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> Milled receivers with curved surfaces and finicky blind holes. AR-15 lower receivers are forged and then milled. Of course, referring to mass produced ones f

> Milled receivers with curved surfaces and finicky blind holes. AR-15 lower receivers are forged and then milled. Of course, referring to mass produced ones for the military. Forged parts are typically stronger than purely machined parts of the same material.

sbierwagen 4y ago
Sure, but I've never seen a 20% forging that had holes through the two main stress points, the buffer tube mount and the magazine well. Won't milling down the exterior remove all the aligned crystal boundaries and take you back to billet strength? Looking at that section again, I totally forgot to actually complete my thought there. Large stamping presses have the attractive quality of sublinear scaling: a press that can punch out twice as many parts per cycle is not twice the price. But if you want to double the production of milled parts, you have to buy twice as many milling machines. Worse yet, you need twice as many machinists, who are going to be in desperately short supply in wartime! But the US was not at war in 1956, and making the tradeoff of increased modularity against ease of manufacture has self-evidently paid off for the AR weapons family.
- systemvoltage 4y ago
  > Won't milling down the exterior remove all the aligned crystal boundaries and take you back to billet strength? Most of the forming is done using a forging press at high temperature (hot forging). The only machining that needs to happen is for holes/threads/bosses/flanges and for cleanup. Forging strength remains as is, since milling is an operation that only affects the newly milled surface atoms, not the internal grain boundries. > Large stamping presses have the attractive quality of sublinear scaling: a press that can punch out twice as many parts per cycle is not twice the price. Interesting, I bet. > But if you want to double the production of milled parts, you have to buy twice as many milling machines. Yes, milling from casted or extruded material is not the best in terms of part strength as well as cost. Usually, forging + milling is very expensive for small volumes; but it is the best way to strengthen the part (Up to 2.5x yield strength!) for a given material. Aluminum forging is often equivalent to mild steel parts in terms of strength.

sbierwagen 4y ago

Sure, but I've never seen a 20% forging that had holes through the two main stress points, the buffer tube mount and the magazine well. Won't milling down the exterior remove all the aligned crystal boundaries and take you back to billet strength? Looking at that section again, I totally forgot to actually complete my thought there. Large stamping presses have the attractive quality of sublinear scaling: a press that can punch out twice as many parts per cycle is not twice the price. But if you want to double the production of milled parts, you have to buy twice as many milling machines. Worse yet, you need twice as many machinists, who are going to be in desperately short supply in wartime! But the US was not at war in 1956, and making the tradeoff of increased modularity against ease of manufacture has self-evidently paid off for the AR weapons family.

systemvoltage 4y ago
> Won't milling down the exterior remove all the aligned crystal boundaries and take you back to billet strength? Most of the forming is done using a forging press at high temperature (hot forging). The only machining that needs to happen is for holes/threads/bosses/flanges and for cleanup. Forging strength remains as is, since milling is an operation that only affects the newly milled surface atoms, not the internal grain boundries. > Large stamping presses have the attractive quality of sublinear scaling: a press that can punch out twice as many parts per cycle is not twice the price. Interesting, I bet. > But if you want to double the production of milled parts, you have to buy twice as many milling machines. Yes, milling from casted or extruded material is not the best in terms of part strength as well as cost. Usually, forging + milling is very expensive for small volumes; but it is the best way to strengthen the part (Up to 2.5x yield strength!) for a given material. Aluminum forging is often equivalent to mild steel parts in terms of strength.