Posted: 1/22/2013 5:02:37 PM EDT
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Is there a specific reason you can't cast an upper and lower receiver before machining rather than forging ? Seems like the shape wouldn't be incredible difficult. |
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Quoted: possibly but you could just oversize it a bit where needed I would think and the machine shop could take care of it. Quoted: Is there a specific reason you can't cast an upper and lower receiver before machining rather than forging ? Seems like the shape wouldn't be incredible difficult. I think shrinkage, etc would actually make it more difficult. |
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Precision casting should get you a good receiver, but that is a relative term for the most part. You're going to have more problems with material properties that can be greatly affected due to seemingly minor variations in temperature, ambient humidity, etc.
While you can create precsion castings by the truck load much cheaper than you usually can other methods of obtaining your net shape, the controls to get a realible quality you will need to put into place are going to cost much more than to just use forgings and make fewer. *ETA* This doesn't even take into account the problems that can and will occur for machining your castings. Variations in a given batch either in ingredients or in process will cause prblems fitting castings into machining fixtures repeatably. I've worked with alot of castings from cheap grey iron sand castings to die cast aluminum for avionics trays and the like. Castings are always castings. |
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Castable alloys aren't nearly as strong as forged alloys. You need 7075-T6 for the current design. If you went with a casting, you'd have to redesign the buffer thread area to reduce the stress. That said, our ability to do precision casting has come along greatly, but doing complicated parts takes a lot of die design to make sure you get a good, even flow of the material into the casting cavity
ETA: There are one or two alloys that nearly compare to 7075 in strength after a temper, but they're not very common. |
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Quoted:
Precision casting should get you a good receiver, but that is a relative term for the most part. You're going to have more problems with material properties that can be greatly affected due to seemingly minor variations in temperature, ambient humidity, etc. While you can create precsion castings by the truck load much cheaper than you usually can other methods of obtaining your net shape, the controls to get a realible quality you will need to put into place are going to cost much more than to just use forgings and make fewer. *ETA* This doesn't even take into account the problems that can and will occur for machining your castings. Variations in a given batch either in ingredients or in process will cause prblems fitting castings into machining fixtures repeatably. I've worked with alot of castings from cheap grey iron sand castings to die cast aluminum for avionics trays and the like. Castings are always castings. I machined investment castings for hydraulic pump internal parts. We held tolerances in the +/- .0005. They were made of bearing bronze. I think with an investment and the correct material you could be successful. |
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Quoted:
Quoted:
Precision casting should get you a good receiver, but that is a relative term for the most part. You're going to have more problems with material properties that can be greatly affected due to seemingly minor variations in temperature, ambient humidity, etc. While you can create precsion castings by the truck load much cheaper than you usually can other methods of obtaining your net shape, the controls to get a realible quality you will need to put into place are going to cost much more than to just use forgings and make fewer. *ETA* This doesn't even take into account the problems that can and will occur for machining your castings. Variations in a given batch either in ingredients or in process will cause prblems fitting castings into machining fixtures repeatably. I've worked with alot of castings from cheap grey iron sand castings to die cast aluminum for avionics trays and the like. Castings are always castings. I machined investment castings for hydraulic pump internal parts. We held tolerances in the +/- .0005. They were made of bearing bronze. I think with an investment and the correct material you could be successful. You can, I muddied those water a little. But, the costs of getting up to speed to get a good quality casting are going to be alot more up front and higher on an ongoing basis than just machining fogings. |
| Forgings are stronger than most casting primarily due to the grain structure being aligned in the forging process and the material is more dense than a casting could ever be, That being said, there is no real reason a cast receiver would not be a viable alternative to a forging especially considering that injection molded polymers have gained a following. In my business we often do mold work for die casting and permanent mold foundries, I have performed destructive testing on several casting alloys that I would stack up against a forging and not blink an eye. We have parts produced from Al-Mag, an aluminum magnesium alloy, that has great potential as a lower receiver material, especially when it is cast near net then form forged, or squeeze cast, leaving minimal amounts for machining. Investment casting is much more costly than forging, die casting or pour casting but it allows for finer detail in the casting with minimal concern for draft, undercuts or costly shell cores. Many investment cast parts are very near net shape only requiring machine work on highly critical areas. |
| I'm going to take a moment here and make a full confession of being racist against castings. I do know that they can be done very well indeed. But, I hates them due to some sort of weird digruntlement from early experience with lots and lots of poor quality ones. I just can't get past despising them. So, you should probably take some of my input with a grain of salt but don't dismiss it outright without running some of the costing down. |
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I thought raw forgings were only 15 bucks a pop or something like that?
Would be way more expensive to create investment castings for them. Also, because 6061 and 7075 grade aluminums don't "pour" well they usually need to add silicon to make them more fluid, which weakens them. Again you need totally different grades of aluminum to make it strong, but the properties they wanted out of 7075-T6 are no longer there. |
| The bottleneck is an unsustainable demand, not a shortage of anything. If manufacturers thought the current demand could be sustained they would be spending every penny they could to ramp up and meet the demand. It's not sustainable though, so no one is going to go into debt to try to meet the current demand. Couple of companies did that back in 2008 and got their asses handed to them when the market dropped out on them. |
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The advantage of investment casting is that you can get it pretty close to the final shape with no machining. The disadvantage is that it's not usually as strong as a forging, and it's often more expensive, though that depends on the amount of machining you save. Really an AR lower doesn't require that much strength. The weakest points are probably the buffer tube ring and threads, the front pivot pin, and trigger guard holes.
You can knock out forgings pretty quick once you've got the die. I expect that they'll get caught up on lower forgings before all that long, and machined lowers not long after that. You can machine Al pretty quick. I'm guessing that barrels and BCGs will be the bottle necks. |