Machinery's Handbook, 31st Edition
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METAL ADDITIVE MANUFACTURING PROCESSES
Conventional Manufacturing
Conventional Manufacturing
Breakeven Point
Additive Manufacturing
Additive Manufacturing
Breakeven Point
Number Units Manufactured
Geometric Complexity
(a) (b) Fig. 30. a) Cost as a Function of Number of Units Manufactured; b) Cost as a Function of Geometric Complexity of a Part
Advantages of AM technology include: • Short lead time and fast prototyping can be achieved using a 3D file. • Design changes easily can be made, facilitating product development. • New designs are possible that are not doable with conventional processes. • Complex assemblies can be combined into a single part. • Flexibility enables production of customized single- and short-run parts. • Multiple 3D files for different parts/customers can be handled simultaneously. Many metal parts currently being made by AM would be cost-prohibitive, difficult, or im - possible to produce using conventional manufacturing methods, such as casting or machin- ing. This gives AM an advantage, but only if the right types of parts are selected. Quality requirements play a major role. With most AM processes, good feature detail and surface finish are possible and comparable to metal castings, but surface quality is not comparable to CNC-machined parts, and additional surfacing adds processing time and expense. If a metal part can be produced by conventional processes at a reasonable cost and the number of units to be produced is relatively high, it usually is best to go that route at the present time. Fig. 30a illustrates cost per unit as a function of number of units manufactured, compar- ing AM and traditional manufacturing methods. The initial cost of traditional methods is high due to the cost of tooling (molds or dies) or CNC machines and programming, but cost per unit manufactured decreases as these costs are shared over each part produced. Meanwhile, the cost of parts by AM remains the same, regardless of the number of units manufactured. Breakeven between the two production approaches occurs where these curves cross. AM is cost-efficient for small quantities, but traditional production methods yield cost advantages at higher volumes, as suggested by the declining cost curve. The breakeven point may be on the order of 100 to 1,000, with this number being higher for complex shapes. Geometric complexity of a part has a significant influence on the cost per unit manu - factured. Increasing complexity leads to exponentially increasing cost of conventional production technologies for small series production, as shown in Fig. 30b. By contrast with conventional production technologies, manufacturing costs for AM technologies do not increase with higher geometric complexity. Additive manufacturing also is efficient in terms of energy and materials. In addition to not wasting quantities of expensive metals, the efficiency of AM processes opens the opportunity to produce lightweight components with a buy-to-fly ratio close to 1. (Buy- to-fly ratio is the ratio of the weight of raw material used for a component to the weight of the component itself.) Fig. 31 illustrates comparative data on energy and material efficiency for production of high-performance parts by conventional CNC machining and AM. (This example is based on using electron beam powder bed fusion to produce a specialized aircraft bracket.) Material waste is extensive in CNC machining, with a buy-to-fly ratio of 8:1, compared to 1.5:1 for AM.
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