Why Proper Torque Verification Matters for Impact Wrench Accuracy

Introduction

Tightening bolts to the proper torque specification is critical across many industries, from automotive assembly to construction projects to aviation manufacturing. Using the right tools for torque verification brings quality, safety, and reliability. This is why impact wrenches accuracy paired with precise torque testing is vital.

What happens when bolts are over or under-torqued? Simply put, the results can range from joint leakage and breakage to large-scale disasters. For example, the NASA Challenger tragedy in 1986 was linked back to an O-ring failure caused by under-torqued bolts.

Clearly, precision matters enormously. However, the typical pneumatic impact wrenches found on most shop floors do not inherently provide the needed accuracy. This is why using a separate torque tester for verification is so important – your impact wrench may hit the right torque value one time, then be significantly off in subsequent uses.

In this article, we’ll cover:

• The importance of proper torque values
• Why impact wrenches lack accuracy
• The role of torque testers and tools
• Tips for impact wrench safety
• Reasons to choose Flexible Assembly Systems

Proper Torque Matters

Torque specifications exist for a reason – to establish just the right clamping force for a given application. Consider head bolts on an engine block or lug nuts holding on a tire – improper torque can lead to catastrophic failure when put under stress.

Many factors are considered when establishing torque values, including the bolt size, grade, thread pitch, materials being joined, expected vibration forces, and acceptable tolerances. Engineers derive the optimal pound-feet (or Newton-meter) figure that will yield the needed preload or stretch on a fastener without yielding or breaking it.

Depending on the application, allowable tolerances around published torque figures can vary. For example, allowable variance on cylinder head bolts is far less than for an exhaust manifold. Given how critical applying appropriate torque is for safety and performance, every assembly environment should adopt processes ensuring accuracy.

The Impact Wrench Accuracy Problem

Impact wrenches provide speed and power for driving fasteners – but not inherently accuracy. Their very purpose centers around generating extremely high torque output for short durations. Squeezing the trigger spins up an internal hammer that strikes the anvil, transmitting torque spikes capable of breakaway and tightening.

However, the torque delivered from each strike depends on several variables:

• Air pressure
• Hose size
• Joint lubrication
• User technique
• Grip
• Age and wear

These factors mean that every subsequent trigger pull will deliver inconsistent torque output somewhere around the tool’s established range. Sometimes you’ll get the needed torque figure spot on – other times too low or high. This inaccuracy puts any assembly requiring specific tolerances at risk when relying on impact tools alone to hit torque targets.

The Vital Role of Torque Testing

Given the inherent accuracy limitation with impact wrenches, using a separate torque testing tool for validation is vital. Purpose built electronic or mechanical torque testers provide precise, calibrated measurements. Common examples like torque wrenches, multi-tools, and twist monitors give fastener technicians critical data for quality control.

Some key capabilities offered by torque testers:

• Highly repeatable readings from fastener to fastener
• Measurements well within tolerance requirements
• Protection against over-torque damage
• Statistical data to pinpoint outliers
• Traceability to standards and calibration
• Multiple adapter heads for different fasteners
• Ergonomic grip and operation

By confirming actual torque figures using these purpose-built testers, mechanics and assemblers prevent defects from incorrect tightening. The precise torque ranges possible accommodate even stringent automotive and aerospace standards. Workers using torque tools gain confidence that the proper preload exists in each bolt to avoid joint failures.

Impact Wrench Use Best Practices

Despite their accuracy limits, pneumatic impact wrenches remain extremely popular for their speed, power, and reliability in assembly environments. Workers tend to love them for saving significant labor compared to using just hand tools when driving multiple fasteners.

By keeping some operational tips in mind, the safety and service life of impact tools improves:

• Use manufacturer recommended air pressures based on tool capability
• Allow the tool to stop spinning before pulling away to avoid lash injuries
• Check for worn hammer/anvil mechanisms periodically
• Use impact rated sockets – don’t use chrome varieties
• Ensure the non-impacting hand stays clear of the work area
• Confirm the tool retains the right torque range through annual calibration checks

Applying these best practices reduces the risk of injury and damage while still allowing efficient use of impact wrenches. Just be sure to check all final torques with a dedicated torque tester as outlined above.

Choose Flexible Assembly From Flexible Assembly Systems

Precision torque control matters deeply for safety and performance. As this article outlines, relying solely on impact guns brings accuracy risks on critical fasteners. While pneumatic impact wrenches drive speed and efficiency for initial tightening, torque testers must provide final verification.

This is why Flexible Assembly developed digital torque tester – for reliably hitting specifications down to +/- 3%. Custom programming lets users set target torque values, fastening angles, and other parameters to meet J1939 standards. Continuous data tracking allows analysis of every fastening for quality control insights.

All torque testers from Flexible Assembly Systems provide the necessary precision and protection required when accuracy matters. Beyond torque, our team creates flexible fastening stations, lift solutions, tool balancers, and more to upgrade assembly ergonomics and efficiency. Contact our engineering team today to discuss how our torque testing and assembly solutions can meet your most demanding tolerances.