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#048 Relationship Between Press Machine and Die (6) Stroke Length of Press Machines

Category : Formed Materials
July 9, 2010

The stroke length of a press machine is selected depending on the details of the job at hand. In blanking formation, the stroke length is short being on the order of 10 to 80mm. In bending or drawing work, it is necessary to select the stroke length taking care about the formed height of the product.
An example of drawing work is described below. See Fig. 1 below.

Fig. 1

The drawing formation starts at the die surface and ends at the bottom dead center. The bottom drawn part of a completely formed product comes above the die surface making it easier to take it out. In addition, unless there is some additional margin, the working becomes difficult. Therefore, in manual operations, a stroke length of more than 2.5 times the product height becomes necessary. When carrying out automatic forming, since time is required for material movement, a stroke length of more than three times the product height can be said to be a safe stroke length. However, caution should be exercised because too long a stroke length decreases the working efficiency. With a short stroke, there are the problems that it is difficult to see inside the die and that it is difficult to take out the product, which also reduces the work efficiency and is dangerous at the same time.

In the relationship with the number of strokes per minute (spm), there is an inversely proportional relationship between spm and stroke length. When spm becomes large, the inertial energy of the slide becomes large, which affects the vibrations, noise, and machine rigidity. Because of this, the stroke is made shorter thereby avoiding these effects. It can also be said that a limit is placed on spm by the stroke length. In a high speed press exceeding 600 spm, the stroke length is about 10 to 30mm. When the stroke length exceeds 200mm, in most cases spm will be less than 50.

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