Metal injection molding

Metal injection molding (MIM) is a metalworking process by which finely-powdered metal is mixed with a measured amount of binder material to comprise a "feedstock" capable of being handled by plastic processing equipment through a process known as injection moldforming. The molding process allows complex parts to be shaped in a single operation and in high volume. End products are commonly component items used in various industries and applications. The nature of MIM feedstock flow is defined by a physics called rheology.Current equipment capability requires processing to stay limited to products that can be molded using typical volumes of 100 grams or less per "shot" into the mold. Rheology does allow this "shot" to be distributed into multiple cavities, thus becoming cost-effective for small, intricate, high-volume products which would otherwise be quite expensive to produce by alternate or classic methods. The variety of metals capable of implementation within MIM feedstock are referred to as powder metallurgy, and these contain the same alloying constituents found in industry standards for common and exotic metal applications. Subsequent conditioning operations are performed on the molded shape, where the binder material is removed and the metal particles are coalesced into the desired state for the metal alloy.

Metal Injection Molding market has grown from $382 million USD in 2004 to $985 million USD in 2009. Further the market is estimated to be about $1.5 billion USD in 2012 by BCC Research, with continued double digit growth expected through 2019.

Process

The powder injection molding process

An early developer of the process during the 1970s was Dr. Raymond E. Wiech Jr., who refined MIM technology as co-founder of a California company named Parmatech, the name being condensed from the phrase "particle materials technology".Wiech later patented^[4] his process, and it was widely adopted for manufacturing use in the 1980s. Competing processes included pressed powder sintering, investment casting, and machining.

MIM gained recognition throughout the 1990s as improvements to subsequent conditioning processes resulted in an end product that performs similarly to or better than those made through competing processes. MIM technology improved cost efficiency through high volume production to "near-net-shape", negated costly, additional operations left unrealized in competing processes, and met rigid dimensional and metallurgical specifications.

The process steps involve combining metal powders with wax and plasticbinders to produce the "feedstock" mix that is injected as a liquid into a hollow mold using plastic injection molding machines. The "green part" is cooled and de-molded in the plastic molding machine. Next, a portion of the binder material is removed using solvent, thermal furnaces, catalytic process, or a combination of methods. The resulting, fragile and porous (2-4% "air") part, in a condition called "brown" stage, requires the metal to be condensed in a furnace process called Sintering. MIM parts are sintered at temperatures nearly high enough to melt the entire metal part outright (up to 1450 degrees Celsius), at which the metal particle surfaces bind together to result in a final, 96-99% solid density. The end-product MIM metal has comparable mechanical and physical properties with parts made using classic metalworking methods, and MIM materials are compatible with the same subsequent metal conditioning treatments such as plating ,passivating, annealing, carburizing, nitriding, and precipitation hardening.

Applications

The window of economic advantage in metal injection molded parts lies in complexity and volume for small-size parts. MIM materials are comparable to metal formed by competing methods, and final products are used in a broad range of industrial, commercial, medical, dental, firearms, aerospace, and automotive applications. Dimensional tolerances of ±0.003 inches per linear inch can be commonly held, and far closer restrictions on tolerance are possible with expert knowledge of molding and sintering. MIM can produce parts where it is difficult, or even impossible, to efficiently manufacture an item through other means of fabrication. Increased costs for traditional manufacturing methods inherent to part complexity, such as internal/external threads, miniaturization, or brand identity marking, typically do not increase the cost in a MIM operation due to the flexibility of injection molding.

Other design capabilities that can be implemented into the MIM operation include Batch codes, part numbers or date stamps moulded into parts; parts manufactured to their net weight reducing material waste and cost; Density controlled to within 95–98%; Amalgamation of parts and Complex 3D Geometries.

The ability to combine several operations into one process ensures MIM is successful in saving lead times as well as costs, providing significant benefits to manufacturers. The metal injection moulding process is also recognised as a green technology due to the significant reduction in wastage compared to "traditional" manufacturing methods such as 5 axis CNC machining for example.

There is a broad range of materials available when utilizing the MIM process. Traditional metalworking processes often involve a significant amount of material waste, which makes MIM a highly efficient option for the fabrication of complex components consisting of expensive/special alloys MIM is a viable option when extremely thin walls specifications are required. Additionally, EMI shielding requirements has presented unique challenges, which are being successfully attained through the utilization of specialty alloys .

Abstract

The powder injection molding (PIM) process offers a fabrication technology for making parts by metal powder injection molding (MIM) and/or ceramic powder injection molding (CIM). It consists of four main steps: mixing of feedstock, shaping by injection molding, debinding, and sintering.

PIM offers considerable economic efficiency in large-scale manufacturing and allows the production of complex shaped devices with usually no postprocessing. A further attraction is the wide range of materials that can be utilized, for example, different kinds of steels (such as 316L or 17-4PH), copper, titanium, refractory metals, hard metals, oxide and nitride ceramics, and so on.

Typical PIM products reveal densities of 95–99% of the theoretical values, maximum part weights of 1 kg (may be higher in certain cases), and wall thicknesses up to more than 20 mm.

Development of the so-called MicroPIM process can help large-scale manufacture of metal and ceramic microcomponents. Presently, the smallest dimensions achievable are less than20 μm of part thickness or minimum structural details of less than 10 μm. Theoretical densities of up to 99% for ceramics have been achieved, while the nominal sizes of the final parts have reached tolerance levels of ±0.1–0.5%.

Current investigations deal with the development of simulation programs taking into account specific features of multimaterial systems as well as the particular effects that occur when processing highly powder filled fluidics.

For the reduction of mounting costs and production of highly integrated devices, two-component injection molding (2 C-PIM) is under advanced development. By the adjustment of the feedstock and sintering parameters, immovable or movable bonds can be generated.