Servo system senses variations in fusion welding process, and adjusts the control parameters to compensate for them. The system assumes a correlation between uniform weld penetration and temperature gradients near the molten puddle. It senses weld properties and makes adjustments to travel speed and weld current

Cook, G.

Mc~campbell, W. M.

English

NASA Technical Reports Server

April 1967 .	 Brief 67-10091 
NASA TECH BRIEF 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
System Maintains Constant Penetration During Fusion Welding 
Reference Source 
Signal Proportional 
ToDesired Penetration 
Electrical Signal 
Proportional to 
Actual Penetration
Work Piece 
Puddle Motor I	 'lAssembly I-?"-- 
Temperature 
Sensor 
The problem: 
In a typical fusion welding process, accurate control 
of voltage, current, and speed to compensate for minor 
variations in joint fitup, plate thickness, and shield 
characteristics has depended on the human operator 
as prime monitor in the feedback loop. A servo sys-
tem is needed that will sense such variations and 
adjust the control parameters to compensate for them. 
The solution: 
On the assumption that a correlation exists between 
uniform weld penetration and the temperature gradi-
ents occurring in the vicinity of the molten puddle, a 
system has been developed to sense direct weld prop-
erties completely from the arc side and by means of 
feedback to a servo, make necessary adjustments to 
travel speed and weld current. 
How it's done: 
The system sensor consists of a single thermocouple 
wire of constantan in sliding contact with the alumi-
num workpiece at a fixed distance from the weld 
area. This sensor is connected to a servo control sys-
tem as shown in the diagram. 
When the output of the thermocouple equals the 
reference voltage, the output of the preamplifier is 
zero, no signal reaches the power am plifier and the
two phase servo motor is held at null position. If 
workpiece temperature at the thermocouple point of 
contact increases, thermocouple output voltage in- 
creases, the preamplifier supplies an input voltage to 
the power amplifier whose output causes the servo 
motor to turn. Through a magnetic clutch, the servo 
motor drives an electrode travel speed potentiometer 
(not shown) in the direction required to increase the 
travel speed. This results in a temperature reduction 
in the workpiece at the thermocouple contact point, 
reducing thermocouple output and effecting a return 
to system equilibrium. If workpiece temperature de- 
creases at the thermocouple contact point, opposite 
polarity voltage is fed to the servo motor to turn it 
in the opposite direction and reduce carriage speed 
until system equilibrium is again effected. 
Notes: 
1. Because the workpiece forms one half of the 
thermocouple junction, radiated torch interference 
is eliminated and the response is essentially in- 
stantaneous. 
Tests with aluminum plates both chemically 
cleaned and not cleaned showed no effect from 
oxide films on the workpiece surface when using 
the single wire technique. 
-	 -	
-	 (continued overleal) 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19670000091 2020-03-11T20:43:13+00:00Z
3. Inquiries concerning this invention may be di-
rected to: 
Technology Utilization Officer 
Marshall Space Flight Center 
Huntsville, Alabama 35812 
Reference: B67-10091
Patent status: 
Inquiries about obtaining rights for the commercial 
use of this invention may be made to NASA, Code 
GP, Washington, D.C. 20546. 
Source: W. M. McCampbell
of Marshall Space Flight Center 
and George Cook
of Merrick Engineering Inc.
under contract to
Marshall Space Flight Center
(M-FS-937) 
Brief 67-10091	 Category 01


System maintains constant penetration during fusion welding

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server