Introduction of MIM Process
Firstly, solid metal and organic binder are mixed evenly to get the feed. In the state of heating plasticization (about 150 C), injection moulding machine inject the feed into the mould cavity to obtain the injection moulding blank and solidified. Then the binder in the injection blank must be removed by chemical or thermal decomposition method. Finally, the product is sintered and densified by vacuum furnace. Some products which need post-process to obtain the final shape and properties.
In short, MIM process steps are:
Mixture-injection moulding-debonding-sintering-post-treatment-products
Design Principles of MIM Products
The wall thickness is uniform.
Sintering support;
Avoid sharp corners and arc transition.
Designable holes and grooves;
Concave and subsidence can be designed.
Designable threads;
Consider reinforcing bars and connecting walls.
It can be designed to roll, print and engrave trademarks.
Select the shape and position of the inlet and outlet;
Pay attention to pits and weld marks.
Surface coating or electroplating;
Heat treatment;
Post processes.
Metal injection molding (MIM), as a near net forming technology for manufacturing high quality precision parts, has incomparable advantages over conventional powder metallurgy, machining and precision casting methods.
–The size shrinkage of raw material powders is usually 1-20 microns, ranging from injection embryo to sintered embryo, which can reach about 16%-20% depending on the material.
–Small metal parts with complex shapes (usually 0.1-200 g in size) can be produced as plastic injection molding.
–Each part of the workpiece has uniform structure and good density. The density can reach 95%-99% of the theoretical density. It can be carburized, quenched, tempered and other heat treatments. Some parts with high dimensional accuracy can also be processed by CNC machining.
–The dimension accuracy of the product can reach +/-0.1-0.5%. The surface is smooth and the one-time accuracy can reach Ra1.6.
–The product quality is stable and the production efficiency is high. In the case of mass and large-scale production, the cost can be greatly reduced.
–Basic principles of MIM product design: Select the shape and position of inlet and outlet, uniform wall thickness, avoid sharp corners, arc transition, design holes and grooves, design concave and sagging, design threads, consider reinforcing ribs and connecting walls, design knurling, printing, engraving trademarks, consider sintering support, pay attention to concave and weld marks, surface coating or coating, heat treatment, secondary processing. Etc.
–MIM parts usually do not need to be machined again unless there are special requirements. MIM technology has large advantages for materials like tungsten alloy and cemented carbide which are hard to process. MIM parts can also be hardened, such as nickel plating, hard chromium plating and other surface treatment processes can be used.
Process advantages
The particle size of raw materials used in MIM is 2-15 urn, while that of traditional powder metallurgy (PM) is 50-100 urn. Fine powder enable MIM to make high density parts. MIM can also make complex shape parts which PM cannot.
The traditional investment casting (IC) is a very effective technology for making complex shape products. In recent years, the ceramic core assistant can be used to complete the products with slits and deep holes. However, due to the strength of the ceramic core and the limitation of the fluidity of the casting liquid, this process still has some technical problems. Generally speaking, this process is more suitable for manufacturing large and medium-sized parts, while MIM process is more suitable for small and complex parts, and the material quality of IC process is limited.
Die casting process is suitable for materials with low melting point and good castability, such as aluminium and zinc alloys, while MIM process is suitable for all kinds of materials.
Precision forging can form complex parts, but it cannot form three-dimensional complex small parts. The precision of the products is low and the products ranges are limited.
Traditional CNC machining: Recently, automation and numerical control have been used to improve the processing ability, and great progress has been made in efficiency and accuracy. However, the basic steps are still inseparable from the gradual processing of parts such as turning, planer, milling, grinding, drilling and throwing. The accuracy and complexity of the machining method are far superior to those of other methods. However, due to low effective utilization of material and the limitation of equipment and tools, some parts cannot be machined. On the contrary, MIM can effectively utilize materials, and the product shape is not limited. For the manufacture of small, complex and difficult shape precision parts, MIM process has lower cost, higher efficiency and competitiveness than CNC machining.
The following is a brief comparison between MIM and several related process technologies:
Comparisons | CNC Machining | Powder metallurgy | Investment casting | MIM |
Weight(g) | 1-10,000 | 5-2,500 | 1-1,000 | 0.01-200 |
Tolerance(%) | ≤0.1 | 0.1 | 0.5-1.0 | 0.3-0.5 |
Density(%) | 100 | 92 | 99 | 98-99 |
Intensity(%) | 100 | 70 | ≥95 | ≥95 |
Wall thickness(mm) | 1-100 | 2-20 | 2-20 | 0.2-10 |
Surface Ra(um) | 0.2-4 | 2-5 | 5 | 1 |
Harber Metal Ltd. is a powder metallurgy manufacturing company created since 2014, with good production facilities and advanced technology, and is now into the production of iron-based powder metallurgy and stainless steel powder metallurgy. The company covers an area of 5,000 square meters, with 1,600 square meters of workshop, and dozens of sets of automatic presses from 100 tons to 5 tons for powder metallurgy. There are dozens of sets of automatic presses for powder metallurgy ranging from 100 tons to 5 tons, as well as complete product testing equipment and matching powder metallurgy mold processing equipment. Now the company has an annual output of 500 tons, about 5 million pieces of powder metallurgy products. products per year.