Droplet splashing during arc spraying of steel and the effect on deposit microstructure

The mechanism by which droplet deposition occurs is important when filling substrate features for the electric arc spray forming of steel tooling. Particle image velocimetry and high-speed video imaging techniques have been used to observe droplet deposition, particularly with regard to the behavior of droplets originating from splashing. Droplet splashing on deposition has been seen to be significant, and splash droplets form a large proportion of the overspray. The splash droplets are smaller and, when first created, move slower than the parent droplet. When spraying into deep features, the lateral and upward movement of splash droplets acts as a mechanism for deposit formation onto surfaces in shadow from the main spray. Microstructural study has shown that oxidation of the splash droplets before redeposition leads to a deposit with a high fraction of oxide. Simultaneous growth of deposit formed directly from the spray, and from splash droplets, results in a banded microstructure containing elongated macropores. A mechanism for such microstructural evolution is proposed.     

手机上盖注射模快速制造

分析了传统手机上盖注射模设计与制造方式的弊端 ,介绍了RPM系统的关键技术———RT技术在注射模制造中的应用 ,强调了RT技术的优点及其在模具制造中的应用价值。     

Mechanical and thermomechanical properties of metal spray invar for composite forming tooling

The subject of this paper is the assessment of the thermal and mechanical properties of Invar steel coatings, deposited using electric arc spraying, and the correlation of these properties to the spray parameters and processes used to offer coatings with characteristics appropriate to the requirements of tools used in the fabrication of precision polymer matrix composite work pieces. In particular, two processing methods, inert and air atomization, and three arc spray gun configurations (air cap design) were evaluated. The low coefficient of thermal expansion (CTE) properties of Invar are maintained in the spray-deposited coatings using both high velocity oxy-fuel (HVOF) and air-atomized arc spraying, although HVOF coatings have significantly lower CTE and greater durability than those deposited by arc spraying. The mechanical properties of the coatings are low compared to bulk Invar, regardless of the spray parameters and hardware used. Inert arc spraying affords more consistent coating characteristics but this comes with a compromised durability. The spray hardware was found to be more significant in determining the coating properties than the parameters employed.     

叠层钢板成形模快速制造技术研究

研究了叠层制造工艺的分层处理技术,提出了一种基于EUCLID软件系统的CAD模型直接分层方法,采用等离子切割方法对板材进行切割,板件依序叠合起来后通过胶粘实现层间的粘接。实例表明该工艺为金属模具低成本快速制造提供了有益参考。     

金属电弧喷涂成型快速制模关键技术与应用

金属电弧喷涂成型制模技术是一种基于"复制"的制模工艺,与传统制模工艺相比,具有制模速度快、周期短、成本低等特点。金属喷涂模具由金属型壳、背衬强化层以及模框等构成,是一种具有梯度材料结构的复合材料模具。关键制模工艺包括:母模制备、金属型壳制造、模框制作、背衬强化层制作、脱模以及后处理等。金属喷涂制模技术可用于制造注塑模具、热成型模具和板料冲压模具等。该文以大型汽车覆盖件模具的快速制造为例进行了详细介绍。     

3D打印技术在模具制造中的应用

介绍了基于3D打印技术的快速模具制造技术,并对快速模具进行分类。阐述了不同种类快速模具的特点及其制造工艺,分析了3D打印技术在模具制造中的优势。     

焊接方法对1000MPa级熔敷金属组织及力学性能的影响

在相同热输入下分别采用熔化极活性气体保护焊(MAG)和钨极氩弧焊(TIG)进行1 000 MPa级熔敷金属试验,通过光学显微镜、透射电镜及断口分析等手段研究焊接方法对其组织和性能的影响. 结果表明,MAG焊熔敷效率明显高于TIG焊,MAG焊中出现了明显的"指状熔深". MAG焊熔敷金属及道间热影响区组织明显较TIG焊粗化. TIG焊熔敷金属组织细化、分布取向多样化且均匀分布的较多残余奥氏体是TIG焊低温冲击韧性优异的原因之一;MAG焊中生成大量非金属夹杂物易成为解理断裂起裂源,是导致熔敷金属冲击韧性恶化的因素之一. TIG焊力学性能明显优于MAG焊,这与焊接方法所导致的组织构成及夹杂物有直接关系.     

真空退火处理对冷喷涂铝基复合材料组织与性能的影响

采用冷喷涂增材制造工艺制备了Al-25Al2O3、Al-50Al2O3和Al-75Al2O3(体积分数,％)具有不同体积含量Al2O3颗粒的铝基复合材料,并采用SEM、EBSD、硬度测试和拉伸测试等测试方法分析了真空退火处理对冷喷涂铝基复合材料的微观结构和力学性能的影响.结果表明,Al2O3颗粒的加入增加了冷喷涂增材材...     

旁路耦合电弧增材制造热过程与组织关系

利用旁路耦合微束等离子弧焊,进行了ER304L不锈钢电弧增材制造的研究.通过进行组织观察和显微硬度测试,并结合增材过程中所测得的热循环曲线,分析了不同旁路电流、堆垛顺序对304不锈钢堆垛样组织和性能的影响.结果表明,旁路耦合微束等离子弧焊增材制造过程中,当旁路电流增大时,堆垛样组织的枝晶间距先减小后增大;堆垛顺序对组织的影响表现为,散热方向的不同导致了枝晶生长方向发生改变.试样的显微硬度沿着堆积高度方向缓慢降低,且随着旁路电流增大,硬度先增大后降低;同时堆垛顺序对硬度的影响并不明显.     

电弧增材制造(WAAM)ZL114A铝合金组织与性能的研究

采用金相显微镜、扫描电镜、电子万能试验机等分析测试手段,研究了电弧增材制造工艺方法对ZL114A铝合金组织与性能的影响。与传统铸造成形方法相比,铸态组织具有更小的枝晶间距、Si相细小分布均匀;化学成分可有效控制;T6热处理后,Si相球化充分,第二相弥散分布在α-Al基体上,力学性能显著提升,抗拉强度、屈服强度及延伸率分为360MPa、315MPa、7.5%,延伸率是砂型铸造试样的2.1倍,拉伸断口呈现韧性断裂特征。WAAM成形试样缺陷主要为小于30μm的气孔,经过热处理后气孔数量减少,尺寸有变大趋势。     

Developments in investment casting process—A review

Investment casting has been used to manufacture weapons, jewellery and art castings during the ancient civilization. Today, its applications include jewellery/art castings, turbine blades and many more industrial/scientific components. The present paper reviews various investigations made by researchers in different stages of investment casting and highlights their importance. The paper initially highlights the investigations made on pattern wax properties, effects of blending, additives and fillers. Different ways through which pattern properties (like surface finish, dimensional accuracy, etc.) could be enhanced by properly controlling the injection processing parameters are thoroughly discussed. The paper also looks into the investigations made to enhance the strength, surface finish, etc. of ceramic shell for ferrous alloys/non-ferrous alloys as well as superalloys in investment casting. Investigations made on incorporation of nylon fibers and polymer additions confirm that a ceramic shell reinforced with nylon fibers attains additional permeability compared to the one with polymer additions.