Impact Wrench

Overview

An impact wrench is a handheld power tool that drives and removes threaded fasteners by delivering a rapid series of high-torque rotary blows rather than steady torque. This lets a compact, lightweight tool loosen seized lug nuts and structural bolts that would stall an ordinary drill or driver, while keeping the reaction torque felt by the operator low, between blows the output is unloaded, so the tool does not try to twist out of the hand. This model is a cordless 18 V unit built around a brushless drive, a single-stage planetary reduction and a hammer-and-anvil impact mechanism feeding a 1/2 in square drive.

Power comes from the Battery Pack, a five-cell Li-ion slide pack. Pulling the Variable-Speed Trigger feeds a variable speed signal to the Motor Controller Board, whose three-phase inverter commutates the Brushless Motor from rotor position reported by Hall sensors. A Forward/Reverse Switch sets rotation direction and a Mode/Speed Selector Switch selects among preset speed and torque limits, including a self-tapping mode that eases into the seat before ramping up.

How it works

The motor pinion drives the Planetary Gearbox, a planetary stage that trades speed for torque and turns the cam shaft of the Impact Mechanism. There the rotating shaft carries a hammer on a pair of V-shaped ball-and-groove cam tracks. While resistance is low the hammer stays engaged with the anvil and the fastener simply spins up. Once the joint tightens and torque rises, the cam profile drives the hammer axially back against its return spring, the hammer lugs disengage and clear the anvil, then the spring snaps the hammer forward so its dogs strike the anvil. Each strike delivers a discrete torque pulse; thousands per minute accumulate into far more fastening torque than the motor could supply continuously.

The anvil is the input end of the Square Drive Output, whose 1/2 in square drive shank carries the socket. A spring-loaded detent ball retains the socket, and the whole drive runs in a bearing at the nose. Cooling air drawn through the Housing Assembly passes over the windings, and a drive-end LED Work Light illuminates the work. The clamshell housing, soft overmould grip and belt hook complete the tool, with the entire mechanism, gear train, hammer and anvil, running in grease and isolated from the electronics by seals at the gearcase.