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#121 Terminology and Surroundings (15) Economic Speed of Press Forming

Category : Terminology
April20, 2012

A large number of people think that increasing the press forming speed (spm) increases the productivity in press forming operations. This is good if you are calculating the numbers while sitting at a table because the problems that occur are not considered, and the numbers come out fine.

However, there are various problems in actual practice. For example, when forming a connector, increasing the speed caused more frequent damages to springs or stripper bolts. The fluttering of the fed material becomes large, causing more frequent misfeeds into the die, which causes the die to break more frequently. Therefore, there will be such problems that were not present before increasing the speed. Since these problems are caused because the die is not suitable for that spm, they can be of course solved by making improvements.

If the spm is increased ignoring the production quantity, the production will be completed early, and hence the waiting period for the next job increases and there will be more frequent changes in preparations, causing the equipment utilization rate to decrease, and as a result there is also the problem that the productivity has not increased.

In addition, even the cost of peripheral equipment such as the feeding device or the uncoiler, etc. increases, the cost of the equipment including the press machine becomes high, and the cost per unit time increases due to the relationship with the cost of equipment depreciation, the cost reduction obtained by increasing the spm gets cancelled out, and the expected cost reduction may not be achieved.

In press forming, there is a state of good balance among the equipment, die life, and production quantity. This kind of state is called the economic speed of press forming. However, although progress will stop if too much importance is given to this state, but it is also necessary to understand that ignoring this and trying to speed up change can lead to obstructions to production. The economic speed should be found out from the contents of the respective press operations and it is important to aim at carrying out the work efficiently.

In the example of forming connectors, the economic speed is about 600 to 800 spm. The range of the spm value depends on the shape and the number of products per shot. There is no hard and fast rule.

In drawing presses, the speed of drawing the product from the material is limited by the spm of the press machine, and it is not possible to increase the spm profusely. Therefore, in progressive forming, the number of products per shot is increased to increase the productivity. Instead of the appropriate value of three in a row, the number of products per shot is made five or seven in a row. The problems do not increase in proportion to the number of products per shot, but there is a multiplication relationship. If stoppages increase due to increasing the number of products per shot, the effect of having multiple products in a row becomes less. Increasing the number per shot to meet a tight deadline can lead to a production in which several of the rows are to be thrown away. Such increases in the number in a row should be limited.

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