| 摘要: | 本文主要是使用射出成型與射出壓縮成型製程探討超高分子量聚乙烯(Ultra High Molecular Weight Polyethylene，UHMWPE)的充填性質、成型參數條件、機械性質、磨耗特性與微結構成型性。其主要研究結果如下： 無縫合線與有縫合線的拉伸試片實驗結果顯示，在成型無縫合線試片時，試片拉伸段與入膠口的橫截面尺寸大小及形狀對抗拉強度有較明顯的影響，相較之下不同的射出製程參數對抗拉強度的影響則是較小；此外，縫合線的產生降低了射出製程參數及橫截面尺寸對試片抗拉強度的影響，且在充填試片厚度較厚的有縫合線拉伸試片時，縫合線兩側有較好的分子鍵結能力；縫合線區域的主要表面缺陷為微孔洞、微裂縫和不完整的分子鍵結組織。在Ball-on-Plane的配對與乾摩擦條件下，不同的射出成型製程參數與磨耗參數會影響UHMWPE摩擦係數值的變化，摩擦係數有隨著接觸負荷與滑動頻率的增加而增加的趨勢，磨耗體積損失則呈現不規則的增減，大致上在較高的射出成型參數設定下有最低的磨耗體積損失；UHMWPE主要的表面磨耗機構為塑性變形、微溝槽(Microgroove)與波浪狀(Wavelike)組織。射出成型微結構時，射出速度對於微結構的高度變化有顯著的影響，且在射出成型尺寸200 μm以下的微結構時，成型品上的微結構外觀容易於脫模過程中發生變形以及在微結構周圍產生拉扯的痕跡；而在射出壓縮成型微結構時，由於射出壓縮成型過程中給予足夠的固定壓縮力(30 tonf)，因此射出壓縮成型製程參數對於微結構高度的變化則較無顯著之影響，但可獲得較為穩定的微結構高度與良好的表面外觀。 The wear behavior, mechanical properties and microstructure of injection molded ultra high molecular weight polyethylene (UHMWPE) parts has been studied. As far as tensile strength is concerned, the influences of process conditions and cross-sectional dimensions on the tensile strength of a weld line are investigated. In addition, the weld line characteristics of structures and different cross-sections are explored in this study as well. Five specimens, with different cross-sections, are injection molded simultaneously. With the Taguchi method, three process variables including melt temperature, mold temperature, and injection velocity were found to be the most significant. Furthermore, in order to understand more about the effect of the process parameter, the single-factor experiments are used. Experimental results show that the parametric influence is relatively little on the cross-sectional dimensions. The results also show that the tensile strength and surface hardness are affected at injection molding conditions and sliding contact loads. As far as wear behavior is concerned, experimental results show that the different wear contact loads and varied injection molding conditions have an influence for friction coefficient and wear volume loss of UHMWPE specimens. The higher sliding contact load results in a lower friction coefficient. Moreover, lower wear volume loss is often occurred in the specimen molded with the highest injection molding level. The morphologies of the worn surfaces and the cross-section of specimens were examined with optical microscope and scanning electron microscope, respectively. Plastic deformation, grooves and wavelike formation are the main wear mechanism on the surface in wear tests of UHMWPE. As far as microfabrication is concerned, replication accuracy was investigated for microinjection molding and microinjection compression molding. The mold insert was fabricated by stainless steel metal etching method. The mold insert includes rectangular groove of 100 μm, circular groove array of 100–300 μm and square groove array of 100–300 μm. Both the microinjection molded part and the microinjection compression molded part were observed under microscope to compare the replication accuracy. To measure the microstructure profile, a high performance surface profiler was used. Among mold insert, microinjection molded parts and microinjection compression molded parts were measured. The experiment results show that the UHMWPE can be filled in microcavities by microinjection molding and microinjection compression molding technology. The height and shape of microstructure were influenced by injection molding process parameters. For an injection molded part, injection velocity was the most influential factor. The height and shape of microstructure shows that microinjection compression molding was a more stable process than microinjection molding, due to it can provide an enough compression force. |
