Types of requirements for materials. Material requirements planning

Allocate how many types of need for material resources. Let's consider them in more detail. The need for the planning period, regardless of whether the stocks are in stock or in the form of production reserves is called gross requirement.

Total Gross Demand- gross demand + additional demand, which includes experiments, samples, increase in demand associated with the repair and maintenance of equipment, a reserve in case of short deliveries.

Net requirement is pure need. It is defined as the difference between gross demand and available availability.

Primary- market need (what you need to sell on the market)

Secondary- raw materials, materials, semi-finished products, components that are necessary for primary needs.

Tertiary - auxiliary materials for other purposes, necessary for primary and secondary needs.

Material requirements planning is a procurement planning system taking into account seasonal trends and dynamics of primary demand, as well as the type of markets in which the company presents its products. When planning requirements, they use data on the amount of necessary stocks and the time they are received in accordance with the production plan, i.e. this system planning determines the quantity and schedule for the release of the required products. This planning system allows you to:

• ensure the availability of raw materials, materials, components in the required quantities;
• reduce the costs associated with ordering and storing inventory;
• increase efficiency scheduling and work in a constantly changing market environment.

The raw material requirement plan is a procurement schedule based on inventory availability and the expected order cycle.

Requirements planning system components:

• schedule of the main production process, which determines the amount finished products broken down by time;
• data on the specific consumption rates of raw materials and materials, which determine the quantity and composition of raw materials and components necessary for the production of each specific type of product;
• inventory data for each component, (quantity available, expected receipts);
• data on the main products that are purchased and all products that are produced by the enterprise itself;
• forecast of the need for materials in accordance with the schedule of the main production process;
• structured list of raw materials and materials;
• inventory data, open orders and lead times to calculate the time and volume of material orders.

Basic principles of planning requirements for raw materials and materials:

• coordination of needs for raw materials and materials (components) and a plan for the production of finished products;
• breakdown by time.

Consider three of the possible methods for determining the need for materials that are used in logistics:

• 1) deterministic- used when known certain period fulfillment of the order and the need for materials in terms of quantity and timing;
• 2) stochastic- when the basis for the calculation are mathematical and statistical methods that give the expected demand .;
• 3) heuristic - the need is determined based on the experience of workers.

The choice of one of these methods depends on:

• enterprise profile;
• customer capabilities;
• product type;
• availability and type of warehouses.

Let's consider the first one deterministic . This method used to calculate the need for materials and components to meet the needs of production, when sales volumes of products are determined. The deterministic method is based on the use of well-defined initial data and serves to determine secondary and tertiary needs with a known primary. Necessary information - primary need, including data on volumes and terms of production; information about the structure of the product in the form of a specification or instructions on the applicability of certain parts; cost rates for materials and types of products; available availability.

The calculation of material resources is carried out separately for social needs, main and auxiliary production, and economic and mathematical models can be used here.

The need for material resources for the main production:

M - need;

H - the rate of consumption of material resources i-ro names pa j type of product;

N - production program] type of product; p - assortment.

Determining the need for material resources for repair and maintenance needs:

T 0 - time to failure of equipment of this type;

R 0 - given level of reliability;

Qj - number of units. equipment of this type;

Well - the consumption rate mat. i-ro type for 1 repair t - delivery time;

L is the number of deliveries.

In a deterministic method, it is important to set the time of consumption of material resources. A cycle chart that fills from right to left can be useful here. The cycle is determined by the longest operation. Based on the cycle schedule, you can determine how many parts to run and when. In order to meet the order on time, the materials must be available as soon as possible, so that the cycle of their receipt and primary processing does not increase the production cycle of the product. Parts must be ready on time so that there is time for assembly. Purchased items must be ordered with the expected delivery time in mind.

Stochastic. Methods of this type are used in the calculation based on the amount of materials used. They are based on prediction. Forecasts can be medium-term (3-5 years), short-term and long-term. Forecasts based on stochastic models have the following features: the situation predicted for the future is based on the time of the forecast. Changing the time point affects the result of the forecast. The assessment of the development of the phenomenon, as well as the collection of the necessary information, is carried out before the development of the forecast; the forecasting process relies on information about the past period.

Task.

A manufacturing agro-industrial enterprise needs to purchase containers for packaging products. It is known that 24 units of products are placed in 1 box. Determine the need for containers for December, if you know how many products were produced from June to November of the same year. The data are presented in the table.

Determination of demand by the method of "Naive forecast".

F-forecast next month,

D(t) - demand of the analyzed month.

Solution:

D(t)=920000/24=38333.3 boxes.

So, as we know that in the previous month the demand for packaging was equal to 38333.3 boxes, therefore, 38333.3 boxes must also be ordered for the month of December.

Determination of demand by the "Simple average" method.

Where F(t + 1) is the expected value of demand t is the month under study t + 1 is the next month t-1 is the previous month

- the weight of each of the n past values ​​of demand (the same).

Solution:

Let us denote the demand for packaging in November D(t)=38333.3 boxes,

demand for packaging in October will be D(t-J)=956000/24=39833.3 boxes;

similarly calculate the demand for September D(t- 2)=1000000/24=41666.7 boxes,

August D(t-3)= 1116000/24=46500 boxes;

July D(t-4)= 1100000/24=45833.3 boxes;

June D(t-5)= 1105000/24=46041.7 boxes.

Substitute the values ​​in the formula (2.4)

Therefore, 43035 boxes must be ordered.

Moving average method.

Used when it is understood that recent data is more important and therefore should have more weight, provided that the sum of the weights is equal to one.

Solution:

Let us substitute the known values ​​of D(t) into formula (2.5). We get:

Determination of material requirements

Need for materials- this is the amount of material, raw materials and components that is necessary to fulfill a given production program and available orders. The need for materials can be primary, secondary, tertiary, as well as a net need and a gross need.

primary need- need in finished goods, assemblies and parts for sale and the need for purchased spare parts. This need is determined by market demand, for its calculation methods of mathematical statistics and forecasting are used. This need is basic for an enterprise engaged in trade.

secondary need- this is the need for component parts and raw materials used for the production of products that make up the primary need, that is, the finished product of the enterprise. To calculate this requirement, a deterministic method is used (using formulas), the initial data here are the primary requirement and specifications. Secondary requirements are used mainly in industrial enterprises.

Tertiary need- the need for auxiliary resources for production purposes. An example would be wearing items. The tertiary need is also determined by the deterministic method, as well as the stochastic method and expert assessments. Based on secondary requirement.

Depending on the accounting of the available stocks of materials, the requirements are classified into:

- gross need- the need for material resources for the implementation production program without taking into account the availability of finished products and materials in stock. This is the sum of primary + secondary + tertiary needs;

- net need- the need for material resources for the implementation of the production program, taking into account the availability of finished products and materials in the warehouse. It is determined by the difference between gross needs - stocks.

In practice, the total demand differs from the gross demand due to defects in production, as well as due to repairs, preventive maintenance of equipment and other works.

Classification of methods for determining needs

For effective work it is necessary to predict the need, a number of methods can be used for this. The methods can be divided into three groups (Table 5.1).

Table 5.1 - Methods for determining needs

Analytical methods include:

The method of level construction of the product - refers to the product of simple products of a single application;

The method of leveling the placement of stocks at each hierarchical stage of the construction of the product, the same requirements must be collected;

Synthetic method - the calculation is based on the cost of material resources for the product. A feature of this method is not a product, but material resources.

The enterprise's need for material resources must be justified by appropriate calculations, taking into account the following types of consumption:

to the main production;

For capital construction (subject to the expansion of the material and technical base of the enterprise);

For implementation new technology and conducting experimental work;

For repair and maintenance needs;

For the manufacture of technological equipment and tools;

To create carryover inventories;

For work in progress (in cases of technological need).

The calculation of the need for material resources is carried out, as a rule, by the method of direct counting. This method assumes by multiplying the consumption rate by the corresponding volume of production (or work) to determine the amount of required resources in the planning period.

Depending on which norms are used for the calculation, the following methods are used:

a) manufactured;

b) detailed;

c) by analogy;

d) by typical representatives.

When using the item-by-product and item-by-item methods, the consumption rates for the production of a unit of output (product), individual parts are applied.

The method of determining the need by analogy is that products (products) for which there are no consumption rates during the calculation period are equated to similar types of products (products) for which there are corresponding consumption rates for raw materials and materials. In this case, it is necessary to take into account characteristics new product (product). For this purpose, correction factors are introduced into the calculation:

Where P- raw materials or materials necessary for the implementation of the production program; H en- the rate of consumption of raw materials or materials for similar products (product); Q pl- the program (volume) of output (product) in the planning period; TO- coefficient taking into account the peculiarities of the consumption of raw materials or materials for production this product(product) compared to a similar product.

In the case when the enterprise produces a wide variety of products and at the same time there are no specified output volumes, for each of its types, the need for raw materials and materials is calculated for a typical product or part. In this case, the consumption rate of raw materials and materials for such products or parts will be a weighted average for the planned group of products (products) or parts.

In the absence of developed norms for the consumption of raw materials and materials in the planned period for certain types the range of products manufactured by the enterprise, the need for material resources is calculated based on the data on the actual use of materials and raw materials for the previous period and its specific reduction in the planned year. To do this, use the formula:

where P pl- the need for this raw material or materials for the planning period; P fak - the actual consumption of this raw material or materials in the previous similar period; At pr.p- index of increase or decrease in the production program in the planning period compared with the previous period; At n- the index of the average decrease in material consumption rates in the planning period.

In the production of products at the enterprise, in addition to raw materials and basic materials, auxiliary materials are also used. They are used as a necessary component in the manufacture of products to ensure normal technological process and for product packaging. Auxiliary materials include, for example, twine, paints, labels, foil, paper, gauze, etc. Their application is multi-purpose. This greatly complicates the development of technically sound consumption rates. The need for auxiliary materials in this case can be established in proportion to the change in the production program for the enterprise as a whole or for individual types of products (products).

With the expansion of the material and technical base of the enterprise (construction of new workshops, industries, etc.), it becomes necessary to determine the need for material resources for capital construction.

Capital construction carried out economic way involves determining the need for material resources to produce according to consumption rates calculated on the basis of design estimates.

For the implementation of measures for the technical development and organization of production at the enterprise, the need for material resources is established on the basis of the scope of work to improve technology, mechanization and automation of production, the development and implementation of new technology, the volume of research, development and other planned work and consumption rates raw materials and materials for these purposes.

Determination of the enterprise's need for material resources for the repair of fixed assets is established based on the volume of fixed assets as of January 1 of the year preceding the planned one. In this case, the approved material consumption rate is used per 1 million rubles. the cost of fixed assets and a correction factor that determines the need for this material for the repair of newly introduced labor tools, industrial and non-industrial buildings and structures.

The need for material resources for the manufacture of technical equipment and tools is determined in accordance with the following formula:

where R And- the need for this type of material (in the corresponding natural units) for the manufacture of equipment and tools in the planned period; H V- the consumption rate of the same type of material (in appropriate units) for the manufacture of equipment and tools in the preplanning period per 1 million rubles. gross output; IN pl- the projected volume of gross output in the planned period, million rubles; TO n- coefficient of change in material consumption rates for the manufacture of equipment and tools; TO m– increase factor technological equipment in the planning period compared to the base period.

At some enterprises, the production process takes a fairly long time period. In this regard, for products (products) with a long production cycle, the need for raw materials and materials is taken into account not only to ensure the planned volume of output, but also taking into account changes in the value of work in progress.

The total amount of raw materials and materials that is constantly in stock (stocks) is determined by multiplying the duration production cycle of production in days for the average daily consumption of raw materials and materials in natural units of measurement.

Provided that the enterprise has data on changes in stocks (reserves) in the volume of products or products (parts) by the end of the planning period compared to its beginning, the need for raw materials and materials for a change in work in progress is determined by the formula:

where R n.p.- the amount of work in progress; D ki, D none- the number of products or products (parts) i- th type in work in progress, respectively, at the end and beginning of the planning period; H i- consumption rate of raw materials and materials per unit of production or product (parts) i- th type; n- the number of items of parts or products for the production of which this raw material or material is consumed.

An integral part of the annual need of the enterprise for material resources is the need to create inventories of raw materials and materials. This is necessary so that the production process does not stop.

The amount of inventories depends on a number of conditions:

The magnitude of the need for various types of raw materials and materials;

The frequency of production of products by integrator enterprises;

The frequency of launching raw materials and materials into production;

Seasonality of supplies of raw materials and supplies;

Relations between transit and warehouse forms supplies;

The amount of transit deliveries.

The value of the production stock is justified by the norm of the production stock, which is the average stock of raw materials and materials during the year in the days of its average daily consumption, planned at the end of the year as a carryover stock. The size of the carryover stock is determined by the formula:

(7.5)

where t p i is the size of the carryover stock for the i-th raw material and materials; t i- the need for the i-th raw materials and materials; M i- the norm of the rolling stock of the i-th raw materials and materials in days; To days - the number of days in the planning period.

When planning inventories, it is necessary to provide for the possibilities of the enterprise aimed at expanding the market for the sale of products by increasing the volume wholesale trade and long-term direct economic relations between producers and consumers.

The main purpose of material requirements planning is to ensure that the required quantity of required materials is available at any given time within the planning period. With the help of requirements planning, it is ensured that the volumes of materials needed for both internal use and sales are purchased or produced on time. The planning process includes continuous inventory control and, in particular, the automatic generation of purchase and production order proposals.

Planning requires all information on stocks of materials, including reserved, in order to calculate the volume of purchases or production.

Drawing up a volume-calendar production plan

When drawing up a volume-scheduling plan, sales are planned for the future by means of a sales forecast (see Technology for passing the sales business process). A volume-scheduling plan is created using planned independent requirements. Planned independent requirement (i.e. demand for the finished product, assemblies, hot goods and parts) uses this information to create a minimum stock level for material requirements planning.

Formation of input information for the MRP system

The input information for MRP consists of three main parts:

Concept and functions purchasing logistics

Procurement logistics is the process of providing enterprises with material resources, placing resources in the warehouses of the enterprise, storing them and issuing them to production.

The purpose of procurement logistics is to meet the production needs for materials with the greatest possible economic efficiency. In doing so, the following tasks are solved:

1. Maintaining reasonable terms for the purchase of raw materials, materials and components.
2. Ensuring that the quantity of supplies exactly matches the needs for them.
3. Compliance with production requirements for the quality of raw materials, materials and components.

Without purchasing logistics, the normal operation of the enterprise is impossible. It is a link between different producers and coordinators of their work.

Procurement logistics performs the following functions:

• formation of a strategy for the acquisition of material resources and forecasting the need for them;
• receiving and evaluating proposals from potential suppliers;
• selection of suppliers;
• determination of the needs for material resources and calculation of the quantity of ordered materials and products;
• agreeing on the price of ordered resources and concluding supply contracts;
• control over the delivery of materials;
• input quality control of material resources and their placement in the warehouse;
• bringing material resources to production units;
• maintenance of stocks of material resources in warehouses at the normative level.

The described functions are implemented by the logistics service (purchasing department) in close relationship with other departments of the enterprise: marketing department, production, production preparation service, accounting, financial and legal departments.

Increasing role of purchasing
logistics in modern conditions

The transition to a market economy determines the role and growing importance of procurement logistics in social production. Market conditions brought to life a series significant changes in the field of material and technical support of production. Among them, the most important were:

• the pressure of a rapidly growing range of products requested by the market;
• reducing the time for introducing new products into production, accelerating the expansion of the range;
• reduction of the duration of the production cycle;
• aggravation of competition between manufacturers against the backdrop of market saturation with the necessary goods.

All these changes have led to the fact that the various activities of the enterprise production, economics, financial activities became increasingly dependent on the state of logistics. It turned out that there are large areas of inefficiency in the supply chain, the rationalization of which can lead to large savings. There was a need to implement new approaches to organizing the processes of material support for production and management.

2.1.2. Acquisition process
materials and its main stages

The process of acquiring materials includes a number of logically interrelated activities. The following stages of the process of acquiring materials are distinguished:

Drafting applications. Requisitions for the purchase of materials are prepared by the relevant staff functional divisions enterprises. They contain information about what types and quantities of materials the company needs, when they should be received and who made the request. Applications are drawn up in such a way that the quantities of materials expected to be received outstrip the actual requirements for them.

The time between the placement of applications and the receipt of materials is called lead time. Employees responsible for compiling requisitions should set the delivery dates of materials with a minimum lead, taking into account the capabilities of the supplier and the needs of the consumer of materials.

Application analysis. Applications for the consumption of materials are analyzed in the logistics service with the participation of specialists from other departments. The purpose of the analysis is to ensure minimum costs for each type of materials, the specific consumer properties of which are supposed to be used in the production of products. Research methods are functional cost analysis and cost construction.

The analysis should answer the following questions:

• Can cheaper materials meet the needs of production?
• Are these needs justified?
• Can other types of materials meet the identified needs?
• Is it possible to simplify the design of the manufactured product?
• Is the supplier able to reduce the cost of materials by participating with the consumer in the development of the product or by analyzing the received specifications?

The supply service has no right to replace the materials specified in the applications. Department employees should analyze incoming requests and offer such options for purchasing materials that can lead to a decrease in the cost of orders.

Choice of suppliers. When choosing suppliers, the main criteria are: supplier reliability, ability to supply necessary resources of proper quality and in the right time, supply of material resources at the lowest possible prices, remoteness of the supplier from the consumer, availability of spare capacities at the supplier, etc.

The main sources of information about suppliers and materials are personal contacts with "sellers", advertisements in advertising publications, descriptions of goods that are given in catalogs and brochures, visits to enterprises and study of the practice of supplying products, information received from banks, trade associations, public institutions etc.

From the list of suppliers with a strong reputation, those who offer the most favorable conditions in terms of price and delivery time are selected. It is advisable to distribute large orders between two or more suppliers in order to check the competitiveness of the main supplier and protect yourself from possible surprises.

Placement of orders. The purchase of materials is carried out different methods depending on the type of materials and components. The main procurement methods are:

• bulk purchases (one large batch at a time);
• regular purchases of materials (the buyer orders the required amount of materials that are supplied to him in small lots over a certain period);
• daily (monthly) purchases (used when purchasing cheap and quickly used materials);
• obtaining material as needed;
• single purchases (material is ordered if it is required and taken out from suppliers' warehouses in cases when it is impossible to receive material as needed).

An order is documented through the conclusion of a contract between the supplier and the consumer of the material.

Basic elements of a contract.

1. Offer and acceptance of the offer. A contract is drawn up if one party offers a certain batch of goods at a specified price, and the other party accepts this offer.
2. Financial conditions. The contract must have a value, i.e. it becomes a contract in the legal sense only when financial terms are stipulated in it.
3. The right to enter into contracts. Only certain officials(director, CEO), authorized by the enterprise and acting on his behalf.
4. Legality. The contract must be legal, i.e. fully comply with the legal norms of the country.

The structure of the contract provides for the definition of the subject of the contract, the indication of the quality and quantity of goods, the amount of the contract, the procedure for the delivery and acceptance of goods, the responsibility of the parties, the procedure for resolving disputes.

Order fulfillment control. The size of the orders and the duration of the period during which these orders are fulfilled are controlled by the Procurement Department. At the same time, it is possible to adjust the schedules for the supply of materials and the corresponding refinement of schedules for the release of products.

Completion of the acquisition process. Receipt of ordered materials in strict accordance with the terms of the contract is a necessary sign of the completion of the transaction. The acceptance of products is important, during which it is necessary to make sure that the material has been delivered:

• the required quality;
• in the right amount;
• at the appointed time;
• for the agreed price.

Purchase and sale are properly documented. Documenting deliveries involves receiving from the supplier a notice of shipment and cover letter, which indicate the quantity of goods and the time of delivery. The receipt of materials at the warehouse is documented by the appropriate invoices and recorded in the goods registration book.

2.1.3. Determination of material requirements

Types of material requirements

Under the need for raw materials and materials is understood as their quantity required by a certain date for a specified period to ensure the implementation of a given production program or existing orders.

The need for materials for a certain period is called periodic need. It is made up of primary, secondary And tertiary.

Under primary the need for finished products, assemblies and parts intended for sale, as well as for purchased spare parts, is understood. Calculation of the primary need is carried out using the methods of mathematical statistics and forecasting, giving the expected need. The risk of an incorrect assessment or an inaccurate forecast of needs is compensated by a corresponding increase in safety stock.

The primary need is the basis of material flow management in enterprises operating in the field of trade. For industrial enterprises primary need should be decomposed into secondary components.

Under secondary understands the need for component parts, parts and raw materials necessary for the production of finished products.

Example 2.1.1. The furniture factory produces work tables for completing kitchen furniture. The sink is located in the table, which, in turn, is completed with a mixer of cold and hot water. The need for a sink and faucets is called secondary, since it can be determined from the primary need (number of work tables). If sinks and faucets are supplied in trading network as necessary spare parts, then there is both a primary and a secondary need for these products.

When calculating dependent requirements, the following are assumed to be specified: primary requirement, including information on volumes and terms; specifications or applicability information; possible additional deliveries; the amount of materials at the disposal of the enterprise. Therefore, deterministic calculation methods are used to determine dependent requirements. If this method of establishing the need is not possible due to the lack of specifications or the insignificant need for materials, then it is predicted using data on the consumption of raw materials and materials.

Under tertiary the production need for auxiliary materials and wearing tools is understood. It can be determined on the basis of the secondary on the basis of indicators of the use of materials by conducting stochastic calculations based on the consumption of available materials or by expert means.

Depending on the accounting of cash reserves, there are gross- And net material requirements.

Under gross need is understood as the need for materials for the planning period, excluding stocks in the warehouse or in production. Accordingly, under net need the need for materials for the planning period is understood, taking into account available stocks. It is defined as the difference between the gross demand and the inventory on hand by a certain date.

In practice, the total need for materials increases relative to the gross indicator by an additional need due to defects in production and work on maintenance and equipment repair. After comparison with the amount of available stock, the residual requirement is adjusted by the amount current stocks. Ratio various kinds requirements for materials is shown in fig. 2.1.1.

Rice. 2.1.1. The ratio of different types of material requirements

Methods for determining needs

Necessary condition effective management material flows is the knowledge of needs for the future. The methods used to determine it are shown in fig. 2.1.2.

Rice. 2.1.2. Classification of methods for determining needs

Deterministic calculation methods are used to calculate the secondary requirements for materials with a known primary. At analytical method the calculation proceeds from the product specification down the hierarchy levels from top to bottom. Synthetic method involves carrying out calculations for each group of parts based on the degree of their applicability at individual levels of the hierarchy.

Stochastic calculation methods allow you to set the expected demand based on numerical data characterizing its changes over a certain period of time. For this purpose, use approximation of mean values, exponential smoothing method And regression analysis.

Average Approximation used in environments where material demand fluctuates from month to month with a steady average. Forecasting by this method is a procedure of averaging the known values ​​of the demand for materials.

Exponential smoothing method are used in the case when the forecasting of the process of changing the need for material resources is made on the basis of the levels of a series of dynamics, the weights of which decrease as the given level moves away from the moment of the forecast. For this purpose, a constant smoothing coefficient a is introduced into the calculations, the value of which is chosen in such a way as to minimize the forecast error.

Regression analysis involves the approximation of known trends in the consumption of material resources using mathematical functions that can be extrapolated to the future period.

2.1.4. Providing production with materials

In the practice of enterprises, several methods of planning the material support of production are used (Fig. 2.1.3).

Rice. 2.1.3. Methods for planning the material support of production

Custom Method assumes that the required material is purchased only when a requirement arises, so no stock is created. This method is used in the conditions of single and small-scale production to meet the need for high-quality materials and bulky parts, which are difficult to store, as well as materials for repair work.

Order-based material supply is possible for single or multiple items. In the latter case, it is carried out at regular intervals, for example, weekly intervals, when a single order is formed, taking into account all applications received over a given period.

Material support based on planned targets. This method is based on a deterministic calculation of material requirements. In this case, it is assumed that the independent requirement for a certain period, the product structure in the form of specifications, which makes it possible to determine the dependent requirement, and the possible additional requirement are known.

When supplying materials based on planned targets, the order size is determined based on the net requirement, taking into account the planned receipt and the availability of materials in the warehouse.

Let us explain the concepts of warehouse, planned and workshop stock.

Warehouse stock this is the amount of materials intended for industrial consumption and available according to accounting data. In order to determine the real need for materials, the warehouse stock is divided into two parts: materials that are available for the planned release program, but are not yet in demand by the shop, and materials that can still be obtained (available stock).

Intended stock is the amount of materials intended for sale and therefore not considered as available.

shop stock these are materials received from the warehouse and located in the workshop for the purpose of further processing.

Material security based on consumption involves the timely replenishment of stocks and maintaining them at a level that would cover any need before a new receipt of materials. In accordance with the goal, the problem of determining the time of an additional order is solved, the issue of the size of the order is not considered.

Depending on the type of check and the rules for issuing additional orders, there are two methods of material supply based on the consumption carried out, known as inventory management systems:

1. Ensuring timely orders (stock management system with a fixed order size);
2. the necessary rhythm (a system of inventory control with a fixed frequency).

Within the framework of these methods, in turn, there are several possible variations, which are determined by the policy pursued in the field of maintaining stocks. They will be discussed in the topic "Inventory management".

2.1.5. Delivery Calculation Methods

Determining the Economic Order Quantity

An economic order size is a material lot size that will minimize the annual total cost of order fulfillment and material storage. The technique for determining the economic order quantity is to compare the advantages and disadvantages of purchasing materials in large and small quantities and to choose an order quantity that corresponds to the minimum total cost of restocking. The ratio of the size of the order and the cost of supply (fulfillment of orders) and storage of materials is graphically shown in fig. 2.1.4.

Rice. 2.1.4. The dependence of the cost of order fulfillment
and storage of materials from the size of the order

Let x be the number of units purchased as a result of one order. As the number of purchased items of material increases, the running costs of storing materials (holding inventory) increase (curve 2). At the same time, as the batch size increases, the number of orders per year decreases. This leads to a decrease in the costs associated with the execution of orders (curve 3). As can be seen from fig. 2.1.4, the curve of total annual expenses (curve 1) has a minimum at x = x 0.

Based on a quantitative assessment of the dependence of the costs of purchasing and storing materials on the amount of purchased material, it is possible to determine the size of the order that minimizes the value of the total costs under the following assumptions:

1. the total number of material units that make up the annual stock is known.
2. demand is unchanged.
3. orders are executed immediately, i.e. orders are fulfilled on time, the lead time is known and constant.
4. registration costs do not depend on their size.
5. the price of the material does not change during the considered period of time.

In accordance with the assumptions made, the cost of order fulfillment and inventory maintenance can be expressed by the formula

Where WITH 1 and WITH 21 are respectively constant and variable costs related to the execution of the order and the content of materials;

n number of orders per year;

q/2 – the average size stock.

Where Q annual material requirement.

The above formula establishes the economic order quantity for conditions of uniform and strictly defined (deterministic) inventory consumption. In the practice of the enterprise, there may be:

• delayed delivery; in this case, the material is delivered not one-time, but over a certain period of time with a certain intensity and is consumed by production evenly; its use begins immediately after the start of supplies before the entire supply is actually completed;
• accelerated use; in this case, the intensity of consumption of stocks is such that a shortage of material is possible.

Taking into account the noted special conditions private models are built to determine the economic order size.

Determination of the optimal production batch size

If the enterprise is its own supplier, then the problem of determining optimal size production batch, i.e. the quantity of products that must be manufactured to replenish the stock of its own components. The scheme of movement of the stock, typical for such a case, is shown in Fig. 2.1.5.

Rice. 2.1.5. Graph of the movement of the current stock
when replenishing materials for a finite interval

As can be seen from the figure, the consumption of the stock occurs gradually, during the entire cycle t, and its replenishment only during the period t 1 , the duration of which is determined by the manufacturing time of the produced batch (production cycle). The necessary components begin to be manufactured upon receipt of the corresponding order and, as soon as they are ready, they are immediately sent to the consumer: to the warehouse of the recipient shop for further processing or to the picking warehouse of the assembly shop. The daily replenishment rate is determined from the condition

Where p annual production of components.

If the rates of production (receipt) and consumption of materials are set, then the stock will grow during the entire replenishment period and will reach a maximum value at the end of it.

The maximum stock level will be

and the average stock will be

Considering that the replenishment period is determined based on the average daily production volume t 1 = 240q opt /p, the total annual costs associated with the replenishment and storage of materials will be

If a volume discount is given, then several calculations must be made to determine the economic order quantity, since the total cost function is no longer continuous. To find the global minimum of such a function, it is necessary to study its local minima, and some of them may be at price break points.

Determination of economic size
order in case of shortage

In the classical economic order quantity model, there is no shortage of products needed for production. However, in cases where the loss due to a shortage is comparable to the cost of maintaining excess inventory, a shortage is acceptable. If available, the economic order size model requires taking into account certain methodological features. The most general case of the movement of the current stock under the assumption of a shortage of material is shown in fig. 2.1.6, where q stock size at the beginning of each delivery interval t(maximum stock in case of shortage). Whole interval t is divided into two periods:

• the time during which the stock in the warehouse is available, t 1 ;
• the time during which there is no stock, t 2 .

Rice. 2.1.6. Cycle of movement of current stocks under the assumption of a shortage

Initial stock size q n under these conditions, slightly less than the optimal lot size is accepted q opt. The task of stock management is reduced to a quantitative determination of the size of the reduction and the establishment of a rational value of the initial stock. The criterion for the optimality of the supply line is the minimum amount of transport and procurement costs, the cost of maintaining the stock and losses due to shortages.

The economic order quantity is determined by the formula

Where C 3 annual losses due to product shortages.

With a significant increase C 3 ratio C 3 /(C 2 +C 3) approaches unity and the optimal lot size tends to the value that it would be in the absence of a shortage of stocks. If losses due to shortages are negligible, then the ratio C 3 /(C 2 +C 3) tends to zero, and the optimal batch size to infinity, i.e. a large stock shortage is allowed.

Review questions

1. The concept of purchasing logistics.
2. Purchasing process.
3. Types of requirements for materials.
4. Methods for determining needs.
5. Material support based on planned targets.
6. Determining the economic order quantity.
7. Calculation of the optimal size of the produced lot.
8. Economical order quantities when allowing for shortages and providing bulk discounts.

(2.1.6)