Tri-Planar Geometric Dimensioning and Tolerancing Characteristics of SS 316L Laser Powder Bed Fusion Process Test Artifacts and Effect of Base Plate Removal

The precision of LPBF manufactured parts is quantified by characterizing the geometric tolerances based on the ISO 1101 standard. However, there are research gaps in the characterization of geometric tolerance of LPBF parts. A literature survey reveals three significant research gaps: (1) systematic design of benchmarks for geometric tolerance characterization with minimum experimentation; (2) holistic geometric tolerance characterization in different orientations and with varying feature sizes; and (3) a comparison of results, with and without the base plate. This research article focuses on addressing these issues by systematically designing a benchmark that can characterize geometric tolerances in three principal planar directions. The designed benchmark was simulated using the finite element method, manufactured using a commercial LPBF process using stainless steel (SS 316L) powder, and the geometric tolerances were characterized. The effect of base plate removal on the geometric tolerances was quantified. Simulation and experimental results were compared to understand tolerance variations using process variations such as base plate removal, orientation, and size. The tolerance zone variations not only validate the need for systematically designed benchmarks, but also for tri-planar characterization. Simulation and experimental result comparisons provide quantitative information about the applicability of numerical simulation for geometric tolerance prediction for the LPBF process.

Application Methods for Refractory Insulation in Hot Particle Storage Bins

The National Solar Thermal Test Facility (NSTTF) at Sandia National Laboratories is conducting research on a Generation 3 Particle Pilot Plant (G3P3) that uses falling sandlike particles as the heat transfer medium. G3P3 proposes a system with 6 MWh of thermal energy storage in cylindrical bins made of steel that will be insulated internally using multiple layers of refractory materials[1]. The refractory materials can be applied by stacking pre-cast panels in a cylindrical arrangement or by spraying refractory slurry to the walls (shotcrete). A study on the two methods determined that shotcrete would be the preferred method in order to minimize geometric tolerance issues in the pre-cast panels, improve repairability, and to more closely resemble commercial-scale construction methods. Testing and analysis was conducted which showed shotcrete refractories could be applied with minimal damage and acceptable heat loss.

The Influence of Automated Machining Strategy on Geometric Deviations of Machined Surfaces

This paper deals with various automated milling strategies and their influence on the accuracy of produced parts. Among the most important factors for surface quality is the automated milling strategy. Milling strategies were generated from two different programs, CAM system SolidCAM, with the help of workshop programming in the control system Heidenhain TNC 426. In the first step, simulations of different toolpaths were conducted. Using geometric tolerance is becoming increasingly important in robotized production, but its proper application requires a deeper understanding. This article presents the measurement of selected planes of robotized production to evaluate their flatness, parallelism and perpendicularity deviations after milling on the coordinate measuring machine Carl Zeiss Contura G2. Total average deviations, including all geometric tolerances, were 0.020 mm for SolidCAM and 0.016 mm for Heidenhain TNC 426. The result is significantly affected by the flatness of measured planes, where the overlap parameter of the tools has a significant impact on the flatness of the surface. With interchangeable cutter plate tools, it is better to use higher overlap to achieve better flatness. There is a significant difference in production time, with SolidCAM 25 min and 30 s, and Heidenhain 48 min and 19 s. In accordance with these findings, the SolidCAM system is more suitable for production.

A mapping model between the workpiece geometric tolerance and the end pose error of CNC machine tool considering structure distortion of cutting process system

Aiming at the problem that the geometric accuracy design index of machine tools is difficult to be determined reasonably in the geometric precision design process of CNC machine tools, this paper presents a mapping model between geometric tolerance of the workpiece and end pose error (positional and orientational error of the tool relative to the workpiece) of the machine tool considering structure distortion of cutting process system. Only considering the factors of the machine tool geometric errors, this paper first establishes the relationship between the geometric tolerance requirements of the workpiece and relative pose error at the end of machine tools, and completes the estimation of the machine tools end pose error. Then this paper analyzes the elastic deformations of the cutting process system caused by the cutting force. These elastic deformations produce machining errors. Based on the above analysis, the estimated variation range of the end pose error can be adjusted by the emulation of the geometric tolerance of the workpiece and used as the geometric accuracy design index of machine tools. This paper takes the international standard small size contour processing test piece as an example to explain the application process of the proposed model.

Transfer Method of Geometric Tolerance Items Based on Assembly Joints

In order to reduce the uncertainty in the selection of geometric tolerance items, a qualitative method for top-down transfer of geometric tolerance items based on assembly joints is proposed. According to the structural characteristics, the assembly joints are divided into meta-assembly joints and composite assembly joints, and the priority rules for assembly joints are proposed. The transfer path of part-level geometric tolerance items is established according to the functional requirements and structural constraints among parts. On this basis, by adding information about the composition and constraint types of assembly joints between parts and the positioning constraint relationship of the general structure surface in the part, the transfer path of part-level geometric tolerance items is extended to the surface-level transfer path. The structural transformation rules for functional requirements based on structural constraints, the tolerance item generation specifications and datum transfer specifications are established. And based on the above specifications, the mapping relationship between functional requirements, structural constraints and geometric tolerance items is defined. The synchronous transmission of geometric tolerance items along with the product design process are realized which provides an effective analysis tool for the top-down design of geometric tolerance items. Finally, the effectiveness of the method is verified by taking the transmission parts and connection parts in the crankshaft-piston mechanism as an example.

Interpretation of Modifier Ⓜ “Circle M” in ASME Y 14.5 GD&T: Intuitive or Deceptive?

Geometric Dimensioning and Tolerancing (GD&T) is a system for defining and communicating engineering tolerances by using a symbolic language on engineering drawings that describe nominal (theoretically perfect) geometry of controlled features, as well as their allowable variation in size, other geometrical characteristics (form, orientation and location) and variation between features. Per this language, dimensions and tolerances are selected to suit function and mating relationship of a part and are subject to a unique interpretation. It allows design engineers, manufacturing personnel, and quality inspectors to describe geometry and allowable variation of parts and assemblies in an efficient and effective manner. When compared to coordinate dimensioning, GD&T has the benefits of reducing the manufacturing cost and number of drawing revisions, describing an important functional relationship on a part, saving inspection time by using functional gages, and improving measurement repeatability. However, GD&T has a fairly complex rule-based system, and as a result can be difficult to teach and learn. One such concept relates to the use of modifier circle M. In GD&T, a feature control frame is required to describe the conditions and tolerances of a geometric control on a part’s feature. The feature control frame may consist of up to four pieces of information, (1) GD&T symbol or control symbol for the feature, (2) Tolerance zone type and its size, (3) Tolerance zone modifiers and (4) Datum references (if required by the GD&T symbol). When circle M is used as a feature tolerance zone modifier, it is relatively easy to understand that there is a possibility of getting bonus tolerance, and in turn, a higher total tolerance. However, what is not very intuitive is the size of the feature counterpart on the functional gage to inspect the given feature control frame. Apparently, it is not the Maximum Material Condition (MMC) size of the feature. Rather, the size is what is called a virtual condition (VC) of the feature, which is defined as the theoretical extreme boundary condition of a feature of size (FOS) generated by the collective effects of MMC and applicable geometric tolerance. When circle M is used as a datum feature/reference modifier, it is even more strenuous to calculate the datum boundary or the size of the datum feature counterpart on the functional gage. In this case, it is the Maximum Material Boundary (MMB); a virtual condition of the datum feature governed by a specific rule of GD&T that establishes this VC with respect to the preceding datum in the feature control frame. This would necessitate one to look for a specific applicable geometric tolerance that is an exclusive relationship between the datum feature and its preceding datum in the feature control frame. Even worse, in case of position tolerance (which, often times, is a lumped sum tolerance controlling orientation and location geometric characteristics of the datum feature simultaneously), it is even trickier to find an exclusive relationship between the datum feature and its preceding datum. In this article, authors have made an attempt to clarify the above-mentioned situations through numerous examples. Hopefully, this can be successfully implemented in undergraduate and graduate education reinforcing the premise that a better educated workforce would be able to contribute significantly higher to advanced manufacturing, design, quality tools and advanced metrology.