基于CMT的不锈钢电弧增材制造温度

发布时间：2018-01-04 01:41

本文关键词：基于CMT的不锈钢电弧增材制造温度场、应力场及成型工艺研究　出处：《南京理工大学》2017年硕士论文　论文类型：学位论文

【摘要】：电弧增材制造是以电弧为热源,均匀送入的焊丝为熔覆材料,直接快速成型致密度高、力学性能优良的金属复杂结构件,可极大提高材料的利用率、生产效率和制造技术的核心竞争力。课题基于CMT的不锈钢增材制造技术,以成型直壁件为研究对象,对增材制造过程中的温度场、应力场、增材制造工艺及成型件组织性能开展了研究。首先对不锈钢CMT增材制造过程中的温度场及应力场进行了研究。建立了基于SYSWELD的增材制造有限元模型,对比了同向连续增材制造、S形连续增材制造及S形间隔时间增材制造三种常用的电弧增材制造路径下温度场及应力场,其结果表明,基板对前四层熔覆层的冷却速率影响较大,且基板能够影响的层数与增材制造方式无关;熔覆层的温度在其上熔覆一定层数后趋于稳定,稳定后的温度在奥氏体不锈钢敏感化温度区间以下,且控制层间温度可以获得较小的稳定温度值;CMT在连续熔覆时热累积作用不明显。奥氏体不锈钢增材制造后残余应力大于屈服强度;同向增材制造时出现较大的残余应力及变形;S形连续增材制造时残余应力分布特点为较大的应力分布在较小的区域,而控制层间温度时表现为较小的应力分布在较大的区域,且都呈现对称分布;增材制造过程中的重热作用相当于进行回火热处理,减小了熔覆层中的残余应力。其次利用MATLAB软件建立了增材制造过程中保护气流量、送丝速度及熔覆速度与成型壁厚的数学模型。该模型表明,送丝速度越大,成型壁厚越大,且当送丝速度超过4.0m/min时,壁厚增加速度明显变慢;保护气流量当与送丝速度交互作用时对成型壁厚影响较为明显;三个因素对成型壁厚影响顺序大致如下:送丝速度=熔覆速度保护气流量。最后对比了S形连续增材制造及S形间隔时间增材制造成型直壁件显微组织和力学性能。成型直壁件中组织按照经历的热循环过程的不同主要分为六个区域,其中Ⅰ区与Ⅱ区为底部及底部过渡区域,含有较多枝晶状的残余铁素体,Ⅲ区为熔覆层之间熔合形成的含有少量奥氏体柱状晶区域,Ⅳ区为中部稳定成型区域,铁素体较少,呈现较小树枝晶,Ⅴ区及Ⅵ六为顶部过渡区域及顶部区域,铁素体含量较多。控制层间温度时增加了相应区域的残余铁素体含量。成型直壁件抗拉强度达到了 304冷轧后退火不锈钢基板的70%,且均高于铸造态及热轧状态,抗冲击性能达到基板的65%,硬度与基板相当;横向与纵向的拉伸强度、抗冲击性能及塑性表现为不明显的差异性;控制层间温度对不锈钢成型直壁件力学性能影响较小。
[Abstract]:The arc is to increase timber manufacturing arc as the heat source, evenly into the wire as cladding materials, direct rapid prototyping of high density and excellent mechanical properties of the metal complex structure, can greatly improve the material utilization and production efficiency and core competitiveness of manufacturing technology. The subject of CMT stainless steel increased material manufacturing technology based on the molding straight wall parts as the research object, on the temperature increasing material manufacturing process, stress field, microstructure and properties of additive manufacturing process and molding are studied. Firstly, CMT stainless steel material manufacturing process to increase the temperature field and stress field are studied. A material increase in manufacturing SYSWELD finite element model based on the comparison with the continuous increase in material manufacturing, S shaped and S shaped continuous increasing material manufacturing interval increasing material manufacturing three kinds of arc material manufacturing growth path under the temperature field and the stress field, the results show that the substrate of four layer of cladding layer The cooling rate has great influence, is irrelevant and can affect the substrate layers and increasing material manufacturing method; cladding temperature tends to be stable in the cladding layers, stable temperature on austenitic stainless steel sensitive temperature range, and the control layer temperature can obtain stable temperature of the lower value of CMT in continuous; cladding heat accumulation effect is not obvious. The austenitic stainless steel material manufacturing increased residual stress is greater than the yield strength; with the increasing material manufacturing occurs when large residual stress and deformation; S type continuous increasing material manufacturing residual stress distribution of stress distribution in a small area is larger, and the control layer when the temperature stress distribution is larger in the small area, and showed a symmetrical distribution; heavy heat increasing material in the manufacturing process of equivalent heat treatment, reduce the residual stress in the cladding layer. The utilization of MATLAB Software to establish a gas flow protection additive manufacturing process, the mathematical model of wire speed and feeding speed and the thickness of cladding forming. The model shows that the wire feeding speed is larger, forming wall thickness increases, and when the wire feeding speed is more than 4.0m/min, the wall thickness increases much slower when the amount of air protection; and the wire feeding speed interaction effect on the forming of wall thickness is obvious; three factors as follows for forming wall thickness influence order: the wire feeding speed = cladding speed protection gas flow. Finally compared the S type continuous increasing material manufacturing and S interval increasing material manufacturing straight wall parts and mechanical micro organization the performance of forming straight wall parts in the organization. According to the different thermal cycling process is divided into six regions, in which area I and II for the bottom and the bottom of the transition region, the residual iron containing more dendritic ferrite, III fusion formed between the cladding layer containing a small amount of The austenite columnar crystal region, Central District IV forming stable region, ferrite is less, a small dendrites, and the top six District V VI for the transition region and the top region, the ferrite content is more. The control layer temperature increases the residual iron ferrite content. The forming of straight wall parts the tensile strength reached 304 annealing of cold rolled stainless steel substrate 70%, and higher than that of casting and hot rolling state, impact resistance to substrate 65%, the hardness and the substrate; transverse and longitudinal tensile strength, impact resistance and ductility performance difference is not obvious; the control layer temperature of stainless steel straight the mechanical properties of the wall a little effect.

【学位授予单位】：南京理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG142.71;TP391.7

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