Tolerances allocation

Today s high technology products and growing international competition require knowledgeable design decisions based on realistic models that include manufacturability requirements. A suitable and coherent tolerance allocation methodology... 

Research looking into tolerance allocation in assembly stacks is by no means new. A current theme is towards an optimization approach using complex routines and/ or cost models (Lin et al., 1997 Jeang, 1995). Advanced methods are also available, such as Monte Carlo Simulation and Method of Moment. ) (Chase and Parkinson, 1991 Wu et al., 1988). The approach presented here is based on empirical process capability measures using simple tolerance models, cost analogies and optimization... 

Cagan, J. and Kurfess, T. R. 1992 Optimal Tolerance Allocation over Multiple Manufacturing Alternatives. Advances in Design Automation, 2, ASME DE-Vol. 44-2, 165-172. 

Soderberg, R. 1993 Tolerance Allocation Considering Customer and Manufacturer Objectives. ASME Advances in Design Automation, Vol. 2, ASME, DE-Vol. 65-2, 149-157. 

Tolerance synthesis it is regarded as a tolerance allocation and a tolerance optimization method taking into account manufacturing and inspection aspects. 

Among all solutions available to perform tolerance allocations, three can be distinguished ... 

Etienne A, Dantan J-Y, Siadat A, Martin P (2009) Activity-based tolerance allocation (ABTA) - driving tolerance synthesis by evalnating its global cost. Int J Prod Res 47(18) 4971 989... 

Schmitt R, Behrens C (2007) A statistical method for analyses of cost- and risk optimal tolerance allocations based on assured input data.In Weckenmann A (ed) Book of abstracts - 10th CIRP conference on computer aided tolerancing, specification and verification for assemblies March 21st - 23rd, 2007 in Erlangen, Germany. Shaker, Aachen... 

The combination of the cost model and the optimization method will then give an augmented model from which the allocation of the component tolerances are optimized for competitive results. Optimization methods have also been extended to include procedures that select the most cost-effective manufacturing process for each component tolerance in the assembly stack (Chase and Parkinson, 1991). 

The final tolerances the designer would allocate to the component dimensions are also shown in Figure 3.16. The tolerance values are given to three decimal places which, if required for practical use, can be rounded off with minimal effect to the overall assembly tolerance, for example 0.191 mm to 0.190 mm. 

The measures of dimensional variability from Conformability Analysis (CA) (as described in Chapters 2 and 3), specifically the Component Manufacturing Variability Risk, q, is useful in the allocation of tolerances and subsequent analysis of their distributions in probabilistic design. The value is determined from process capability maps for the manufacturing process and knowledge of the component s material and geometry compatibility with the process. In the specific case to the th component bilateral tolerance, it was shown in Chapter 3 that the standard deviation estimates were ... 

Spotts, M. F. 1973 Allocation of Tolerances to Minimise Cost of Assembly. ASME Journal of Engineering for Industry, 95, 762-764. 

Total allocations of less than 100% of the tolerable intake are recommended to account for, e.g., those media for which exposure has not been characterized, and cross-route exposure. The proportion of the total intake, which is not allocated, should vary according to the adequacy of the exposure characterization from all media. 

For the process measurement and control instrumentation the loop schedule enables allocation of a unique identifier (tag number) to each instrument used in the operation of the plant. This will allow application details to be added to the schedule (e.g., range, accuracy, set-point tolerance, signal type, description, location and any other information thought necessary to provide a clear understanding of the requirements for each instrument). 

THINK considers fuzzy two-, three- or four-center pharmacophores. If a given molecule contains more than three or four centers, then all possible groups of two to four centers are taken. The distances (including a tolerance) between the pharmacophore centers are measured exactly and then allocated to distance bins, each distance being represented by the bin into whose range it falls. The distance bins are used to transform the distances within each pharmacophore into a set of integers that give a more compact representation of the pharmacophores. 

As discussed previously, if you cannot tolerate your investment portfolio declining by 30% percent in one year, you do not want to have an all-stock portfolio (because the largest historical one year decline was 43.3%). But how should you allocate your resources Suppose that you can tolerate a 20% decline or a 10% decline Based on historical returns and using large stocks and long-term bonds as major asset classes to design a portfolio, you should not have more than 40% stocks in your portfolio ifyou cannot tolerate agreater than 20%... 

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