Orbital Weld Schedule Programming: Setup Guide for Operators

What Is a Weld Schedule?

A weld schedule is the complete set of programmed parameters that the orbital power supply executes during a weld cycle. It controls everything: how the arc starts, how much current flows at each point around the joint, how fast the weld head rotates, how the arc tapers off at the end, and how long shielding gas flows before and after the weld.

Think of it as a recipe. The power supply reads the schedule and runs the weld automatically — the operator's job is to build the right schedule for the tube size, wall thickness, and material being welded. A good schedule produces a consistent, code-compliant weld every time. A bad one wastes coupons, gas, and time.

Every orbital power supply stores schedules differently, but the underlying parameters are the same across brands — whether you are running an AMI, Arc Machines, Linarc, or Swagelok system. Learn the parameters once and you can program any machine.

Sectors Explained

Orbital welding divides the 360-degree rotation around the tube into segments called sectors (sometimes called levels or zones). Most schedules use between 4 and 12 sectors.

Why not just use one set of parameters for the whole rotation? Gravity. Molten metal behaves differently depending on weld position. At the 12 o'clock position (flat/1G), the puddle sits in the joint naturally. As the weld head rotates toward the 3 o'clock position (vertical/2G), gravity pulls the puddle downward. At 6 o'clock (overhead/4G), the puddle wants to sag away from the joint entirely.

To compensate, most schedules reduce current in the overhead sectors and increase travel speed slightly. The most common approach:

• Sector 1 (12 o'clock start): Highest current — the tube is still cold and you need full penetration to establish the weld.
• Sectors 2–3 (descending toward 6 o'clock): Gradually reduce peak amperage by 5–15% as heat builds in the tube and gravity starts pulling the puddle.
• Sectors 4–5 (6 o'clock, overhead): Lowest current — the puddle tends to sag. Reducing amperage and sometimes increasing travel speed keeps the bead profile controlled.
• Sectors 6+ (ascending back toward 12 o'clock): Ramp current back up slightly, but not to sector 1 levels — the joint is already hot from the first half of the weld.

The overlap zone where the endpoint meets the start point requires a controlled downslope to avoid a thick spot or crater crack.

On thin-wall tube (under 0.049"), many operators run successfully with 4 sectors. Heavier wall and larger diameters benefit from 8–12 sectors for tighter control.

Key Parameters to Program

Every weld schedule consists of the following parameters. You will set most of these for each sector individually.

Current Parameters

• Peak Amperage (Primary Current): The higher current level during the pulse cycle. This is what drives penetration.
• Background Amperage: The lower current between pulses. Keeps the arc lit and allows the puddle to partially solidify. Typically 40–60% of peak amperage.
• Pulse Frequency (PPS): How many times per second the power supply cycles between peak and background. Common range is 0.5 to 5 pulses per second. Lower frequencies (0.5–2 PPS) produce a visible "stacked dimes" bead profile. Higher frequencies smooth the bead out.
• Pulse Ratio / Peak Time Percentage: The percentage of each pulse cycle spent at peak amperage. A 50% ratio means equal time at peak and background. Increasing peak time adds more heat per cycle.

Travel Parameters

• Travel Speed (IPM or RPM): How fast the weld head rotates. Measured in inches per minute at the tube OD surface or in RPM. Travel speed directly affects heat input — slower travel means more energy per inch.
• Rotation Direction: Most schedules run clockwise when viewed from the weld head motor side. Some operators reverse direction for the second pass on multi-pass welds.

Start and End Parameters

• Pre-Purge Time: How long argon flows before the arc strikes. Displaces oxygen from the weld zone and backside of the tube. Minimum 5–10 seconds for small tube; longer for large diameters.
• Post-Purge Time: Argon flow time after arc extinction. Protects the hot weld and tungsten from oxidation. Typical range: 10–30 seconds depending on wall thickness and tube size.
• Upslope Time: How quickly current ramps from arc start to the programmed peak level. A controlled upslope (0.5–3 seconds) prevents blowing through thin material at ignition.
• Downslope Time: The taper-down at the end of the weld that fills the crater and feathers the endpoint into the start. Typical range: 2–8 seconds.

Gas Parameters

• Shield Gas Flow (external): Argon flow through the weld head, typically 15–35 CFH depending on head size and tube diameter.
• Purge Gas Flow (internal): Argon flow inside the tube. Critical for stainless steel and reactive alloys. Flow rate depends on tube volume — enough to displace oxygen without excessive turbulence. Target oxygen levels below 50 ppm for stainless, below 10 ppm for titanium.

Starter Weld Schedule Chart

The table below provides starting parameters for autogenous (no filler wire) orbital fusion welds on 316L stainless steel tube using 2% ceriated or lanthanated tungsten at 3/32" diameter. These are starting points — expect to adjust based on your specific material heat, fit-up, and equipment.

Tube OD	Wall Thickness	Peak Amps	Background Amps	Travel Speed (IPM)	Pulse Rate (PPS)	Pre-Purge (sec)	Post-Purge (sec)	Electrode Diameter
1/4"	0.035"	12	6	4.0	3.0	8	15	1/16"
1/2"	0.049"	25	12	4.5	2.5	8	15	3/32"
1"	0.049"	35	17	5.0	2.0	10	20	3/32"
1.5"	0.065"	55	27	5.0	1.5	12	20	3/32"
2"	0.065"	65	32	5.5	1.5	15	25	3/32"
3"	0.065"	80	40	5.5	1.0	20	30	3/32"
4"	0.083"	100	50	5.0	1.0	25	30	1/8"

Notes on the chart:

• Peak amps listed are for sector 1 (12 o'clock). Reduce by 5–10% for overhead sectors.
• Travel speed may need to increase 5–10% in overhead sectors to prevent sag.
• Background amps are set at approximately 50% of peak as a starting point.
• Pre-purge times assume the tube interior has been purged separately before starting the weld cycle. If relying only on the weld head purge port, increase pre-purge time significantly.
• All values assume argon shielding at 20–30 CFH external and adequate internal purge.

Adjusting the Schedule: Troubleshooting by Defect

When your test coupons show defects, adjust one parameter at a time and re-weld.

Lack of Penetration (ID bead too flat or nonexistent)

• Increase peak amperage by 2–5 amps
• Reduce travel speed by 0.5 IPM
• Increase peak time percentage (pulse ratio)
• Verify tungsten is sharp and electrode-to-work distance is correct (typically 0.030"–0.060")

Excessive Penetration (ID bead drooping, concavity, or melt-through)

• Reduce peak amperage by 2–5 amps
• Increase travel speed by 0.5 IPM
• Decrease peak time percentage
• Check for excessive heat buildup from previous sectors — may need to reduce amps in earlier sectors

Oxidation (Discoloration on ID or OD)

• Increase post-purge time
• Increase internal purge gas flow
• Verify purge gas purity — check for leaks in gas lines and fittings
• Ensure tube ends are properly capped or dammed for purge containment
• Reduce travel speed if the weld head is outrunning the trailing gas shield

Arc Wander (Unstable arc, uneven bead)

• Re-grind tungsten electrode — contamination or improper geometry causes arc instability
• Verify electrode is centered in the weld head
• Check electrode-to-work distance consistency
• Clean tube ends thoroughly — contaminants on the tube surface deflect the arc
• Reduce arc gap if it is too large

Uneven Bead Width Around the Joint

• Add more sectors to the schedule for finer positional control
• Reduce amps in the sectors where the bead is wider
• Check weld head clamping — if the tube is not concentric in the head, arc length varies

Common Programming Mistakes

Using the same parameters all the way around. Gravity exists. If you do not reduce current for the overhead position, you will get sag and inconsistent penetration around the joint.

Setting background current too low. If background amps are below 30–40% of peak, the arc can become unstable between pulses. The puddle freezes too much and you get a rough, inconsistent bead.

Skipping test coupons. Every heat of material welds slightly differently. Every change in fit-up tolerance affects the result. Never run production welds on a new schedule without cutting and inspecting at least two test coupons.

Ignoring purge. Even a perfect weld schedule produces sugared, oxidized welds if the internal purge is inadequate. The schedule parameters and the purge setup are equally important.

Over-adjusting between coupons. Change one parameter at a time, typically in 2–3 amp increments for current and 0.5 IPM increments for travel speed. Changing multiple variables at once makes it impossible to isolate what worked.

Not recording what works. When you dial in a good schedule for a specific tube size and material heat, save it. Document the parameters, the material heat number, and the results. The next time you run that size, you have a proven starting point instead of starting from scratch.

Equipment and Next Steps

Weld schedule programming is the core skill that separates operators who produce consistent results from those who chase defects all day. Start with the chart above, run test coupons, and adjust methodically. The process is the same whether you are working with a basic power supply or a top-tier system with touchscreen programming.

For a comparison of power supply features that affect schedule programming — including memory capacity, number of sectors supported, and programming interfaces — see our Orbital Welding Machine Comparison. If you are sorting out whether your application calls for tube welding heads or pipe welding equipment, review Pipe vs Tube: Differences for Orbital Welding. And for dialing in your electrode prep before programming, check the Tungsten Grinding Angle Chart.

Need equipment for an upcoming job? Rent Orbital Equipment at TechSouth — we carry AMI and Arc Machines power supplies, weld heads, and accessories for short-term and long-term rental.