Failure analysis of a hot extrusion die used for Al-Li alloy processing

Al-Li alloys being developed as lighter, substitutes for conventional high strength Al alloys are to be processed by routine methods. During extrusion of a 8090 Al-Li alloy, the extrusion die container failed causing some alarm. This failed die container was analysed to examine if the failure was caused by interaction of Li diffusing out of Al-Li alloy with the carbides of die steel. The evidence, although not conclusive, is sufficient to exercise caution during such processing.     

On the demand distributions of spare parts

Spare parts have become ubiquitous in modern societies, and managing their requirements is an important and challenging task with tremendous cost implications for the organisations that are holding relevant inventories. Demand for spare parts arises whenever a component fails or requires replacement, and as such the relevant patterns are different from those associated with ‘typical’ stock keeping units. Such demand patterns are most often intermittent in nature, meaning that demand arrives infrequently and is interspersed by time periods with no demand at all. A number of distributions have been discussed in the literature for representing these patterns, but empirical evidence is lacking. In this paper, we address the issue of demand distributional assumptions for spare-parts management, conducting a detailed empirical investigation on the goodness-of-fit of various distributions and their stock-control implications in terms of inventories held and service levels achieved. This is an important contribution from a methodological perspective, since the validity of demand distributional assumptions (i.e. their goodness-of-fit) is distinguished from their utility (i.e. their real-world implications). Three empirical datasets are used for the purposes of our research that collectively consist of the individual demand histories of approximately 13,000 SKUs from the military sector (UK and USA) and the Electronics Industry (Europe). Our investigation provides evidence in support of certain demand distributions in a real-world context. The natural next steps of research are also discussed, and these should facilitate further developments in this area from an academic perspective.     

Failure analysis of H13 working die used in plastic injection moulding

The present study is focused on the failure of a die used in plastic injection moulding. The die was made from AISI H13 steel and was intended for the production of plastic cups used for the outer closure of cylindrical aluminium cans in coffee packaging. The appearance of the die provides a clear picture of degradations. Extended corrosion damage on various areas of the metallic part and a wide crack can be observed by the naked eye. Hardness measurements and chemical analysis eliminated the probability of faulty material selection or improper heat treatment. Visual inspection, macro-examination and microscopic observations of representative failed parts revealed that the failure was caused by corrosion that led to the total cracking of the die. The design deficiency and improper cooling conditions generated a complex fatigue-corrosion cracking mechanism that lead to the damage of the die after half of it’s predicted service life.     

Modelling,analysis and improvement of an integrated chance-constrained model for level of repair analysis and spare parts supply control

In traditional practices, maintenance system and spare parts inventory control are usually considered in isolation, resulting in suboptimality. In a military system, the level of repair analysis (LORA) is often employed to help operate its repair networks. In this paper, we consider an integrated LORA and inventory control problem and formulate this problem as a mixed-integer nonlinear programming problem with chance constraints. Two second-order cone constraints are proposed to approximate the chance constraints. Furthermore, we propose an outer approximation (OA) algorithm based on the OA cuts. Extensive numerical results show that the OA algorithm significantly improves the computational efficiency under various types of components and network complexity. Next, we investigate the influence of service level and resource capacity, and propose the findings. Our results indicate that a higher service level leads to steeper costs, more resources, larger storage and heavier repair burdens at operating sites. Moreover, enhancements in resource capacity from the status quo lead to improvements in repairs and shrinkage in discards, bringing direct economic benefits. The insights extend to uncertain settings. It may be initially counterintuitive for many practitioners that demand uncertainty poses relatively subtle impacts.     

Failure analysis of an open die forging drop hammer

This paper analyses the failure of a large open die forging drop hammer. The analysis had to be semi-destructive as it was wanted to repair the equipment and to return it into service. A visual examination was performed at the forging shop and fatigue initiated at two internal defects blamed for the failure. A small sample was extracted from the fracture surface. Unfortunately, due to the desire of recovering the drop hammer this sample did not belong to those zones which were identified to be the origins of the failure but to the zone of progression of the crack by fatigue close to the overload final failure. Fractographic analysis by scanning electron microscopy revealed the presence of some ductile dimples pointing to an acceleration of the cracking process at this stage.     

Failure analysis of automotive battery parts

In the injection molding process defective pieces are sometimes detected, showing weak points which break easily. In this work, the possible causes of these failure points are evaluated. Thermal analysis techniques were applied to the material to better understand the degradation that takes place with relation to the transformation process. Simulations were made to determine the possible causes of deterioration and at the same time reproduce the effects of this fragility. The creation of the weak points was simulated and their origins were determined.     

Failure analysis of a pull rod actuator of an ATOX raw mill used in the cement production process

A failure analysis of a forged and machined pull rod made of a quenched and tempered high strength steel – namely DIN 34CrNiMo6 – is presented in this paper. The pull rod under study is one of the three rods that connect the three existing hydraulic cylinders to the roller mill and it is used to exert grinding pressure on the roller in an ATOX raw mill. The study of the failure involved the mechanical system's simulation, as well as the fatigue damage assessment based on the application of the Rainflow Method and Fracture Mechanics principles. The pull rod's stress state was determined from in situ strain gages rosettes measurements, and system's simulation showed that the pull rod was designed to support axial loadings only. To ensure this stress state, a proper functioning of the plain bearings and a good condition of the elastomers of the horizontal rod buffer are required. According to the stress-life approach given in the FKM guideline, the current design solution should provide a useful life of 50 years to the pull rod. However, fatigue crack growth calculations made with the strain spectra registered demonstrated that the presence of an initial surface crack is extremely harsh to the lifespan of the rod, which will reach a critical value in a much shorter period of time. Surface finish, corrosion protection and maintenance actions to ensure the correct functioning of the plain bearings, could be important to ensure the desired longevity of the pull rod.     

Spare parts management for technical systems: resupply of spare parts under limited budgets

In this paper, we study the operational availability of a complex technical system consisting of several components. The components are subject to breakdowns, and hence for each component a limited number of spare parts are held in stock. If a system's component fails and it can not be replaced immediately, due to a lack of spares, the system becomes unavailable until a new component is installed. Failed components are disposed of and hence, to keep the spare parts stock at an appropriate level, new components have to be purchased. We assume that only a limited annual budget is available for procurement, while any further procurement requires a considerable lead time. We investigate at an aggregate level what budgets are needed to attain a target availability level for the system. In addition, we develop various operational strategies for spending the annual budget during each year. Numerical results indicate that the so-called Balance Focussed strategy provides the best results in terms of system availability as a function of time.     

Evaluating the manufacturability of machined parts and their setup plans

Design-for-manufacturability is an approach that requires product designers to consider the manufacturing issues of a product concurrently with the geometrical and design aspects. This paper presents a manufacturability evaluation methodology that incorporates design, machining and work-holding issues. The evaluation is carried out in two parts. The first part is related to the machinability of the features of the part, whereas the second part is concerned about the fixturability of the part with regards to its planar faces. The methodology uses the fuzzy sets theory and the analytical hierarchy process method to evaluate the accessibility, orientation, dimensional tolerances, and surface finish specifications of a part. The former is used to model the various ill-defined boundaries of the criteria, while the latter allows for differences in opinions from designers/machinists to be incorporated into the evaluation process. The quantitative machinability and fixturability indices found can be used to evaluate designs and generate redesign suggestions. A setup plans evaluation module has been developed to determine the merit indices of setup plans for machining a part using these machinability and fixturability indices.     

Dozor roughness testers for workshop noncontact inspection of the surface of machined parts

Reflectometric results are given for a nonparallel incident beam at various wavelengths. A number of different original portable testers have been developed on the basis of those results for checking the roughness parameter R_a of outside surfaces. The devices are described and their specifications are given.Translated from Izmeritelnaya Tekhnika, No. 11, pp. 21–25, November, 2004.     

Failure analysis of the suspension spring of a light duty truck

In this paper the failure of the rear suspension spring is analyzed in detail. The rear axle suspension system of the truck and fractured flat spring is investigated. Fracture surface, mechanical and chemical properties and microstructure of the spring material is analyzed. Forces acting on the spring is determined and strength calculations are carried out. Later, failure behaviour and cause of fracture is revealed after carefully analysis of microstructure and results of calculations. At the end precautions to be taken to prevent a similar failure is recommended.     

Failure analysis of driveshaft of truck body caused by vibrations

In recent years, a current trend of mechanical engineers is to design such mechanical drives which will have a guaranteed life time. In this guaranteed operating life it is many times expected to be failure-free and service-free operation of a drive. The considerable problem is a condition of drive when a failure occurs during the guaranteed lifetime. Consequently, the identification of the failure is processed. Regarding the complexity of the drive, the failure identification is often difficult and it requires analytical as well as experimental procedures, methods and processes. The experimental methods are very useful for identifying the actual state of individual drive components, or to verify the utility of proposed solutions. The mentioned methods are difficult, especially for time-consuming and the need of technical equipment is required. On the other hand, the analytical procedures could be use mainly in experiment preparation phase and after the experiment realization; it means at the design stage of review procedures or during preparing new solutions. The issue being dealt with in the present article focuses mainly on the experiment stage.This paper deals with identification of excitation of vibrations causing the failures of driveshaft of truck body. From results analysis we found that a source of vibration is particularly main exciting frequency of the combustion engine, as becomes clear from the character of the combustion engine, it is necessary to take measures to reduce vibration.     

On the implementation of a control-based forecasting system for aircraft spare parts procurement

The implementation of a new control-based forecasting system (SDF) in 1989-1991 at the Aviation Supply Office, Philadelphia, Pennsylvania, is documented. The philosophy, experience, principles and formulas are presented with results from three implementations.