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GD&T in Aerospace Assembly: Use of Multiple Datum Targets for N-2-1 Location of Fuselage

Datum Based Alignment of Fuselage

This post will present a possible case in the aerospace industry for locating a fuselage part with 9-2-1 location, using datum target areas. For more detailed information on datum targets, you may refer to the ASME standard, section 4.24 [1].

N-2-1 Location with Datum Target Areas

In a previous post, we talked about using 3-2-1 precision location to create an accurate and repeatable datum reference frame for the part, while avoiding overconstraint. However, for most sheet metal manufacturing processes, the main dimensional problem is the sheet metal deformation normal to the surface [2]. This deformation cannot be neglected, even under the self-weight of the workpiece. Analysis shows that the average deflection of a sheet steel plate 400 mm x 400 mm x 1 mm under its self-weight can be between 1-3 mm with a 3-2-1 location layout. Therefore, an adequate fixturing system for sheet metal usually requires N>3 locators on the primary datum to properly restrain workpiece deformation. Read More

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GD&T in Automotive Assembly: Surface Profile Tolerances

Car Door Surface Profile Tolerances

In a previous post, we presented an application of datum targets for 3-2-1 location of a car door. In this post, we will follow up with the same part to verify the surface profile tolerances along the side surfaces of the door, for optimal assembly conditions.

Surface Profile Tolerances

A surface profile tolerance zone is a three-dimensional volume establishing permissible boundaries of feature(s) of a part. A surface profile tolerance can be used to define a tolerance zone to control combinations of size, form, orientation and location of a feature relative to true profile.  For additional information about profile tolerances, please refer to the section 8 of the ASME Y14.5-2009 standard [1]. In Figure 1, we can observe the car door part located through datum targets with surface profile tolerances. In the next sections, we shall analyze these tolerances further to better understand their functions. Read More

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GD&T in Precision Engineering: Use of Diamond Pins in Precision Location Applications

Diamond Pin Assembly GD&T

In a previous post, we elaborated on the principles of precision location and presented one of the techniques for achieving it: The use of slots. However, with slots, we can still have the problem of high manufacturing cost if the part has substantial thickness.  This is because manufacturing a slot is simply more complex than drilling a hole, in relatively thick parts. One technique to have the best of both worlds is to use diamond pins. Read More

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GD&T in Automotive Assembly: Use of Datum Targets for Precision Location of Large Surfaces

Automotive Datum Targets

In manufacturing and assembly, parts must be accurately and repeatably located in a well-defined reference frame to ensure consistent quality. For many automotive parts, because of the large and irregular surfaces involved, the entire surface of the feature cannot be used as a datum. In these cases, we use datum targets to establish a datum reference frame. This post will present a possible case in the automotive industry for locating a car door with the 3-2-1 location method, using datum target areas. For more detailed information on datum targets, you may refer to the ASME standard, section 4.24 [1]. Read More

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GD&T in Precision Engineering : Use of Slots in Precision Location Applications

GD&T Pin and Slot DRF

Precision location can be very important in various engineering applications, such as machining and assembly. In machining, the tool follows a very precise path and a workpiece must be located precisely and stably at a precise position. In assembly, the positions of assembled parts must be assembled easily and overconstraint of the parts must be avoided. One of the common techniques for accomplishing these targets is the use of slots as part features. Read More