铸造3D喷墨打印砂型尺寸精度测量评定方法研究

随着铸造行业的转型发展,3D打印技术已经成熟的应用于制造铸造砂型,所制作的砂型不再单单作为铸造过程中的半成品,而是可以作为产品面向各铸造厂进行销售。但是目前对于砂型的检验标准存在缺失,对于砂型质量的把控和评定缺少依据。针对铸造砂型的尺寸精度,通过设计制作测量试块,给出了一种3D喷墨打印砂型的测量方法及评定标准,填补了目前铸造行业中这一领域在标准上的空白,对推动3D打印技术在铸造行业的应用以及砂型的产品化有着重要的意义。     

呋喃树脂砂生产铸铁件临界吃砂量的模拟试验研究

为确定呋喃树脂砂的合理吃砂量,研究了以硅砂为原砂制备的呋喃树脂砂在100～500℃内的溃散性,确定了型砂全部溃散时的最低温度为350℃；然后,运用ProCAST软件模拟了不同壁厚的圆筒形铸铁件的凝固过程及铸型和型芯的温度场,并研究了圆筒形铸铁件壁厚(模数)与呋喃树脂砂临界吃砂量的关系,最终得到了两者之间的回归方程.     

Cooling control for castings by adopting skeletal sand mold design

The cooling control of the melt during the casting process is of great significance. A comprehensive closed-loop cooling control of castings by adopting a skeletal sand mold design was proposed. The skeletal sand mold consisting of an adaptive shell, functional cavities and a support was designed and created based on the finite difference meshes of a casting. It was applied to a round wall test casting. Two kinds of skeletal sand molds, one with lattice support and the other with enforcing ribs for this casting were designed and printed out by the 3 D printing(3 DP) method. Aluminum alloy A356 was cast by using these two sand molds. The first mold was cooled by natural convection, the other one by water spray cooling. Two sound castings were obtained. The sand mold temperature, cooling curves, microstructures, mechanical properties, residual stress and deformation were measured, compared and discussed. Water spray cooling hastened the cooling rate by 62%, increased the content of Mg and Cu in the α-Al matrix, improved the mechanical properties, and altered the surface residual stress state.     

Development of a new instrument for measurement of high temperature mechanical properties of resin-bonded sand

The mechanical properties of resin-bonded sand mixtures at high temperatures significantly affect the quality of casting. However, the existing instruments for high-temperature performances testing mainly focus on inorganic binder-bonded sands no matter the test items or the atmospheric protection, while the instrumentss specially designed for resin-bonded sand are not yet available. A new instrument for testing the hightemperature performance of resin sand was designed including the confirmation of the testing parameters, loading, measurement and control systems, and the design of the frame shape and heating furnace. This instrument can test the compressive strength, heat tolerance time and restraining load of phenol-formaldehyde resin coated sand, self-hardened furan resin sand, and trimethylamine(TEA)-based resin bonded sand at high temperatures. The developed instrument has a high accuracy offering smaller than 0.3% deviation at a full scale in the measurement of the high temperature compressive strength and the restraining load over the range of 0-6.8 MPa and 0-2,000 N, respectively. The high temperature heat tolerance time range is 0-300 s and its measurement accuracy is ±1 s.     

聚氨酯砂改性工艺研究

采用红外光谱技术研究了聚氨酯砂的固化反应机理, 通过向聚氨酯砂中加入呋喃树脂砂进行改性处理, 并采用热失重及扫描电子显微分析技术研究了聚氨酯砂的改性机理。结果表明, 聚氨酯砂中加入呋喃树脂砂以后, 由于在高温下树脂膜分解速度下降, 高温强度得到提高。呋喃树脂砂合适加入量为１０ ％ , 改性聚氨酯砂具有良好的综合性能     

呋喃树脂砂铸钢阀体裂纹及防止对策

详细地阐述了呋喃树脂砂铸钢阀体产生裂纹的原因，解释了呋喃树脂砂和水玻璃砂铸件裂纹形状的区别并提出了防止铸钢阀体裂纹的措施。     

三维光学扫描技术在3D打印中的应用

采用先进的三维光学扫描技术,借助计算机软件对SLS打印的缸盖上水夹层砂芯进行三维数字化全尺寸扫描,检测分析了SLS打印砂芯尺寸精度及尺寸变化规律。检测结果显示:上水夹层砂芯不满足打印设备精度要求,需要改进打印工艺。根据三维光学扫描检测分析结果明确了3D打印工艺调整方向,改进了工艺打印的缸盖上水夹层砂芯,经过三维光学扫描检测,砂芯尺寸精度得到了有效地提高。通过对三维光学扫描技术在3D打印中的应用研究,对SLS打印砂芯精度检测提供了一种更为准确直观的测量方法,三维光学扫描检测结果作为SLS打印工艺参数调整依据,为SLS打印出合格的砂芯奠定基础。     

酮醛改性呋喃树脂砂制备工艺研究

介绍了一种新型酮醛改性呋喃树脂制备工艺,通过对呋喃树脂砂抗拉强度的测定、呋喃树脂游离甲醛含量的测定以及多元醇B剂替代试验,分析了丙酮与甲醛摩尔比、碱性反应时间以及酸性反应时间对改性呋喃树脂砂强度的影响.结果 显示:(1)当丙酮与甲醛摩尔比为1∶1.25,碱性反应温度为80℃,碱性反应时间为2h,碱性反应pH值为9.5,...     

高退让性呋喃树脂砂对铸钢件热裂纹的有效防止

在呋喃树脂合成过程中引入柔性基团并添加高温增塑剂，用热变形量测试仪分析了树脂砂的高温性能。结果表明：研制的高退让性呋喃树脂能明显降低型芯热膨胀，延长高温塑性时间，改善型芯退让性，有效防止铸钢件热裂纹的产生。     

高端汽车冲压模铸钢件的3DP打印砂型铸造技术

研究了三维喷墨打印(3DP)工艺在中大型冲压模铸钢件制造生产中的应用。测试了打印砂型的抗拉强度、透气性、发气量等性能,并基于3DP工艺设计了砂型。结果表明,3DP打印砂型的抗拉强度可达1.70MPa,透气性大于400,最大发气量为14.6mL/g,均可满足合金钢铸造的使用要求。3DP打印砂型(芯)具有无需模具、可以采用砂型和砂芯整体化工艺等特点,提高了铸件的精度。通过对3DP砂型设计,并通过特殊工艺方法,解决了打印砂型的铸字清晰度的问题。     

Effect of reclaimed sand additions on mechanical properties and fracture behavior of furan no-bake resin sand

In this work,the effects of reclaimed sand additions on the microstructure characteristics,mechanical properties and fracture behavior of furan no-bake resin sand have been investigated systematically within the temperature range from 25 to 600 ℃.The addition of 20％-100％ reclaimed sand showed dramatic strength deterioration effect at the same temperature,which is associated with the formation of bonding bridges.Both the ultimate tensile strength (UTS) and compressive strength (CS) of the moulding sand initially increase with the increase of temperature,and then sharply decrease with the further increase of temperature,which is attributed to the thermal decomposition of furan resin.The addition amount of reclaimed sand has a remarkable effect on the room temperature fracture mode,i.e.,with the addition of 0-20％ reclaimed sand,the fracture mode was mainly cohesive fracture;the fracture mode converts to be mixture fracture mode as the addition of reclaimed sand increases to 35％-70％;further increasing the addition to 100％ results in the fracture mode of typical adhesive fracture.The fracture surface of the bonding bridge changes from a semblance of cotton or holes to smooth with the increase of test temperature.     

固化剂自动控制仪在自硬砂造型线上的应用

在酸硬化呋喃树脂砂造型线上配置固化剂自控仪，再生砂的树脂加入量为砂质量的0．65％-0．85％，A＋B固化剂加入量为树脂质量的30％～40％，解决了自硬砂造型中再生砂砂温对固化速度影响的问题，保证了铸型和砂芯的品质。     

树脂砂型(芯)热开裂及其铸件产生脉纹缺陷的理论判据的研究

本文应用弹性力学和传热学等理论导出了树脂砂型(芯)在铸造过程中的热应力和机械应力关于厚度方向的一维空间z和受热时间t的二元方程,据此提出了一种新颖的树脂砂型(芯)热开裂的理论判据,并首次建立了铸件产生脉纹缺陷的理论判据。文中对该热开裂理论判据进行了简化分析,结果表明:以前的一些判据只是该判据的特例或简化式。文章还根据所得的理论判据提出了防止砂型(芯)热开裂和铸件产生脉纹缺陷的措施。     

G32柴油机球铁飞轮的生产

G32柴油机球铁飞轮原采用全呋喃树脂砂型铸造,采用大冒口补缩,工艺出品率低,并需采用大量冷铁。为此改用覆砂铁型替代呋喃树脂砂型,采用合成球铁的熔炼工艺,结果表明:G32飞轮球化率高、力学性能好,每个铸件的生产成本约降低1.1万元。     

新型酯硬化水玻璃砂在铁路车辆铸钢件生产中的应用

介绍了新型酯硬化水玻璃砂造型制芯生产线以及所用原材料、型芯砂配方和工艺性能,分析了影响酯硬化水玻璃砂性能的因素,并且对新型水玻璃酯硬化自硬砂和呋喃树脂自硬砂进行了经济效益对比分析.     

Controlled cooling of an aluminum alloy casting based on 3D printed rib reinforced shell mold

3D printing technology has been used for sand molding and core printing, but they simply substitute the traditional molding and core making method without changing the shape or size of the sand mold(core) and their dense structure. In this study, a new type of hollow mold based on 3D printing is presented. The new type of mold is a rib reinforced thickness-varying shell mold. This mold design can realize the controlled cooling of castings, i.e., different cooling rates at different areas, and improve the temperature uniformity of a casting after its solidifi cation. Therefore, the performance of castings can be improved and their residual stress and deformation can be reduced. This kind of new mold was applied to a stress frame of A356 aluminum alloy. The 3D printed rib reinforced thickness-varying shell mold was compared with the traditional dense mold, and the castings obtained by these two kinds of molds were also compared. The experimental results showed that the rib reinforced shell mold increased the cooling rate of the casting by 30%, tensile strength by 17%, yield strength by 11%, elongation by 67%, and decreased its deformation by 43%, while sand consumption was greatly reduced by 90%.     

树脂砂自动控制仪的研制与应用

为彻底解决呋喃树脂砂生产中砂温波动对固化速度的影响,研发了树脂砂自动控制仪.为满足仪器的要求,对自控仪专用液料进行了开发与研制.结果表明,新型吠喃树脂及其配套的快慢固化剂能很好地适用于该自控仪,且适用生产的砂温和起模时间的范围较大,固化剂与树脂保持最佳配比,较低加入量就能得到较高砂型强度,经济效益显著.     

便携式扫描仪在3D打印砂芯精度测量中的应用

为确保能快速测量、分析3D打印砂芯从而得出合适的打印工艺参数,本文分析了原砂粒度与粒形、黏结剂覆膜与渗透对打印砂芯精度的影响,介绍了扫描仪测量误差的影响因素。通过对便携式扫描仪所测量的砂芯精度尺寸的分析,提供合适的修正参数,从而生产出符合要求的高精度砂芯,也印证了便携式扫描仪能够在砂芯精度测量中广泛使用。     

B81D缸体气孔、砂眼缺陷的防止措施

介绍了B81D缸体的铸件结构及原生产工艺,分析气孔、砂眼等缺陷的产生原因,最终通过采用低发气量的FS粉;将树脂加入量降至1.4%;在边芯上增加省砂块,减轻曲轴箱砂芯质量;增加3根明通气针,并增大部分排气针尺寸,增设通气针之间排气通道;增大内浇道的圆滑过渡,使气孔缺陷得以解决。通过减少排气孔内残留型砂,使用风管吹扫,减少型砂掉入型腔的几率;取消部分顶芯杆和通气塞;适当提高CE;在第七轴承增设内浇道;在有可能的前提下,对该部位进行适当加厚,并规范清理标准,使砂眼缺陷得以解决。     

Binder jetting 3D printing process optimization for rapid casting of green parts with high tensile strength

Binder jetting 3D printing is a rapid, cost effective, and efficient moulding/core making process, which can be applied to a large variety of materials. However, it exhibits a relatively low green-part strength. This may cause the collapse of the printed parts during de-caking and the pick-up procedure, especially in the case of small-scale structures, such as thin walls, tips, and channels. In this work, polyvinyl alcohol (PVA) was used as the additive in coated sand powder. By exploiting the binding effect between the two composites (thermoplastic phenolic resin and PVA) triggered by the binder, bonding necks firmly form among the sand particles, improving the green-part strength of the coated sand printed parts. Experiments based on the Taguchi method were used to investigate the relationship between the process parameters and the green-part tensile strength. The following set of optimal process parameters was identified:50wt.% alcoholicity of the binder, 75% binder saturation, 0.36 mm layer thickness and 4.5wt.% PVA content. Further, the effect of such parameters on the green-part tensile strength was determined via statistical analysis. The green part of an engine cylinder head sand pattern with complex cavity structures was printed, and the green-part tensile strength reached 2.31 MPa. Moreover, the ZL301 aluminum alloy impeller shape casting was prepared using sand molds printed with the optimal process parameters. The results confirm that the proposed binder jetting 3D printing process can guarantee the integrity of the printed green parts and of small-size structures during decaking and the pick-up procedure. Furthermore, the casting made from the printed sand molds exhibits a relatively high quality.