Ok before we get into arguments about technical processes let’s define what this debate about the term “Semi-Forged” really means. Let’s start with a few definitions.
The term is made up of two parts namely a prefix:
Semi; - Synonyms - half, partially, partly. Antonym – fully.
And the word, Forged; in this case meaning -To form (metal) by a mechanical, or hydraulic, press.
Ok, some people contend that an object e.g. a piston, can’t be Semi-forged, it can only be forged. If you use one connotation of the prefix semi, they are indeed correct, in that once you form it by applying pressure it is forged. It’s not half forged, the object has had pressure applied to it from a press, and, therefore, it’s forged. Nothing semi- about it.
That’s fine, but what if forging wasn’t the only process used to create the item? Such that it’s partially, or partly, cast and partly forged, so in the English language it can rightly be called Semi-Forged, or for that matter Semi-Cast if you so choose. Such a process is squeeze casting, which usually involves pouring molten metal into the bottom half of a mould, and then pressing the top half in and squeezing the metal into shape. Depending on how long you wait to press the two (or more) parts of the mould together, would determine if this process could be described as “Semi-Solid” forging.
Which brings me to a quirk of the, ever evolving, English language, namely the tendency to drop parts of words or phrases. In the name of brevity, or perchance marketing, such deletions can completely change the meaning of the word/phrase. Hence “Semi-Solid Forged”, becomes “Semi-Forged”. Which is a misnomer for a process like thixo-forming, because the item has never been subject to any other forming process other than forging, but would be correct if the product was squeeze cast.
Now to the question of the correct description for Toyota pistons. Well for a start they are “Forged”, as can be seen from the grain pattern it’s easy to tell that the piston was formed in a press, and, given that they are hypereutectic, which is not easy to form in a solid state, it’s a fairly safe assumption that they are forged in a semi-solid condition. IMO they are unlikely to be squeeze cast because hypereutectic alloys are supersaturated with silicon, which tends to crystallise on cooling creating pockets of pure silicon, if you don’t use special, expensive, fluxes.
So the correct term form the pistons in question is “Semi-Solid Forged”, “Semi-Forged” is marketing speak, stemming from the aforementioned need for brevity in getting your message across, and easily remembered, by your average petrolhead. Judging by the literacy standards displayed on most automotive forums, that’s not an easy task. In fact it was probably a petrolhead who first coined the term, when he/she forgot the word when he was telling his mate about the you beaut new wheels that they had purchased “Yeah mate,they um…Semi..umm…umm, Semi Forged, yeah that’s it, Semi-Forged. Buggered if I know what it means, but it sound cool”, and before you know it a new term has entered the English language.
Dropping the word “Solid” might just be all that’s needed for a potential customer to remember that your product is better than a cast one, and, depending on the spin you put on it, may even be as good as a forged one. Given the right marketing spiel it could even be touted as being better (and IMO in some cases it is better).
So now we have a solution to the age old hotly debated topic of whether or not semi forged is a true and correct description. Namely, there is no clear answer unless we know the exact process used. In the case of pistons, it’s probably not right, but wait around a few more years for the marketing BS to insinuate it’s way into the vernacular and it soon will be. For those vehemently opposed to this foul deed being perpetrated on the Queen’s English, just make sure you know how to use the big words before they’re all eradicated from vocabulary that we all abuse each and every day.
My comment was directed at Dr-X, though if the cap fits... (j/k)
(me thinks a couple of CT20b's on my 308 should prove interesting though)
. Titanium exhaust sounds wonderful (