Archangel14
Member
- Joined
- Mar 16, 2012
- Messages
- 596
What's the difference? I often see this terminology, but don't know the difference. Thanks!
Forged or billet?
- Thread starter Archangel14
- Start date
- Status
adcoch1
Member
A billet is a solid block of metal with the part machined out, forged is melting down the metal and casting it into a shape. Usually requiring finish machining afterwards in the case of guns
rbernie
Contributing Member
Correct. The starting hunk of metal may have been cast, or most likely was extruded/rolled from a casting, but in the end the hunk was transformed from a lump into the final shape via direct machine work.
Well, not as I learned it. Forged means that a hunk of metal was hammered into a shape (either at room temp or heated to make it softer), and then it was finish machined. The starting hunk of metal may have been cast, or most likely was extruded/rolled from a casting, but in the end the hunk of metal was hammered under pressure into something resembling the final shape.
d2wing
Member
- Joined
- Nov 10, 2008
- Messages
- 6,435
In general, forged means very hot metal hammered into shape. I am not sure but maybe it refers to molten metal forced into a mold or stamped. Billet means a block of metal carved into shape with milling machines. Someone else may provide a more technical explanation.
ljnowell
Member
HoosierQ
Member
Billet is carved...like wood. Cold.
Forged is squished/smashed/hammered into shape...like clay. Red hot.
Cast is molded...like lead. Molten.
We tend to think of forging as the work a blacksmith does...which it is. But a forged piece today is often smashed with two or three blows from a very heavy press...like 100 tons...into it's nearly final shape with then just a bit of grinding or finishing to make it complete.
Forged is squished/smashed/hammered into shape...like clay. Red hot.
Cast is molded...like lead. Molten.
We tend to think of forging as the work a blacksmith does...which it is. But a forged piece today is often smashed with two or three blows from a very heavy press...like 100 tons...into it's nearly final shape with then just a bit of grinding or finishing to make it complete.
justin22885
member
- Joined
- Nov 9, 2009
- Messages
- 2,102
thought when they forged something they took a white hot piece of metal, stick it into a mould and a large press comes down and crushes it into shape
tark
Member
I believe a forging can result in a billet, which is then machined. A casting is just that, heat the metal, pour in into a mold, let it cool.
and there are two types of forgings, cold and hot, which are self explanatory. Just remember that a forging involves beating the metal with a hammer of some kind.
Bet the OP is totally confused now!
and there are two types of forgings, cold and hot, which are self explanatory. Just remember that a forging involves beating the metal with a hammer of some kind.
Bet the OP is totally confused now!
adcoch1
Member
Wow I should think before typing! Yes forging is hammering or pressing metal into shape. Sheesh, and I am from a family of machinists!
"and there are two types of forgings, cold and hot, which are self explanatory. Just remember that a forging involves beating the metal with a hammer of some kind."
Not necessarily. Forging can be free hand hammer a forge work, or open or closed die work. Open die work can be hammered (usually by massive machinery) or pressed: closed die work usually pressed. Both almost always hot.
A steel "billet" usually is, or cut from, a bar or plate which is formed by rolling, which is itself a forging operation.
Not necessarily. Forging can be free hand hammer a forge work, or open or closed die work. Open die work can be hammered (usually by massive machinery) or pressed: closed die work usually pressed. Both almost always hot.
A steel "billet" usually is, or cut from, a bar or plate which is formed by rolling, which is itself a forging operation.
justin22885
member
- Joined
- Nov 9, 2009
- Messages
- 2,102
forging generally takes some pretty big machinery, some very expensive equipment, multiple process, significant danger to the workers around the machines.. machining from bullet just requires CNC machinery which can be almost as small as a drill press, of course those CNCing to produce billet parts to sell are using bigger machines than this, i still believe it to be more small-shop friendly than forging
i dont think one is inherently better or stronger than the other, if a company has a lot of money they'll probably go for the larger up front cost of forging thatll be cheaper in the long run.. if its a smaller company without so much dough to drop on that kind of machinery they will probably produce billet parts and take a small hit on their profit margins by doing so... suppliers of forged will give you their excuses as to why its the greatest and those who make billet parts will do the same
i dont think one is inherently better or stronger than the other, if a company has a lot of money they'll probably go for the larger up front cost of forging thatll be cheaper in the long run.. if its a smaller company without so much dough to drop on that kind of machinery they will probably produce billet parts and take a small hit on their profit margins by doing so... suppliers of forged will give you their excuses as to why its the greatest and those who make billet parts will do the same
Last edited:
In the bicycle world this is called "melt forging" and it's a cheaper method of making high stress aluminum parts such as the crankset. It has a more proper engineering term but I'm an EE and can't recall it
Maybe this will help.
Steel billets dome from the steel mill in some form, usually called "bar stock", cut to some convenient length. Gun companies order that steel to their own specifications, so it will be suited to their specific needs.
Once the billet or bar stock is received, it can be made into the final product in one of two ways, as chosen by the manufacturer's engineers.
The simplest is to cut off a suitable length of stock, and put it through a series of machines to shape it into the final product, say a pistol frame. This is a very time consuming process, very labor intensive and with a lot of waste in terms of chunks of steel and chips. The process is called making from a billet. It is slow and costly but fairly clean, with relatively low capital investment.
When the customer uses forging, the end of the bar is heated white hot, then put in a forging press which squeezes it between two heavy dies and shapes it into a rough shape of the finished product.
The forged piece is then shaped and finished by machines into the final product. Again the process is labor and machine intensive, and costly in terms of capital investment (forging presses don't come cheap) and environmental impact (the ground literally shakes when a big forging press comes down). But the forging process itself strengthens the steel, and for that reason is often used for firearms manufacture.
When casting is to be used, it can begin with steel from the steel mill, and will include scrap from failed work and chips and scrap from previous work. In the firearms industry, casting is usually done by the so-called "lost wax" process. A copy of the needed product is made in wax, which is then repeatedly dipped in a ceramic slurry until a mold is made that can contain the molten steel. When the hot steel is poured into the mold, the wax burns away, leaving the metal in the rough shape of the product. But, like the forging, it still requires machine operations to bring it to the final product. Capital investment is moderate, and there is little environmental impact.
Small parts are often made by a process called Metal Injection Molding (MIM). A relatively new process, it is often considered inferior simply because it is not understood, and is often confused with molding of plastic products or cheap non-ferrous metals. MIM begins with powdered metal, ordered to specification, and a binder. The materials are melted and injected into molds. Some early users did not have the process perfected; the result was some failures and people who had no understanding of it immediately claimed it was inferior and even dangerous. In fact, MIM is a perfectly good production method and can be so precise that no machine finishing work is ever needed, making it very cost effective. There is almost no environmental impact, though capital investment is high.
One note, revolver cylinders are made from round bar stock from the mill, with little preliminary work needed. Some fans of one revolver make or another claim their favorite makers uses superior steel for cylinders, but I have been told by knowledgeable people that the major revolver makers obtain their cylinder stock from the same mill and to the same specifications.
Jim
Steel billets dome from the steel mill in some form, usually called "bar stock", cut to some convenient length. Gun companies order that steel to their own specifications, so it will be suited to their specific needs.
Once the billet or bar stock is received, it can be made into the final product in one of two ways, as chosen by the manufacturer's engineers.
The simplest is to cut off a suitable length of stock, and put it through a series of machines to shape it into the final product, say a pistol frame. This is a very time consuming process, very labor intensive and with a lot of waste in terms of chunks of steel and chips. The process is called making from a billet. It is slow and costly but fairly clean, with relatively low capital investment.
When the customer uses forging, the end of the bar is heated white hot, then put in a forging press which squeezes it between two heavy dies and shapes it into a rough shape of the finished product.
The forged piece is then shaped and finished by machines into the final product. Again the process is labor and machine intensive, and costly in terms of capital investment (forging presses don't come cheap) and environmental impact (the ground literally shakes when a big forging press comes down). But the forging process itself strengthens the steel, and for that reason is often used for firearms manufacture.
When casting is to be used, it can begin with steel from the steel mill, and will include scrap from failed work and chips and scrap from previous work. In the firearms industry, casting is usually done by the so-called "lost wax" process. A copy of the needed product is made in wax, which is then repeatedly dipped in a ceramic slurry until a mold is made that can contain the molten steel. When the hot steel is poured into the mold, the wax burns away, leaving the metal in the rough shape of the product. But, like the forging, it still requires machine operations to bring it to the final product. Capital investment is moderate, and there is little environmental impact.
Small parts are often made by a process called Metal Injection Molding (MIM). A relatively new process, it is often considered inferior simply because it is not understood, and is often confused with molding of plastic products or cheap non-ferrous metals. MIM begins with powdered metal, ordered to specification, and a binder. The materials are melted and injected into molds. Some early users did not have the process perfected; the result was some failures and people who had no understanding of it immediately claimed it was inferior and even dangerous. In fact, MIM is a perfectly good production method and can be so precise that no machine finishing work is ever needed, making it very cost effective. There is almost no environmental impact, though capital investment is high.
One note, revolver cylinders are made from round bar stock from the mill, with little preliminary work needed. Some fans of one revolver make or another claim their favorite makers uses superior steel for cylinders, but I have been told by knowledgeable people that the major revolver makers obtain their cylinder stock from the same mill and to the same specifications.
Jim
Driftwood Johnson
Member
Howdy
A few years ago I took a tour of the Smith and Wesson factory in Springfield Mass. We were not allowed to actually watch the hammer presses in operation, but I saw bins and bins of forgings for the extra large 45 Colt/410 shotgun revolver frames.
Smith starts with bars of round stock. The bars are cut off to a set length, then hammer forged to a shape that can be further refined by machining. I was surprised to see they start everything with round stock, but that is what they do.
Here is a video that will give you an idea of what the hammer forges look like at S&W. This is not actually S&W, but the forge is about the same size as the ones Smith uses. Notice these guys are taking glowing, hot work pieces out of a furnace. The press has several different molds on it. Notice they move the work piece from one mold to another as the part progressively takes shape.
https://www.youtube.com/watch?v=6022lxm0LdU
This is what the frames look like after hammer forging. Actually, these frames have already been through at least one process to remove the excess metal left behind by the forging process. These frames will become N frame revolvers. They will be further shaped by CNC machining.
Forging causes the grain of the metal to flow, following the general shape of the part. Making the part completely by machining the grain will nor follow the shape and the part will not be as strong. In addition, there is less waste if the part starts out as a forging, and forging is quicker than machining the part from scratch.
Incidentally, when S&W built their current factory around 1950, when they moved the old hammer presses to the new location, they discovered the presses had cracked the foundation of the old building, where they had been pounding away since the 1850s.
This is kind of a 'story board' that used to hang in the S&W factory. You can see the progression followed to make each of the major parts. It appears at this time Smith was starting with rectangular billets before they forged the parts to shape, but all I saw was round stock, and I saw frames that still had the remainder of the round stock attached. Anyway, you can see the progression of the major parts which were hammer forged; frame, crane, hammer, trigger, and barrel. S&W Cylinders have always been machined from round stock, not hammer forged. Other companies do not hammer forge barrels if the basic shape of the barrel is cylindrical, like the barrel of a Colt Single Action Army. In that case, the barrel will be machined to shape with no hammer forging.
A few years ago I took a tour of the Smith and Wesson factory in Springfield Mass. We were not allowed to actually watch the hammer presses in operation, but I saw bins and bins of forgings for the extra large 45 Colt/410 shotgun revolver frames.
Smith starts with bars of round stock. The bars are cut off to a set length, then hammer forged to a shape that can be further refined by machining. I was surprised to see they start everything with round stock, but that is what they do.
Here is a video that will give you an idea of what the hammer forges look like at S&W. This is not actually S&W, but the forge is about the same size as the ones Smith uses. Notice these guys are taking glowing, hot work pieces out of a furnace. The press has several different molds on it. Notice they move the work piece from one mold to another as the part progressively takes shape.
https://www.youtube.com/watch?v=6022lxm0LdU
This is what the frames look like after hammer forging. Actually, these frames have already been through at least one process to remove the excess metal left behind by the forging process. These frames will become N frame revolvers. They will be further shaped by CNC machining.
Forging causes the grain of the metal to flow, following the general shape of the part. Making the part completely by machining the grain will nor follow the shape and the part will not be as strong. In addition, there is less waste if the part starts out as a forging, and forging is quicker than machining the part from scratch.
Incidentally, when S&W built their current factory around 1950, when they moved the old hammer presses to the new location, they discovered the presses had cracked the foundation of the old building, where they had been pounding away since the 1850s.
This is kind of a 'story board' that used to hang in the S&W factory. You can see the progression followed to make each of the major parts. It appears at this time Smith was starting with rectangular billets before they forged the parts to shape, but all I saw was round stock, and I saw frames that still had the remainder of the round stock attached. Anyway, you can see the progression of the major parts which were hammer forged; frame, crane, hammer, trigger, and barrel. S&W Cylinders have always been machined from round stock, not hammer forged. Other companies do not hammer forge barrels if the basic shape of the barrel is cylindrical, like the barrel of a Colt Single Action Army. In that case, the barrel will be machined to shape with no hammer forging.
Last edited:
Archangel14
Member
- Joined
- Mar 16, 2012
- Messages
- 596
Is one better than the other for a a lower? And is there a big difference between 7075 and 6061?
ColoradoMinuteMan
Member
- Joined
- May 8, 2015
- Messages
- 704
The short of it is that all things remaining equal, the forged tend be stronger due to the orientation of the grain of the metal. Billets tend to look prettier because the entire surface is carefully machined into shape. Many billet lower manufactures also take advantage of their modern milling technology to produce more intricate visual designs into the lower. Many billet receiver manufactures will add additional metal in areas such as the threads for the receiver extension, trigger guard, etc. to strengthen the weaker areas. For the most part, lower receivers are not high stress parts so the difference durability between a well built billet receiver and a forged receiver may be difficult to measure from a practical perspective.
rcmodel
Member in memoriam
Mil-spec m-16's have to be forged to pass the requirements of the military.
That's good enough for me.
rc
That's good enough for me.
rc
lysanderxiii
Member
It is only stronger in the direction of the grain, it loses some strength in the transverse direction.
ColoradoMinuteMan
Member
- Joined
- May 8, 2015
- Messages
- 704
Good evening,
Can you elaborate more on these comments? Perhaps I'm misunderstanding what you're saying but this comment would at face value be contrary to my understanding of billet vs forged materials.
I'm not a metallurgist and I won't pretend to be an expert. However, I have taken industrial technology and metal working classes, and have been exposed to a lot of fabrication activities throughout my life, be it my uncle's bus building company, my father's passion for restoring cars and airplanes, etc. I've been taught that the grain of metal conforms to the shape of the forging. This allows the grain to stay mostly intact and continuous throughout the body of the forging. When you machine an object from solid piece of extruded metal, the grain is broken by the machining process. Of course, much of the grain is broken in the machining of the forging as well. What this tells me is that the main body of the lower receiver, where much of the grain stays intact from one end of the receiver to the other there is not much difference in the strength between a forging and billet. However, in areas like the trigger guard, and the top-most area around the receiver extension there could be many more broken strands of the metal grain when machined from a billet, thus making it weaker in theory. As I mentioned above, between the fact that the AR15 lower is mostly low stress, and the fact that manufactures beef up the more susceptible areas, it may be difficult to practically measure the difference in real durability even if one is technically stronger than the other.
Again, I'm not an expert, I'm only going off of what my bit of education and exposure has taught me. If I'm wrong I'm happy to be corrected by someone who can provide some facts that teach us otherwise.
This is a decent illustration of what I'm talking about.
Jackal
Member
I've had both forgings and billet uppers/lower. I solidly prefer forged lowers and the only tangible reason to use a billet upper is if it has a feature not found on a forged upper, such as side charging. The only usual advantage of billet is minor features, such as no roll pins, beebles/bobbles. Forgings almost always weigh less and lose nothing in actual use.
Properly designed forgings are stronger than parts cut from a straight billet.
Aluminum billets are usually formed by extrusion where the material is run through rollers that press the billet into it's shape, whether it's rectangular, round, Ll angle, tee angle, etc. In reality, billets are usually just a very simple forging or extrusion where the grains run straight and parallel to each other.
Metal has three states, depending on temperature- Solid, plastic and liquid.
When making a casting, metal is heated until it's liquid so it can be poured into a mold.
When making a forging, metal is heated until it's plastic. The metal still retains it's shape and it' granular structure, but can be forced into shape using pressure, such as from hammering or a press. The grain of the metal follows the flow as it's hammered or pressed into shape. Where the grain changes direction, or is forced to go from a thick area to a thin area, grain density increases as the grains are pressed closer, strengthening that area.
There are aircraft parts, such as the frame around the windscreens of some airliners that can only be made durable enough by using a one piece forging because the grain flow follows the shape. When made from billet, the frame would fail where the grain runs perpendicular to the frame structure instead of parallel.
The first M16s used in Vietnam had receivers made from 6061 forgings. It was found that when 6061 is forged into more complicated shapes, imperfections in the material called granular inclusions are created which cause inter-granular corrosion, which is very destructive. They switched to 7075 and eliminated the problem.
Billet receivers are good enough for use in civilian ARs in most cases, but the downside is they are usually heavier in order to be as strong as a forged receiver and cost much more. The advantage is that it's easier to set up a machine tool to cut a receiver from a billet than a forging
Aluminum billets are usually formed by extrusion where the material is run through rollers that press the billet into it's shape, whether it's rectangular, round, Ll angle, tee angle, etc. In reality, billets are usually just a very simple forging or extrusion where the grains run straight and parallel to each other.
Metal has three states, depending on temperature- Solid, plastic and liquid.
When making a casting, metal is heated until it's liquid so it can be poured into a mold.
When making a forging, metal is heated until it's plastic. The metal still retains it's shape and it' granular structure, but can be forced into shape using pressure, such as from hammering or a press. The grain of the metal follows the flow as it's hammered or pressed into shape. Where the grain changes direction, or is forced to go from a thick area to a thin area, grain density increases as the grains are pressed closer, strengthening that area.
There are aircraft parts, such as the frame around the windscreens of some airliners that can only be made durable enough by using a one piece forging because the grain flow follows the shape. When made from billet, the frame would fail where the grain runs perpendicular to the frame structure instead of parallel.
The first M16s used in Vietnam had receivers made from 6061 forgings. It was found that when 6061 is forged into more complicated shapes, imperfections in the material called granular inclusions are created which cause inter-granular corrosion, which is very destructive. They switched to 7075 and eliminated the problem.
Billet receivers are good enough for use in civilian ARs in most cases, but the downside is they are usually heavier in order to be as strong as a forged receiver and cost much more. The advantage is that it's easier to set up a machine tool to cut a receiver from a billet than a forging
lysanderxiii
Member
In the picture the lines are the grain flow, in the direction of the line the strength is increased, in the direction perpendicular to the lines, up and down, and in and out of the page, the strength may be decreased depending on several factors.
Let's say that picture is a crankshaft, it would be much stronger than the others in bending, and since there is no loading in the transverse direction, no drawbacks.
However, for large complex parts that are loaded in several directions, you may have loading across the grain.
Here is a good short article from "Forge", an E-magazine dedicated to forging and the forging industry.
Grain Flow in Forgings - The Basics
Figure 1.
Grain flow is one of the major benefits cited for the use of forgings. Unfortunately, there are misconceptions on the topic, which include the underlying causes of grain flow, the benefits that can be accrued from grain flow and how to achieve an optimum grain flow. In the best case, grain flow results in a delighted customer and a forging that thrives in a critical service application.
To begin, let us provide a definition of grain flow in forgings. Grain flow is a directional orientation of metal grains and any inclusions that have been deformed by forging. Individual grains are elongated in the direction of the metal flow or plastic deformation. More importantly, nonmetallic inclusions, particles and other imperfections inherited from the casting process are elongated in the direction of grain flow. It should be noted that grain flow occurs to some degree in all metal-forming processes, not just forging.
Observations of Grain Flow
When examining the interior of a forging, the grain flow becomes obvious. Figure 1 shows the grain flow in a forged and machined component. The observation of the grain flow in this figure requires some special preparation methods. After the forging has been sectioned, it needs to be ground and polished similar to a metallographic sample. The major difficulty with this step in the process is that forgings are usually substantially larger in size than small samples for metallographic analysis. Care must be taken in the preparation to ensure that the surface is flat and not beveled. After polishing is completed, an etchant (a solution with acid) is applied to the polished surface. The standard method for preparation of the steel forging for examination of the grain flow is described in ASTM E-381 – Method of Macroetch Testing, Steel Bars Billets, Blooms and Forgings. This etchant is called a macroetchant since it will reveal features of the forging on a scale that can be observed with the human eye rather than requiring a microscope.
ASTM E-340 provides a standard test method for the macroetching of metals and alloys. This standard states: “Forge shops … use macroetching to reveal flow lines in setting up the best forging practice, die design and metal flow. For an example of the use of macroetching in the steel forging industry, see ASTM E-381. Forging shops and foundries also use macroetching to determine the presence of internal faults and surface defects.”
This standard also provides the chemical composition for the etchants that can be used on a variety of metal forging alloys, including steels, aluminum alloys, stainless steels, high-temperature alloys (superalloys), nickel alloys, titanium alloys and magnesium alloys. Macroetching methods are also well described in Volume 9 of ASM Handbook Metallography and Microstructures.
It should be understood that the macroetching can be very aggressive and needs to be done in a safe manner. Also, because of the acid content in the etchant, the attack on the forging is substantial. The observed grain flow is due to the presence of particles and inclusions. The etchant will attack the interface region between these inclusions as well as the base metal. The etched surface appears to show inclusions that are very large, but that is not the case because of the acid attack. The actual area that is eaten away in the forging is much larger than the inclusions themselves. Do not be deceived into thinking that the steel or other metal is extremely dirty because of the methods that are used to observe grain flow. Even with relatively clean material, the grain-flow lines can be seen from an aggressive acid etch even though the number and size of the inherent inclusions are relatively small.
Effect on Mechanical Properties
The important implication about grain flow is that some mechanical properties vary with respect to orientation relative to grain flow. This fact is one of the major benefits ascribed to forgings. This variation in mechanical properties can be exploited so that the actual product has superior properties in a critical direction relative to those expected from the alloy composition itself.
However, we should be clear that not all of the mechanical properties will vary significantly with the grain flow. For example, strength and hardness are primarily controlled by the alloy chemistry and the heat treatment that is given to the forging. Grain flow will not have a major effect on the strength or the hardness of the alloy. In contrast, desirable properties associated with retarding crack propagation can see significant differences depending on the grain flow and the direction of the moving crack. So, properties like fatigue strength, impact toughness and ductility, which are measures of a material’s resistance to cracking (measured after fracture), can be significantly improved if the crack propagation direction and the grain flow are properly aligned. The optimum alignment occurs when the maximum principal stress (perpendicular to a potential crack or fracture) is aligned with the grain-flow lines.
When the properties of a metal are independent of direction, the material is described as being isotropic. Plastically deformed metals with grain flow have anisotropic properties. Figure 2 illustrates this principle of anisotropy with respect to grain flow. In this example, the grain flow is indicated in the block of metal.
Figure 2.
Test samples are machined with three different orientations. The longitudinal sample has the grain flow along the direction of the long axis. The transverse and short transverse are oriented so that the grain flow is perpendicular to their long axis. When the longitudinal sample is tested, the crack or final fracture will be perpendicular to the long axis of the sample. So, for the longitudinal sample the crack propagation is perpendicular to the grain flow, whereas for the transverse and short transverse the crack or fracture that forms is somewhat parallel to the grain flow. Note that there is not a significant variation in the yield strength of this material with test-sample orientation. Going from the short-transverse sample to the longitudinal sample, the increase in yield strength is less than 3%. Since yield strength is a measure of when plastic deformation starts in the metal, it does not have a crack or fracture involved in the property measurement.
In contrast, the reduction in area and the elongation are measured in the sample after it has broken or fractured. Likewise, the impact energy is a measure of the material’s resistance to rapid crack propagation through it. The reduction in area increases by a factor of more than 5 and the elongation increases by a factor of 3 when comparing the short transverse test sample to the longitudinal test sample. The increase in the impact energy is almost a factor of 2.5. These changes are remarkable increases in these mechanical properties. The increases in fatigue and impact properties vary by material, processing conditions and microstructure. With proper design and understanding of the application, a forging offers an opportunity for significant improvements in critical mechanical properties.
The fundamental reason for the enhancement of properties when the test sample and the grain flow are aligned is due to the manner in which a crack or fracture will propagate through the material. Like the fractures that are observed in wood, a crack preferentially propagates in the direction of the grain flow. When the crack forms perpendicular to the grain flow, it will undergo numerous deflections as it moves across the sample. Each of these small deflections requires more energy and makes the material more resistant to this cracking or fracture. Hence, certain mechanical properties are increased when a sample is tested in the longitudinal direction.
When tested in the transverse or short transverse directions, the crack can propagate very easily along some of the inclusions, requiring less energy for the fracture process. This reduction in energy requirement causes the mechanical property to be lower. It is this change in the ease or difficulty of crack propagation that is the root cause for the change in the mechanical properties due to grain flow.
Summary
We have provided a definition of grain flow in this introductory article. We have also examined how grain flow is observed in forgings and some of the implications of grain flow in general on the mechanical properties of a forging – especially those that are a measure of crack or fracture resistance. Depending on the orientation of the grain flow and the direction in which a crack propagates, these mechanical properties can be enhanced or diminished.
Last edited:
The point that Armalite was making in using forgings was to elevate the level of fabricating parts in a mass production environment. Forging the receivers allowed the exterior dimensions to largely be finished by the process - a forged upper or lower doesn't get fully machined to make every surface. Only those few surfaces the process can't finish get further machining. In the case of the AR lower, it's the interior of the part that gets the bulk of the tool work - trigger, mag well, and buffer tube threading. With the original carry handle upper, the sight channel only needed a few holes to mount the peep, with an A3 railed upper most of the rail gets machined.
In volume production - thousands of units a week - less machining means higher numbers of finished parts faster. The overall costs of forging and finish machining are lower when large numbers are done.
With CNC every surface of the part has to be cut, in three dimensions. For smaller numbers overall, CNC can be economical up to a point, and offers a much higher level of custom work - change the program and you get a different part. At the volume levels of AR production, tho, it goes to more than 8 million of them being forged, with just a few thousands being CNC in recent years.
Armalite chose forging because the concept of a firearm then was to have a set design with few changes over a long period. That keeps the cost of the forging dies low as they are only changed due to wear, not fashion, and the same parts are produced over long production runs. That divides the cost of a forge, dies, and overhead over a lot of units.
And we see that on the marketplace, with forged receivers as low as $40 each retail, vs CNC as high as $200. Forging does offer increased part strength, but the major reason was to keep the part cost down in high volume production. Same economics for 5.56 from Lake City being cheaper than .300BO - there's a bunch of machines which can run 24/7/365 all making the same thing, vs a smaller civilian plant running a batch of rounds then changing to the next order in the pipeline. You don't spread out costs if you make just a few. Forging AR recievers makes them faster and cheaper.
In volume production - thousands of units a week - less machining means higher numbers of finished parts faster. The overall costs of forging and finish machining are lower when large numbers are done.
With CNC every surface of the part has to be cut, in three dimensions. For smaller numbers overall, CNC can be economical up to a point, and offers a much higher level of custom work - change the program and you get a different part. At the volume levels of AR production, tho, it goes to more than 8 million of them being forged, with just a few thousands being CNC in recent years.
Armalite chose forging because the concept of a firearm then was to have a set design with few changes over a long period. That keeps the cost of the forging dies low as they are only changed due to wear, not fashion, and the same parts are produced over long production runs. That divides the cost of a forge, dies, and overhead over a lot of units.
And we see that on the marketplace, with forged receivers as low as $40 each retail, vs CNC as high as $200. Forging does offer increased part strength, but the major reason was to keep the part cost down in high volume production. Same economics for 5.56 from Lake City being cheaper than .300BO - there's a bunch of machines which can run 24/7/365 all making the same thing, vs a smaller civilian plant running a batch of rounds then changing to the next order in the pipeline. You don't spread out costs if you make just a few. Forging AR recievers makes them faster and cheaper.
- Status
Similar threads
- Locked
