The Ultimate Guide to Closed AMI Weld Heads

Orbital Tube Welding - Closed AMI Weld Heads


Enclosed AMI weld heads – the Model 9, Model 9E, and Model 8 – are weld heads designed for Tungsten Inert Gas (Tig) welding of tube, pipe, fittings or other components. They are a vital piece in the orbital welding process.

They are closed, as the name suggests, creating an inert atmosphere chamber that surrounds the weld joint. This encapsulated environment helps to create fusion welds on tube or pipe with a decreased risk for blemishes or other imperfections. Internally, the weld head rotor holds the tungsten electrode in place as it orbits around the tube or pipe, creating a fusion weld.

These weld heads have control cables extending to the power source, providing greater flexibility to perform welds farther away from the power supply. If the standard control cables are not long enough, extension cables are available. The clamp style design of the weld head makes for an accurate and easy fit up but if tacking is necessary there is an option for pre-tack programs as well.

The oldest AMI orbital weld heads are from a series designed in 1976 – meaning they have had a lot of time to perfect them. Today, Arc Machines has an extensive line of orbital weld heads full of various shapes and sizes to accommodate a wide range of applications.


New to orbital welding? Download our guide, Orbital Welding Essentials: Your  Guide to Orbital Welding.


AMI Model 9 Weld Head

This original fusion weld head now comes in several different versions. A pair of collets sit on both sides of the AMI Model 9 weld head, clamping around the pieces of tube or pipe.

Features & Benefits

  • Dual clamping
  • No tacking necessary
  • Available in 3 versions and 10 sizes
  • Configured in 60+ ways to operate on diameters from 3/32" to 7.5"
  • Viewing window

Model Options

  • Model 9-250
  • Model 9-500/C
  • Model 9-750
  • Model 9-1500
  • Model 9-2500
  • Model 9-3500
  • Model 9-4500
  • Model 9-7500

Note that the secondary number signifies the maximum OD. For Model 9-2500, the max OD is 2.5”

AMI Weld Heads

AMI Model 9E Weld Head

This is one of the 3 versions of the Model 9. The “E” stands for extended capabilities. This weld head series features only one collet for specialty fit-ups. Standard Model 9 weld heads can be used as a 9E with a conversion kit.

Features & Benefits

  • Single clamp allows for off-set electrode fusion
  • Designed for tig welding of tube or thin-wall pipe range of 3/32” to 7.5”
  • Available in 5 sizes
  • Must pre-tack unlike the 9 series
  • Allows for short tangent fittings
  • Conversion kits can enhance this head’s flexibility to adapt to alternate configurations
  • Can utilize the tungsten mushroom extender
  • Viewing window

Model Options

  • Model 9E-1500
  • Model 9E-2500
  • Model 9E-3500
  • Model 9E-4500
  • Model 9ER-4500
  • Model 9E-7500

AMI Model 8 Series Weld Head

The AMI Model 8 series was introduced in the year 2000. The updated design makes it the thinnest AMI weld head at 1.75” – ideal for narrow applications.

Features & Benefits

  • Designed for welding of fittings, tubing, and thin-wall pipe
  • Narrow width ideal for restricted space applications
  • Ideal for stainless steel, titanium, hastelloy, and other weldable alloys
  • Unique cooling unit, allowing high duty-cycle welding
  • A variety of clamps are available to suit every welding application
  • Clamps require the least amount of stick out
  • All model sizes have 1.75” thickness
  • Ergonomic handle
  • Viewing window

Model Options

  • Model 8-2000
  • Model 8-4000
  • Model 8-6625

Schedule Development

To save time, Arc Machines has developed a schedule development quick reference guide for simplified operation of its Model 8 and 9 fusion weld heads. Weld Schedule Development Reference Guide

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