Numerical simulation and experimental validation of the cladding material distribution of hybrid semi-finished products produced by deposition welding and cross-wedge rolling

The service life of rolling contacts is dependent on many factors. The choice of materials in particular has a major influence on when, for example, a ball bearing may fail. Within an exemplary process chain for the production of hybrid high-performance components through tailored forming, hybrid solid components made of at least two different steel alloys are investigated. The aim is to create parts that have improved properties compared to monolithic parts of the same geometry. In order to achieve this, several materials are joined prior to a forming operation. In this work, hybrid shafts created by either plasma (PTA) or laser metal deposition (LMD-W) welding are formed via cross-wedge rolling (CWR) to investigate the resulting thickness of the material deposited in the area of the bearing seat. Additionally, finite element analysis (FEA) simulations of the CWR process are compared with experimental CWR results to validate the coating thickness estimation done via simulation. This allows for more accurate predictions of the cladding material geometry after CWR, and the desired welding seam geometry can be selected by calculating the cladding thickness via CWR simulation. © 2020 by the authors. Licensee MDPI, Basel, Switzerland

Numerical analysis of the skew rolling process for main shafts

The paper discusses a new technique of skew rolling with three tapered rolls and its application to the production of long main shafts of steel that are used in light trucks. First, the design of this forming technique is described. Then the paper stresses the universality of this process, as the skew rolling technique enables forming various products using one set of rolls. The reported numerical results (workpiece shape change during rolling, maps of effective strains and temperatures as well as loads and torques) confirm that the discussed technique is suitable for producing long shafts

Hybrid Bulk Metal Components

In recent years, the requirements for technical components have steadily been increasing. This development is intensified by the desire for products with a lower weight, smaller size, and extended functionality, but also with a higher resistance against specific stresses. Mono-material components, which are produced by established processes, feature limited properties according to their respective material characteristics. Thus, a significant increase in production quality and efficiency can only be reached by combining different materials in a hybrid metal component. In this way, components with tailored properties can be manufactured that meet the locally varying requirements. Through the local use of different materials within a component, for example, the weight or the use of expensive alloying elements can be reduced. The aim of this Special Issue is to cover the recent progress and new developments regarding all aspects of hybrid bulk metal components. This includes fundamental questions regarding the joining, forming, finishing, simulation, and testing of hybrid metal parts

Book of abstracts of the 14th International Symposium of Croatian Metallurgical Society - SHMD \u272020, Materials and metallurgy

Book of abstracts of the 14th International Symposium of Croatian Metallurgical Society - SHMD \u272020, Materials and metallurgy held in Šibenik, Croatia, June 21-26, 2020. Abstracts are organized in four sections: Materials - section A; Process metallurgy - Section B; Plastic processing - Section C and Metallurgy and related topics - Section D

Tribological optimisation of the internal combustion engine piston to bore conjunction through surface modification

Internal combustion (IC) engines used in road transport applications employ pistons to convert gas pressure into mechanical work. Frictional losses abound within IC engines, where only 38- 51% of available fuel energy results in useful mechanical work. Piston-bore and ring-bore conjunctions are fairly equally responsible for circa 30% of all engine friction - equivalent to 1.6% of the input fuel each. Therefore, reduction in piston assembly friction would have a direct impact on specific performance and / or fuel consumption. In motorsport, power outputs and duty cycles greatly exceed road applications. Consequently, these engines have a shorter useful life and a high premium is placed on measures which would increase the output power without further reducing engine life. Reduction of friction offers such an opportunity, which may be achieved by improved tribological design in terms of reduced contact area or enhanced lubrication or both. However, the developments in the motorsport sector are typically reactive due to a lack of relative performance or an ad-hoc reliance, based upon a limited number of actual engine tests in order to determine if any improvement can be achieved as the result of some predetermined action. A representative scientific model generally does not exist and as such, investigated parameters are often driven by the supply chain with the promise of improvement. In cylinder investigations are usually limited to bore surface finish, bore and piston geometrical form, piston skirt coatings and the lubricant employed. Of these investigated areas newly emerging surface coatings are arguably seen as predominate. This thesis highlights a scientific approach which has been developed to optimise piston-bore performance. Pre-existing methods of screening and benchmarking alterations have been retained such as engine testing. However, this has been placed in the context of validation of scientifically driven development. A multi-physics numerical model is developed, which combines piston inertial dynamics, as well as thermo-structural strains within a thermoelastohydrodynamic tribological framework. Experimental tests were performed to validate the findings of numerical models. These tests include film thickness measurement and incylinder friction measurement, as well as the numerically-indicated beneficial surface modifications. Experimental testing was performed on an in-house motored engine at Capricorn Automotive, a dynamometer mounted single-cylinder ‘fired’ engine at Loughborough University, as well as on other engines belonging to third party clients of Capricorn. The diversity of tests was to ascertain the generic nature of any findings. The multi-physics multi-scale combined numerical-experimental investigation is the main contribution of this thesis to knowledge. One major finding of the thesis is the significant role that bulk thermo-structural deformation makes on the contact conformity of piston skirt to cylinder liner contact, thus advising piston skirt design. Another key finding is the beneficial role of textured surfaces in the retention of reservoirs of lubricant, thus reducing friction

자동차용 판재성형 해석 적용을 위한 다중 스케일 마찰 모델 개발 및 평가

학위논문(박사) -- 서울대학교대학원 : 공과대학 재료공학부, 2022.2. 이명규.Sheet metal forming of advanced high strength steels (AHSS) has drawn significant attentions in automotive industry for their improved fuel efficiency by lightweightness and passenger safety by higher strength. However, the manufacturing of automotive parts with the AHSS accompanies inferior springback and formability compared to the conventional lower strength steels, which results in more time consuming trial and error in the tool design stage. To overcome this challenges in applying the AHSS to the automotive parts, finite element simulations have been commonly used as a numerical tool for predicting springback and formability of sheet metal parts prior to real try-out. Accurate modeling of finite element simulation in sheet metal forming process requires reliable numerical techniques, constitutive models, realistic boundary conditions, etc. Among these, the friction is one of important factors to determine the accuracy of the simulation, but it has been overlooked in most simulations. The frictional behavior in sheet metal forming is known to be very complex and depend on various parameters such as surface roughness, contact pressure, sliding velocity, lubrication condition, etc. However, it is a common practice to use the simplest Coulomb friction law in the finite element modeling. In the present study, a microscale asperity based friction model is further modified by imposing new model parameters for satisfying force equilibrium between contact surfaces. In addition, a geometrical shape model of the tool surface is newly proposed to determine the plowing effect of the friction. The tool geometry is modeled based on primary summits in tool height distribution determined by the measured wavelength, rather than the summits dependent on the resolution of surface measurement instrument. The friction models are required not only in the preceding boundary lubrication condition, but also in the mixed-boundary lubrication condition where sufficient lubrication exists in non-contacting surface valleys. The hydrodynamic friction model uses a load-sharing concept that considers the lubrication area and metal-to-metal contact separately. In this study, the hydrodynamic friction model is combined with the boundary lubrication friction model to account for the friction in the mixed lubrication domain. The lubricant film thickness, calculated as the volume of non-contacting surface valleys, is used to realize the coupling. The film lubrication behavior is implemented by the finite element coding of the Reynolds equation, which enables the calculation of the hydrodynamic pressure. To validate the boundary lubrication friction model, the calculated friction coefficient and the measured friction coefficient are compared according to the contact pressure under boundary lubrication conditions. Also, the boundary lubrication friction model is verified by the finite element simulation that is applied to the U-draw/bending process. Finally, the boundary lubrication friction model and the mixed boundary lubrication friction model are applied to the finite element simulation of the newly developed press-forming process, which represents the influence of various variables such as contact pressure, sliding speed and lubrication. The results of the validations show that the developed multi-scale friction models and their implementation can be efficiently used to the sheet metal forming simulations where the frictional behavior is critical for the quality of the automotive parts.AHSS(고장력강판)의 판금 성형은 경량화에 의한 연비 향상과 고강도화에 의한 승객 안전으로 자동차 산업에서 큰 주목을 받고 있습니다. 그러나 AHSS를 이용한 자동차 부품 제조는 기존의 저강도 강재에 비해 스프링백 및 성형성이 좋지않기에 툴 설계 단계에서 시행착오가 더 많이 발생하게 됩니다. 자동차 부품에 AHSS를 적용할 때 이러한 문제를 극복하기 위해 유한 요소 시뮬레이션은 실제 시험 전에 판재 성형 부품의 스프링백 및 성형성을 예측하기 위한 수치해석적 도구로 일반적으로 사용되었습니다. 판재 성형 공정에서 유한 요소 시뮬레이션의 정확한 모델링은 신뢰할 수 있는 수치해석적 기술, 구성 방정식, 정확한 경계 조건 등이 필요합니다. 이 중 마찰은 시뮬레이션의 정확도를 결정하는 중요한 요소 중 하나이지만 대부분의 시뮬레이션에서 간과되어 왔습니다. 판재 성형에서 마찰 거동은 매우 복잡하고 표면 거칠기, 접촉 압력, 미끄럼 속도, 윤활 조건 등과 같은 다양한 매개변수에 따라 달라지는 것으로 알려져 있습니다. 그러나, 대부분의 유한 요소 해석에서 가장 간단한 쿨롱 마찰 법칙을 사용하는 것이 일반적입니다. 본 연구에서는 접촉면 사이의 힘 평형을 만족시키기 위해 새로운 모델 매개변수를 부과하여 마이크로 스케일 돌기 기반 마찰 모델을 추가로 수정했습니다. 또한 마찰의 쟁기질 효과를 결정하기 위해 툴 표면의 기하학적 형상 모델이 새로 제안되었습니다. 툴 형상은 표면 측정 장비의 분해능에 의존하는 정점이 아니라 측정된 파장에 의해 결정되는 툴표면 높이 조도의 서밋을 기반으로 모델링됩니다. 마찰모델은 경계윤활조건뿐만 아니라 충분한 윤활이 존재하는 혼합경계윤활조건에서도 필요하다. 유체역학적 마찰 모델은 윤활 영역과 금속 대 금속 접촉을 별도로 고려하는 하중 공유 개념을 사용합니다. 본 연구에서는 유체역학적 마찰 모델을 경계 윤활 마찰 모델과 결합하여 혼합 윤활 영역의 마찰을 설명합니다. 비접촉 표면 밸리의 부피로 계산된 윤활유 필름 두께는 커플링을 구현하는 데 사용됩니다. 필름 윤활 거동은 유체역학적 압력의 계산을 가능하게 하는 Reynolds 방정식의 유한 요소 방법을 사용해 구현됩니다. 경계 윤활 마찰 모델을 검증하기 위해 경계 윤활 조건에서 접촉 압력에 따라 계산된 마찰 계수와 측정된 마찰 계수를 비교합니다. 또한 경계 윤활 마찰 모델은 U-draw/bending 과정에 적용된 유한 요소 시뮬레이션을 통해 검증되었습니다. 마지막으로 경계 윤활 마찰 모델과 혼합 경계 윤활 마찰 모델을 새로 개발된 프레스 성형 공정의 유한 요소 시뮬레이션에 적용했는데, 이는 접촉 압력, 미끄럼 속도 및 윤활과 같은 다양한 변수의 영향을 나타냅니다. 검증 결과는 개발된 다중 스케일 마찰 모델과 그 구현이 마찰 거동이 자동차 부품 품질에 중요한 판재 성형 시뮬레이션에 효율적으로 사용될 수 있음을 보여줍니다.1. Introduction 1 1.1. Sheet metal forming and deep drawing process 1 1.2. Motivation and objective 2 1.3. Literature review 5 1.3.1. Friction modeling on the boundary lubrication condition 6 1.3.2. Friction modeling on the mixed-boundary lubrication condition 22 2. Friction model in boundary lubrication 35 2.1. Framework of friction model in boundary lubrication 35 2.2. Statistical contact model for describing surface deformation 38 2.2.1. Assumptions for modeling 39 2.2.2. Flattening of workpiece asperity due to normal load 41 2.2.3. Flattening of workpiece asperity due to normal load and sliding 48 2.2.4. Flattening of workpiece asperity due to normal load and bulk strain 50 2.3. Friction model through a new approach 53 2.3.1. An elliptical paraboloid asperity model 53 2.3.2. A tool geometry model 56 3. Friction model in mixed-boundary lubrication 65 3.1. Overview of the mixed-boundary friction model (Hol [106]) 67 3.2. Finite element modeling for film fluid behavior 71 3.3. Verification of the developed finite element modeling 75 4. Application of boundary lubrication and mixed-boundary lubrication friction model to sheet metal forming process 82 4.1. Friction model parameters 82 4.1.1. Material properties 82 4.1.2. Surface data 83 4.1.3. Friction experiments 86 4.2. Application to sheet metal forming processes under non-lubrication conditions 91 4.2.1. Application to U-draw/bending simulation 94 4.2.2. Application to prototype press-forming process without lubricant 105 4.3. Application to sheet metal forming processes under lubrication conditions 116 5. Conclusions 129 Reference 134박

Transient elastohydrodynamic analysis of piston skirt lubricated contact under combined axial, lateral and tilting motion

Most modern engines utilise pistons with an offset gudgeon pin. In internal combustion engines, the offset is to the major thrust side of the piston. The piston thrust side is the part of the piston perpendicular to the gudgeon pin that carries the majority of side loading during the power stroke. Primary reason for having the gudgeon pin positioned eccentrically is to prevent the piston from slamming into the cylinder bore after the connecting rod journal passes the top dead centre. This phenomenon is referred to as piston slap, and is more pronounced in compression ignition and high performance engines due to higher combustion pressure than that of commercial spark ignition engines. The coming together of the piston and the bore results in scuffing, at best, or, catastrophic failure at worst. Clearance space between bore and piston is filled by a lubricant film. The main role of the lubricant is to separate the piston and bore by reacting to the applied load. Investigating the above problem requires a holistic approach, whereby a dynamic three degree-of-freedom piston model is coupled with a lubrication model to represent the actual system. The dynamic model determines the motion of the piston in combined axial, lateral and rotation about the gudgeon pin. The reactive forces due to lubricant films on the major and minor thrust sides of the piston play significant roles in piston dynamics and are evaluated by either quasi-static or transient solution of the lubricant contact conjunctions. The novel quasi-static analysis is carried out in the sense of its detailed approach, including many key practical features. not incorporated in other analyses, hitherto reported in literature. These features include first and foremost the development of a specific contact mechanics model for evaluation of conforming contacts for piston skirt against liner or bore. The quasi-static analysis includes many practical feature not encountered in other literature on the subject, such as detailed surface irregularities and modification features, and with thermal distortion. The analysis has been extended to thermohydrodynamics, as well as micro-hydrodynamics, all with high computational mesh densities, and robust methods of solution in space and time domains, including effective influence Newton-Raphson method and linear acceleration integration scheme. The transient tribo-elasto-multi-body dynamics problem includes physics of motion study from film thickness prediction and secondary motion evaluation of the order of micrometers and minutes of arc to large rigid body dynamics, including simultaneous solution of the contact problem at both major and minor thrust sides. Such a comprehensive solution has not hitherto been reported in literature. The thesis discusses many aspects of piston dynamics problem, through the broad spectrum of vehicle manufacture, with many pertinent practical engineering issues. In particular, it provides solutions for high performance Formula 1 racing engines. This is the first ever comprehensive analysis of piston tribodynamics for this range of engines at very high combustion pressures. This study has shown the paramount influence of profile of piston in promoting lubrication between the contiguous bodies, as evident from the pattern of lubricant flow through the contact. Deformation of the bodies increases the volume of lubricant in the contact. During the reversal in direction of piston motion, when the entraining velocity momentarily cases and reversal takes place, the load is held by an elastic squeez