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SCS® Spot Welding GuidelinesAs prepared by Richard Dunbar of Welding Engineering Associates, Inc., Fischers, IN

Actual weld testing was performed at Unitrol Electronics, Northbrook, IL

This project indicates that SCS processed steel is suitable for the resistance welding process. Findings show that SCS issuperior in weldability to hot-rolled black (HRB) steel, and equivalent to hot-rolled pickled & oiled (HRP&O) steel.

Spot welding SCS processed steel requires regular cleaning of the electrodes, but oxide pick-up when spot welding SCSis considerably less than HRB or HRP&O. Without cleaning, the SCS surface oxide will accumulate on the electrodefaces causing misshaped weld nuggets. Electrode life when welding SCS is equivalent to life when welding HRP&O.

Basics of Welding Sequence for SCSThe table below lists the parameters included in a resistance welder control, a brief description of each, and a startingpoint for settings that should yield good results for spot welding SCS processed material. Base settings were acquiredusing .100” thick (12 gauge) of ASME specification SA-414-99 addenda GR-6 pressure vessel quality steel, a low alloyhigh strength material. See pages 3 - 5 of this document for guidelines on determining weld quality.

Important note: settings tuned to weld SCS to SCS should also yield good results when welding SCS to HRP&O aswell as when welding HRP&O to HRP&O, so no switching is required.

NOTE: if you are using Soft Touch Software produced by Unitrol Electronics Inc., it requires anadditional hardware item to increase sensitivity for SCS material. Contact Roger Hirsh at UnitrolElectronics for additional information. (800) 621-4244

Parameter Name Parameter Description Recommended Starting Point for SCSProcessed Material

Electrode Varies with specific application. Use RWMA Class 2 pointed nose electrodes5/8” diameter with 3/8”diameter face.

Tip force Weld force required in psi 2000 psi +/-100 psiSqueeze Time This is the time value for bringing the

electrodes together capturing parts to bewelded with intimate contact prior toelectronically energizing the secondaryweld current power.

Weld machine dependant; open tip spacingvaries with welder set up

Preheat Percent of heat lower than weld heat 5500 amperes +/-200Preheat Time Time in cycles (Hz) for preheat 10 HzUpslope Percent of heat lower than the weld

percent to ramp of weld heatUpslope Time Time period for ramp up

Often used with coated materials. Notnormally required for SCS or HRP&O.

Weld (Heat) In percentage of weld transformer outputat a given tap switch positionNote: if constant current feature isavailable this will be set in desiredamperage value (with a high/low window)

12,000 amperes +/-300

Weld Time Time of weld function 5-10 HzWeld Pulsation Number of pulses 4 pulses (this weld pulse is at the 12,000

amp weld heat setting)Pulsation Time Time duration of pulse 10 HzPulsation Cool Off time between pulses 4 HzDownslope Power ramp downDownslope Time Time period for power ramp down

Often used with coated materials. Notnormally required for SCS or HRP&O.

Quench Time Off time used with or in place of squeezetime for permitting the weld to cool priorto post heat or temper

15Hz

Post Heat and/or Temper Heat Percent of heat lower than the weldsetting for annealing the weld and theheat affected zone.

3100 amp +/-200

Post Heat and/or Temper Time Time period for above sequence 30 HzHold Time Time applied at the end of the weld

procedure to assure full nuggetsolidification and subsequent functiontreatments prior to releasing air pressuretip force and allowing the upper weldelectrode to return to its neutral position.

5-10 Hz

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General Rules for Making Good Spot Weldsas derived by Richard Dunbar from Rules for Spot Welding out of the

Resistance Welder Manufacturers Association’s Resistance Welding Manual

a. Too short squeeze time can result in metal expulsion, overheating electrodes, bad welds, marked work.

b. Too long weld time will shorten electrodes life, cause excessive indentation at surfaces and cause internal cracksin the weld nugget.

c. A peel destructive test on test strips of the same material and combination is recommended.

d. Too short weld time will result in low weld strength, in proportion with weld heat.

e. Too short hold time can result in surface expulsion, electrodes sticking, and internal cracks in the weld nugget.

f. Weld pressure too low can result in expulsion of metal, electrode sticking, short electrode life, and possibleinternal cracks in the weld nugget.

g. Weld pressure too high can result in variable weld strength, excessive weld current requirements, mushroomingof electrodes, and excessive indentation.

h. With all other settings correct, adjust weld current to meet weld quality standards using recommended startingpoints.

i. Electrode contact face too small will result in too small a spot, excessive electrode mushrooming, and excessiveindentation. Too large an electrode contact area will result in too large a weld (assuming current is setaccordingly). Use RWMA charts for electrode manufacturer recommendations.

j. Electrodes misaligned or miss-matched will result in expulsion, and displaced weld nugget and excessiveelectrode wear.

k. Insufficient cooling will result in mushrooming and short electrode life. Adequate water cooling of the weldingsystem is crucial.

The following comparison, as tested by Richard Dunbar of Welding Engineering Associates, shows that SCSprocessed material has no more resistance to spot welding than does HRP&O and in fact has considerably lessresistance than HRB.

Electrical Resistivity of Surface Oxides and ContaminantsHRB 80-100 ohmsHRP&O 15-30 ohmsSCS 15-30 ohms

Note: The surface oxides resulting from any surface contaminants (including oil and dirt) are non-conductive and aredetrimental to any welding process. In the case of resistance spot welding it requires additional electrical power tobreak through these surface contaminants and expel the refuse so as to prevent entrapment within the weld metalnugget.

Properly fused weld metal from the two members being joined must be free of oxides formed from surfacecontaminants during welding for sound weld results.

Pages 3 - 5 are excerpts from the Specification for Automotive Weld Quality - ResistanceSpot Welding section of the American Welding Society Standard for more information onhow to determine weld quality.

Page 3 of 5

This page is an excerpt from the Specification for Automotive Weld Quality - Resistance Spot Weldingsection of the American Welding Society Standard.

Page 4 of 5

This page is an excerpt from the Specification for Automotive Weld Quality - Resistance Spot Weldingsection of the American Welding Society Standard.

Page 5 of 5

This page is an excerpt from the Specification for Automotive Weld Quality - Resistance Spot Weldingsection of the American Welding Society Standard.