Capacity $=1/20$ units$/$min

Processing time $=20$ minutes$/$unit

Substituting these values into the equation, we get:

Optimal batch size $=(1/20)/20$

Optimal batch size $=0\mathrm{.}05$ units

Therefore, the optimal batch size for the Die Stamping process is $0\mathrm{.}05$ units.

If the batch size is smaller than the optimal batch size, the process will be less efficient and the flow rate will be slower than the capacity of the Assembly process. This will result in a longer lead time and increased costs.

If the batch size is larger than the optimal batch size, the process will be more efficient and the flow rate will be faster than the capacity of the Assembly process. This will result in a shorter lead time and reduced costs. However, there may be other factors that affect the overall efficiency of the process, such as the quality of the parts and the reliability of the equipment.

Final answer: In conclusion, the optimal batch size for the Die Stamping process is $0\mathrm{.}05$ units. A smaller batch size will result in a slower flow rate and longer lead time, while a larger batch size will result in a faster flow rate and shorter lead time. The optimal batch size depends on the capacity and processing time of the process.