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Basic Process Steps of Best Precision Metal Powder Injection Molding

time:2020-04-21Views:174 Author:Best Seiko

金属粉末注射成形的基本工艺步骤是:首先是选取符合MIM要求的金属粉末和粘结剂,然后在一 定温度下采用适当的方法将粉末和粘结剂混合成均匀的喂料,经制粒后在注射成形,获得的成形坯经过脱脂处理后烧结致密化成为终成品。

1.MIM粉末及制粉技术

  MIM对原料粉末要求较高,粉末的选择要有利于混炼、注射成形、脱脂和烧结,而这往往是相互矛盾的,对MIM原料粉末的研究包括:粉末形状、粒度和粒度组成、比表面等,表1中列出了适合于MIM用的原料粉末的性质。

  由于MIM原料粉末要求很细,MIM原料粉末价格一般较高,有的甚至达 到传统PM粉末价格的10倍,这是目前限制MIM技术广泛应用的一个关键因素,目前生产MIM用原料粉末的方法主要有羰基法、超 高压水雾化法、高压气体雾化法等。

2.粘结剂 

  粘结剂是MIM技术的核 心,在MIM中粘结剂具有增强流动性以适合注射成型和维持坯块形状这两个基本的职能,此外它还应具有易于脱除、无 毒性、成本合理等特点,为此出现了各种各样的粘结剂,近年来正逐渐从单凭经验选择向根据对脱脂方法及对粘结剂功能的要求,有针对性地设计粘结剂体系的方向发展。

  粘结剂一般是由低分子组元与高分子组元加上一些要的添加剂构成。低分子组元粘度低,流动性好,易脱去;高分子组元粘度高,强度高,保持成形坯强度。二者适当比例搭配以获得高的粉末装载量,终得到高 精 度和高均匀性的产品。

3.混炼 

  混炼是将金属粉末与粘结剂混合得到均匀喂料的过程。由于喂料的性质决定了终注射成形产品的性能,所以混炼这一工艺步骤非 常重要。这牵涉到粘结剂和粉末加入的nents to make them melt, then cool, add low melting point components, and then add metal powder in batches. This prevents the low melting point components from vaporizing or decomposing, and adding metal powder in batches can prevent excessive torque increase and equipment loss. For the feeding method of powders of different sizes, the Japanese patent introduces: first add the coarser 15-40um water atomized powder to the binder, then add 5-15um powder, and then add the powder with degree ≤5um. The shrinkage of the final product changes little. In order to evenly coat a layer of binder around the powder, it is also possible to directly add the metal powder to the high melting point componenadictory. Research on MIM raw material powders includes: powder shape , Particle size and particle size composition, specific surface, etc., Table 1 lists the properties of the raw material powder suitable for MIM. Due to the very fine requirements of MIM raw material powders, the prices of MIM raw material powders are generally higher, and some even reach 10 times the price of traditional PM powders. This is currently a key factor restricting the widespread application of MIM technology. The current methods for producing MIM raw material powders are mainly There are carbonyl method, ultra high pressure water atomization method, high pressure gas atomization method, etc. 2. Binder Binder is the core of MIM technology. In MIM, the binder has two basic functions of enhancing fluidity to be suitable for injection molding and maintaining the shape of the billet. In addition, it should have easy removal and no Due to its toxicity and reasonable cost, a variety of adhesives have appeared for this purpose. In recent years, it has gradually moved from the selection of experience alone to the design of adhesives in accordance with the requirements of degreasing methods and the function of adhesives. The development of the agent system.   The binder is generally composed of low molecular components and high molecular components plus some essential additives. Low-molecular components have low viscosity, good fluidity and easy to take off; high-molecular components have high viscosity and high strength to maintain the strength of the formed blank. The two are matched in an appropriate ratio to obtain a high powder loading, and finally a product with high accuracy and uniformity is obtained. 3. Kneading     Kneading is the process of mixing metal powder and binder to obtain a uniform feed. Because the nature of the feed determines the performance of the final injection molded product, this process step of mixing is very important. This involves the addition of binders and powders

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