47). High material costs currently limit the use of 3-D printing to applications that are high value, and/or when speed or privacy is critical. To d a y, 3-D printing works with plastics, resins, and metals, with a precision of around one-tenth of a millimeter (‘‘ Pr in t Me,’ ’ 2011). According to one source, the robot arm of a 3-D printer needs to be 10 times more precise before it can compete with industrial engineering processes (Rudd, 2011). There are also some strength issues relating to weak bond- ing between layers that can lead to delamination and breakage under stress; additionally , the materials’ strength, viscosity , dimensional stability , resistance to heat and moisture, and color stability need careful evaluation (Sherman, 2009; Stemp-Morlock, 2010). Strength-related issues are especially critical when parts made with 3-D printing are load bearing. As the prices of raw materials drop and material quality gets better , the use of 3-D technology will expand beyond its present scope. Applications that can increase include bridge manufacturing, to fill orders prior to product commercialization and to fill emergency orders; custom manufacturing for jewelry and hobby applications; parts for machin- ery and aircraft, where strength is a major issue; emergency shipments of parts; and situations where inventory carrying costs are high relative to production costs. A secondary promise of 3-D printing lies in sepa- ration of product design from product manufactur- ing. As 3-D printing evolves, consumers will be able to purchase designs online and then build products at home. Appliance companies can also contract out the manufacturing of spare parts to third parties, which will then build parts based on CAD software provided by the appliance manufacturer . Since no inventories will have to be kept, parts costs could decrease. Spare parts availability can also expand, as it is less costly to retain old designs than excess inventories of spare parts. Within the next 5 years or so, one can reasonably forecast a number of significant 3-D printing supply chain developments on not only the design side, but also the production side. A large number of firms will soon offer CAD-CAM designs for downloading by final consumers, as well as retailers.