Machine Control: Cartridge Maker Boosts Efficiency

What does it take to bring an old, cam-and-gear-driven mechanical process into the 21st century? Even when the mechanical functionality of a machine has been refined over decades of production, major improvements can be made by taking a step back and evaluating how newer automation technologies can be applied.

The management team at ATK Security and Sporting Group, in Lewiston, Idaho, had just such an opportunity as they made upgrades to a series of cartridge case manufacturing machines.

A cartridge, or “round” of centerfire ammunition consists of the shell casing, the primer, the bullet and the propellant. The “mouth” end of the cartridge is where the bullet and propellant are inserted during loading. The “head” end of the cartridge contains the primer.

Typically, when cartridge casings are cold-formed in a mechanical header, the draw process leaves an uneven mouth. As part of the case manufacturing process, a mouth trim machine cuts the end of the casing to ensure that it is perpendicular to the longitudinal axis of the shell and that it is cut at the correct place so that the height of the casing meets the standard specification for the type of cartridge.

Shell casings are fed and indexed mouth-upward in a rotary dial for transportation between stations on the manufacturing machine. When an untrimmed shell is indexed into the mouth-trim location, a high-speed spindle with a cutting tool is moved down in the vertical axis to trim the mouth. Before exiting, the case is optically inspected for 100 percent verification that the flash hole is present.   

After the mouth is trimmed, the machine indexes and the shell casing gravity feeds to the lower portion of the machine, where another mechanical machine cuts the extractor groove in the head-end of the cartridge case.

Project goals

As ATK’s management team considered how the machine could be improved, they listed a few goals for the project.

One of the main goals was to minimize changeover time. The old machine required many changeover steps to reconfigure it mechanically for producing different cartridge types. To accomplish this, the following changes were made:

• The trim height adjustment went from a mechanical screw to a servo controlled adjustment, which allows for an easy product changeover and the ability to make fine adjustments during operation.

• The case fixturing hardware went from being made for a specific product to “one size fits all,” due to the ability to tune feed rates with servo actuation.

Another project goal was to reduce maintenance expense. The old machines were mechanical, gear-driven with lots of chains and bearings, requiring a high degree of skill to maintain. As parts wore out, getting the machine running again would cost a lot in downtime and machine-builder labor hours. According to ATK Manufacturing Engineer Jeff Williams, many of the machine’s moving assemblies needed to be rebuilt every month. 

Williams observed that both changeover time and maintenance expense could be reduced if some new technology could be included that would reduce the number of moving parts. In addition to making it easier to maintain, this change would also make the machine safer.

The ATK managers were also looking for an improved operator interface. They wanted the control system to be capable of storing build recipes for push-button changeovers, and they welcomed the safety improvements that would come from eliminating the lifting of heavy steel components during maintenance. They also wanted the machine to provide point-of-use operator feedback and control using a touch screen. This would allow the operator to tune the process to maintain consistency of output.

The machines typically operate to a tolerance of ±0.005-inch, but operators of the older machines tended to run them at the outer ends of their control limits, as adjustments were tedious and meant powering down and restarting, sometimes more than once, while they ‘honed in’ on the target settings. With the new system, ATK wanted operators to be able to make tolerance adjustments on-the-fly, using the operator interface, rather than the standard practice of shutting the machine down and searching for hand tools to make adjustments. An improved operator interface would also provide better troubleshooting information to operators and maintenance personnel to help them quickly identify and resolve problems, which also helps to minimize machine downtime.

ATK’s management team looked for a system integrator that had experience with control system development who could help them create the new system. They contacted Concept Systems Inc., of Albany, Ore., an industrial systems integrator with experience in developing control systems and human interfaces for a wide range of motion applications.

Concept Systems engineer Mike Dodds visited ATK to observe their process and discuss the goals for the new project. Then, working closely with ATK engineers, Dodds set out to design a system to meet their expectations. He recommended a programmable motion controller as a cornerstone to begin bringing flexibility to the new design.

“We showed ATK how we could get coordinated motion between multiple axes,” says Dodds. “Originally [for the prototype], indexing drives (stand-alone motion controllers) with an Allen-Bradley MicroLogix 1500 (from Rockwell Automation Inc., Milwaukee) were being used. They were not tied together, so developing coordinated motion profiles was difficult to achieve. We put in servo drives that were connected with a fiber optic network and controlled and synchronized by Allen-Bradley’s CompactLogix PLC (programmable logic controller).  This enabled the design to be more flexible and allows for better maintenance and tuning information to be available at the PLC.”

Reconfigure at will

Dodds also helped add recipe management to the operator interface. He programmed in the parameters for five different cartridge types, and enabled the motion controls and set points to be reconfigured for different production runs at the touch of a button.

“ATK can reconfigure the system at will,” says the Concept Systems engineer. “Before, in order to minimize downtime due to changeovers, they often dedicated individual machines for different cartridge types. Now, the new machines are recipe-configured.” 

“We decreased our changeover time by 75 percent, and the flexibility helps our production planning” adds ATK’s Williams. 

Because many of the components being used in the upgraded machines are available off-the-shelf, new machines can be brought online more quickly and replacement parts obtained, should something break or wear out.

ATK is currently enjoying the system’s inherent ease-of-maintenance, but because of the improved controls and elimination of gearboxes and other mechanical components, ATK also expects to see improved productivity as the performance of the new machines is pushed past the old production rates.

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