A.O. Smith in Ashland City, TN manufactures residential water heaters.
The Challenge
Achieve high production rates while producing a part made from thick steel which requires a significant draw.
Process Details
Mild steel round blanks are drawn symmetrically to produce the tops and bottoms of residential hot water tanks. Blank diameters are from 14”-20”. The draw depth is as much as 4”. The required tonnage is 340 tons 2” off bottom dead center.
Issues Addressed in Finding the Best Solution:
• For the 4” draw, the press stroke needed to be 12-14”, and 16” might be even better. A hydraulic press would be ideal for the draw because it would have no issue with tonnage capacity or working energy no matter how high in the stroke. But, a hydraulic press would be too slow to achieve the desired production rates of 18 cpm (CPM to include the blank loading, part unloading, and operator movements).
• A mechanical press with standard crank motion would certainly be able to achieve the required CPM, but might have problems successfully drawing the material at the inherently higher slide velocities. Also, a press built to “typical” standards might have difficulty with the higher rating point and working energy required to do the job unless it was a much higher tonnage and larger press than actually needed (the bed size only needed to be 108” l-r). For a new or used press, the cost of this “oversized” press might become cost prohibitive. In addition, a used press with the proper specifications might be impossible to find.
• A mechanical press with link motion would help with achieving higher speeds while having a lower slide velocity through the working portion of the stroke, but again the cost might become prohibitive, and the desired rating point of 340 tons at 2” off bottom might be a problem to achieve.
Final Solution
To get a press with the optimal combination of specifications at a reasonable cost, A.O. Smith opted for a new Stamtec S2-660-108-60, 660 ton press, with a smaller than average bed; a higher than average tonnage rating point; a high-energy flywheel; oversized clutch, brake, variable frequency drive and other components as required.
Phase II of the Process Improvement
For more details, check the upcoming November Issue of Stamping Journal. The full article will include phase II where A.O. Smith replaced two human press operators with two articulated arm ABB robots, and one human helper/supervisor, for loading and unloading the press. The CPM and product throughput remained about the same, but they achieved significant savings in costs and downtime.