All the parts used for the assembly are standard. There are several types of some parts, but these have no effect on the processing speed. Also, there is always an adequate stock of parts to supply the line.
Although the first four processes are fully automated, it has not been possible to synchronize them precisely. Axle to frame assembly (A) takes an average of 15 minutes, as does attach-ing the underside to the frame (B). Assembling the sides to the frame (C) requires an aver-age of 18 minutes, and the roof assembly (D) is a precision process and only three trailers per hour can be completed. Final assembly and quality check (E) is a manual operation and take an average of 18 minutes.
As mentioned above, the actual parts used at each stage does not affect the processes. The first four processes follow a uniform distribution with a range of 2 minutes, so a 15 minute process implies a range from 14 to 16 minutes. The processing time for the final operation follows a normal distribution with a standard deviation of 3 minutes.
In the factory, the working day consists of 8 hours and 5 working days form one working week. Production starts every working day where the day before has ended.
The robots are not completely trouble-free. The robot’s supplier guarantees that the robots will get failures only once an hour (negative exponentially distributed and including repair time). Internal checks have kept the average repair time within reasonable bounds, and as a result this time seems to be exponentially distributed with an average of 6 minutes.