Forming is used to obtain internally homogeneous and dense ceramic blanks and is an important part of the preparation process for aluminum nitride ceramics, since the forming technology for structural ceramics largely determines the homogeneity of the blanks and the ability to prepare complex-shaped parts, and directly affects the reliability of the ceramic material and the efficiency and cost of manufacturing ceramic parts. Defects caused by the forming process are often the main defects of ceramic materials. In general, ceramic blanks with high uniformity and high density as well as near net dimensions can effectively reduce the sintering temperature and blank shrinkage, speed up the densification process, and reduce the subsequent machining of the product.
There are several molding processes for aluminum nitride ceramics: dry press molding, isostatic molding, cast molding, injection molding, etc.
Dry Press Forming
Dry pressing is the most widely used molding process, with the main advantage of high molding efficiency. It is particularly suitable for the preparation of ceramic products with small cross-sectional thicknesses, such as ceramic sealing rings, ceramic valve spools, ceramic plates and ceramic parts with complex two-dimensional shapes.
The process is to fill the metal die cavity with granulated material with good fluidity after spray granulation, and apply pressure through the pressure head, which moves in the die cavity, and the powder in the cavity is rearranged by the pressure head force, and the gas is discharged from the space between the particles to form a ceramic blank with certain strength and shape.
The common defects of dry press molding are delamination, cracks, surface flaking, etc. The generation of delamination and cracks is mainly due to the uneven distribution of axial pressure, resulting in inconsistent elastic response of the various parts of the billet during demolding. The main reasons for the inconsistent elastic response of the various parts inside the billet are:
1) the stress gradient caused by the friction of the mold wall inside the billet;
2) the low strength of the material and the low binder content;
3) the mold wall The surface is not smooth or poor lubrication leads to delamination caused by the resistance during mold release.
Defects improvement measures:
1) high mold finish to reduce frictional resistance;
2) the use of bi-directional pressing to reduce the pressure difference between the upper and lower parts;
3) the use of appropriate strength binder to improve its ability to resist elastic recovery;
4) the addition of lubricant to the powder to improve the frictional effect between the particles and the frictional resistance with the mold wall, while obtaining high density.
Advantages: dry compression molding method is simple to operate, with few process steps and high efficiency.
Disadvantages: it is not possible to press complex geometry of the blank; it is necessary to strictly control the pressure, too large or too small is not conducive to obtain high density AlN ceramic sintered parts.
●Dorst, SMS Meer, Komage, Schuler, Germany
●Tamagawa, Ryotsuka, Japan
●China Steel Research Technology Group Co.
●Sichuan Aviation Industry Chuanxi Machinery Co.
●Ningbo Huizhong Powder Machinery Manufacturing Co.
●Tian Tong Ji Cheng Machine Technology Co.
●Ningbo Jingda Machinery Manufacturing Co.
Isostatic molding is a method of forming the powder in closed molds with uniform pressure in all directions at the same time. It uses liquid or gas as the pressure transfer medium, which can make the pressure transfer uniformly to all directions of the blank, so as to obtain a uniform density of the formed blank.
Isostatic molding requires pretreatment of powder, improving the fluidity of powder through granulation process, adding binder and lubricant to reduce the friction within the powder, improving the bond strength and meeting the requirements of molding process.
Isostatic molding process has the characteristics of uniform product structure, high density, low sintering shrinkage, low mold cost and high production efficiency. It is mainly used for forming large-size tubes, rods and blocks, and is also applied to cold isostatic pressing after wrapping the products after dry pressing forming to further improve the density of the billet.
Currently, large size aluminum nitride ceramic discs are dry pressed into regular shapes and then cold isostatically pressed to further improve the density and density distribution of the billet, reduce warpage and dimensional instability caused by uneven density distribution during the sintering process, and improve product quality.
Advantages: Higher density of the billet, uniform density distribution, and near net size forming.
Disadvantages: The molding equipment is expensive, and there are problems with demolding, which limits the large-scale industrial production.
● ASEA, Sweden
●Zhejiang Delong Technology Co.
●Taiyuan Zhongping Technology Co.
●Shanxi Golden Open Source Industry Co.
●Sichuan Aviation Industry Chuanxi Machinery Co.
●Sichuan Sohaipu Isostatic Technology & Equipment Co.
●Shanghai Haopu Lisheng Hydraulic Electromechanical Manufacture Co.
●Chengdu Junsui Technology Co.
●Beijing Erlinvicor Furnace Technology Co.
Cast molding refers to the addition of solvent, dispersant, binder, and plasticizer components to ceramic powders, which are ground and mixed to obtain a uniformly dispersed stable slurry. The slurry requires a flowing slurry with pseudoplastic fluid properties without thixotropy to prevent fluctuations in viscosity during the molding process. The slurry is defoamed under vacuum and then cast on the cast machine. By controlling the movement rate of the substrate, the slurry is rapidly passed through the lower surface of the scraper under the shear force of the scraper, forming a certain thickness of cast film on the substrate, then dried to remove most of the solvent, then the film is separated from the tape, the cast film is cut, laminated, glued, sintered and the ceramic is obtained.
According to the choice of solvent different from the military, cast molding is divided into organic cast system and water-based cast system two categories.
Organic cast molding solvents are mostly ethanol, acetone, butanone, toluene, xylene, etc. The most common is ethanol - methyl ethyl ketone, ethanol - trichloroethylene, xylene - ethanol, trichloroethane - acetone and other binary or ternary azeotropes. The volatilization rate of each component in the azeotropes is the same, so the same stoichiometric ratio can be maintained during the drying process to avoid precipitation in advance during the drying process due to a certain organic additive dissolved in only one solvent.
Water-based cast molding uses water as a solvent, which is less costly and environmentally friendly. However, due to the higher surface tension of water, the ball milling process is easy to produce bubbles, poor wettability of the powder, high viscosity of the slurry, bubbles in the blanks are easily produced inside the blanks, evaporation of the drying process requires higher heat, and the channel volume required for evaporation is larger than that of organic solvents. The most critical is the reaction with easy hydrolysis materials such as aluminum nitride powder, making the application of water-based flow delay in the production of aluminum nitride ceramic substrates is limited, the need to improve the resistance to hydrolysis of aluminum nitride powder, before it is possible to use water-based flow delay system for the production of aluminum nitride substrates.
The main advantage of cast molding is the ability to prepare large, thin, flat ceramic sheets, while other methods to manufacture large thin sheets are more difficult. For example, in the dry pressing process, uneven mold filling makes holes and uneven density distribution in the flakes, and deformation after sintering.
The current multilayer ceramic devices require the realization of multilayer circuit, through the substrate on the hole, the hole inside the metalization, can realize the interconnection and conduction of multilayer ceramic circuit, currently applied to the electronic packaging industry, the vast majority of aluminum nitride ceramic substrates using the flow delay method of production.
Advantages: simple equipment, continuous operation, high productivity, high degree of automation.
Disadvantages: Strict requirements, the slurry is very sensitive to changes in process parameters; molding blank surface roughness and insufficient bonding, low strength, easy to blistering and cracking, bending and deformation during the drying process; at the same time, the flow casting can only be used for the production of sheet materials.
● Slovenia KEKO Equipment Ltd
●U.S. HED International inc.
●Japan Yokoyama Manufacturing Co.
●Beijing Oriental Taiyang Technology Co.
●Wuhan Kunyuan Flow Delay Technology Co.
●Zhaoqing Honghua Electronic Technology Co.
●Xi'an Xinyi Electronic Technology Co.
●Zhoushan Jinqiu Machinery Co.
●Zhejiang Delong Technology Co.
●Dongyang Shengberlin Special Equipment Technical Service Co.
was established in June 2001, is a national high-tech enterprise specializing in the research and development, production and operation of ultra-precision grinding and polishing materials in China, and is a pioneer in the industry
Welcome to visit and consult us ！！！
With specialized, serialized and
matching and customized products.
Precise service to help customers succeed!
【Precision Polishing Nano Material Expert--Grish 】
【Specializing in precision grinding & polishing for 20 years】