【正文】 demand for the heavy gas engine is increased sharply and the quality requirement is more severe. The heavy crankshaft is the key ponent in the gas engine, the quality of which will determine the gas engine’s performance and reliability. Production of the heavy crankshaft with continuous grain flow has undergone a long history, from the very beginning opendie forging to the upsetbending forging process, among which the TR and RR method are two major processes in the modern heavy crankshaft’s manufacturing [1]and[2]. In the RR upsettingbending process, owing to the forging equipment’s limitation, the forging force remains constant during the whole stroke, which is not in accordance with the requirement of forging process. Whereas in the TR upsettingbending process, the forging force increases with the cam block descends, which makes sure the TR method is superior to the RR . 1a shows a heavy crankshaft with the continuous grain flow, which was manufactured by the TR upsettingbending process, Fig. 1b illustrates the hydraulic press for the production of the heavy crankshaft. The turning radius of this crankshaft is 250mm and the weight is 7tons, which is the biggest crankshaft manufactured in China by now. This case study describes a TR upsettingbending process for this crankshaft, in which the crankshaft’s formation was changed from the semi closeddie forging to the plete closeddie forging for the dimensional accuracy improvement, machining allowance decreasing and material saving. But the die base in the TR upsettingbending equipment was broken in the first service when the plete closeddie forging was adopted, which raised extensive concerns at the manufacturing pany. The bulky die base has long manufacturing cycle and accordingly is very expensive, the failure of which causes loss of production and high economic loss. Fig. 2a and b illustrates the broken upper die base and broken lower die base in the TR upsettingbending equipment respectively. Based on experimental and putational analysis, the failure study on the broken TR upsettingbending equipment was conducted systematically. The rest of the paper is organized as follows. Section 2 presents the experimental failure analysis on the broken die base, including the visual inspection on the fracture area, material check for the broken die base, SEM observation and the metallurgical analysis. Besides the experimental failure analysis, the putational failure analysis is carried out in Section 3, which is based on the forging process simulation. In Section 4 the die base’s structure is optimized according to the structure strength calculation, the objective of which is to decrease the stress magnitude in the dangerous area and to enhance the load capacity of the TR upsettingbending equipment. Finally Section 5 is the conclusion and further discussion.Macroscopic fractography Visual inspection on the fracture of the broken die base reveals that the cracks in the upper die base and the lower die base locate both in the chamfering fillet area, which is shown in Fig. 2. The angle between the crack orientation and the axis direction of the upper die base is 45176。. Fig. 3a shows a typical brittle fractography in the upper die base. In the fracture area of the upper die base the casting flaw is inspected, the length of which is 80mm and the width of which is 20mm. In the fracture area of the lower die base, the casting defects also exist, which is illustrated in Fig. 3b. Compared to the casting flaw in the upper die base, the size of the casting defect in the lower die base is larger, the length of which is 170mm and the width of which is 32mm. By visual study, two oxidation layers are observed in the fracture of the lower die base. The above ellipse in Fig. 3b shows the severe oxidation layer, while the below ellipse area indicates the mild oxidation layer. The other casting defect existing in the fracture of the lower die base is also found out, which is denoted in the circle area of Fig. 3c.Hardness When the TR upsetbending equipment was in service, the hydraulic press put pressure on the upper die base, while the upper die base pushed the lower die base through the thrust surface to form the crankshaft. So the thrust surface of the die base must undergo quenching process, the hardness of which should be in the range of HRC 50–56 and the hardened layer should be in depth of 4–6mm. Table 3 shows the test data of the thrust surface’s hardness. It can be seen clearly that the most area of the thrust surface had undergone the quenching process except for the chamfering fillet area, . position “R30”, and the area near the upper boundary of the thrust surface, . position “40mm under the upper surface”, the hardness of which were severely lower than the specification. Compared to the Fig. 2b, it is clear that the crack of the lower die base just locates in the position “R30”.介紹 近年來，隨著造船、石油和天然氣貿(mào)易、電力、鐵路動(dòng)車組的快速發(fā)展使得重型燃?xì)獍l(fā)動(dòng)機(jī)的市場(chǎng)需求量急劇增加，質(zhì)量要求更加苛刻。大型曲軸是的燃?xì)獍l(fā)動(dòng)機(jī)關(guān)鍵部件，它質(zhì)量的高低將決定燃?xì)獍l(fā)動(dòng)機(jī)的性能和可靠性。全纖維曲軸生產(chǎn)經(jīng)歷了一段較長(zhǎng)的歷史，從一開始的自由鍛造工藝發(fā)展到現(xiàn)在的以TR和RR的方法為主的現(xiàn)代大型曲軸制造的彎曲鐓鍛鍛造工藝。在RR彎曲鐓粗過程中，由于鍛壓設(shè)備限制，鍛造力在整個(gè)的行程中保持不變，這是與鍛造工藝要求不一致的。而在TR鐓粗彎曲過程中，所需鍛造力隨凸輪塊下降而減小，這使得TR法明顯優(yōu)于RR法。圖1A顯示TR鐓彎工藝制造的全纖維曲軸，圖1B展示了大型曲軸的生產(chǎn)所用的液壓機(jī)。這個(gè)是現(xiàn)在中國(guó)制的造最大的曲軸曲軸，它的轉(zhuǎn)彎半徑250毫米，重量為7噸。本文將研究介紹一種TR鐓彎成形方法，它能使曲軸在在經(jīng)過半閉式模鍛到完整閉模鍛以后尺寸精度提高，加工余量減少，節(jié)約材料。但是這個(gè)TR鐓粗彎曲設(shè)備的模具在第一次閉式模鍛時(shí)破壞了，這件事引起了制造企業(yè)的廣泛關(guān)注。這個(gè)模具體積大，制造周期長(zhǎng)，所以非常昂貴，它的失效將會(huì)造成巨大的生產(chǎn)損失和經(jīng)濟(jì)損失。圖2A和B是TR鐓彎設(shè)備上的被破壞的上模及下模。基于實(shí)驗(yàn)和計(jì)算分析，對(duì)破壞的TR鐓粗彎曲設(shè)備進(jìn)行系統(tǒng)地失效分析。具體的分析安排如下。第二節(jié)介紹了破壞模座的實(shí)驗(yàn)失效分析,包括視覺檢查開裂區(qū)域,破壞的模具材料檢查、掃描電鏡觀察和金相分析。除了實(shí)驗(yàn)失敗分析，基于鍛造過程模擬的計(jì)算失效分析將在第3節(jié)中進(jìn)行。第4節(jié)是模具的結(jié)構(gòu)強(qiáng)度的優(yōu)化計(jì)算，其目的是減少在危險(xiǎn)區(qū)域的應(yīng)力，提高TR彎曲鐓粗設(shè)備的負(fù)荷能力。最后一節(jié)5是結(jié)論和進(jìn)一步的討論。斷口宏觀分析 目測(cè)模具的斷裂處可以發(fā)現(xiàn)上下模的裂紋都出現(xiàn)在焊接倒角區(qū)域,如圖2所示。裂紋方向與上模軸向的角度為45176。圖3A顯示上模座的衣柜典型的脆性斷口。上模座的斷口部分檢查出一個(gè)長(zhǎng)80毫米寬20毫米的鑄造缺陷，下模座的斷口區(qū)域也存在鑄造缺如圖3B示。與上模座鑄造缺陷的相比,下模座的鑄件缺陷尺寸較大，其長(zhǎng)度是170毫米寬度為32毫米。通過觀察研究，在下模座上的斷裂部分發(fā)現(xiàn)兩個(gè)氧化層。橢圓的上部分