Filling Rules of Bevel Gears in the Closed-die Cold Forging

The closed-died cold forging technology of the bevel gears used in Jada car was investigated. With the analysis of the strain field and velocity field of the plastic deformation and the endured forces of the dies, the filling rules for the metal were analyzed by the elastic-plastic finite element method （FEM）. The results show that there is a great difference among closed-die cold forging, extrusion and forging, as far as the metal flowing is concerned. The outer addendum cannot be filled completely in the closed-die cold forging of the bevel gears, and the round angle will be formed. But it does not influence the application of the bevel gears. At the beginning, the rigid area is formed in the cavity of the lower die. And then it will move upwards to supply the metal for the gear filling. For the closed-die cold forging of the bevel gears, the force acting on the upper die and the lower die is significantly different.

Homogeneity of microstructure and Vickers hardness in cold closed-die forged spur-bevel gear of 20Cr Mn Ti alloy

Cold closed-die forging is a suitable process to produce spur-bevel gears due to its advantages, such as saving materials and time, reducing costs, increasing die life and improving the quality of the product. The homogeneity of microstructure of cold closed-die forged gears can highly affect their service performance. The homogeneity of microstructure and Vickers hardness in cold closed-die forged gear of 20 Cr Mn Ti alloy is comprehensively studied by using optical microscopy and Vickers hardness tester. The results show that the distribution homogeneity of the aspect ratio of grain and Vickers hardness is the same. In the circumferential direction of the gear tooth, the distribution of the aspect ratio of grain and Vickers hardness is inhomogeneous and they gradually decrease from the surface to the center of the tooth. In the radial direction, the distribution of the aspect ratio of grain and Vickers hardness is inhomogeneous on the surface of the gear tooth; while it is relatively homogeneous in the center of the gear tooth. In the axial direction of the gear tooth, the distribution of the aspect ratio of grain and Vickers hardness is relatively homogeneous from the small-end to the large-end of the gear tooth.

Microstructure and mechanical properties of Mg-Si alloys processed by cyclic closed-die forging

Mg-xSi （x=0, 1.5, 3.3） alloys were fabricated and subjected to cyclic closed-die forging （CCDF）, a new severe plastic deformation process, at 450 ℃ for 1, 3, and 5 passes. With applying CCDF, tensile strength, elongation and hardness increase, while coarse Mg2Si particles break into smaller pieces and exhibit more uniform distribution. Mg-1.5%Si alloy exhibits a combination of improved strength and elongation after 5 passes of CCDF processing. The tensile strength is about 142 MPa and elongation is about 8%. The improvement in mechanical properties was further characterized by dry sliding wear testing. The results show that wear resistance improves with silicon content and CCDF process passes, particularly the first pass. The wear resistance increases by about 38% for Mg-3.3%Si after 5 passes of CCDF compared with pure Mg. The improvement of wear is related to microstructure refinement and homogenization based on the Archard equation and friction effect.

3D FEM simulation of flow velocity field for 5052 aluminum alloy multi-row sprocket in cold semi-precision forging process

Based on the design of the multi-row sprocket with a new tooth profile,a cold semi-precision forging process for manufacturing 5052 aluminum alloy multi-row sprocket was presented.Through simulating the forging process of 5052 aluminum alloy sprocket billet with 3D rigid-viscoplastic FEM,both the distributions of flow velocity field in axial(U_Z),radial(U_R) and circumferential(U_θ) directions and the curves of velocity component in different deformation regions were respectively obtained.By comparison and analysis of the velocity varying curves,the velocity component relation conditions for filling the die cavity were clarified.It shows that when the die cavity is almost fully filled,the circumferential velocity U_θ increases sharply,implying that U_θplays a key role in fully filling the die cavity.

Finite element analysis and simulation for cold precision forging of a helical gear

To investigate the effects of billet geometry on the cold precision forging process of a helical gear, six different billet geometries were designed utilizing the relief-hole principle. And the influences of the billet geometry on the forming load and the deformation uniformity were analyzed by three-dimensional （3D） finite element method （FEM） under the commercial software DEFORM 3D. The billet geometry was optimized to meet lower forming load and better deformation uniformity requirement. Deformation mechanism was studied through the distribution of flow velocity field and effective strain field. The forging experiments of the helical gear were successfully performed using lead material as a model material under the same process conditions used in the FE simulations. The results show that the forming load decreases as the diameter of relief-hole do increases, but the effect of do on the deformation uniformity is very complicated. The forming load is lower and the deformation is more uniform when do is 10 mm.

Controlled Rolling and Cooling Process for Low Carbon Cold Forging Steel

Effect of controlled rolling and cooling process on the mechanical properties of low carbon cold forging steel was investigated for different processing parameters of a laboratory hot rolling mill. The results show that the specimens with fast cooling after hot rolling exhibit very good mechanical properties, and the improvement of the mechanical properties can be attributed mainly to the ferrite-grain refinement. The mechanical properties increase with decreasing final cooling temperature within the range from 670 ℃ to 570 ℃ due to the finer interlamellar spacing of pearlite colony. The specimen with fast cooling after low temperature rolling shows the highest values of the mechanical properties. The effect of the ferrite grain size on the mechanical properties was greater than that of pearlite morphology in the present study. The mechanical properties of specimens by controlled rolling and cooling process without thermal treatment were greatly superior to that of the same specimens by the conventional rolling, and their tensile strength reached 490 MPa grade even in the case of low temperature rolling without controlled rolling. It might be expected to realize the substitution medium-carbon by low-carbon for 490 MPa grade cold forging steel with controlled rolling and cooling process.

Upper-bound and finite element analyses of multi-row sprocket during cold semi-precision forging process

The cold semi-precision forging of a multi-row sprocket was investigated using upper-bound （UB） and finite element methods combined with experiments. Based on the design of a new tooth profile for the sprocket, a cold semi-precision forging process and a kinematically admissible velocity field for filling the die cavity were proposed. Using the UB method, the velocity fields of the sprocket billet in the forming process were divided theoretically and calculated. The process of forging a multi-row sprocket was simulated using the FEM package Deform-3D V6.1 to obtain the distributions of the velocity field and the effective stress field in filling the die cavity. Similar to the simulated results, the experiment on cold forging a 5052 aluminum alloy sprocket was successfully performed. By comparing the calculated （UB method）, experimental and simulated load-stroke curves, the calculated and simulated results were basically in accordance with the experimental results. The study provides a theoretical foundation for the development of the precision forging of multi-row sprockets.

Volume calculation of the spur gear billet for cold precision forging with average circle method

Forging spur gears are widely used in the driving system of mining machinery and equipment due to their higher strength and dimensional accuracy.For the purpose of precisely calculating the volume of cylindrical spur gear billet in cold precision forging,a new theoretical method named average circle method was put forward.With this method,a series of gear billet volumes were calculated.Comparing with the accurate three-dimensional modeling method,the accuracy of average circle method by theoretical calculation was estimated and the maximum relative error of average circle method was less than 1.5%,which was in good agreement with the experimental results.Relative errors of the calculated and the experimental for obtaining the gear billet volumes with reference circle method are larger than those of the average circle method.It shows that average circle method possesses a higher calculation accuracy than reference circle method(traditional method),which should be worth popularizing widely in calculation of spur gear billet volume.

Experimental study of the mechanical property of barrel processed by cold radial forging

The cold radial forging process usually introduces some changes of the material, such as the increased strength, the decreased plasticity and the introduction of anisotropic mechanical prop- erty. To obtain the changes of mechanical property of barrel processed by cold radial forging, the tangential mechanical properties of the barrel blank and the forged barrel are measured with a de- signed test based on the plastic deformation analysis for a barrel and by applying internal pressure, and their axial mechanical properties are measured by the tensile test. The changes of mechanical property of barrel processed by cold radial forging are obtained by comparing the mechanical proper- ties of the barrel blank and the forged barrel. The tangential and axial flow stresses of the barrel blank and the forged barrel are also presented.

Modelling and simulation of contact force in cold rotary forging

Cold rotary forging is an advanced and complex metal forming technology with continuous local plastic deformation.Investigating the contact force between the dies and the workpiece has a great significance to improve the life of the dies in cold rotary forging.The purpose of this work is to reveal the contact force responses in cold rotary forging through the modelling and simulation.For this purpose,a 3D elastic-plastic dynamic explicit FE model of cold rotary forging is developed using the FE code ABAQUS/Explicit.Through the modelling and simulation,the distribution and evolution of the contact force in cold rotary forging is investigated in detail.The experiment has been conducted and the validity of the 3D FE model of cold rotary forging has been verified.The results show that: 1) The contact force distribution is complex and exhibits an obvious non-uniform characteristic in the radial and circumferential directions; 2) The maximum contact force between the upper die and the workpiece is much larger than that between the lower die and the workpiece; 3) The contact force evolution history is periodic and every period experiences three different stages; 4) The total normal contact force is much larger than the total shear contact force at any given time.

Effect of key factors on cold orbital forging of a spur bevel gear

Cold orbital forging is an advanced spur bevel gear forming technology. Generally, the spur bevel gear in the cold orbital forging process is formed by two steps: the preforming step and the final step. Due to the great importance of the final step to gear forming and its complication with interactive factors, this work aims at examining the influence of key factors on the final step in cold orbital forging of a spur bevel gear. Using the finite element(FE) method and control variate method, the influence rules of four key factors, rotation velocity of the upper tool, n, feeding velocity of the lower tool, v, tilted angle of the upper tool, γ, friction factor between the tools and the billet, m, on the geometry and the deformation inhomogeneity of the cold orbital forged gear are thoroughly clarified. The research results show that the flash becomes more homogeneous with increasing v, increasing m, decreasing n or decreasing γ. And the deformation of the gear becomes more homogeneous with increasing v, decreasing n or decreasing γ. Finally, a corresponding experiment is conducted, which verifies the accuracy of FE simulation conclusions.

Numerical and experimental study on new cold precision forging technique of spur gears

A new cold precision forging technique is proposed to form a spur gear from a hollow billet, that is blocking the divided flow region and then final forging by the relief hole. 3D FEM simulation of the whole process of a pure aluminium spur gear is performed using DEFORM 3D TM . The load stroke curve, effective stress distribution, effective strain distribution, velocity distribution, and so on, are achieved. These results are compared with those achieved using the conventional closed die forging in the same conditions. The results show that this new technique has many advantages over the conventional one. The deformation load is reduced by near 30% and the filling ability of the tooth profile is also improved. Precision forging experiments of spur gears with the new process were performed using material Pb. The experimental results show a good agreement with the numerical results.

Fatigue Behavior of Cemented Carbide Die in Cold Forging of Steel

The fatigue behavior of cemented carbide die under service load in the multistage cold forging of steel was investigated. It was found that the fatigue cracks do not initiate at the stress concentration position and the crack initiation position can be classified to three types. The crack initiation position can be predicted by FEM only when the plastic deformation of the die is considered.

Deformation and Densification Laws of Powder Cold Forging

The deformation and densification laws of preform upsetting and closed-die forging were researched based on experimental results of cold forging of deoxidized Fe powder sintering porous material under different initial conditions such as friction factor, ratio between height and diameter and relative density. The fracture limit criteria＂ for powder cold-forging upsetting and the limit strain curve were achieved. The effect of friction facto,, ratlt, between height and diameter and relative density on fracture strain limitation was emphatically analyzed. The limit process parameter curves for the deformation of upsetting were also confirmed. Laws of deformation, densification and density distribution for closed-die forging of powder perform during cold-forging were further analyzed and discussed with the help of experimental phase analysis. As a result, this experiment established theoretical foundations for the design of preform and die as well as optimization of technological process parameters.

Effect of Mo and cold forging deformation on strength and ductility of cobalt-based alloy L605

Mo element was added to cobalt-based alloy L605,and cold forging deformation was performed.The effects of the addition and cold forging deformation on the microstructure and mechanical properties of the alloy were studied by thermodynamic calculation,electron backscatter diffraction,transmission electron microscopy,and X-ray diffraction.The stacking fault energy(SFE)of the alloy decreased after the addition,and the formation of stacking faults and intersections were promoted to improve the strength and hardness.The tensile strength of the alloy with Mo increased from 1190 to 1702 MPa after 24%cold deformation,producing significant work hardening.The strengthening mechanism is strain-induced martensitic transformation(SIMT)and deformation twinning.The alloy,combined with Mo and after 24%deformation,had both high strength and ductility in comparison with the original cobalt-based alloy L605.This is attributed to the lower SFE which caused the increase in stacking fault density.During the tensile process,theε-hcp phase was easily generated at the stacking fault to reduce the stress concentration and increase the ductility.Controlling SIMT by adjusting the density of stacking faults can improve the mechanical properties of cobalt-based alloys.Theε-hcp phase,the interaction between deformation twins and dislocations,and the interaction between e-hcp phases during cold forging deformation caused local stress concentration,lowering ductility and toughness.

半轴齿轮的热—冷复合锻造中冷锻充不满缺陷的成形数字仿真及工艺研究

针对半轴齿轮热—冷复合锻造中冷锻整形时出现的充不满缺陷,利用UG、Geomagic-Design和Deform-3D等软件,对冷锻毛坯(热锻成形的工件)进行了重新设计和冷锻整形工序仿真模拟,全面考查齿厚、齿高参数变化对产品质量的影响。从模拟结果来看,当冷锻整形开始合模时,毛坯初始位置齿顶和冷锻模具型腔之间的间隙越大(齿厚增加越大/齿高减小越大)时,终锻时所需的锻压力越大,在产品小端齿顶处越易形成折叠缺陷。毛坯初始位置齿顶与型腔贴合(齿厚增加量为零或为负),则不易产生折叠缺陷,齿侧和冷锻模具型腔之间的间隙越大(实际齿厚越小),所需锻压力越大。经过实际生产验证,在相应的齿轮参数条件下,冷锻毛坯比冷锻模具型腔轮廓的齿高增加0.1 mm、齿厚不变时,冷锻整形后齿槽和齿高全部压满,成型质量好,产品废品率达到预期要求。

Microstructural evolution during hot and cold deformation of Ti-36Nb-2Ta-3Zr-0.35O alloy

The Ti-36Nb-2Ta-3Zr-0.350 （mass fraction, %） （TNTZO） alloy was produced by cold isostatic pressing and sintering from elemental powders, followed by hot and cold deformation. The effects of deformation process on microstructures and mechanical properties were investigated using the SEM, TEM, OM and the universal material testing machine. Results show that the alloy can be easily hot forged and cold swaged due to the fine-grained microstructure. Only after cold swaging by 85%, the alloy shows the typical ＂marble-like＂ structure. And thecold deformation is accompanied by stress-induced a＂ phase transformations. Moreover, both the strength and the ductility of the alloy are significantly improved by hot and cold working.

挤压工艺对冷锻用6061合金棒材组织的影响

本文采用热挤压、冷锻造及高低倍观察等方式研究了合金成分、挤压温度及挤压速度对冷锻毛坯组织的影响。结果表明:合金中添加Cr和Mn合金元素能显著改善挤出棒材的内部晶粒组织形貌;采用高温高速的挤压工艺可以使低Cr和Mn合金挤出棒材整个截面呈完全细晶状态,满足了冷锻工艺对原材料品质的需求,同时也大幅提升了挤压生产效率,是最经济、有效的工业化生产方案。

钢管管端高频锻打成形设备研究

介绍了冷拔钢管打头工艺流程和技术装备,分析了打头机组设备技术创新特点,认为该设备核心技术及核心机构是分段倾斜式锤头臂,此机构改善了驱动主轴轴承受力状况,降低了锤头臂球面支撑的接触应力,实现了钢管管端高频次500次/min平稳径向锻打,且可实现无级调速,生产节奏提升1倍以上,产品成品率达到98%,提高了整机的工作寿命。

锻钢冷轧工作辊表面剥落原因

某冷轧厂锻钢冷轧工作辊表面发生剥落事故,采用宏观观察、化学成分分析、硬度测试、超声检测、金相检验等方法分析表面剥落原因,结果表明:轧制过程中有异物压入,使冷轧工作辊表面局部产生应力集中点并萌生裂纹,裂纹在轧制力的作用下沿晶界扩展;冷轧辊表面缺陷和次表层夹杂是轧辊表面剥落的根本原因。