Decentralization—The Management Key to Effective Accuracy Control

1987 ◽  
Vol 3 (02) ◽  
pp. 75-86
Author(s):  
Tamara S. Upham ◽  
W. Mark Crawford
Keyword(s):  
Organizational Structure ◽  
Statistical Methods ◽  
Dimensional Accuracy ◽  
Accuracy Control ◽  
Statistical Accuracy ◽  
Three Phase ◽  
Control Department

This paper presents the organizational structure, methods, and results of National Steel and Shipbuilding Company's (NASSCO) efforts to decentralize the responsibility of statistical accuracy control from a central Accuracy Control Department to the hourly production workforce. It includes an accounting of the problems and successes encountered during implementation. The results are both quantitative and qualitative in form, including methods for measuring reductions in rework. During this study, workteams were established in the Hull Fabrication Shop. A three phase methodology was used to introduce the workteams to statistical methods for improving the dimensional accuracy of their products.

Study on the Propagation of Dimensional Deviation in the Hull Block Building Process

2020 ◽  
Vol 36 (02) ◽  
pp. 143-151
Author(s):  
Changhui Liu ◽  
Jianfeng Liu ◽  
Yansong Zhang ◽  
Sun Jin ◽  
Can Wang ◽  
...  
Keyword(s):  
Critical Role ◽  
Dimensional Accuracy ◽  
Butt Joint ◽  
Measured Data ◽  
Accuracy Control ◽  
Bottom Block ◽  
Whole Process ◽  
Building Process ◽  
Dimensional Deviation ◽  
Industry Practice

Dimensional accuracy of hull block plays a critical role in guaranteeing the whole ship accuracy and reducing the hull butt-joint cost. The current industry practice of dimensional control in shipbuilding mainly focuses on the prediction of cutting and welding deformation based on engineering experience. Its main limitation is that the propagation and accumulation of deviations in the whole building process are neglected. In this article, cutting errors, assembly deviations, welding shrinkages, turnover distortions, and thermal expansions generated at different stages are analyzed. The propagation and accumulation of deviations and variations in the double-bottom block building process are studied based on the measured data in the whole process. Finally, the correlations of deviations between the adjacent stage are concluded. The conclusions can be used to guide the accuracy control in the hull block building process and reduce dimension trimming.

Statistical accuracy test in measurements of circular dichroism

1979 ◽  
Vol 44 (4) ◽  
pp. 1312-1317 ◽  
Author(s):  
Petr Pančoška ◽  
Ivo Frič ◽  
Karel Bláha
Keyword(s):  
Circular Dichroism ◽  
Statistical Methods ◽  
Spectral Range ◽  
Probable Error ◽  
Statistical Accuracy ◽  
Sample Concentration ◽  
Accuracy Test ◽  
Circular Dichroïsm ◽  
Intensity Reading

A collection of one hundred circular dichroism measurements (in acetonitrile) of the model cyclohexapeptide cyclo(glycyl-L-phenylalanyl-L-leucyl-glycyl-L-leucyl-L-phenylalanyl) has been evaluated using standard statistical methods. The reproducibility of the experimental intensity values is discussed with respect to the sample concentration and the particular regions of the CD curve. The maximum probable error in the intensity reading varies with wavelength from ±20 to ±10 000 deg cm2 dmol-1 in the spectral range from 274 to 196 nm, i.e. by 5-15% of the observed intensity.

Stochastic Assessment and Applications for Welding Shrinkage Impact on Production Cost

2012 ◽  
Author(s):  
H. Y. Heo ◽  
D. H. Youn ◽  
H. Chung
Keyword(s):  
Production Cost ◽  
Value Added ◽  
Dimensional Accuracy ◽  
Control Procedure ◽  
Total Production ◽  
Accuracy Control ◽  
Element Analysis ◽  
Intermediate Products ◽  
Welding Sequence

Since ship hull blocks are constructed by assembling numerous intermediate parts, negligible dimensional variations in the parts can easily accumulate to cause serious misalignment in block erection stage. Considering the welding – the primary joining process in ship production which inherently causes distortions, the quality of block’s dimensional variations during the assembly would deteriorate even faster. Thinking that the intermediate products with low dimensional quality in the ship production are not scrapped but reworked, the productivity of each workstation greatly depends on the dimensional quality of these dimensionally critical intermediate products. Reworks such as recutting, mechanical and/or thermal correction against misalignment, excessive welding for wide gap and thermal straightening are commonly subsequently increases the total production cost. One of the major dimensional accuracy control activities is the shrinkage margin design. The optimal length of excess edge is assigned to plates in order to compensate welding shrinkage. In the past, the welding shrinkage is predicted based mostly on the empirical formula or just designer's experience, so the accuracy of the assigned was relatively poor and could not effectively help reducing non-value-added rework activities. The simplified margin calculation procedure could not consider the welding sequence as well as process variations such as welding heat input. This work aims to develop the optimal shrinkage margin calculation system for dimensional quality improvement. The proposed system calculates the optimal shrinkage margin using computer-aided engineering toolsets based on finite element analysis as well as design point searching procedure adopting the quality loss function and statistical values considering shrinkage variation values during welding. The developed scheme improves the accuracy control procedure in the ship production process thus enhance competitiveness of shipbuilders in dimensional accuracy technology by minimizing the accuracy impact on productivity.

PARAMETER

PEDIATRICS ◽  
1982 ◽  
Vol 70 (2) ◽  
pp. 287-287
Author(s):  
Keyword(s):  
Organizational Structure ◽  
Statistical Methods ◽  
Arbitrary Constant ◽  
Clear Distinction ◽  
Statistical Population ◽  
Independent Variable ◽  
The One ◽  
The Universe

Parameter is currently a very popular word, particularly among bureaucrats. I think it's generally used as a mispronunciation of "perimeter." A typical sentence from, say, a TV interview might go, "We've bent every effort to incorporate those subfunctions within the parameters of our organizational structure." As perimeter, that might make sense, perimeters being boundaries. I was puzzled as to why so many bureaucrats had decided to pronounce perimeter as parameter. I wondered if perhaps parameter meant nearly the same thing. Maybe a parameter was like a perimeter only better. I looked it up. Webster's New International, third edition: pa·ram·e·ter. . . 1: the relative intercept made by a plane on a crystollographic axis, the ratio of the intercepts determining the position of the plane 2a: an arbitrary constant characterizing by each of its particular values some particular member of a system (as of expressions, curves, surfaces, functions) < a ∼ is a quantity which may have various values each fixed within the limits of a stated case or discussion—T. F. Weldon > specif: a quantity that describes a statistical population < a clear distinction should always be drawn between ∼s and estimates, i.e., between quantities which characterize the universe, and estimates of these quantities calculated from observations—Statistical Methods in Research & Production > < estimation of the values of the ∼s which enter into the equation representing the chosen relation—Frank Yates > b: an independent variable through functions of which other functions may be expressed < four ∼s are necessary to determine an event, namely the three which determine its position and the one which determines its time—P. W. Bridgman >

The Use of Statistical Methods in Dimensional Process Control

1986 ◽  
Vol 2 (03) ◽  
pp. 125-135
Author(s):  
Stephen Krajcsik
Keyword(s):  
Process Control ◽  
Statistical Methods ◽  
Cost Reduction ◽  
Dimensional Accuracy ◽  
Control Program ◽  
Fine Tuning ◽  
Statistical Process ◽  
Shipbuilding Industry ◽  
High Degree ◽  
Viable Method

In shipbuilding, the stage of construction which lends itself to the most time and cost reduction is unit erection in the basin or on the ways. This requires all units to be complete and accurately assembled in order to eliminate costly rework during and after erection. To achieve this high degree of unit accuracy, the author's company has undertaken a pilot dimensional control program that has set the guidelines for systematically monitoring each stage of the production process prior to erection. Through the collection and analysis of data, steps can be taken to control each process and insure achievement of the desired degree of accuracy. The cumulative effects of "fine tuning" each individual work process will ultimately lead to improvement in the dimensional accuracy of completed units. This paper discusses the company's experience in applying statistical methods in the collection and interpretation of dimensional data on automatic burning machines. The results obtained and the benefits derived from the pilot program have proved that statistical process control, as applied successfully in Japanese shipyards, is a viable method for improving productivity in the shipbuilding industry.

Modeling and Simulation of Material Removal Rates and Profile Accuracy Control in Abrasive Flow Machining of the Integrally Bladed Rotor Blade and Experimental Perspectives

2017 ◽  
Vol 139 (12) ◽  
Author(s):  
Kai Cheng ◽  
Yizhi Shao ◽  
Rodrigo Bodenhorst ◽  
Mitul Jadva
Keyword(s):  
Dimensional Accuracy ◽  
Accuracy Control ◽  
Abrasive Flow Machining ◽  
Virtual Machining ◽  
Computational Environment ◽  
Component Form ◽  
Simulation Based ◽  
Machining System ◽  
Bladed Rotor ◽  
Profile Accuracy

Abrasive flow machining (AFM) technology is getting more and more interest by the industry and research community particularly in the context of increasing demands for postprocessing of the additively manufactured and complex components. It is essentially important to develop an industrial feasible approach to controlling and improving the profile accuracy (form and dimensional) of components as well as their surface roughness. In this paper, a multiscale multiphysics simulation-based approach is presented to model and simulate the AFM process against the component form and dimensional accuracy control in particular. The simulation is developed in comsol which is a multiphysics computational environment. Well-designed AFM experiment trials are carried out on a purposely configured blade “coupon” to further evaluate and validate the simulations. The AFM machine and specific machining media for the experiments are provided by the industrial collaboration company, with their further industrial inputs. Both the simulation and experimental trial results illustrate that the approach is applicable to the blade profile prediction and accuracy control, which is used as a foundation for developing the simulation-based AFM virtual machining system.

Accuracy and Distortion Control Challenges in Lightweight Structural Unit Assembly at Northrop Grumman Ship Systems

2006 ◽  
Vol 22 (03) ◽  
pp. 147-154
Author(s):  
M. Spicknall ◽  
E. Hodges ◽  
T. D. Huang
Keyword(s):  
Dimensional Accuracy ◽  
Steel Structures ◽  
Cost Effective ◽  
Naval Research ◽  
Accuracy Control ◽  
Contributing Factors ◽  
Quality Performance ◽  
Lightweight Structures ◽  
Office Of Naval Research ◽  
Welding Processes

Shipboard applications of lightweight structures have increased over the past decade in both military and commercial vessels. Severe distortions have emerged as a major obstacle to the cost-effective fabrication of such lightweight structures. With a recent major initiative funded by the US Navy Office of Naval Research, Northrop Grumman Ship Systems (NGSS) has undertaken a comprehensive assessment of lightweight structure technology. This program includes a comprehensive investigation of the fabrication and assembly processes for thin steel structures and their contributions to the final dimensional accuracy and distortion. As part of this effort, substantial work was done to characterize current dimensional quality performance in partial subunit (PSU) and combined partial subunit (CPSU) assemblies, and to identify contributing factors to dimensional inaccuracy and distortion in unit assembly stages. This information will be used by NGSS as a basis for improvements in fitting and welding processes, jigging and fixturing methods, dimensioning and tolerancing, and accuracy control processes. This paper summarizes the current dimensional quality performance in PSU and CPSU at NGSS, and the factors contributing to current performance.

Simulation of Welding Deformation for Dimensional Accuracy Control

2007 ◽  
Author(s):  
M Onoe ◽  
◽  
K Uno ◽  
K Mizutani ◽  
◽  
...  
Keyword(s):  
Dimensional Accuracy ◽  
Welding Deformation ◽  
Accuracy Control

Accuracy and Distortion Control Challenges in Lightweight Structural Unit Assembly at NGSS

2005 ◽  
Author(s):  
M. Spicknall ◽  
E. Hodges ◽  
T. D. Huang
Keyword(s):  
Dimensional Accuracy ◽  
Steel Structures ◽  
Cost Effective ◽  
Naval Research ◽  
Accuracy Control ◽  
Contributing Factors ◽  
Quality Performance ◽  
Lightweight Structures ◽  
Office Of Naval Research ◽  
Welding Processes

Shipboard applications of lightweight structures have increased over the past decade in both military and commercial vessels. Severe distortions have emerged as a major obstacle to the cost-effective fabrication of such lightweight structures. With a recent major initiative funded by the U.S. Navy Office of Naval Research, Northrop Grumman Ship Systems (NGSS) has undertaken a comprehensive assessment of lightweight structure technology. This program includes a comprehensive investigation of the fabrication and assembly processes for thin steel structures and their contributions to the final dimensional accuracy and distortion. As part of this effort, substantial work was done to characterize current dimensional quality performance in partial sub-unit (PSU) and combined partial sub-unit (CPSU) assemblies, and to identify contributing factors to dimensional inaccuracy and distortion in unit assembly stages. This information will be used by NGSS as a basis for improvements in fitting and welding processes, jigging and fixturing methods, dimensioning and tolerancing, and accuracy control processes. This paper summarizes the current dimensional quality performance in PSU and CPSU at NGSS, and the contributing factors to current performance.

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