Pulling and pushing production systems - Logistics and supply chain management

Pulling and pushing production systems

Logistic support for production differs depending on the flow of the material flow system: pushing (pushing, pushing , pulling, pulling system) .

Push systems are characterized by the fact that the execution time of each operation is set by the general schedule, by which time the operation must be completed. The resulting product is pushed further and becomes a stock of work in progress at the beginning of the next operation. This option ignores what is currently doing the next section, and it can be busy or wait for the receipt of work in progress. The result is delays in work and (or) growth in inventories of work in process.

The ejection type systems are based on a strict production schedule and enable the use of resource planning systems (MRP I, MRP II). Planning in the MRP I system is based on the following information sources:

• the main chart, which indicates the volume of each product produced in each time interval;

• Material specification lists, which list materials required for the production of each type of product;

• Inventory records for inventories that show the availability of materials.

The MRP II system includes the functions of the MRP I system in terms of determining the material requirements, as well as the process control functions (Figure 5.10).

Pulling systems are characterized by the following: when the processing of a unit of production ends in one operation, a signal is sent to the previous operation and it is reported that another unit is required for operation. In other words, the previous operation sends the processed unit only when it receives a request for this.

The advantages of pulling systems are obvious: lower inventories, shorter lead times and production times, more complete equipment utilization, higher productivity, simpler

Functional diagram of the MRP II system

Fig. 5.10. Functional diagram of the MRP II system

Chipping planning and dispatching, improving the quality of materials and products, etc.

In industrial pull-type logistics systems, the following problems occur:

• long time before significant improvement;

• Dependence on the high quality of materials supplied by the supplier;

• Dependence on the ability of suppliers to meet the need for exact time frames;

• the need to develop dynamic charts;

• Dependence on the time of equipment readjustment;

• Work of employees in an environment of increased stress, etc. Drawing systems work in accordance with the concepts just in time and quick response to customer requests. There are several types of pulling systems, among which the most common are the supermarket systems (supermarket replenishment) and limited queues FIFO (capped FIFO LANES).

The idea of ​​replenishing inventories in production, following the example of a supermarket, was realized by the Japanese concern Toyota. The diagrams of such a pulling system are shown in Fig. 5.11 and 5.12. In Fig. 5.11. One card (KANBAN production) is used, in Fig. 5.12 - two (KANBAN production and KANBAN displacement, or selection), while between sites is also a storage area of ​​work in process. The KANBAN card is the carrier of information about the production process, the size of the order lot. The number of parts, material, etc., which must be taken either in the previous section or in the storage area of ​​the work in progress, is indicated in the transfer or selection card. The production card contains information on the number of parts that must be manufactured at the manufacturing site-supplier.

The production system operates as follows:

• for each production lot, the level of required materials is calculated (minimum, or critical, stock);

• Site 2 (consumer site) uses the contents of the cells of the "supermarket" (or container);

Scheme of the production system of replenishment

Fig. 5.11. The scheme of the production system of the filling up of the supermarket

KANBAN system with two cards

Fig. 5.12. The KANBAN system with two cards

• Site 1 (supplier site) is sent a request for the supply of the necessary components when their level in the consumer area approaches the critical level. In Fig. 5.11 and 5.12 such a request is indicated as KANBAN production. In production systems, the card is replaced by a light signal, and sometimes simply an empty container - this is the request for delivery;

• Site 1 fulfills the order for replenishment of the container, or the cells of the "supermarket", carries out the necessary production operations;

• Site 1 moves necessary materials, blanks to empty cells or sends filled containers to the work in progress storage area.

So, the pulling system has a number of features: minimizing the duration of the production cycle; production support and shipment of finished products are performed on time; production units do not have warehouses of raw materials, materials, components; Inter-operative stocks are reduced to a minimum; production planning is very detailed for the customer site, and the supplier site plans are formed in real time, depending on the work of the customer site. If several production sites are located to the site with a detailed plan, then their work is organized according to the planning principle of the supplier site.

Using a pull system with KANBAN allowed Japanese companies to significantly reduce inventory and increase productivity. Thus, in Japanese enterprises, compared to the US, the KANBAN system resulted in a 50% reduction in inventories and an increase in labor productivity by 10-25%. The time of storage in Japan does not exceed 6 hours, while in Western Europe it is from two to six days. Inventory turnover during the implementation of the KANBAN system has reached 150 revolutions per year.

In production systems organized by the principle of replenishment of the "supermarket", the customer site can use any part from the cells or container, process incoming materials in any sequence, and in systems with limited queues FIFO (first in, first out - in the English translation "first came, first left") the consumer does not have such an opportunity. The order of materials processing is established by the order of receipt.

The system of limited queues has a number of advantages that distinguish them from the systems of the "supermarket". First of all, this is even lower level of inventory and easier management of the production process. In addition, in systems with limited queues, it is possible to define a process that limits overall performance. Most often, such systems are used in mass and large-scale production.

Planning in pull systems can be based on the principles of constraint theory developed by E. Goldratt. This planning is based on the "drum-buffer-rope" technology. (drum-buffer-mount). Under the drum is understood bottleneck (or limiting resource), which does not allow you to produce as much as you need or possible.

Consider an example of a constraint in the production chain (Figure 5.13).

Constraint in the production chain

Fig. 5.13. Limit in the production chain

As can be seen from Fig. 5.13, bottleneck & quot ;, or drum & quot ;, is an assembly site. If the drilling and soldering areas will work at full capacity, the semi-finished products will accumulate in front of the assembly site. To avoid this undesirable stock, it is necessary to organize the supply of materials to the production in accordance with the rhythm set by the "drum". The parts of drilling and soldering, obviously, will not work at full capacity. To increase output with increased demand for it, it is necessary to duplicate sections with low power, in our example it should be a duplicate assembly site.

Under the buffer the amount of stock that accumulates before the drum is understood. In Fig. 5.13 shows that the drum is the assembly site, then, in order to avoid the downtime of this site, a stock will be created ( buffer ). Moreover, in pull systems, planning and stock control is only performed before the drum & quot ;, before other parts in the stocks there is no need. Changing the power of the drum will affect the size of the buffer.

Rope Is what binds the drum with submission of materials in production. The materials should be fed at the rate of work of the "drum", increasing the feed rate will lead to an increase in the stock. In our example (see Figure 5.13), materials should be fed into production at a speed of assembly - 12 articles per hour. Plots of drilling and soldering will be idle for some time. Increasing the power of the drum & quot ;, you can achieve increased productivity of other sites.

Real production is much more complicated than in the example considered, it is possible that it will be a system with several "drums" and buffers & quot ;. However, regardless of the complexity of production, the idea of ​​the technology considered does not change.

It should be noted that in pulling systems, great importance is given to personnel, training of employees and compliance with all rules of organization of production processes. The work of each employee involved in securing pull production is clearly regulated. Here is an example of the regulation of the work of personnel employed in pulling systems.

Practice questions

In Table. 5.9 and 5.10 show the actions of two specialists engaged in providing pulling production: the operator to provide jobs for the main components and the operator for the order of parts. These tables allow to understand, how much the work of the personnel engaged in logistics of pulling production systems is regulated.

Table 5.9. Actions by the content provider

No.

Operator Action

Time, s

1

Take the cart, check the KANBAN cards with the manifest

3

2

Roll up the cart to the rack

2

3

Take a detail of X

5

4

Check for dirt

3

5

Expand in boxes

4

6

Take the lock with the lock

5

7

Check the caliper with the lock

6

8

Expand in boxes

4

76

Get the Y right

from the wireframe

6

77

Put on the cart

3

78

Get the detail to the left from the frame wagon

6

79

Roll the cart to the assembly line

10

Total

318

Table 5.10. Operator actions for ordering parts

No. n/n

Operator Action

Time, s

I

Enable Personal Computer

60

2

Enable Monitor

3

Open Mail

120

4

Check mail

60

5

Open 1C

180

...

...

9

Print daily report and bug report

120

10

Complete daily report

7

11

Check detail sheet

120

12

Go to the KAN BAN checkout board

10

13

Clear the board by marking the KANBAN delivery

240

...

...

160

Sign the workaround

2

Total

389

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