A. Passannanti

Optimum tool replacement policies with penalty cost for unforeseen tool failure

Abstract Models for tool replacement strategies in manufacturing systems introducing a penalty cost if the tool fails during the cut are proposed. These models are developed for general stochastic tool life distribution and applied to the case of a log-normal distribution.

Interdependence Between Tool Fracture and Wear

Wear and fracture are the main causes of tool scrapping. However fracture plays a major role for increasing values of the hardness and brittleness of tool materials or when low-cobalt tungsten carbides are used or in interrupted cutting conditions where it is the most relevant factor for tool scrapping. In order to obtain the optimal values of the cutting speed both these factors should be considered. The hypothesis of stochastic independence among them simplifies the mathematical formulation of the optimization problem; but experimental investigations do not agree with this assumption and, as a matter of fact, the probability density function of tool fracture results to be dependent on the wear conditions. In the paper some experimental results will be reported; these results are then applied to the evaluation of the optimal cutting speed and tool replacement policy.

A Quality Risk Management Model Approach for Cell Therapy Manufacturing

International regulatory authorities view risk management as an essential production need for the development of innovative, somatic cell-based therapies in regenerative medicine. The available risk management guidelines, however, provide little guidance on specific risk analysis approaches and procedures applicable in clinical cell therapy manufacturing. This raises a number of problems. Cell manufacturing is a poorly automated process, prone to operator-introduced variations, and affected by heterogeneity of the processed organs/tissues and lot-dependent variability of reagent (e.g., collagenase) efficiency. In this study, the principal challenges faced in a cell-based product manufacturing context (i.e., high dependence on human intervention and absence of reference standards for acceptable risk levels) are identified and addressed, and a risk management model approach applicable to manufacturing of cells for clinical use is described for the first time. The use of the heuristic and pseudo-quantitative failure mode and effect analysis/failure mode and critical effect analysis risk analysis technique associated with direct estimation of severity, occurrence, and detection is, in this specific context, as effective as, but more efficient than, the analytic hierarchy process. Moreover, a severity/occurrence matrix and Pareto analysis can be successfully adopted to identify priority failure modes on which to act to mitigate risks. The application of this approach to clinical cell therapy manufacturing in regenerative medicine is also discussed.

The Effects of the Fracture, Chipping and Wear of Cemented Carbide Tools on the Determination of the Optimum Metal-Cutting Conditions

A computer program has been prepared to optimize machining conditions when the stochastic tool-life has a probability density function resulting from fracture, chipping and wear. The optimization has been performed under the assumption that the fracture and the chipping probability density functions are indipendent from the cutting velocity. This hypotesis is well confirmed by several interrupted cutting tests showing two different probability distributions for fracture and chipping both having parameters which remain constant when cutting velocity is varied.

Optimum Tool Replacement Policies with Running-in of the Cutting-Edge

Summary The influence of the preliminary running-in of the cutting-edge to reduce the risk of unforeseen tool failures has been studied with reference to different tool replacement strategies. Models are developed to select the optimal tool replacement policy using the minimum production cost criterion.

Cost Analysis of FMS Throughput

Abstract The need for an effective cost planning and control system is stressed in today highly competitive manufacturing environment. The conventional approaches of machining economics to cost analysis are no more able to cope with the new structure of the production costs in the highly automated - highly integrated manufacturing systems. Suitable cost analysis procedures should provide a strong integration between process planning data and overall system performances. The here proposed procedure for the estimate of the unit manufacturing cost in FMSs achieves this integration by using performance evaluation techniques like discrete event simulation or queueing network models.

Dynamic cutting coefficients in three-dimensional cutting

Abstract A new theory to predict the dynamic cutting coefficients from steady state cutting data is developed. The derived expressions are able to take into account the effect of the main angles defining the tool geometry on the chatter stability limit and show a good agreement with experimental results. The proposed model allows the identification of a parameter as an index for chatter sensitivity of the work material.

Machining Economics in FMS by a Fuzzy Approach

Abstract In a conventional manufacturing system, cutting parameters have to be fixed in order to pursue the economical and productive target related to each cutting operation. In a Flexible Manufacturing System (FMS), as a consequence of the unbalanced workload due to the mutual interaction among the shared resources, the optimization of each operation does not allow the optimum of the global production system to be reached. A fuzzy programming model is developed in this paper in order to select cutting speeds of the operations in the production plan as a satisfying compromise solution between single operation and the integrated system targets.

Lower and upper bounds of manufacturing cost in FMS

Abstract The use of traditional techniques of product costing, cost control and performance evaluation in advanced manufacturing environment supplies poor results to operations management. In this paper, after a brief review of the major drawbacks of traditional machining economics, a new framework for product costing will be presented. The basis of the proposed approach lies on an analysis of the production process aimed at single out proper cost drivers for the use of the various employed manufacturing resources. As a consequence, the quota of the manufacturing cost of uncertain allocation is drastically reduced. A lower and an upper bound value of the unit production cost are also defined with reference to the given manufacturing system. The range between the above bounds is used for accounting the costs of uncertain allocation.

On Line Tool Life Prediction for Tool Replacement Strategy in FMS Workstation

In FMS environment a large variety of tools are shared resources being employed to process different part type varying the cutting parameters during their useful life. The paper suggests a new methodology to predict the tool life on line using the information deriving from the control station of the production system to gain information about the tool wear.