Question

Give an example of a manufacturing process and discuss how we can use the Statistical Control Charts for monitoring that process.

(Question is related to Lean six sigma)

Answer 1

There are a lot of manufacturing processes. Some of the manufacturing processes are:

• Casting
• Labeling and Painting
• Moulding
• Forming
• Machining
• Joining
• Additive Manufacturing: 3D Printing, Laser etc
• Others: Mining, Assembly Line, Packaging and Labeling, Logistics etc

Assembly Line

Assembly line is a manufacturing process where the goods are manufactured using a process that is broken down into small parts. The process follows a pre-defined sequence. Each part of the process is dependent on the output of the previous part. Some part of the product is developed at every workstation of the assembly line.

Assembly lines are used when the goods are to be produced in a bulk quantity and continuously. Assembly lines help to decrease the costs and optimize the effort. The labor cost is also reduced significantly because the labor needs to be trained to do a particular task, instead of being trained to completely build the whole product.

The assembly lines can be manual, robotic or hybrid. The manual assembly line is operated by human whereas the robotic or automatic assembly line is operated by the robots. The hybrid assembly line is an optimized mix of the manual and robotic.

There are various types of Assembly Lines:

• Modular Assembly
• Cell Manufacturing
• Team Production
• U-Shaped

Using Statistical Control Charts on Assembly Line Process

The statistical control charts are used to study the behavior of the process over a period of time. They help to find the irregularities that appear in the process and hence can be fixed before taking a severe turn. The chart has three main components:

• Upper Control Line
• Average
• Lower Control Line

Control lines are calculating using average +/- 3 Sigma

Control lines gives us the maximum and minimum tolerance levels. The reading falling between these two lines are said to be stable.

In assembly line, there are many ways we can implement the control charts. Some examples are below:

• The time per workstation can be plotted on the control charts. If any workstation shows a reading which is out of control limits, then that can be addressed immediately
• Defects per workstation can be plotted on the control charts which can indicate if there is any requirement of training for the personnel