08-17-2012, 04:03 AM
Just to clarify;
Yes Ron the process in the post was exactly the process I described.
The only reason I chose to contradict Dallen in the first place, which is something I rarely do online, was that taking Billet machining as a "Normal process" for piston manufacture in context with the discussion that was taking place people might incorrectly influence folks to choose to use, or not to use pistons as raw materials for casting Which could lead to any number of issues. It was never my intention to offend in any way, I only post on any forums in order to share my accrued knowledge in order to help people acheive their goals in this case in "Fun Metal work"
But to further outline piston manufacturing processes, it's true that Pistons are manufactured by Casting, Forging and Billet machining, In that order I was given the following percentages when working on the forging press I don't know their origin but they are broadly in line with what I have seen in practice;
Casting is used for 90%+ of Petrol/Gasoline engined cars, they are cheap and cheerful to manufacture have suitable metallurgical grain structures and do not suffer from the heat expansion issues that affect Forged pistons.
Forging is used for most of the rest of the Car pistons and probably much more than 90% of the Pistons used in Diesel Engines (more like 99%), as Diesel engines require much heavier pistons than Petrol engined cars and also suffer from much greater stresses than all but very high performance petrol engines, Forged pistons require more piston to bore clearance than either cast or billet machined as a result of their "Thermal growth characteristics" which can cause them change shape a little more than the other two when heated, this I was taught, is as a result of the various stored stresses in the grain structures as a result of the forging, these grain structures are not entirely removed by normalising as this would ruin the strength benefit from forging.
Of the three processes Billet machining is by far the rarest method, as it is both much more expensive to do in numbers (and even a small car,truck or plane engine uses at least four) and the metalurgical results are less than satisfactory, with all of the important grain structures being cut at the most critical places(around the base of the wrist pin bosses). To my knowledge no current OEM uses billet machined pistons, and in the tearing down of hundreds if not thousands of OEM engines as a part of my R&D career I have not yet found a single billet machined piston. They are used in areas of motorsport where specific geometric properties require pistons to be manufactured to suit when no dies or patterns exist to cast or forge, JE pistons(One billet piston manufacturer) claims they get greater strength by billet machining but to my knowledge they have never backed this up with testing against an identical forged item, choosing to use FEA instead which didn't take grain structure into account assuming homogenius material properties instead.
Once again, with respect to the original context, "casting fodder" It is completely acceptable to use cast pistons as raw casting materials, as for the other two, I'm sure they melt and solidify, I suppose if you are just using scrap anyway they will be as good as anything but the materials used were not formulated with the specific intention of casting so should be used with caution. The reason I described Forging as opposed to casting was simply that the Deutz pistons in the original post are, I believe, forged items.
A further note being that cast pistons don't usually polish well, nor do things cast from using cast pistons as feed stock, but as this isn't easily measured please accept this single point is just a matter of opinion.
Best regards
Rick
Yes Ron the process in the post was exactly the process I described.
The only reason I chose to contradict Dallen in the first place, which is something I rarely do online, was that taking Billet machining as a "Normal process" for piston manufacture in context with the discussion that was taking place people might incorrectly influence folks to choose to use, or not to use pistons as raw materials for casting Which could lead to any number of issues. It was never my intention to offend in any way, I only post on any forums in order to share my accrued knowledge in order to help people acheive their goals in this case in "Fun Metal work"
But to further outline piston manufacturing processes, it's true that Pistons are manufactured by Casting, Forging and Billet machining, In that order I was given the following percentages when working on the forging press I don't know their origin but they are broadly in line with what I have seen in practice;
Casting is used for 90%+ of Petrol/Gasoline engined cars, they are cheap and cheerful to manufacture have suitable metallurgical grain structures and do not suffer from the heat expansion issues that affect Forged pistons.
Forging is used for most of the rest of the Car pistons and probably much more than 90% of the Pistons used in Diesel Engines (more like 99%), as Diesel engines require much heavier pistons than Petrol engined cars and also suffer from much greater stresses than all but very high performance petrol engines, Forged pistons require more piston to bore clearance than either cast or billet machined as a result of their "Thermal growth characteristics" which can cause them change shape a little more than the other two when heated, this I was taught, is as a result of the various stored stresses in the grain structures as a result of the forging, these grain structures are not entirely removed by normalising as this would ruin the strength benefit from forging.
Of the three processes Billet machining is by far the rarest method, as it is both much more expensive to do in numbers (and even a small car,truck or plane engine uses at least four) and the metalurgical results are less than satisfactory, with all of the important grain structures being cut at the most critical places(around the base of the wrist pin bosses). To my knowledge no current OEM uses billet machined pistons, and in the tearing down of hundreds if not thousands of OEM engines as a part of my R&D career I have not yet found a single billet machined piston. They are used in areas of motorsport where specific geometric properties require pistons to be manufactured to suit when no dies or patterns exist to cast or forge, JE pistons(One billet piston manufacturer) claims they get greater strength by billet machining but to my knowledge they have never backed this up with testing against an identical forged item, choosing to use FEA instead which didn't take grain structure into account assuming homogenius material properties instead.
Once again, with respect to the original context, "casting fodder" It is completely acceptable to use cast pistons as raw casting materials, as for the other two, I'm sure they melt and solidify, I suppose if you are just using scrap anyway they will be as good as anything but the materials used were not formulated with the specific intention of casting so should be used with caution. The reason I described Forging as opposed to casting was simply that the Deutz pistons in the original post are, I believe, forged items.
A further note being that cast pistons don't usually polish well, nor do things cast from using cast pistons as feed stock, but as this isn't easily measured please accept this single point is just a matter of opinion.
Best regards
Rick
Whatever it is, do it today, Tomorrow may not be an option and regret outlasts fatigue.