Injection molding,debinding and sintering of ZrO2 ceramic modified by silane couping agent

In this paper, Injection molding, debinding and sintering of ZrO₂ ceramic modified by silane coupling agent (A151) were studied by measuring the melt index of feedstocks, the soluble removal ratio of green parts, the bending strength of green and sintered parts, the surface and fractural morphologies of sintered parts. The results showed that the melt index of ZrO₂ feedstocks, the weight removal ratio of soluble binders, and the bending strength of green parts increased after adding A151. When the density of sintered parts was between 5.97–6.03 g/cm³, it was not the main factor influencing the bending strength. However, the bending strengths of sintered parts decreased due to microcrack formation when thermal debinding process was too fast or slow. The interesting phenomenon of the abnormal grain growth with transgranular fracture in the sintered parts obviously occurred above 1550 ℃, which made the effect of sintering temperature on the strength become complex.     

Yttria stabilized zirconia formed by micro ceramic injection molding: Rheological properties and debinding effects on the sintered part

Micro Ceramic Injection Molding (μCIM) is a near net-shape process to produce smaller and intricate parts at a competitive cost. The application of nano-sized ceramic powder in μCIM has the advantages of fine grain size growth and good surface finish. However, the nano size effect causes agglomeration and low powder loadings, which result in defects during the μCIM process and in the sintered components. This study extensively investigated the debinding and sintering of yttria-stabilized zirconia (YSZ), as well as its rheological properties, using polypropylene (PP) as the primary binder and palm stearin as the secondary binder. 50 nm Yttria stabilized zirconia (YSZ) powders were mixed with palm stearin and PP at a powder loading of 37–43 vol%. The results of rheological studies showed that the feedstock had a dilatant flow characteristic and a viscosity of around 10–40 Pa s. Feedstock with 38 vol% powder loading had the lowest activation energy of 9.48 kJ/mol. The green part of the injected feedstock had flexural strength ranging from 13 to16 MPa, within which the feedstock with 43 vol% powder loading had the highest green density. Solvent debinding was carried out at three temperatures (50, 60, and 70 °C) using heptane. A large porous region was clearly identified at 70 °C compared with 50 °C. A debinding split furnace with argon gas was used to remove PP at 450 °C for 4 h. The debound samples did not shrink when 94%–98% of the binder system was removed. All debound samples sintered at 1350 °C and 41 vol% had the highest mechanical properties with hardness of 900 HV and a flexural strength of 400 MPa.     

Supercritical Carbon Dioxide debinding in metal injection molding (MIM) process

The conventional debinding process in metal injection molding (MIM) is critical, environmentally unfriendly and time consuming. On the other hand, supercritical debinding is thought to be an effective method appropriate for eliminating the aforementioned inconvenience in the prior art. In this paper, supercritical debinding is compared with the conventional wicking debinding process. The binder removal rates in supercritical CO₂ have been measured at 333.15 K, 348.15 K, and 358.15 K in the pressure range from 20 MPa to 28 MPa. After sintering, the surface of the silver bodies were observed by using SEM. When the supercritical CO₂ debinding was carried out at 348.15 K, all the paraffin wax (71 wt% of binder mixture) was removed in 2 hours under 28 MPa and in 2.5 hours under 25 MPa. We also studied the cosolvent effects on the binder removal rate in the supercritical CO₂ debinding. It was found that the addition of non-polar cosolvent (n-hexane) dramatically improves the binder removal rate (more than 2 times) for the paraffin wax-based binder system. This paper is dedicated to Dr. Youn Yong Lee on the occasion of his retirement from Korea Institute of Science and Technology.     

Rheological and thermal debinding behaviors of silicon nitride in powder injection molding

In powder injection molding process, it is important to analyze the rheological and thermal debinding behaviors of feedstock, because they can directly affect the final quality of products. Therefore, for the silicon nitride based feedstocks, the rheological and thermal debinding behaviors were investigated and compared between feedstocks prepared with the combination of two types of powders and sintering aid ratios. At first, the optimal solids loading for each feedstock was determined based on the results of the torque rheometer experiment. The viscosity of the feedstocks was measured using the capillary rheometer, and rheological properties were evaluated with the Power Law-Arrhenius model. Silicon nitride (JPN) feedstock with 5 wt% yttria and 2 wt% alumina (JPN+5Y2A) had the highest moldability index among all feedstocks. The powders with sintering aid ratio of 5 wt% yttria and 2 wt% alumina made the feedstocks have a high moldability index. Thermogravimetric experiment was also performed to analyze the pyrolysis behavior of the feedstocks, and the apparent activation energies for each feedstock were obtained using Kissinger method with the thermogravimetric analysis results. Based on the results, the master decomposition curve (MDC) was developed, and the utility of MDC for optimizing the thermal debinding process was verified.     

薄壁塑件注射成型翘曲变形的工艺优化

本文以注射成型照相机前壳为研究对象,以注塑成型中的翘曲量为优化目标,利用正交试验结合CAE模拟技术,研究模具温度、熔体温度、注射时间、保压时间、保压压力和冷却时间对制品翘曲的影响规律。用均值分析法得到最小翘曲变形的一组优化工艺参数组合,并进行CAE模拟验证。再运用方差分析确定各个工艺参数对翘曲变形的影响程度。     

薄壁塑件注射成型翘曲变形的工艺优化

本文以注射成型照相机前壳为研究对象,以注塑成型中的翘曲量为优化目标,利用正交试验结合CAE模拟技术,研究模具温度、熔体温度、注射时间、保压时间、保压压力和冷却时间对制品翘曲的影响规律。用均值分析法得到最小翘曲变形的一组优化工艺参数组合,并进行CAE模拟验证。再运用方差分析确定各个工艺参数对翘曲变形的影响程度。     

两厢后灯体多级注塑工艺

根据两厢后灯体的使用要求,本文通过对该产品要求的描述,采用多级注塑工艺进行加工,解释材料、设备等选择,特别是产品注塑位置采用欠充注射法来确定,就注塑成型工艺等参数对产品影响等方面提出一些具体的看法和介绍。多级注塑工艺经生产实践验证,参数设置合理,操作可行,能保证产品质量,产品能得到用户的认同。     

YN5前灯装饰圈注塑工艺研究

YN5前灯装饰圈采用PBT(增强)加工,本文通过对该产品要求的描述,就注塑成型工艺等提出一些具体的看法和介绍。注塑工艺经生产实践验证,参数设置合理,操作可行,能保证产品质量,产品能满足使用要求。     

激车后灯外罩注塑工艺优化

灯具外罩通常用透明PMMA制作,外罩采用两次注塑成型,先做成嵌件,然后把嵌件放在男一副模具中注塑合成,通过对嵌件、外罩注塑成型工艺等的介绍,围绕外罩产品特点,进行产品重量的控制,用重量控制法达到产品质量。经生产实践验证,用重量控制法优化工艺能满足外罩成型要求,符合生产需要操作简便可行,产品能得到用户的认同。     

Surface modification of ceramic powders by titanate coupling agent for injection molding using partially water soluble binder system

In the conventional process of ceramic injection molding (CIM), wax-based binders could only be removed by thermal or organic solvent debinding. Recently, water solvent debinding, with its high efficiency and environmental acceptability, has appeared as a good alternative. In this study, zirconia powder modified by titanate coupling agent was applied in partially water soluble binder system for injection molding. In contrast to previous researches about titanate modification mainly focusing on rheological behavior and modification mechanism, investigations on the sintering behavior and densification process were also made in this study. Experimental results reveal that titanate modified powder exhibits densification temperature almost 100 °C lower than that required for the pure, original powder, giving rise to finer microstructure and therefore hopefully improved mechanically properties. It suggests a novel modification route to fabricate injection molded ceramic components using partially water soluble binder system.     

后灯遮光罩浇口改进及注塑工艺设定

后灯遮光罩是用Bayer公司共聚碳酸脂Apec料制造,通过对Apec与标准PC作工艺比较和介绍,围绕遮光罩产品特点,对原来的浇口两点进料改为一点进料,进行必要注塑成型加工射胶量计算和工艺调整,并对成型工艺进行介绍。经生产实践验证,工艺参数设定符合生产需要,操作可行,遮光罩产品能得到用户的认同。     

Influence of feedstock preparation on ceramic injection molding and microstructural features of zirconia toughened alumina

Feedstocks for ceramic injection molding of ZTA containing 90 vol.% of sub-μm alumina and 10 vol.% of zirconia nanopowder were prepared by different processing techniques. Feedstocks were prepared by mixing in a sigma-blade kneader and subsequent homogenizing by twin-screw extrusion or shear roll compaction. Two other feedstocks were previously bead milled and subsequently processed by the same procedure. Compounding technology strongly influences the injection molding behavior and microstructures of the final product. Despite higher energy input of the shear roll compactor, powder agglomerates cannot be completely avoided. Pre-milling is effective to disperse and deagglomerate ceramic powders. Injection pressures of feedstocks from pre-milled powders were about 200 bar lower compared to pressures needed for non-milled feedstocks. Present feedstock preparation methods are feasible to produce homogeneous feedstocks, which strongly influence microstructures. In order to produce high solid loaded sub-μm/nm feedstocks, processing methods, pre-treatment and solid content have to be carefully chosen.     

Densification and mechanical properties of boron carbide with micro-hole array by micro-powder injection molding

For the purpose of obtaining fully dense B₄C with micro hole array of high quality and precision, synthesis of B₄C powders were carried out by micro powder injection molding. Five kinds of additive systems were used and their influences on mechanical properties were investigated. The relative density, Vickers hardness, bending strength, and fracture toughness of the B₄C ceramics with BS10AY additive sintered at 2000 °C for 2 h could reach 97.56%, 3580.4 HV, 355.3 MPa and 5.87 MPa m^1/2, respectively. The temperature was generally 100–200 °C lower than reported temperatures which was attributed to the additives. The improvement in mechanical properties was attributed to grain refinement. A mixture of intragranular and transgranular fractures occurred due to the fine microstructures and the additive systems in the B₄C ceramics after sintering. Micro-hole array with the diameter of 450 μm and the length-diameter ratio of more than 8 were obtained. The inhomogeneous filling of feedstock from the substrate to the thin wall between two adjacent micro holes caused the inhomogeneous shrinkage of the substrate and micro holes.     

BP神经网络在注射成型工艺参数优化中的作用

本文研究的是注射工艺参数对塑件翘曲变形的影响。通过CAE模拟计算,以工艺参数为输入参数,以翘曲量为输出参数,构建BP神经网络模型。以CAE分析结果作为训练样本和检测样本,分析BP神经网络在工艺参数优化方面的作用。     

Multi-material ceramic material extrusion 3D printing with granulated injection molding feedstocks

Material Extrusion (MEX) is an advanced technology for polymer 3D printing and countless printers are commercially available. MEX has also been demonstrated for ceramics. For that purpose, thermoplastic binders are filled with high loads (>40 vol%) of a ceramic powder. The printed parts are subsequently debound and sintered. In contrast to most MEX printers, the ceramic printer presented herein works with granulated feedstock instead of filaments. Therefore, the development of novel feedstocks is faster and more straightforward since the challenges associated with filament production are omitted. Furthermore, commercial ceramic injection molding (CIM) feedstocks can be used which allows fast prototyping with the same material that is later used in high-quantity industrial production by CIM.In this study, a method to fabricate multi-material ceramic parts using a granulate-fed printer is presented. Examples of multi-material printing include colored ZrO₂ parts as well as ceramic high-temperature heating elements in various shapes consisting of an electrically conductive and a non-conductive component. Light- and electron microscopy confirms that the layer adhesion before and after sintering is flawless, even between different materials if the material combination is chosen carefully. All feedstocks are based on a commercially available CIM binder filled with the desired ceramic powder. Consequently, the feedstock preparation as well as optimizing of debinding and sintering conditions are simple and reproducible.     

Injection molding of ceramic cutting tools for wood-based materials

In this study a mutable mold for ceramic cutting tools with inserts of different cutting angles and two different injection positions was designed. Three alumina-based ceramic feedstocks with different types and amount of second phases were developed. A mold filling study was carried out for both sprue positions in order to prove the molding behavior of the feedstock and the functionality of the mold. Debindering and sintering of molded green parts was arranged for each composition, respectively. Mechanical properties, microstructure and achieved cutting edge sharpness of produced tools were investigated. Results show that the mold design and injection molding process play a key role in order to manufacture cutting tools of best possible sharpness enabling a wood machining process. Feedstocks exhibit a good mold filling behavior resulting in comparatively sharp cutting edges of ≈10 μm after sintering. Mechanical properties show high potential for application of wood machining cutting tools.     

基于正交试验和MPI二次开发技术多目标优化注射工艺参数

工艺条件是影响注射成型制品质量的重要因素,采用CAF模拟软件进行注射成型的工艺优化不但能降低成本,提高效率,而且能提高注射制品的质量。本文通过MPI二次开发技术开发出注射成型工艺方案优选分析器,采用正交试验方法为用户提供多目标值下的最优工艺参数组合,进一步提高了工艺优化的效率,也为用户提供了实用方便的工艺优化工具。     

Effects of the binder compositions on the homogeneity of ceramic injection molded compacts

In this study, the effects of different binder compositions on the homogeneity of injection molded ceramic compacts are discussed from the standpoint of the rheological properties of the feedstocks, density, density deviation, and flexural strength of the as-prepared compacts, and the microstructures of the as-prepared compacts, compacts after solvent debinding, and compacts after thermal debinding. Also the pore size distribution of the compact after thermal debinding was characterized to examine the distribution of the binders in the as-prepare compacts. The feedstock with 30% macromolecular binders attains the minimum power-law index n value at 160 °C, hence it is the most appropriate feedstock for injection molding. The optimal composition is feedstock B30, which is the most homogeneous at an injection temperature of 160 °C. The macromolecular binder-to-PW weight ratio of 3:7 allows best mixing of feedstock and more homogeneous binder distribution. B30 has the highest density, the lowest density deviation and the lowest deviations in flexural strength of the as-prepared compact. Compacts prepared with B30 have the most homogenous pore size distribution after thermal debinding, as determined from the sharp, narrow peaks on the pore size distribution curves.     

Improved infinite horizon LQ tracking control for injection molding process against partial actuator failures

Focusing on injection molding processes with partial actuator failures, a new design of infinite horizon linear quadratic control is introduced. A new state space process model is first derived through input–output process data. Furthermore, an improved infinite horizon linear quadratic control scheme, whereby the process state variables and tracking error can both be regulated separately, is proposed to show enhanced control performance against partial actuator failures and unknown disturbances. Under the circumstances of actuator faults, the closed-loop system is indeed a process with uncertain parameters. Hence, a sufficient condition is proposed to guarantee robust stability is presented using Lyapunov theory. The proposed concepts are illustrated in an injection velocity control case study to show the effectiveness.