Gaurav Ameta

A Comparative Study Of Tolerance Analysis Methods

This paper reviews four major methods for tolerance analysis and compares them. The methods discussed are (1) 1D tolerance charts, (2) variational analysis based on Monte Carlo simulation, (3) vector loop (or kinematic) based analysis, and (4) ASU T-Maps© based tolerance analysis. Tolerance charts deal with tolerance analysis in one direction at a time and ignore possible contributions from the other directions. Manual charting is tedious and error-prone, hence attempts have been made for automation. Monte Carlo simulation based tolerance analysis is based on parametric solid modeling; its inherent drawback is that simulation results highly depend on the user-defined modeling scheme, and its inability to obey all Y14.5 rules. The vector loop method uses kinematic joints to model assembly constraints. It is also not fully consistent with Y14.5 standard. ASU T-Maps based tolerance analysis method can model geometric tolerances and their interaction in truly 3-dimensional context. It is completely consistent with Y14.5 standard but its use by designers may be quite challenging. T-Maps based tolerance analysis is still under development. Despite the shortcomings of each of these tolerance analysis methods, each may be used to provide reasonable results under certain circumstances. No guidelines exist for such a purpose. Through a comprehensive comparison of these methods, this paper will develop some guidelines for selecting the best method to use for a given tolerance accumulation problem.Copyright

Navigating the Tolerance Analysis Maze

AbstractThis paper classifies and reviews geometric tolerance analysis methods and software. Two of the most popular methods, 1-D Min/Max Charts and Parametric Simulation, are reviewed in detail. The former is fully consistent with international tolerance standards but limited to decoupled analysis of variations in one direction at a time. It is also hard to automate. The latter can handle variations in all directions but is not fully compatible with the standards. The results are highly dependent on the expertise of the analyst. New methods are emerging to overcome these problems. One such method called T-maps is also reviewed. It maps geometric variations from physical space to 3, 4, or 5 dimensional virtual space and computes tolerance accumulations using Minkowski sums. The method so far has shown to be consistent with tolerance standards and can handle all tolerance classes applicable to planar and cylindrical features.

Tolerance-Maps Applied to a Point-Line Cluster of Features

In this paper, groups of individual features, i.e., a point, a line, and a plane, are called clusters and are used to constrain sufficiently the relative location of adjacent parts. A new mathematical model for representing size and geometric tolerances is applied to a point-line cluster of features that is used to align adjacent parts in two-dimensional space. First, tolerance-zones are described for the point-line cluster. A Tolerance-Map® (Patent no. 69638242), a hypothetical volume of points, is then established which is the range of a mapping from all possible locations for the features in the cluster. A picture frame assembly of four parts is used to illustrate the accumulations of manufacturing variations, and the T-Maps® provide stackup relations that can be used to allocate size and orientational tolerances. This model is one part of a bilevel model that we are developing for size and geometric tolerances. At the local level the model deals with the permitted variations in a tolerance zone, while at the global level it interrelates all the frames of reference on a part or assembly.

Carbon weight analysis for machining operation and allocation for redesign

The objective of this research paper is to explore and develop a new methodology for computing carbon weight (CW) – often referred to as carbon footprint, in manufacturing processes from part level to assembly level. In this initial study, we focused on machining operations, specifically turning and milling, for computing CW. Our initial study demonstrates that CW can be computed using either actual measured data from process level information or from initial material and manufacturing process information. In mechanical design, tolerance analysis principles extend from design to manufacturing and tolerances accumulate for parts and processes. By extending this notion to CW, we apply mechanical tolerancing principles for computing worst case and statistical case CW of a product. We call this the CW tolerance approach (CWTA). Two case studies demonstrate the computation of CW. Based on the tolerance allocation concepts; CW allocation is also demonstrated through specific redesign examples. CWTA helps in identifying carbon intensive parts/processes and can be used to make appropriate design decisions.

Tolerance-Maps Applied to the Straightness and Orientation of an Axis

Among the least developed capabilities in well-developed mathemati cal models for geometric tolerances are the representation of toleranc es on form, orientation, and of Rule #1 in the Standards, i.e. the coupling between form and allowable var iations for either size or position of a feature. This paper uses Tolerance-Maps ®1 (T-Maps ®1 ) to describe these aspects of geometric tolerances for the straightness and orientation of an axis within its tolerance-zone on position. A Tolerance-Map is a hypothetical poi nt-space, the size and shape of which reflect all variational possibilities for a targ et feature; for an axis, it is constructed in four-dimensional space. The Tolerance-Map for straight ness is modeled with a geometrically similar, but smaller-sized, four-dimensional s hape to the 4D shape for position; it is a subset within the T-Map for position. Another interna l subset describes the displacement possibilities for the subset T-Maps that limits for m. The T-Map for orientation and position together is formed most reliably by trun cating the T-Map for position alone.

Using Tolerance-Maps to Generate Frequency Distributions of Clearance and Allocate Tolerances for Pin-Hole Assemblies

A new mathematical model for representing the geometric variations of lines is extended to include probabilistic representations of one-dimensional (1D) clearance, which arise from positional variations of the axis of a hole, the size of the hole, and a pin-hole assembly. The model is compatible with the ASME/ ANSI/ISO Standards for geometric tolerances. Central to the new model is a Tolerance-Map (T-Map) (Patent No. 69638242), a hypothetical volume of points that models the 3D variations in location and orientation for a segment of a line (the axis), which can arise from tolerances on size, position, orientation, and form. Here, it is extended to model the increases in yield that occur when maximum material condition (MMC) is specified and when tolerances are assigned statistically rather than on a worst-case basis; the statistical method includes the specification of both size and position tolerances on a feature. The frequency distribution of 1D clearance is decomposed into manufacturing bias, i.e., toward certain regions of a Tolerance-Map, and into a geometric bias that can be computed from the geometry of multidimensional T-Maps. Although the probabilistic representation in this paper is built from geometric bias, and it is presumed that manufacturing bias is uniform, the method is robust enough to include manufacturing bias in the future. Geometric bias alone shows a greater likelihood of small clearances than large clearances between an assembled pin and hole. A comparison is made between the effects of choosing the optional material condition MMC and not choosing it with the tolerances that determine the allowable variations in position.

Extending the notion of quality from physical metrology to information and sustainability

In this paper we intend to demonstrate the need for extending the notion of quality from the physical domain to information and, more comprehensively, to sustainability. In physical metrology there are well established principles such as fundamental units, precision, accuracy, traceability and uncertainty. In order to understand and define quality for information and sustainability we need to develop metrological concepts similar to those of physical metrology. Research efforts related to information quality (IQ) are scattered. IQ is primarily defined in terms of several characteristics (dimensions) which lack consensus definitions and are sometimes subjective. However, the notion of IQ is currently in practice and has provided some useful insights towards defining formal approaches to IQ. In order to extend the notion of quality to sustainability we need, as in the case of information, a well defined metrology similar to physical metrology. Sustainability is currently getting attention in many areas of human endeavor. One proposal is to measure sustainability in terms of a triple bottom line, namely social, economical and environmental aspects of human endeavor. Sustainability metrics are continuously evolving and their clear definition is fundamental to the understanding of the notion of sustainability quality. As an example we consider evaluation of carbon footprint, as a metric towards sustainability, for manufacturing a simple turned part. After analyzing the current literature, we identify the following needs for characterizing the notion of sustainability quality: (a) standardized terminology of terms and concepts, (b) metrics and metrology, (c) harmonization and extension of standards, (d) conformance testbeds for standards and (e) development of information models that support sustainability.

Investigating the Role of Geometric Dimensioning and Tolerancing in Additive Manufacturing

Additive manufacturing (AM) has increasingly gained attention in the last decade as a versatile manufacturing process for customized products. AM processes can create complex, freeform shapes while also introducing features, such as internal cavities and lattices. These complex geometries are either not feasible or very costly with traditional manufacturing processes. The geometric freedoms associated with AM create new challenges in maintaining and communicating dimensional and geometric accuracy of parts produced. This paper reviews the implications of AM processes on current geometric dimensioning and tolerancing (GD&T) practices, including specification standards, such as ASME Y14.5 and ISO 1101, and discusses challenges and possible solutions that lie ahead. Various issues highlighted in this paper are classified as (a) AM-driven specification issues and (b) specification issues highlighted by the capabilities of AM processes. AM-driven specification issues may include build direction, layer thickness, support structure related specification, and scan/track direction. Specification issues highlighted by the capabilities of AM processes may include region-based tolerances for complex freeform surfaces, tolerancing internal functional features, and tolerancing lattice and infills. We introduce methods to address these potential specification issues. Finally, we summarize potential impacts to upstream and downstream tolerancing steps, including tolerance analysis, tolerance transfer, and tolerance evaluation. [DOI: 10.1115/1.4031296]

Simulation and analysis for sustainable product development

PurposeSimulation plays a critical role in the design of products, materials, and manufacturing processes. However, there are gaps in the simulation tools used by industry to provide reliable results from which effective decisions can be made about environmental impacts at different stages of product life cycle. A holistic and systems approach to predicting impacts via sustainable manufacturing planning and simulation (SMPS) is presented in an effort to incorporate sustainability aspects across a product life cycle.MethodsIncreasingly, simulation is replacing physical tests to ensure product reliability and quality, thereby facilitating steady reductions in design and manufacturing cycles. For SMPS, we propose to extend an earlier framework developed in the Systems Integration for Manufacturing Applications (SIMA) program at the National Institute of Standards and Technology. SMPS framework has four phases, viz. design product, engineer manufacturing, engineer production system, and produce products. Each phase has its inputs, outputs, phase level activities, and sustainability-related data, metrics and tools.Results and discussionAn automotive manufacturing scenario that highlights the potential of utilizing SMPS framework to facilitate decision making across different phases of product life cycle is presented. Various research opportunities are discussed for the SMPS framework and corresponding information models.ConclusionsThe SMPS framework built on the SIMA model has potential in aiding sustainable product development.

Statistical Tolerance Allocation for Tab-Slot Assemblies Utilizing Tolerance-Maps

A new mathematical model for representing the geometric variations of tabs/slots is extended to include probabilistic representations of 1D clearance. The 1D clearance can be determined from multidimensional variations of the medial-plane for a slot or a tab, and from variations of both medial-planes in a tab-slot assembly. The model is compatible with the ASME/ANSI/ISO Standards for geometric tolerances. Central to the new model is a Tolerance-Map (Patent No. 6963824) (T-Map), a hypothetical volume of points that models the range of 3D variations in location and orientation for a segment of a plane (the medial-plane), which can arise from tolerances on size, position, orientation, and form. Here it is extended to model the increases in yield that occur when the optional maximum material condition (MMC) is specified and when tolerances are assigned statistically rather than on a worst-case basis. The frequency distribution of 1D clearance is decomposed into manufacturing bias, i.e., toward certain regions of a Tolerance-Map, and into a geometric bias that can be computed from the geometry of multidimensional T-Maps. Although the probabilistic representation in this paper is built from geometric bias, and it is presumed that manufacturing bias is uniform, the method is robust enough to include manufacturing bias in the future. Geometric bias alone shows a greater likelihood of small clearances than large clearances between an assembled tab and slot. A comparison is made between the effects of specifying the optional MMC and not specifying it with the tolerance that determines the allowable variations in position of a tab, a slot, or of both in a tab-slot assembly. Statistical tolerance assignment for the tab-slot assembly is computed based on initial worst-case tolerances and for (a) constant size of tab and slot at maximum material condition, and (b) constant virtual-condition size.