Cutting the Cord
As fastening applications become more complex, power tools are becoming more specialized.
When precise torque control is required, assemblers reach for DC electric tools. When ergonomics are the primary concern, pneumatic pulse tools often get the call. And, when assemblers need to drive fasteners in close quarters, a growing number are putting cordless tools to the test.
According to a 1997 study conducted by Business Trend Analysts (Commack, NY), battery-powered hand tools have captured 11 percent of the industrial power tool market and continue to post the fastest sales growth in the industry. Assemblers and other industrial users spent a healthy $383 million on cordless tools during 1996, a 7.7 percent increase from the previous year. Some 90 percent of that total was spent on driver-drills.
"There’s demand across the board for cordless tools," says Jim Griffin of Makita USA Inc. (La Mirada, CA). "Professionals want to cut the cord on everything—drills, saws, any tool that has a cord."
Cordless tools can be found at Chrysler Corp., Harley-Davidson Motor Co. and Vulcan-Hart Inc. Why the surge in popularity for cordless? Rich Tisza, technical advisor with Fein Power Tools Inc. (Pittsburgh), says the answer is simple—mobility.
"The main drawback with electric or pneumatic tools is that operators can only go as far as the cords allow," says Tisza, whose company makes 9.6- and 12-volt cordless screwdrivers and drills. "If they need to reach to high places, the cord drags on the tool. If they have to walk up and down the assembly line—maybe 70 feet—the cord limits that movement." With cordless tools, operators don’t have to worry about the clutter of the cord or where they are going to plug in. With an electric tool, they have to worry about somebody running over the cord and the risk of electrical shock, says Tisza.
Preserving the cosmetic appearance of a product is another factor in the growing popularity of cordless tools. Bruce Fowler, senior product engineer for Cooper Power Tools Intool Operation (Houston), says many automakers use cordless tools to assemble trim components in vehicle interiors.
"Beside the fact that they are difficult to maneuver inside a vehicle, air hoses and electrical cords can pick up dirt from the shop floor," says Fowler. "Assemblers don’t want to risk messing up the interior."
Technology ImprovementsAlthough home repair enthusiasts have used cordless tools for years, manufacturers have been slow to embrace the tools because early models lacked the power, repeatability and durability for assembly applications. However, cordless tools have improved significantly during the past several years. Batteries have become more powerful and longer lasting. Gears and clutches produce more torque with less energy. There are even hybrid cordless tools available—pulse tools in which the hydraulic pulse mechanism is powered by a battery instead of compressed air.
The first 2.4-volt cordless screwdriver, powered by a lead-acid battery, was introduced for the home market 20 years ago. Since then, cordless tools have gradually increased in power. Today, 7.2-, 9.6-, 12-, 14.4- and 18-volt industrial models are available.
"With the increases in voltage, cordless tools can achieve more power and more inch-pounds of torque. This allows them to be used in a wider range of applications," says E.J. Loferski, product manager for Milwaukee Electric Tool Corp. (Brookfield, WI). "Before, cordless tools could just be used to drive screws. Now, they can be used to auger holes and saw wood."
Assemblers still won’t be able to secure lug nuts with cordless tools. The most powerful models can only generate 25 ft-lb of torque. But for light assembly tasks, cordless tools compare favorably with corded tools. In fact, many cordless tools are built with the same components and have the same features as their corded cousins.
"Our cordless Saws-All has the same front end as the corded version," says Loferski. "The only difference between the two is the electrical system has been changed to DC, so it can run off the battery."
Because of their batteries, cordless tools are slightly heavier than their pneumatic counterparts. For example, a pistol-grip pneumatic screwdriver, capable of generating a maximum torque of 11 ft-lb, weighs 1.6 to 3.1 pounds. A similar cordless tool weighs 3.5 to 4 pounds. As a rule of thumb, the higher the voltage, the heavier and more expensive, the cordless tool.
Although cordless tools produce considerably fewer revolutions per minute than comparable pneumatic tools, they don’t necessarily sacrifice power. A fast cordless tool tops out at about 1,500 rpm, and cordless pulse tools can hit free speeds of 2,200 rpm. In contrast, comparable pneumatic tools can hit 9,500 rpm.
Noise levels are also comparable. Most cordless tools produce 70 to 80 decibels of noise, which is comparable to pneumatic pulse tools. Some cord-less models operate at less than 70 decibels.
Batteries ‘Take Charge’The biggest technological improvement in cordless tools has been in batteries, which have benefited from the development of products such as camcorders, laptop computers and cellular phones. The original lead-acid batteries, which were heavy, bulky and short-lived, were abandoned in favor of nickel-cadmium batteries. These batteries were lighter and had higher power capacities than lead-acid batteries. However, early versions of nickel-cadmium batteries had a problem with "memory."
"If the battery was recharged before it was fully drained, it would ‘remember’ that level as its low point. As a result, the battery would lose its ability to fully recharge," says Fowler. "In a three-shift operation, that could cause real problems."
During the past 5 years, tool makers have solved that problem and are now concentrating on extending the run time, or amp-hours, of their batteries. Milwaukee’s Loferski likens the concept of amp-hours to an automobile gas tank. "The larger its gas tank, the further a car will go after a fill-up," he says. "Similarly, the more amp-hours the battery has, the more work the tool can do on a full charge. A 2 amp-hour battery will drill more holes and drive more screws than a 1.3 amp-hour battery."
Most nickel-cadmium batteries have run times of under 2 amp-hours, but a few high-end models are rated as high as 2.4 amp-hours. Nickel-metal hydride batteries offer assemblers 2 to 3 amp-hours.
"Of course, the longer the run time, the higher the price," says Griffin. "A 1.3 amp-hour battery will be half the price of a 2.2 amp-hour battery."
Tool makers are also making the batteries more convenient to use. For example, the battery pack on Milwaukee’s 18-volt Power-Plus cordless screwdriver is reversible, creating clearance to fit into cramped work spaces and allowing the operator to adjust the balance of the tool. Bosch Auto-mation Technology (Buchanan, MI) offers a "fuzzy logic" recharger that constantly monitors voltage and battery temperature to prevent undercharging and overcharging.
The future holds even more promise for batteries. Several tool manufacturers are working on lithium-ion batteries that will be lighter, more compact and longer lasting than nickel-cadmium and nickel-metal hydride batteries. These batteries, which could be available in 5 to 6 years, will have run times exceeding 3 amp-hours. And in the distant future, cordless tools could be powered by fuel cells.
Behind Every Silver Lining…Like any type of tool, cordless tools are not without disadvantages. Indeed, the chief advantage of cordless tools—the lack of a connection to a power source—is also their chief disadvantage. Batteries eventually run out of "juice" and have to be recharged. Depending on the tool, the fastener and the hardness of the joint, a 9.6-volt nickel cadmium battery can drive 600 to 1,500 fasteners before it needs to be recharged.
To ensure uninterrupted use, most tool manufacturers supply two batteries with their cordless tools, so one battery can be used while the other recharges. Charging times are also getting faster. Some nickel-cadmium batteries can be recharged in less than 60 minutes.
In addition, batteries eventually wear out.
"Batteries don’t live forever," says Griffin. "Most batteries can be recharged 800 to 1,000 times before they go dead. That varies, depending on the amp-hours of the battery. And, the battery has a shorter life with high-torque applications that put a constant drain on it. High temperatures will shorten battery life; heat is very bad for them."
Another problem with cordless tools is that torque values can vary as the battery drains. Tool suppliers have addressed this problem several ways. For example, Bosch’s cordless tools are equipped with a switch block that prevents the tool from operating when the battery power is too low to maintain torque levels within ±5 percent of the set value. Intool’s cordless screwdriver has an LED that illuminates when the preset torque is reached. The LED fails to illuminate when the battery requires charging.
Security is another issue. Pneumatic tools are rarely lost or stolen, simply because they can almost never be used outside of an assembly plant. Because cordless tools are so portable, there is always a risk that they will "grow legs and walk out" of an assembly plant.
At least one tool manufacturer has addressed this problem by offering an optional antitheft device for its cord-less tools. Atlas Copco Tools Inc. (Farmington Hills, MI) offers three models of 9.6-volt cord-less screwdrivers with a combined torque range of 6 to 90 in.-lb.
"When the battery is taken off, the tool locks itself," says Michael Christopher, market manager for light assembly at Atlas Copco. "Before the battery can be replaced, the tool has to be passed over an infrared scanner. An infrared detector inside the tool reads the infrared beam and unlocks the tool. Without the scanner, the tool is useless."
In the end, the decision whether to use a cordless tool depends on the operator and the application. "Every tool has pros and cons," says Griffin. "A corded tool provides more power, higher torque and endless run time, but there is that problem of the cord. A cordless tool is more convenient, but it’s heavier. The operator has to decide if the weight of the battery is going to be more of a problem than drag of the cord."