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Investigation of the particular crystallization behaviour of semi- crystalline thermoplastic powders processed by selective laser sintering.

by:Tuowei     2019-09-11
1.
The introduction of additive manufacturing and incentive products have become more and more important, and now it is not just the object of the presentation.
This is also one of the reasons why many committees (such as ASTM F42 or VDI) are currently working on new standards for additive manufacturing technology.
One of their main challenges is to reproduce part properties in one layer
A wise manufacturing process.
The influence parameter is to use an updated powder with elastic properties due to towarm-
Policy, but also affected by component placement.
Especially stl-
Documents of different volumes in the building interior are essential for overall performance. Fig.
1 shows the construction work of the mobile phone shell above different volumes.
Due to the heat transfer of the components placed below, pre-
The heating of the surrounding powder, resulting in the accuracy of the size, stability and mechanical properties of each shell being affected.
There\'s a new half.
Crystalline thermoplasticg. polypropylene (PP)
Or ether ketone (e. g. PEEK HP-3)
On the edge of entering the market.
In addition, other important thermoplastic materials, such as polyethylene, may be found recently (PE-HD)
And formaldehyde (POM)
SLS can also be processed. (Rietzel et al. ,2010; Rietzel et al. , 2008)
The research focus of this paper is to study the influence of phase transition (
Molten crystal)
In order to gain an understanding of the process of occurrence, it is used as the basis for direct manufacturing in the future.
In particular, the melting and solidification behavior must be known because they are very important for the laser sintering process.
A quasi
Laser sintering process (
Schmachtenberg andSeul, 2002)
It is usually used as the basis for polymer processing behavior.
Therefore, the influence of time
In order to enhance the existing models, the related crystalline effects were studied. [
Figure 1 slightly]2.
Materials and methods for commercial laser sintering powder made of PA12 (
PA2200 EOS Co. , Ltd)and PEK (PEEK HP-3, EOS GmbH)
Their processing properties were tested and compared with alternative thermoplastic powders.
[Frozen grinding of the following granularityd. sub. 3,max]= 80 [micro]
POM particles (BASF SE)
, Then mix the resulting powder with 0. 2 wt. -% of Aerosil[R](Degussa AG)
To improve liquidity. PE-HD (DuPont, [d. sub. 3,50]=24-36 [micro]m)and PP (DuPont,[d. sub. 3,50]=30-45 [micro]m)
Supplied in the form of powder with spherical geometry. By adding 0. 4 wt. -
% Of carbon blackR](Degussa AG)
The penetration depth of the laser can be limited to about 100 [micro]m for PE-
HD because of its poor energy absorption behavior at the wavelength of C [O. sub. 2]-laser.
In order to study the melting and crystalline behavior of thermoplastic materials used, the SLS process was simulated by DSC measurements.
According to DIN 53765, 10 or 20 K/min is the standard heating and cooling rate for thermoplastic plastics.
By using different cooling speeds, it can be displayed in previous works (Rietzel et al. , 2010)
This crystal has a high time dependence and is a quais-as part of laser sintering-
The standard measurement technique is not suitable for fully describing the real process. [
Figure 2:
Basic idea of accuracy
The constant temperature laser sintering realizes the hypothesis of melting and will not crystallize for a long period of time at a point slightly lower than its melting point.
According to Fehler, specimens are heated in a defined procedure!
Verweisquelle konnte nicht gefundenwerden. .
Constant temperature (Tiso)
In the dynamic DSC operation, the temperature of the measurable crystals described above was determined.
Heat Flow and Crystal time (
Time from the beginning of the constant temperature measurement t0 to the Crystal Peak [t. sub. pc])
A kinetic model of Crystal was established.
Commonly used Sestak-
The crystalline process was studied by Berggren kinetic model. (
Sestak and Berggren, 1971)
In order to describe the change in the crystalline rate as a function of temperature, the Arrhenius equation is used for uniform dynamics in the process of constant temperature (ASTM, 2008).
Subsequently, the activation energy of the crystal can be calculated from the gradient of an approximate straight line.
The gradient describes the effect of temperature changes on the crystal. ln[[DELTA][t. sub. pc]]= -[E. sub. A]/R[T. sub. iso]+ c (1)[E. sub. A]
= Activation energy (J/mol)
R = gas constant (8. 314 (J/mol K)[T. sub. iso]
= Constant temperature (K)
C = after the approved building temperature was determined in the previous thermal analysis test, from POM, PE-
On the improved DTM sintering station 2000, HD, PP and PA12 follow different irradiation strategies. 3.
Results and discussion the phase change time between the differential thermal temperature and time of all polymers was measured
Stability of both
Phase area is analyzed.
The activation energy of the Crystal was calculated by constant temperature DSC measurement.
Results inTab.
1 show POM and peep HP-
The activation energy of 3 is the highest.
Therefore, in the measured temperature interval, the gradient of the function describing the phase transition caused by the crystal is the highest.
On the other hand, the slope and activation energy of PP and PA12 are the lowest.
Therefore, the temperature changes. g.
By adding a colder powder layer, the start and overall dynamics of the crystals are not serious near the temperature of the crystals, which means that there are two-
The stage area is available for a long period of time during the building process. Fig.
3 shows the slicer taken out of the upper area of the pa12 and POM stretch test Rod, sintering at LKT.
Both pictures show that the large globes grow due to constant temperature conditions, but especially at the interface between the surrounding powder and the melting area, the two materials are very different.
The PA12 part has molten particles on the interface between the part and the surrounding powder bed, acting as the nucleus, fig. 3 (left).
Contrary to this effect of POM, no unmelted particles are visible, but the directional crystals above the cross-section indicate that the crystals occur before the particles of the continuously applied layer are melted, fig. 3 (right).
This confirms the discovery of rapid crystals at low temperatures.
The density of all the sintering samples is high and there are few pores and defects. [
Figure 3 slightly]4.
Conclusion and prospect of considering process behavior (e. g.
Time related crystals)
Compared to faster crystalline polymers such as PEEKHP-from other studies, the type of PA12 studied is certainly a very solid material3 and POM.
However, due to the improvement of Machine Engineering, the commercial potential of other laser sintering powders is also increasing.
The results show that both exist
The Phase model is generally not delivered to all types of polymers.
Further studies will focus on melting and crystals, but Dynamics and time
Temperature behavior of phasechanges.
For the purpose of direct manufacturing, it is necessary to produce parts with constant performance and mass by form and degree of crystal.
Thermal analysis tests point out that it is very important to understand the whole building work, rather than focusing only on the individual parameters of the surface of the building chamber.
The patent in this field today is only focused on controlling and measuring the current layer, not on the in-depth study of z-direction(
Mark Zhong and Alan, 2004).
Finally, the concept proposed is the first method to predict and simulate the performance of laser sintering elements. 5.
Reference ASTM. (2008)
Standard Test Method for thermal dynamics parameters using differential scanning volume by constant temperature method, BeuthVerlag. pp. 1-
11 Alan A. Mark Zhong-L. (2004)
Munchen European Patent Office uses thermal image feedback sintering. pp. 10 Rietzel D. , Kuhnlein F. , Drummer D. (2010)
Selective laser sintering method to characterize new thermoplastic materials for additive manufacturing, Wendel B. , Feulner R.
Shi ma business(2008)
New Thermoplastic powder for selective laser sintering.
Kunstoffer International 98: 42-
45 Steinberg, Seul T. (2002)
Constant temperature laser sintering model.
60 sessions of the Society of Plastic Engineers (ANTEC)
San Francisco, California. , Berggren G. (1971)
Study on the mechanism of solid dynamics --
React at rising temperatures.
Acta thermochimica 3:1-
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