Fig.4.1.6 Time schedule for a mass produced car body panel
The timetable of an SE project
Within the context of the production process for car body panels,only a minimal amount of time is allocated to allow for the manufacture of the dies.With large scale dies there is a run-up period of about 10 months in which design and die try-out are included.In complex SE projects,which have to be completed in 1.5 to 2 years,parallel tasks must be carried out.Furthermore,additional resources must be provided before and after delivery of the dies.These short periods call for pre-cise planning,specific know-how,available capacity and the use of the latest technological and communications systems.The timetable shows the individual activities during the manufacturing of the dies for the production of the sheet metal parts(Fig.4.1.7).The time phases for large scale dies are more or less similar so that this timetable can be considered to be valid in general.
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Data record and part drawing
The data record and the part drawing serve as the basis for all subsequent processing steps.They describe all the details of the parts to be produced. The information given in the
Fig.4.1.7 Timetable for an SE project
part drawing includes: part identification,part numbering,sheet metal thickness,sheet metal quality,tolerances of the finished part etc.(cf.Fig.4.7.17).
To avoid the production of physical models(master patterns),the CAD data should describe the geometry of the part completely by means of line,surface or volume models.As a general rule,high quality surface data with a completely filleted and closed surface geometry must be made available to all the participants in a project as early as possible.
Process plan and draw development
The process plan,which means the operational sequence to be followed in the production of the sheet metal component,is developed from the data record of the finished part(cf.Fig.4.1.1).Already at this point in time,various boundary conditions must be taken into account:the sheet metal material,the press to be used,transfer of the parts into the press,the transportation of scrap materials,the undercuts as well as the sliding pin installations and their adjustment.
The draw development,i.e.the computer aided design and layout of the blank holder area of the part in the first forming stage–if need bealso the second stage–,requires a process planner with considerable experience(Fig.4.1.8).In order to recognize and avoid problems in areas which are difficult to draw,it is necessary to manufacture a physical analysis model of the draw development.With this model,the
forming conditions of the drawn part can be reviewed and final modifications introduced,which are eventually incorporated into the data record(Fig.4.1.9).
This process is being replaced to some extent by intelligent simulation methods,through
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which the potential defects of the formed component can be predicted and analysed interactively on the computer display.
Die design
After release of the process plan and draw development and the press,the design of the die can be started.As a rule,at this stage,the standards and manufacturing specifications required by the client must be considered.Thus,it is possible to obtain a unified die design and to consider the particular requests of the customer related to warehousing of standard,replacement and wear parts.Many dies need to be designed so that they can be installed in different types of presses.Dies are frequently installed both in a production press as well as in two different separate back-up presses.In this context,the layout of the die clamping elements,pressure pins and scrap disposal channels on different presses must be taken into account.Furthermore,it must be noted that drawing dies working in a single-action press may be installed in a double-action press(cf.Sect.3.1.3 and Fig.4.1.16).
Fig.4.1.8 CAD data record for a draw development
In the design and sizing of the die,it is particularly important to consider the freedom of movement of the gripper rail and the crossbar transfer elements(cf.Sect.4.1.6).These describe the relative movements between the components of the press transfer system and the die components during a complete press working stroke.The lifting movement of the press slide,the opening and closing movements of the gripper rails and the lengthwise movement of the whole transfer are all superimposed.The dies are designed so that collisions are avoided and a minimum clearance of about 20 mm is set between all the moving parts.
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4 金属板料的成形及冲裁
4. 模具制造原理
4.1.1模具的分类
在金属成形的过程中，工件的几何形状完全或部分建立在模具几何形状的基础上的。与机械加工相比，在成形时明显更大的压力是必要的。由于零件的复杂性，往往不是只进行一次操作就能成形的。根据零件的几何形状，通过由一个或几个生产过程例如成形或冲裁的几个操作步骤进行生产。一个操作也可以同时完成几个过程。 在设计阶段，合理的生产步骤、生产次序以及生产工序数都由生产计划来决定（如图4.1.1）。在这个计划中，应该对机器的可利用性、零件的计划生产量和其他限制条件予以考虑。
其目的是在保证高水平的操作可靠性的同时最大限度地减少需要使用的模具数量。通过部件设计部和生产部之间的紧密合作促使几个成形和有关的冲裁过程能在一个成形操作中完成，如此一来，仅仅在设计阶段就可以大大地简化部件。
显然，越是更多的操作集成到一个单独的模具上，模具结构就必然更为复杂。其后果是成本较高、产量下降和可靠性较低。
图4.1.1 油底壳的生产步骤
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模具类型
模具的类型和模具之间零部件的密切相关运输是根据成形步骤、预算的部件的尺寸、要生产的部件的生产量来确定的。
大型钣金零件的生产几乎完全采用单套模具来实现的。典型零件可在汽车制造、国内家电业以及散热器的生产中找到。适当的转移系统，例如真空抽吸系统，可以使双动模安装在一个足够大的安装面上。例如，用这种方式可以使汽车左右车门在一个工作行程中一起成形。（参考图4.4.34）。
尺寸大的单套模具需安装在大型压力机上。部件从一个成形点到另一个成形点的运输是机械化地执行的。工人或机器人可以使用与单工序压力机一前一后安装的冲压线(对比图4.4.20与 4.4.22)，同时，在大型多工位压力机上，系统还配备了夹钳轨（如图4.4.29）或交叉抽吸系统（如图4.4.34）来运输部件。
多工位转换模是用于小型和中型零件的大批量生产（如图4.1.2）。它们由几个安装在同一个基准平面上的单工序模具组成。金属板料的送进主要以机械手运送的方式，也可以人工地从一个模具运到另一个模具。如果这部分的运输自动化，那么此时的压力就称为转换压力。在大板料转换冲压线上，最大的多工位转换模要与单工序模具配合使用（参考图4.4.32）。
级进模，也称为渐进冲裁模，钣金件是分阶段冲裁的； 一般来说，没有实实在在的成形操作。钣金是以金属圈或金属条的形式送进的。通过使用尺寸适宜的金属板料和优化的材料利用率可以达到对板料的合理利用（对比图Fig.4.5.2与图4.5.5）。工件一直固定在载体上，直到最后一次操作。冲裁完成后，整个条料按照工序流动方向移动时，该部件随着转移。移动的长度等于模具间中心线的距离，它也被称为步距。切边，通过使用非常精确的进给装置或试点引脚确保相关进给零件精度。在最后一个工位，即最后一道工序，已成形的部分于载体断开。例如电动机金属转子和定子的生产就是渐进冲裁模的一个应用领域（如图.4.6.11和4.6.20）。
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