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Marking out and measuring
Published in Andrew Livesey, Alan Robinson, The Repair of Vehicle Bodies, 2018
A flat surface is one of the fundamentals of engineering, and the flatness of a surface can be verified by testing it against the flatness of a standard surface, the surface plate. Surface plates are similar in construction and grading to the standard of finish of a marking table but are smaller in size and have two carrying handles. The back is strongly ribbed to give rigidity to the surface. In use, the surface plate is covered with a special marking compound and then lightly rubbed on the workpiece to be tested. The marking dye is transferred to the parts of the workpiece which actually come into contact with the surface of the plate, and if the surface of the workpiece is uneven, only the high spots will be marked. Any high spots must be scraped, and the workpiece must be retested until the whole surface comes in contact with the surface plate. Surface plates should be kept covered at all times when not in use.
Form Controls
Published in James D. Meadows, Geometric Dimensioning and Tolerancing, 2017
Flatness is a geometric control in which a part surface (feature) is compared to a perfectly flat geometric counterpart of itself. A part surface is real; therefore, it has flaws--ridges, grooves, pits, bumps, etc. Since a feature cannot be flat to something else, as in parallelism or perpendicularity of one feature to another, no datums are proper or allowed in the feature control frame. So, we check the surface to see how much irregularity an indicator registers when it is run across that surface. Since we are not checking for parallelism, we may not get an accurate reading if we simply set the part down on its opposing surface when running the indicator over the controlled surface and reject the part on that basis (although it could be accepted on that basis). Therefore, at times, we must look into other ways of setting up the part.
Geometric Dimensioning and Tolerancing
Published in Godfrey C. Onwubolu, Introduction to SOLIDWORKS, 2017
Flatness is the condition of a surface having all elements in one plane. Flatness tolerances are used to define the amount of variation that is permitted in an individual that is surfaced. A flatness tolerance specifies a tolerance zone that is defined by two parallel planes within which the surface must lie. Figure 32.22 shows a rectangular object that varies in height from 25.5 to 24.5. How flat is the top surface? This question can be better answered if an additional flatness tolerance value is added (0.3 in this case). Although the feature can vary based on the tolerance of ±0.5 that is specified, the surface could not vary by more than 0.3. When a flatness tolerance is specified, the feature control frame is attached to a leader that is directed to the surface or to an extension line of the surface. It is placed in a view where the surface elements to be controlled are represented by a line. Where the considered surface is associated with a size dimension, the flatness tolerance must be less than the size tolerance. Notice that the value of the flatness tolerance is normally less than the feature tolerance (0.3 < 0.5).
Thermo-Mechanical Distortion of Tungsten-Coated Steel During High Heat Flux Testing Using Plasma Arc Lamps
Published in Fusion Science and Technology, 2022
Adrian S. Sabau, Kazutoshi Tokunaga, Sarma Gorti, Yoshio Ueda, Yutai Katoh, Lance L. Snead
These profilometry data indicate that the surfaces are not smooth; that is, they have local roughness. By contrast, surface flatness indicates that a surface does not have obvious curvatures over large areas. To assess the large-scale deformation and identify any surface curvature, the flatness error in these two directions was estimated using a similar procedure to that of Zhang et al.28 First, curve fits of the profiles in these two directions were obtained using a least-squares algorithm and are shown in Fig. 1b. These curve-fit lines represent the reference lines, which are defined as . The A and B coefficients are shown in Table I together with their standard deviation. Second, for each direction, the deviation from the reference plane of each data point was calculated as , where . Finally, the flatness error was calculated as and it is shown in Table I. The flatness error is less than 1 μm over a length of 3.52 and 2.64 mm in the X and Y directions, respectively. Thus, the flatness error per unit length FE/L is very small at ~0.26 μm/mm (Table I), indicating that the surface profile of the as-received surface is flat.
Multi-channel non-destructive testing of steel strip stress based on magneto-elastic effect
Published in Nondestructive Testing and Evaluation, 2023
Mingyang Yu, Bin Wang, Bo Li, Boyang Zhang, Qingdong Zhang
The root cause of the flatness defect lies in the fact that during the rolling process, due to the uneven reduction of the metal thickness of the strip in the width direction, longitudinal fibres with uneven lengths are formed, and they are pulled together to generate internal stress. When the critical stable stress value is exceeded, the strip becomes unstable, resulting in buckling deformation [3,4]. Therefore, it is possible to directly detect the longitudinal tensile stress distributed along the width direction of the strip and then estimate the degree of the flatness defects of the strip due to the uneven reduction of the metal thickness [5,6]. The accurate detection of the tensile stress distribution of the strip is key to realising the automatic control of shape quality.
Flatness measurement of large flat with two-station laser trackers
Published in International Journal of Optomechatronics, 2018
Jie Li, Jie Yang, Shibin Wu, Xuedong Cao
Therefore, we present a new method to accurately measure the flatness of a large flat using two laser trackers. An additional laser tracker is used to compensate for angular error of the primary laser tracker, therefore, high accuracy is achieved.