Steel Crankshafts Research Articles

G0300804 高周波焼入れクランクシャフトの残留応力解析

Residual stress that is mainly caused by heat treatment is one of the important factors in mechanical products such as internal combustion engines, since it affects the maintenance of peak performance and operational durability in competitive scenarios. In past, a phase transformation analysis method, in which volume fraction of 4 phases (Ferrite, Pearlite, Bainite and Martensite) during heat treatment process can be individually taken into account, was constructed for the prediction of residual stress caused by heat treatment such as induction hardening. In this paper, elasto-plastic analysis combines with this and applies to prediction of residual stress of S50C steel crankshaft to verify the validity of this method.

Evaluation of FEM based Fracture Mechanics Technique to Estimate Life of an Automotive Forged Steel Crankshaft of a Single Cylinder Diesel Engine

Abstract Crankshaft is one of the critical components of an IC engine, failure of which may result in disaster and makes engine useless unless costly repair performed. It possesses intricate geometry and while operation experiences complex loading pattern. In IC engines, the transient load of cylinder gas pressure is transmitted to crankshaft through connecting rod, which is dynamic in nature with respect to magnitude and direction. However, the piston along with connecting rod and crankshaft illustrate respective reciprocating and rotating system of components. the dynamic load and rotating system exerts repeated bending and shear stress due to torsion, which are common stresses acting on crankshaft and mostly responsible for crankshaft fatigue failure. Hence, fatigue strength and life assessme nt plays an important role in crankshaft development considering its safety and reliable operation. The present paper is based on comparative studies of two methods of fatigue life assessment of a single cylinder diesel engine crankshaft by using fracture mechanics approach viz. linear elastic fracture mechanics (LEFM) and recently developed critical distance approach (CDA). These methods predict crack growth, time required for failure and other parameters essential in life assessment. LEFM is an analytical method based on stress intensit y factor which characteristics the stress distribution in the vicinity of crack tip, whereas CDA is a group of methods predicts failure using stress distance plot. The maximum stress value required for both the methods are obtained using finite element analysis based commercial software known as ABAQUS. The present paper provides an insight of LEFM and CDA methods along with its benefits to the designers to correctly assess the life of crankshaft at early stage of design. This paper also gives a detailed overview of failure analys is process including theoretical methods and result integration for predicting life of components as compared to life estimation by means of software.

Evaluation of a cast-joining process of dual-metal crankshafts with nodular cast iron and forged steel for medium speed diesel engines

A new nontraditional way of manufacturing crankshafts for medium speed diesel engines is proposed and evaluated by the state of the art of multibody dynamic analysis. Introduced for the first time in this paper, the new approach makes use of commercially unprecedented dual-metal cast-joining of nodular cast iron and forged steel. The strength of the dual-metal interface is validated by tensile tests with specially prepared dual-metal test coupons. The tensile tests revealed that the tensile strength of the dual-metal interface could be controlled to have over 700 MPa, which provides a fundamental basis to a dual-metal crankshaft. Given the reliable dual-metal cast joining, two dual-metal crankshafts, the so-called DM1 and DM2, are suggested and evaluated for two operational cases: an actual case of 100 bars of gas pressure; and a virtual case of 210 bars of gas pressure. The analysis results of the two cases demonstrated that one of the two dual-metal crankshafts, DM2, showed equivalent or outperforming fatigue performance over the traditional steel crankshaft. Therefore, by virtue of the new materialistic combination and the cast-joining technology introduced in this paper, the dual-metal crankshaft of nodular cast iron and forged steel presents a strong possibility to replace the traditional forged steel crankshaft, which is costly and low productive.

Development of Ductile Iron Material, Simulation and Production Technology to Locally Strengthen Castings

A lot of innovations in molding and casting technology and also simulation techniques have made ductile iron more and more competitive and it even competes meanwhile against steel forgings. A successful substitution of steel forgings for example is the wheel carrier for a high volume car with the Georg Fischer new ductile iron material 'SiboDur', a ductile iron family with high strength and high elongation at the same time. But there is still a great potential for ductile iron castings to substitute steel forgings, in particular in the automotive industry. One example is the crankshaft for the engine: Quite a lot of gasoline engines are equipped with ductile iron crankshafts, but for instance most of the diesel engines are still running with forged steel cranks. The reason is mostly the belief of design engineers that it is not possible to get similar fatigue limit with castings com-pared to forged steel. This belief may often be correct, but using local strengthening technologies, such as roller burnishing of bearing fillets or inductive hardening of highly stressed areas can raise the fatigue limit of casted crankshafts dramatically. The paper presents studies which show that using the right ductile iron material and optimized roller burnishing conditions can raise the fatigue limit of cast crankshafts to values even higher than forged steel ones (material 38MnVS6). But even quenched and tempered forged steel crankshafts are in the focus to be substituted by castings. It is well known that ductile iron also can be induction hardened, but the induction hardening of ductile iron is still an empirical technology. This leads to the second part of the paper: In a cooperation of Georg Fischer and RWP a research project was carried out to develop a simulation technology to predict the residual stresses in a cast crankshaft due to induction hardening under different condi-tions. The results are very encouraging and enable us today to predetermine the induction hardening conditions to get optimized fatigue behavior of ductile iron crankshafts. Of course, the findings can also be used for other applications than crankshafts.

Experimental study of the fatigue behaviour of fillet rolled steel crankshafts

Studies on fillet rolled crankshafts were the main focus of a joint research project by the Institut fur Werkstoffkunde (IfW, Institute for Materials Technology) and the Fachgebiet fur Systemzuverlassigkeit und Maschinenakustik (SzM, System Reliability and Machine Acoustics) of the TU Darmstadt in cooperation with the Fraunhofer LBF. Among other things, the project involved a detailed analysis of the fatigue strength due to bending as well as combined bending and torsion loading with constant amplitude loading and single overloads.

Optimization of a Forged Steel Crankshaft Subject to Dynamic Loading

In this study a dynamic simulation was conducted on a forged steel crankshaft from a single cylinder four stroke engine. Finite element analysis was performed to obtain the variation of the stress magnitude at critical locations. The dynamic analysis resulted in the development of the load spectrum applied to the crankpin bearing. This load was then applied to the FE model and boundary conditions were applied according to the engine mounting conditions. Results obtained from the aforementioned analysis were then used in optimization of the forged steel crankshaft. Geometry, material, and manufacturing processes were optimized using different geometric constraints, manufacturing feasibility, and cost. The first step in the optimization process was weight reduction of the component considering dynamic loading. This required the stress range under dynamic loading not to exceed the magnitude of the stress range in the original crankshaft. Possible weight reduction options and their combinations were considered. The optimization and weight reduction were considered in an interactive manner and evaluated by manufacturing feasibility and cost. The optimization process resulted in an 18% weight reduction, increased fatigue strength, and a reduced cost of the crankshaft.

Throttle seals for crankshaft bearings

At high operating temperatures, differences in the coefficients of thermal expansion for light metal engine blocks and steel crankshafts cause large bearing gaps to open up between the crankshaft and the main bearing shells. In such cases, significant amounts of oil are needed to ensure an adequate supply of oil to the crankshaft main bearing and the connecting rod bearing. There is also the additional risk of insufficient lubrication at low speeds, e.g. at hot idle. Adapting the oil pump to suit these operating conditions does not get to the root of the problem. Throttle seals by Freudenberg that are integrated into the bearing shells offer a completely new approach.

Failure Analyses of Six Cylinder Aircraft Engine Crankshafts

Results of failure analyses of two aircraft crankshafts are described. These crankshafts were forged from AMS 6414 (similar composition to AISI 4340) vacuum arc remelted steels with sulfur contents of 0.003% (low sulfur) and 0.0005% (ultra-low sulfur). A grain boundary sulfide precipitate was caused by overheat of the low sulfur steel, and an incipient melting of grain boundary junctions was caused by overheat of the ultra-low sulfur steel. The precipitates and incipient melting in these two failed crankshafts were observed during the examination. As expected, impact fractures from the low sulfur steel crankshaft contained planar dimpled facets (PDF) along separated grain boundaries with a small spherical manganese sulfide precipitates within each dimple. In contrast, PDFs along separated grain boundaries of impact fractures from the ultra-low sulfur crankshaft steel contained a majority of small spherical particles consisting of nitrogen, boron, iron, carbon, and a small amount of oxygen. Some other dimples contained manganese sulfide precipitates. Fatigue samples machined from the ultra-low sulfur steel crankshaft failed internally at planar grain boundary facets. Some of the facets were covered with nitrogen, boron, iron, and carbon film, while other facets were relatively free of such coverage. Results of experimental forging studies defined the times and temperatures required to produce incipient melting overheat and facets at grain boundary junctions of ultra-low sulfur AMS 6414 steels.

Hot Forging Simulation Analysis and Application of Microalloyed Steel Crankshaft

Abstract In this paper, the hot forging process of microalloyed steel for crankshaft was investigated. The crankshaft model was built according to the data, directly measured from the blocker crankshaft blank. The simulation of crankshaft forging was carried out by FEM software ansys/ls-dyna. The changes of structure and temperature field were simulated in the course of hot forging. The relationships between the metal flow rules and temperature field in the crankshaft were described. And the shapes of centerline defects were analyzed during the crankshaft forging. In order to improve the material utilization ratio, a near-net-shape design is put forward according to the reversed analysis.

ADI Lost-Foam: Synergy of Process and Material

A consortium of SME and RTD partners from Germany, Poland, Italy and Finland was established in the ambit of the fifth European framework programme for the development of a process that combined Lost-Foam with a high performance ADI – Austempered Ductile Iron Cast Iron. In the Lost-Foam process foam patterns are used as models for complex and near net shape castings. These models are coated with a special refractory paint. The models are surrounded by unbonded sand and then filled with liquid metal. As the alloyed ductile iron melt decomposes the foam, the coating material is of great importance for the effective extraction of the foam decomposition products. By means of a posterior special heat treatment it is possible to achieve tensile strengths ranging from 800 to 1600 MPa with elongations ranging from 1 % to 12 %. The main achievements of the performed investigations were the development of the alloy and respective heat treatment parameters for the base ductile iron as well as a suitable coating material. Moreover, these investigations showed that it is possible to produce ADI castings capable of achieving the same mechanical properties as forged steel crankshafts with a significant weight reduction. Additionally, the production of such castings through the Lost-Foam process have a yield of more than 87 % as opposed to the typical yield of the traditional green sand process which can reach 55 %.

MINIMUM QUANTITY LUBRICATION (MQL) APPLICATIONS IN AUTOMOTIVE POWER-TRAIN MACHINING

ABSTRACT Minimum Quantity Lubrication (MQL) is a near-dry machining method that may be applied to reduce coolant usage in operations such as drilling, which cannot be performed completely dry. Although significant research has been reported on MQL, relatively little information on production applications and experience has appeared in the technical literature. The most common high-volume production application for MQL is cross and oil hole drilling on steel crankshafts. This paper reviews MQL test results for deep hole drilling of forged steel and cast nodular iron under conditions similar to crankshaft oil hole drilling. The results show that MQL can yield tool life equivalent to gun drills at higher penetration rates under these conditions. This result is consistent with production experience with steel crankshafts, and shows that MQL may also be useful for cross and oil hole drilling of cast crankshafts. Limited test and production data for MQL machining of aluminum prismatics is also described. Significant areas for future research and development, including chip management, air quality, capability and robustness, and cost are also discussed.

Bainitization heat treatment for steel crankshafts using finite element analysis

PSA., leader in the fabrication of Diesel engines, aims at increasing its productivity for the manufacture of forged steel crankshafts and controlling perfectly their quality. All industrial partners of PSA are contributing to the achievement of this goal. Detailed metallurgical studies and numerical simulation have been used internally to describe the microstructural transformations involved. It has been shown that numerical simulation allows to identify trends for the effect of the modification of various parameters without the need for expensive and time-consuming prototype studies.

Crankshaft failure and why it may happen again

This case study involves two continuously cast steel crankshaft failures. Three parties performed their own failure analyses: (1) the engine manufacturer responsible for component design, specification, and application; (2) the steel supplier and forging supplier responsible for making the steel, forging the shape, and preliminary heat treatment; and (3) a supplier that provided induction hardening, finish machining, and inspection. An independent fourth party engineering firm was subsequently involved, but because each party had their own agenda, there was no agreement on the metallurgical failure cause and therefore no continued analysis to pin-down and eliminate the root cause. A classic case showing how we may be doomed to repeat our failures because sound engineering was not allowed to proceed.

Austempered ductile iron: a competitive alternative for forged induction-hardened steel crankshafts

The mass-production considerations in replacing forged and induction-hardened steel crankshafts with ADI are described for a four-cylinder 120 h.p. petrol engine and a single-cylinder diesel engine. Microstructure, mechanical property, solidification, casting system, heat treatment and machining problems are examined for castings made using the sandwich and inmould treatment methods. Analysis of the results shows that the steel crankshafts can be replaced without a change in design by ADI components with a 10% weight saving and 30% lower production costs. It was found also that successful production of a heavy-duty ADI component requires close control over all the manufacturing processes.

Quenchants for surface induction hardening of parts

1. Intense water spray quenching in surface induction hardening may be used successfully not only for carbon but also for alloy steels in place of emulsion, watersoluble polymers, and other quenchants, which was shown using tractor engine crankshafts as an example. 2. Hardening of the journals of carbon and alloy steel crankshafts with an intense water spray does not lead to the formation of cracks and increased distortion of the parts.

Nitriding of restored crankshafts

The following technology is recommended for restoration of steel crankshafts: facing with an Sv-08 electrode wire under an AN-348A flux with chromium and niobium introduced into the melt in accordance with the method used at automotive-repair plants and subsequent gas nitriding at (570±10)°C for 12 h.

型打鍛造クランク軸の疲れ限度

A study has been made on the fatigue limit of die forged crankshafts with 100 mm and 150 mm in journal diameter. It is found that the crankshaft shaped by die forging method has higher fatigue limit than those of the conventional forged ones, especially when the higher hardness layer than of their inner part is given on their outer layer by heat treatment. The required depth of this high hardness outer layer is estimated more than 0.2⋅R4 to increase fifty per cent in fatigue limit, where R4 is fillet radius.In the last part, a proposal for the estimation method of the fatigue limit of solid type forged steel crankshafts has been made based on our whole fatigue test results obtained on the actual sized crankshaft specimens with various dimensions and shaped by various methods.

Comparison between the strength of steel and cast iron crankshafts in large-scale routine fatigue bending tests

1. We have developed and verified under fatigue-test conditions a constructionally simple and technological efficient model of a crankshaft, manufactured from circular cylindrical blanks by simple machining. 2. The bending fatigue strength of crankshafts with SPD-strengthened hollow chamfers of small radius (r:d=0.02) equals that of crankshafts with chamfers of large radius (r:d≥0.040–0.09). 3. The high efficiency of the technological process for strengthening chamfers of small radii by SPD is confirmed by a statistical analysis of the results of fatigue tests at a reliability level of 95%. 4. The efficiency of the SPD strengthening of small-radius chamfers will in 95 cases out of 100 lie in the range 272–346 and 240–309% for steel 45 and HTI crankshafts respectively. 5. The strength procedures and the geometry of the chamfers before and after strengthening here assumed ensure a very efficient strengthening process, i.e., stress concentrations in the chamfer junction are almost completely eliminated. 6. Engine crankshafts may be designed with small-radius chamfers (r:d=0.02) instead of those with large radii (r:d≥0.04–0.09) recommended in the corresponding engineering standards; this allows the support surface of the pivots to be increased by up to 8%, so reducing the wear on the shaft pivots and bearings, i.e., increasing the life of the engines.

LUBRICATING MINIATURE BEARINGS

At Stockholm, recently, the F.A.I. world championship control‐line team race was won for Britain with an aircraft equipped with an Eta 15 Mk. II engine, built by Eta Instruments Ltd., and believed to be the most powerful engine in its class in the world. This is a 2.5 c.c. diesel engine. With an engine of such a diminutive size operating with 15,000 and 20,000 r.p.m. the method utilised to support the crankshaft is obviously of great importance; it must be rigidly held and yet subjected to the minimum rotational constraint. Two Hoffmann miniature ball bearings are used to locate the crankshaft and are mounted at either end of an extended one‐piece aluminium alloy housing that is bolted directly on to the front of the aluminium pressure diecast crankcase. A Hoffmann N6358 ball bearing (⅝‐in. o.d.) is fitted at the front and a Hoffmann S1 V2 (¾‐in. o.d.) at the rear of the housing. The counter‐balanced forged steel crankshaft has a main shaft 0.25 in. o.d.