Which is better forged or machined?

[Blowdown1]

Andre pointed out a number of good points. machined billet aluminum parts seem to fail the most. Going along with his bike thread, a lot of the aftermarket companies that started making billet parts had failures. Now the favored option is forging with minor machining for a more finished look and strategic removal of material for weight.

Arias pistons seems to do the same thing. Forged blanks that are then machined to have the lands, valve cutouts, etc. Wiseco has had problems in the past with their motorcycle pistons as well (in racing applications). I don't know what they were using for manufacturing, but there was considerable machining.

Stock parts typically didn't have the failures and there was much less machining of the surfaces. Take that for what it is worth. (or someone let us know what it is worth)

 

[Mange]

Mange Im speaking purely automotive. I have not seen any after market billet parts for chainsaws and not saying you can't get them cause if the price is right you can have anything made. As much as some people like to speed their saws up, the billet parts would be a real +. Im sure sometime back I read where billet crankshafts were being used now by J reds but could have been another brand. Not for sure on that. Im to lazy to show links but trust me if you were building a high performance street engine and you started priceing cast, forged and billet rods and pistons, the price of the forged rods and pistons would look a lot better then the price of the billet rods and pistons.

I have worked at racing cars, and built a few street racers, I know about the subject at hand.
I am also a interested reader, I am well awere of what you wrote, but this thread is in a chain saw forum and the thought of using these pistons is not new, so there might be someone that actually had experiance with this.
This I wrote was not intended to get under your skin, I just got corius.

 

[Al Smith]

I was merely making a point about manufacture of pistons.There is no way that I know of to hot forge an aluminum piston.They are either cast using break away metal molds or pressure cast[die cast]Now,you could thump the rough shape out a piece of aluminum alloy,then machine it.I am not trying to be a smart alec but I could fill several pages on this subject.There are many heat treat,anodizing and machining procedures that must be preformed before you get a finished product.It's not nearly as simple as taking a 5 axis CNC mill and carving out a piston from a piece of aluminum stock.Yes,you could do this but it would not last very long.

 

[average joe]

You do have a multitude of questions.I have never figured out how a person would forge an aluminum piston.Then again ,I haven't seen every thing having worked in the auto industry,in one form or another for over 30 years.I'm willing to learn,please enlighten.

Wiseco has been forging pistons for years.
Forging has some advantages in that the finished parts are stronger than their cast counterparts, and a forged piston will not crack like a cast piston. A forged piston will also melt at a lower temperature than the cast version.
In a nutshell the differances in the types of pitstons is caused by the material used. Cast pistons use a very high silicone content , which makes them hard and heat resistant, but also brittle. Forged pistons use a lower silicone content and have a higher tensile strength, but tend to soften up under heat.

 

[Al Smith]

Well I suppose it is all in the terminology.Forging ,in my opinion ,is hot forging such as a con rod,crankshaft,straight truck axle,etc.Cold forming I think would be a better term when applied to punch blanking a rough piston.Although I also imagine the process has been widely accepted as being called forging.As a matter of interest in the making of cast pistons,the first process is a trip through the annealing oven to remove a degree of brittleness,after they are first cast.

 

[eric_271]

I have worked at racing cars, and built a few street racers, I know about the subject at hand.
I am also a interested reader, I am well awere of what you wrote, but this thread is in a chain saw forum and the thought of using these pistons is not new, so there might be someone that actually had experiance with this.
This I wrote was not intended to get under your skin, I just got corius.

Mange I am not offended by your post and understand the need to ask qustions. I should have left the automotive part of things out. I still cant remember which company use's billet crankshafts in there saws but I think its Jonsered. ehp should know as well as anyone what a person can get for chainsaw pistons. Im still waiting for him to jump in.

 

[average joe]

I have actually seen pistons being forged, Al. And the process is like you described in that the piece isnt heated. Basicly a slug of billet alluminum is placed into a stamp and the thang is punched out in steps, much like the process to stamp metal sheet into auto body parts. After the cold blanking is done the piece goes through a maching step to bore the pin hole and clean the part up, a cam grinding process to shape the exterior of the piston(they are not round like one would think), and a heat treatment/stress removal process.

 

[046]

Nascar teams have their own CNC machines and can custom make internal engine parts to spec's

 

[andrethegiant70]

Cool thread guys, I think I learned somethin'!!

 

[Al Smith]

As Joe said a piston has ovality and taper,in the skirt area.One design had a "barrel " shape.The older method for the ovality and taper used a "cat head" turner,for the ovality and the taper was set with a wedge,similar to a taper attatchment on and engine lathe.The barrel design used a machine made by Giddings and Lewis,which was the most complex CNC machine I had seen up to the time.It used 4 different programming languges[ugh].At the time,there were about 15 of these machines in the world.4 were in China,the rest were here,4 of which I worked on.I on occasion,had a brew or 3 with the head design engineer,cool guy.I have no idea how they machine the telflon coated pistons in use today.

 

[ehp]

Making a piston is easy but to make a piston that works is alot harder , first it is a 2 stroke motor so the aluminum is alot different, and it needs to be different , myself I like lots of silicon because you can make the piston lighter with this materail and it has less drag on the cly. wall, the first piston I ever made was made out of 6061 T6, it didnot work very well cause it gained more size than the jug under heat and had to much drag on the cly. wall, it never broke or was hurt in any from and I used it in a 3120 for 12 tanks of fuel and it cut fine but was no good in a alcohol saw so I moved on, try to find someone to make you a 2 stroke piston, good luck , besides wiseco there are very few that will, now wiseco has gone to even less silicon in there piston but the skirts dish bad now they collaspes and then skirt breaks.
now there is alittle more in making a piston than most would think, a piston is oval and smaller on top because it grows the most under heat, the thickness of the dome , skirts , pin bosses all have to be correct to work. the biggest thing on making a piston for a chainsaw is the alumimum and to get a high silicon you most likely have to use a pour type of materail, the stuff I am using right now is 18 % silicon

 

[jimbo1490]

I agree with TimberMaster. I have never seen a "machined" piston. Granted all pistons are machined after the molding process to clean them up and make them true. Are you possibly refering to cast vs. forged vs. hyperutectic? All of which are different ways the metal is heated for strength and durability. I might be wrong though?

Gary

The term hypereutectic actually refers to a type of metal alloy rather than a manufacturing process like casting or forging. In the case of Kieth Black pistons, they are cast out of a hypereutectic alloy. The term eutectic refers to the proportion of one metal mixed with another such that the melting point of the mixture falls no further. At this proportion, both metals will always solidify together. Unfortunately, this type of alloys of aluminum are not the strongest.

The 'Hypereutectic ' alloys are made of constituents in such proportions that they will not solidify together under 'normal' conditions, but they can be forced to solidify together under carefully controlled conditions of temperature and pressure. This is usually done in the 'billet' or ingot stage of production, when the metal is made into big heavy slabs.

So hypereutectic alloys have been limited in the past to certain rolled, machined and extruded goods because these goods are formed into final shape well below the melting point. If a hypereutectic alloy is ever brought to melting temp and then allowed to cool and solidify under 'normal' conditions, the result will no longer be the same metal alloy. Instead, there will be a mass of the eutectic alloy of the constituents plus inclusions of the excess alloying metal. This is very undesirable and fatally weak. This is why some alloys of aluminum are said to be either 'weldable' or 'unweldable'.

Note that the unweldable alloys are always the strongest as they are hypereutectic. The trick that KB pulled off was figuring out how to cast hypereutectic alloys into near net shape so that only minor machining was needed; no forging. Much of the strength of forged pistons comes from the different alloys used (see above). Only a little bit of the strength of forged aluminum comes from 'grain flow' from the forging process.

Jimbo

 

[Johnsonlong]

Which is better forged or machined pistons?

To make this question more of what I think you're looking for there are three kinds of Pistons typically, and all of them are machined to final shape and size. The three basic types are ingot or billet which is machine from a ingot or billet of aluminum. Then we have cast with your machine from a cast piston basic shape. Then we have forged with her machine from a forged piston base shape. We also have nowadays a more rare form of 3D printed as well as sintered powder metal. Most of us who are familiar with the race industry would assume that forged pistons would be best however they are going to require a longer warm-up of the engine previous to use otherwise there will be a heat seizure between the cylinder and the piston due to the expansion rate of the forged piston. It's actually hard to say which would be the best it would depend on your application as each one serves a different purpose. Unfortunately there is no direct answer for your question the way it was asked. However you can now Google some of the terms I used here and broaden your knowledge of Pistons and their applications. Again the three basic types are billet, forged, cast. Lots of people refer to Billet as machined even though they're all machined except for the some of powdered metal process type which is going to be rare for you to find a manufacturer admitting that they're making them this way. That said I haven't seen any powdered metal Pistons sold on eBay however I have found a few really cheap ones on Amazon that were powdered metal.