators below that the PTZ represents. This ensures that the cap plate will fit over the rods. 下图红轴线边界表示投射公差带。这样可以确保板件与拉杆装配到位。
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