Lean production line material distribution planning and design

In logistics management, the distribution logistics of the production line refers to the logistics operations that deliver from suppliers or distribution centers to the production line in the workshop.

1: Focus and analysis tools

For the analysis of production line distribution logistics, the business model should be determined based on demand, and the business model determines the operational method. The principle is to first investigate the demand for 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 confirm the corresponding handling method based on the replenishment model.

2: Demand for production line distribution logistics operations

Production line distribution logistics operations serve production and must comply with the overall requirements of production operations for distribution logistics operations:

① Processing or assembly at the production site must be continuous operations, so there must be a certain amount of line-side inventory.

② Since production operations are value-added processes, limited space should be maximally inclined towards production operations during layout: line-side inventory should occupy the smallest space possible, and more space should be allocated to production operations.

③ At the same time, the destination for component delivery should be as close as possible to the operators to reduce the non-value-added operational time spent by operators walking, turning, and bending.

The time spent on non-value-added operations such as bending;

④ Moreover, distribution logistics operations (delivery, loading and unloading, placement, unpacking, handover, etc.) are non-value-added processes, so operations should be simplified or omitted as much as possible.

By organizing the above demands of the production line for distribution logistics operations, we will find that: if unit design and line-side planning are adopted, they can effectively solve the demand issues in items 3 and 4; items 1 and 2 are a contradictory unity, which can be summarized as: how to meet continuous production with the minimum inventory. That is: to produce the necessary products, only in the necessary quantity, at the necessary time (delivered).

The demand is already clear, and it is necessary to choose appropriate dimensions to describe logistics for the next step of analysis, which can be divided into many categories.

For example: according to the logistics destination, it can be divided into direct supply mode and distribution center mode; according to the initiator of the logistics operation process, it can be divided into supply logistics, manufacturing logistics, and distribution logistics; according to the initiator providing logistics services, it can be divided into first-party logistics, second-party logistics, and third-party logistics; according to the function of logistics, it can be divided into supply logistics, sales logistics, production logistics, reverse logistics, recycling logistics, and waste logistics.

From what angle can we solve the contradiction of meeting production with the lowest inventory? Through the description of the demand 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 modes 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 quantity, storage location, upstream or supplier, downstream, etc. Therefore, essentially, Kanban is a visual representation of replenishment information and a carrier of replenishment information.

② Two-bin or three-bin method: This replenishment mode is similar to the ordering signal sent out after the Kanban accumulates to a certain quantity within the process, both belonging to a quantitative and irregular ordering mode, except that the material box itself replaces the Kanban as the carrier of delivery information, i.e., the ordering signal. The applicable range is similar to Kanban, more inclined to small-sized general-purpose parts.

③ Light signal: The light signal referred to here specifically refers to the light signal mode required 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, therefore, under the same operational environment, the setting of the ordering point for the light signal is lower than that of the Kanban, that is, using lower inventory to meet production, but at the same time, logistics costs, especially hardware equipment investment, are also higher, requiring consideration of return on investment.

④ Sorting operation: Sorting operation is a replenishment mode 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, reduce work-in-progress inventory, and eliminate redundant transshipment operations.

The planning and issuing method of sorting operations mostly adopts a combination of long-term forecasting plans and rolling plans: long-term forecasting plans are beneficial for suppliers to prepare materials, and rolling plans allow suppliers to only produce the products needed by customers, which can minimize inventory and benefit the overall reduction of supply chain costs.

⑤ Logistics basket (Warenkorb): The logistics basket, also known as the kit-to-one model, is a replenishment mode 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 parts like dashboard assemblies and window lifter assemblies.

The logistics basket can be seen as a manifestation of sorting operations.

(1) The logistics basket model is suitable for small-sized components, while sorting operations are suitable for larger components.

(2) The variety of components in the logistics basket is more diverse, while the variety of components in sorting operations is singular.

(3) There is an assembly relationship between the components in the logistics basket, while sorting operations only involve one type of component, so there is no assembly relationship issue.

(4) The logistics basket model belongs to parallel feeding, moving with the production line, while sorting operations belong to vertical feeding, with materials stored stationary relative to the production line.

By analyzing the principles and characteristics of the five replenishment modes for components, we can choose the appropriate replenishment mode for specific components and select the corresponding handling method.

4: Choose the corresponding handling method

① External ordering Kanban belongs to a periodic and irregular ordering mode, 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 at different times, with the same vehicle responsible for transporting a specified quantity of goods. The so-called dedicated vehicle handling refers to transporting 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.

The Kanban and two-bin method within the process both belong to a quantitative and irregular ordering model, with the two-bin method being more suitable for smaller components. From the perspective of production line delivery, the use of what Toyota calls "chihong handling" (also known as group handling), which involves back-and-forth transportation 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 types of components are combined and delivered regularly. If we consider the production line as a customer and the storage areas for different types of materials as different suppliers, it can also be seen as a mixed loading method (Milk Run) from the distribution center to the production line.

The light method belongs to a quantitative and irregular replenishment model, and due to high logistics costs, it is suitable for high-value, small-volume components. The handling method is the same as the Kanban & two-bin method, mostly using chihong handling.

Sorting operations are suitable for larger components with more characteristics, arranged in the same order as the production line's requirements within unitized packaging, generally using direct delivery handling methods. They can also be sorted at the distribution center before being delivered to the production line.

Logistics baskets are suitable for small-volume components that have a first assembly relationship, arranged in the same order as the production line's 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 work in conjunction with the production line through workstation tools or logistics carts to improve assembly efficiency.