13.51327 六、發明說明： 【發明所屬之技術領域】 本發明係關於一種可簡化加工步驟'降低加工成本並 可保持曲柄表面完整的自行車空心曲柄鍛胚製造方法。 【先前技術】 自行車為了讓騎乘者能夠省力的踩踏前進，除了各式 的變速設計外，構成其車體的各項構件也無不朝輕量化= 方向設計，其中在各種使車輛得以輕量化的方式中，主要 是利用密度小且材質堅固的金屬來製作自行車車體的各項 桿件，並在不影響各桿件結構強度的原則下減少各桿件的 厚度’例如將各桿件成型為空心管狀，俾有效達到減少車 體重量且保持車體結構強度的目的。 其中，曲柄是自行車上用以連接踏板與齒盤的構件， 在其中一種對該曲柄進行輕量化設計的現有技術之方式 中’係將該曲柄成型為一斷面呈〔型之桿冑，此種型離之 曲柄固然可有效達到輕量化且節省材料之目的，但結構強 度部不足，尤其無法承受曲柄在踩踏時所承受的扭轉之 力，因此在受到碰撞容易彎折損壞。 此外，在其他對該曲柄進行輕量化設計的現有技術之 方式中，'亦有將曲柄成型為空心管狀者，其製造方法主要 係先將一金屬塊成型為空圓瞢 π二匕圓e後，再以平面鍛造方式利 用兩對合之鍛模將該金屬塊沖壓成斷面略呈長方形之管 體； 此種型態之曲柄雖然可有效達到輕量化且節省材料， 更兼顧結構強度之目的，作於盥 於取k過程中，必須先在該圓 U51327 管内填充流體’利用該流體支撐該圓管管壁，以防止空心 圓管在進行平面鍛造時產生變形損壞，待成形為長方形管 體之後，再對該管體進行破孔，來排出管體内的液體； 其中’填充液體後再破孔排出液體的步驟雖然不可或 缺’卻又顯的多餘’而且還會增加加工成本，此外，因為 必須對曲柄的管體進行破孔，故曲柄管體的表面無法保持 完整’勢必會影響曲柄成品的美觀及強度，且在進行進一 步的表面處理時，所使用的酸液也會由破孔處滲入而侵蝕 φ 曲柄内部，故現有技術之自行車空心曲柄的製造方法實有 - 其待進一步改進之處。 【發明内容】 有鑑於上述現有技術的缺點，本發明提供一種自行車 空心曲柄鍛胚製造方法，希藉此設計解決目前現有技術之 製知·方法加工步驟繁複、加工成本高而且必須破壞曲柄管 體結構的缺點》 為了達到上述的發明目的，本發明所利用的技術手段 # 係、使-自行車空心曲柄難製造方法依序包含下列各步 —擠壓成型步驟，盆係刹田 咕 ’、利用一第一沖頭將設於一第一 模具内的一金屬塊擠壓成刑盔 或型^ 一桿體，令該播壓成型後之 為一第一端部與一 金屬塊的中段部分為一頸部 靖谇，兩端分別為一第一 第二端部； 利用兩對合之鍛模對該金屬塊 平面鍛造步驟，其係 進行沖壓； 呈長桿狀的第二沖頭由 一锻抽内孔步驟，其係利用 4 1351327 再利用鍛抽内孔步驟及縮口步驟加工形成其内部之穿槽 (14)，因此無須先填充流體，再對曲柄管體進行破孔以排 出流體，故可確實達到簡化加工步驟、降低加工成本以 及保持曲柄表面的完整性的發明目的。 【圖式簡單說明】 第一圖為本發明之步驟流程圖。 第二圖為本發明於擠壓成型步驟前側視之部分元件剖 面之圖。 馨第三圖為本發明於擠壓成型步驟後側視之部分元件剖 . 面之圖。 ' 第四圖為本發明於平面鍛造步驟後金屬塊之立體外觀 圖。 第五圖為本發明於鍛抽内孔步驟前之側視圖。 第六圖為本發明於鍛抽内孔步驟後之側視圖。 第七圖為本發明於縮口步驟前側視之部分元件剖面 圖。 • 第八圖為本發明於縮口步驟前端視之部分元件剖面 圖。 第九圖為本發明於縮口步驟後側視之部分元件剖面 圖。 第十圖為本發明之成品的立體外觀圖。 第十圖為本發明之成品進一步加工而呈可使用狀雜 之立體外觀圖。 【主要元件符號說明】 8 13.51327 (10)金屬塊 (11)頸部 (12)第一端部 (121)爪部 (122)組裝孔 (123)組裝孔 (13)第二端部 (131)組裝孔 (14)穿槽 (21)第一模具 (211)模型槽 (22)第一沖頭 (30)第二沖頭 (40)第二模具13.51327 VI. Description of the Invention: [Technical Field] The present invention relates to a bicycle hollow crank forging manufacturing method which can simplify the processing step 'reducing the processing cost and keeping the crank surface intact. [Prior Art] In order to allow the rider to step on the pedal with a labor-saving effort, in addition to various shift designs, the components constituting the vehicle body are also designed to be lightweight = direction, in which various vehicles are lightened. The main method is to use the metal with low density and firm material to make the rods of the bicycle body, and reduce the thickness of each rod without affecting the structural strength of each rod. For example, the rods are formed. The hollow tubular shape effectively achieves the purpose of reducing the weight of the vehicle body and maintaining the structural strength of the vehicle body. Wherein, the crank is a member for connecting the pedal and the toothed disc on the bicycle, and in one of the prior art methods for lightweight design of the crank, the crank is formed into a section of the shape, Although the type of the crank can effectively achieve the purpose of weight reduction and material saving, the structural strength portion is insufficient, and in particular, it cannot withstand the torsional force of the crank when it is stepped on, and therefore it is easily bent and damaged by the collision. In addition, in other prior art methods for lightweight design of the crank, 'the crank is also formed into a hollow tubular shape, and the manufacturing method mainly comprises first forming a metal block into an empty circle 瞢 π 匕 circle e Then, the metal block is punched into a tube having a slightly rectangular cross section by means of a planar forging method; the crank of this type can effectively achieve weight reduction and material saving, and the purpose of structural strength. In the process of taking k, it is necessary to first fill the U51327 tube with a fluid to support the tube wall with the fluid to prevent deformation of the hollow tube during planar forging, and to form a rectangular tube. After that, the tube body is punctured to discharge the liquid in the tube body; wherein the step of filling the liquid and then puncturing the liquid to discharge the liquid is indispensable, but it is redundant, and the processing cost is increased. Because the tube of the crank must be broken, the surface of the crank tube cannot be kept intact', which will affect the appearance and strength of the finished crankshaft, and further In the surface treatment, the acid used also penetrates from the hole to erode the inside of the crank. Therefore, the manufacturing method of the bicycle hollow crank of the prior art is practical - it is to be further improved. SUMMARY OF THE INVENTION In view of the above-mentioned shortcomings of the prior art, the present invention provides a method for manufacturing a hollow crank forging embryo of a bicycle, which is designed to solve the conventional methods and methods of the prior art. The processing steps are complicated, the processing cost is high, and the crank tube body must be broken. Disadvantages of the structure In order to achieve the above object, the technical means utilized by the present invention, the method for manufacturing a bicycle hollow crank is sequentially included in the following steps - an extrusion molding step, a basin-type brake field, and a utilization The first punch extrudes a metal block disposed in a first mold into a torture helmet or a type of body, so that the first end portion and the middle portion of a metal block are formed after the pressure molding. The neck of the Jingjing, the two ends are respectively a first and second end portions; the plane forging step of the metal block is performed by using two pairs of forging dies; the second punch having a long rod shape is forged by a forging The inner hole step is processed by using the 4 1351327 and the forging inner hole step and the shrinking step to form the inner through groove (14), so that the crank tube body is not required to be filled first, and then the crank tube body is broken. The fluid is discharged, so that the object of simplifying the processing steps, reducing the processing cost, and maintaining the integrity of the crank surface can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS The first figure is a flow chart of the steps of the present invention. The second figure is a cross-sectional view of a portion of the components of the present invention in a side view prior to the extrusion molding step. The third figure of the present invention is a cross-sectional view of a part of the side view of the invention after the extrusion molding step. The fourth figure is a three-dimensional appearance of the metal block after the plane forging step of the present invention. Figure 5 is a side elevational view of the present invention prior to the step of forging the inner bore. The sixth figure is a side view of the invention after the step of forging the inner hole. Figure 7 is a cross-sectional view of a portion of the device in a side view of the present invention before the necking step. • Figure 8 is a cross-sectional view of some of the components of the present invention in the front end of the shrinking step. Figure 9 is a cross-sectional view of a portion of the component of the present invention in a side view after the necking step. The tenth figure is a perspective view of the finished product of the present invention. The tenth drawing is a perspective view of the ready-to-use of the finished product of the present invention. [Description of main components] 8 13.51327 (10) Metal block (11) Neck (12) First end (121) Claw (122) Assembly hole (123) Assembly hole (13) Second end (131) Assembly hole (14) through groove (21) first mold (211) model groove (22) first punch (30) second punch (40) second mold