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May 10, 2022

Additive Manufacturing - Innovations in Forging

The additive manufacturing process is just the inverse of subtractive manufacturing, where the material is removed from a single piece of material using milling, cutting or turning; it is the method of adding or joining materials together using heat, pressure or magnetism/electricity.

Additive Manufacturing

One clear thought probably comes to mind – 3D printing. From aerospace applications to medical devices in materials ranging from plastic to metals, 3D printing is swooping into manufacturing as an option for making highly complex parts that need to be strong and lightweight. The additive manufacturing process is just the inverse of subtractive manufacturing, where the material is removed from a single piece of material using milling, cutting or turning; it is the method of adding or joining materials together using heat, pressure or magnetism/electricity. From that perspective, there are many different approaches to additive manufacturing, including metal extrusion, ultrasonic additive manufacturing, sintering or diffusion bonding.

Metal Extrusion

Metal extrusion in additive manufacturing, like 3D printing, is a method where a spool of material is pushed through a heated nozzle and placed by a "printer" to layer material and create a workpiece. This process may take a few attempts to find the best parameters, design and orientation for building a component, but once found, the process is reliable for creating small intricate pieces for noncritical applications.

Ultrasonic Additive Manufacturing

Ultrasonic additive manufacturing is another method of layering material, using a process of stacking metal strips and combining them using an ultrasonic weld, so to speak, to create complex geometries with internal passageways, including parts with embedded components and even parts made from dissimilar metals. Unlike metal extrusion, the solid-state weld produced by the ultrasonic process provides a reliable way to join different metals without creating brittle metallurgy, as the bonding temperature is below their melting temperature.

Sintering

Sintering is a little different; while it still uses heat and pressure, this process begins with powdered metal, which is heated to fuse into one solid mass, just under the material's melting point. When using a laser, this process is known as Selective Laser Sintering, which creates intricate parts through micro-welding powdered metal layer by layer.

While ultrasonic additive, metal extrusion and sintering have significant capability in part complexity, they are severely limited by size as parts cannot be larger than the machine's build platform, and these processes face scalability issues. Materials for metal extrusion manufacturing and sintering can be limiting for manufacturers since only a small variety of metals can be used in these applications. In addition, there is a considerable cost of entry for the machine and material design and engineering and setting parameters. In extreme cases, it can take years of research and effort to develop the process parameters for specified materials in specific machines. And at the current moment, there is a lack of skilled labor and industry standards for these methods. Finally, since additive manufacturing creates many interfaces through the layering method, the part's integrity becomes a concern.

Diffusion Bonding

On the other hand, diffusion bonding is different in that it can be accomplished with the age-old process of forging. Solid-state diffusion bonding is the process of adding dissimilar/similar material to a started workpiece with elevated temperature (about 50%-90% of the absolute melting point of the parent material) using applied pressure. Without melting, there is no liquation or fusion zone, which can have unpredictable structures, grain size, porosity and liquation cracking. Additionally, other types of metals that cannot be combined through traditional welding practices can be combined through diffusion.

This bonding procedure is suited for bulk items with significant size and weight and the ability to be scalable. Like ultrasonic additive, combining two or more metals has advantages for strength, ductility, corrosion, designed fail-safes, cost savings, reduced in-service inspections and more. Diffusion bonding can also provide additional benefits such as corrosion resistance or added strength while eliminating costly welding or cladding operations. Additionally, the bonded interface can be tested through conventional mechanical methods such as tensile, charpy and microstructure. At the same time,traditional non-destructive examinations,如超声波测试或液体的钢笔etrant testing, can be completed to provide insight into the bonded surface and the base material.

This is an exciting time for manufacturing and R&D, with all of the innovations coming to fruition. But, before selecting an additive manufacturing method, or any manufacturing method, it's important to think about what you need from your project. For example, are you looking for a morebudget-friendly option, do you have detailed design requirements, need to use more robust build materials or require testing? Send in your design to a Scot Forge employee-owner and explore your options.

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