生胚密度與燒結溫度對粉末冶金件正齒輪精度之影響

Abstract

齒輪為傳動系統中重要機械元件之一。工業界廣泛使用的金屬材質齒輪的製造方法，大致可分為切削法與非切削法。粉末冶金法製造齒輪屬於非切削法，具有低成本、可大量生產和生產速率快等優點，再加上粉末冶金技術的不斷改良，包含粉末配方之研發與成形技術的提升，大幅地改善粉末冶金齒輪的機械強度與提高密度，使得粉末冶金齒輪之市場擴展迅速。 粉末冶金齒輪的精度和其所使用之原料粉、成形過程與燒結方法等息息相關。粉末變化率、生胚密度、模具設計、燒結時間與燒結溫度等都是造成粉末冶金齒輪之齒面幾何誤差的主要因素。粉末冶金之製程參數非常繁多，只要有一參數變動，即可能影響產品之品質及精度。對於要求高精度的齒輪，粉末冶金齒輪仍有待研究與突破的地方。 本論文將採用實際上粉末冶金齒輪的製程條件，進行試作實驗與齒輪精度的量測，以探討生胚密度與燒結溫度這兩個製程參數對齒輪精度的影響，提供粉末冶金正齒輪生產時製程參數調整的參考依據，進而提升粉末冶金正齒輪製造之精度。實驗與分析結果顯示，生胚密度對於粉末冶金齒輪件的尺寸變化及齒形誤差的影響不大。在一般燒結溫度時，粉末冶金齒輪件之齒面隨著燒結溫度之提高而膨脹，齒形壓力角則變小，但隨著燒結溫度的再提高或燒結時間的增長，會使得粉末冶金齒輪件之齒面膨脹量減少，甚至由膨脹變為收縮，而導致其齒形壓力角變大。

A gear is one of the important transmission elements in a machine system. The manufacture methods of gears can be categorized into the cutting method and the non-cutting method. Manufacturing of a sintered powder-metallurgy gear belongs to the non-cutting method. The sintered powder-metallurgy gears have great advantages of cost down, suitable for mass production and fast production, etc. As the result of the improvement of powder-metallurgy manufacturing technology, including the research and development of the powder prescription and the improvement of forming methods, improves the mechanical strength substantially and raises the density of the powder-metallurgy gears. It enables the market of the powder-metallurgy gears to expand rapidly. The precision of the powder-metallurgy gears is related as closely with the powder, forming and sintering process. Powder variation, green density, sintering temperature, sintering time and the design of a forming die are some major factors affected on gear surface deviations. The number of powder-metallurgy process parameters are large, and a change of any parameter may be influences the products’ quality and precision. Research and making a breakthrough on powder-metallurgy gears are necessary for the requirements of high precision powder-metallurgy gears. This study refers to the conditions of practical powder-metallurgy manufacture process, and proceeds to experiments and gear precision measurements as well as investigation on the effects of two parameters, green density and sintering temperature, on gear precision. To provide reference materials of some amendment on the parameters of the powder-metallurgy spur gears manufacture process, and then to improve the gear manufacture precision. According to the experimental and analytical results, the effect of green density plays a very little role on the change of the produced gear size and profile precision while the sintering temperature is a very important factor. In the range of normal sintering temperature, the gear surface expands while the increase of sintering temperature, and this results in the decrease of gear pressure angle. However, the amount of gear surface expansion decreases or even becomes shrinkage when the sintering temperature continues increasing. The shrinkage of the gear profile results in the increase of gear pressure angle.