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Metal Injection Molding: Cost-Effective Process for Complex Metal Shapes

Metal Injection Molding

There are few manufacturing processes that can form intricate parts, even unitize separate pieces into a single form, while saving production steps and still achieve nearly 100% wrought properties.

Metal Injection Molding represents the merging of two established technologies: injection molding and powdered metal. It combines the strength and durability of metal with the flexibility of injection molding. The result provides for intricately formed parts, repeatable in high production manufacturing and available in a wide selection of alloys approaching wrought properties.

While the MIM process is generally limited to smaller parts, it is especially suitable for complex geometries. Thin wall sections, contoured or sharp corners and edges and other design details, that are very expensive to achieve with other manufacturing methods, are all within the realm of MIM capabilities.

Advanced Forming Technology, Longmont, CO, whose proprietary MIM technology was developed by its in-house staff of specialized engineers, has proven that this state-of-the-art method of metal forming is highly successful in providing high volume cost reduction solutions. Currently, AFT produces parts for a wide variety of customers that include the world's largest manufacturers of computer peripherals, medical and dental devices, aerospace, electronics, office products, firearms and ordnance.

Working with an organization of highly trained sales representative such as Technical Sales, Inc. of Mountain View, CA, AFT produces parts in many materials, including low carbon and stainless steels to copper based alloys with weights ranging from 0.5 to 150 grams or more.

Dedicated to TQM and Continuous Improvement

Any company that wants to maintain market leadership must constantly refine its methods, policies and management accountability. These refinements represent a drive for constant improvement, and are especially crucial for the manufacture of custom, high volume parts. Order-driven manufacturing places extraordinary demands on a market-responsive organization in such areas as estimating and job scheduling which is affected by material planning, purchasing and cost accounting. Total quality management is absolutely critical.

Since its organization in 1987, AFT has become a leader in custom metal injection molding. This has been accomplished by selecting and training its representative organization to work with customer's engineers in designing hardware for metal injection molding.

This design is then converted in AFT's mold design lab, employing the latest in CAD/CAM technology including mold flow analysis, into an efficient molding tool. tool. In-house capability to produce single and multiple cavity tools, taking advantage of advanced injection molding features such as side coring, internal threading and other complex part molding techniques, assures high quality, efficiently produced parts.

Finished tools are released to AFT's pre-production staff of dedicated engineers who work with customer and AFT production personnel to assure that all manufacturing processes are defined, capable and tested. After the customer's first article approval, the project is released to production manufacturing.

Why MIM With AFT

MIM basically is a cost-effective process for complex metal shapes where the strength and durability of metal are combined with the flexibility of injection molding. With their full service capabilities, Advanced Forming is well equipped to handle varying production runs efficiently. Services offered include initial design to final assembly using state-of-the-art material preparation, molding, sintering, secondary and inspection equipment.

Advanced Forming Technology's manufacturing team consists of specialized teams or work cells. Each cell is composed of personnel trained and experienced in the needs of specific product applications such as electronics, medical and dental devices, automotive and business machines.

AFT is equipped with the latest technology in molding machines. With the introduction of microprocessor controls and "closed loop" injection systems, it is now possible to apply statistical process control to molding operations. Such equipped machines are capable of repeatable performance and are flexible in setup to accommodate a wide variety of production molds and part runs.

Statistical molding data is automatically monitored Most molding machines are equipped with 3 or 4 axis robotics to remove parts from molds and/or stage parts for post mold processing. Many machines are also equipped with computerized vision systems which assure mold filling and properly functioning robotics. Parts are produced in monthly volumes varying from 1,000 to 1,000,000 pieces.

How MIM Works

It is often possible to combine several previously separate parts into a single, unitized piece saving production steps and often providing a stronger finished design. For this reason, and for the efficiency of the injection molding process, MIM can provide an alternative to traditional investment casting or machining.

The first step in MIM production is to determine whether the part is economically and physically suited to the process. This is often accomplished at the field sales level. Certain design changes might be appropriate in order to derive the maximum MIM cost and quality benefits. Actual production begins with the creation of the mold, similar to the kind used in plastic injection molding.

Next, very fine metal powders are mixed with a binder material. Particle diameters are usually less than 15 microns, as compared with greater than 40 micron diameters typical in conventional powder metallurgy. In fact, the powders used in MIM are sometimes referred to as metal dust.

The powder's flow characteristics are crucial. A powder that does not flow well, often the case with poor particle geometry, or when larger particles are present, may produce voids in the finished piece. AFT closely controls particle geometry and size to avoid this problem. Both prealloyed metal powders and combination of elemental metal powders are suitable for MIM processing. Usually, pre-alloyed powders achieve the most desirable properties. The variety of metals and ceramics available for MIM processing is constantly expanding.

Designing for MIM

In many cases, MIM can facilitate the design of parts not previously achievable in metal. At the very least, it can streamline the manufacturing process and result in substantial benefits over traditional manufacturing methods. Still, designers resist taking advantage of MIM because, like any other emerging process, it requires changes in design parameters.

As in plastic injection molding, wall thicknesses should be uniform to avoid uneven shrinkage during sintering. Size and shape specifications can also affect the economics of staging, debinding, sintering and injection molding cycle time. These limitations, however, are easily balanced by the greater latitude inherent in the injection molding process.

In designing a part for MIM, it is important to consider its basic form, fit and function, and how these can be adapted to be compatible with the process. Designers often insist on maintaining existing specifications when switching to a new process, and this can actually neutralize the benefits of MIM production. Design specifications, for example, may not actually require uniform wall thicknesses. Carrying such parameters over to MIM will create more expensive parts and sacrifice potential benefits of MIM that might otherwise be possible.

AFT always recommends going back to the original 'form, fit and function" and design the part to take the greatest advantage of MIM's flexibility, economy and creative latitude. The company's Design Guide gives more complete guidelines for designers new to the process.

Process and Quality Control

Moderate to High Volumes of Small, Complex Parts

AFT's process produces net to near net shapes, with densities of 95 to 99%, while reducing material waste, yet is easily repeatable. The result is accurate, volume production of complex parts. AFT produces parts from various stainless steels, low alloy steels, nickel iron alloys, Kovar® and others.

All manufacturing and engineering personnel are trained in SPC/SQC and monitor query constantly while striving for continuous improvement. Every person at AFT, from manufacturing to office staff, is responsible for maintaining the very highest of quality levels designed to meet the standards of "Good Manufacturing Practice" and MIL-Q-9858A.

The company employs the latest in automated optical inspection as well as conventional metrology equipment. A fully equipped and staffed metallurgy lab is maintained to assure that parts produced meet AFT metallurgical specifications. All aspects of the manufacturing process are traceable and controlled through the use of a computerized manufacturing planning and control system.


Metal injection molding brings the shaping capabilities of injection molding to metal and ceramic parts At AFT, their proprietary process has proven effective for parts weighing less than 1/10 gram to over 100 grams.

MIM is free from the traditional limitations of metal manufacturing. AFT can often completely re-engineer parts to take advantage of the flexibility and cost saving potential of the process. The MIM design can consolidate multiple pieces into a unitized, highly reliable part, eliminating pins, welds, threads, or other bonding requirements. umbersome serial operations Eke stamping, bending and coining also fail away.

The properties of MIMed pieces closely approaches those of the wrought metal. Customers receive the durability, strength and integrity of metal with the flexibility and repeatability of molding.

Metal injection molding is changing the shape and economics of business machines, medical and dental equipment, electronic devices and electronic packaging and more. Its influence is certain to spread, both within and beyond its current areas of use.

Kovar is a registered trademark of Carpenter Technology Corporation

This technical information has been contributed by
ASH Industries

Click on Company Name for a Detailed Profile

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