Production cells u s v t. Commodity slave villa as the main production cell. Organization of the economy. Working principle of U-shaped cells

Based on the materials “Cellular Manufacturing with Kanbans Optimization in Bosch Production System” Pedro Salgado, Leonilde R. Varela, 2010

A study of current production practices identified a number of bottlenecks that needed to be addressed. Firstly, excessive costs - in particular, for the purchase of twelve laser machines for printing codes on boards. Secondly, the existing production system lacks flexibility - it was unable to quickly adapt to changes in demand, which required corresponding changes in product design and technological requirements. Thirdly, equipment downtime is common, since the failure of one machine can often cause the entire production cycle to stop.

This article proposes to modify the production system through the creation of production cells, which will allow production operations to be performed in a clear sequence without interruptions due to layout various types equipment on one site. In the case of Bosch Car Multimedia Portugal, S.A. redistribution of equipment makes it possible to reduce the number of lines from twelve to seven, thus reducing the number of required laser installations. Considering that there are already three installations in production, the company needs to purchase only four new ones in addition to the existing ones in order to completely solve the problem of marking boards in the automatic assembly area. Such a decision will allow the company to save a significant amount.

The proposed scenario includes the creation of Just-in-Time Cells (JITC) and Quick Response Cells (QRC). The former follow the JIT principles in everything, aim to achieve the same key goals (zero defects, zero installation time, zero inventory, zero unnecessary manipulations, zero equipment breakdowns) and use unified Kanban containers. The latter make it possible to significantly reduce inventory, since the stock that ensures the continuity of the production process between successive deliveries does not exceed the amount consumed during the time during which the order is placed and fulfilled.

The just-in-time logistics principle is increasingly used in cell organization as it makes the production system more flexible and adaptive to changes in the production of product families, and in modern economic environment this is important competitive advantage. This factor is of great importance for the Bosch Production System, since the boards produced belong to the same product family and therefore share several characteristics regarding production and handling requirements, including similarities in design and materials.

When Bosch was faced with the need to satisfy more wide range requirements for product specifications, management has come to understand how important it is today to be able to quickly adapt the production system and key processes, and it is flexibility and rapid response that have become the most important characteristics production cells. In addition, cell production allows for more high performance product quality while maintaining process efficiency at high level and minimization warehouse stocks and movements of goods, materials and employees during work. In Fig. 1 shows the recommended cell layout.

Such a production environment also has a number of advantages in relationships with customers, since production cells are focused on fast production rates to meet customer requirements in the shortest possible time.

Domestic supplies are planned to be organized according to the milkman principle. When removing a container from storage in the automatic assembly area, the final assembly work areas leave a full empty container in place. This signals the start of a new cycle, and once the container of materials moves into the final assembly area, the kanban cards are returned to the board.

Accordingly, when a need for materials arises in the automatic assembly area, workers pick up a full container from the supermarket - the storage point for the minimum required stock. Whenever a Kanban card is returned to the board, it serves as a signal that a new batch of product needs to be created. When the required production volume is reached, the cards are placed in a buffer, from where they are released on a FIFO (first in, first out) basis.

From the buffer, the cards are sent to the planning sector, located at the very bottom of the board. Here, based on the data presented on the cards, production planning for three working periods. The cards are then passed through the line, attached to a container and sent to the supermarket, where the materials are stored until needed in an automatic or manual assembly area.

For a more clear comparison of the existing and alternative scenarios, we use the already discussed example with the production of boards (Fig. 2) and the same calculation formula:

In the proposed scenario, only the indicators of effective production time (NPT) and product replenishment time (RT loop) differ. This is due to the fact that production in cells reduces the preparation and changeover time of equipment and the processing time. Thus, effective production time is increased, product processing time (25 minutes) and cycle time (9 seconds) are reduced.

Table 1. Calculation of production parameters under an alternative scenario

PR - demand per unit of time [units/time];

SNP - standard number of parts in a kanban container;

WA - volume of selected products [units/time];

NPT - effective production time [min./period];

RT loop - product replenishment time [min.];

LS - batch size [unit];

ST - “safety” time (hours).

Using these values, we can calculate, respectively, the indicators of the total replenishment time (RE), the total lot volume (LO), the total peak of product “taking” (WI), the total downtime (TI), the total “safety” time (SA) - see Table 2.

Table 2. Calculation of production parameters under an alternative scenario

RE - cumulative replenishment time;

LO - total batch volume;

WI is the cumulative peak of product withdrawal;

TI - total downtime;

SA - cumulative “safety” time;

As follows from the calculations, the organization of production cells makes it possible to reduce the number of kanban containers from 35 to 30. Considering the pace of production, this means a saving of 5 containers per day, 100 per month (with 20 working days) while fully satisfying the entire volume of demand. Thus, in six months we will save 600 containers, which is a very significant indicator.

The reduction in the number of containers occurs due to an increase in effective production time, on the one hand, and a reduction in replenishment time, on the other.

Taiichi Ohno noted that reducing the number of kanban containers leads to a reduction in interim and ending inventory, allowing the company to better adapt to fluctuations in demand. And Shigeo Shingo also recorded that eliminating excess inventory can reduce labor costs by 40%.

Based on available product and demand data, a forecast of the company's product requirements was made six months in advance for an alternative production scenario (Figure 3).

According to estimates, by the end of the allocated period the number of containers will be 2,581.

By comparing the calculation results, we will find that by moving to production cells, we will significantly reduce the total number of kanban containers. In six months of work, instead of 2936 containers under the current scenario, we will get 2581 containers (355 less). Thus, the savings over six months will be 12%.

Demand is expected to experience some fluctuations over the months. When demand increases, the number of containers will correspondingly increase to meet customer needs and vice versa. Taiichi Ohno has shown from his experience that fluctuations of 10-30% can be easily controlled without increasing the number of containers. However, it is worth remembering that the most reliable indicator is practice - each company has its own strategy for responding to changes in demand.

On the other hand, according to J. T. Black, the main advantage of cell production is not even the reduction in the number of kanban containers in the production chain, but the increased flexibility of production, its increased ability to quickly respond to changes caused by both external factors(most often changes in demand) and internal (related to changes in product design or expansion of the product line).

The efficiency benefits of manufacturing cells over traditional manufacturing models have been discussed extensively by Roger Eskin and Nanua Singh. The benefits were established as a result of simulation modeling, analytical studies, and practical implementation and are summarized as follows:

• Reduced changeover time. The production cell is organized to handle parts of similar shape and size, so similar clamping fixtures may be used to hold them. Common fixtures can be designed across a product family, significantly reducing the time required to change fixtures or tooling.
• Batch size reduction. By reducing changeover times, it is possible to use smaller batch sizes, making the production process more consistent and reducing costs.
• Reduction of finished goods inventories and products in the process of processing, due to smaller batch volumes and reduced changeover time. Eskin pointed to the possibility of reducing the products in the processing process by 50% with a 50% reduction in changeover time. In addition, the volume of stored finished products is significantly reduced, since instead of production at the warehouse, smaller batches are manufactured on a just-in-time basis.
• Reduced production cycle time- by reducing changeover times and time spent on operations with raw materials and supplies.
• Reduced individual tooling requirements. Parts are produced in cells and have similar shapes, sizes and structures. They often have similar requirements.
• Reduced overall production cycle time. In a traditional manufacturing system, parts are moved between stages of the manufacturing process in batches. In cells, the finished part immediately moves to the next processing stage, which can significantly reduce waiting time.

As a result of the above factors, product quality also increases because, due to the fact that each part is transported from one stage to another individually, feedback is strengthened, and the process can be stopped immediately when a defect is detected.

Summarizing the analysis of the existing logistics system at Bosch Car Multimedia Portugal, S.A. and the alternative proposed to it, we can conclude that the transition to production cells can significantly reduce the costs of the enterprise, improve its production system and management production tasks. It is also a step towards making materials easier to handle.

In conclusion, I would like to note that the results recorded here can be achieved simply by changing the production layout and creating cells. Having improved some other aspects - such as: production planning, inventory flow, management control etc. - you can achieve even more outstanding results.

By definition, a production cell is the arrangement of equipment and work stations in such a sequence as to ensure the rhythm of materials, components and other components in production process with minimal, in particular, delays for their transportation.

We can say that cell alignment is the arrangement of machines in accordance with the sequence of operations, when small and inexpensive equipment is allocated exclusively for a specific product.
Based on the above, the production cell requires a combination of professions, because a worker or several in a cell must be able to work on different types equipment (possibly on all) included in the cell. It is necessary to define and clearly define, plan the quantity and frequency of movement.

According to the types of construction, there are L-shaped, T-shaped, V-shaped, I-shaped and others, depending on the technology, the layout of the area where they are located and other factors. The most popular are U-shaped production cells.
In any option, the layout of the cell must be organized in such a way that equipment, tools, materials, standards are at hand, and their location ensures the safe performance of work.

Algorithm for forming a production cell quite simple (see picture).

To begin with, you need to carry out selection of assortment. Despite the similarity with, here the emphasis is not on goals, but on the mass production of the product, since the formation of a cell involves a physical change in a certain area (moving jobs and equipment). This should be the most widespread nomenclature, selected according to the principles of ABC analysis and visualized using the Pareto equation, covering greatest number thread operations, i.e. with the longest technological chain. If you are already at the stage of choosing a product for considering such a product, then you are at the right way. Otherwise, it is necessary to consider the possibility of organizing the cell in the light of a different set of nomenclatures for various products.

Do the capacities allow and is it advisable to form a cell?
Is it possible to create a production cell using a different product or several types at once?
After selecting the assortment, it is formed current state plan, which consists of a site layout indicating the technological equipment, a diagram of the worker’s movements in the process of transforming the selected product, and possible necessary instructions, for example, quality control, the need for a special skill, special attention to safety precautions, etc. Drawing up a plan allows us to understand the current state, see and begin to generate ideas for improvement. Here it is necessary to carry out each operation (on the corresponding piece of equipment) according to the Spaghetti diagram, i.e. indicate the time spent on each worker action.

As a rule, the current state reflects the technological sequence of transformation of a product, passing through several types of equipment and several operators, i.e. operations, at the input and output of which there is a certain amount of work in progress. Timing data is needed to construct the diagram and equipment grouped into a cell for the required . Balancing under is the next step in cell formation. Here you can use not only the redistribution of actions and elimination, but also experiment with different layout options and the amount of equipment. Operations that for some reason cannot be balanced are not included in the cell.

Based on the balancing results, required takt time and equipment movement capabilities a plan for the production cell of the target state is formed, i.e. as we want. The plan includes a diagram with the required arrangement of equipment in the form of a cell and the minimum number of workers, as well as a summary table containing a list of actions performed in the production cell, broken down into the automatic operation of the equipment and the direct actions of the worker himself (including movements, removal and installation of products, etc.). A more visual summary table of standardized work in the form of a cyclogram.

For example, when organizing a cell for a bicycle assembly operation, if you know the sequence and duration of each operation, as well as the necessary one, the table of standardized work may look like this (see table):

Data for calculation:

Total time = 2190 seconds without taking into account the movements of workers. In this case, we deliberately simplify the example by rounding up the time required to complete each operation to whole minutes, thereby taking into account the movement of the product and possible losses.
In the example given, the cell operation was calculated at a clock cycle of 600 seconds (10 minutes).
Thus, 2190/600=4 assembly operators were required to complete the work on time.

Like many other Lean methodologies and practices, production cells came into use through the Toyota Production System in the late 1950s. They are part of the concept: the movement of goods, materials and services occurs only when it is necessary for the work process.

A cell of employees in an office is a group of trained specialists who are prepared to quickly solve a number of problems or work with certain clients.

Difference between traditional conveyor and U-cell

A typical assembly line is a sequence of machines that transforms raw materials into finished products.

The material remains at the machine for some time while a number of tasks are performed. Operators are assigned to a specific workstation or several. Typically, machines on a conveyor are arranged in a straight line. Raw materials arrive at one end and leave the conveyor belt as finished products at the other end.

U-cells are more flexible to changes in demand and production levels than traditional conveyors.

In the figure below we see how, when demand is very high, an operator is assigned to each machine. With a decrease in demand (high, medium and low), the number of employees can be reduced to 5, then 3 and even to 1.

The figure shows how three workers A, B and C are busy at 5 workstations with a U-shaped conveyor arrangement.

Japanese is often used Chaku-Chaku principle. It is a compromise between completely handmade and automation. The operator starts one of the machines, which produces the part and unloads it, picks up the part and loads it into another machine.

According to , which studied 114 companies in the US and Japan in 2001, on average their U-shaped cells consisted of 10.2 workstations and 3.4 operators. In companies that previously used traditional conveyors, productivity increased by an average of 76%; the time required to complete major operations decreased by 86%; the number of defects fell by 83%.

Working principle of U-shaped cells

Advantages

1. Requires fewer operators to operate than a traditional conveyor
2. Workers are more flexible due to their multi-machine skills, so they can quickly change tasks
3. If an operator has an excessive workload or is not busy all the time, it is easy to identify
4. More space in the work area
5. Improved work safety due to the absence of awkward or static postures
6. There are no additional costs - just arrange the equipment in the right order

When placing a U-cell, answer these questions:

Consider occupational safety when placing the U-shaped cell

To make a plan for placing a U-shaped cell, you will need:

• operator movement diagram, aka Spaghetti diagram.

Here is an example for a bank branch where customer movements were recorded

• list of operations performed, divided into automatic and manual ones

• quality criteria
• Special Skills
• safety precautions

After making a plan, enter timing for each operation according to the Spaghetti diagram. This data will be required to compile Yamazumi diagrams. It shows the load of operators that can be balanced under takt time in case of uneven distribution.

Takt time is the period within which the customer wants to receive the first unit of finished product. It is calculated as the ratio of the total available working time in this interval to the customer’s needs - required quantity products.

When balancing loads, you can redistribute operations between workers, arrange machines differently, or use a different number of them.

Verdict

U-shaped cells provide rhythmic flow and help create products and services on time and without overproduction. The concept does not require additional costs, You just need to group and place the existing equipment.

However, for U-cells to operate effectively Skilled operators are needed who are ready to operate several or even all machines. Multifunctionality of workers provides flexibility of the solution: depending on fluctuations in demand, the number of operators can be changed.

The transition from organizing production and placing equipment focused on technological process, the organization of production on the principle of group technology involves three stages.

1. Grouping product components into families that have common processing steps. This stage requires the development of a computerized system for classifying and coding parts. This stage is often the most expensive, even though many companies have developed short procedures for identifying and forming part families.

2. Determination of the structure of the dominant flows of families of components on the basis of which technological processes are located or re-allocated.

3. Physical grouping of equipment and technological processes into cells. At this stage, sometimes some components cannot be included in any family, and specialized equipment cannot be placed in one of the cells due to the fact that it often

used to perform work related to different cells. Such non-grouped product components and equipment are placed in a separate “residue” cell.

Scheme in Fig. 10.13 illustrates the process of developing 1 technological cells, which is used in the company Rockwell Telecommunication Division – manufacturer of waveguide components.

Into parts A rice. Figure 10.13 shows the initial process-oriented layout; on IN - a plan for the relocation of technological operations based on the common stages of processing product components combined into families; on C - placement of equipment and operations in a technological cell in which all operations are performed, except for the last one. The organization of a technological cell in this case is most appropriate, since:

there were separate families of product components;

there were several machines of each type, so removing any machine from a cell did not reduce its throughput;

work centers were easily movable, free-standing machines, heavy, but quite easily fixed to the floor.

These three production features should always be taken into account when deciding whether to create cells.

"Virtual" process cell

If the equipment does not move easily, it is not included in a set of homogeneous pieces of equipment when forming a process cell. If, in addition, homogeneous families of components are produced for a short time, say, two months, temporary conditional (“virtual”) cells of group technology are formed, consisting, for example, of one drilling machine in the drilling area, three milling machines in the milling area and one assembly line at the assembly site. At the same time, in accordance with the principle of group technology, all work with a specific family of product components must be carried out in a specific cell.

4. Placement of equipment according to the principle of servicing a stationary object

Placing equipment according to the principle of servicing a stationary object is used for a relatively small number of units of manufactured products, but, as a rule, large-sized and complex ones. When designing the layout of equipment to produce a stationary product, you can think of it as the hub of a wheel, with materials and equipment arranged concentrically around the point of production in the order they are used and when they need to be moved. For example, in shipbuilding, rivets used throughout the entire structure of a product must be placed close to or directly in the hull. Heavy engine parts, which are transported to the housing only once, can be placed at a greater distance, and cranes, since they are constantly used, should be located next to the body.

To organize the production of a stationary product, it is necessary to establish the order of work, which is determined by the production stages. The placement of equipment and components around a fixed object should be designed according to the principle of grouping materials according to their technological priority. This principle is used when installing large-sized equipment, such as a stamping press, performing installation work on which it is carried out in strict sequence. The same principle is followed when assembling products, when it starts from the very base of the product, and then components are added to it in the form of standard blocks.

As for the use of quantitative methods when placing equipment around a stationary object, little attention has been paid to this problem in the relevant literature, although the principle of placement itself has been used for hundreds of years. However, for specific situations, it is possible to define objective criteria and design the placement of equipment around a fixed object using quantitative methods. For example, if the cost of transporting materials is significant and the construction site allows for more or less movement of materials in a straight line, then the CRAFT method can be applied.

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