[larry lee]

Multiplaz-3500 Evaluation, Part 04: Testing the Cutting Torch

DISCLAIMER!
Let me emphasize that I will not be able to tell you whether the Multiplaz-3500, or any other piece of equipment, will be a good investment for you. Only you can decide that. My intent is to provide as much factual information as I can about the Multiplaz-3500 so that others in our company can make an informed decision about that. The company has no objection to my sharing the information with you as long as I leave their name out of it and make it clear that I am not endorsing any particular product.
DISCLAIMER!

The performance of the cutting torch was measured by determining the rate (inches per minute) at which it could cut completely through metal sheet of various types and thicknesses in one pass. The results are shown in the table below for 6061-T6 aluminum, 304 stainless steel, and 1018/1020 mild steel. (At some point we may also measure brass and copper.) The torch was held in fixed position with the nozzle pointing straight down. The metal sheet was held horizontally and moved by a variable speed welding positioner under the torch. The distance between the torch nozzle and the metal sheet was held constant at 1.5 mm (1/16”) by a height positioning rod attached to a metal ring around the torch nose. (The metal ring and the height positioning rod are supplied as part of the Multiplaz-3500 kit.) The height positioning rod is electrically insulated from the torch nozzle. This arrangement was used to make the measurements independent of any particular operator and of the variations in rate of movement that always occur when moving a torch by hand. This is especially a problem at low speeds. Even with the weld positioner, there was some jerkiness at the lowest speeds (< 4 ”/min). Each measurement was repeated several times.

Measurements were also made with the torch nozzle pointing slightly (about 10 degrees) in the direction of travel (towards the uncut metal), as one might do with an oxy-fuel torch. No significant difference in cutting rate was observed. The appearance of the cut surface when cutting at the “severance” rate (the maximum rate at which there was a complete cut through, i.e., the cut piece dropped off by itself) was similar to that of a “severance” cut using a standard oxy-acetylene cutting torch. The cut edge was somewhat ragged, there was some dross hanging down from the lower edge of the cut, the surface of the cut was fully oxidized, and there was a noticeable Heat Affected Zone (HAZ). This was true of all three of the metals tested.

As with an oxy-fuel cutting torch, the steel reacted with the oxygen in the “cutting flame” (plasma) once the steel started to get hot. At this point the heat into the metal is noticeably more (as determined by the color change) and the rate of melting of the metal also is noticeably more. The force of the plasma gas to blow the melted metal out of the cut (kerf) is then not enough to keep up with the rate of melting and so the melted metal hangs as a large drop(s) under the kerf due to surface tension. Then a layer of cooling metal tends to fuse the bottom edge of the kerf back together as the plasma moves forward. The thickness of the fused layer (~1/32") seems to be almost independent of the thickness of the steel, at least for the thicknesses tested (1/16” to 1/4”).

The metal thicknesses and maximum cutting rates shown in the table below are for single-pass cuts. In general, a partial second pass is all that is required to make a complete cut. If one were using the torch manually, that is what one would do. But in order to have a consistent basis of comparison, we have chosen to use the maximum cutting rate for single-pass cuts.

The Multiplaz Operating Manual states: “A cutting rate of 7 mm per second (17 IPM) can be achieved for low-alloyed steels with thicknesses of up to 2 mm (5/64”), and up to 1 mm per second (3 IPM) for thicknesses of 10 mm (3/8”).”

We have not yet tested 3/8” thick metal sheets, but it would appear from the results shown in the table below that one might obtain “UP TO 1 mm per second (3 IPM)” for 3/8” aluminum and perhaps stainless steel in the horizontal position. It is also possible that higher cutting rates would be obtained for mild steel if the sheet were in the vertical position and the cut were downward. (This is the way that cutting is shown being done in the drawing in the manual.) If the cut is vertical downward (or perhaps even vertically sideways), then gravity would tend to pull the melted metal down and ahead of the cut. This would help to keep the melted metal out of the kerf and prevent bridging. Any large drop of melted metal that formed would tend to be pulled down the back of the metal and towards the floor. Under these conditions, the force of the plasma gas might be adequate to blow the melted steel out of the kerf.

We will try cutting vertically down and vertically sideways in the next measurements.

I will discuss the importance of the balance of the melting rate and the gas force in Part 05 of this evaluation.

to be continued

larry lee


TABLE (The posting software insists on taking out tabs and extra spaces, so I put in colons to try to make it readable)

Multiplaz-3500 Cutting Torch Maximum Cutting Rates For Single-Pass Cuts
(Metal Sheet Horizontal, Torch Vertical with plasma down)

Metal: Thickness: In/Min: Settings: Comments

Al 6061: 1/8”: 12: II, 4 (6A): Taper at bottom

Al 6061: 1/8”: 15: II, 6 (9.5A):

Al 6061: 3/16”: 7: II, 6 (9.5A):

Al 6061: 1/4”: 5: II, 6 (9.5A):


SS 304: 1/16”: 20: II, 6 (9.5A):

SS 304: 1/8”: 15: II, 6 (9.5A):

SS304: 3/16”: 4.5: II, 6 (9.5A):

SS 304: 1/4”: 2.7: II, 6 (9.5A):


MS 1018: 1/16”: 11: II, 4 (6A):
Could not get cutoff in one pass once metal heated up
MS 1018: 1/16”: 13: II, 6 (9.5A):
Could not get cutoff in one pass once metal heated up
MS 1018: 1/8”: 6: II, 6 (9.5A):
Could not get cutoff in one pass once metal heated up
MS 1018: 3/16”: 2.5: II, 6 (9.5A):
Could not get cutoff in one pass once metal heated up
MS 1018: 1/4”: -: II, 6 (9.5A):
Could not get cutoff in one pass at any speed


The Multiplaz Operating Manual states: “A cutting rate of 7 mm per second (17 IPM) can be achieved for low-alloyed steels with thicknesses of up to 2 mm (5/64”), and up to 1 mm per second (3 IPM) for thicknesses of 10 mm (3/8”).”

Settings:
All are mode II (Transferred arc), either Position 4 (6 A) or Position 6 (9.5 A = maximum)
The average arc voltage (cathode to workpiece) is about 265 VDC in either Position.

[larry lee]

Correction:

Rather than say "cutting vertically sideways", I should have said "cutting sideways with the sheet vertical".

If this were a weld, it would be called a horizontal weld.

larry lee

[Otto Nobedder]

Thank you, Larry, for another concise summary.