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Need some pics: NATO variant magwell

ByronF

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Guys,

Looking at some features in magwell, wondering if they are defects, or if they're supposed to be this way.

First view: see that gap right down the centerline?
1694131705725-1063300433.jpg

Similar gap looking aft in the magwell.
1694131786860244984768.jpg
 

ByronF

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What I'm looking at is a gap between "halves". If this was a glue-together model its as if no glue was applied at these points. But I'd have to think these are injection moulded as a single piece so hard to imagine how there would be a cold-shut, lack of fusion, occurring by some miracle at exactly vertical plane. But would feel better with confirmation that thus is just how they are.
 

Impala_Guy

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Guys,

Looking at some features in magwell, wondering if they are defects, or if they're supposed to be this way.

First view: see that gap right down the centerline?
View attachment 334119

Similar gap looking aft in the magwell.
View attachment 334120
Ain't no defect, Hoss, they're all like that. The AUG stock is molded in two halves and then fused together, external seams only. I designed some fuel tanks for Koehler powered industrial fans that were manufactured similarly. In my case the tanks were hot plate welded and pressed together, their final thickness established by some internal ribs. Not sure if the AUG stock halves are hot plate welded all at once, or seam welded. In the latter case, there are plastic weld tools that melt the seam, displace material, and shoot in molten plastic at the same time as the weld tool moves along the seam.

Either way on any AUG stock you can see where they ground the melt plastic that squished out all around the outside of the stock. Other internal features or the weld fixture itself establish the critical internal width dimensions of the stock, that small gap on the mag well ribs is there by design to prevent molding flash / tolerances etc from holding the halves too far apart as they are welded together.

Here's my gen-U-whine Austrian made one:

20230908_203411.jpg 20230908_203340.jpg 20230908_203335.jpg
 
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ByronF

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Groovy. Thanks. I emailed the Steyr service people this morning. Prompt reply confirms what you are saying. Friction welded, he says. Not sure how that works, I thought that worked for ID/OD shafts and hubs and such. Whatever. If its normal then I'm cool with it.

I'm less cool that aluminum mags catch on those same areas either front or back, depending on how the mag is held. It's a small thing that I'll fix myself. It's really a small amount of material, but matters a whole lot.
 

Impala_Guy

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Groovy. Thanks. I emailed the Steyr service people this morning. Prompt reply confirms what you are saying. Friction welded, he says. Not sure how that works, I thought that worked for ID/OD shafts and hubs and such. Whatever. If its normal then I'm cool with it.

I'm less cool that aluminum mags catch on those same areas either front or back, depending on how the mag is held. It's a small thing that I'll fix myself. It's really a small amount of material, but matters a whole lot.
Also called ultrasonic welding. There is a weld bead molded into one half and a groove in the other half. The two halves are joined in a ultra high frequency vibrating nest....the micro friction melts the bead and the halves are pressed together.

 

raubvogel

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Also called ultrasonic welding. There is a weld bead molded into one half and a groove in the other half. The two halves are joined in a ultra high frequency vibrating nest....the micro friction melts the bead and the halves are pressed together.

Where does the vibrator go to create the vibration required to vibrate the pieces so they rub against each other until they get squishy so they can be squeezed tight together? And how do you control the goo that is created so it does not spurt where it should not, and you cannot reach to clean?
 

Impala_Guy

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Where does the vibrator go to create the vibration required to vibrate the pieces so they rub against each other until they get squishy so they can be squeezed tight together? And how do you control the goo that is created so it does not spurt where it should not, and you cannot reach to clean?
One side of the fixture, the one that touches the half with the triangular rib, is made of aluminum and called the "horn" and thats what the high frequency vibrations are passed through to the part itself as the parts are pressed together by the machine. The melty rib is pointed in its cross section to concentrate all this vibration on a small area like a fire stick to build up heat quickly. Sometimes a part will have several small melt ribs running concentrically all around the seam of the part. The fixed square rib on the inside of the joint keeps the molten material from squirting into the assembly interior, material is allowed to squeeze out of the exterior of the assembly as one sign that a good weld has been achieved. Once cool this extra material is ground off, as you can see by the marks all around the outside of the AUG stock.
 

raubvogel

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One side of the fixture, the one that touches the half with the triangular rib, is made of aluminum and called the "horn" and thats what the high frequency vibrations are passed through to the part itself as the parts are pressed together by the machine. The melty rib is pointed in its cross section to concentrate all this vibration on a small area like a fire stick to build up heat quickly. Sometimes a part will have several small melt ribs running concentrically all around the seam of the part. The fixed square rib on the inside of the joint keeps the molten material from squirting into the assembly interior, material is allowed to squeeze out of the exterior of the assembly as one sign that a good weld has been achieved. Once cool this extra material is ground off, as you can see by the marks all around the outside of the AUG stock.
So, using your drawing as reference,
  • The top bit is what is attached to the "horn" and is vibrated
  • The w/3 region of the bottom bit is the fixed square rib you mentioned, that keeps goo from flowing into the assembly interior.
  • The horn is vibrated at the same time the top bit is pressed at, say, constant force/pressure/whatever, so as soon as it starts melting it is pushed down. And it keeps moving down until the amount of force required to move is more than that, indicating it should have reached the desired depth
 

Impala_Guy

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So, using your drawing as reference,
  • The top bit is what is attached to the "horn" and is vibrated
  • The w/3 region of the bottom bit is the fixed square rib you mentioned, that keeps goo from flowing into the assembly interior.
  • The horn is vibrated at the same time the top bit is pressed at, say, constant force/pressure/whatever, so as soon as it starts melting it is pushed down. And it keeps moving down until the amount of force required to move is more than that, indicating it should have reached the desired depth
More or less. Theres some trial and error at the beginning, the size and number of the ribs, where the horn actually touches the part to deliver the vibrations and the frequency etc. Its usually a pretty fast process to weld parts once you have it set up. Hot plate welding holds the two halves very close together, then a red hot plate is held between the parts till the edges are molten and the plate is retracted, then the parts are pressed together. Its not as precise as friction welding because the latter only melts the parts at the points of contact before being pressed together.
 
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