摘要
板料的拉深成形是生产汽车车身覆盖件最基本、最常用的冲压成形工序。当前,为了应对日益严重的能源危机和环境污染,汽车车身的轻量化势在必行。铝合金、铝镁合金薄板及双相薄钢板等新型材料的比重比普通钢板低很多,能满足汽车车身轻量化的要求,是普通钢板的理想替代品,但是这些新型材料在室温下的成形性能不及普通钢板,不适用于现有的成熟、高效的薄板成形技术。因此,研发出能在室温条件下大幅提高板料拉深成形性能的新技术是非常必要的。
本文的目的就在于研发出一种实用、高效的薄板成形新技术,该技术不仅要能在室温条件下显著地提高板料的拉深成形性能,而且要能方便地应用于实际生产之中。
为了理清研发思路,本文归纳与整合了现有的冲压成形研发方法,并以此为基础,有针对性地提出了适用于本次研发的新方法,该方法明确了新技术的研发流程,全文的结构和内容都是据此编排和组织的。
本文首先用上限法对覆盖件拉深过程的力学特征做了分析,发现在形状为非回转面的覆盖件拉深过程中,板料法兰面上的流动阻力分布极为不均匀,尤其是在圆角区域与直边区域之间的过渡区域上流动阻力的值为极大,即流动阻力最大或明显大于相邻区域。因此,提高板料拉深成形性能的关键就是要降低过渡区域上的流动阻力。为此目标,本文提出了一项能显著地降低过渡区域上流动阻力的新技术-拉深孔成形技术。
为了验证基于拉深孔成形技术的新工艺是否合理,本文总结了前人采用有限元的方法对三个典型制件(圆筒件、长方盒形件和复杂油底壳)的成形过程进行模拟的结果,发现新工艺相比于常规工艺能大幅提高板料的成形性能。
虽然有限元数值模拟是当前最为精确的理论分析方法,其结果有很强的参考价值,但由于它受到理论假设和软件功能的限制,其分析结果与实际情况必然存在差异,所以工艺实验仍然是最基本、最可靠的研究方法。本着先易后难的原则,本文首先对相同实验条件下分别采用新工艺和常规工艺拉深成形的圆筒件进行了对比,结果表明:新工艺的拉深效能比常规工艺高50%左右,并且在实验中拉深孔成形技术也表现出了能方便地应用于实际生产的能力。实验研究的结果初步验证了拉深孔成形技术是可行和有效的。
Drawing of sheet metal is one of the most popular stamping processes. It is widely used to manufacture panel parts of car body. Nowadays, we must try hard to cut down the weight of automobile in order to decrease emission of contamination and relieve consume of energy. Sheet metals of some new type of materials, such as Al-alloy, Al-Mg-alloy and two-phase steel etc., meet the requirement of decreasing the weight of car body because they are much lighter than ordinary steel sheets. So these sheet metals are ideal substitutes for ordinary steel sheets. However, under room temperature, these sheet metals cannot be formed easily comparing with ordinary steel sheets. So that it is necessary to research and develop new process methods to improve the formability of sheet metal in drawing process remarkably.
In this thesis, a new process method for drawing sheet metal is put forward, which could not only effectively improve the formability of sheet metal in drawing process but also be applied in practicality.
Firstly, current investigative methods for stamping process are summed up in this thesis. Then a new investigative method, which is applicable to study deep drawing process of sheet metal, is put forward to instruct us how to research and develop a new process method to improve the formability of sheet metal in drawing process effectively.
Secondly, according to the new investigative method, mechanics characteristic of deep drawing process for panel parts is analyzed with upper-bound method. It is concluded that the formability of sheet metal in deep drawing can be remarkably improved by decreasing the flow resistance in the transition region between the circular angle area and the straight side area. Consequently the Drawing-Hole Forming Technology is put forward and used to decrease the flow resistance in the transition region.
In order to verify the feasibility and efficiency of the new process method, FEM (finite element method) simulation and experiment are employed to analyze the drawing process with drawing holes for three of representative work pieces. By contrasting the forming results between new and conventional process, a primary conclusion is drawn that Drawing-Hole Forming Technology is an applicable and effective method to greatly improve the formability of sheet metal in deep drawing.
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