Pulse tools

When speed, accuracy and ergonomics really count: Selecting pulse tools and getting the most out of them

In assembly plants, delivering repeatable torque to threaded fasteners is an important issue. However, as plants continue to implement lean initiatives and develop streamlined processes, a huge emphasis is being placed on speed and ergonomics.

When it comes to fastening applications, managers should consider the application’s requirements, both on the assembly line and in the maintenance department. If speed and ergonomics are important considerations, pulse tools may be the right fit for the job.

The right tool for the application
Comprised of an air motor and hydraulic impulse mechanism, a pulse tool creates a “rotary-type” blow resulting from an internal pressure differential in the mechanism. By adjusting the pressure differential with a bypass valve, the mechanism controls torque output. This makes a pulse tool more accurate than a standard impact wrench. And, because pulse tools use hydraulic mechanisms instead of relying on the metal-on-metal hammer blows of standard impact wrenches, noise and vibration levels are significantly lower while the tool delivers the same near reactionless performance.

Torque criticality
When deciding if a pulse tool is the right tool for an application, one important question to ask is: “Is torque important, or is it absolutely critical?” For applications with specific tightening strategies or extremely precise torque requirements, it may be necessary to implement a fastening system such as a transducerized DC electric system. Often used for critical assembly applications, transducerized DC electric systems can apply, measure and record extremely precise torques.

For other applications where critical accuracy is not required, pulse tools deliver consistent torque at a fraction of the cost.

Pulse tools are also much quicker than other systems, providing additional flexibility on the line while delivering virtually no torque reaction to the operator.

The type of joint in an application is also an important consideration. Pulse tools perform best on applications with hard to medium-soft joints. Joints that are extremely soft increase the number of pulses required, and can wear out the tool’s internal mechanisms prematurely. For these types of joints, an air nutrunner may be more appropriate.

Additionally, prevailing-torque applications where resistance is encountered during rundown, are not recommended for pulse tools. Like the soft joint mentioned above, these applications increase the number of pulses required and put additional strain on internal mechanisms. In the long-term, pulse tools perform optimally in applications with a free rundown. These applications require the tool to pulse only when the fastener meets the workpiece instead of during the whole cycle, creating less wear and tear on the tool.

Finally, applications requiring long or multiple extensions may not be a good fit for pulse tools. These extensions lower the torque delivered to fasteners because of increased mass and torsion in the system.

The right pulse tool: torque, type and training
The first consideration in selecting the right pulse tool is the torque requirement of the application. Pulse tools have a variety of torque ranges to meet application demands. When selecting the tool, the target torque for its application should be in the middle of the tool’s torque range. After the tool is installed on the line, it should be periodically calibrated to verify torque accuracy.

Pulse tools are also available in a variety of configurations to provide optimal comfort for the operator. In applications that are difficult to reach or space-restricted, operators may want to choose an angle configuration. For horizontal or vertical applications, standard pistol-grip or inline configurations often provide greater comfort.

Additionally, when used on a medium or hard joint, shut-off pulse tools prevent wear and tear on internal mechanisms. However, in the hands of a trained operator, non-shut-off pulse tools can deliver accuracy equal to or greater than that of their shut-off counterparts.

It’s also important to evaluate operator training when selecting a pulse tool. In situations with an untrained operator or where turnover is frequent, a shut-off pulse tool may be the best choice. The valve in a shut-off pulse tool stops airflow to the pulse mechanism at the preset torque level. This reduces the risk of new operators under-torquing a fastener or letting the tool run longer than necessary.

Tool maintenance
Supplying quality compressed air is the first step in ensuring consistent and long lasting tool performance. Contaminated air can cause erratic performance, serious damage to the air motor and a reduction in power output. Maintaining an air system means regularly cleaning the filter and checking for proper lubrication.

An air dryer should also be utilized to make sure moisture does not reach the tool and rust internal components. Additionally, an air system must supply both the correct volume and pressure. An air regulator ensures that air is at a consistent pressure as long as the compressor can handle the volume requirements of the tool. Tools operating at low air volume or pressure may perform inconsistently and are more susceptible to damage.

Although many new versions feature lube-free motors, proper lubrication of older models is important in tool maintenance. Even though most air systems provide some lubrication, operators should oil their tool at the end of a shift, especially when storing it over the weekend. The most effective way to lubricate the tool is to drop oil in the air inlet and depress the trigger to circulate the oil through the motor. In addition, before using the tool, operators should warm up the impulse mechanism by placing it on a joint and running it.

Perhaps most important, operators should schedule regular maintenance for their tools to prevent damage. Taking tools off the line regularly according to the recommended maintenance schedule and sending them to a service center saves money and prevents tool damage, leading to better performance over the life of the tool.

For pulse tools, changing the hydraulic fluid is one of the most important maintenance procedures. Since the hydraulic mechanism is a sealed component, fluid needs to be drained and replaced without introducing air. Air bubbles in the hydraulic mechanism will result in poor tool performance.

Even though many manuals give step-by-step instructions, it’s best to have an experienced technician with the proper equipment change the hydraulic fluid.

This article appeared in the June/July 2007 issue of MRO Today magazine. Copyright 2007.

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