Lincoln Electric LN-15 User Manual

PROCESS

WAVEFORM CONTROL TECHNOLOGY

Surface Tension Transfer®(STT®)

Surface Tension Transfer

(STT®) welding is a GMAW, controlled short circuit transfer process developed and patented by The Lincoln Electric Company.

Unlike standard CV GMAW machines, the STT

machine has no voltage control knob. STT®uses current controls to adjust the heat independent of wire feed speed, so changes in electrode extension do not affect heat.The STT process makes welds that require low heat input much easier without overheating or burning through, and distortion is minimized. Spatter and fumes are reduced because the electrode is not overheated–even with larger diameter wires and 100% CO

shielding gas. This gas and wire combination lowers consumable costs.

Conventional CV short circuit transfer using CO2and .045" solid wire.

STT®using CO2and

.045" solid wire.

advantages

GOOD PENETRATION AND LOW HEAT INPUT CONTROL

Ideal for welding on joints with open root, gaps, or on thin material with no burnthrough.

REDUCED SPATTER AND FUMES

Current is controlled to achieve optimum metal transfer.

REDUCED COSTS

Ability to use 100% CO2or argon shielding gas blends with larger diameter wires.

GOOD BEAD CONTROL AND FASTER TRAVEL SPEEDS

Can replace GTAW in many applications without sacrificing appearance.

Patented.This product is protected by one or more of the following United States patents: 4,717,807; 4,897,523; 4,866,247; 4,835,360; 4,954,691; 4,972,064; 5,001,326; 5,003,154; 5,148,001;5,961,863; 6,051,810; 6,160,241; 6,274,854; 6,172,233; 6,215,100; 6,204,478.The application of the STT process for root pass pipe welding and wallpapering of industrial vessels with nickel alloy sheets are patented.The application of processes marketed by other welding manufacturers that are similar to STT may infringe on these patents: 5,676,857; 5,742,029; 5,981,906; 6,093,906.

NX-2.20 11/06

WAVEFORM CONTROL TECHNOLOGY®™

PROCESS

Surface Tension Transfer®(STT®)

How

STT®works

A BACKGROUND CURRENT between 50 and 100 amps maintains the arc and contributes to base metal heating. After the electrode initially shorts to the weld pool, the current is quickly reduced to ensure a solid short. PINCH CURRENT is then applied to squeeze molten metal down into the pool while monitoring the necking of the liquid bridge from electrical signals. When the liquid bridge is about to break, the power source reacts by reducing the current to about 45-50 amps. Immediately following the arc re-establishment, a PEAK CURRENT is applied to produce plasma force pushing down the weld pool to prevent accidental short and to heat the puddle and the joint. Finally, exponential TAIL-OUT is adjusted to regulate overall heat input. BACKGROUND CURRENT serves as a fine heat control.

THE STT PROCESS

PINCH CURRENT

BACKGROUND CURRENT

PEAK TIME

C D E A

PEAK CURRENT

TAIL-OUT SPEED

2/4

The TAIL-OUT CONTROL adjusts the rate that the current is changed from PEAK to BACKGROUND. Basically, the TAILOUT is a coarse heat control.

A. STT®produces a uniform molten ball and maintains it until the “ball” shorts to the puddle.

B. When the “ball” shorts to the puddle, the current is reduced to a low level allowing the molten ball to wet into the puddle.

C. Automatically, a precision PINCH CURRENT waveform is applied to the short. During this time, special circuitry determines that the short is about to break and reduces the current to avoid the spatter producing “explosion”.

D. STT®circuitry re- establishes the welding arc at a low current level.

E. STT®circuitry senses that the arc is re-established, and automatically applies PEAK CURRENT, which sets the proper arc length. Following PEAK CURRENT, internal circuitry automat-ically switches to the BACKGROUND CURRENT, which serves as a fine heat control.

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