After sintering metal injection molded products, due to various reasons, the surface smoothness is relatively rough, with slight burrs, and there may be small stainless steel powder particles adhering to the surface of the product. In order to achieve surface smoothness (some products even require mirror effect, such as smartphones, logos on them, and brackets on laptops) and deburring requirements, surface treatment processes such as grinding, polishing, sandblasting, PVD, etc. are often added. With the rapid development of consumer electronics in recent years, it has driven the growth of the MIM industry, as well as the development of industries such as post-processing, polishing, and grinding.

One Types of materials that MIM needs to polish

Generally, MIM metal materials are divided into two categories (iron-based and stainless steel materials), with stainless steel materials (316L/17-4PH) having a wider range of applications

316 material is the preferred star material for MIM appearance parts due to its unique properties. Stainless steel is a high alloy steel that can resist corrosion in air or chemical corrosive media. Stainless steel has an elegant appearance and good corrosion resistance, and does not require surface treatment processes such as plating to exert its inherent appearance properties. It is commonly used in various types of steel and is commonly referred to as stainless steel. From a metallographic perspective, stainless steel contains chromium, which forms a very thin chromium film on the surface. This film acts as a barrier to prevent corrosion from the invading oxygen inside the steel. In order to maintain the inherent corrosion resistance of stainless steel, the steel must contain at least 12% chromium.

II The commonly used polishing methods currently include the following:

2.1 Mechanical polishing

Its advantage is good flatness and high brightness of the processed parts. Its defects are high labor intensity, severe pollution, inability to process bulky parts, inconsistent gloss, short gloss maintenance time, stuffiness, and rust. Comparatively suitable for processing simple parts, medium and small products.

Mechanical polishing is a polishing method that obtains a smooth surface by cutting and plastic deformation of the material surface to remove the convex parts after polishing. Generally, oilstone strips, wool wheels, sandpaper, etc. are used, and manual operation is the main method. For special parts such as the surface of rotating bodies, auxiliary tools such as turntables can be used. For those with high requirements for surface quality, ultra precision grinding and polishing can be adopted. Ultra precision polishing is a special grinding tool that is pressed tightly against the surface of the workpiece being processed in a polishing solution containing abrasives, and undergoes high-speed rotational motion. This technology can achieve a surface roughness of Ra0.008 μ m, which is the highest among various polishing methods. This method is commonly used for optical lens molds.

2.2 Chemical polishing

Its advantages include low investment in processing equipment, the ability to dispose of large and miscellaneous items, fast speed, high efficiency, and good corrosion resistance. Its shortcomings are poor brightness, gas leakage, the need for ventilation equipment, and difficulty in heating. Suitable for processing small batches of bulky and miscellaneous items, as well as products with low brightness requirements for small parts.

Chemical polishing is the process of allowing the macroscopic protruding and concave parts of a material to dissolve preferentially in a chemical medium, resulting in a smooth surface. The important advantage of this method is that it does not require bulky equipment and can polish workpieces with complex shapes. It can polish many workpieces at the same time and has high efficiency. The core issue of chemical polishing is the preparation of polishing solution. The surface roughness obtained by chemical polishing is generally around 10 μ m.

2.3 Magnetic Grinding and Polishing

Magnetic grinding and polishing is the process of using magnetic abrasives to form abrasive brushes under the action of a magnetic field for grinding and processing workpieces. This method has high processing efficiency, good quality, easy control of processing conditions, and good working conditions.

At present, the main polishing methods for parts produced by MIM technology are still magnetic grinding polishing and mechanical polishing. After polishing, PVD treatment is generally required, which can be made into different colors. The main purpose is to improve the appearance, decorative performance, and color of the workpiece, while making it more wear-resistant, corrosion-resistant, and extending its service life; The most widely used field currently is consumer electronics.

3.Factors affecting polishing process

3.1 The influence of different hardness on polishing process

The increase in hardness makes grinding more difficult, but the roughness after polishing decreases. Due to the increase in hardness, the polishing time required to achieve lower roughness correspondingly increases. At the same time, as the hardness increases, the possibility of excessive polishing decreases accordingly.

3.2 Density

The purity of the material, powder particle size, and sintering density are also key factors affecting polishing. During sintering, the material density needs to be controlled within a reasonable range in order to achieve the polishing effect. Improper density control can result in defects such as sand holes and pitting

4、 Sandblasting is a method of cleaning the surface of parts by using compressed air to blow quartz sand out at high speed

In the factory, it is also called sandblasting, which not only removes rust but also removes oil, which is very useful for painting. Commonly used for rust removal on the surface of parts; Surface modification of parts (this is the purpose of small wet sandblasting machines sold in the market, where the sand particles are usually corundum and the medium is water); In steel structures, the application of high-strength bolts for connection is a relatively advanced method. As high-strength connections use friction between the joint surfaces to transmit force, the quality requirements for the joint surface are very high. In this case, sandblasting must be used to treat the joint surface.

Sandblasting is used for complex shapes, easy manual rust removal, low efficiency, poor on-site environment, and uneven rust removal.

Most sandblasting machines have various specifications of sandblasting guns, and as long as the box is not particularly small, the gun can be put in and cleaned.

Sandblasting is also one of the most common surface processing techniques for MIM products.

Shenzhen Yujiaxin Tech. Co., Ltd., as a leading metal processing expert in the industry, leverages its exceptional metal powder injection molding technology to provide high-quality, high-precision customized products and services across multiple sectors, including medical, industrial, consumer electronics, household, and smart technology. The company not only emphasizes technological innovation and process optimization but also commits to fulfilling the diverse needs of clients, ensuring that every product meets the highest industry standards. This has earned it widespread praise and trust from both domestic and international customers.