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Jami J. Shah - One of the best experts on this subject based on the ideXlab platform.

  • Statistical Tolerance Allocation for Tab-Slot Assemblies Utilizing Tolerance-Maps
    Journal of Computing and Information Science in Engineering, 2010
    Co-Authors: Gaurav Ameta, Joseph K. Davidson, Jami J. Shah
    Abstract:

    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.

  • Using Tolerance-Maps to Generate Frequency Distributions of Clearance and Allocate Tolerances for Pin-Hole Assemblies
    Journal of Computing and Information Science in Engineering, 2007
    Co-Authors: Gaurav Ameta, Joseph K. Davidson, Jami J. Shah
    Abstract:

    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.

  • Using Tolerance-Maps to generate frequency distributions of clearance for tab-slot assemblies
    Volume 2: 27th Computers and Information in Engineering Conference Parts A and B, 2007
    Co-Authors: Gaurav Ameta, Joseph K. Davidson, Jami J. Shah
    Abstract:

    A new mathematical model for representing the geometric variations of tabs/slots is extended to include probabilistic representations of 1-D clearance which can be determined from multi-dimensional 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 (T-Map), a hypothetical volume of points that models the range of 3-D 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 1-D 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 choosing the optional MMC and not choosing it with the tolerance that determines the allowable variations in position of a slot.

  • Using Tolerance-Maps to Generate Frequency Distributions of Clearance for Pin-Hole Assemblies
    Volume 1: 32nd Design Automation Conference Parts A and B, 2006
    Co-Authors: Gaurav Ameta, Joseph K. Davidson, Jami J. Shah
    Abstract:

    A new mathematical model for representing the geometric variations of lines is extended to include probabilistic representations of 1-D clearance which arise from multidimensional variations of an axis, a 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), a hypothetical volume of points that models the 3-D 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 increase in yield that occurs when Maximum Material Condition (MMC) is specified. The frequency distribution of 1-D 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 focused on geometric bias and manufacturing bias is presumed to be 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.Copyright © 2006 by ASME

M. M. Sfantsikopoulos - One of the best experts on this subject based on the ideXlab platform.

  • process capability requirement under Maximum Material Condition
    Proceedings of the Institution of Mechanical Engineers Part B: Journal of Engineering Manufacture, 2006
    Co-Authors: S. C. Diplaris, M. M. Sfantsikopoulos
    Abstract:

    A frequently used geometrical tolerance is the position tolerance. When it is assigned at the Maximum Material Condition (MMC), an increase in the position tolerance is allowed, equal to the departure of the particular feature from the Maximum Material Condition size. Neither concept - position tolerance and Maximum Material Condition - analytically related with the exact coordinate dimensions that locate the feature. A feature position is usually allocated on the basis of its theoretically exact co-ordinate dimensions, whereas positional accuracy is pursued through an appropriate planning of the machining process in conjunction with appropriate machine tool(s) and/or jig(s). Exploitation of the MMC tolerance bonus is taken into account mainly during part inspection in order to reduce rejects. Such an approach is not systematic, considering that the MMC benefits are not taken directly into account in the process planning stage in order to control the overall process cost. In this paper, the permitted manufacturing errors of a feature size and position are considered and studied simultaneously in an analytical way. It is shown that a lower process capability (PC) requirement can then be established that leads to a significant process cost reduction. An application example demonstrates the use of the method and the obtained results are discussed.

  • process capability requirement under Maximum Material Condition
    Proceedings of the Institution of Mechanical Engineers Part B: Journal of Engineering Manufacture, 2006
    Co-Authors: S. C. Diplaris, M. M. Sfantsikopoulos
    Abstract:

    A frequently used geometrical tolerance is the position tolerance. When it is assigned at the Maximum Material Condition (MMC), an increase in the position tolerance is allowed, equal to the departure of the particular feature from the Maximum Material Condition size. Neither concept - position tolerance and Maximum Material Condition - analytically related with the exact coordinate dimensions that locate the feature. A feature position is usually allocated on the basis of its theoretically exact co-ordinate dimensions, whereas positional accuracy is pursued through an appropriate planning of the machining process in conjunction with appropriate machine tool(s) and/or jig(s). Exploitation of the MMC tolerance bonus is taken into account mainly during part inspection in order to reduce rejects. Such an approach is not systematic, considering that the MMC benefits are not taken directly into account in the process planning stage in order to control the overall process cost. In this paper, the permitted manufacturing errors of a feature size and position are considered and studied simultaneously in an analytical way. It is shown that a lower process capability (PC) requirement can then be established that leads to a significant process cost reduction. An application example demonstrates the use of the method and the obtained results are discussed.

  • Maximum Material Condition in process planning
    Production Planning & Control, 2006
    Co-Authors: S. C. Diplaris, M. M. Sfantsikopoulos
    Abstract:

    Appropriate and cost effective assignment and interpretation of dimensional and geometrical tolerances, in conjunction with tolerancing principles such as the Maximum Material Condition (MMC), constitute a major area of concern for manufacturing SMEs. This is particularly true for the process planning stage, where production operations and parameter values establish the final product quality and cost. A frequently used geometrical tolerance is the position tolerance. It allows at least 57% more space for feature allocation without affecting product quality and is very useful for accurate specification of multiple-hole assemblies. Feature allocation becomes further relaxed in case a position tolerance is assigned to the MMC. This assignment is mainly exploited during inspection, because it permits fewer rejections. In terms of cost, it is advantageous to systematically integrate the MMC tolerance bonus into the position tolerance at the process planning stage. A methodology that allows a new MMC-adapted po...

Kevin W. Lyons - One of the best experts on this subject based on the ideXlab platform.

  • A scheme for mapping tolerance specifications to generalized deviation space for use in tolerance synthesis and analysis
    IEEE Transactions on Automation Science and Engineering, 2006
    Co-Authors: Haoyu Wang, N. Pramanik, Utpal Roy, Rachuri Sudarsan, Ram D. Sriram, Kevin W. Lyons
    Abstract:

    Tolerances impose restrictions on the possible deviations of features from their nominal sizes/shapes. These variations of size/shape could be thought of as deviations of a set of generalized coordinates defined at some convenient point on a feature. Any tolerance specification for a feature imposes some kind of restrictions or constraints on its deviation parameters. These constraints, in general, define a bounded region in the deviation space. In this paper, a method has been presented for converting tolerance specifications as per Maximum Material Condition (MMC)/least Material Condition (LMC)/regardless of feature size (RFS) Material Conditions for standard mating features (planar, cylindrical, and spherical) into a set of inequalities in a deviation space. Both virtual Condition boundaries Virtual Condition boundary: A constant boundary generated by the collective effects of a size feature's specified MMC or LMC Material Condition and the geometric tolerance for that Material Condition. (VCB) and tolerance zones are utilized for these mappings. The mapping procedures have been illustrated with an example. Note to Practitioners-This paper deals with methods to convert tolerance specification as per ASME Y14.5M into a set of generalized deviation of features and vice-versa. These are intermediate relationships that are required for use in deviation-based tolerance synthesis methods. In this work, different examples have been presented to show how different tolerance specifications (such as positional tolerance at Maximum Material Condition (MMC), least Material Condition (LMC), etc.) applied to different features could be treated on a generalized basis for tolerancing of manufactured parts.

  • Functional Tolerancing of a Gearbox
    2003
    Co-Authors: H. Wang, Utpal Roy, Rachuri Sudarsan, Ram D. Sriram, Kevin W. Lyons
    Abstract:

    This paper proposes a scheme for the tolerance specification that uses the features’ function information and mating Condition attributes in the assembly to derive an appropriate tolerance specification as per the design intents. The proposed mirror method provides a way to locate the critical components. It helps the user identify functional features and group them into clusters. Temporary DRF (Datum Reference Frame) is first generated for each cluster of features on critical components by selecting specific features as datum features. Other features (that are not datum features) present in the same cluster are then toleranced with respect to those datum features. The temporary DRFs as well as the tolerancing scheme are then copied (a mirror image of the critical component) to the other mating components (which are mating with the particular critical component). The final DRFs on the critical components are then decided by analyzing the temporary DRFs and the given functional requirements of each component. Appropriate geometric tolerance types and Material Conditions for toleranced features are generated following the standards and the industrial practices. INTRODUCTION Traditionally tolerances for manufactured parts are specified using symbolic schemes of GDT 2) representative of mating or sitting features and/or alignment edges (to assure that if they are inspected and accepted while oriented to, or located from datums constructed from those features, the controlled features will, indeed, mate and/or sit); 3) repeatable in manufacturing; 4) accessible during manufacturing and inspection operations. Conditions 1) and 2) are more important than Conditions 3) and 4), because Conditions 1) and 2) establish direct relationships between functions of the feature to the datum feature. We may add form or orientation tolerance to control datum feature so that they are repeatable in manufacturing and inspection. Some times, a functional feature may not be a good candidate for a datum feature if it has any accessibility problem during manufacturing, assembly and inspection. In that situation, we need to find out other feature that is accessible and whose orientation to the other functional features can be controlled by applying orientation tolerances. Functions and mating Conditions must guide the datum selection process. Other practical needs should also be considered in selecting datum features. It should be noted that planar and cylindrical features are the most common features in any component. With sufficiently large surfaces, they are able to control the Maximum number of DOFs (degree of freedom) of the orientation of any surface. They are easy to be simulated by surfaces of instruments used in manufacturing and inspection, such as working table of machine tool and inspection machine or surfaces of gages and fixers. Before introducing the proposed mirror method, it is important that we define the function and mating Condition attributes of features that will guide clustering of features, selection of tolerance type, and selection of datum features. FUNCTION AND MATING Condition ATTRIBUTES OF FUNCTIONAL FEATURES In this paper, we differentiated mating Condition attributes from function attributes because they serve differently in the tolerance selection process. Details of both attributes are provided in the following. Functional attributes serve some specific purposes in a part’s operation, such as seal, rotate, balance, gearing, fastening, press fit, clearance fit, and sliding etc. They should be used to guide the selection of tolerance types, tolerance values, and Material Conditions (Maximum Material Condition, Least Material Condition, Regardless of Feature Size MMC, LMC and RFS). Let us investigate some of the function attributes and examine how their requirements affect the tolerancing process. • Seal: arrests any leakage between two components. It requires tight form and size control (assuming no flexible sealing parts used). • Rotate: preserves the rotation between two components. The feature for “rotate”, such as cylindrical features that mate with bearings, requires tight location and form control. • Balance: preserves balance (symmetry) between two components. The feature for “balance”, such as a center hole or a boss to control the relative position of two components, doesn’t allow MMC referenced to it if it is chosen as a datum feature. • Gearing: preserves gear mesh between two components. Requires profile control of the gear mesh. • Fastening: connects two components. Requires projected tolerance zone consideration and MMC control for interchangeability. • Sliding: preserves sliding between two components (such as piston assembly). Requires form control on the contacting surfaces. • Press fit: does not allow any relative movement; The components after press fitted are considered as one single component. RFS is recommended. • Clearance fit: relative movement allowed. MMC is recommended. Mating Condition attributes serve purposes in part’s location and orientation in the assembly. They can be categorized as: locate, sit, contact, align, etc. They can be used in guiding selection of datum features. • Locate: preserves the relative location of two components, such as a pin interface. The features that are used to locate, such as pin or pinholes, are normally short enough so that they will not control the orientation of component in the assembly but only location. They are not good candidates for primary datum features. However, as they control the position of component in the assembly, they are good candidates for secondary datum features. • Sit: preserves 3-points contact between two planes, controls 3 DOFs (Degrees Of Freedom): 2 rotations and 1 translation. If the two planes are large enough (for stability purpose), they can be best candidates for primary datum features. • Contact: preserves 1-point contact between two surfaces, controls 1 DOF: 1 translation. The surfaces are perfect candidate for tertiary datum feature. • Align: preserves 2-points contact between two surfaces, controls 2 DOFs: 1 rotation and 1 translation. The surfaces are perfect candidate for secondary datum features.

  • A scheme for transformation of tolerance specifications to generalized deviation space for use in tolerance synthesis and analysis
    Volume 2: 28th Design Automation Conference, 2002
    Co-Authors: Haoyu Wang, N. Pramanik, Utpal Roy, Rachuri Sudarsan, Ram D. Sriram, Kevin W. Lyons
    Abstract:

    Traditionally tolerances for manufactured parts are specified using symbolic schemes as per ASME or ISO standards. To use these tolerance specifications in computerized tolerance synthesis and analysis, we need information models to represent the tolerances. Tolerance specifications could be modeled as a class with its attributes and methods [ROY01]. Tolerances impose restrictions on the possible deviation of features from its nominal size/shape. These variations of shape/size of a feature could be modeled as deviation of a set of generalized coordinates defined at some convenient point on the feature [BAL98]. In this paper, we present a method for converting tolerance specifications as per MMC (Maximum Material Condition) / LMC (Least Material Condition) / RFS (Regardless of Feature Size) Material Conditions for standard mating features (planar, cylindrical, and spherical) into a set of inequalities in a deviation space for representation of deviation of a feature from it’s nominal shape. We have used the virtual Condition boundaries (VCB) as well as tolerance zones (as the case may be) for these mappings. For the planar feature, these relations are linear and the bounded space is diamond shaped. For the other cases, the mapping is a set of nonlinear inequalities. The mapping transforms the tolerance specifications into a generalized coordinate frame as a set of inequalities. These are useful in tolerance synthesis, and analysis as well as in assemblability analysis in the generalized coordinate system (deviation space). In this paper, we also illustrate the mapping procedures with an example.Copyright © 2002 by ASME

Gaurav Ameta - One of the best experts on this subject based on the ideXlab platform.

  • Statistical Tolerance Allocation for Tab-Slot Assemblies Utilizing Tolerance-Maps
    Journal of Computing and Information Science in Engineering, 2010
    Co-Authors: Gaurav Ameta, Joseph K. Davidson, Jami J. Shah
    Abstract:

    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.

  • Using Tolerance-Maps to Generate Frequency Distributions of Clearance and Allocate Tolerances for Pin-Hole Assemblies
    Journal of Computing and Information Science in Engineering, 2007
    Co-Authors: Gaurav Ameta, Joseph K. Davidson, Jami J. Shah
    Abstract:

    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.

  • Using Tolerance-Maps to generate frequency distributions of clearance for tab-slot assemblies
    Volume 2: 27th Computers and Information in Engineering Conference Parts A and B, 2007
    Co-Authors: Gaurav Ameta, Joseph K. Davidson, Jami J. Shah
    Abstract:

    A new mathematical model for representing the geometric variations of tabs/slots is extended to include probabilistic representations of 1-D clearance which can be determined from multi-dimensional 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 (T-Map), a hypothetical volume of points that models the range of 3-D 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 1-D 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 choosing the optional MMC and not choosing it with the tolerance that determines the allowable variations in position of a slot.

  • Using Tolerance-Maps to Generate Frequency Distributions of Clearance for Pin-Hole Assemblies
    Volume 1: 32nd Design Automation Conference Parts A and B, 2006
    Co-Authors: Gaurav Ameta, Joseph K. Davidson, Jami J. Shah
    Abstract:

    A new mathematical model for representing the geometric variations of lines is extended to include probabilistic representations of 1-D clearance which arise from multidimensional variations of an axis, a 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), a hypothetical volume of points that models the 3-D 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 increase in yield that occurs when Maximum Material Condition (MMC) is specified. The frequency distribution of 1-D 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 focused on geometric bias and manufacturing bias is presumed to be 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.Copyright © 2006 by ASME

S. C. Diplaris - One of the best experts on this subject based on the ideXlab platform.

  • process capability requirement under Maximum Material Condition
    Proceedings of the Institution of Mechanical Engineers Part B: Journal of Engineering Manufacture, 2006
    Co-Authors: S. C. Diplaris, M. M. Sfantsikopoulos
    Abstract:

    A frequently used geometrical tolerance is the position tolerance. When it is assigned at the Maximum Material Condition (MMC), an increase in the position tolerance is allowed, equal to the departure of the particular feature from the Maximum Material Condition size. Neither concept - position tolerance and Maximum Material Condition - analytically related with the exact coordinate dimensions that locate the feature. A feature position is usually allocated on the basis of its theoretically exact co-ordinate dimensions, whereas positional accuracy is pursued through an appropriate planning of the machining process in conjunction with appropriate machine tool(s) and/or jig(s). Exploitation of the MMC tolerance bonus is taken into account mainly during part inspection in order to reduce rejects. Such an approach is not systematic, considering that the MMC benefits are not taken directly into account in the process planning stage in order to control the overall process cost. In this paper, the permitted manufacturing errors of a feature size and position are considered and studied simultaneously in an analytical way. It is shown that a lower process capability (PC) requirement can then be established that leads to a significant process cost reduction. An application example demonstrates the use of the method and the obtained results are discussed.

  • process capability requirement under Maximum Material Condition
    Proceedings of the Institution of Mechanical Engineers Part B: Journal of Engineering Manufacture, 2006
    Co-Authors: S. C. Diplaris, M. M. Sfantsikopoulos
    Abstract:

    A frequently used geometrical tolerance is the position tolerance. When it is assigned at the Maximum Material Condition (MMC), an increase in the position tolerance is allowed, equal to the departure of the particular feature from the Maximum Material Condition size. Neither concept - position tolerance and Maximum Material Condition - analytically related with the exact coordinate dimensions that locate the feature. A feature position is usually allocated on the basis of its theoretically exact co-ordinate dimensions, whereas positional accuracy is pursued through an appropriate planning of the machining process in conjunction with appropriate machine tool(s) and/or jig(s). Exploitation of the MMC tolerance bonus is taken into account mainly during part inspection in order to reduce rejects. Such an approach is not systematic, considering that the MMC benefits are not taken directly into account in the process planning stage in order to control the overall process cost. In this paper, the permitted manufacturing errors of a feature size and position are considered and studied simultaneously in an analytical way. It is shown that a lower process capability (PC) requirement can then be established that leads to a significant process cost reduction. An application example demonstrates the use of the method and the obtained results are discussed.

  • Maximum Material Condition in process planning
    Production Planning & Control, 2006
    Co-Authors: S. C. Diplaris, M. M. Sfantsikopoulos
    Abstract:

    Appropriate and cost effective assignment and interpretation of dimensional and geometrical tolerances, in conjunction with tolerancing principles such as the Maximum Material Condition (MMC), constitute a major area of concern for manufacturing SMEs. This is particularly true for the process planning stage, where production operations and parameter values establish the final product quality and cost. A frequently used geometrical tolerance is the position tolerance. It allows at least 57% more space for feature allocation without affecting product quality and is very useful for accurate specification of multiple-hole assemblies. Feature allocation becomes further relaxed in case a position tolerance is assigned to the MMC. This assignment is mainly exploited during inspection, because it permits fewer rejections. In terms of cost, it is advantageous to systematically integrate the MMC tolerance bonus into the position tolerance at the process planning stage. A methodology that allows a new MMC-adapted po...