Automobile Crankshafts Research Articles

Failure Analysis of Ductile Iron Crankshaft in Four-Cylinder Diesel Engine

Spheroidal graphite cast iron is widely used in automobile crankshafts due to features such as high strength, high toughness, good machinability, low cost, and ductility. The purpose of this paper is first to analyze the fatigue failure in fractured truck crankshafts between 400,000 and 1,350,000 km and then to predict the stress field under the influence of the mechanical loads caused by gas combustion. Several experimental studies including chemical composition, material strength, hardness, and microstructure are performed to evaluate the failure analysis. A nonlinear three-dimensional stress analysis model by the elastic–plastic finite element method is used to estimate the crankshaft stress field under cyclic bending combined with steady torsion. Failure analysis showed that the fracture surface consisted of three zones: fatigue crack initiation, fatigue crack propagation, and static fracture; therefore, the failure is in fatigue. Also, the microstructure results showed that the crankshaft nodularity is about 70%, which crankshaft structures are usually acceptable greater than 80% of nodularity. Besides, hardness gradient showed that the crankshaft crankpin had no hardened surface layer. Finally, numerical stress analysis indicated that the highest stress is in the crankpin–web fillet zone that it is in good agreement with those obtained in the experimental field measurements.

Ймовірнісна модель показників деформування колінчастих валів унаслідок відновлення їхніх шийок наплавленням

Для відновлення ресурсу колінчастих валів автомобільних двигунів широко застосовують різні способи наплавлення їхніх шийок. Встановлено, що найкращі результати за твердістю наплавленого матеріалу в разі відновлення колінчастих валів, без застосування термічного оброблення, отримують під час наплавлення пружинним дротом під флюсом АН 348А за легування металу вуглецем та хромом через флюс. Виявлено, що під час наплавлення деталі під флюсом відбувається значне нагрівання наплавлених ділянок, яке поширюється також на ділянки, що не піддаються наплавленню. Цьому сприяють лінійні та об'ємні розширення нагрітих ділянок деталі, осадження затвердлого розплавленого металу та перебіг структурних змін і перетворень у ньому. Як з'ясувалося, це супроводжується появою у наплавленому та основному металі розтягувальних або стискувальних напружень, під дією яких змінюється початкова геометрична форма деталі, тобто вона деформується. Встановлено, що деформування деталі може виникнути також і від згину, перекосу або її скручування у затискному пристрої, від надмірного стиснення у центрах верстату або від теплового видовження у процесі наплавлення тощо. У випадку невеликих величин деформування правлення колінчастих валів після наплавлення не обов'язкове, оскільки їхня співвісність за корінними шийками може бути досягнута в процесі механічного оброблення. Для цього необхідно спочатку шліфувати всі шатунні шийки й в останню чергу – корінні. За величин деформувань, більших від допустимих, деталі піддають правленню або утилізуванню. Для оцінки впливу на величину деформування колінчастих валів двигунів ЗМЗ 511.10 після їхнього відновлення наплавленням і подальшого шліфування побудовано ймовірнісну модель. На основі статистичного опрацювання результатів досліджень встановлено закономірності зміни випадкової величини (деформувань) за допомогою побудови емпіричного розподілу і кривої теоретичного розподілу, які підпорядковуються нормальному закону (Крива Гауса). Перевірка узгодження теоретичного та емпіричного розподілів за критерієм Пірсона показала задовільний збіг.

Digital Image Correlation (DIC) Technique for Fatigue Crack Growth Analysis Using ∆CTOD Criteria

The present paper deals with an experimental determination of fatigue crack growth rate (FCGR) of microalloyed steel (38MnVS6) to study the crack propagation in forged automobile crankshafts. The criterion based on crack tip opening displacement range (∆CTOD) is used to investigate the fatigue crack growth rate. In the current work use of 2D-digital image correlation (DIC) technique for the measurement of crack tip opening displacement (CTOD) and crack length (a) is proposed. Digital Image Correlation (DIC) is a full field displacement and strain measurement technique. It is easier to measure the crack tip opening displacement (CTOD) and crack length (a) with this technique than other. Fatigue crack growth curve based on crack tip opening displacement (CTOD) criteria is presented using DIC.

Mechanical failure analysis of automobile crankshafts under service reconditioned modelling approach

Abstract Mechanical failure of automotive crankshaft is modelled under varying service reconditioning. Primary factors (torsional vibration, bending vibration and twisting) and secondary factors (lubricity of engine, oil quality, and lubrication effectiveness) responsible for failures were identified. The stated factors were modelled using service life of main journal bearings at varying operation speeds as the crankshaft failure predictors under different reconditioning. Modelling was carried out based on standard relationships among the stated factors. The system model was implemented using experimental data from the selected vehicular crankshafts. The results showed that the service life (failure) time of the crankshafts were dissimilar. Unequal useful life of the crankshafts was attributed to variation in torsional vibration and lubricity. The findings will serve as guides for selecting right vehicular crankshaft(s) based on targeted useful life and reconditioning limits.

IMPROVED MANUFACTURING PROCESS FOR MOVABLE RETAINING PINS USING OPTIMIZATION METHOD

Movable retaining pins are generally used in automobile gears, axles, crankshafts, and seatbelt assemblies. The original manufacturing procedures comprise three-stage forming and then drilling. However, a clamp in the drilling process always causes rod surface damage and dents, and the resulting depth tolerance that always exceeds specified dimensions. This study modifies the cold-forging process by replacing the original mechanical drilling stage with one additional forming stage comprised of backward extrusion. The finite element method is applied to analyze and simulate the forming load at each stage, and the Taguchi method is utilized to optimize the product quality in the key second stage. Analytical results show that transforming the original three forging processes and one drilling process into four forging stages overcomes the problems in part manufacturing. Simultaneously, the dimensional accuracy obtained from experiment and numerical analyses shows in good agreement and trusty.

New Cold Forging Process of Retaining Pin Using FEM Based Simulation

Retaining pins are generally used as the parts of automobile gears, axes, crankshafts, and seat belts, which are proceeded three-stage forming and then drilling processing in the original manufacturing procedure. However, the fixture seizing in the drilling processing could result in rod surface damage and dent, and the depth tolerance exceeding the drawing specifications after the drilling causes the major defects in product manufacturing. This study attempts to modify the cold forging process by adding one stage and replacing the original mechanical drilling processing with backward extrusion and forging engineering. In the research process, Finite Element Method is utilized for analyzing and simulating the forming load at each stage. The analysis results show that increasing the original 3-stage forging process to 4-stage could assist in solving the problems of rod dent and depth tolerance exceeding the drawing specifications after the drilling. Although the die cost would increase with an increasing stage, the new process allows the forging force being more even and the die life being prolonged, in consideration of the overall production costs.

Evaluation of failures in mechanical crankshafts of automobile based on expert opinion

In this study, mechanical crankshaft failures for automobiles are evaluated based on experts’ opinion. This was done using data obtained using techniques based on oral interviews and questionnaire administration on mechanical failure of crankshafts from the experts working in the areas of automobile maintenance and crankshafts reconditioning. The data collected were analyzed using statistical methods based on probability. With this technique, probability of failure for each category of automobiles namely private, commercial cars and buses were evaluated. The results obtained show that private cars had lowest failure rate at the initial stage while commercial buses had the highest failure rate. At later periods all categories of automobile crankshafts considered had their failure rates converged steadily with stable reliability. Application of 6-sigma continuous improvement tool to the process indicated a further reliability improvement through improved oil lubrication system, especially in the thrust bearing. This showed that increased enlightenment campaign among the various stakeholders in automobile industries will improve on the choice of reliable mechanical crankshafts.

Development of Austempered Ductile Iron (ADI) for Automobile Crankshafts

Development of Austempered Ductile Iron (ADI) for Automobile Crankshafts

Continuing increases in the diversification of Japanese manufacturing in the USA [1

This paper reports the findings from a third series of studies of the progressive geographical and industrial dispersion of Japanese manufacturing operation in the USA. The first focused on the production of steel, automobile parts and television sets in the Midwest. The second analysed an array of West Coast plants producing semiconductors, ASICs, computers and advanced television sets. This presentation covers a further five more recently initiated Japanese operations in the South, including not only computers and semiconductors, but also automobile crankshafts, microcontrollers and air conditioner compressors. In addition to such industrial diversification, these studies have also covered successive changes in ownership arrangements, in the extent of their reliance on Japanese technologies and in their dependence on imports from Japan. Moreover, associated advances in competitiveness have increased the shares of such production not only in the USA, but also in exports to Europe, Latin America and even to Japan.

Application of Barkhausen effect measurements for detection of near surface stress (abstract)

Barkhausen effect emissions have been shown to be dependent on stress in previous work. This paper shows how the technique has been applied to evaluation of stress in automobile crankshafts. These components often fail prematurely due to residual tensile stress in the surface of the components, which leads to cracking and sudden fatigue failure. The measurements were made using an excitation frequency of 8 or 128 Hz with signal detection bandwidths of 3–15, 20–70, and 70–200 kHz. These corresponded to nominal magnetic field penetrations of 0.2, 0.07, and 0.02 mm. Results showed that measurements from the near surface (0.02 mm) were most sensitive to stress. A number of calibration experiments on different materials confirmed this result. In addition, it was found that low values of the root-mean-square Barkhausen voltage correlated with low tensile strength of the material. This measurement could, therefore, be used for detection of components that were likely to encounter early failure. A calibration of the Barkhausen voltage signal as a function of stress was obtained and this was in accordance with earlier theoretical calculations.

Simple Modeling and Analysis for Crankshaft Three-Dimensional Vibrations, Part 1: Background and Application to Free Vibrations

To simplify the analysis of the three-dimensional vibrations of automobile engine crankshafts under firing conditions, the crankshaft was idealized by a set of jointed structures consisting of simple round rods and simple beam blocks of rectangular cross-section. The front pulley, timing gear, and the fly-wheel were idealized by a set of masses and moments of inertia. The main journal bearings were idealized by a set of linear springs and dash-pots. For each constituent member, the dynamic stiffness matrix was derived (in closed form) from the transfer matrix. Then the dynamic stiffness matrix for the total crankshaft system was constructed, and the natural frequencies and mode shapes were calculated. The modeling and analysis procedures were applied to the analysis of free vibrations of four kinds of crankshafts: single cylinder, three-cylinder in-line, four-cylinder in-line, and V-six engines. The different coupling behavior of the three-dimensional vibrations in the planar-structure and the solid-structure crankshaft is discussed, and the influence of the bearing oil film stiffness on the crankshaft natural frequency is also analyzed.

Fatigue Failure of Ductile Iron Crankshafts

Automobile crankshafts can be produced as either steel forgings or ductile-iron castings. In the latter case, because of the high structure-sensitivity of fatigue strength, mechanical test requirements must be very specific. A detailed investigation of two series of crankshafts produced from pearlitic nodular-graphite iron, grade SG 60, is described. Normal tensile tests and microstructural examinations were supplemented by determination of fatigue life and fatigue limit. Fatigue tests under axial bending conditions were carried out on segments taken from two series (I, II) of machined crankshaft castings. Satisfactory bending moment and performance data were obtained for one series of samples. In the other series, sub-surface microporosity in the cast structure was exposed during subsequent machining and led to premature fatigue failure after less than 2 × 105 cycles of testing.

Development of austempered ductile iron (ADI) for automobile crankshafts

The trend toward reduced size and increased power output in current engine designs has placed great demands on component materials. Traditional cast irons often cannot meet these demands and designers have been forced to specify expensive forgings in place of castings. To avoid the cost penalty, high strength ADI has been developed for crankshaft applications.

Formation of fillet transitions in cast iron crankshafts by the action of local contact

Automatic electric arc welding is currently used extensively for restoring worn pins on automobile engine crankshafts [i, 2]. However, the efficiency of the restoration technique used depends mainly on article material. In a number of cases use of electric arc welding or another restoration method associated with thermal effects on the article material may markedly reduce fatigue resistance characteristics.

Toughening of reconditioned automobile engine crankshafts

Toughening of reconditioned automobile engine crankshafts

Investigation of the effectiveness of electromechanical hardening of metallized crankshafts of car engines

The article describes the results of an investigation of the feasibility of using an electromechanical surface treatment as a means of hardening automobile engine crankshafts reconditioned by high-frequency induction metallizing. Metallographic examination of the metal structure, determination of residual stresses in the connecting rod journals and fatigue tests on actual parts established that electromechanical hardening ensures a high endurance of crankshafts reconditioned by high-frequency metallization.

Nodular Cast Iron—its Present Position and Future Prospects as an Engineering Material, with Special Reference to its Suitability for Crankshafts

The historical development of iron having graphite present in the nodular form as cast, is traced from the patent application by Morrogh and the British Cast Iron Research Association (1946)† to its selection as a crankshaft material by the Ford Motor Co. in 1952. The economics of the production of nodular iron by various methods is discussed and it is concluded that material produced by the magnesium-nickel process now in use cannot compete in price with established materials such as carbon steel and malleable iron. Methods for direct addition of magnesium to molten iron are described, and it is concluded that application of these methods to low-sulphur irons from basic cupolas may completely alter the situation. The engineering properties of nodular cast iron are compared with those of other ferrous metals. It is concluded that nodular irons in the as-cast condition may be used instead of high grade flake-graphite irons for components not subject to shock loading, and instead of malleable irons in applications where 2–4 per cent elongation at fracture is adequate. The annealed nodular cast irons may be used, where their extra ductility and impact resistance are considered essential, to replace malleable irons and cast or forged carbon-steels. Their chief advantage over malleable irons lies in the shorter heat-treatment they require, which becomes economically more important as the size of a casting increases and as its selling price per lb. falls. As a replacement for carbon steel, nodular cast iron will be attractive for components which are difficult to cast or which require high surface-hardness with medium strength and impact resistance. However, the extent to which nodular cast iron replaces any of these materials will be determined largely by the price at which it can be produced; this will have to be decreased very considerably before it becomes competitive. Ultimate output of nodular cast iron in Britain in peace time is likely to be limited by the high cost of the low-phosphorus ore which is necessary for its production; in war time, its output might be severely restricted by the difficulty in importing this ore. The particular application of nodular cast iron to crankshafts is discussed in detail. It can replace alloy flake-graphite irons with a gain in ductility and impact resistance, and is already replacing graphitic cast steel, chiefly because of its better founding properties, and because its lower pouring-temperature facilitates the use of mass-produced shell moulds. It seems doubtful whether its fatigue properties will permit of its replacing the forged low-alloy steel which is used for most British automobile crankshafts, unless some reduction in engine specific-power output is accepted.