From trigger sprayers to disposable shavers, high-speed automation systems assemble consumer products by the millions.
Precision Valve Corp. is one of the largest manufacturers of disposable plastic valves in the world. Its assemblies top bottles of glass cleaner, pesticide, fragrance, shaving cream, styling mousse and myriad other products. In 2004, the company assembled some 4 billion trigger sprayers, finger pumps, spouts and other products. That’s more than 13 valves for every person in the United States!
Even the fastest automated assembly system can’t keep up with that kind of volume, not by itself, anyway. At a production rate of 1,000 parts per minute, an automation system operating nonstop, 24 hours per day, 7 days per week, can produce 524 million assemblies, or just over 13 percent of 4 billion.
But that’s not all. Precision Valve is one of at least five U.S. manufacturers of disposable plastic valves, and several more are located in Europe and China. When you throw in the innumerable other small plastic assemblies produced by the millions each year-pens, shavers, lighters, cosmetics containers, air fresheners-you begin to get an idea of the importance of high-speed automation to the consumer products industry.
Consumer products are assembled on both synchronous and asynchronous automation systems, depending on the number and shape of the parts, the processes for assembling them, and the production volume and variety.
A relatively simple assembly, such as a valve with a few round parts, is an ideal candidate for a continuous motion system, says Scott Corbin, product manager at systems integrator Haumiller. These machines can easily produce 150 to 900 assemblies per minute, and some can output more than 1,200 assemblies per minute. On a continuous motion system, the transfer mechanism doesn’t start and stop, as with an indexing system. Rather, assembly operations are carried out as the parts are moving, and the tools travel with the work in process.
The heart of a continuous motion assembly system is a rotating cylindrical turret. The turret consists of a round dial with a series of tools, called pins, arrayed around its circumference. Parts enter the system single file on tracks from feeders or upstream operations. A star wheel, moving synchronously with the turret, strips off parts one after another and transfers them into nests around the dial. As the turret rotates, each pin is actuated in turn until the process is complete and the assembly is unloaded.
“If most of the components are circular and symmetrical, and if they can be assembled without any radial orientation from one part to the next, then they will be easy to feed into a continuous motion system,” says Bob Ensminger, CEO of systems integrator Arthur G. Russell Co. Inc. “They can easily be snapped or pressed together. This can be done at high speeds and in a relatively small footprint.”
Fives Group recently built a continuous motion system for assembling pen caps. The dial has 80 fixtures and assembles caps a rate of 300 per hour. Caps are fed from a vibratory bowl and placed into the fixtures horizontally. Metal clips are fed from a vibratory bowl to a wheel mechanism. As the wheel rotates, it places a clip, tangs down, onto a cap. Then, a cam-actuated crimping tool pushes the clip against the cap with enough force for the tangs to penetrate the plastic. A spring-loaded mandrel is then inserted into the cap to fold down the tangs against the inside wall of the cap, securing the clip. The crimping tool is then cammed down and the finished cap is inspected. Good assemblies are unloaded, while bad assemblies are rejected.
More complex assemblies require a rotary indexing dial or an indexing carousel. A rotary dial can have up to 16 stations mounted around a turntable driven by a central, vertical shaft. The primary actions of the stations are produced by cams connected to the main drive by horizontal shafts and bevel gears. Secondary movements are carried out by pneumatic mechanisms that are also controlled by the main drive. Depending on the application, rotary indexing dials can achieve assembly rates of up to 200 indexes per minute.
If space is an issue, or if more than 16 stations are needed to assemble the product, a carousel might be a better choice. In a carousel system, fixtures are mounted to a continuous steel belt strung between two wheels. A central camshaft drives the two wheels, as well as the assembly stations, which can be installed both inside and outside the belt loop.
“If there are a lot of parts and you need multiple feeders, a carousel chassis works nicely, because you have lots of space,” observes Ensminger. “An indexing dial can get very congested with too many parts feeders around it. A carousel system can index at up to 60 cycles per minute, and you can typically double- or triple-tool the machine to increase the production rate.”
An asynchronous system is another possibility, particularly if some assembly processes take longer than others. An asynchronous system is also advantageous if the manufacturer requires some flexibility. For example, Isthmus Engineering & Manufacturing recently designed a power-and-free system to assemble and test two types of aerosol pumps. Each assembly consists of four parts, which are fed into the system from vibratory bowls. The assemblies, four to a pallet, travel from station to station on a plastic-chain conveyor. The assemblies are inspected after each part is added, and linear and rotary force tests are performed on the assemblies before they are unloaded. The system produces 30 assemblies per minute.
In some cases, different types of systems are combined. For example, a continuous motion system might feed subassemblies into a rotary indexing dial. Or, an asynchronous system might be used to accommodate processes, such as testing or packaging, that are too slow or too bulky to integrate into a continuous motion system.
For example, Haumiller recently designed a system that combines both continuous motion and rotary indexing machines. The system assembles and tests finger pumps for a small plastic bottle. Most of the pump is assembled on the continuous motion system. Supply tubes are inserted into the pumps on the dial, since those parts are larger and more flexible than the pump’s other parts. The system assembles pumps so quickly that a high-speed video camera is needed to analyze its performance.
“When you’re running 1,000 parts per minute, it’s hard to see what’s going on when there’s a fault,” explains Corbin, whose company has designed machines to assemble some 813 different nozzle and valve designs.