1. As Wet-Land Drilling, Inc. had filed a complaint that the bags it received from Bayfield were short-weight by about 5%, they had to determine the cause of the discrepancy. They discovered through checking 50 of the bags that they only had an average net weight of 47.51 pounds. In order to identify the errors that had occurred in the operation, and why the weight has become inconsistent, Bayfield’s quality managers may consider using Statistical Process Control (SPC).
As mentioned, past shipments had bags that averaged at 50 pounds, which will be the desired mean, X=50, and that had an acceptable standard deviation of 1.2, which will be the desired = 1.2.
x = σn=1.26=0.4899
At a confidence interval of 99.7%, z = 3
UCL= x+ 3σx=50+3 x 0.4899=51.4697
LCL= x – 3σx=50-3 x 0.4899=48.5303
Percentage of Bags with Average Weight within Control Limits (Per Shift) Day Shift = 23 bags/24 bags = 96%
Afternoon/Evening Shift = 12 bags/24 bags = 50%
Night Shift = 12 bags/ 24 bags = 50%
2. As Bayfield had decided to add new shifts due to increased demand, the abrupt decision had caused inefficiencies when it came to making sure that the weights of the bags be as close to 50 pounds as possible. While the most experienced foremen were assigned to supervise the new employees of the night shift, they failed to make sure that the double-checking of the weight of the bags be as accurate as possible, as they only occasionally reminded the employees of this procedure.
The management of Bayfield must make sure that stricter supervising of the double-checking of the bag weight-feeder must be implemented, such as having scheduled checks (e.g. before the morning shift every day). They also have to remind employees that lighter-weight bags cause more than just a weighing problem, as they might result in poor chemical control during the drilling operation and might adversely affect drilling efficiency. Also, among the 25 samples that are considered as above UCL and below LCL, 23 of these are light-weight bags; therefore, the weight-feeder must be adjusted as needed, to prevent its frequent production of lighter-weight bags.
As it can clearly be seen that much of the inefficiencies occur during the afternoon/evening shift and the night shift, Bayfield’s managers must also consider conducting additional training, especially for the new employees.