Nammo Composite Solutions (Salt Lake City, Utah, USA) reports it has developed an automated composite manufacturing process for the production of a next-generation military missile launcher assembly. The new work cell features automated solutions for high-volume, affordable composite manufacturing.
The automated work cell is not limited to simply composite fabrication; it also features pre-production automated grit blasting of incoming metallic liners and permits easy installation and co- curing of complex electrical wiring harnesses. With demand as high as 100 parts per day, an automated process was the obvious solution for Nammo to implement.
The composite manufacturing process used to fabricate the missile launcher assembly is resin transfer molding (RTM). In this RTM process, dry fabric preforms are built over metallic mandrels and subsequently inserted into matched metal molds for wet-out through injection of liquid resin. Matched metal tools permit the integration of two integral subassemblies: a complex shaped metal liner and a flexible electrical harness. Like other closed volume molding processes, RTM provides a fully tooled part surface for dimensional control and thus net shape molding of product with minimal finish machining required.
The new work cell at Nammo Composite Solutions was designed and built by the company's manufacturing engineering and controls engineering staff. The composite work cell comprises roughly 2,500 ft2/232m2 of streamlined floor space. Nammo developed a 3-D CAD model of its entire 67,000-ft2/6,225m2 shop floor to best determine the layout and flow of product throughout the site.
The cornerstone of Nammo’s work cell design is the concept of One Piece Flow. With the customer’s demand for product as high as 100 parts per day, Nammo was initially inclined to meet rate through the use of multicavity tools for curing of composites in a batch style sequence. However, after analyzing the process, it was determined that a single-cavity tool and one-piece flow approach was the best solution.
The one-piece flow approach results in the fastest production of launchers as the supply of molded parts meets the demand of the next process step. For example, since the bonding, painting, part marking, and inspection processes are all single-piece processes, the supply of composite launchers always meets the quantity demand of the next step in the manufacturing process. Were a multi-cavity tool approach used, the resulting batch of products would overload the incoming material bin of the next process step. A batch style approach would be costly in that piles of work in process would be stored at the subsequent process stations.
Nammo also found the use of a single-cavity tool to be safest and lowest risk solution. When the Nammo design team evaluated workforce safety as a design consideration, it found that size and weight of a single-cavity tool is significantly less than that of a large multicavity tool.
While performing a process risk mitigation analysis, Nammo found that the one-piece flow work-cell design also came out on top. With the one piece flow approach, if something were to go wrong in the cure or resin injection process, the potential resulting scrap is only limited to one part, rather than an entire batch.
In the work cell, multiple heated presses control the closure of the tools and temperature ramping, while integrated software records both tool temperature and vacuum during the resin injection sequence. These platen presses are also designed and built by the engineering team at Nammo. The presses are linked to a conveyor oven for post curing and cooling of the matched metal tools. Up to 500 lb/227 kig of resin is housed in a central storage station and fed to each press via automated precision dispensing, resulting in rapid yet efficient movement of the 2.25 lb/1 kg of resin to each injection station. Bar coding is employed to reduce the amount of shop floor paperwork that is collected for part traceability.
The work cell design permits data acquisition, which results in generation of an electronic file containing the cure cycle and tool temperature history for each component. This U-shaped work cell design permits the production of up to 100 parts per day by shuttling tooling from room temperature preform/liner/harness assembly stations to elevated temperature cure and post cure, then back to room temperature conditions for part demolding and tool cleaning. This automation of tool movement with integrated temperature ramping, dwell and cooling allows Nammo to meet the aggressive demands for product from its customer.
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