Читать книгу Metal Additive Manufacturing - Ehsan Toyserkani - Страница 18

From the early days of AM, the technology has been evolved substantially. Advancement after advancement in AM is announced almost daily. While AM has been substantially changed from 30 years ago, it will be unrecognizable form the current status in 2030. But why such enthusiasm exists in industry and academia to try to understand metal AM and work hard to address its challenges and adopt it to their products? There are several main factors for this motivation:

 On‐demand low‐cost rapid prototyping: One of the major applications of AM is the manufacture of functional prototypes. Such prototyping usually carries at a fraction of the cost compared with other conventional processes and at usually non‐disputable speeds. This rapid turnaround usually accelerates the design cycle (design, test, revision, and redesign). Products such as molds that would require more than 4–6 months to develop can be ready for operation in 2–3 months if being made by AM.

 Simpler supply chain for effective low‐volume production: Low‐volume niche production usually requires more investment. Due to this issue, conventional manufacturers usually do not embrace low‐volume production; however, AM companies can level this niche. Many time‐consuming and expensive manufacturing techniques can be superseded by rapid and efficient metal AM for low‐volume manufacturing. However, for mass production, AM is still lagging behind conventional techniques such as casting and forging. One of the reasons of this feature is that AM usually needs a simpler supply chain with fewer players involved. Although AM's supply chain is still under development by industry, it is expected to see more and more low‐volume manufacturing by AM as the supply chain is reliably in place. Lowering the AM material costs will be another factor to foster AM adoption for low‐volume manufacturing when the technology moves toward series manufacturing eventually. Initial costs are usually lower for AM than conventional methods because of the minimum need for tools and jig/fixtures needed for assembly costs. In conventional manufacturing (e.g. casting), each part needs a unique mold. To compensate for the cost of tools for each identical part, the number of products should be very high. AM does not usually need any specialized tooling; therefore, there are essentially no initial costs (called fixed costs too). Due to this saving, it is possible to get to the breakeven point sooner and make profits even with lower volumes.

 Geometric complexity may be free: AM enables the fabrication of complex shapes that cannot be produced by any other conventional manufacturing methods (Figure 1.3). The additive nature of AM offers an opportunity where geometric complexity may not come at a higher price. Unlike conventional methods, AM offers a platform for “design for use” rather than “design for manufacture.” Parts with complex or organic geometry optimized for performance may cost lower; however, attention must be given to the fact that not all complex parts and geometrical features are manufacturable by AM. Process constraints in metal AM (e.g., overhanging features) may cause issues in terms of residual stresses and defects, thus complexity may not come with full freedom!

 Lightweighting: Manufacturers have been trying to fabricate both greener and more economical products. Lightweight components provide two goals: (i) the parts with reduced weight take less energy to move; thus, energy consumption drops, and (ii) less raw materials are used. Both reasons indicate that the production of lightweight components has a positive impact on costs, resources, and the environment. Resource prices are virtually going up worldwide; thus, reducing material consumption is vitally important for product development. AM is nicely linked with topology optimization, making it possible to design and manufacture high‐strength but lightweight structures, where conventional manufacturing processes fail to do so. Chapter 10 highlights how topology optimization and lattice structure design handshake with AM to make the fabrication of lightweight structures possible. Many lightweight but high‐strength components are widely used in the aerospace industry. Any weight reduction is translated into a considerable amount of money saved in terms of the part price itself as well as fuel consumption (Figure 1.4).

Figure 1.3 Complex parts made by AM. The spherical nest has three spheres inside.

Figure 1.4 Lightweight structure made by AM. In this typical bracket, the weight has been reduced by 60% when the mechanical strength and stiffness remain the same.

 Parts consolidation: Mechanical assemblies are common in industrial products. In complex mechanical machines, there are more than tens, hundreds, or even thousands of components that are either welded, or bolted, or press‐fit to each other. Parts consolidation offers many advantages due to the reduction of the number of individual parts needed to be designed, manufactured, and assembled to form the final system. Part consolidations offer multiple benefits: (i) design simplification; (ii) reduction of overall project costs; (iii) reduction of material loss; (iv) reduction of weight; (v) reduction of overall risk where the number of risks associated with too many suppliers of individual parts drops; (vi) better overall performance, as it enables geometries that are desirable but cannot be made with conventional manufacturing.

AM allows for parts consolidation, even removing the need for assembly in some cases. Several applications of AM have obvious benefits for fostering product performance through lightweighting/consolidation without compromising high strength are: optimizing heat sinks to dissipate heat flux better, optimizing fluid flow to minimize drag forces, and optimizing energy absorption to minimize energy consumption. Figure 1.5 shows an example conducted by GE Additive. Almost 300 parts were consolidated in one part for the A‐CT7 engine frame. This consolidation also reduced the seven assemblies to one where more than 10‐pound weight was chopped off.

Figure 1.5 Consolidation of around 300 parts to one part printed by AM.

Source: Courtesy of GE Additive, open access [7], reproduced under the Creative Commons License.

 Functionally graded materials (FGMs) and structures (FGSs): The integration of multiple advanced materials into one component is one of the most rapidly developing areas of AM technology. The capability to create multiphase materials with gradual variations in compositions is one of the important features of AM. During the layer‐by‐layer step of AM processes, the material composition can gradually be altered to obtain the desired functionality. AM also enables the development of FGSs with a single‐phase material, where the density is gradually changed through the addition of cellular/lattice structures; and embedding objects (e.g. sensors) within structures. Among AM processes, DED is the most promising technology to develop such structures, where different powders can be switched insitu to develop desired composition and alloys. Figure 1.6 shows different FGMs that can effectively be developed by DED. Figure 1.7 shows a cutting tool with an embedded fiber optic, as an FGS, developed by an AM‐based process.

 Parts with conformal cooling channels for increased productivity: Cooling systems play a vital role in the productivity and performance of many parts. For example, in an injection molding process, the cooling period of a production cycle counts for more than 40% of cycle time. If this period drops by means of taking the heat out of the mold, the productivity increases dramatically. In an active antenna, developing conformal channels will be very important as the generated heat can be dissipated from the zone much effectively, not to affect the antenna performance. With AM, designers can have much more freedom to incorporate conformal cooling channels into their designs that facilitates uniform cooling over the entire surface. Sub‐conformal channels can be included in the optimization process. Figure 1.8 shows a design of an insert used in molds. The design includes a conformal cooling channel wherein the support cells are used to enhance the heat transfer.

 Parts repair and refurbishment: Machining errors or last‐minute engineering changes can affect on‐time delivery of tooling and potentially impact the introduction date of a new product. AM, especially DED processes, can be applied as a safe technology to repair tooling, especially on critical contacting surfaces. AM increases tool life and, in many cases, can save a high‐value tool that would otherwise need to be replaced. Figure 1.9 shows an LDED process used in the in‐situ repair of turbine blades.

Figure 1.6 Functionally graded materials (FGMs); (a) Laser DED with multiple powder feeders is widely used for FGMs; (b) FGM with two alloys with gradual interface (c) FGM with two alloys with one sharp interface, (d) FGM with multiple interfaces, (e) FGM with three alloys, (f) FGM with selective deposition of secondary alloy.

Source: Redrawn and adapted from [8].

Figure 1.7 A fiber optic embedded in a metallic cutting part using a combined AM‐based process.

Source: Republished with permission from Elsevier [9].

Figure 1.8 A mold insert with (a) conformal cooling channels, (b) conformal and lattice structures to improve heat dissipation.

Source: Republished with permission from Elsevier [10].

Figure 1.9 LDED used to rebuild turbine blades.

Source: Courtesy of Rolls Royce [11].

 A solution to supply shortages in critical crises: Interruption to the global supply chain during crises can be catastrophic to the health and well‐doing of society. The 2020 pandemic is evidence of how the supply chain of medical supplies could have been affected. AM processes can provide remedies during such crises. In March 2020, the 3D printing community got together to help in making medical devices during a very hectic period when medical centers were suffering from a lack of personal protective equipment (PPE). For example, the 3D printing community of the Waterloo region of Canada responded to the call from a local company called InkSmith to locally produce parts of PPEs. The call was received very well, and in a short period of time, more than 200 000 face shields were made and donated to hospitals until the global supply chain started to provide supplies seamlessly. The same model can be used in any crisis. The governments should proactively develop a workflow for critical crises when the AM community can be of tremendous help.

 An effective solution to localized manufacturing: The 2020 pandemic has changed the world forever. The globalization idea has been hammered, and governments are now incentivizing local manufacturing to boost not only local communities but also be ready for future crises. AM will play an important role in the realization of local manufacturing. Besides, as reported in [12], more innovators and user entrepreneurs are turning into on‐demand manufacturers, utilizing the opportunities of access to flexible local production. Further advancements in AM will shift the production of innovative products from a centralized to a local production platform. A shift toward local manufacturing has been started.

 Health and humanitarian benefits: The medicine has been benefiting from AM for almost 20 years. Prosthetics and implants customized and tailored for specific patients are already being manufactured by AM. Many developments on the fabrication of soft tissues, for the realization of the fabrication of organs as well as a host of other personalized medical items and sensors, are underway. It has been proved that the use of precise AM replicas would reduce surgery time significantly for many patients.

Alongside the obvious benefits to industry and medicine, AM is explored as a potential aid to humanitarian issues. Intensive research is already taking place in 3D printed food and 3D printed houses to assist in the provision of food and homes/shelters in areas of humanitarian need.

Developing countries can benefit significantly from AM. In general, AM narrows the path for less developed economies to industrialize [13].