Experimental Study on Entropy Features in Machining Vibrations of A Thin-Walled Tubular Workpiece

In machining processes,chatter vibrations are always regarded as one of the major limitations for production quality and efficiency.Accurate and timely monitoring of chatter is helpful to maintain stable machining operations.At present,most chatter monitoring methods are based on the energy level at specified chatter frequencies or frequency bands.However,the spectral features of chatter could change during machining operations due to complexity and time-varying dynamics of the physical machining process.The purpose of this paper is to investigate the time-varying chatter features in turning of thin-walled tubular workpieces from the perspective of entropy.The airborne acoustics was selected as the source of information for machining condition monitoring.First,corresponding to the distinguishing surface topographies relevant to machining conditions,the features of the sound signal emitted during turning of the thin-walled cylindrical workpieces were extracted using the spectral analysis and wavelet packet transform,respectively.It was shown that the dominant vibration frequency as well as the energy distribution could shift with the transition of the machining status.After that,two relative entropy indicators based on the spectrum and the wavelet packet energy were constructed to identify chattering events in turning of the thin-walled tubes.The experimental results demonstrate that the proposed indicators could accurately reflect the transition of machining conditions with high sensitivity and robustness in comparison with the traditional FFT-based methods.The achievement of this study lays the foundations of the online chatter monitoring and control technique for turning of the thin-walled tubular workpieces.

Die Casting Mold Design of the Thin-walled Aluminum Case by Computational Solidification Simulation

Recently, demand for the lightweight alloy in electric/electronic housings has been greatly increased. However, among the lightweight alloys, aluminum alloy thin-walled die casting is problematic because it is quite difficult to achieve sufficient fluidity and feedability to fill the thin cavity as the wall thickness becomes less than 1mm. Therefore, in this study, thin-walled die casting of aluminum （Al-Si-Cu alloy： ALDC 12） in size of notebook computer housing and thickness of 0.8 mm was investigated by solidification simulation （MAGMA soft） and actual casting experiment （Buhler Evolution B 53D）. Three different types of gating design, finger, tangential and split type with 6 vertical runners, were simulated and the results showed that sound thin-walled die casting was possible with tangential and split type gating design because those gates allowed aluminum melt to flow into the thin cavity uniformly and split type gating system was preferable gating design comparing to tangential type gating system at the point of view of soundness of casting and distortion generated after solidification. Also, the solidification simulation agreed well with the actual die-casting and the casting showed no casting defects and distortion.

Machining Deformation Prediction of Thin-Walled Part Based on Finite Element Analysis

For the problems of machining distortion and the low accepted product during milling process of aluminum alloy thin-walled part,this paper starts from the analysis of initial stress state in material preparation process,the change process of residual stress within aluminum alloy pre-stretching plate is researched,and the distribution law of residual stress is indirectly obtained by delamination measurement methods,so the effect of internal residual stress on machining distortion is considered before finite element simulation. Considering the coupling effects of residual stress,dynamic milling force and clamping force on machining distortion,a threedimensional dynamic finite element simulation model is established,and the whole cutting process is simulated from the blank material to finished product,a novel prediction method is proposed,which can availably predict the machining distortion accurately. The machining distortion state of the thin-walled part is achieved at different processing steps,the machining distortion of the thin-walled part is detected with three coordinate measuring machine tools,show that the simulation results are in good agreement with experimental data.

Thin-Wall Aluminum Die-Casting Technology for Development of Notebook Computer Housing

Silicon-based aluminum casting alloys are known to be one of the most widely used alloy systems mainly due to their superior casting characteristics and unique combination of mechanical and physical properties. However,manufacturing of thin-walled aluminum die-casting components,less than 1.0 mm in thickness,is generally known to be very difficult task to achieve aluminum casting alloys with high fluidity.Therefore,in this study,the optimal die-casting conditions for producing 297 mm×210 mm×0.7 mm thin-walled aluminum component was examined experimentally by using 2 different gating systems,tangential and split type,and vent design.Furthermore,computational solidification simulation was also conducted.The results showed that split type gating system was preferable gating design than tangential type gating system at the point of view of soundness of casting and distortion generated after solidification.It was also found that proper vent design was one of the most important factors for producing thin-wall casting components because it was important for the fulfillment of the thin-wall cavity and the minimization of the casting distortion.

激光冲击+机械喷丸复合强化对铆接件微动疲劳性能的影响

研究机械喷丸、激光冲击+机械喷丸复合强化2种表面强化技术对铝合金铆接构件微动疲劳行为的影响。利用微动磨损实验机、疲劳实验机、X射线衍射仪、激光共聚焦显微镜、场发射扫描电镜等设备,测试表面强化技术对铝合金表面完整性、耐磨性、疲劳性能和微动损伤特征的影响。结果表明:机械喷丸、激光冲击+机械复合强化均可提升铆接件微动疲劳性能,机械喷丸提高12倍,复合强化提升5.4倍。表面强化处理改变疲劳裂纹源位置,原始件裂纹萌生于铆接件圆孔30°左右,喷丸强化后裂纹在圆孔接近90°位置萌生。复合强化的残余压应力层深度为1.00 mm,远大于机械喷丸的0.25 mm。总体上,复合强化效果不理想,这是由于激光冲击技术不便于在小尺寸的铆接孔实施,同时强化过程连接孔变形,影响服役性能。

Effect of blank quenching on shear spinning forming precision of 2219 aluminum alloy complex thin-walled components

The quenching-spinning(Q-S)process,i.e.,shear spinning after blank quenching,has been increasingly utilized to form 2219 aluminum alloy complex thin-walled components.However,the changes in material property,shape and stress of the blanks after quenching will affect the spin-ning forming precision.In this study,the rules and mechanisms of these effects are investigated based on a combined finite element(FE)model including blank quenching and component spinning process.The results indicate that the increase of material strength and the existence of distortion of the quenched blank lead to a notable increase in the non-uniformity of the circumferential compres-sive stress in the spinning area and the increase of the flange swing height during spinning.These changes result in an increase in the wall thickness and component-mandrel gap of the components.The quenching residual stress has little effect on wall thickness and roundness but can noticeably reduce the component-mandrel gap.This is because that the existence of quenching residual stress of the blank can lead to the decrease of the maximum circumferential compressive stress of the workpiece in spinning and an obvious drop in the maximum compressive stress after reaching the stress peak.Quenching distortion is the main factor affecting the roundness.Moreover,the opti-mized installation way of the blank for spinning is obtained.

Residual Stress Relaxation of Thin‑walled Long Stringer Made of Aluminum Alloy 7050‑T7451 under Transportation Vibration

Thin-walled long stringer made of aluminum alloy 7050-T7451 is prone to deformation during transportation,so a research of residual stress relaxation was launched in this paper.The transport resonance stress of long stringer was analyzed based on the power spectral density of road transport acceleration.The residual stress relaxation experiment of aluminum alloy 7050-T7451 under different equivalent stress levels was designed and carried out.According to the amount of residual stress relaxation in the experiment,an analytical model was established with the equivalent stress level coefficient.The deflection range of long stringer was evaluated under different damping ratios.The results show that when the equivalent stress exceeds 0.8σ0.2,the residual stress relaxation of the thin-walled samples occurs.The residual stress relaxation increases linearly with the equivalent stress,which is logarithmically related to the loading cycle.The deformation caused by residual stress relaxation of the long stringer is proportional to the square of the length and the bending moment caused by stress rebalance,and inversely proportional to the moment of inertia of the structure.As the damping ratio decreases from 0.03 to 0.01,the total deflection of the long stringer increases from 0 to above 1.55 mm.

Forming limits under multi-index constraints in NC bending of aluminum alloy thin-walled tubes with large diameters

With increasing diameters of aluminum alloy thin-walled tubes (AATTs), the tube forming limits, i.e. the minimum bending factors, and their predictions under multi-index constraints including wrinkling, thinning and flattening have been being a key problem to be urgently solved for improving tube forming potential in numerical control (NC) bending processes of AATTs with large diameters. Thus in this paper, a search algorithm of the forming limits is put forward based on a 3D elastic-plastic finite element (FE) model and a wrinkling energy prediction model for the bending processes under axial compression loading (ACL) or not. This algorithm enables to be considered the effects of process parameter combinations including die, friction parameters on the multi-indices. Based on this algorithm, the forming limits of the different size tubes are obtained, and the roles of the process parameter combinations in enabling the limit bending processes are also revealed. The followings are found: the first, within the appropriate ranges of friction and clearances between the different dies and the tubes enabling the bending processes with smaller bending factors, the ACL enables the tube limit bending processes after a decrease of the mandrel ball thickness and diameters; then, without considering the effects of the tube geometry sizes on the tube constitutive equations, the forming limits will be decided by the limit thinning values for the tubes with diameters smaller than 80 mm, while the wrinkling for the tubes with diameters no less than 80 mm. The forming limits obtained from this algorithm are smaller than the analytical results, and reduced by 57.39%; the last, the roles of the process parameter combinations in enabling the limit bending processes are verified by experimental results.

基于钢结构主体工程的玻璃幕墙及铝板幕墙施工技术研究

以上海某厂房项目为例,对玻璃幕墙、铝板幕墙的主要做法和技术措施进行研究。针对玻璃幕墙、铝板幕墙系统中埋件的安装、连接件、打胶与防渗漏施工、转角部位的安装、收边收口、施工质量通病等重、难点问题,根据现场实际情况,确定保温节能、层间防火封堵等施工工艺的构造做法,最终完成的玻璃幕墙、铝板幕墙观感较好,达到设计方案最初的预计效果,为后续不同材料的幕墙系统的选择提供了设计和施工的经验,可在后续类似项目中借鉴和推广。

大型铝合金板热压成形变形规律的研究

为了实现大尺寸超厚5083铝合金板热压过程的精确成形,对其热压成形、回弹、保压和冷却至室温的过程进行了热力耦合的数值模拟,分析了整个过程板材的变形及应力变化的规律,并利用缩比试验件验证了数值模拟方法的可靠性,结果表明,板材热压时,卸载后的变形规律为“扩张”,冷却过程的变形规律为“收缩”,最终的变形为回弹过程的“扩张”与冷却过程的“收缩”的综合结果。

铝模加固体系最优选型研究

在高层住宅项目中,铝模已被普遍使用,其中铝模加固最常使用对拉螺杆式与拉片式2种形式。针对这2种加固形式,通过施工现场实际验证和对比分析,归纳出不同需求场景下最优加固形式,使施工单位实现利益最大化。

Aluminum tanning of hide powder and skin pieces under microwave irradiation

The application and mechanism study of microwave irradiation in traditional industries have attracted considerable attention owing to the unique thermal and athermal effects that could lead to unexpected benefits in high-efficiency and clean production.Herein,we report the investigation of the aluminum tanning under microwave irradiation upon using hide powder and skin pieces,respectively,as simulants of real hide or skin.The aluminum tanning process and the tanned products under microwave heating(MWH)were studied and compared with those of conventional water bath heating(WBH)as the controls.For the tanning system of hide powder,the tanning effluents were analyzed in terms of pH,conductivity,dielectric constant and aluminum content,and the tanned powder was investigated by differential scanning calorimetry(DSC),thermogravimetric(TG)analysis,and FT-IR spectroscopy.For the skin piece system,the pH and aluminum content of tanning effluents were also determined,and at the same time,DSC,TG,SEM,FT-IR and shrinkage temperature were used to illustrate the actions of microwaves on the structure and properties of the tanned pieces.The results show that aluminum reactivity in the penetration and binding process of collagen fibers in hide powder and skin pieces improved using microwave treatment.The residual aluminum content was greatly reduced by microwave heating action,and the increased amount of aluminum with evener distribution was observed in the tanned products.Microwave irradiation also resulted in the tanned products with better thermal stability and thermal decomposition resistance.This work further promotes application of microwave treatments for aluminumbased tanning in leather industry.

大直径6061铝合金筒形件旋压工艺及性能研究

利用数控旋压设备研究了内径Ф400 mm、长度达到1 300 mm的6061铝合金筒形件的错距旋压减薄工艺,并借用金相显微镜、力学拉伸试验分析了旋压筒形件固溶、时效后的显微组织和室温力学性能。结果表明,通过控制合适的减薄率、进给比、轴向错距量等因素,利用错距旋压工艺制备此种筒形件是可行的,研制出的工件尺寸完全符合图纸要求,且精度较高;固溶、时效后旋压筒形件的力学性能完全满足要求值。

中国罐料生产现状与展望

1993年西南铝业(集团)有限责任公司交付1.971 kt罐料,开中国罐体料批量生产的先河。2010年全国的产量155 kt,2011年中国罐料的进出口量可能平衡。2010年南山轻合金有限公司出口了少量的罐体料,2012年中国可能成为罐料净出口国。2010年中国可生产罐料的企业有3家;2013年将增至7家,总产能1 000 kt/a;2015年的生产企业可达到12家左右,总产能将在2 250 kt/a以上,从而超过美国的。2010年全球罐料贸易总量约750 kt,中国罐料出口有一定的潜力。

锌铝合金阀片断裂失效分析

采用X射线衍射仪、扫描电子显微镜及能谱仪等研究了合金元素对铝锌合金组织的影响。结果表明,锌铝合金中含有Si、Cu、Fe等元素与Al或者Zn易生成金属间化合物。锌铝合金呈现枝状晶形貌,合金中存在大量不规则熔池组织。合金中的杂质元素及氧化物均存在于熔池组织中,这些熔池组织在高倍观察下可见为分散性的微孔。在受到外力时,这些缩孔将成为应力集中点,大量微小缩孔是合金在外力下发生断裂的主要原因。

汽车玻璃钢化模具风栅铝片三轴加工

为了解决汽车玻璃钢化模具生产中依赖五轴机床加工的问题,提出以离散化曲面片拟合钢化模具工作型面的方法。首先根据玻璃模型的微分几何特征计算得加权平均弧长,按照等弧长等原则剖分玻璃模型,并设计风栅片的尺寸、公差,确定其技术要求;研究了风栅铝片三轴铣削加工中装夹方法、刀具选择、走刀规划以及切削参数确定方法;通过设计纵向靠尺的方法实现大量铝片的精确装配。结果表明,该方法生产出的风栅成型模具符合生产要求。

移动磁场铸造法改善铝薄壁件充型能力的试验研究

针对超薄壁铝铸造成形这一技术难题,利用自制的直线电机并采用石膏铸型,探讨移动磁场铸造法制取超薄壁铝质散热片的成形工艺。结果表明,采用直线电机移动磁场铸造法可增强液态金属的充型压头,有效改善铝合金充型能力,当电压达到220～250V之间,采用不锈钢作为铸型可以浇注出较完整的铸件。

开发有特色的汽车铝合金及其冲挤件

2015年国外汽车工业原铝与再生铝的用量约7 500 kt,约占铝总消费量的25.7%。中国的用量约3 200 kt,不到铝消费总量34 000 kt的10%,这说明中国汽车用铝潜力还很大。中国宜尽快使已建成的ABS(汽车车身薄板)项目达产,在建项目尽快建成外,还需要开发有企业特色的ABS铝合金;中国也需要建设冲挤汽车铝合金零件项目,国内至今尚无这类企业,冲挤件性能优于铸件的,而接近锻件的,其生产成本比锻件的低不少。

试样形状对管材力学性能检测结果的影响

研究了试样形状对铝合金管材力学性能检测结果的影响。结果表明,用圆形试样测得的伸长率比扁条试样的高;不同宽度扁条试样的测量结果相差不大。

铝制毛坯筒形件双轮强力旋压仿真模型的建立

部分筒形铝制毛坯在强旋过程中需要利用尾顶将其顶紧在芯模上,但由于毛坯较软以及所需顶紧力较大等原因,导致尾顶嵌入毛坯,使毛坯件发生轻微变形的现象,毛坯的局部变形会造成减薄量的改变,从而导致旋压工艺参数设置的偏差,最终使旋压制品的尺寸精度难以保证,需要经过反复的旋压工艺实验修正工艺参数才能使最终的成形制品达到设计要求。提出了一种尾顶力的计算方法,并利用该算法对毛坯进行加载,利用修正的Thamasett算法建立毛坯与旋轮的关系,从而以Ansys为平台建立了一个针对铝制毛坯的筒形件双轮强力旋压仿真模型。利用旋压工艺实验对仿真模型进行验证,其结果与仿真结果一致。该仿真模型可用于指导旋压生产企业的生产,可为企业节约大量的毛坯实验件成本以及旋压工艺实验时间。