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1、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-circular gearsy to obtain those strok
2、e-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 was built by the Institute for Metal
3、 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 drive mechanism with non-circular gear
4、s 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 necessity to make production economic
5、al. 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 production of parts by metal forming,
6、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 methods of optimization, according to th
7、e 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 operations in line with the priori
8、ty 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, especially in sheer cutting. For
9、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 cycle time. The requirement of a sh
10、ort 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 number of strokes in order to reduc
11、e 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 drawing operations, the velocity of
12、 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 strain rate which creates greater for
13、ces 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 counteracted by the enhanced mech
14、anical 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 method 3. In addition to cost avoid
15、ance 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 machine technology which takes into acco
16、unt 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 design 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 i
