Page 211 - DMGT501_OPERATIONS_MANAGEMENT

Unit 7: Process Control Charts

Telco had a Forge Division created to meet its need for forgings. In July of 1974, the Forge Division Notes
was planning to buy forging equipment to manufacture the ‘connecting rod’. A ‘connecting rod’ is
a component used in the engine of a TATA truck. It is the link between the piston and the crankshaft.
In an engine the linear motion of the piston is converted into rotational motion by the crankshaft.
The connecting rod functions as a lever connecting the engine to the crankshaft. It can rotate at
both ends so that its angle can change as the piston moves and the crankshaft rotates. Figure 7.1
shows a forging of the ‘connecting rod’.
Let us start by analyzing the processes. In 1974 the cost of a 2 tonne drop hammer was around
` 30.00 lacs. The price of a 2000 Tonne forging press, which is equivalent equipment for doing the
same job, was ` 2.00 crores.

Figure 7.1: Metal Forging of a Connecting Rod

The study that was made by the engineering department considered two alternative processes
for manufacture of the component.
Drop forging is a destructive process, using brute force—a large part of which is absorbed by
the machine, dies and the foundation. Consequently, the life of the die in drop forging is around
one third of that of a forging press. A drop forging die gives around 1500 components per sink
compared to about 4500 in the case of the forging press.
A sink is a technical term used in die-making which indicates that a new impression is made on
the die block. Normally, this does not involve a fresh die block.
1. Due to the large time required to remove the used dies and fi t new dies, the setting time
of a Drop Hammer was nearly four times that of a forging press. This reflected in lower

equipment availability. The machine availability in case of a forging press was higher by
nearly 25 per cent both because it was easier to change the dies and also because it required
less frequent die changes.
2. This difference in the number of components produced per machine setting also involved
higher cost in die-making in the case of drop forgings. There would be more consumption
of die steel (for the making of dies) and also greater number of machine hours required
in the die shop for the sinking of dies. This would impact the cost of each piece of forging
manufactured.
3. The lower die life, all other parameters remaining constant, translated into higher levels
of rejections. This is because when it was detected that the components were not being

produced to specifications by the operator, the piece went to inspection and a decision
had to be taken whether to rectify the die or change it. With shorter die lives, this process
resulted in a higher number of rejects. As a percentage, in the case of drop forgings, it was
nearly three times that of the press.
4. Due to longer set up times in drop forging, the furnace was not utilized to the same extent.
Due to this, consumption of energy also was higher for a drop forging. This amounted to
approximately 8 per cent per piece.

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