If we are to build a better world, politicians tell us, power must be placed in the right hands. This statement will draw no protest from assemblers. After all, these skilled workers require state-of-the-art power tools to build long-lasting quality products on a daily basis.
These tools include continuous-drive screwdrivers and nutrunners that are powered by air, electricity or a rechargeable battery. And while their uses and capabilities may vary, all of these tools have helped assemblers work more efficiently for many decades.
At one large automotive OEM plant in Detroit, assemblers use Cleco LiveWire DC electric tools to tighten critical joints. In the dashboard subassembly area specifically, the assembler uses a LiveWire screwdriver to tighten multiple fasteners with torque requirements ranging from 4 to 9 newton-meters. The assembler selects the correct socket from the socket tray, which automatically sets the tightening parameters.
According to Adrian Hetzel, global product manager for DC electric tools at Apex Tool Group LLC, this OEM uses battery-powered Cleco LiveWire screwdrivers and nutrunners throughout the plant to tighten critical joints below 50 newton-meters.
Power-tool-usage scenarios like this one are equally common on assembly lines that produce white goods, consumer electronics and airplanes. The reason, according to suppliers, is the dual evolution these tools have undergone the past several decades.
Design-wise, the tools have become sleeker and lighter to improve assembler ergonomics. Equally important, state-of-the-art technology inside the tools enables them to more accurately control speed, torque and angle while gathering specific data.
All power tools, regardless of power source, are classified according to either of two clutch types: continuous drive or discontinuous drive. Continuous-drive screwdrivers and nutrunners feature a clutch that delivers power continuously without interruptions.
In contrast, discontinuous-drive tools (impact wrenches, pulse tools) deliver power in short bursts with no torque between each burst. Pulse tools generate torque hydraulically, whereas impact wrenches generate it mechanically.
“Through the 1980s, impact wrenches were used widespread for all types of fastening,” notes Ken Maio, business development manager at AIMCO Global. “In recent years, though, their high vibration levels have raised manufacturers’ ergonomic concerns and led to a continual decline in the tools being used for assembly. Part of this is because many manufacturers in Europe and the United States are required by law to limit worker exposure to excessive vibration.”
There are three main types of continuous-drive clutches: automatic shut-off (when final torque is reached), stall (caused by torque resistance in the fastener) and cushion (the clutch slips once final torque is reached). Recently, Mountz Inc. developed electric screwdrivers with a soft-stop clutch that prevents shock to sensitive assemblies like disk drives, plastics and electronics.
Continuous-drive tools are usually gear-driven. In a typical pneumatic power tool, for example, the driveshaft is connected to a gear train that is connected to the clutch. During operation, the gear train turns some of the speed of the air motor into torque. When the desired torque has been reached, the clutch either disengages the gear train or shuts off the tool.
Suppliers recommend assemblers use these tools on soft joints (those that require more than 720 degrees of rotation to go from snug to final torque) and joints with high prevailing torque, because tool speed does not change much during run-down and under load. As for assembling critical joints, a continuous-drive tool may be used if it has an automatic shut-off clutch.
The term ‘old reliable’ is an appropriate one to describe pneumatic power tools because they’ve been around for so long. Charles King invented the air hammer in 1890, about 30 years before Desoutter Industrial Tools began making large air-powered screwdrivers and nutrunners. The company introduced handheld models of both tools in the early 1940s.
In terms of operation, all pneumatic tools are powered by compressed air running through an air motor. This action is analogous to a strong wind blowing against a windmill to turn a driveshaft. Eventually, that rotary motion is transferred to the fastener.
Although the air motor in pneumatic tools hasn’t changed much in the past 60 years, suppliers have taken steps to increase pneumatic tools’ fastening accuracy. Many tools feature a transducer that feeds torque data to electronic monitors for error-proofing, statistical process control and counting fasteners installed during a sequence. Others are equipped with sensors to measure how deep the screw goes into the part. In addition, an accessory air controller can be attached to the air line to monitor air flow to the tool.
“One of the main challenges manufacturers that use pneumatic power tools face is making sure the air is always, dry, clean and lubricated,” explains Tim Haper, regional sales manager at ASG, Div. of Jergens. “An FRL (filter, regulator and lubricator) prepackaged assembly is essential to maintain air quality, especially the lubricator because it adds a fine mist to the line to lessen wear. The FRL also optimizes air use by keeping the pressure at 80 psi, thereby preventing air from being too powerful and damaging small components in the tool.”
ASG’s 26C APU series pneumatic screwdriver has a torque range of 0.4 to 4 newton-meters and is used upside down. It features a 0.25-inch hex drive and a pistol grip, which enables assemblers to comfortably install or remove fasteners in tight spaces. The tool is also equipped with the TRACS torque control system (for accuracy, reliability and repeatability) and auto shut-off technology.
Four years ago, DEPRAG Inc. developed the pneumatic Variomat combination tool: A handheld drill that quickly converts to a screwdriver with an adapter. Lori Logan, marketing manager at DEPRAG, says one well-known air conditioning manufacturer uses the tool quite often for assembly. Ergonomically designed and lightweight (2 pounds), the tool has a maximum speed of 1,900 rpm and accepts various screwdriver clutches. The slip clutch requires the operator to manually shut off the screwdriver, whereas the shutoff clutch automatically stops the screwdriver once it reaches preset torque.
APEX makes the 19-Series of pneumatic nutrunners and screwdrivers that includes right-angle, inline and pistol-trigger models. Torque range for more than 50 models is 0.3 to 15.8 newton-meters. The Clecomatic clutch ensures a tightening tolerance of ±10 percent, which is comparable to electric tools. An adjustable reverse lever near the trigger allows one-hand operation for left- or right-handed users. There is also a port to connect a torque verifier.
Electric is Current
When the first DC electric screwdrivers were developed in the early 1930s, they were fairly heavy and definitely not user friendly. After manufacturers showed no interest in using these tools, suppliers stopped making them. They reintroduced them in the 1960s, but it took another two decades before these screwdrivers were sleek and light enough for comfortable handheld use on the assembly line. By the mid-1980s, product quality concerns nudged manufacturers to consider using electric screwdrivers and nutrunners instead of air-powered models.
For many manufacturers, the main impediment to purchasing electric tools 30 years ago was that the tools cost significantly more than pneumatic models. This is still generally the case. For example, an electric tool may cost $5,000 compared to $1,000 for a comparable-power pneumatic model. Suppliers point out, though, that electric tools typically have a lower total cost of ownership because they are more efficient, use less energy and require minimal maintenance.
More importantly, electric tools have greater error-proofing, repeatability and traceability capabilities due to advanced sensors, state-of-the-art software, a closed-loop transducer system and flexible controllers. These features provide immediate process feedback and torque verification, while allowing customized data gathering.
Last year, AIMCO introduced its AcraDyne Gen IV Controller that enables manufacturers to simultaneously control a wide variety of electric power tools with just one cable. It is compatible with more than 300 models of tools having a torque capacity from 0.05 to 8,100 newton-meters. As the core of the modular AcraDyne DC system, this controller enables a user to work in program mode with one tool, review real-time curves on another tool and watch diagnostics on a third. Its comprehensive software enables operators to easily add and change parameter settings, and control tools using a Web-enabled mobile device. The controller stores up to 10,000 rundowns, including curves.
Consumer electronics manufacturers with high production levels like the E-D IV NF-Series of electric screwdrivers from Mountz. The tools produce minimal heat buildup even when operated continuously and feature a durable brushless motor that limits maintenance.
Tool torque ranges from 0.3 to 4.4 newton-meters. Standard Plus models feature a double hit mode for soft joint applications. Angle control and auto reverse models are also available. All models prevent the occurrence of electrostatic discharge.
Last December, Desoutter unveiled its extensive line of economical SLBN electric screwdrivers. Since then, several automotive and white goods manufacturers have begun using the tools for fastening applications that require up to 12 newton-meters of torque. A total of 50 lever- and push-start inline models are available. The lowest-power model (SLB001-L1000-WS4) has a torque range of only 0.02 to 0.15 newton-meter.
Complex and multi-stage screwdriving sequences are possible with DEPRAG’s upgraded Minimat-ED digital electric screwdriver. The operator sets the required torque (0.24 to 4.8 newton-meters) for a screw assembly by pushing a button. When the torque value is reached during installation, the tools shuts off and a green or red LED lights up to indicate whether the assembly was successful or not. The tool’s adjustable screwdriving program enables an operator to easily install several screws with varying tightening parameters.
Mobility and More
“Without a doubt, the trend is toward electric and battery-powered tools,” says Logan. “Five years ago, pneumatic accounted for about 80 percent of power tools, compared to about 60 percent today. The automotive industry leads this trend, but aerospace, medical and transportation manufacturers are also seriously looking at electric and battery-powered tools.”
Several factors account for the growing popularity of cordless tools. First and foremost, they significantly increase worker mobility. Battery-operated tools allow assemblers to more easily work on platforms, inside vehicles and other tight spaces.
By eliminating air hoses and electrical cords, plant managers greatly lessen trip hazards. Assemblers can freely walk up and down an assembly line without worrying about dragging an umbilical behind them, or having it scratch or mar surfaces.
A plant floor without cords and hoses also makes it easier to improve worker efficiency as part of implementing lean manufacturing initiatives.
Desoutter’s B-Flex series of battery-powered nutrunners and screwdrivers are transducerized, stand-alone tools. The nutrunners have a torque range of 3 to 95 newton-meters, and the pistol-grip screwdrivers offer a range of 1.5 to 17 newton-meters. Both types of tools run off an 18- or 36-volt lithium-ion battery. Russ Hughes, product marketing manager at Desoutter, says these tools are popular with automotive and agricultural-equipment manufacturers.
Cordless Flex Power screwdrivers from Mountz offer precise torque control and user comfort, notes Dave Cash, product manager of torque arms at Mountz. The pistol-grip tools are powered by a 10.8-volt lithium-ion battery and designed for applications where air or electric power is not easily accessible.
According to Cash, LED indicators provide an audible and visual alarm signal for the operator when the tool achieves preset torque value. The four models in the series have a torque range of 1 to 12 newton-meters.