非圆齿轮与机械压力机运动学优化毕业论文外文翻译.docx

1、非圆齿轮与机械压力机运动学优化 毕业论文外文翻译附录一:英文文献原文Optimized Kinematics of Mechanical Presses with Noncircular GearsE. Doege ( l ) , M. HindersmannReceived on January 8, 1997Abstract：The quality of parts manufactured using metal forming operations depends to a large degree on the kinematics of the press ram. Non-cir

2、cular gearsy to obtain those stroke-time behaviours we aim at as an optimum for the various metal forming ope with a rotational-angle-dependent speed ratio in the press drive mechanism offer a new wa rations in terms of manufacturing. The paper explains the principle using a prototype press which wa

3、s built by the Institute for Metal Forming and Metal Forming Machine Tools at Hanover University. It will present the kinematics as well as the forces and torques that occur in the prototype. Furthermore, the paper demonstrates using one example of deep drawing and one of forging that the press driv

4、e mechanism with non-circular gears may be used advantageously for virtually all metal forming operations.Keywords: Press, Gear, Kinematics1 lntroductiorIncreasing demands on quality in all areas of manufacturing engineering, in sheet metal forming as well as in forging, go hand in hand with the nec

5、essity to make production economical. Increasing market orientation requires that both technological and economic requirements be met. The improvement of quality, productivity and output by means of innovative solutions is one of the keys to maintaining and extending ones market position.In the prod

6、uction of parts by metal forming, we need to distinguish between the period required for the actual forming process and the times needed to handle the part.With some forming processes we have to add time for necessary additional work such as cooling or lubrication of the dies. This yields two method

7、s of optimization, according to the two aspects of quality and output. In order to satisfy both aspects, the task is to design the kinematics taking into account the requirements of the process during forming; also to be considered is the time required for changing the part as well as for auxiliary

8、operations in line with the priority of a short cycle time.2 Pressing Machine RequirementsOne manufacturing cycle, which corresponds to one stroke of the press goes through three stages: loading,forming and removing the part. Instead of the loading and removal stages we often find feeding the sheet,

9、 especially in sheer cutting. For this, the press ram must have a minimum height for a certain time. During the forming period the ram should have a particular velocity curve,which will be gone into below. The transitions between the periods should take place as quickly as possible to ensure short c

10、ycle time. The requirement of a short cycle time is for business reasons, to ensure low parts costs via high output. For this reason stroke numbers of about 24/min for the deep drawing of large automotive body sheets and 1200/min for automatic punching machines are standard practice.Increasing the n

11、umber of strokes in order to reduce cycle times without design changes to the pressing machine results in increasing strain rates, however. This has a clear effect on the forming process, which makes it necessary to consider the parameters which determine the process and are effected by it.In deep d

12、rawing operations, the velocity of impact when striking the sheet should be as low as possible to avoid the impact. On the one hand, velocity during forming must be sufficient for lubrication. On the other hand, we have to consider the rise in the yield stress corresponding to an increase in the str

13、ain rate which creates greater forces and which may cause fractures at the transition from the punch radius to the side wall of the part.In forging, short pressure dwell time is desirable. As the pressure dwell time drops the die surface temperature goes down and as a result the thermal wear This is

14、 counteracted by the enhanced mechanical wear due to the greater forming force, but the increase due to the strain rate is compensated by lower yield stress because of the lower cooling of the part. The optimal short pressure dwell can nowadays be determined quantitatively using the finite element m

15、ethod 3. In addition to cost avoidance due to reduction in wear, short pressure dwell time is also an important technological requirement for the precision forging of near net shape parts, which has a promising future.The requirements of high part quality and high output will only be met by a machin

16、e technology which takes into account the demands of the metal forming process in equal measure to the goal of decreasing work production costs. Previous press designs have not simultaneously met these technological and economical requirements to a sufficient extent, or they are very costly to desig

17、n andmanufacture, such as presses with link drives 6. This makes it necessary to look for innovative solutions for the design of the press. Its design should be largely standardized and modularized in order to reduce costs 6.Fig 1. Prototype press3 Press Drive with Noncircular Gears3.1 PrincipleThe

18、use of non-circular gears in the drive of mechanical crank presses offers a new way of meeting the technological and economic demands on the kinematics of the press ram. A pair of non-circular gears with a constant center distance is thus powered by the electric motor, or by the fly wheel, and drive

19、s the crank mechanism itself.The uniform drive speed is transmitted cyclically andnon-uniformly to the eccentric shaft by the pair of noncircular gears. If the non-circular gear wheels are suitably designed, the non-uniform drive of the driven gear leads to the desired stroke-time behaviour of the r

20、am. Investigations at the Institute for Metal Forming and Metal Forming Machine Tools (IFUM) of Hanover University have shown that in this simple manner all the relevant uninterrupted motions of the ram can be achieved for various forming processes 2. Apart from, the advantages of the new drive, whi

21、ch result from the kinematics and the shortened cycle time, the drive concept is distinguished by the following favourable propertties. Because it is a mechanical press, high reliability and low maintenance may be expected. In comparision to linkage presses the number of parts and bearings is clearl

22、y reduced. Above all, a basic press type can be varied without further design changes by installing different pairs of gears, designed according to the demandsof the customer. Unlike link drives, bearing locations and installations do not change within one loadclass as a result of different kinemati

23、cs. Thus the above mentioned requirement of modularization and standardization is taken into account Reductions in time and costs are possible for the design and press manufacture.3.2 PrototypeAt the Institute for Metal Forming and Metal Forming Machine Tools (IFUM) a C-frame press has been remodele

24、d and a pair of non-circular gears was installed. The previous backgears were replaced by a planetary gear set for this purpose. The work carried out shows that remodeling of existing presses for the new drive is possible. The state of the press at the end of the remodelling is shown in fiqure 1. Th

25、e press is designed for a nominal ram force of 1,000 kN and 200 kN of the die cushion. The center distance of the non-circular gears is 600 mm. The pair of non-circular gears has an average transmission ratio of 1.Each gear wheel has 59 gear teeth, straight-toothed,module 10 mm (fiaure 2). The face

26、width is 150 mm. The gears have involute gear teeth. We assume a non-circular base curve for the design of the flank geometry. As a result the tooth geometry of a non-circular gear varies along the circumference. In spite of this, it can be derived from the well-known trapezium rack, however 4, 51.

27、An algorithm for the computation, which takes the addendum and dedendum into account exactly, has been developed.Fig. 2 View of the gears from the rearThe press is designed for deep drawing of flat parts in single stroke operation mode. The maximum ram stroke is 180 mm, the number of strokes 32/min.

28、 At a stroke of 140 mm the ram velocity almost remains constant 71 mmls from 60 mm before lower dead center until lower dead center, see fiqure 3. Thus the velocity corresponds to the working velocity of hydraulic presses. The velocity of incidence of a crank mechanism with the same number of stroke

29、s would be 220 mmls, in comparison. In order to keep the same average velocity with a crank press, the number of strokes would have to be halved. The shortcycle time of the remodelled machine results from the fast upward motion. Because the press is run in single stroke operation mode, no particular

30、 requirements were made concerning handling time during design.The drive mechanism of the prototype with non-circular gears has in addition a favourable effect on the ram forces and the driving torques (ficlure 4). For a crank press the nominal force is normally available at 30 rotation of the crank

31、 shaft before the lower dead center. This corresponds to a section under nominal force of only 7 5% relative to the stroke. To reach the nominal force of 1,000 kN, the drive has to supply a torque of 45 kNm at the crank shaft. The prototype only requires 30 kNm on account of the additional transmiss

32、ion of the non-circular gears. They are transmitted to a cyclic. non-uniform crank shaft torque, resulting in a nominal force range from 60 to the lower dead center. This corresponds to 27.5% of the stroke. We always find similar conditions if the pair of non-circular gears is stepped down in the op

33、erating range of the press. This will almost always be the case with sheet metal forming and stamping. It is thus possible to design some machine parts in a weaker form and to save costs this way.4 Further Design ExamplesUsing the examples of two stroke-time behaviours the design is illustrated in the following. A range