As each MIM manufacturer has to make the fundamental decision in MIM parts production process, whether to purchase feedstock form specialist suppliers, or develop their own custom feedstock. There is no perfect choice here, only most suitable decision. Both selections have advantages and disadvantages.
In nowadays, various ready-to-mold feedstock suppliers provide a diverse range of off-the-shelf feedstock, as well as custom materials. However, there is a critical issue we need to consider for successful metal injection molding production. Absolute batch to batch consistence in feedback will affect all following MIM process. Any issue in this point will give rise to defects in molding, and distortion in sintering.
With our custom materials development, we can guarantee material consistence in each batch. As for purchase form feedstock suppliers, our engineers will make sure feedstock consistence by analyzing feedstock composition with professional equipment, selecting long term suppliers with high reputation, and investigating factory for purchase preparation.
In order to provide high quality MIM parts, ZCMIM will not only monitor our feedstock consistence, but also make sure feedstock composition– metal powder & binder achieve our required standard.
Metal Powders for Metal Injection Molding
Our metal injection molding service provides widely MIM metal diversity, form stainless steels, iron-based alloy to titanium, supper-alloy. Metal particle size play the most important role in powder characteristic, which will determine sinterability and surface quality of final parts. As general rules, metal powders with finer size will have better performance of properties. As following, we will introduce 2 typical kind of metal power in MIM process.
Carbon iron and nickel powders
This kind of fine carbon iron and nickel powers are already in industrial production before MIM technology development. So it is widely applied in electronic, medical, automotive industry for precise parts production. These powder has spherical form and excellent flowability, which also has size less than 10 µm. This is finer than common atomized and reduced iron powder size.
Carbon iron powders have excellent sintering properties, these fine particle size result to high sintered density, high strength and excellent surface texture quality for final parts. In addition, uniform spherical form shape guarantee precise dimension accuracy.
There are various ferrous MIM alloys based on carbon iron and nickel, these powders can be mixed with key elemental or mater alloy powders to create desired alloy composition with specific properties in chemical and physical. Please check our MIM material properties for detail information of iron-based ally composition and properties.
Water and gas atomized powders
Water and gas atomized powder are predominantly applied for prealloyed metal powder with specific property requirement. Such as high alloy steel, nickel and cobalt based alloys. All these alloy will satisfy special property requirement of high strength, corrosion resistance, high surface hardness or bio-compatibility.
As gas atomized alloy powders have spherical shape, in some case, we need to add water atomized powders with irregular shape. With high demand for fine metal powders, atomizing technique is improved to provide many kind of alloy power with less than 10 µm in average size. Which results to high sintered density, high strength and excellent surface texture quality for final parts.
Incorporate with high volume of fine metal or ceramic powders, typically achieve 60% in volume.
Form coherent mass which can be plastified and injection molded in high temperature.
Main binder constituent can be removed in environmental friendly process with reasonable short time.
Backbone binder can still provide enough structural strength after debinding process.
Form in regular granular for easily feeding into injection molding machines.
Consistent and uniform properties in batch to batch supply.
As development of binder composition and corresponding debinding technology, MIM technology has excellent capacity to create various custom parts. We provide most suitable binder compositions and debinding technology for custom parts requirement. Our main debinding technology are thermal, catalytic and solvent.
In original MIM process, binder is consist of polymer mixtures such as polyethylene or polypropylene, wax and stearic acid. These kinds of binder system are still successfully applied in nowadays. Feedstocks based on this type of binder are easy to mold in MIM process, but the debinding process need carefully heating in thermal process with 24 or more hours, until final network and interconnected porosity is created. The remaining binder can be evaporated easily without any destroy in parts structure.
As the invention of Catamold system based on polyoxymethylene by BASF, this polyacetal binder system provides excellent moldability and good shape retention. Catalytic debinding is processed in a gaseous acid environment, for example high concentration of nitric or oxalic acid with temperature of approximate 120°C(below softening temperature of this binder). Acid is a catalyst in polymer binder decomposition process, and final create yields parts with interconnected porosity in almost 3 hours. The final reaction material of binder can be burnt into gas flame at temperature above 600°C. Many MIM parts are produced through this debinding process, particularly in consumer electronic sector.
As binder removal techniques development, the most successful type is solvent debinding. This binder system contains a constituent, which is easily dissolved into liquid solventia at low temperature. Finally left a part with network of interconnected porosity once immersed in solvent for specific time. Water soluble binder composition is preferred in reason of water solvent is easier to handle than organic solvent, especially for solvent distillation and recycling after debinging process. However, we still apply acetone or heptane as solvent for special binder composition which is difficult to dissolved into water.
Solvent debinding take longer time than catalytic binder removal, but it still has competition with lower investment and operating cost in total process. Particularly with environmental advantages comparing to other binder removal process.