Effects of copper-coated MoS_(2) on friction performance of bronze-graphite-MoS_(2) self-lubricating materials

Two kinds of bronze-graphite-MoS_(2) self-lubricating materials with copper-coated MoS_(2) and uncoated MoS_(2) were prepared by powder metallurgy.Friction and wear experiments were carried out under 4 N and 10 N loads respectively,and the effects of copper-coated MoS_(2) on the friction performances of the materials were studied.Results showed that the way of copper-coated on the surface of MoS_(2) could reinforce the bonding between MoS_(2) and matrix,and inhibited the formation of MoO_(2).Moreover,both materials formed a MoS_(2) lubricating film on the surface during the friction process.While the lubricating film formed after copper coating on MoS_(2) was thicker and had uneven morphology,it was more conducive to improving the friction performance of the material.Compared with conventional materials,the wear rate of copper-coated materials was reduced by one order of magnitude,and the friction coefficient was also reduced by 22.44% and 22.53%,respectively,when sliding under 4 N and 10 N loads.It shows that copper-coated MoS_(2)can improve friction properties of bronze-graphite-MoS_(2)self-lubricating materials furtherly.

Study on Solid Self-Lubricating Material for Plasma Facing Components in EAST

In this study, the friction performance of self-lubricating material with the counterpart steel ball-plate rubbing was investigated in vacuum conditions and the thermal distortion of the heat sink sample was tested. The analysis and test results show that the self-lubricating ma- terial has excellent anti-friction properties in high vacuum condition and can decrease the thermal stress and avoid damage to the PFCs during physical experiments.

Tribological Properties of Self-lubricating Laminated Ceramic Materials

In order to improve the tribological properties of ceramic composites, Al2O3/TiC-Al2O3/ TiC/CaF2 self-lubricating laminated ceramic composites were prepared by vacuum hot pressing sintering. Experiments were conducted to get mechanical properties and the friction and wear properties were also measured with friction and wear tester. The worn surfaces were observed by scanning electron microscope （SEM） and energy dispersion spectrum （EDS）. The wear resistance properties and the self-lubricating effect of ceramic composites were analyzed. Results show that the Al2O3/TiC-Al2O3/TiC/CaF2 self-lubricating laminated ceramic composites layers are well-defined with a higher bonding strength and the mechanical performances are uniform enough to overcome the anisotropy of weak laminated ceramic composites. In addition, the fracture toughness of Al2O3/TiC layers is also improved. Its friction coefficient and wear rates decrease with the increase of rotation speed and load. Al2O3/TiC-Al2O3/TiC/CaF2 self-lubricating laminated ceramic composites have good wear resistance because of the tribofilm formed by the CaF2 solid lubricants. The wear mechanisms of Al2O3/TiC/ CaF2 layers are abrasive wear and Al2O3/TiC layers are adhesive wear.

Numerical simulation and experimental verification of a novel double-layered split die for high-pressure apparatus used for synthesizing superhard materials

Based on the principles of massive support and lateral support, a novel double-layered split die(DLSD) for high-pressure apparatus was designed to achieve a higher pressure-bearing capacity and larger sample cavity. The stress distributions of the DLSDs with different numbers of divided blocks were investigated by the finite element method and compared with the stress distributions of the conventional belt-type die(BTD). The results show that the cylinders and first-layer supporting rings of the DLSDs have dramatically smaller stresses than those of the BTD. In addition, increasing the number of divided blocks from 4 to 10 gradually increases the stress of the cylinder but has minimal influence on the stress of the supporting rings. The pressure-bearing capacities of the DLSDs with different numbers of divided blocks, especially with fewer blocks, are all remarkably higher than the pressure-bearing capacity of the BTD. The contrast experiments were also carried out to verify the simulated results. It is concluded that the pressure-bearing capacities of the DLSDs with 4 and 8 divided blocks are 1.58 and 1.45 times greater than that of the BTD. This work is rewarding for the commercial synthesis of high-quality, large-sized superhard materials using a double-layered split high-pressure die.

STUDY ON DESIGN TECHNIQUES OF A LONG LIFE HOT FORGING DIE WITH MULTI-MATERIALS

A new design technique for the long life hot forging die has been proposed. By finite element analysis, the reason .for the failure of hot forging die was analyzed and it was concluded that thermal stress is the main reason for the failure of hot forging die. Based on this conclusion, the whole hot forging die was divided into the substrate part and the heat-resistant part according to the thermal stress distribution. Moreover, the heat-resistant part was further subdivided into more zones and the material of each zone was reasonably selected to ensure that the hot forging die can work in an elastic state. When compared with the existing techniques, this design can greatly increase the service life because the use of multi-materials can alleviate the thermal stress in hot forging die.

Die wall lubricated warm compaction of iron-based powder metallurgy material

Lubricant is harmful to the mechanical properties of the sintered materials. Die wall lubrication was applied on warm compaction powder metallurgy in the hope of reducing the concentration level of the admixed lubricant. Iron based samples were prepared by die wall lubricated warm compaction at 175 ℃, using a compacting pressure of 550 MPa. Emulsified polytetrafluoroethylene(PTFE) was used as die wall lubricant. Admixed lubricant concentration ranging from 0 to 0.5% was tested. Extremely low admixed lubricant contents were used. Results show that in addition to the decrease in ejection forces, the green density of the compacts increases with the decrease of admixed lubricant content until it reaches the maximum at 0.06% of lubricant content, then decreases with the decrease of admixed lubricant content. The mechanical properties of the sintered compacts that contain more than 0.06% admixed lubricant are better than those of the samples that contain lesser lubricant. No scoring was observed in all die wall lubricated experiments.

High Temperature Mechanical Properties of Ni-Al-Cr Based Alloys for Advanced Die-Materials Applications

In this study, we report on advanced Ni3Al based high temperature structural alloys with Zr and B addition in order to apply in the fields of die-casting and high temperature press forming as die materials. Microstructures and mechanical properties of Ni3Al based intermetallic alloys produced by vacuum arc melting were investigated in terms of phase analysis by using a scanning electron microscope （SEM） equipped with an X-ray energy dispersive spectrometer （EDS）, an X-ray diffractometer （XRD） and tensile test. The duplex microstructural feature consisting of γ＇ matrix phase and small intermetallic dispersoids was observed to be distributed over the whole microstructure. The ultimate tensile strength of the present alloy was superior to commercial iron-based and Ni-based die-materials especially in the high temperature region.

Composition,Processing Technology and Property of Ceramic Die Materials Containing Rare Earth Additives

Development and application of new ceramic die materials is one of the important topics in the field of die research. The composition, processing technology, mechanical property and engineering performance of the ceramic materials such as cermet, ZTA, TZP, TZP/Al2O3, TZP/TiC/Al2O3, PSZ and Sialon, etc., with rare earth yttrium, lanthanum and cerium, and so on working as additives, were investigated and analyzed in the present study. Problems existed in the research and application of rare earth ceramic die materials were discussed. Rare earth additives can effectively improve the mechanical property and engineering performance of ceramic die materials. Thus, it will have further perspectives of wider application. More attention should be paid in the future to the toughening and strengthening of the ceramic die materials, the adding forms and kinds of rare earth elements and acting mechanisms of rare earth additives in ceramic die materials.

Wear behavior of SiC/PyC composite materials prepared by electromagnetic-field-assisted CVI

Silicon carbide/pyrolytic carbon (SiC/PyC) composite materials with excellent performance of self-lubrication and wear resistance were prepared on SiC substrates by electromagnetic-field-assisted chemical vapor infiltration (CVI). The composition and microstructure of the SiC/PyC materials were investigated in detail by XRD, SEM and EDS, etc. The effects of the deposition temperature on the section features and wear resistance of the SiC/PyC were studied. The results show that the PyC layers were deposited onto SiC substrates spontaneously at a lower deposition temperature. The SiC substrates deposited with PyC can significantly reduce the wear rate of the self-dual composite materials under dry sliding condition. The wear tests suggest that the SiC/PyC composite materials own a better wear resistance property when the deposition temperature is 800 °C, and the wear rate is about 64.6% of that without the deposition of PyC.

Effect of sintering parameters on warm compacted iron-based material

Iron-based powder metallurgy material was prepared by warm compaction at 125 ℃ using a compacting pressure of 700 MPa. Sintering temperature ranging from 1 100 ℃ to 1 300 ℃ and sintering time ranging from 40 min to 80 min were used to study the effects of sintering parameters on the compacts. Die wall lubrication polytetrafluoroethylene(PTFE) emulsion was also applied in combination with warm compaction in hope to increase the compact density and the mechanical properties of the sintered material. Green and sintered density, spring back effect and sinter shrinkage were measured. Mechanical properties of both as-sinter and heat treated samples were also measured. Results show that mechanical properties of the sintered compacts increase with the increase of sintering temperature and sintering time. Sample prepared by die wall lubricated warm compaction always shows higher density and mechanical properties.

Compression properties of cost-efficient porous expanded clay reinforced AA7075 syntactic foams fabricated by industrial-oriented die casting technology

In today’s manufacturing industries,hard competition between rival firms makes it compulsory for researchers to design lighter and cheaper machine components due to the megatrends of cost-effectiveness and anti-pollution.At this point,aluminum syntactic foams(ASFs)are new-generation engineering composites and come into the upfront as a problem-solver.Owing to their features like low density,sufficient elongation,and perfect energy absorption ability,these advanced foams have been considerably seductive for many industrial sectors nowadays.In this study,an industrial-oriented automatic die casting technology was used for the first time to manufacture the combination of AA7075/porous expanded clay(PEC).Micro evaluations(optical and FESEM)reveal that there is a homogenous particle distribution in the foam samples,and inspections are compatible with the other ASF studies.Additionally,T6 aging heat treatment was operated on one half of the produced foams to explore the probable impact of aging on the compressive responses.Attained results show that PEC particles can be an alternative to expensive hollow spheres used in the previous works.Besides,a favorable relationship is ascertained between the aging treatment and mechanical properties such as compression strength and plateau strength.

LOW CYCLE FATIGUE BEHAVIOR OF AZ91HP ALLOY IN AS HIGHP RESSURE DIE CASTING

Fully reversed total strain-controlled low-cycle fatigue tests were conducted at room temperature in air to study the fatigue behavior of AZ91HP magnesium alloy in as high pressure die casting and subsequently heat treatment. All the specimens in different heat histories exhibit cyclic strain hardening in different degrees. It is difficult to distinguish the fatigue behavior of the die casting specimens from that of the solution aging specimens. The solution treated specimens show longer fatigue life at high strain amplitude and shorter fatigue life at low strain amplitude than the die casting and solution aging specimens though they have the lowest yield strength with higher strain hardening. Fatigue fracture surfaces for strain amplitude larger than 0.005 show very similar to those found by monotonic tensile tests. The SEM examination reveals that the regions of fatigue crack growth and final fracture can be characterized by quasi-cleavage mechanisms, but some shallow dimples, slip bands and secondary cracks are found on the fracture surface in the fracture crack growth areas.

Effect of Rare Earth Composite Modification on Microstructure and Properties of a New Cast Hot-Work Die Steel

The effects of RE modification on structure and the properties of a new cast hot work die (CHD) steel were investigated. The grains of the CHD steel are refined by RE modification. With the increase of RE addition, both grain size and inclusion amount are reduced. Appropriate amount of RE results in decrease in inclusion amount and formation of spheroidal inclusions uniformly-distributed in steel, so that the morphology and distribution of inclusions are improved. RE composite modification favors the formation of bainite, austenite and fine lath martensite with dense dislocation. When the residual RE content reaches 0.02%, no obvious changes in strength and hardness are found, while fracture toughness and threshold of fatigue crack growth are increased. The impact toughness, elongation and reduction of cross sectional area are increased by a factor of two, and thermal fatigue resistance is also improved.

Study on the Corrosion Properties of Several Kinds of High-temperature Solid Self-lubricating Material

In some adjusting mechanism,solid self-lubricating material that has hot-resistant and corrosion-resistant is need for adapting the work condition.In the present article,by the comparison study of mass loss and surface topography after corrosion in acid solution and vapour of the four kinds of material,graphite,polymer,BN composite and cermet,it was found that,graphite has good corrosion-resistant to acid solution and vapour under 200℃,but the corrosion-resistant will become worse dramatically under 400℃,polymer has worse corrosion-resistant behavior above 200℃.By comparison,BN self-lubricating composite has better hot-resistant and corrosion-resistant,which can meet the demand of the work condition.

Survey of the 4th China International Diecasting Exhibition

Die casting machines, dies, die castings, peripheral equipments, die lubricants, raw materials for die casting, melting & holding furnaces, cleaning equipments, etc. were exhibited during the 4th China International Die Casting Exhibition, which was surveyed in the paper.

Effects of TiCN Composite Die with Low Thermal Conductivity on Hot Forging Performances

Titanium carbonitride based composite （TiCN-metallic binder） was developed as die material for replacement of cemented tungsten carbide. The effects of thermal conductivity characteristic of the TiCN composite on hot forging performances were investigated using a servo press with ram motion control. Three types of the die materials; （a） tool steel for hot working, （b） cemented tungsten carbide with high thermal conductivity and （c） TiCN composite with low thermal conductivity were compared. In hot upsetting of a chrome steel workpiece, the TiCN composite die was confirmed to reduce the forging load by approximately 20% at slow forging speed. This is because the die with low thermal conductivity could prevent the workpiece from rapid cooling induced by heat transfer at the die-workpiece interface. In addition, the material flow of the workpiece to a die cavity was improved. Furthermore, the wear depth/wear coefficient of the TiCN composite was lower than that of the tool steel and the cemented tungsten carbide in the numerical analysis of wear due to the combination of low thermal conductivity and high hardness.

材料物性参数对双层微管气体辅助共挤出胀大的影响

建立了单腔双层微管的传统微共挤和气辅微共挤流动模型,采用数值模拟技术研究了零剪切黏度(η_(0))、松弛时间(λ)、材料参数ε和ξ等对挤出胀大率的影响规律。结果表明,传统微共挤过程中,挤出胀大率受η_(0)和λ的影响较大,随着外层熔体η_(0)增大,由29.15%增大至43.77%后趋于稳定;挤出胀大率受ε和ξ的影响较小,随着ε和ξ的增大略有减小,胀大率在37%~39%区间变化。而气辅共挤过程中,当η_(0)、λ、ε和ξ变化时,挤出胀大率始终接近零,无明显胀大和变形现象。

深轮辐齿坯多工位闭式模锻材料流动规律研究

探索闭式热模锻成形时材料的流动规律是控制充填不满等成形缺陷、获得高精度模锻件的理论基础。针对深轮辐齿坯件热模锻成形时易出现填充不满的问题,以某SCr420H深轮辐齿坯为研究对象,基于齿坯件结构分析,设计了“下料-加热-镦粗-预锻Ⅰ-预锻Ⅱ-终锻”的多工位闭式热模锻工艺方案;基于Deform软件,构建了深轮辐齿坯件多工位闭式热模锻全流程有限元模拟模型;采用试验验证了有限元模型的可靠性,并对多工位闭式热模锻成形过程中材料的流动规律进行了研究。结果表明:镦粗比为3.7时,可获得外形良好的圆饼形预制坯,镦粗时受上下表面摩擦效应的影响,材料径向流动不均匀,在坯件腰部出现鼓形;预锻Ⅰ工位成形出用于定位的底面内凹结构,同时减小了后续工位材料填充难度;预锻Ⅱ和终锻成形时的材料流动规律相似,成形前期材料集中流向轮缘部分、成形中期主要流向轮毂部分、末期流向圆角处;终锻成形时未出现材料填充不满的缺陷,在成形后期,少量金属材料从终锻上下模的导向间隙中流出,形成纵向飞边。通过生产试验,成形出填充良好的深轮辐齿坯件,模拟数值获得温度与实际生产数值最大误差不超过3.15%,纵向飞边高度小于0.5 mm,零件各尺寸偏差均小于0.2 mm,验证了所设计多工位闭式模锻工艺的合理性。

“双高计划”背景下高职“冲压模具设计”教材改革与实践

为提升高职教育“模具设计与制造技术”高素质技术技能人才培养质量,以“冲压模具成形工艺与设计”课程建设与教材改革为研究对象,遵循项目导向、任务驱动、理实一体相结合的原则,创新“冲压模具设计”教材的人才培养策略与教材体系内容,突出能力本位的职业教育改革思想和思政教育理念。通过教材改革与实践,有效激发了学生的学习兴趣,培养了实践能力与创新思维,提升了冲压模具设计的自信心,提高了教学质量。

一体压铸技术的应用及挑战

一体压铸技术是将熔融金属注入到预先制备好的模具中,凝固后形成一体化零部件的新型金属加工技术,它相较于传统的压铸技术具有更高效、更精密的特点,在工业生产领域得到了广泛应用。一体压铸技术具有诸多优点,例如高生产效率、良好的表面质量、优秀的机械性能等,因此被广泛应用于汽车、航空航天、电子、能源等领域。然而,一体压铸技术在应用过程中也面临着一些挑战:如材料选择和性能要求等,为了解决这些挑战,研究人员和工程师们提出了许多创新的解决方案。本论文旨在探讨一体压铸技术的应用及其面临的挑战,并提出解决方案,通过对相关领域的案例研究和理论分析,将为一体压铸技术的进一步发展和应用提供有益的参考和指导。