Design And Simulation Of Multilayer Stagger-split Type Ultrahigh Pressure Die

Ultrahigh pressure technology plays an irreplaceable role in the fields of modernscientific research and industrial production. As the core component of ultrahighequipment, mold not only to withstand enough high pressure, also need to provide enoughcavity volume. Because of the large volume of the cavity is not only able to provideenough sample space, also can form stable and small gradient of pressure field andtemperature field. This shows large-scale mold is the inevitable requirement of moderndevelopment of ultrahigh pressure technology. But the main problem with large-scalemold is the difficulty of manufacturing large size carbide.Multilayer stagger-split type ultrahigh pressure die is a novel assemble mold. It ismainly composed of divided bodies and supported ring. And it doesn’t need to use largesize tungsten carbide, but provides the access to producing large-scale die. Whatsmore,it not only can expanded the cavity, but also improve the cavity pressure. In this thesis,the performance of multilayer stagger-split die was investigated by finite elementsoftware. The comparison and analysis on stress distribution characteristics of multilayerstagger-split die and belt type die were presented. And then brought forward an improvedstructure for multilayer stagger-split die. This article explored the rupture mechanism ofthe mold parts, and predicted the pressure capacity of multilayer stagger-split die, andthe related experiment was carried out to verify the simulation results. The influences oftemperature on stress and cavity volume of multilayer stagger-split die were analyzed byelectrical-thermal-structure coupling calculation. The results can provide theoreticalbasis for the design and processing of multilayer stagger-split type ultrahigh pressure die.The main contents and conclusions of this contribution are as follows:1. Principle and characters of multilayer stagger-split dieMultilayer stagger-split die has been constructed based on the principle of “dividing dies before cracking”, this solved the problem with manufacturing large-scaleultrahigh pressure mold from the structure. According to the principle of pressuremultiplier, the larger force loaded on inner face of cylinder can be translated on the innerwall of outer supported ring as small force. The contact force between divided block andsupport ring was further reduced through the effect of frictional resistance. Andmechanical analysis of multilayer stagger-split die was performed by the analytic method.The translation mechanical model of the internal pressure to give to support ring isdeduced. It provides a basis for the preliminary design of stagger-split die.2. The stress analysis and structure optimization of multilayers stagger-splittype ultrahigh pressure dieThe boundary conditions for numerical simulation of multilayer stagger-splitultrahigh pressure die are introduced, and the finite element model was established basedon ANSYS/Workbench. The stress distribution disciplinarian were analyzed by adoptingstatic implicit algorithm, and the results were compared with that of belt type die. Alsothe structure of multilayer stagger-split die was further improved. The results shows thatthe cylinder circumferential stress of multilayer stagger-split die pressure is far less thanthat of belt type die. In spite of there is stress concentration phenomenon in the outersupported ring of multilayer stagger-split die, but as a whole, the die is still in theadvantage. The stress of support ring and cylinder can be reduced at the same timethrough the arrangement that the number of divided blocks gradually dwindled down frominside to outside, and the support ring stress can be further reduced by increasing thenumber of divided layers and the coefficient of friction. The stress concentrationphenomenon of supported ring can be avoided by modifying its inner wall contour shape,and then the supported ring stress is more evenly. The junction between inner wall andthe cone of cylinder adopted transition fillet can eliminate the peak stress in the region.The stress value of cylinder can be significantly reduced if the inner wall of the cylinderpressure is design as flat or convex.3. The influence of preload to cavity volume of multilayer stagger-split die.Based on the unique structure of multilayer stagger-split die, the method of preloadapplication was discussed. The preload application can be realized not only by theinterference of inter-layers or between layers, but also by using steel wire or strip to intertwine the divided body assembly. And the influence of preload exerted on the cavityvolume of multilayer stagger-split die was analyzed by the example of inter-layerinterference. The results showed that: the increase amount of cavity volume under innerwall pressure could be greatly reduced by applying a preload force, especially by usingdouble layers support ring. Furthermore, by using different sizes of the mold cavities, itwas found that the normal displacement of inner wall of cylinder increases with theincrease of cavity radius, but both the variation and the increase amplitude becomesmaller when the preload is applied to the cylinder. For example, under the pressure of5400MPa, when the multilayer stagger-split die whose cavity radius is50mm is appliedsuitable preload, the normal displacement of inner wall of cylinder is only0.15mm.4. The pressure capacity calculations of multilayer stagger-split type ultrahighpressure die.The pressure capacity of multilayer stagger-split die was calculated by responsesurface methodology. And the influences of die size, divided layers and preload on thepressure capacity were analyzed, and compared with that of the belt type die. The resultsindicated that when the size or layers of multilayer stagger-split die were insufficient, thepressure capacity was determined by the strength of its support ring, and when the sizeor layers were sufficient, the pressure capacity was determined by the strength of carbide.After applying preload, as the increase of inner wall force, the equivalent stress ofcompression cylinder showed the trend of decrease at first and then increase, but wasconsistent with the equivalent stress without applied preload in the end. The support ringhas been in a high state of stress, will not significant change with the change of theloading on the inner wall of cylinder. And the applying of preload will not affect thepressure capacity of multilayer stagger-split die. According to the finite elementcomputation, the pressure capacity of multilayer stagger-split die is5times higher thanbelt type die, it can reach to8GPa. And corresponding physical experiment also indicatesthat the pressure capacity of multilayer stagger-split die is much higher than belt type die.5. The influences of temperature and pressure on performance of multilayerstagger-split die.The influences of temperature and pressure on the performance of multilayerstagger-split die were analyzed by the calculation of multi-physics coupling. The resultsshow that the cylinder temperature is about213℃, when the chamber temperature is up to1500℃. Temperature loading has no effect on the stress of cylinder, the stress ofcylinder increases nonlinearly with the increase of pressure loading on the inner wall ofcylinder. Both temperature loading and pressure loading affect the variation of cavityvolume, and the variation increased nonlinearly as the temperature and pressure increased.When the die is not applied preload, temperature loading almost showed no effect onstress of supported ring, but the stress of supported ring is increased nonlinearly as thepressure increased. When the die is applied preload, the supported ring stress reduces bynon-linear relationship with temperature load, but no matter with pressure load. Themultilayer stagger-split die which applied to preload is more suitable for synthesis ofhigh quality diamond.