This article highlights the next generation of can decorating machines by packagers and the manufacturers of packaging machinery. To build their new next-generation decorator, Alcoa Packaging Machinery’s (APM) engineers were given the rare opportunity to develop the machine from a “white sheet.” The four-color decorator is a continuous-motion, rotary machine, which holds each can body upright on a mandrel. Each can rolls against a blanket cylinder, which transfers an inked pattern from a plate cylinder. APM’s engineers were especially interested in finding out how the mandrel shafts would deflect under load. Deflection is an important consideration for any rotary printer because it determines how well an image will transfer between rolls. APM is planning to unveil its new can decorator at a metal packaging trade show in Germany. The machine has yet to be proven in production, but the design has progressed.
Imagine walking down the soda aisle of your supermarket and seeing among the collection of six-packs a bunch of cans remarkably more colorful than the ones you usually see. These new cans are not limited to two, or three, or even four colors, but reflect every hue of the rainbow, much like the printing you’d find on the pages of a glossy magazine.
Would you buy the product based on its new packaging alone? That’s not likely. Yet the people at Alcoa Packaging Machinery and its parent company, Alcoa, of Pittsburgh, are banking on the fact that at least you would give the product a second look.
Packagers and the manufacturers of packaging machinery hunt for “whatever we can do to differentiate our packages,” said Paul Choate, the engineering manager at Alcoa Packaging Machinery in Englewood, Colo. That could mean developing the next generation of can decorating machines. Or it could mean designing machines capable of embossing raised lettering along the side of a can and printing the letters in full register. To help Alcoa sell more aluminum, the engineers at the packaging machinery unit have been designing both kinds of machines lately, adding to a product mix that includes can forming and base coating machines as well.
To build their new next-generation decorator, APM’s engineers were given the rare opportunity to develop the machine from a “white sheet,” said Choate. Unlike many developmental projects in which designs evolve from existing products, the new decorator made a few departures from the company’s previous machines. Most notably, the new decorator uses a different print process, known as four-color process printing. Where APM’s earlier decorators printed flexographically, applying each color to cans without overlapping the different inks, the new machine prints cans in nearly any color imaginable by superimposing inks of four colors: yellow, magenta, cyan, and black. It is the same principle of color reproduction that is used in printing this magazine.
Because each color required a separate ink, earlier machines could apply only a limited number of colors; the new decorator uses four inks to mix a palette whose size has almost no limit.
Alcoa’s next-generation decorator was also one of the first products that the packaging machinery unit designed using what Choate calls midrange computer software packages, which the company brought in as a new standard.
A Better Mandrel
The four-color decorator is a continuous-motion, rotary machine, which holds each can body upright on a mandrel. Each can rolls against a blanket cylinder, which transfers an inked pattern from a plate cylinder. This happens at production rates of 1,600 to 2,400 cans a minute. The ink applied to each can as it rolls past any one of four blanket cylinders must dry before the next color goes on. Otherwise, the wet ink from the first imprint would smear with ink from the second imprint and produce a color far from that desired. To speed drying, engineers had to specify interstage curing, which bathes each can in ultraviolet light.
One focus of attention during the design of the decorator was the shaft of the can mandrels. The can bodies would be presented to the decorator without lids—completely open on the top ends and capped only later, after filling. The bottoms of the cans, though, would be fully formed at this stage. Cans would slide onto the mandrels, open ends first. The mandrel shafts would be hollow, providing paths through which air evacuated from the cans could escape. The resulting vacuum would hold the cans on the mandrels.
Since the cans were closed at one end, the mandrel shafts could not be supported between bearings. Instead, each mandrel and shaft had to be supported as a cantilevered assembly, with two bearings holding it from one side.
Engineers first laid out the machine in sections, using 2-D drafting software, Personal Designer, a product that was discontinued earlier this year by Parametric Technology Corp. of Waltham, Mass. Designers imported individual parts into a solid modeling program, Solid Edge, from Unigraphics Solutions of St. Louis, to create 3-D models. These models were, in turn, imported to Working Model Motion, a kinematics and dynamics analysis program from MacNeal-Schwendler Corp. of Los Angeles. The engineers used the software to “create restraints that mimic how the part is loaded on the machine,” Choate said.
APM’s engineers were especially interested in finding out how the mandrel shafts would deflect under load. Deflection is an important consideration for any rotary printer because it determines how well an image will transfer between rolls. Once Choate and his team had the model of the mandrel shaft in their analysis program, they could, by factoring in acceleration parameters and estimating loads at various points in the machine cycle, determine a fairly accurate value for deflection.
Choate said that the design team performed “a lot of deflection analysis” in designing the new machine. As the results came in, engineers would trim material from a part and run the analysis again. They ran this procedure many times over until each part reached a material condition of just enough.
Due to the speed at which the new machine operates and the forces that act upon it—both process forces, such as those of the blanket cylinder rolling against the can body, and inertial forces, such as those manifested by the high rotational rate of the decorator—engineers had to call for tight tolerances in their design, while reducing the weight of each component as much as possible.
Choate said, “We were always striving for a fine balance between light weight and strength.” Part size was another important engineering consideration as there was “only so much space to put these things in because of the requirements of the machine.”
In addition to making 3-D models of individual parts, engineers translated entire 2-D subassemblies into three dimensions. The largest assembly, consisting of a 300-part inker subassembly and several other subassemblies, contained 1,000 components. The ability to assemble them all in software allowed the designers to spot interferences.
Choate said the question was not always one of cost versus performance, but in many instances it was, “Do you want the machine to work?” Scrimping was to be avoided. Several times engineers ran up against the strength limits of everyday steels and had to fabricate components from the more exotic, and more costly, high-strength steels.
The role of the computer software was a departure for the company on two counts. APM had only recently begun to consolidate its software to settle on a unified system, and the system in use was less expensive than much of the software the company was phasing out.
To decide how to consolidate their software, APM’s engineers took a look at what their actual computing requirements were. They did not do a lot of complex modeling, said Choate, nor did they do any molding. Mostly, the APM designs involved what Choate termed “analytic parts,” things like cylinders and blocks. Midrange software packages offered the tools that the company’s engineers needed without being overly powerful.
Once the engineers had identified their needs in terms of software power, the company brought economics back into the picture. Choate estimates that the CAD software the engineers were using had cost the company approximately $20,000 per seat, with annual maintenance fees near $3,000 per seat. APM realized it could reduce costs per seat to $5,000. Maintenance fees paid annually would drop to about $1,300. Choate emphasized that cost, although a factor in deciding what software to buy, was not the only factor. “If we had needed any of the capabilities of the high-cost systems, of course we would have paid for them,” he said.
APM decided to use Solid Edge from Unigraphics Solutions for CAD and compatible software from other suppliers. Engineering software includes MacNeal-Schwendler's Working Model Motion and Cosmos/Edge from Structural Research & Analysis Corp. of Milford, Ohio.
Packaging has installed 50 seats of Solid Edge at facilities in Colorado, New York, and Germany, and stores files locally at each location. A server at the Colorado facility makes the files available to all three sites through the Pro-File PDM system from ProCAD Inc. of Duluth, Ga. The cooperative marketing effort is promoted as the Solid Edge Voyager Program.
Alcoa Packaging also has stations of Pro/Engineer from Parametric, which is not part of the Voyager cooperative.
APM is planning to unveil its new can decorator at a metal packaging trade show in Germany. The machine has yet to be proven in production, but Choate said he is pleased with how well the design has progressed.
If all goes according to plan, it may be only a matter of time before you’ll be skipping the magazine rack at the supermarket and going straight to the soda aisle in order to track down a few visual (not to mention, gustatory) confections.