PUNCHING AND STAMPING - DALCOS - #7

Fig. 11

Products produced by punching from coil (safety door frames).

be calculated that N = [Press tool cost] / ([coil punching hourly cost] x [hours per piece in coil punching machine]). For example, suppose that it costs 8000 euro to make the tool. he hourly cost of the coil punching machine is 40 euro and the machine takes 20 seconds (equal to 0.0056 hours) to make the actual piece.

he discriminant number N will be equal to 35,700 pieces. For smaller production runs it will be more economic to produce with the coil punching machine. For larger production runs it will be more economic to make a die. It should be noted that the suggested formula, due to the approximations, is incomplete, as it lacks the cost of the punch press tools (which increases the formula denominator) and the cost of the hours of production with the press (which instead increases the numerator). Apart from the advantage of simplicity, this formula also offers a valid indication regarding the discriminant number N and leads to certain reflections. Consider the hourly cost of the punching machine and the cost of the press tool as constant. he graph of the trend of the discriminant N in relation to the punching machine time-cycle shows the trend as can be seen in fig. 12. he discriminant number N increases as the coil production time-cycle

decreases; in other words they are inversely proportional. Lastly, if the coil punching machine hourly cost and the coil production time-cycle are considered as constant in the formula, then the discriminant number N increases as the die cost increases.

CONCLUSIONS

Firstly the structure of the production costs

and the hourly cost of punching from sheet,

punching from coil and stamping with press

and die has been analysed.

Punching from sheet and from coil were then

compared.

he result is that punching from sheet is indicated for manufacturing pieces with complex shapes or for very small production runs (from 1 to 50 pieces). For simpler shaped pieces (rectangles, squares, notched and punched panels) and for medium and small productions (from 200 to 500,000 pieces), punching from coil is always preferable. Lastly punching from coil and stamping by press were compared. he result is that stamping by press is to be preferred for large and volume mass production (millions of pieces), while, again, punching from coil is more indicated for medium and small production runs. In more general terms, a simple formula has been obtained that, given the tool cost, the hourly cost of the coil punching machine and its production time, gives the number of pieces N below which it is more economic to punch from the coil than to stamp by press.

Fig. 12

Discriminant number N in relation to the coil production time.

£= E O Q

Time-cycle in coil punching machine

LAMIERA • OCTOBER 2005

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