Optimized Production Technology (OPT) was proposed by Israeli physicist Dr. Eli Goldratt in the 1970s. Initially, he designed a set of computer software for manpower and material dispatch for his friend's troubled manufacturing plant, which helped the factory get out of it. Later, Godrat developed management software, namely OPT software, which is widely used in the manufacturing industry.

OPT was originally called the Optimized Production Timetable, and was renamed the Optimized Production Technology in the 1980s. Later, Godrat developed it into the Theory of Constraints (TOC). Although OPT has a short appearance, it has achieved remarkable achievements. It is another new production organization method after MRP and JIT (Just in Time). It has been quickly accepted by the Western business community due to its unique management ideas and significant economic benefits.

OPT aims to make the entire production process work in a coordinated manner to achieve company goals. Any manufacturing organization can be regarded as a system that converts raw materials into products, and manufacturing resources are a key part of it. It is generally believed that when designing an enterprise, the production capacity balance can be achieved at each stage, but since production is a dynamic process and demand is constantly changing, it is difficult to achieve production capacity balance in reality. Therefore, uneven resource load will occur during the production process, resulting in bottlenecks and Non-bottleneck resources.

Bottleneck (defined by OPT) refers to resources whose actual production capacity is less than or equal to the production load. Such resources limit the output speed of the entire production system; the remaining resources are non-bottleneck resources. The basis of OPT's organization of production is to strictly distinguish bottleneck resources from non-bottleneck resources, focus on bottleneck resources, and give priority to formulating operation plans for bottleneck resources to ensure that their load does not exceed production capacity.

Bottlenecks and non-bottlenecks resources: Manufacturing organizations convert raw materials into products, and manufacturing resources include all resources required for production, such as machines, workers, factories and fixed assets. In actual production, due to the dynamic nature of production, production capacity is difficult to balance at each stage, resulting in bottleneck resources with excessive resource load, while the rest are non-bottleneck resources. To determine whether a resource is a bottleneck, it is necessary to examine its actual production capacity and production load (or the demand for it by related resources is not necessarily the market demand).

Classification of enterprises by logistics: The enterprise production process can be regarded as an activity chain from raw materials to finished products. In fact, this activity chain is often disturbed by random events. By classifying "logistics" in enterprises, we can recognize the weaknesses or "bottlenecks" of different types of "logistics", and then plan and control them in a targeted manner. Generally, "product logistics" is divided into three types: "V", "A" and "T":

In fact, there are often more than one type of "product logistics" for enterprises, and enterprises can be divided accordingly according to the dominant "product logistics". From the perspective of manufacturing resources, there is a difference between bottlenecks and non-bottlenecks in the resources that "materials" pass through. There are bottlenecks to non-bottleneck resources, from non-bottlenecks to bottleneck resources, bottleneck resources and non-bottleneck resources to the same assembly center, bottleneck resources, and bottleneck resources. The four basic relationships between them and non-bottleneck resources. [Table: Comparison of different characteristics of "V" type, "A" type, and "T" type enterprises]

This table compares the types of raw materials, finished products, product processing processes, parts, equipment, process flow, production lead time, bottleneck identification and production control coordination of "V" type, "A" type, and "T" type enterprises, etc., in terms of raw materials, finished products, product processing processes, parts, equipment, process flow, production lead time, bottleneck identification and production control coordination, etc. Different characteristics of the aspects show that from "V" to "A" to "T" enterprises, the types of raw materials are gradually increasing, the types of finished products and process flows are changing, and the difficulty of bottleneck identification and production control coordination is increasing. trend.

Pursuing balance of logistics rather than balance of production capacity: pursuing balance of production capacity when designing a new factory is to make full use of production capacity, but for multiple varieties of production enterprises that have been put into production, pursuing balance of production capacity may lead to product backlog because the product may not necessarily meet the requirements. At that time, the market demand.

The degree of utilization of "non-constraint" is not determined by itself, but by the system's "constraint": that is, the degree of utilization of non-bottleneck resources is restricted by the bottleneck resources in the system.

The "Utilization" and "Activation" of resources are not synonyms: "Utilization" refers to the degree to which resources should be utilized, and "dynamic" refers to the degree to which resources can be utilized. Traditional views often regard the two as synonyms, but In fact, they differ.

One hour loss on "constraint" is one hour loss on the entire system: production time includes adjustment preparation time and processing time. In terms of constraint resources, the meaning of adjustment preparation time is different from that of non-constrained resources. Constrain resource control and reduce output by one hour if interrupted, saving one hour of adjustment preparation time can increase one hour of processing time and correspondingly increase system output. Therefore, special protection measures should be taken for constrained resources, such as reducing the adjustment of preparation time and frequency, implementing a continuous working system, setting up quality checkpoints, setting up buffer links, etc., to increase their output.

One hour saved by "non-constraint" is not helpful to increase the effective output of the system: non-bottleneck resources have idle time in addition to production time. Saving their production time will increase idle time, although it may reduce processing batches and increase batches to reduce products in production Inventory and production lead times, but these impacts on the fundamental goals of the system are still subject to constraints on resource constraints.

"Constraints" control inventory and effective output: effective output is restricted by the company's production capacity and market demand, and is controlled by resource constraints and market constraint bottlenecks. If the "constraint" is within the enterprise, it indicates insufficient production capacity and limits effective output; if the enterprise's resource capacity is higher than market demand, then market demand becomes a "constraint". At the same time, "non-constraint" should be synchronized with "constraint", "constraint" controls the inventory level, and excessive inventory is a waste.

Transport batches may not be equal to (and in many cases should not be equal to) processing batches: In workshop on-site planning and control, batch determination affects enterprise inventory and effective output. OPT adopts a unique dynamic batch system to divide the in-product inventory into transportation batches (the number of parts transported between processes) and processing batches (the number of the same parts prepared for processing can be adjusted at one time, which can be the sum of one or several forwarding batches) . Determining the processing batch requires consideration of the reasonable application of resources and product-in-process inventory. Determining the transportation batch requires consideration of the continuity and parallelism of the production process, as well as reducing waiting time and transportation workload and expenses. The starting points of the two are different, so the transportation batch does not necessarily have to be processed. Batches are equal.

The batch size should be variable, not fixed: this is the direct application of Principle 7. The transportation batch is considered from the perspective of product-in-production, and the processing batch is considered from the perspective of resource type. When the same workpiece is processed on constrained resources and non-constrained resources, and is transmitted between different processes, different batch sizes can be dynamically determined according to actual needs.

When organizing the operation plan, the system resource constraints are taken into account. The lead-up period is the result of the operation plan, not the predetermined value: MRPII uses the unlimited capacity planning method to prepare the operation plan according to the pre-prepared lead-up period. When the production lead-up period is large and the actual entry and exit, The plan is difficult to implement. OPT considers the system resource constraints during the planning period, and uses the limited capacity planning method to first arrange the production progress plan of the key parts on the constraint resources, and then use it as a benchmark to schedule and optimize the previous and subsequent processes in different ways, and finally prepare non-critical work plan. Therefore, the lead time in OPT is a function of batch, priority and many other factors, and is the result of the preparation of the production plan.

OPT’s nine principles emphasize that in enterprise production activities, we must grasp key issues, solve bottlenecks, and obtain large profits with a small amount of investment.

OPT advocates believe that the real goal of any manufacturing company is to make money now and in the future. To achieve this goal, it is necessary to increase production and sales rates while reducing inventory and operating expenses. Measure whether a company makes money, it usually uses three indicators: Net Profit (NP), return on investment (ROI) and cash flow (Cash Flow (CF): It is the company that makes money. The absolute amount of the net profit is generally higher, the better the company's efficiency is. > - Return on Investment (ROI): represents the ratio of returns to investments in a certain period, and is used to compare the benefits of enterprises of different investment scales. For example, the annual net profit of both companies is 500,000 yuan, one invests 1 million yuan and the other invests 2 million yuan. The former has a higher investment rate and better efficiency. > - Cash Flow (CF): represents the money from income and expenditure in the short term, which is a necessary condition for the survival of the enterprise.

These three indicators mainly consider the effective utilization and arrangement of existing resources, but cannot directly guide production, if the production batch cannot be judged based on this. Therefore, OPT proposed three operating indicators: Throughput, T, Inventory, I, and Operating Expenses, OE, as bridges. If these operating indicators perform well, it means that the company has strong profitability: > - Production and sales rate (T): It is not the general pass rate or output rate, but the amount produced and sold within a unit of time, that is, obtaining money through sales activities The rate of production and unsold products belong to inventory. > - Inventory (I): Including raw materials prepared to meet future needs, products in process, parts that are not used for the time being, unsold finished products, and fixed assets after deduction, etc. Inventory occupies funds and incurs related expenses. > - Operating fee (OE): is all expenses in the process of converting inventory into production and sales, including direct and indirect expenses.

As measured in currency, T is the money entering the system, I is the money stored in the system, and OE is the money paid to turn I into T. When T increases and I and OE remains unchanged, NP, ROI and CF are all increased; when OE decreases and T and I remain unchanged, NP, ROI and CF are also increased; when I decrease and T and OE remains unchanged, ROI will increase; when I decrease and T and OE remains unchanged, ROI will increase; when I decrease and T and OE remains unchanged, ROI will increase; , CF will increase, but NP will not change. Typically, the reduction of I can reduce OE, which in turn increases NP, ROI, and CF, but when I drop to a lower level, the effect of continuing to reduce I on reducing OE is reduced. 【formula】

$NP=T - OE$

$ROI=(T - OE) / I$

These formulas show the relationship between operating indicators and financial indicators, indicating that by reasonably adjusting production and sales rates, inventory and operating fees, the company's net profit and investment rate can be affected, and thus the company's goal of making money can be achieved.

The basic idea of ​​OPT is to find out the weakest links in product production that affect production progress and concentrate on ensuring full load work. The specific principles include:

Try to ensure full load of key resources: Key resources (such as people, equipment, materials, etc.) are weak links that limit the productivity of the production system, and their working hours directly affect the output of the enterprise. To ensure that critical resources work at full capacity, the following measures can be taken:

The utilization and productivity of non-critical resources are determined by the capacity of critical resources: the logistics volume or output of the production system depends on the ability of critical resources to pass, and the load and productivity of critical resources determine the utilization and productivity of non-critical resources. If the critical resource situation is not taken into account and blindly increasing the utilization and productivity of non-critical resources will lead to the production of unsuited excess workpieces or products, increase inventory, and backlog of working capital, which will not improve economic benefits.

Different planning methods are adopted for the leading and subsequent processes of key processes: in order to avoid excessive backlog of workpieces before the key processes and quickly complete sets after the key processes, the OPT system uses a pull method to prepare plans for the leading processes of key processes (according to subsequent processes) Process requirements determine the production date and quantity of the leading process), and the subsequent processes of key processes are promoted to prepare plans (the production time and quantity of the subsequent processes are determined according to the completion of the leading process). This planning method takes into account the constraints of key resources and limited production capacity, enhancing the implementability of the plan.

Based on the above principles, in the process of preparing production plans, enterprises should first prepare production plans for key parts of the product, and then prepare production plans for non-critical parts on the premise of confirming the production progress of key parts.

At present, there are many views on the theoretical community's understanding of OPT. Some people regard it as a new planning idea, a simulation language for operational planning, a software package for generating production planning related plans, or an attempt to process data accuracy. However, OPT emphasizes that the workshop site is focused on the decision-making volume at the enterprise workshop site. By using a set of weighting functions of "management coefficients" to determine the number of operation priority and batches, a reasonable production plan is formulated. These management coefficients involve product portfolio, delivery time, Factors such as safe inventory levels and the use of bottleneck resources.

The key to OPT implementation lies in the implementation of the plan, but the traditional cost accounting assessment system will hinder it. Because traditional cost accounting ignores the difference between bottlenecks and non-bottlenecks, focuses on local optimization, and assesses the utilization rate and production costs of equipment and operators, it is easy for people to blindly produce, pursue high equipment utilization rate, and ultimately lead to high inventory and waste. OPT assesses bottlenecks and non-bottlenecks from a global perspective, pays attention to "utilization" rather than "energy", and evaluates non-bottleneck resources with effective product volume.

In addition, OPT software needs a lot of data support, such as product structure files (BOM), processing process files, as well as accurate processing time, adjustment preparation time, minimum batch, maximum inventory, alternative equipment and other data. The successful implementation of the OPT also requires managers to have confidence in their plans and change old ways of working, such as accepting lunch and continuous work systems.

OPT is more suitable for basic and simple products, as well as production situations with large batches and fewer processes required, and is not effective in a single-piece production workshop. Its applicable conditions include relatively stable bottlenecks, ability to ensure that the bottlenecks can reach 100%, relatively stable demands, and employees are willing and able to obey planned scheduling arrangements. At the same time, OPT requires accurate dynamic data, bottlenecks and data close to bottleneck resources, and employees need to be trained so that they can use OPT methods to solve problems.

Calculate the load of the equipment (work center) and find the bottleneck equipment (work center): The first step of the OPT job control method is to find the bottleneck in the system. By distributing production to key equipment, calculating its load, and comparing it with available capacity, the equipment with the most load exceeding the available capacity is the location of the bottleneck.

Determine the control point and establish the control flow: Any production system needs a control point to control the flow of materials. If there are bottleneck equipment in the system, the bottleneck is the best control point, because its output rate determines the system pass rate. After determining that the bottleneck is the control point, an information communication relationship needs to be established at the two endpoints of the control point and the input and output of the production process, namely the control flow.

Arrange the output or flow of bottleneck equipment: The production plan starts with the bottleneck equipment or bottleneck work center, and arranges the output or flow according to process and equipment parameters.

Calculate the output or flow of other equipment: After determining the output or flow of bottleneck equipment, the output or flow of non-bottleneck equipment will be arranged from behind to front with the bottleneck as the center, and the output or flow of non-bottleneck equipment will be arranged from front to back with the "push" The output or flow rate of subsequent processes.

Ensure the full-load work of bottleneck equipment: In order to make bottleneck equipment reach full-load work and make full use of system capabilities, buffers and checkpoints need to be set up at the bottleneck equipment to reduce the impact of productivity fluctuations on it.

OPT's planning and control system is also called DBR system (Drum - Buffer - Rope approach, "drum", "buffer" and "rope" are referred to as DBR method for short), and consists of "drum", "buffer" and "rope" three types. Parts:

"Drum Drum": In the DBR method, "drum" represents "drum beat", which is the beat. Just like the drum beats that command, drive and uniformly tune in the marching queue, "drum" is the driving force of OPT production plan. It determines the output rhythm of the entire production system. By controlling the "drum" it can coordinate the production of each process and make the production process proceed in an orderly manner.

"Buffer": The purpose of setting the "buffer" is to ensure a high output rate of the "bottleneck", so that the bottleneck can be fully utilized and the cost is minimal. There are generally two types: "time buffering" and "inventory buffering". Unlike MRP's safe inventory and safety lead time, DBR's buffering is specially set for bottleneck resources to ensure that bottleneck resources will not be stopped due to insufficient raw material supply or fluctuations in the previous process.

"Rope": The function of "rope" is to establish a connection between the "drum" and its upstream processes, transmit production instructions, and all parts of the drive system are produced according to the rhythm of the "drum". In the implementation of DBR, the "rope" is implemented through a detailed operation plan involving feeding raw materials to each workshop, and its function is similar to the MRP instructions or the "kanban" of the JIT. The "rope" must ensure the minimum inventory or the quantity of products in production. By controlling the entry of materials, the non-bottleneck equipment before the bottleneck can be produced evenly, reduce the processing batch and transportation batch, shorten the lead time and reduce the inventory of products in production, and avoid bottlenecks being suspended. material situation.

The implementation of the DBR system mainly includes the following steps:

Identifying bottlenecks: This is a key step in planning and control. Because bottlenecks restrict the output capacity of an enterprise, generally when demand exceeds capacity, the machine with the longest queue is often the "bottleneck". By calculating the task working hours of various machine tools and comparing them with the capacity working hours, the machine tool with the highest load is the bottleneck. After determining the bottleneck, use it as a control point to ensure that its operations are not mass-produced and prevent excessive product-in-production inventory.

Based on bottleneck constraints, establish product production plans:

The use of "rope": The function of "rope" is to minimize inventory. Bottlenecks determine the output rhythm of the production line. The upstream processes implement traction production, connecting the bottlenecks with the upstream processes through "ropes", so that materials can quickly pass non-bottleneck operations according to the product production plan to meet the production needs of bottlenecks. The "rope" is realized by a detailed operation plan involving feeding raw materials to the workshop. Its essence is the same as the "Kanban" idea, that is, the latter process collects parts and processes them from the front process as needed, and the previous process only supplements the mobilized parts to achieve the benefit of Control production to ensure that the production rhythm is consistent with bottleneck output, and avoid production chaos and inventory backlog.

5.1.1. Conceptual meaning

5.1.2. Core content

5.1.3. Tool application

5.1.4. Comparison of TOC with MRPⅡ and JIT