About 3D printing, and metal material science
This burst of several posts of 3D printing.Many people who do not understand the material, the principle of 3D printing and the preparation of metal materials forming some misunderstanding.Simple say a few words here.Because the book at hand, and the things I learned long ago, all depends on the impression here, the term is not necessarily accurate.The analysis of 3D printing is also a personal opinion.Correct me if there are any errors, welcome to discuss.
1, flawed, and will not be able to use the material?
Material defect is a specific term.And the feeling of ordinary people, on the other hand, the strengthening of the metal material, are almost completed by increasing defects.And the lack of defects of metal, its performance is difficult to use.(about why the engine need to use single crystal, behind)
Whether adding alloying elements when smelting, or after molding pressure, the former is to increase the point defect to strengthen the metal, the latter is increased to strengthen the metal line defects.
And the influence of forging defects of metal is more complex, but the main strengthening mechanism is through the non-equilibrium phase change, the coarse grain into tiny grain - is also increasing surface defects (boundary).Not only increase the strength and increasing toughness.So to get the best comprehensive mechanical properties.
These defects will hinder the process of metal deformation, thus can improve the strength of the metal.
That is to say, the defects are not as little as possible.In many cases, it is the more the better.
Control of the defect is the most important subject, metal material science is an important approach to control the micro structure of the metal.Forging, heat treatment, the final principle is the control defects of reinforced metal (not to less control, but to eliminate harmful defects, more beneficial defects)
Defects can lead to other problems, of course, there are other negative effects on the performance of the material.Such as the internal stress, eliminate need to temper.
Hua-ming wang 3D printing, because is the alloy melt rapidly cooling, will inevitably produce internal stress.Subsequent also need to eliminate heat treatment.But the performance of workpiece, mainly lies in the rapid cooling process produces a large amount of surface defects, similar to the principle of forging.So can also be performance comparable to forging workpiece.
PS: the so-called weld defects, but also for high temperature resulted in the welding place recrystallization
happens, small grain size, less surface defects, led to the decrease of the strength and toughness.Welding defects, the casting defects, these arguments in the "defect" refers to the process of metal performance degradation, and the micro structure of the metal flaws, but it is not the same thing.
2, good hua-ming wang of 3D printing exactly?
Hua-ming wang also said in the speech, he the biggest breakthrough is solved the problem of the cooling and defects.And before that made in the United States to increase material company is bankrupt, is also unable to breakthrough on this issue.
Here, he said, he is with "making", but anyway, he solved.
Because solves this problem, so his technical artifacts are excellent in performance.As mentioned above, he can gain by laser cladding with beneficial defects of metal substrate.That is to say, he invented a senior "forging", don't need a hydraulic press, forging hammer, grain that is also available to small organizations.And this organization is through the equilibrium phase transition "watering" bit by bit, but not is unbalanced phase transformation "hit", should be more fine than forging, and more uniform.
So it does, and as a result.
And the future potential of this technology is far more than that.If hua-ming wang can mechanism of research on mechanism of crystallization process, so the organization can be further refinement, to further improve the performance of metal materials and even through the orientation to create design of heterogeneous materials.
3, 3D printing can not used for mass production?
As mentioned earlier, hua-ming wang laser cladding technology for artifacts in performance, far more than casting and forging parts.
Some say 3D printing, only to make a sample, when mass production with other process.
This kind of view ignores the basic facts.Is the process of different components, different performance, strength, fatigue life is different.In particular, if a prototype with 3D printing manufacture, using the characteristics of 3D printing made of complex shape parts, then the other technology can't use.Even to be able to use, its performance will decrease sharply.
Just think, a prototype with 3D printing, with production machine, overload also fell, the life also fell, the
empty important rise sharply, this prototype done good?Bear these, even if the strength experiment also want to redo.
Some might say, the speed of 3D printing.But the existing laser 3D printing also can do 5 pounds per hour, but even the ship's main shaft, the reactor shell that hundreds of tons of things ready to print, obviously speed is not a problem.
Aviation on multiple component heaviest?
4, 3D printing can replace existing process?
The current 3D printing is limited by the laser power and cooling process, the printing speed.But the potential has been early now.Titanium alloy components, forming, complex shape components is very have an advantage.Just think, aircraft designers once tasted 3D printing artifacts in shape, bearing, and life a huge advantage, how willing to return to the previous era of casting forging, why so?
If you can print out the strength and fatigue life are better gear, why use the original process?
3D printing, of course, not used for steel plate, steel tube of the existing process can be completed.It is not necessary, is also a waste of time.
Mature 3D printing will take time, to the influence of the traditional molding process, a few years later will appear.(from some rumours, now have some institutes of catic.)
5, single crystal, 3D printing and aircraft engine
Have friends think single crystal is very good, no flaws.Single crystal crystal, there is only one grain growth, sound is very perfect.
However, said at the beginning, less defect crystals, poor comprehensive mechanical properties.
So why do engine blade with cast single crystal?
Because, at room temperature and high temperature, performance of the single crystal and polycrystalline metals is the opposite.
In simple terms, polycrystalline crystal at room temperature, grain boundary can prevent dislocation movement, improved strength and toughness, but became oxidation at high temperature and creep happen
first area, become fragile.
And while a single crystal has other shortcomings, because there is no boundary, no this fatal weakness, which is applied in high temperature environment.
3D printing now, unable to produce single crystal alloy, so the highest temperature in aircraft engine application on hot end components co., LTD.
But it is said that at present have been able to make the organization of the columnar crystal, at least can be used in the second stage turbine.This message is a little evidence, is hua-ming wang for the cooling of the laser cladding process research is quite thorough, directional solidification can make.
Although 3D printing can't manufacturing single crystal, but blade can be printed directly on the turbine disc, increase longevity, reduce weight.This capability at least can be used on compressor blades.Directly print out the complex structure of hollow blade, may have higher requirements on accuracy.
A turbine disc manufacturing seems to have physical.How to performance, temporarily do not know.