Assemblers Pull the Plug
Once upon a time, battery-powered screwdrivers and torque wrenches were confined to workbenches and toolboxes. However, cordless tools now offer a serious alternative to traditional electric and pneumatic production equipment. Torque and repeatability are still important concerns, but the performance gaps are closing.
Construction workers and weekend do-it-yourselfers have been strong proponents of cordless tools ever since the technology appeared more than 20 years ago. In most plants, battery-powered tools are still confined to the maintenance department. But, more and more manufacturers are going cordless on the assembly line.
"It has been driven by a desire for a cleaner work area and lower initial cost," says Steve Bulleit, director of training and marketing at AIMCO (Portland, OR). "As [the technology] becomes more sophisticated, engineers have permitted the use of cordless tools in applications previously only served by pneumatic or electric tools."
Cordless, battery-powered tools offer unique advantages for assemblers. For instance, they can fit in tight spaces where an umbilical, such as an air hose or electrical cord, may restrict easy access and maneuverability. They also help eliminate headaches on the plant floor associated with cords, cables and hoses.
Air hoses and electrical cords stretched across a work area pose trip hazards, warns David Smith, executive vice president of Metabo Corp. (West Chester, PA). In addition, Smith says they consume valuable production time, especially when an operator has to detangle a cord or hose when it gets snagged on workstations, parts bins, fixtures, tool carts and other items. In today's flexible assembly environment, cordless tools also allow manufacturers to avoid costly plant floor changes when production lines need to be reconfigured to meet changing market conditions.
"Demand for cordless tools is increasing within the screwdriver sector, especially in Europe," notes Colin Schroder, a product manager at Textron Fastening Systems (Troy, MI). Many European assembly plants have fewer air hoses and more cordless tools than their North American counterparts. "In North America, this trend is a lot slower," Schroder points out. "[But], the fact that there are [tools] that can last for an entire shift on one charge, combined with the flexibility of not having to rely on a stationary power source, is attractive to certain customers."
Shroder says cordless tools allow assemblers to work easily on platforms, overhead lifts and other awkward places where space is at a premium and where taut cords or hoses can drag on tools. Operators can freely walk up and down an assembly line without worrying about dragging an umbilical behind them.
Battery-powered tools also help manufacturers address quality concerns. Cords and hoses that snag on corners or sharp edges can break off key parts or components. Wayward cords and hoses can scratch or mar the paint or surface finish of a product being assembled. Cords, cables and hoses dragging on a floor can pick up dirt, dust, oil and other contaminants.
"[Manufacturers] are beginning to see that cordless tools can perform better than many air tools and DC hand tools in the market," says William Staiger, major accounts manager at Bosch Production Tools (Mount Prospect, IL). "Cordless tools produce great results, give more features than air and eliminate the need for cables or hoses, which contributes to making the assembly process more efficient, reducing injury, and changing how people design an assembly line. We are seeing applications where the use of cordless vs. air has decreased the process cycle time of a particular job by as much as 40 percent."
According to Staiger, cordless tools are more repeatable, because they don't rely on constant air pressure or flow. Many tools monitor battery voltage and disable the tool before the speed of the tool can change as the battery discharges. They also provide operator feedback on battery condition and joint status. "An air tool can't tell you if it successfully fastened a screw, but a cordless tool can," claims Staiger, who says battery-powered tools are "100 times more energy efficient than air tools."
Staiger says Bosch has conducted research studies that prove this. For example, the application of 1,000 shut-off clutch air tools in a plant running 1.5 million fasteners each over three years will consume more than $525,000 worth of electrical energy to run the compressors (at 5 cents per kilowatt). "The same 1,000 cordless tools [installing] the same number of fasteners over the same three years will use $6,000 of electricity," Staiger points out.
Despite all those benefits, not all manufacturing engineers are ready to go cordless. Indeed, many fastening applications are not appropriate for battery-powered tools, especially when a critical joint is required. Sometimes, cordless devices can be inferior to other tool options, such as DC electric or pneumatic screwdrivers.
Although they are the most portable, battery-powered tools can be inconvenient and costly in terms of backup battery storage and the downtime involved in changing battery packs. Because batteries need to be replaced and recharged, cordless tools tend to require higher maintenance than other types of fastening tools.
Battery capacity and lifecycle issues are other drawbacks to cordless tools. "Advances in battery technology tend to move slower than mechanical advances," says Christine Potter, product manager at DeWalt Industrial Tool Co. (Baltimore). "However, battery capacity and amp power has been growing." The big challenge is finding a way to get more battery capacity without adding weight.
"Operators tell us that they are usually satisfied with a battery that will last half of a shift on a moderately used tool," says AIMCO's Bulleit. "A typical battery lasts for about 1,000 fasteners before needing recharging. But, a joint with a high prevailing torque or a soft joint will sap the charge more quickly."
Many manufacturers are waiting for battery technology to improve further. "We only use battery-powered tools to run down threaded fasteners prior to torquing with a controllable torque tool," says Jerry Devee, a torque engineer at Caterpillar's wheel loader and excavator division (Aurora, IL). "Even in this application, we use very few. The reason is that they are not repeatable within our torque specification."
Alex Stoltz, manufacturing-continuation engineering manager at ETC Inc. (Madison, WI), says his plant has been using cordless tools for several years to assemble theatrical light and sound control equipment. "Battery-powered screwdrivers offer greater flexibility than electric tools," he points out. "It's a great way for operators to reach odd angles or reach inside an assembly."
However, Stoltz says battery life is never long enough. "If battery life gets longer, we'll use more cordless tools in the future," he adds. "However, the ability to control and calibrate torque are still limited."
Tool manufacturers are addressing those issues. But, before deciding to go cordless, AIMCO's Bulleit says it is important to understand the difference between the clutch and the power source.
"The application normally dictates the clutch choice-pulse, shut-off clutch, ratchet clutch or stall clutch," explains Bulleit. "The application specifics, such as a hard or soft joint and amount of prevailing torque, will be more appropriate for a specific clutch type. The power source of compressed air, electricity or batteries is, for the most part, a user preference."
Cordless fastening tools are available in either pistol-grip or inline designs and a wide variety of options are available. For example, AIMCO offers 25 different cordless tools. Most tools feature T-handle designs to evenly distribute the weight of the tool and the battery. Cordless tools weigh heavier than air and electric-powered devices. Indeed, the typical battery adds more than 1 pound to the weight of a cordless tool, which is heavier than its corded cousins. Electric tools typically weigh 10 to 15 percent more than air tools.
Battery-powered tools are available with a wide variety of clutches, such as cordless pulse tools, cordless shut-off clutch tools, cordless ratchet clutch tools and cordless impacts. Traditionally, any fastening task that required less than 12 newton-meters of torque was a potential application for cordless tools. However, this threshold has changed. Suppliers currently offer cordless tools ranging from 0.5 to 30 newton-meters.
For instance, Bosch offers five models of cordless angle nutrunners ranging from 0.7 to 30 newton-meters. "Our shut-off clutch is shared between air and cordless tools, so the accuracy and durability are identical to our air tools," claims Staiger. His company plans to unveil a line of cordless impulse tools with shut-off capability ranging from 6 to 60 newton-meters by the end of this year.
Most cordless production tools are used for screwdriving and nutrunning applications. However, battery-powered tools can also be used for riveting. Engineers at Textron Fastening Systems have developed cordless tools for installing blind and pierce rivets. The tools use an electric motor to drive a hydraulic pump to produce the pulling or pushing force required.
"A huge amount of work is required from the battery, compared to screwdriving," says Schroder. However, he claims the cordless tool can install up to 600 rivets with one charge.
"It has not been possible to create the same performance of a pneumatic tool," Schroder points out. "With screwdrivers, a rotating force is used to install the fastener. Hence, it is very easy to produce a high-performing battery tool. For [cordless riveting tools], we have to convert a rotating force into a pulling or pushing action, which is much more difficult to achieve."
Before cordless tools find widespread acceptance for assembly applications, manufacturing engineers must change the way they perceive the technology. "[They] used to think of cordless tools as dumb drills with poor battery life, low durability, poor quality, and no accuracy or torque control," says Staiger. "[Operators] were always tethered to an air hose or DC tool, which limited how [manufacturing engineers] could build products and design assembly lines.
"We are seeing a big change as [cordless tools] outperform customer expectations," adds Staiger. "We have seen customers go from air-powered impulse tools to cordless shut-off tools, because the process time of fastening goes down when you do not have an air hose to drag around the floor."
According to AIMCO's Bulleit, cordless tools still suffer from an image issue. "Many people think that all cordless tools are the same," he explains. "But, that's simply not the case. The cordless tool you can buy for $250 at your local Home Depot is a different animal than a cordless pulse tool that costs more than $1,000."
"The biggest hurdle to overcome is always the same: The customer thinks of cordless as a dumb drill-driver with poor battery life," adds Staiger. "Some manufacturers prohibit the use of battery tools, because they have a perception that the tool is not able to produce accurate, consistent results. Their experience with cordless technology has been poor battery life, poor durability, lack of process control, and poor power and weight ratios."
On the other hand, many large manufacturers are eager to find cost-effective alternatives to pneumatic tools. They are willing to invest in cordless technology to eliminate or reduce miles of air hoses in their factories. According to Staiger, automotive and aerospace manufacturers have been the "most accepting" of the technology, but appliance makers are not far behind.
"Automotive and truck assembly plants have been key players in utilizing cordless tools," says Bulleit, especially for applications that involve awkward areas such as interior trim screws. In addition, "large painted or finished surfaces are often scratched or damaged by the air hose or metal fittings of pneumatic tools, making cordless tools a good alternative for improving product quality," Bulleit points out.
However, some manufacturers have been more reluctant to adopt battery-powered production tools. "Cordless tools have a lower duty cycle than industrial pneumatic assembly tools," says Bulleit. "So, when used in applications or industries where the cycle rate is very high, pneumatic assembly tools are more reliable."
Furniture manufacturers have not been as eager to jump on the cordless band wagon. "This is primarily due to the fact that it's hard to use a shut-off clutch in wood, since the density of wood varies so much," says Staiger. "As a result, they use cushion clutch-type tools or standard drill- drivers that are significantly lower in cost. The demand is simply not there yet." However, Staiger claims that there are "significant changes on the horizon for cordless products that will shift the paradigm of manufacturing in the very near future."