Planning and Design of Material Distribution for Lean Production Lines
The planning and design of material distribution for lean production lines in logistics management refers to the logistics operations that deliver materials from suppliers or distribution centers to the production lines in workshops.
1: Focus Points and Analytical Tools
For the analysis of production line distribution logistics, the business model should be determined based on demand, as the business model dictates the operational methods. The principle is to first investigate the needs of production line distribution logistics, combine it with the ordering model, confirm the specific replenishment model for the components required by the production line, and then determine the corresponding handling methods based on the replenishment model.
2: Demand for Production Line Distribution Logistics Operations
The operations of production line distribution logistics serve production and must comply with the overall requirements of production operations for distribution logistics:
① Processing or assembly at the production site must be continuous, so there should be a certain amount of line-side inventory.
② Since production operations are value-adding processes, limited space should be maximally allocated to production operations during layout: line-side inventory should occupy minimal space, while more space should be allocated to production operations.
③ Additionally, the destination for component delivery should be as close as possible to the operators to reduce non-value-adding time spent walking, turning, or bending.
④ Moreover, distribution logistics operations (delivery, loading and unloading, placement, unpacking, handover, etc.) are non-value-adding processes, so operations should be simplified or omitted as much as possible.
By organizing the above demands for distribution logistics operations on the production line, we find that if unit design and line-side planning are adopted, they can effectively address the demands in items 3 and 4; items 1 and 2 are a contradictory unity, which can be described comprehensively as how to meet continuous production with minimal inventory. That is: to produce the necessary products only in the required quantities at the necessary times (delivered). The demand is clear, and it is necessary to choose appropriate dimensions to describe logistics for further analysis, which can be categorized in many ways. For example: by logistics destination, it can be divided into direct supply mode and distribution center mode; by the initiator of the logistics operation process, it can be divided into supply logistics, manufacturing logistics, and distribution logistics; by the initiator providing logistics services, it can be divided into first-party logistics, second-party logistics, and third-party logistics; by the function of logistics, it can be divided into supply logistics, sales logistics, production logistics, reverse logistics, recycling logistics, waste logistics, etc. From which angle can we resolve the contradiction of meeting production needs with the lowest inventory? Through the description of the demands for production line distribution logistics operations, it is not difficult to see that for specific components, they can be described in two dimensions: time (when necessary) and quantity (necessary quantity). Therefore, using time and quantity as two dimensions to describe production line distribution logistics operations is undoubtedly the most appropriate.
3: Different Replenishment Models and Their Principles
① Kanban: The Kanban referred to here is the receiving Kanban, not the production instruction Kanban. Kanban is an external label for unitized packaging, carrying relevant information about varieties, unitized packaging quantities, storage locations, upstream or suppliers, downstream, etc. Therefore, essentially, Kanban is a visual representation of replenishment information and a means of carrying replenishment information.
② Two-bin or Three-bin Method: This replenishment model is similar to the ordering signal sent out after accumulating a certain quantity of Kanban within the process, both belonging to a quantitative and irregular ordering model, except that the material box itself replaces the Kanban as the carrier of delivery information, i.e., the ordering signal. Its applicable range is similar to Kanban, leaning more towards smaller, general-purpose parts.
③ Light Signal: The light signal mentioned here specifically refers to the light signal mode needed for logistics distribution, excluding quality issues of production line operation, equipment maintenance, etc. Relatively speaking, the information transmission speed of the light signal is faster than that of the Kanban, so under the same operational environment, the ordering point set by the light signal is lower than that of the Kanban, meaning that lower inventory can meet production needs, but at the same time, logistics costs, especially hardware investment, are higher, requiring consideration of return on investment.
④ Sorting Operations: Sorting operations are a replenishment model where suppliers produce, load, and transport in the same order according to the varieties and quantities required by customer orders. Sorting operations can achieve synchronous production with customers, significantly reduce the number of unitized packages, decrease work-in-progress inventory, and eliminate unnecessary transshipment operations. The planning for sorting operations is mostly done through a combination of long-term forecasting and rolling plans: long-term forecasting helps suppliers prepare materials, while rolling plans allow suppliers to produce only the products needed by customers, maximizing inventory reduction and benefiting the overall reduction of supply chain costs.
⑤ Logistics Basket (Warenkorb): The logistics basket, also known as the kit mode (Kittoone), is a replenishment model that arranges certain parts according to the order of production line vehicle types, placing them in a unitized package or logistics cart, running synchronously with the production line. It is widely used in the automotive industry, especially for components like dashboard assemblies and window lift assemblies. The logistics basket can be seen as a manifestation of sorting operations.
(1) The logistics basket model is suitable for smaller components, while sorting operations are suitable for larger components.
(2) The logistics basket contains a variety of components, while sorting operations typically involve a single type of component.
(3) The components in the logistics basket have an assembly relationship, while sorting operations only involve one type of component, thus not having assembly relationship issues.
(4) The logistics basket model involves parallel feeding, moving with the production line, while sorting operations involve vertical feeding, with materials remaining stationary relative to the production line.
Through the analysis of the principles and characteristics of the five replenishment models, we can select the appropriate replenishment model for specific components and choose the corresponding handling methods.
4: Choosing Corresponding Handling Methods
① External Ordering Kanban belongs to a periodic and irregular ordering model, suitable for most general-purpose components. The handling methods for Kanban can include the following: Milk Run, transfer handling, and dedicated vehicle methods. The so-called Milk Run refers to: different suppliers being responsible for transporting a specified quantity of goods at different times using the same vehicle. The so-called dedicated vehicle handling means that a vehicle is used for transportation according to customer requirements within a factory, ensuring continuous transportation without increasing handling costs. In short, it is a dedicated vehicle for a specific purpose.
② In-process Kanban and the two-bin method both belong to quantitative and irregular ordering models, with the two-bin method being more suitable for smaller components. From the perspective of production line distribution, adopting the "Toyota's piggyback transport" (also known as group transport) between preceding and succeeding processes can minimize inventory due to frequent handling and short delivery cycles; however, for actual logistics operations, it is still preferable to have a certain delivery interval to facilitate the organization of logistics operations. Therefore, when delivering to the production line, different varieties of components will be combined and delivered regularly. If we consider the production line as a customer and the storage locations for different varieties of materials as different suppliers, it can also be seen as a Milk Run from the distribution center to the production line.
③ The light signal method belongs to a quantitative and irregular replenishment model, and due to higher logistics costs, it is suitable for high-value, small-volume components. The handling methods are similar to those of in-process Kanban and the two-bin method, mostly adopting piggyback transport methods.
④ Sorting operations are suitable for larger components with more characteristics, arranged in unitized packaging in the same order as production line requirements, generally adopting direct delivery to workstations. They can also be sorted at the distribution center before being delivered to the production line.
⑤ The logistics basket is suitable for smaller components that have a primary assembly relationship, also arranged in the same order as production line requirements, combined in specially designed workstation tools or material carts. Since the sorting of logistics baskets is mostly done by customers or third parties, the components are usually first transported to the logistics center for secondary sorting, and then through workstation tools or logistics carts, they operate in conjunction with the production line to improve assembly efficiency.
