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Metal Injection Molding Of Titanium And Stainless Steel Provides Cost And Quality Advantages For Today’s Aircraft Manufacturers

Jim Beyer, Account Manager

Advanced aerospace materials using the metal injection molding (MIM) method are providing an alternative, and often better processing method than casting and machining. Important, smaller aerospace components that never make headlines in aerospace manufacturing are candidates for cost savings, weight savings, durability improvements and even enhanced cosmetic appearance using the MIM process.

Smith Metal Products 65,000 sg ft facility
capacity to handle high volumes of parts required by the Aerospace industry

Smith Metal Products 65,000 sg ft facility has capacity to handle high volumes of parts required by the Aerospace industry.

Today’s commercial and military aircraft require huge quantities of fasteners, screws, seatbelt components, wing flap screw seals, bushings and dozens of similar related components. As an example, there are an estimated 700,000 components in a Boeing 737NG with over 7000 of those planes built to date. Traditional manufacturing methods of current aircraft components more often than not require die casting and value added processes such as machining, metal finishing and plating. With today’s MIM technology, these older methods come up short by comparison.

Use Of MIM Is Historically Proven As An Appropriate Aerospace Manufacturing Process And Is Even More Appropriate In The Current High Volume Aircraft Era

In-the-know aerospace designers have specified MIM for key aircraft components since as far back as the 1980’s. These parts range from latches and fittings to seat belt assemblies and a wide range of adjustment levers. Similarly, Smith Metal Products has been producing many aircraft components dating to the company’s MIM startup in the mid-1990’s. From an industry standpoint, MIM hasn’t attracted the number of customers and users of its technology that it rightly deserves. Until now when designers are searching for better ways to ensure quality while saving money with their designs.

The pace of new aircraft designs and sheer volume of new planes manufactured have ramped up considerably compared to the 1980’s. Just in the ten-year period from 2007-2016, over 45,000 commercial and military aircraft were built, according to Aerospace and Defense Manufacturing 2017 Yearbook. And for the future, over 49,000 aircraft are projected to be manufactured between 2017 and 2026. There’s tremendous component volume in these new aircraft quantities and MIM has a preferred role. Here’s why:

Metal Injection Molding (MIM) Technology Meets The Challenges Of The Aerospace Age

Just as composite fiber has replaced aluminum in fuselage and wing structures and ceramics have replaced key engine components, MIM is replacing the smaller, traditional metal components. Here’s why:

Metal injection molding (MIM) is a net-shape molding process for producing solid metal parts that combines the design freedom of plastic injection molding with superior material properties near that of wrought metals.

Dedicated Smith Metal Products MIM facility
Dedicated Smith Metal Products MIM facility has newest, high capacity molding machines and continuous debinding and sintering furnaces. All on-site, needed support equipment includes mold-making, laser etching/engraving, inspection lab and more.

Metal injection molding mixes metal powder with a thermoplastic binder and is molded into a cavity. The molded part is thermally processed (sintered) removing the binder while producing a net shaped, high density component. Because it is a molding process, it is capable of producing an almost limitless array of highly complex three dimensional geometries in many different metal alloys. Among these are stainless steel, Titanium and other custom ferrous alloys preferred by the aerospace industry.

What Are MIM’s Advantages Over Other Processes?

For many years, aerospace manufacturers have used powdered metallurgy, plastic molding and precision machining processes in smaller part designs. A comparison reveals several advantages for MIM:

MIM is a superior process to powder metallurgy (PM) because MIM parts have greater metal density and three times the fatigue strength. For safety reasons, aerospace components must provide maximum durability often well past the service life of the aircraft. Also, MIM parts tensile strength is consistent with the metal selected for the process. In other words, a MIM processed part has the tensile strength of the original material. Also, powdered metallurgy parts are limited to 2D features while MIM allows complex aerospace geometry including undercuts, holes perpendicular to the main axis and precision 3D features.

MIM Advantages
Shown on left is a molded green part prior to sintering. Part on right is a sintered to final size. Part is a tool for fastening specialize airplane screw heads.

MIM is often a superior process to precision machining, a common aerospace component manufacturing method. However, each machined feature adds time and cost to the part price. When excess material is left in the part to save time and removal cost, excess weight is retained. And today’s aircraft designs strive for lighter weight. In contrast, MIM parts can have many features incorporated into the tooling with excess material cored out, saving part weight, manufacturing time, material and money in the final component cost. Smith Metal Products offers free Design for Manufacturability assistance, and will help designers identify areas where component wall thickness are excessive, and then make recommendations for alternate, cost-saving designs and lower tooling costs.

MIM is superior to plastic components because MIM parts are conductive, magnetic, strong, stiff, tough, chemically resistant and can operate at temperatures far over the melting range of most polymers.

Electronic components can be great MIM candidates
Electronic components can be great MIM candidates with excellent mechanical properties such as micro-switches, connectors, solenoids, heat sinks, optic connectors and distribution frames.

Recognizing Good Aerospace Part Candidates

MIM should be considered when part production quantities are over 10,000 pieces, are an appropriate size range, have complex shape, require material performance and necessitate reduced cost. MIM almost always has a cost advantage where the shape complexity is outside the range of the other manufacturing processes previously described.

Part size is important because MIM is not a large part process. Parts measuring 3 inches in all directions or smaller and weigh 25 grams or less are the best MIM candidates. Combining multiple parts into a single component (assembly) is often possible with MIM to eliminate screws, adhesive bonding, soldering, welding while reducing both weight and the cost of multiple components. Light-weighing is a long-term aircraft design goal. The MIM process can help lighten that load.

MIM Cockpit components
MIM seat components
MIM seat belts

Cockpit components, seat components and seat belts are just a few examples which can be great MIM candidates. Properties include excellent mechanical, strength, appearance, light weight and much more.

Shape complexity is an area where MIM is strongest. MIM is often specified for components ranging from 20 specifications (dimensions, locations, surface finish, material density, etc.) on the design drawing to over 250 specifications. Surface finish flexibility is one of MIM’s many specification features attractive to aircraft designers. From matte, stainless steel and highly polished surface finishes and color shades, there’s everything cosmetically that a designer could envision that’s possible and practical when specifying MIM.

MIM Turnaround Time

Aircraft manufacturing cycles are tight with demands for just-in-time delivery required from part suppliers. MIM suppliers are in tune with demanding production and delivery schedules with experience not only in aerospace but also automotive and medical industries. So naturally requirements for aerospace manufacturers can be met equally as well.

Every MIM project begins with mold design and build which can take up to 16 weeks. Once the tooling is set, manufacturing time for batch quantities of 2,500 and higher usually can be accomplished in 4 weeks or less for “as sintered” parts.

The aircraft designer should think in terms of the initial mold cost and the price of a one year quantity of parts. Then amortize both over the projected design life of that part. With a minimum annual requirement of 10,000 pieces for starters, the aircraft manufacturer can easily specify quarterly part quantities and delivery with an anticipated 4-week lead time. Releases should run at no less than 2500 to 3000 parts with three or four releases a year. Compared to both inside or outsourced precision machining for needed parts, this type of MIM relationship is far more consistent and reliable both in terms of quality, price and on-time delivery.

The Aircraft Designer Challenge – More MIM Awareness

Staying up-to-date with MIM progress is a worthwhile investment for today’s aerospace designer. Access to the latest information has never been easier available on the Smith Metal Products website.

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