For the conditions of serial and small-scale production, the annual program for the release of the product is not carried out all at once, but is divided into batches. Lot of details- this is the number of parts that are simultaneously launched into production. The breakdown into batches is explained by the fact that the customer often does not need the entire annual program at once, but needs a uniform flow of ordered products. Another factor is the reduction of work in progress: if it is necessary to assemble, for example, 1000 gearboxes, then the production of 1000 shafts No. 1 will not allow to assemble a single gearbox until at least one set is available.
The batch size of parts affects:
1. On process performance and his cost price due to the share of preparatory and final work time (T p.z.) for one product
t piece-to. = t pcs + T p.z. / n , (8.1)
where t piece-to. - piece-calculation time for a technological operation; t pcs - piece time for a technological operation; n- lot size of parts. The larger the batch size, the less piece-calculation time for the technological operation.
Preparatory-final time (T p.z.) - this is the time to perform work to prepare for the processing of parts at the workplace. This time includes:
1. time to receive a task from the foreman of the site (operational map with a sketch of the part and a description of the processing sequence);
2. time to get acquainted with the task;
3. time to get the necessary cutting and measuring tools, technological equipment (for example, a three-jaw self-centering or four-jaw non-self-centering chuck, a drilling chuck, a rigid or rotating center, a fixed or movable steady rest, a collet chuck with a set of collets, etc.) in the tool room pantry;
4. time for the delivery of the required blanks to the workplace (with non-centralized delivery of blanks);
5. time to install the required devices on the machine and align them;
6. time to install the required cutting tools on the machine, adjust to the required dimensions when processing two to three test parts (when processing a batch of parts);
7. time for the delivery of processed parts;
8. time for cleaning the machine from chips;
9. time to remove attachments and cutting tools from the machine (if not used in the next work shift);
10. time to check in fixtures, cutting and measuring tools (which will not be used on the next work shift) in the tool pantry.
Typically, the preparatory and final time is from 10 to 40 minutes, depending on the accuracy and complexity of processing, the complexity of aligning fixtures and adjusting to dimensions.
2. For the area of the workshop: The larger the batch, the more storage space is required.
3. On product cost through unfinished production: the larger the batch, the larger the work in progress, the higher the cost of production. How more cost materials and semi-finished products, the greater the impact of work in progress on the cost of production.
The batch size of parts is calculated by the formula
n = N´ f/F , (8.2)
where n– batch size of parts, pcs.; N- the annual program for the manufacture of all parts of all groups, pieces; F- the number of working days in a year; f- the number of days of stock to store parts before assembly.
In this way, N/F– daily release program, pcs. Number of days of stock to hold parts before assembly f= 2…12. The larger the size of the part (more space required for storage), the more expensive the material and manufacturing (more money required, more to give back on loans), the less the number of days of stock to store parts before assembly is set ( f= 2..5). On practice f= 0.5…60 days.
In-line production is characterized by a start-up cycle and an exhaust cycle.
t h =F d m/N zap, (8.3)
where t h - start cycle, F d m- the actual fund of equipment time for the corresponding shift work m, N zap - a program for launching blanks.
The release cycle is defined in the same way.
t in =F d m/N vyp, (8.4)
where N issue - program for the release of parts.
Due to the inevitable appearance of defects (between 0.05% and 3%), the launch program should be larger than the release program by an appropriate proportion.
Production type:
Output volume - the number of products of certain names and sizes manufactured or repaired by the enterprise during the planned time interval.
Release program - a list of products manufactured at the enterprise, indicating the volume of output for each item during the calendar period.
The product release cycle is understood as the time interval between the release of two successive machines, parts or blanks.
That is, the release cycle is the length of time required to manufacture one part with 100% completion of the release program. When designing technological processes the value of the release cycle is determined by the formula:
The actual annual fund of equipment operation, hour;
m is the number of work shifts;
N is the annual product release program, pcs.
Coefficient definition.
The serialization coefficient shows the number various operations assigned to one machine, and is calculated by the formula:
Tact of production of products, min;
Piece time for operations, min.
The criterion for serialization is the coefficient of consolidation of operations () - the ratio of the number of all technological operations performed or to be performed within a month to the number of jobs.
There are three main types of production: single, serial and mass. Values = 21-40 are typical for small-scale production, 11-20 for medium-scale production, and 2-10 for large-scale production.
Single production is characterized by a small volume of production of identical products, remanufacturing which are usually not provided.
It is this kind of production that is typical for technical service enterprises, repair shops and mechanical repair shops of timber industry enterprises.
Serial production is characterized by a limited range of products manufactured or repaired in periodically repeated batches and a relatively small output. Depending on the number of products in a batch or series, small-batch, medium-batch or large-batch production is distinguished.
Mass production is characterized by a large volume of products produced continuously for a long time. Most workplaces perform one constantly repetitive operation (=1).
Comparative technical and economic characteristics of production types are presented in Table. four.
Table 4. - Comparative technical and economic characteristics of production types:
|
Production types |
|||
|
unit |
serial |
mass |
|
|
Product range |
Unlimited |
limited series |
One name |
|
Nomenclature constancy |
Doesn't repeat |
Repeats periodically |
Constant release of products of a narrow range |
|
Job specialization |
Missing. Miscellaneous operations |
Periodically recurring operations |
One repetitive operation |
|
Operations pinning coefficient () |
Small-scale 20…40 |
Medium series 10.. 20 Large series 1…10 |
|
|
Equipment |
Universal |
Universal, CNC, Specialized |
Mainly special |
|
Location of production (technological) equipment |
Technological principle (by groups of machines) |
Subject and technological principle (by groups, by sections, by technological process) |
Subject principle on the technological process |
|
Technological equipment (devices, cutting and measuring tools, etc.) |
Universal, standard normalized and unified. |
Standard, normalized and specialized. Versatile and ultimate. |
Special and normalized. Ultimate and Special |
|
Detailing the development of technological documentation |
Route |
Route operating room |
Detailed route-operational up to the development of individual techniques |
|
Qualification of key workers |
Medium, high on CNC machines |
Low on production lines, high on GAL |
|
|
Product cost |
|||
|
The production cycle |
Long |
Minimum |
|
|
Labor productivity |
low |
Maximum |
|
|
Labor rationing |
Experimental-statistical |
Estimated and experimental-statistical |
Estimated with experimental verification |
The type of production has a decisive influence on the efficiency of the use of enterprise resources.
Pilot production belongs to an independent type. Its purpose is to produce samples, batches or series of products for research work, testing, fine-tuning the design and, on the basis of this, the development of design and technological documentation for industrial production. Pilot production products are not commercial products and usually do not go into operation.
Sometimes in articles and trainings, some basic production concepts are called differently. The source of confusion seems to be translations of foreign literature by people who do not have the appropriate education. And some "gurus" of production management carry these incorrect terms to the masses. Today we would like to deal with such concepts as " the production cycle” and “release stroke” with what they mean, how they are measured or calculated.
We have chosen these two concepts, as they are sometimes confused with each other. But, before moving on to strict definitions, we would like to make a reservation that we will only talk about those types of industries that are found in the furniture industry.
Consider the classic simplest sequence of parts passing through the production chain in the manufacture of furniture cases: cutting, edge banding, additive (drilling), commissioning (sorting by orders), packaging of parts with the addition of accessories or assembly of the case, shipment or storage.
Each operation from this process starts only after the previous operation is completed. Such a process is called sequential. And here we come to the definition of a cycle. In general, a cycle is a sequence of events, processes or phenomena that repeats in time. For production, this is a sequence of technological operations. The total time of such operations in a sequential manufacturing process is the cycle time or cycle time.
Often in the literature and even in the standards, a cycle is called not the sequence of events itself, but its duration. For example, say that the cycle is 36 hours. In our opinion, it is more correct to say that the duration (or time) of the cycle is 36 hours, the cycle lasts 36 hours. But we will not judge strictly, it is much more important that something completely different is not called a cycle.
Once again, the duration of the product manufacturing cycle as a whole or part of it is the calendar period of time during which this object of labor goes through all the stages from the first operation (cutting) to shipment or delivery to the warehouse of the finished product (assembled body or packages of finished panels with fittings) .
The cycle can be depicted graphically in the form of a step diagram - a cyclogram. Figure 1 shows a cyclogram of the serial production process of a part, consisting of 5 operations, each of which lasts 10 minutes. Accordingly, the cycle time is 50 minutes.
It is important to note that the cyclogram can display the sequence of operations for processing both one part and the sequence of manufacturing the product as a whole. It all depends on the level of detail with which we consider the process. For example, we can take into account the total installation time of a cabinet, or we can decompose this process into separate components - connecting the bottom and top with side walls, mounting the back wall, hanging facades. In this case, we can talk about the operating cycle. A separate cyclogram can be built for it, and then the overall production cycle will consist like a nesting doll - of internal mini-cycles.
Some novice furniture makers make the following mistake. Wanting to determine the productivity of future production and the cost of production, they time the operations for the manufacture of any product, sum up the time obtained and try to divide the duration of the shift of 480 minutes by the estimated cycle time. However, in real production, things are not so simple.
First, the parts are processed not one at a time, but in batches. Therefore, until all the parts from this batch are processed, the rest can lie in anticipation. These are the so-called batch breaks and their duration must be taken into account when determining the total processing time.
In addition, after finishing the processing of one part (or batch), the worker does not turn off the machine and does not leave. He starts processing the next part (or batch). Figure 2 shows an example of a cyclogram, which shows that as soon as a part is transferred to the next operation, the production of the next part (for the same or another product) immediately begins at this workplace. For clarity, the periods of processing of various parts are shown in different colors.
In Figure 2, all operations last exactly 10 minutes. The process of processing each part (product) is represented by a colored “ladder”, while the steps of the “ladder” of a different color are tightly “pressed” to each step of this ladder, since each next part is processed without delay.
But what happens if some operations are slower or faster than others? In figure 3, operation 2 lasts not 10, but 20 minutes. And no matter how hard we try to “compress” the multi-colored “stairs”, that is, the processing cycles of sequentially processed parts (products), they “rest” against each other with the longest steps. And between the other steps, there are gaps - these are breaks in inter-operational expectations.
These breaks are of two types. The next one after a long operation is quickly released and idle waiting for details. And the previous one is waiting for the release of the next machine. At the same time, in the previous operation, nothing prevents the processing of the following parts from continuing, however, this creates an excess of heterogeneous workpieces before the slow operation and leads to an increase in the volume of work in progress.
For example, a part requires edging on only two longitudinal sides, but at the same time it has a very large number of holes in the filler operation. Therefore, the part that comes out of the edgebander has to wait until the drilling machine is free. If the edge banding machine continues to work, then soon mountains of workpieces will appear in front of the additive site.
The opposite situation is also possible - the edges are lined on all four sides of the part, moreover, with material of different thicknesses with rounded corners, and only a couple of holes need to be made on the additive. As a result, the drilling machine is released earlier and idles while waiting for the next parts to arrive.
If the processing of the next batch of parts requires equipment adjustment, then the time for this procedure must also be taken into account when calculating the cycle time. In some industries, setup times can last hours or even days. For furniture makers, this is usually a few minutes, and if CNC equipment is used, the changeover time can be practically reduced to zero.
And, finally, there are breaks between shifts, for cleaning, for lunch, smoke breaks, a night break. Since the production cycle in the furniture industry usually lasts several days, such interruptions will also affect its duration.
The cycle time for different processes is different. As a rule, the production of cases requires from 1 to 5 days (depending on the batch size), for complex products with a variety of technologies and materials (painting, drying, veneering, working with solid wood) it may take 2-3 weeks.
We have described the simplest sequential process above. However, if we turn to real experience furniture production, we will see that the finished product consists not only of the body, but also of facades, glassware, metal, decor. These parts are made in other areas and these processes can be performed in parallel in time. Total time production in this case, determine the longest cycle. As a rule, this is the time for the manufacture of painted facades or solid wood parts.
In case we use the Just In Time (JIT) production principle, it is important to get all the parts from the parallel process by the time of packaging, so complex facades begin to be manufactured long before an order is sent to the shop for the production of simple ones. case manufacturing.
Let's go back to our sequential process of making cases. If the product design calls for panels with curved edges, the process becomes more complicated. The cutting parts go all together, but then some of the parts go to CNC machining centers, where figured parts are formed, which are transferred to edge banding machines for "curvilinear". A nesting operation can also be used, when non-rectangular parts are cut directly from full-size slabs. At the same time, in order to increase useful output sometimes a part of rectangular parts is added to the cutting maps, which are then returned to the stream for facing straight edges.
Thus, some of the operations in such a thread are performed sequentially, and some are performed in parallel. Such a process is called parallel-sequential (sometimes vice versa - serial-parallel). It is more difficult to calculate the cycle time for this case - you have to take into account simultaneous processing and simple summation does not work here anymore. It is most convenient to carry out the calculation on the basis of the analysis of cyclograms of processes. In more complex cases, it is built network model process.
Let's return to the cyclogram in Figure 2. It is obvious that at the output of the production process every 10 minutes we get a finished part or product. This time is called the release stroke. This is the interval between the manufacture of this and the next part (kit, package, product). In the above example, the cycle coincides with the duration of each of the 5 operations.
If the operations differ in time, then the cycle is determined by the slowest of them. In Figure 3, the cycle is dictated by operation 2. That is, despite the fact that all operations except the second last 10 minutes, we can receive finished products only every 20 minutes.
Value reverse tact output is called rhythm. This is the number of parts produced per unit of time.
Speaking of tact and rhythm, you must always understand what units we are talking about - individual parts, batches, kits for one product, kits for one order.
A takt can also be called the time interval between the release of shift (daily) tasks. If we analyze the progress of a shift task in sections, then as a rule one can see that this volume of parts moves unevenly, stretching in space and sometimes mixing with parts from other applications. It is very important to achieve such a clear rhythm of production, so that on each day of the week it is clear in which area of the shop the parts put into production on a certain day should be located.
Thus, we cannot give an unambiguous answer to the question of whether production is fast. At the exit, we can have a very short cycle - relatively speaking, each cabinet can leave the factory every minute. But at the same time, in production, the same cabinet can “freeze” up to several weeks. Or maybe a short cycle, that is, what we sawed in the morning is already shipped in the form of finished products in the evening. However, the number of products produced per day may be insignificant.
Strict definitions of tact, rhythm and cycle can be found in GOST 3.1109 82. However, it is important not to remember word for word the definition of this or that term, but to understand its meaning and role in the evaluation of the technological process.
Production characteristic
Working hours and time funds
The mode of operation includes the number of working days per year, excluding weekends and holidays, with two shifts per day, because. an automated section is being developed. The full calendar annual fund of time shows the number of hours in a year 24363=8670h.
Excluding weekends and holidays, based on a five-day working week lasting 41 hours, we get the nominal fund of time FN = 4320 hours.
We take into account equipment downtime for repairs, FD - the actual annual fund of equipment operation time for 2-shift operation.
PD = 3894 hours.
Determination of the release cycle
To justify the organization of the production process and determine the type of production, it is necessary to calculate the average production rate - and the average piece time - Tsh.sr. production of the product in the main operations.
The release cycle is determined by the formula:
(min/pcs) (3.3.1)
where Fd = 3894 hours;
Ng = 20000pcs - annual program for the production of parts;
fs = 3894 60/20000 = 11.7 min/pc
Determining the type of production
The type of production can be determined by the numerical value of the operation fixing coefficient, the calculation of which is carried out in accordance with GOST 3.11.08-74. Approximately the type of production can be determined by the value of the coefficient - Kc
where Tsht.sr - the average piece time of manufacturing the product, is determined according to the data of the current technical process.
Tsht.av. = 71.43/17 = 4.2 min.
Kzo \u003d 11.6 / 4.2 \u003d 2.7
1< Кс?10 - крупносерийное производство
Analysis of the manufacturability of the design of the part "Drive shaft"
Manufacturability - a property of the product, according to which the design of the part must comply with the use of the most advanced processing or assembly methods in the manufacture.
Rational designs of machines that provide the necessary operational requirements cannot be created without taking into account the labor intensity and material consumption of their manufacture. Compliance of the design of machines with the requirements of labor intensity and material consumption determines the manufacturability of the design. In an objective assessment of the manufacturability of the design of machines, their parts and assemblies, a number of positive factors are taken into account that determine the manufacturability of the design.
In an objective assessment of the manufacturability of the design of machines, their parts and assemblies, a number of positive factors are taken into account that determine the manufacturability of the design. These include:
The optimal shape of the part, which ensures the manufacture of the workpiece with the smallest allowance and the smallest number of machined surfaces;
The smallest weight of the machine;
The smallest amount of material used in the construction of machines;
Interchangeability of parts and assemblies with the optimal value of tolerance fields;
Normalization (standardization) and unification of parts, assemblies and their individual design elements.
The basic requirements for the manufacturability of the design of machine building parts are set out in the literature.
Part designs must consist of standard and unified structural elements (QED) or be standard as a whole. Parts must be made from standard or unified blanks. The dimensions of the part must have optimal accuracy. Surface roughness must be optimal. Physico-chemical and mechanical properties the material of the part, its rigidity, shape, dimensions must comply with the requirements of the manufacturing technology (including the processes of finishing and hardening treatment, applying anti-corrosion coatings, etc.), as well as storage and transportation.
The base surface of the part must have optimal indicators of accuracy and surface roughness, which provide the required accuracy of installation, processing and control.
Blanks for the manufacture of parts must be obtained in a rational way, taking into account the material, the given output volume and the type of production. The method of manufacturing parts should allow the simultaneous production of several parts. The design of the part must ensure the possibility of using standard and standard technological processes for its manufacture.
We will test the manufacturability of the “Drive shaft” part for manufacturability in accordance with Guidelines.
The main condition for efficiency production system is the rhythm of shipment of products in accordance with the needs of the customer. In this context, the main measure of rhythm is the takt time (the ratio of available time to the customer's established need for products). In accordance with the cycle, the workpieces are sequentially moved from process to process, and the finished product (or batch) appears at the output. If there are no big difficulties with the calculation of the available time, then the situation is not unambiguous with the determination of the number of planned products.
In modern production conditions, it is extremely difficult to find a single-product enterprise that would produce only one product name. One way or another, we are dealing with the release of a range of products that can be either of the same type or completely different. And in this case, a simple recalculation of the number of products to determine the volume of production is not acceptable, since the products different kind cannot be mixed and counted as part of the total.
In some cases, to facilitate the accounting and understanding of the overall dynamics of productivity, enterprises use certain qualitative indicators that are to some extent inherent in the products produced. So, for example, finished products can be taken into account in tons, square, cubic and linear meters, in liters, etc. At the same time, the release plan in this case is set in these indicators, which, on the one hand, allows you to set specific, digitized indicators, and, on the other hand, the connection between production and the need of the customer who wants to receive a certain period products according to the nomenclature. And often a paradoxical situation arises when the plan in tons, meters, liters is completed during the reporting period, and the customer has nothing to ship, since there are no necessary products.
In order to carry out accounting and planning in a single quantitative indicator, while not losing touch with the order nomenclature, it is advisable to use natural, conditionally natural or labor methods for measuring output.
The natural method, when output is calculated in units of output, is applicable in limited conditions for the production of one type of product. Therefore, in most cases, a conditionally natural method is used, the essence of which is to bring the entire variety of similar products to a certain conventional unit. The role of a quality indicator by which products will be correlated can be, for example, fat content for cheese, heat transfer for coal, etc. For industries where it is difficult to single out a quality indicator for comparing and accounting for products, the labor intensity of manufacturing is used. The calculation of the volume of production by the labor intensity of manufacturing each type of product is called the labor method.
The combination of labor and conditionally natural methods of measuring the volume of production in accordance with a certain nomenclature most accurately reflects the needs of the majority industrial productions in accounting and planning.
Traditionally, a typical representative (the most massive) of manufactured products with the least labor intensity is chosen as a conventional unit. To calculate the conversion factor (k c.u. i) are related technologically to the complexity i th item of the nomenclature and the item that is accepted as conditional:
k c.u. i— coefficient of conversion to arbitrary units for i-th product;
Tr i— technological complexity i-th product, standard hour;
Tr c.u. - technological labor intensity of the product accepted as a conditional unit.
After each product has its own conversion factors into conventional units, it is necessary to determine the quantity for each of the positions of the nomenclature:
OP c.u. - the volume of production of conventional units, pieces;
- the sum of the products of the conversion coefficient in conventional units for i-th product and planned production volume i-th product;
n- the number of positions in the nomenclature.
To illustrate the methodology, consider an example in which it is necessary to manufacture three types of products (see Table 1). When converted into conventional units, the output plan will be 312.5 pieces of products A.
Table 1. Calculation example
|
Product |
Quantity, pcs. |
Labor intensity, standard hour |
Amount of c.u., pcs. |
|
Based on an understanding of the total volume of production in the planned period, it is already possible to calculate the takt time (the main indicator for synchronizing and organizing production flows) using the well-known formula:
BT c.u. - takt time for a conventional unit, minutes (seconds, hours, days);
OP c.u. - the volume of production of conventional units, pieces.
It should be noted that an indispensable condition for using the labor method is the validity of the norms used in the calculations, their compliance with the actual time spent. Unfortunately, in most cases this condition cannot be met for various reasons, both organizational and technical. Therefore, the use of the labor method can give a distorted picture of the dynamics of production volume.
However, the use of the labor method in the framework of calculating the conventional unit of measure of planned output does not have such a strict limitation. The use of even overestimated standard indicators, if the overestimation is of a systemic nature, in no way affects the results of calculations (see Table 2).
Table 2. Applicability of the method at overestimated rates
|
Quantity, pcs. |
Labor is standard, standard hour |
k c.u. i |
Amount of c.u., pcs. |
Actual labor, standard hour |
k c.u. i |
Amount of c.u., pcs. |
|
As can be seen from the above example, the final value of the output volume does not depend on the "quality" of the used normative material. In both cases, the volume of production in arbitrary units remains unchanged.
Calculation of available time for the selected item
In addition to the conditionally natural method, an approach is proposed to determine the available time for the selected range of manufactured products in the event that the calculation of the takt time is not performed for the entire production volume. In this case, there is a need to allocate from the total available time a share that will be used for the production of the selected product.
To calculate the total planned production volume is used labor method calculation of labor productivity, both for the entire volume of production, and for the nomenclature, the takt time of which is supposed to be set in the future:
OP tr - the volume of production in the labor dimension, norm-hour (man-hour);
Tr i- normative labor intensity i-th product, norm-hours (man-hours);
OP i- release plan i-th product;
k v.n. i- the coefficient of compliance with the norms.
It is important that in this case the coefficient of compliance with the norms is used in order to ensure that the calculated data correspond to the real production possibilities. This coefficient can be calculated both for each type of product, and for the entire volume of production.
DV i- time available for i-th product;
OP tr i- volume of production i-th product in the labor dimension, standard hour (man-hour);
DV - total available time, min. (hours, days).
For verification, the total available time is the sum of the calculated shares for each item, determined by the production plan:
Table 3. Example of calculating available time
|
Product |
Release plan, pcs. |
Labor, standard hour |
Rate of fulfillment of norms |
Release plan, standard hour |
Available time |
|
Nomenclature 1 | |||||
|
Product 1.1. | |||||
|
Product 1.2. | |||||
|
Product 1.3. | |||||
|
Nomenclature 2 | |||||
|
Product 2.1. | |||||
|
Product 2.2. | |||||
|
1483 |
1500 |
OD 1 = 100 × 2.5 × 1.1 + 150 × 2 × 1.1 + 200 × 1.5 × 1.1 = 935 standard hours
OP 2 = 75 × 3 × 1.1 + 125 × 2.2 × 1.1 = 548 standard hours
hour.
hour.
As a result, we calculate the takt time for Nomenclature 1, as a conditional unit we take Product 1.3.:
PCS.
These approaches to the calculation of the main production indicators make it possible to quickly and close to reality make basic calculations to determine the target takt time. And in cases where there is an extensive range of typical products, these methods make it possible to balance and synchronize production based on existing data on the cycle time of each process and the takt time set by consumer demand.
