Metal deposition is an emerging manufacturing process that offers the potential for dramatic reductions in the use of metal to generate geometric shapes for manufactured product. Metal deposition is a process for producing components directly from a computer aided design (CAD) file in a layered approach allowing the 3-dimensional creation of a solid. This reduction of metal to generate product can yield huge savings in energy, industrial waste streams, excess machining and chip reclamation, and generate significant cost reductions. The transformation of metal from a simple bulk form such as wire into a 3-D solid shape can reduce material lead times up to 70%. The rapid production of low-lot size parts has the potential to transform the way metal product is produced in the U.S. industry. This can also be known as Art to Part.
Metal deposition is known by several names; Direct Digital Manufacturing (DDM), Additive Manufacturing, Layered Manufacturing, Laminated Object Manufacturing, Light Engineered Net Shaping, Laser Assisted Manufacturing, and Electron Beam Freeform Fabrication (EBFF) to cite examples. These names generally refer to the generation of a fully functional part or component from a computer aided design file using any one of several means of depositing material placed by a numerically driven machine. Electron Beam wire feed methods have emerged as the process of choice for high-rate, high quality metal deposition.
Most of the metal deposition approaches being worked for metal components are derived from welding methods. The heat source can be an electron beam, laser, arc, or plasma, but electron beam (EB) has emerged as the most energy efficient and most suited for high-rate deposition. EB deposition generally requires the use of weldable alloys for fabrication. Methods for the delivery of metal to the workpiece can be via powder, wire, rod, or strip, but weld wire has proven to be the lowest cost and easiest to control quality of all the material forms.
The Electron Beam (EB) deposition process has proven its capability to directly manufacture complex shapes from CAD files, and as an additive manufacturing process to produce or repair components by adding features to forged or cast components. The method is significant in that it does not require tooling, and material utilization factors are near unity. Significant reductions in machining are possible by generating very near-net shapes (NNS). The concept of direct digital manufacturing can be extended further, integrating multiple manufacturing functions into a single process able to build a deposited, machined, inspected, and finished component in layers, although, this integrated technology capability is far from mature. The process for building a geometry is shown in Figure 1.
The metals applicable to deposition methods include aluminum, steel, titanium, and nickel-base alloys. Titanium deposition has been explored extensively since this metal seems particularly suited to metal deposition approaches and applicable to airframe structural components. Aluminum has an increasing application with the cold spray process, relying on its low-strength characteristics to allow a high-velocity gas stream to deliver powder particles that deform on impact creating a solid-state bond. The smaller nozzle size and particle stream diameter make cold spray a potential process for building complex part geometries, but in general, the class of metal coating methods such as flame spray and plasma spray are not considered in the overall class of metal deposition. These processes are well established for applying specialized coatings and buildups, but in general are not capable of building complex geometry due to the wide exit plume and surface area of the deposited material.
Cost savings over forged product are generally derived form significant reductions in input material and a corresponding reduction in rough machining for the parts made from metal deposition. The key benefits arising from metal deposition technologies are as follows:
- Reduced material input/material waste, reduced machining
- Reduced component lead time
- Reduced energy, infrastructure, and waste streams
- Reduced labor content
- Simplified production of complex (even hollow) components
- Simplified repair.
Figure 4. Pictures of the Successive Building of an EB Wire-Feed INCO 718 Deposited Engine Case. This Component is 22 Inches in Diameter and 12 inches Tall.
Metal deposition can play a significant role in the reduction of lead time in the development and manufacture of components. Prototype and demonstrator hardware and components can be made with metal deposition interactively with the design process. Design changes can be easily incorporated to prototypes during the manufacture of the 3-D shape, as well as material added to the component after manufacture for rapid incorporation of design evolutions. Perhaps the most significant use for this technology is in component repair and out-of-production spares wherein it will lead to dramatic reductions in procurement costs.
The implications for green manufacturing are dramatic when metal deposition is compared to forged product. Often direct manufacturing can produce a shape with a buy-to-fly ratio of 1.5:1 to 2:1 where most forgings range from 6:1 to 23:1 buy-to-fly. This radical reduction in material to generate equivalent product translates to huge energy savings from the metals processing infrastructure and the associated thermal and chemical waste streams. Rough machining requirements can be reduced by nearly 70%, gaining significant reductions in energy, chip reclamation processing waste streams, and cutting fluids. In producing a forging, each pound of metal is typically heated to a high temperature 8 to 10 times in its life from forming the ingot through final heat treatment. A metal deposited part can be limited to 4 to 6 heat cycles resulting in over 50% reduction of energy per pound while also using 50% or less of the pounds of metal. to produce product. A much smaller metals infrastructure is required to support wire production or powder atomization as opposed to the current large infrastructure that is based on large ingot production.
Developing a shaped geometry layer-by-layer can rapidly grow to be a large new industrial supply base that will displace some forged product and many castings. Forgings inherently have a significant amount of excess material, suffer from long lead times, and require extensive machining. Castings require long mold development times and can suffer from quality issues such as porosity and shrinkage defects in the thinner complex forms.
High-deposition rate processes such as Electron Beam wire feed deposition are emerging for engine and airframe structural components under government funded initiatives but no effective large-scale supply base has been established. Methods for understanding and controlling high-rate deposition processes are being developed as well as tools for path planning, distortion analysis and reduction, and thermal management. Equipment producers for the small prototype market and for high rate deposition are available to the industry, but only a few emerging companies are establishing a production parts-producing supply base capability.
Written by Ray Walker
Keystone Synergistic Enterprises Inc.
Edited by Don Christensen