Bringing Metal Parts to Life with Complex Geometry and Precision Tolerances. Phillips-Medisize Corporation April 2016

Transcription

1 Bringing Metal Parts to Life with Complex Geometry and Precision Tolerances Phillips-Medisize Corporation April 2016

2 Introduction Metal injection molding (MIM) is an effective way to produce complex and precisionshaped parts from a variety of materials from low to extremely high volume capabilities which can be produced cost effectively and with significantly reduced lead-times. Metal injection molding can produce relatively small, highly complex geometries with excellent surface finish, high strength, and superior corrosion resistance. MIM Process Overview Metal Injection Molding (MIM) is the process of producing a complex, net shape metal components using injection molding technologies. It involves converting metal powders to behave like a plastic by mixing them with polymer binders to form a feedstock which is a pelletized blend of ~60% metal powder and ~40% polymer powder by volume, and is molded in a machine and auxiliary equipment in a process very similar to that of plastic injection molding to provide a green part. The green part is then processed through de-bind and sintering process in which the polymer powder is removed, resulting in 14 22% linear shrinkage and a theoretical density of 97 99%. The shrinkage is consistent to.3.5% of each specified materal. De-binding and sintering may be done in batch systems, typically for smaller volumes, larger parts or less common materials, or in continuous systems for larger volumes or common materials. In many cases, MIM can be used to produce parts much more economically than with the CNC machining or investment casting methods; in addition, parts have improved surface finish and metallurgical properties over competing metal forming processes. The ability of the MIM process to support mid-to-high volumes of mid-to-high geometric complexity has resulted in significant growth of applications in the medical, automotive, consumer, industrial and defense industries, especially in the last five years. Common Materials MIM is suitable for a variety of materials ranging from low-carbon steels, stainless steels, soft magnetic alloys, to other specialty alloys. While some MIM processors procure powders and compound the feedstocks in-house, others utilize production-ready feedstocks from sources such as the Catamold line-up by the industry s longstanding innovator, BASF. Competing Processes When selecting a manufacturing process, MIM is most often compared to CNC machining, investment casting, or conventional press & sinter powder metallurgy. MIM offers the following advantages compared to these processes: CNC machining: MIM has greater ability to provide harder materials, is more cost effective as volumes increase, and results in lower weights due to the additive nature of injection molding vs. the subtractive nature of CNC machining. Investment casting: MIM allows for thinner wall sections, and provides a better surface finish; it requires less secondary machining and is better suited for higher volume manufacturing. Powder metallurgy: MIM allows for greater part complexity and a thinner wall section, and provides higher density, higher strength parts with better corrosion resistance. Bringing Metal Parts to Life with Complex Geometry and Precision Tolerances 2

3 While MIM is cost competitive on mid-to-high complexity shapes and for volumes as low as 2,000 pieces annually, the process does not lend itself to competition with parts that can be stamped or screw machined, or parts with a simple geometry designed for CNC machining. Metallurgical capabilities allow for the maintenance of tight control of all aspects of the MIM process. Secondary Operations Phillips-Medisize can provide secondary operations to meet an array of specific requirements. With typical tolerances for the MIM process within to inches per inch, ( %), many parts are sintered to final dimensions. If tighter tolerances are required in certain areas, secondary machining operations can be applied. Tapping operations can produce internal threads with tolerances tighter than can be achieved via the metal injection molding process. Tumbling and polishing can provide an aesthetic surface. Parts can be heat-treated, coated, and plated in similar fashion to investment cast or machined parts. Suppliers with ITAR (International Traffic in Arms Regulations) registration should be considered for firearms and defense programs. Applications for MIM MIM has experienced rapid growth in medical, automative, consumer, industrial and defense applications over the past 5 years. This growth has been driven by two main factors: 1. Increased emphasis on cost reduction, without sacrificing quality has led companies to seek alternatives to traditional processes such as CNC machining. 2. Increased understanding of the MIM process by designers, who have subsequently designed new products to leverage the MIM process and its inherent advantages. Today, MIM can be found in many areas such as: Defense: firearms Automotive: turbochargers, fuel pressure regulators, fuel injectors, transmission components, rocker arms Consumer: cell phone hinges and clips, hand tools Industrial: punch down tool, bobbins, door locks, analyzers Manufacturers using the MIM process expect to see continued future growth in all of these areas as designers gain more experience and become more comfortable designing for MIM. However, the greatest growth is expected to be in areas with volumes which support the tooling investment required for MIM. MIM Process Bringing Metal Parts to Life with Complex Geometry and Precision Tolerances 3

4 Factors of Successful MIM Applications When developing products, designing for the MIM process requires specific knowledge, similar to the way in which products are designed for plastic injection tooling and molding. Design considerations determined up front during the initial product development will ensure the part is optimized for the MIM process and tight tolerances, which may be beyond the capability of the process, are minimized. Continuous debind and sintering furnaces provide quality processing and large volume capacity while maintaining consistent quality. The most common design considerations for MIM are: g finished part weight Generally speaking, MIM parts are in this size range. Larger parts are less suitable and may be more cost effective to produce with an alternate metal forming process. Part geometry that fits inside a tennis ball Generally speaking, MIM parts are of this order of size. Larger parts are less suitable and may be more cost effective to produce. Uniform wall sections of This is variable. A consistent wall section is critical. Wall sections can be thicker or thinner based on the size of the part and where the thick or thin wall section is located near the gate. Draft angles of degree to aid part ejection This aids part ejection and minimizes part distortion during the molding process. Dimensional tolerances of 0.5% to achieve capability In other words, a tolerance over 1 would be.005 to achieve a capability of 1.33 CPK. A two inch dimension would require.010 to achieve the 1.33 CPK. The tightest tolerance we can achieve within capability is.0015 for any given dimension to ensure capability. Anything tighter would require secondary machining operations. Corner radii to reduce stress Generous radii at transitions eliminate stress and distortion potential. Geometries which support the component through the high temperature sintering process, in order for the part to shrink and densify to the final dimensional requirements. A flat sintering support is beneficial for dimensional stability and control. It is not necessarily required for very small components of less than 1 gram. Threads formed by unscrewing cores in the tooling are a possibility, and can result in significant cost and lead time savings by eliminating secondary tapping operations. This option is dependent upon the volume and adds a significant amount of cost to the tooling. It is therefore only practical for higher volume applications. Annual volumes as low as 2,000 units, but more commonly 5,000 to several million units annually. The higher the volume the quicker is the pay back for the customer-purchased tooling. Generally speaking, 10,000 pieces annually is at the low end. The greatest advantage can be derived from the MIM process by properly designing from the outset, which, after molding, de-binding, and sintering, achieves a net shape part and thereby eliminates the need for secondary machining operations. This results in a low cost and low manufacturing lead time solution. As with all molding and casting processes, the most favorable outcome is achieved by involving the manufacturing source early in the design of the system not just the Bringing Metal Parts to Life with Complex Geometry and Precision Tolerances 4

5 components in order to obtain Design for Mouldability and Assembly (DFM/DFA) input, eliminate part count, reduce assembly steps, and achieve a balance between tooling investment and part costs. Summary MIM is an alternative manufacturing route which can offer solutions for metal parts that in the past have either been very difficult or too costly to produce. When properly designed for MIM, the process provides the design flexibility typical for plastics combined with the material properties of metal. MIM offers numerous advantages over die casting, investment casting, and machining and is changing the face of metal produced components as we know them. Today, Phillips-Medisize is reshaping the face of MIM by offering new material options, advanced design capabilities, processing options, and the ability to serve a variety of markets that may not have originally considered this capability. phillipsmedisize.com info@phillipsmedisize.com All rights reserved.