Back in the 1940s, Crosley had the CoBra. It was made from sections stamped out of sheet metal and welded together to save weight. Now, Crosley screwed this up, by using dissimilar metals, so the engine would literally eat itself to pieces. Presumably, if they’d have made it out of compatiable metals, it would have worked, at least as far as the demands of the era were (it had a jaw dropping 26 HP).
Modern engines, of course, produce much more HP per cubic inch than ones made 60 years ago, but metallurgy has vastly improved as well, and I’m wondering if it would be possible to make a modern engine in such a manner and have it perform as well as a cast block engine does. It’s also possible that someone does make such an engine, but if they do, I’m not aware of it.
So, any of our engineering types care to take a stab at figuring this out?
Because a few pieces of sheet metal welded together are going to weigh less than a casting. You also won’t have to deal with cores, cleaning the sand out, cleaning up the casting and machining it to the final dimensions.
I realise the material properties of sheet metals and castings aren’t exactly the same, but in modern engines, isn’t the weight of the casting largely dictated by the amount of material physically required to withstand the pressures and other mechanical stresses experienced by the engine?
Since WWII, stamping and casting have been used extensively in the firearms industry. Each has advantages and disadvantages. Modern casting techniques give a product that requires pretty minimal final machining and finishing. Stamping gives a product that, likewise, requires little additional machine work. You can make perfectly functional guns either way. Ruger, for example, makes very extensive use of casting in all their guns. Most modern military weapons, on the other hand, make extensive use of stampings.
Which manufacturing technique is chosen is driven both by cost and by what gives the most suitable final product for the purpose.
So, a stamped and welded engine is certainly possible. Whether, in the long run, it will be less expensive than a cast engine and whether it performs and lasts as well as a cast engine are the questions that would need answered.
Yes, but for the low-stress parts only. Are there any commonly-used weapons that do not have a forged barrel? I ask because that would be roughly analogous to a cylinder in an engine.
Hell, I can’t think of any non-commonly used weapons that don’t have a forged barrel. I’m sure there’s some sort of ceramic matrix exotic stuff out there, but I’ve been working on this idea since you’ve posted it and I can’t think of a one.
Not to divert this into a gun thread, but the implication of what I asked was that there is some other mechanism other than stamping used to create the barrel. So, getting back to the engine, while you could make an engine largely out of sheet metal, I don’t know that you could make it entirely out of sheet metal because the cylinders (and reciprocating parts) would not withstand the stress. Or would they?
Depends on how you want to define sheet metal, I guess. Would you consider extruded metal tubing used as cylinders or cylinder liners to be sheet metal or are we restricting this to flat metal formed into the required shape through stampings?
I have often wondered the same thing: the engine of a modern car represents about 20% of the cost of the car. If you made a cheap engine out of stampings, that would last maybe 30,000 miles, could you produce a lighter, cheaper car? Such an engine could be made to run at maximum output, and be much lighter than a cast-block engine. You run the thing for 30K miles, then replace it.
I wonder if this would work?
I guess the most damning thing behind the fact that it’s not feasible – for whatever reason – is the fact the no one is doing it.
Sheet metal is a single thickness. Castings are formed so that you have the correct thickness (=strength) at all the appropriate parts of the engine. It also allows you machine connection points right into the casting. If you were going to use sheet metal, you’d use a uniform thickness of sheet metal to meet the most demanding parts of the application, which would be too strong and weigh too much for the less demanding parts of the application. If you wanted to weld different thicknesses together (tailor- or laser-welded blanks), then you’re introducing more cost. If you wanted to weld post formed sheets together, then take it from me (a real subject matter expert in this case!), that you won’t get the production quality and throughput that you want.
Don’t forget all of the machined connector points now how to be manufactured separately, and then added on, or otherwise added in the die process. Multiple steps for the welding assembly. Limited ability to guarantee the welds. Dimensional control issues. A longer dock to dock time, more manpower, more operations – yuck!
Sheet metal is great for car bodies! For a casting, well, you just cast it, and then machine it, and you’re done.
There are dimensional stability issues with sheet metal. When you stamp it, you leave a lot of stress. If you then weld or braze it, this stress is relieved, and the part distorts…A LOT. Bodywork gets around this by only spot welding on flanges in fixtures that prevent the distortion. The resulting stressed parts are not a problem in the mostly cosmetic function of body work.
An engine, though, has to go through lots of heat cycles. By machining it in stages, and aging and annealing between rough and fine operations, it might be possible to build a sheet metal engine that would hold it’s tolerances, but such processing would probably eat up any cost savings and then some.
Modern lost foam casting is really cheap. Pretty hard to compete with on economics.
From a functional standpoint, the structural requirements for an engine block are driven by stiffness, not strength so much. You don’t worry about the cylinder exploding, you worry about keeping it round and aligned with the crank. You don’t worry about the heads exploding, you worry about them warping so that the valves don’t seal. The main bearing supports need to stay in line so that they don’t cause the crankshaft to fatigue. Doing these things requires some bulk material, and thus the near universal use of cast engine blocks. By the time you have enough material to get the required stiffness, strength really isn’t an issue.
I don’t think the auto-buying public would tolerate engines that had to be replaced every two or three years. As repair jobs go, engine replacement is pretty dramatic and labor-intensive surgery, especially once you get into hours of time spent removing and re-installing all of the zillions of non-engine bits that are attatched to an engine, such as the water pump, alternator, intake manifold, fuel injectors, exhaust, clutch, transmission, etc.
IIRC, GM’s Northstar engine was intended to be basically ignored for 100,000 miles, then replaced, assuming the rest of the car was still servicable. That’s a much more palatable replacement lifespan.
As for sheetmetal engines, the biggest problems I can envision are dimensional tolerances and durability. So you take four (or however many) cast cylinders and weld or screw them to a sheetmetal frame. How long before the thing flexes to the point that cylinders break loose from metal fatigue? How much assembly labor is taken up by having to weld all the seams perfectly to be water-tight for the cooling jacket? How about the labor to precisely place brackets to hold bearings and/or mounts for the camshafts and valves?
I really don’t think we’ll see cast engine blocks going away for decades. The whole thing is cast in one self-supporting structural lump, and today’s high-precision and almost endlessly repeatable (semi-?)automated casting and machining techniques yield an engine block out of the mold that pretty much just needs to be cleaned up and machined to final dimensions.