Monday, February 3, 2014
Control methods in Lean Manufacturing
The lean aims to reduce any types of waste (muda). It categorize the waste in the following 7 types: the waste from over manufacturing, waste from long lead time, waste from moving parts, waste from manufacturing itself, waste from inventory, waste from unnecessary actions and waste from mal-quality.
The lean provides a set of tools to eliminate those waste in the manufacturing process. We are going to look at 3 types of control methods. Kanban Control, CONWIP control and Hybrid control.
The Kanban control
The blue shows the movements of parts, the red shows the circulation of Kanban, circle represents machines and triangle represents buffer. In this way, once the part is manufactured and moved to the buffer, the Kanban card will go upstream to give signal for another manufacturing. This reduces the waste from over manufacturing.
CONWIP means Constant Wok-In-Process. This type of control strategy controls the total incoming parts to the manufacturing system. As we can see from the below chart, only the finished goods have been “pulled” by customer demand, new parts will be allowed to enter the manufacturing process.
The combination of Kanban control and CONWIP control, this is particularly useful when the system is heavily utilized. The CONWIP will help to control the overall input and Kanban controls the internal buffer level.
The three types of lean manufacturing control have similar but different ideas, how should you choose your control methods? What are the bases of choosing the control method?