压力铸造中模具脱模剂和防粘蜡的选择分析实验

压力铸造中模具脱模剂和防粘蜡种类繁多,如何正确选择对于铸件外观品质和模具寿命有着重要的影响。采用H13试样,在不同的涂敷工艺下,对于脱模剂和防粘蜡的成膜性和涂敷厚度进行实验考察,并且利用扫描电镜观察涂敷防粘蜡后的试样浸入铝液中的时间对其显微组织影响。实验和分析表明,防粘蜡皮膜性能在模具温度为300℃左右时涂敷,并保温2~5m in为最好。     

On-machine tool resharpening process for dry machining of aluminum alloys employing LME phenomenon

Dry machining of aluminum alloys is known to be one of the most difficult metal cutting operations. The issues involved are that without use of cutting fluids, these materials severely adhere to the tool surface and form a built-up edge due to their low melting point and high ductility, leading to deterioration of the surface integrity of the workpiece and tool failure. To overcome this problem, the present study proposes a novel strategy for removing the adhesion layer from the tool surface and recovering the cutting tool performance without detaching the cutting tool from the machine tool, namely, an on-machine tool resharpening process. To achieve efficient removal of the aluminum adhesion layer from the tool surface, the phenomenon of liquid metal embrittlement (LME), which is defined as a brittle fracture, or loss in ductility, of a ductile material in the presence of a liquid metal is employed. A series of experiments using a WC-Co cemented carbide tool and liquid gallium showed that the newly developed strategy employing LME is highly effective in removing the adhesion layer without damage to the tool substrate and has great potential for addressing the issues related to the dry machining of aluminum alloys.     

Dry Lubricant Films for Aluminum Forming

During metal forming, lubricants are necessary to prevent direct contact, adhesion, transfer, and scuffing of workpiece materials and tools. Boric acid films, which can be firmly adhered to clean aluminum surfaces by spraying their methanol solutions, provide extremely low friction coefficients (≈0.04). The adhesion strengths of the bonded films vary with the type of aluminum alloy (6061, 6111, and 5754). Sheet metal forming tests indicate that boric acid films and combined films of boric acid and mineral oil can enable larger strains than commercial liquid and solid lubricants, showing that their lubricities are excellent for aluminum forming. Scanning electron microscopy analyses indicate that the dry boric acid films effectively separate the workpiece and die materials and, thus, prevent direct contact and preserve the surface qualities. Because boric acid is nontoxic and easily removed by water, the authors can expect these films to be environmentally friendly, cost-effective, and very efficient lubricants for sheet aluminum cold forming.     

硅橡胶与金属黏附效应的产生与影响分析

为探讨橡胶密封件与金属法兰之间的黏附效应产生的原因及黏附效应对密封的影响,根据硅橡胶密封结构的使用特点,设计硅橡胶密封圈与金属法兰在不同温度、不同时间下的黏附实验.通过硅橡胶密封圈与防锈铝合金和2种不锈钢材料的对比实验发现,硅橡胶密封圈与不锈钢金属法兰易发生黏附,与防锈铝合金金属法兰不易发生黏附.通过对金属法兰表面接触...     

蜂窝状铝合金高速加工刀具粘附行为及其作用机理研究

通过高速铣削试验方法对蜂窝状铝合金高速铣削刀具的粘附行为及粘附机理进行了研究。结果表明,由于初期铝屑粘附在刀具表面上,致使后期切削加工中的铝切屑与刀具表面的化学活性近似,使得铝屑进一步强化粘附在刀具表面,且由于高速加工中产生的高温和高压作用,使得粘附层材料发生变形。后续切屑划擦初期的粘附层,使粘附层出现变形和犁沟现象,加剧刀具与工件间的摩擦状态。同时,铝合金高速加工中高的塑性变形特征是发生粘附磨损的另一重要作用机制。此外,切屑表层材料受到剧烈剪切变形引起表面积增加,使切削形成的金属表面膜破裂,在与刀具表面紧密接触的近乎为真空环境下刀具不断切削新的表面,活性非常高,极易发生摩擦化学反应,较高摩擦化学反应形成的表面厚度达到临界值时将发生磨损,导致刀具粘附磨损加剧。     

CVD金刚石涂层拉拔模的制备

针对拉制铝管用尼龙模具寿命短和硬质合金模具粘铝的问题,采用微波等离子体CVD法在硬质合金拉拔模内孔壁涂覆金刚石薄膜。通过设计一个特殊支撑结构,引导等离子体进入拉拔模内孔,可实现在内孔8mm深度范围一次沉积出金刚石膜。现场拉拔试验表明,金刚石涂层模拉制的铝管光洁度介于尼龙模和硬质合金模之间,可满足使用要求。     

Effect of clearance on new shearing method with horizontal tool movement of 1100 aluminum sheet

Sheet metal cutting is a general metal forming process. A new cutting method has been invented for sheet metal by the authors. It has been named the MM-shearing method. There are several advantages in the method, for example small cutting force, beautiful cutting surface and no burrs on the cut surface. Moreover, the equipment used in the method is inexpensive. However, there are some important parameters to consider in the MM-shearing method, such as tool angle, clearance between the tool and die, sheet thickness, and cutting speed. In this paper, a series of experiments was carried out to examine the suitable clearance. The experimental material is 1100 aluminum sheet (Japanese Industrial Standard). The cutting force, ratio of sheared and fractured surfaces, inclination angle, burr height, roughness, and Vickers hardness of the cutting surface are examined corresponding to the clearance change. The principle and characteristics of the MM-shearing method are made clear in this paper in terms of the clearance between the tool and die.     

Precision forging technology for aluminum alloy

Aluminum alloy is a preferred metal material for lightweight part manufacturing in aerospace, automobile, and weapon industries due to its good physical properties, such as low density, high specific strength, and good corrosion resistance. However, during forging processes, underfilling, folding, broken streamline, crack, coarse grain, and other macro- or microdefects are easily generated because of the deformation characteristics of aluminum alloys, including narrow forgeable temperature region, fast heat dissipation to dies, strong adhesion, high strain rate sensitivity, and large flow resistance. Thus, it is seriously restricted for the forged part to obtain precision shape and enhanced property. In this paper, progresses in precision forging technologies of aluminum alloy parts were reviewed. Several advanced precision forging technologies have been developed, including closed die forging, isothermal die forging, local loading forging, metal flow forging with relief cavity, auxiliary force or vibration loading, casting-forging hybrid forming, and stamping-forging hybrid forming. High-precision aluminum alloy parts can be realized by controlling the forging processes and parameters or combining precision forging technologies with other forming technologies. The development of these technologies is beneficial to promote the application of aluminum alloys in manufacturing of lightweight parts.     

A novel assembly technology of aluminum alloy honeycomb structure

In this study, the authors applied the low-temperature ultrasonic soldering method to solder aluminum alloy honeycomb structure and investigated the effects of soldering time and soldering temperature on the properties of the solder. The following results were obtained: The wetting angle changed with applied time and applied temperature. The solder region is mainly composed of four kinds of microstructure zones: rich Sn zone, rich Pb zone, Sn–Pb eutectic phase, and rich Al zone. Microanalysis identified a continuous reaction product at the alumina–solder interface as a rich Pb zone. The wet angle data had significantly greater variability, with values ranging from 10° to 90°. The highest value was obtained for the samples soldered with Sn–Pb–Zn alloy for 30 s. Fractures occurred along the solder–alumina interface for the 6061 aluminum alloy. Fracture surface included hybrid tough fracture of dimple and tear ridge. The interface could firstly strip at the rich Bi zone with the effect of shear stress.     

Numerical simulation and metal flow analysis of hot extrusion process for a complex hollow aluminum profile

The most important way to improve the quality of aluminum profiles is to assure the material flow through die land exit with the same velocity. In this paper, a numerical model was developed to investigate metal flow behavior during aluminum profile extrusion. Firstly, the numerical model for a complex hollow aluminum profile was built based on the arbitrary Lagrangian–Eulerian program HyperXtrude. Then, with the numerical model, metal flow behavior at each stage during the whole extrusion process was analyzed and dead zones in the die cavity were also investigated by means of the particle tracking method. Finally, the numerical results were validated by comparing with the nose ends of two extrudates in practice, and the comparison showed that the numerical model developed in this work could provide the effective guidance for practical production.     

The Tribological Behavior of As-Sprayed Graphene Oxide–Tungsten Disulfide Hybrid Coatings

Abstract

The application of solid lubricants in the metal forming of aluminum alloys is imperative due to their potential for the reduction of both friction and aluminum adhesion. This study focuses on examining the potential application of hybrid graphene oxide–tungsten disulfide (GO/WS₂) coatings in the forming of aluminum alloys. A series of experiments with different GO/WS₂ concentrations (between 1:1 and 12:1) was conducted to investigate the effects of increasing GO concentration on the tribological performance of the coatings. The coefficient of friction (COF) was evaluated using pin-on-disc experiments. The durability of the coatings (the sliding distance prior to the initiation of coating failure) was also recorded. Subsequent surface characterization was performed from within the sliding tracks induced on the coated Al-Mg discs and the mechanisms responsible for friction and wear are discussed. The GO/WS₂ hybrid coatings provided low COF values (within the range of 0.18?0.27) and mitigated against aluminum adhesion before failure. An optimum GO/WS₂ ratio (6:1) was noted as providing the optimum combination of low friction and improved durability. The concentration of GO in the hybrid coatings influenced the friction performance and durability of coatings, which was related to the formation of tribolayers on the aluminum surface and wear-induced transfer layers on the counterface surface. The formation of the tribolayers was attributed to the mixture of fragmented WS₂ platelets, GO flakes, and carbon binder comprising the tribolayer.     

An experimental study of contact pressure distribution in panel stamping operations

This paper presents an analysis of the dynamic contact pressure distribution at the sheet metal-tooling interface in normal and defective panel stamping operations. Specifically, the stamping of a 1.27?×?20?×?15?cm rectangular aluminum alloy panel has been simulated using finite-element modeling methods. The modeling results are leveraged to determine the forces acting on sensors embedded in the die structure. Based on these results, a customized stamping test bed has been designed, which incorporates an array of force sensors embedded into the stamping die to enable online measurement of the forces in the die. The force measurements are processed by the thin plate spline numeric surface interpolation method to evaluate a continuous contact pressure distribution map of the die cavity. The pressure distribution in the die cavity in normal and defective scenarios has been presented along with a suggested volume thresholding method for automated defect detection. By leveraging the numeric surface generation method to analyze experimental data, the present study establishes the basis for intelligent tooling and in-process monitoring for improved observability in sheet metal stamping.     

Experimental and numerical study of stamp hydroforming of sheet metals

The objectives of this research was to experimentally and numerically study the stamp hydroforming process as a means for shaping aluminum alloy sheets. In stamp hydroforming, one or both surfaces of the sheet metal are supported with a pressurized viscous fluid to assist with the stamping of the part thereby eliminating the need for a female die. The pressurized fluid serves several purposes: (1) supports the sheet metal from the start to the end of the forming process, thus yielding a better formed part, (2) delays the onset of material failure and (3) reduces wrinkle formation. This paper focuses on the experimental and numerical results of the stamp hydroforming process utilizing a fluid pressure applied to one surface of the sheet metal. The effects of applying a constant, varying and localized pressure to the surface of 3003-H14-aluminum sheet alloy were evaluated. Experiments demonstrated draw depths improvements up to 31% before the material failed. A failure prediction analysis by Hsu was also carried out to predict an optimal fluid pressure path for the varying fluid pressure case. The commercial finite element analysis code Ls-Dyna3D was used to numerically simulate the stamp hydroforming process. Both isotropic and anisotropic material models were used and their predictions compared against the experimental results. The numerical simulations utilizing Barlat's anisotropic yield function accurately predicted the location of the material failure and the wrinkling characteristics of the aluminum sheet.     

Interfacial heat transfer coefficient between metal and die during high pressure die casting process of aluminum alloy

The present work focused on the determination of the interfacial heat transfer coefficient (IHTC) between metal and die during the high pressure die casting (HPDC) process. Experiments were carried out on an aluminum alloy, ADC12Z, using “step shape” casting—so-called because of its shape. The IHTC was successfully determined by solving one of the inverse heat problems using the nonlinear estimation method first used by Beck. The calculation results indicated that the IHTC immediately increased after liquid metal was brought into the cavity by the plunger and decreased as the solidification process of the liquid metal proceeded. The liquid metal eventually solidified completely, a condition when the IHTC tended to be stable. Casting thickness played an important role in affecting the IHTC between the metal and die not only in terms of its value but also in terms of its change tendency. Also, under the test conditions, different change tendencies of the metal solid fraction were found between castings with different thicknesses and the die. __________ Translated from Acta Metallurgica Sinica, 2007, 43(1): 103–106 [ 译自: 金属学报]     

提高T/R 组件LTCC 大面积焊接钎透率的先进工艺

在生产T/R组件时,低温共烧陶瓷(LTCC)的大面积焊接常常遇到钎透率偏低的情况。由于焊接面和焊片上存在污染和氧化层,因而焊接面和焊料润湿性偏差;由于大面积焊接时没有恰当的保护气氛和还原气氛,因而焊接面和焊料非常容易重新氧化;焊剂的不恰当使用也会产生一些焊剂残留:这一切都是钎透率偏低的重要原因。文中介绍了改善焊接面和焊料润湿性的一些有效方法,如等离子体化学清洗和新颖的氢等离子体再流焊接技术。采用这些先进技术可以实现大面积焊接的无焊剂化,这些先进技术在提高LTCC基板大面积焊接钎透率方面将发挥重要作用。     

基于氮化铝HTCC基板的化学镀镍硼工艺研究

氮化铝(AlN)高温共烧陶瓷(High Temperature Co-fired Ceramic,HTCC)基板具有高的热导率以及与芯片匹配的热膨胀系数,是高功率多芯片组件首选的基板材料和封装材料。为了满足封装要求的良好钎焊性能,文中采用化学镀工艺在氮化铝HTCC基板钨导体表面沉积了化学镍钯金镀层。文中对化学镀镍溶液体系和高温热处理的工艺条件进行了研究,对化学镍层的厚度进行了优化。结果表明,高温热处理促使薄镍层向基板表面钨导体扩散,进而提高化学镀层与基底之间的附着力,镀层附着力良好,满足金丝键合和锡铅焊的要求,为微波高功率组件的研制提供了技术支撑。     

片式微波组件激光软钎焊气密封装技术研究

文中对片式微波组件激光软钎焊气密封装工艺开展研究,优化了影响焊缝成形的焊接结构、热台温度、助焊剂、离焦量、激光功率、焊接速度等工艺参数,分析了激光软钎焊密封接头微观组织,测试了激光软钎焊密封组件的气密性。结果表明:激光软钎焊封盖过程是一个温度场不断变化的动态过程,因此激光功率和焊接速度两参数也应在一定范围内通过程序设计动态调节。钎料可完全填充壳体与盖板之间形成的间隙,钎料中无空洞和裂纹,钎料未溢流到壳体内部。钎料与镀Ni 层接触并润湿良好,在钎料与壳体和盖板界面未形成粗大脆性的金锡金属间化合物。接头上部钎料基本保持(Sn)+(Pb)共晶组织状态,接头下部镀Ni层与钎料之间形成薄且均匀连续的金属间化合物层AuSn和AuSn₂。采用优化后的工艺参数激光软钎焊密封的组件气密性满足机载有源天线阵面应用要求。     

Measurement of in-plane deformation by surface inclusion (proposed measuring method and some experimental results)

A new measuring technique is proposed for measuring the in-plane deformation of soft metal surfaces when indented by a hard indenter, using the displacement of inclusions on the soft metal surface as sensors. In in-plane deformation, the soft metal surface flows along the hard indenter surface. In this paper, the principle of this new measuring technique is explained and some example measurements obtained from the experiments with aluminum and copper beryllium alloy plates, are presented.     

低温切削7075铝合金鳞刺形成规律及抑制措施

针对干切削铝合金工件表面易产生鳞刺、表面完整性较差的问题,采用液氮冷却方式在不同切削参数下对7075铝合金进行了正交切削试验,使用扫描电子显微镜和3D光学轮廓仪分别表征了已加工表面形貌、鳞刺分布和鳞刺尺寸,分析了切削速度、进给量、刀具前角和冷却方式(干切削、液氮冷却、切削液)对已加工表面鳞刺分布和尺寸的影响,并基于鳞刺...     

EFFECT OF PROCESS PARAMETERS AND TOOL SHAPE ON THE MACHINABILITY OF A PARTICULATE FILLED-POLYMER COMPOSITE MATERIAL FOR RAPID TOOLING

This paper presents the results of an experimental study on the effects of machining parameters (cutting speed, feed, depth of cut) and tool shape on chip formation, surface topography, resultant cutting force and surface roughness produced in flat and ball end milling of the Ren Shape-Express 2000™ aluminum particulate filled-polymer composite material. This material is shown to exhibit a brittle-to-ductile transition in chip formation with decreasing cutting speed. The transition is explained by the strain-rate sensitivity of the polymer matrix and is found to correlate well with a corresponding change in the surface roughness. The absence of clear feed marks on the milled surface explains why molds made from the composite material require less hand polishing than machined metal molds. The influence of cutting conditions and tool shape (flat end vs. ball-nose) on the cutting force, surface roughness, and workpiece breakout are discussed and relevant comparisons with conventional metal and polymer machining are made.