The effect of shrink fitting ratios on tool life in bolt forming processes

Increasing the service life of cold forging dies with respect to fatigue is a key issue in the highly competitive tool manufacturing market. In industry, achieving a lower level of stress in a die insert is known to be preferable when deciding the amount of shrink fit for a stress ring. However, it was found that stress amplitude is a more significant factor in increasing the cold forging tool life with respect to high cycle fatigue. With higher shrink fitting ratios, undesirable pre-stresses were induced in the tool insert, resulting in an increased stress amplitude between the forging/extrusion and unloading/ejection stages in a bolt forming process that lowered the high cycle fatigue life of the die insert. In the present investigation, the effect of the shrink fitting ratio on the level of die stresses, including the pre-stressing due to shrink fitting, was numerically investigated for a two-stage hexagonal bolt forming and gear extrusion operation. The study shows that optimum values of the shrink fitting ratios tended to increase the high cycle fatigue life based on the level of the stress amplitude in the die insert.     

A design approach for intermediate die shapes in plane strain forgings

A new technique has been developed for the design of die shapes in the plane strain forging process. The objective of this research work is to develop a design procedure to obtain the number of stages and the shape of each die for manufacturing a desired product. Metal flow during the forging is considered in the design of the intermediate die shapes in multistage forgings. The two approaches developed for the preform shapes design are conformal mapping techniques and ideal material flow simulations. The forging process is simulated using a nonlinear rigid visco plastic finite element program ALPID (analysis of large plastic incremental deformation). Staging criteria is developed from the results of the forging simulation and the number of stages are based on the stress ratio parameterg (mean stress/effective stress) and strain rate gradient information. This paper presents two examples of forgings to demonstrate an optimal die shape design methodology.     

280曲轴RR法成形的三维有限变形弹塑性有限元模拟

大型曲轴的全纤维成形工艺是保证曲轴能够在复杂的应力状态下正常工作的一种有效的工艺方案，由于其成形过程复杂，变形过程的应力场和应变场很难用实验方法确定。本文基于ＡＮＳＹＳ工作平台，利用开发的三维有限变形弹塑性有限元程序，模拟了２８０曲轴的ＲＲ法成形过程，得到了不同摩擦条件变形过程的应力场、应变场和载荷位移曲线，为确定合理的成形工艺方案和模具形状及提高成形质量和模具寿命提供了可靠的依据     

A three-step approach to designing a metal-forming process

This paper presents a hierarchical design and analysis approach for the design of metal-forming processes. The methodology entails a three-step design process comprising conceptual design, preliminary design, and final design. The conceptual design stage is based on methodologies such as axiomatic design and is followed by a preliminary design that is accomplished through simplified forming models and design confirmation using more accurate finite-element methods. This methodology provides a scientific approach to design and analysis and considerably reduces the time and effort necessary to achieve a workable solution.     

链节成形工艺与复合弯曲成形模设计

分析了链节成形工艺及加工工艺方案,设计了1副半自动推(送)料及自动卸件复合弯曲成形模,一次推料可完成一道弯曲和二道复合弯曲成形。通过基于Pro/E的模具设计,提高了模具设计的可靠性和一次设计成功率,并介绍了模具结构和工作过程。     

Monte Carlo simulation of extrusion die life

Due to the high cost of metal forming tools (especially in hot extrusion), one of the major goals in tool design is a longer service life. Estimation and prediction of tool life thus becomes critically important for performance evaluation of the tools. The two most dominant failure mechanisms for extrusion dies (solid, hollow, and semi-hollow dies all taken together) are fracture and wear. In the first part of the paper, a fracture mechanics based fatigue life prediction model is described. A similar treatment is then presented for wear-related failures. Fracture and wear usually coexist as failure modes, and final die breakdown occurs due to the mechanism that becomes dominant. Therefore, a competing fracture–wear model has been later developed to represent the complete die failure situation. Attempt has been made to correlate the stochastic nature of various fatigue and wear related die parameters to die life. Monte Carlo simulation has been used to predict the life distribution of a die for a given set of manufacturing conditions and mechanical properties. In comparison with actual life data from the industry, the simulated life yields very realistic predictions.     

固定页板弯曲成形及模具设计研究

介绍了弯曲件的弯曲成形工艺方案、工艺参数的计算与选取以及弯曲模具结构与设计,得出采用多道弯曲成形工序是合理的。由于对弯曲成形凸凹模间隙,回弹值等工艺参数进行了较为准确的计算与选取,并采取了相应的限制回弹的技术措施。取得了较好的效果。经实际应用表明,其工艺与模具设计合理,实用可靠,达到并超过了图纸的技术要求。     

压铸模镶块的热疲劳失效行为

对工作1200模次发生热疲劳失效的压铸模镶块进行失效机理分析,同时建立了压铸过程的热-力耦合数值分析模型,研究了镶块在压铸服役过程中温度场和应力场的演变规律,并对其寿命进行预测。结果表明,镶块的失效是由于压铸过程中受到高温铝熔液的冲刷和冷却液的急冷引起的热疲劳行为所致;在循环压铸过程中,镶块凸台转角处出现应力集中,最大等效应力约为788 MPa,热疲劳裂纹在该处萌生和扩展;采用低周疲劳寿命预测模型对镶块热疲劳寿命进行预测,镶块热疲劳寿命约为1651次,与镶块实际热疲劳寿命非常吻合,这表明本文建立的热-力耦合数值模型可为压铸模镶块的可靠性设计提供借鉴。     

Fatigue strength of hot-stamped spot welded joints*—study on spot welding tailored blank technology

Hot stamping spot welding tailored blank (TB) technology is a process to produce spot welded automotive body parts by the following process: Spot welding steel sheets in lap configuration → Hot stamping (Heating to about 900°C → Quenching and forming in water-cooled die → Shot blasting to remove scale). This process has the advantage of producing high strength lap welded automotive body parts without increasing the number of forming dies. In this study, the tensile shear fatigue strength of the spot welding TB joints (Spot welding → Hot stamping) and conventional spot welded joints (Hot stamping → Spot welding) of the 1500MPa class uncoated boron steel sheets are compared. The obtained results are as follows. The fatigue life of the spot welding TB joints was more than two times longer than that of the conventional spot welded joints. The long fatigue life of the spot welding TB joints was not caused by the heating and quenching process but by the shot blasting process after heat treatment. Shot blasting on the outer sheet surface caused the high compressive residual stress on the outer surface and did not affect the residual stress on the lapped surface. Shot blasting on the outer sheet surface increased the initiation life of fatigue crack which occurred on the lapped surface and also reduced the crack propagation speed which propagates from the lapped surface to the outer surface. FE-analysis suggested that compressive residual stress on the outer surface reduce the opening of sheet separation of joints in fatigue tests and reduce the maximum principal stress around the edge of corona bond.     

长寿命热锻模的磨损分析与寿命预测

连续锻压生产中,热锻模承受热负荷与机械负荷,将导致热锻模因磨损、断裂、塑性变形、机械疲劳等形式失效,其中磨损失效所占比例最大.基于功能梯度材料和表面熔覆相结合的强化技术试制了长寿命热锻模试样,分析对比了均质热锻模和长寿命热锻模的磨损分布,并对两种热锻模使用寿命进行预测.研究结果表明,采用基于功能梯度材料和表面熔覆相结合...     

曲轴TR法成形的三维有限变形弹塑性有限元模拟

大型曲轴的全纤维盛开有工艺是保证曲轴能够在复杂的应力状态下正常工作的一种有效的工艺方案。由于其成形过程复杂,变开吕的应力场和应变场很难用实验方法确定。本文基于ＡＮＳＹＳ工作平台,利用开发的三维有限变形弹塑性有限元程序,并利用开发的三维网格重划功能模块,模拟了曲轴的ＴＲＩ地成形过程,得到了曲轴在成形全过程中的应力场、应变场以及载荷位移曲线,为制定合理的成形工艺方案,优化模具设计,提高成形质量,以及提     

Structural Performance of Inconel 625 Superalloy Brazed Joints

The purpose of this work was to investigate tensile and fatigue behaviors of Inconel 625 superalloy brazed joints after transient liquid-phase bonding process. Brazing was performed in a vacuum furnace using a nickel-based filler metal in a form of paste to join wrought Inconel 625 plates. Mechanical tests were carried out on single-lap joints under various lap distance-to-thickness ratios. The fatigue crack initiation and crack growth modes were examined via metallographic analysis, and the effect of local stress on fatigue life was assessed by finite element simulations. The fatigue results show that fatigue strength and endurance limit increase with overlap distance, leading to a relatively large scatter of results. Fatigue cracks nucleated in the high-stressed region of the weld fillets from brittle eutectic phases or from internal brazing cavities. The present work proposes to rationalize the results by using the local stress at the brazing fillet. When using this local stress, all fatigue-obtained results find themselves on a single S-N curve, providing a design curve for any joint configuration in fatigue solicitation.     

电缆保护卡弯曲成形模的改进

分析了电缆保护卡的成形工艺 ,对原成形模具结构进行改进 ,解决了原模具中凸模受力弯曲变形的问题 ,提高了模具使用寿命     

数字化技术在齿轮精锻成形模中的应用

介绍了数字化技术在齿轮精锻成形模设计制造中的应用框架,详细叙述了齿轮精锻模数字化技术的具体应用,通过数字化技术在齿轮精锻模设计制造中的普及和应用,提高了齿轮新产品开发一次成功率,明显缩短了新产品开发周期,同时提高了模具使用寿命、制造精度和制造过程的稳定性。     

Development of ultrasonic thread root rolling technology for prolonging the fatigue performance of high strength thread

Fatigue failure commonly occurs at mechanical products, especially the threaded joints with high stress concentration. Even though various high strength alloys are adopted, accidence due to fatigue failure of thread still happens. As a novel method to improve the thread fatigue life, ultrasonic thread root rolling (UTRR) process is developed in this paper. The configuration of the UTRR apparatus together with the principle of the UTRR is first introduced and described. Rolling experiments are then conducted on AerMer100 thread specimens by use of the UTRR process and conventional thread root rolling (CTRR) process respectively. Mechanical characteristics and fatigue properties for these treated specimens and untreated specimens are tested. Compared with CTRR, surface finish of thread root is farther improved from Ra 0.106 to Ra 0.051, and higher residual stress is achieved for UTRR. The depth of microstructure-refined zone induced in UTRR is about 20 μm, while that of CTRR is approximately 12 μm. These further enhanced mechanical properties greatly contribute to the improvement of fatigue performance, and it is well proved by fatigue results that an increase of about 7 times for fatigue life of AerMet100 specimens is achieved after UTRR, while only 3 times is achieved for CTRR. Striations from fracture surface explicitly confirm this result.     

特大型刮煤板铸锻复合塑性成形工艺研究

介绍了特大型刮煤板铸锻复合塑性成形工艺,扬长避短了传统模锻与传统铸造的优缺点,从输入到输出具有循环经济和绿色制造的特点,确保了铸锻件与传统模锻件具有相同的形状与尺寸以及具有相同或相近的使用功能和使用寿命,实现了使用性能、工艺性能和经济性的有机统一,达到了优质、高效和低耗以及更精、更省和更净的效果,扭转了特大型刮煤板应在≥160kN模锻锤或≥120~125MN电动螺旋模锻压力机等特大型设备上成形或依赖国外进口的被动局面。     

连杆热模锻过程有限元分析及锻模寿命预测

建立了连杆热模锻过程有限元分析二维模型 ,计算了热机械耦合结果。分析了变形过程、温度变化、应力应变情况 ,预测了因锻模热机械疲劳裂纹出现而导致锻模失效的模具寿命     

Using simulation for heat treatment process design: matching quenching process with steel grade and product geometry

Abstract

The performance of steel parts is heavily dependent on the heat treatment process applied. The alloy content of the steel establishes the steel hardenability. The severity of the quenching establishes the local temperature history throughout the body of the part. In combination, the steel hardenability and the quenching process determine the final microstructure, mechanical properties, residual stress state and the performance of the part. The residual stress state, especially the surface stress state, is a significant factor in affecting fatigue life of the part. The steel hardenability and quenching practice can be adjusted to enhance residual surface compression and improve the fatigue life of a component. Computer simulation of the heat treatment process that includes calculation of the metallurgical phase transformations during the heating and cooling processes offers a method for scientifically designing the heat treatment process and selecting the steel alloy to optimise the performance of a particular product. In this paper, the DANTE heat treatment simulation software will be used to demonstrate this design methodology for a spur gear.     

Multi-pass deformation design for incremental sheet forming: Analytical modeling,finite element analysis and experimental validation

Incremental sheet forming (ISF) is a promising rapid prototyping technology with high potential to shape complex three-dimensional parts. However, a common technical problem encountered in ISF is the non-uniform thickness distribution of formed parts; particularly excessive thinning on severely sloped regions. This may lead to fracture and limit the process formability. Design of multi-stage deformation passes (intermediate shapes or preforms) before the final part, is a desirable and practical way to control the material flow in order to obtain a more uniform thickness distribution and avoid forming failure. In the present paper, a systematic methodology for designing multi-stage deformation passes considering the predicted thickness strains given the design shape is proposed based on the shear deformation and the strain compensation mechanism. In this methodology, two analytical models (M1 and M2) are developed by taking into account; the global average thickness strain and only the material in the final part region used in the forming (M1), and the local weighted average thickness strain and the additional material around the final part region used in the forming (M2), respectively. The feasibility of the proposed design methodology is validated by finite element analysis (FEA) and experimental tests using an Amino ISF machine. The results show that a more uniform thickness strain distribution can be derived using M2. The incurrence of the highest strains can be delayed in the intermediate stages and the flow of material is allowed into the deformed region, thereby allowing a compressive stress state to develop and enabling steeper shapes to be formed. Therefore, the process formability can be enhanced via the optimized design of deformation passes.     

冷挤压活塞销凸模复合强化研究

分析了冷挤压活塞销凸模的受力情况和主要失效形式。采用热处理、磨削、低温氮碳共渗和滚压的复合强化 ,能够提高其疲劳强度和使用寿命