August, 2019


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Page 53 Building Complex Metal Parts Layer by Layer By Jeff Elliott A


unique additive manufacturing process is helping precision machine shops to create metal parts with complex internal cooling


passageways or channels for dispensing liquids or gas layer-by-layer before final machining. The additive manufacturing process can be


used to build a part from the ground up with millimeter-thin sheets of metals and alloys. As with similar techniques, 3D modeling software is used to map out sophisticated internal chan- nels or passageways prior to CO2 laser cutting of each layer. The key to the process is diffusion bonding,


which essentially fuses the combined layers together under pressure and heat, without the need of brazing or other filler material. Traditional machining is then used to bring the exterior of the part to its final shape. Using this technique, finished


parts as large as 35.43 x 49.21 x 19.69 in. (900 x 1,250 x 500 mm) can be con- structed from stainless steel, titani- um, zirconium, beryllium, high alloyed aluminum, Inconel, and tung- sten. The process can also be used to weld dissimilar metals like copper to titanium, copper to aluminum, cop- per to tungsten and even molybde- num to aluminum. For precision machine shops


that serve the medical, aerospace, semiconductor, and automotive industries, the technique provides a method to create parts that are diffi- cult, if not impossible, using tradi- tional CNC equipment or less effec- tive brazing/welding techniques.


Sophisticated Internal Pathways For metal parts that require


sophisticated internal channel


geometries, whether with an inlet and outlet, or neither, there can be many twists and turns. Examples include heat exchange applications, where channels are machined into aluminum to disperse heat by air or liquid cooling. Given that the surface area of the cooling zone is a primary factor in heat transfer, the more extensive the channels, the better. Conformal cooling channels also


can increase the efficiency and cycle times of plastic injection molds. These cooling passageways follow the shape or profile of the mold core or cavity to perform a rapid uniform cooling process for injection and blow molding. There are also applications with


liquid and gas dispensing equipment. In semiconductor and microelectron- ics fabrication, for example, sophisti- cated “showerhead” style gas distri- bution assemblies are used to dis- pense processing gases into semicon- ductor etching and deposition cham- bers. These dispensing heads often have multiple, separate internal pas- sageways.


Bonding Layers of Metals and Alloys


Given that traditional CNC cut-


ting tools cannot be used for this pur- pose, one alternative already in use for items such as showerhead assem- blies is a similar additive process that varies in how it joins the layers: with brazing material. Brazing is a metal-joining pro -


cess in which two or more metal items are joined together by melting and flowing a filler metal into the joint. The filler metal flows into the gap between the layers through capillary action. Although brazing has the ability


Where Accuracy Meets Throughput.


Enabling technology. Let us help with your next motion control project.


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Diffusion bonding can create complex internal structures with no interface lines or striations.


to join similar or dissimilar metals with consider- able strength, it also has significant drawbacks when internal passageways are involved. Brazing can cause small “fillets” to form in


the passageways that obstruct flow and can even break off during use. Too little brazing material can create voids where liquid or gas accumulates and corrosion sets in, particularly in the presence of harsh chemicals like those used in the semicon- ductor industry. The result can be delamination of the layers


and premature replacement of what can be extremely expensive parts made out of exotic materials. Diffusion bonding, on the other hand, creates a superior bond without the need of any


Continued on page 58


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