PUNCHING AND STAMPING - DALCOS - #3

the production. All this is summed up by the formula: [production cost] = [raw material] + [tools] + [hourly cost] x [hours of production]. Fig. 6 gives the meaning of this formula in graphic form.

HOURLY COST: FOUR FACTORS

Four other factors must be added together to calculate the hourly cost of a machine. he first cost factor is the labour connected with the machine. When the machine needs continuous supervision, the cost of an operator dedicated to the machine must be taken into account (from 20 to 25,000 euro a year to be divided by 1800 hours per year). he second factor is the annual maintenance costs, which include the expendable materials, the hydraulic oil and the lubricants, the cost of technical assistance and spare parts. he cost of maintenance incurred for the machine in one year, divided by 1800 hours per year, gives this value. he third factor is the cost of the electricity consumed by the plant each hour. Lacking data regarding plant absorption of electricity, a prudent calculation could be half the installed power.

he fourth factor is the cost of amortization of the machine. To calculate this hourly cost it is sufficient to divide the envisaged amortization rate for the machine during the year in progress and once again divide it by 1800 hours per year. If the machine has been purchased by leasing, the annual instalment divided by 1800 hours may be considered instead of the cost of amortization. In this way, upon completion of machine amortization or upon expiry of the leasing contract, there will be a reduction in the hourly cost of the machine.

THE SPEED OF PRODUCTION

To complete the calculation of the production cost, it is necessary to multiply the hourly cost by the hours required for the machine to carry out the work.

Knowing the time-cycle of one piece (in hours/piece), this figure is multiplied by the total number of workpieces N. In a sheet-fed punching machine the cycle time depends heavily on the type of machine, the route of the tool over the surface of the sheet metal and the number of tool changes required. To this punching time should then be added the time for loading the sheet and unloading the product (from 30 to 50 hundredths of a minute). In the coil punching machine, the production time is obtained with empirical formulas as follows: [Production time] = [Number of operations per piece] x [Average time per operation] + [Length of piece in metres] x [Time per metre]. In this case the coil punching machine time is equal to the total production time, since the loading and unloading times do not exist. Lastly, the production time in the stamping press is minimum: every press stroke produces one piece. Productivity therefore depends on the press speed (60, 80, 120 and more strokes a minute). In conclusion, the die press is the fastest production system, followed by the coil punching machine and lastly the sheet-fed punching machine. It has been pointed out in

Fig. 4

Coil punching line with decoiler, straightener and coil punching unit.

Fig. 5

Stamping line with press.

LAMIERA • OCTOBER 2005

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