people and vehicles in any weather condition. Its capabilities include global positioning, a laser range fi nder, and the ability to pinpoint and provide coordinates of hostile forces, whether they are on foot or in vehicles. LRAS3 is mounted on vehicles
such as Humvees and Strykers, but it can be used dismounted, as well. It enables Army Scouts to conduct 24- hour reconnaissance and surveillance missions while remaining outside the fi ring range of their adversary.
Challenging Considerations T e critical constraint the team
encountered with mechanical com- ponents used to create the LRAS3 involved design and development of the main sensor housing. T is rect- angular housing (approximately 16 x 18 x 24 inches) needed to serve as an electronics housing, thermal manage- ment system, optical bench and system superstructure (Fig. 2). Lead time and system cost
would be driven by success or fail- ure to achieve these functions. And, because this product was intended for light vehicles or dismounted applications, every bit of weight reduction would be valued by the final customer—the Scout. To meet the program objectives
for a robust yet cost eff ective system, Raytheon engineers performed a trade study comparing fabrication process alternatives including com- posites, weldment, metal assembly and casting. T e aluminum invest- ment casting process was selected because of its ability to provide complex confi guration details that would reduce the piece count, shorten the design cycle, streamline assembly steps and ultimately lead to the low- est total cost for the system.
Design and Development Casting design and development
is not new to Raytheon. T e North Texas design team supporting Combat Systems programs has 40+ years of experience with complex casting appli- cations, including a team of mechani- cal producibility engineers who serve as subject matter experts in the design application of manufacturing processes
Figure 1. The LRAS3 is used by U.S. Army Scouts.
and technologies. T e Raytheon Precision Manufacturing organiza- tion provides stereolithography rapid prototyping, quick-turn prototype machining, and turnkey machining and fi nishing processes for production rate requirements. It is supported by an in-house supply chain organiza- tion. Each of these skills would prove vital throughout the development and fabrication phases of this project. T e overall size of the housing was
predicated on the subsystems, includ- ing electronics and optical elements. Once the ballpark size was estab- lished, it became important to defi ne the required casting wall thickness. Although calculations showed thin walls would satisfy the anticipated structural loads throughout the hous- ing, the practical aspects of fl uidity and castability tilted the ultimate design toward a compromise that would be
both lightweight and producible. As bosses, mounts and other
functional features were modeled into the interior of the housing, wall sec- tions were relieved with cutouts and confi gurations to maintain a consistent wall thickness for castability and fur- ther reduce the weight. T is created a signifi cant challenge for the toolmaker and wax injection personnel (over 300 inserts were required), but ultimately was key to the success of this confi gu- ration. While the structural analysts were crunching their numbers based on estimates of internal component mass, the thermal analysts were devel- oping the approach required to heat sink the circuit cards and electronics. T eir solution resulted in a tall and dense forest of external fi ns, suffi cient to provide required cooling through radiation to the environment (Fig. 3).
Determining Castability Once the general confi guration
parameters were set, it became possible to evaluate the relative castability of these concepts. Stereolithography patterns were produced in several variations using the in-house capabil- ity of the Rapid Prototyping Lab at Raytheon Precision Manufacturing (Fig. 4). T ese patterns were invested and cast to evaluate feeding, fi ll and aspects of metal fl uidity. One signifi cant advantage is that
Figure 2. This is a concept drawing for the LRAS3 sensor housing.
this process creates metal parts from the investment casting process, using
Jul/Aug 2013 | METAL CASTING DESIGN & PURCHASING | 21
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60