Flow production: organizational and economic characteristics. Let's understand the terms: cycle and tact. Definition of the production cycle in mechanical engineering by tact.
Takt time is one of the key principles of lean manufacturing. Takt time sets the speed of production, which must exactly match the existing demand. Takt time in production is similar to the human heart rate. Takt time is one of the three elements of a just-in-time system (along with in-line production and the pull system), which ensures uniform workload and determines bottlenecks. To design manufacturing cells, assembly lines, and create lean manufacturing, an absolute understanding of takt time is essential. This article discusses situations in which an artificial increase or decrease in takt time is possible.
What is takt time? The word tact comes from the German takt, which means rhythm or beat. The term beat time is related to musical terminology and refers to the rhythm that the conductor sets so that the orchestra plays in unison. In a lean production system, this concept is used to ensure the rate of production with the average rate of change in the level of consumer demand. Takt time is not a numerical indicator that can be measured, for example, using a stopwatch. The concept of takt time must be distinguished from the concept of cycle time (the time it takes to complete one operating cycle). The cycle time can be less than, greater than, or equal to the takt time. When the cycle time of each operation in a process becomes exactly equal to the takt time, one-piece flow occurs.
There is the following formula for calculation:
Takt time = available production time(per day) / consumer demand (per day).
Takt time is expressed in seconds per product, indicating that consumers purchase products once every certain amount of time in seconds. It is incorrect to express takt time in units per second. By setting the pace of production in accordance with the rate of change in consumer demand, lean manufacturers thereby ensure that work is completed on time and reduces waste and costs.
Reduced takt time. The purpose of determining takt time is to work according to customer demand. But what happens if takt time is artificially reduced? The work will be completed faster than required, resulting in overproduction and excess inventory. If other tasks are unavailable, workers will waste time waiting. In what situation is such an action justified?
To demonstrate a similar situation, let’s calculate the required number of workers on an assembly line on which the flow of single products is carried out:
Group size = sum of manual cycle times / takt time.
Thus, if the total cycle time for a process is 1293 s, then the group size will be 3.74 people (1293 s / 345 s).
Since it is impossible to employ 0.74 people, the number 3.74 must be rounded. Three people may not be enough to keep production pace as customer demand changes. In this case, improvement activities must be carried out to reduce the cycle time of manual operations and eliminate waste in the process.
If the cycle time is fixed, then it is possible to round up by reducing the takt time. Takt time can be reduced if available production time decreases:
3.74 people = 1293 s per product / (7.5 hours x 60 min x 60 s / 78 parts);
4 people = 1293 s / (7 hours x 60 min x 60 s / 78 parts).
By employing four people, reducing takt time and producing the same volume in less time, the team's workload is evenly distributed. If these four people can keep production up to speed with customer demand in less time than usual, they will need to be rotated or assigned to process improvement issues.
Increasing takt time: 50 second rule. In the example above, we show when takt time can be reduced to improve efficiency. Let us now consider the case where the takt time should be increased.
A rule of thumb is that all repetitive manual operations should have a cycle time of at least 50 seconds (start to start time). For example, the operation of company assembly lines Toyota determined by the takt time 50 60 s. If the company needs to increase production volume by 5-15%, then introduce extra time or in some cases using multiple assembly lines configured for longer takt times (for example, two lines with a takt time of 90 s instead of one line with a takt time of 45 s).
There are four reasons why the 50 second rule is important.
- Performance. If the takt time is small, then even seconds spent as a result of unnecessary movements result in large losses of cycle time. Losing 3 s out of 30 s cycle time results in a 10% reduction in productivity. Losing 3 seconds out of a 60 second cycle results in a 5% reduction in performance. Losing 3 s out of a 300 s cycle to only 1%, etc. Therefore, if the takt time is a larger value (50 s or more), then this will not be a significant loss in productivity.
Using one assembly line with a large number of operators working in a short takt time (eg 14 s) saves on investment costs (number of lines), but will result in higher operating costs. We have found that assembly lines designed to operate at speeds of 50 seconds or more are 30% more productive than lines with low takt times. - Safety and ergonomics. Performing the same manual tasks for a short period of time can lead to fatigue and muscle pain due to repetitive strain. When various operations are performed over a longer period of time (for example, in 60 seconds instead of 14 seconds), the muscles have time to recover before starting the operation again.
- Quality. By performing a wide range of responsibilities (for example, five operations instead of two), each employee himself becomes an internal consumer of every operation except the last one. If a worker performs five operations, it forces him to pay more attention to quality, since an unsatisfactory result in operation 3 will be reflected in the performance of operation 4 and, therefore, will not be passed on unnoticed to the next stage.
- Attitude to the work performed. It has been noted that workers experience greater job satisfaction when performing a task repeatedly, For example every 54 s, not 27 s. People enjoy learning new skills, they experience less fatigue from repetitive movements, but most importantly, employees feel that they are making a personal contribution to the creation of the product, and are not just doing mechanical work.
Takt time and investment. The importance of the 50 second rule can be illustrated by the example of a company engaged in the production and assembly of pumps for industry. The company used one long assembly line to create its product. As a result of increasing customer demand and additional testing requirements, the design of a new assembly line became necessary. At this stage, the company decided to apply lean manufacturing principles. One of the first steps was to determine takt time.
The takt time for this product of 40 s was calculated based on greatest demand. Considering the 50 second rule, the engineers responsible for this project, decided to design either one assembly line with a takt time of 80 s, operating in two shifts, or two conveyors with a takt time of 80 s, operating in one shift. Work on designing the assembly line was offered to several engineering companies. According to their estimates, the design of one line required from 280 to 450 thousand dollars. The development of two lines meant doubling the equipment units and the amount of initial investment capital. However, by using two conveyors, each could be configured to produce specific types of products, allowing production to become more flexible. In addition, increased productivity, employee satisfaction, and reduced safety and quality costs can offset the cost of designing an additional line.
Thus, sticking to simple rule, according to which the speed of any manual operation should not be less than 50 seconds, losses can be avoided. When designing lean manufacturing processes, it is necessary to use the 3P (Production Preparation Process) method 1 and conduct a thorough analysis of takt time.
1 A method of designing a lean manufacturing process for a new product or fundamentally redesigning a manufacturing process for an existing process when there is a significant change in product design or demand. For more information, see: Illustrated Glossary of lean manufacturing/ Ed. The Marchwinskis and John Shook: Trans. from English M.: Alpina Business Books: CBSD, Center for the Development of Business Skills, 2005. 123 p. Note ed.
Based on the article Job Miller, Know Your Takt Time
and books by James P. Womack, Daniel T. Jones Lean Manufacturing.
How to get rid of losses and achieve prosperity for your company.
M.: Alpina Business Books, 2004
prepared by V.A. Lutseva
Calculation of the release stroke. Determination of the type of production. Characteristics of a given type of production
The dependence of the type of production on the volume of production of parts is shown in Table 1.1.
If the part weight is 1.5 kg and N = 10,000 parts, medium-scale production is selected.
Table 1.1 - Characteristics of the type of production
|
parts, kg |
Type of production |
||||
|
Single |
Small-scale |
Medium production |
Large-scale |
Mass |
|
Serial production is characterized by a limited range of manufactured parts, manufactured in periodically repeating batches and a relatively small volume of output than in single production.
Main technological features of mass production:
1. Assigning several operations to each workplace;
2. The use of universal equipment, special machines for individual operations;
3. Arrangement of equipment by technological process, type of part or groups of machines.
4. Wide Application specialist. Devices and tools.
5. Compliance with the principle of interchangeability.
6. Average qualifications of workers.
The release stroke value is calculated using the formula:
where F d is the actual annual operating time of the equipment, h/cm;
N - annual parts production program, N=10,000 pcs.
Next, you need to determine the actual time fund. When determining the operating time fund for equipment and workers, the following initial data were accepted for 2014 with a 40-hour work week, Fd = 1962 h/cm.
Then according to formula (1.1)
The type of production depends on two factors, namely: on the given program and on the complexity of manufacturing the product. Based on the given program, the product release cycle t B is calculated, and the labor intensity is determined by the average piece (piece-calculation) time T SHT for operations operating in production or similar technological process.
In mass production, the number of parts in a batch is determined by the following formula:
where a is the number of days for which it is necessary to have a supply of parts, na=1;
F - number of working days in a year, F=253 days.
Analysis of requirements for accuracy and roughness of machined surfaces of a part and description of accepted methods for ensuring them
The “Intermediate shaft” part has low requirements for the accuracy and roughness of the machined surfaces. Many surfaces are processed to the fourteenth precision level.
The part is technologically advanced because:
1. All surfaces are provided with free access for tools.
2. The part has a small number of exact dimensions.
3. The workpiece is as close as possible to the shape and dimensions of the finished part.
4. The use of high-performance processing modes is allowed.
5. There are no very precise sizes, except: 6P9, 35k6, 30k6, 25k6, 20k6.
The part can be obtained by stamping, so the configuration of the outer contour does not cause difficulties in obtaining the workpiece.
From a machining point of view, a part can be described as follows. The design of the part allows it to be processed on pass, nothing interferes this species processing. There is free access of the tool to the surfaces being processed. The part provides the possibility of processing on CNC machines, as well as on universal machines, and does not present difficulties in positioning, which is due to the presence of planes and cylindrical surfaces.
It is concluded that from the point of view of the accuracy and cleanliness of the machined surfaces, this part generally does not present significant technological difficulties.
Also, to determine the manufacturability of a part, use
1. Accuracy coefficient, CT
where K PM is the accuracy coefficient;
T SR - average quality of accuracy of part surfaces.
where T i is the quality of accuracy;
n i - number of surfaces of a part with a given quality (Table 1.2)
Table 1.2 - Number of surfaces of the “Intermediate shaft” part with this quality
Thus
2. Roughness coefficient, KSh
where KSh is the roughness coefficient,
Ra SR - average roughness.
where Ra i is the surface roughness parameter of the part;
m i is the number of part surfaces with the same roughness parameter (Table 1.3).
Table 1.3 - Number of surfaces of the “Intermediate shaft” part with a given roughness class
Thus
The coefficients are compared to unity. The closer the coefficient values are to unity, the more technologically advanced the part. From the above we can conclude that the part is quite technologically advanced.
1.Calculation of production volume, production cycle. Determining the type of production, launch batch size.
Part output volume:
Where N CE =2131 pieces per year – product production program;
n d =1 piece – the number of assembly units of a given name, standard size and design in one assembly unit;
α=0% – percentage of products produced for spare parts;
β=2%п – probable defect of procurement production.
Part release stroke:
font-size:14.0pt; font-family:" times new roman>Where
F o =2030 hours – actual annual operating time of the equipment;m =1 shift – number of work shifts per day.
Let's determine the type of production by the serialization coefficient.
Average piece operation time basic version Tshsr=5.1 minutes. According to the basic option:
Conclusion. Since the calculated coefficient
kc is in the range from 10 to 20, this allows us to conclude that the production is medium-scale.Number of products:
Where is tx =10 days – the number of days during which the stock is stored;
Fdr=250 days – number of working days in a year.
We accept n d = 87 pieces.
Number of launches per month:
font-size:14.0pt; font-family:" times new roman> We accept i = 3 launches.
Specifying the number of parts:
font-size:14.0pt; font-family:" times new roman> We accept n d = 61 pieces.
2.Development of the technological process for machining the body.
2.1.Service purpose of the part.
The “Body” part is the base part. The base part defines the position of all parts in the assembly unit. The body has a rather complex shape with windows for introducing tools and assembled parts inside. The housing does not have surfaces that ensure its stable position in the absence of assembly. Therefore, during assembly it is necessary to use a special device. The design of the rotary damper does not allow assembly while the position of the base part remains unchanged.
The part operates under high pressure conditions: operating pressure, MPa (kgf/cm2) – ≤4.1 (41.0); operating temperature, 0С – ≤300. The selected design material, Steel 20 GOST1050-88, meets the requirements for the accuracy of the part and its corrosion resistance.
2.2.Analysis of the manufacturability of the part design.
2.2.1. Analysis of technological requirements and accuracy standards and their compliance with the official purpose.
The designer assigned a row to the body technical requirements, including:
1. Tolerance for the alignment of holes Ø52Н11 and Ø26Н6 relative to the common axis Ø0.1mm. Displacement of hole axes according to GOST. These requirements provide normal conditions work, minimal wear and, accordingly, the nominal service life of the sealed rings. It is advisable to process these surfaces from the same technological bases.
2.Metric thread according to GOST with tolerance range 6N according to GOST. These requirements determine the standard thread parameters.
3. Tolerance for the symmetry of the axis of the hole Ø98Н11 relative to the general plane of symmetry of the holes Ø52Н11 and Ø26Н8 Ø0.1mm. These requirements ensure normal operating conditions, minimal wear and, accordingly, a nominal service life of the sealed rings. It is advisable to process these surfaces from the same technological bases.
4. Positional tolerance of four holes M12 Ø0.1mm (tolerance dependent). Metric thread according to GOST. These requirements determine the standard thread parameters.
5. Unspecified maximum deviations of dimensions H14,
h 14, ± I T14/2. Such tolerances are assigned to free surfaces and correspond to their functional purpose.6. Perform hydrotests for strength and density of the material at pressure Rpr. = 5.13 MPa (51.3 kgf/cm2). The holding time is at least 10 minutes. Tests are necessary to verify the tightness of gasket and stuffing box seals.
7. Mark: steel grade, heat number.
The assignment of accuracy standards to individual surfaces of a part and their relative position is associated with functional purpose surfaces and the conditions in which they work. Let us give a classification of the surfaces of the part.
Actuating surfaces are absent.
Main design bases:
Surface 22. Deprives four degrees of freedom (double guide explicit base). 11th grade accuracy, roughness
R a 20 µm.Surface 1. Deprives the part of one degree of freedom (support base). 8th grade accuracy, roughness R a 10 µm.
The basing scheme is not complete, the remaining degree of freedom is rotation around its own axis (it is not necessary to deprive this degree of freedom by basing from the point of view of fulfilling the official purpose).
Auxiliary design bases:
Surface 15. Threaded surface, responsible for locating the studs. Design auxiliary double guide explicit base. Thread accuracy 6H, roughness R a 20 µm.
Surface 12 defines the position of the sleeve in the axial direction and is the mounting base. 11th grade accuracy, roughness R a 10 µm.
Surface 9 is responsible for the accuracy of the bushing in the radial direction - a design auxiliary double support implicit base. 8th grade accuracy R a 5 µm.
Figure 1. Numbering of surfaces of the “Body” part
Figure 2. Theoretical scheme for basing a part in a structure.
The remaining surfaces are free, so they are assigned accuracy of 14th grade, R a 20 µm.
Analysis of technological requirements and accuracy standards showed that the dimensional description of the part is complete and sufficient and corresponds to the purpose and operating conditions of individual surfaces.
2.2.2. Analysis of the design shape of the hull.
The “Case” part refers to body parts. The part has sufficient rigidity. The part is symmetrical.
Part weight – 11.3 kg. Part dimensions – diameter Ø120, length 250mm, height 160mm. The weight and dimensions do not allow it to be moved from one workplace to another or reinstalled without the use of lifting mechanisms. The rigidity of the part allows the use of fairly intense cutting conditions.
Part material Steel 20 GOST1050-88 - steel with fairly good plastic properties, therefore, the method of obtaining the workpiece is either stamping or rolling. Moreover, considering design features parts (difference in outer diameters 200-130mm), stamping is the most appropriate. This method of obtaining a workpiece ensures the waste of a minimum volume of metal into chips and the minimum labor intensity of machining the part.
The design of the housing is quite simple in terms of machining. The shape of the part is formed mainly from surfaces of simple shape (unified) - flat end and cylindrical surfaces, eight threaded holes M12-6N, chamfers. Almost all surfaces can be processed with standard tools.
The part contains untreated surfaces. There are no discontinuous treated surfaces. The treated surfaces are clearly demarcated from each other. The outer diameters decrease in one direction, the hole diameters decrease from the middle to the ends of the part. Cylindrical surfaces allow processing for a pass, the tool can work for a pass Ø98Н11 and Ø26Н8, and a stop Ø10.2 with a depth of 22mm.
The design has a fairly large number of holes: stepped central hole Ø52H11, Ø32, Ø26H8, threaded off-central holes M12. Which requires repeated reinstallation of the workpiece during processing. Chip removal conditions are normal. When machining with an axial tool, the entry surface is perpendicular to the tool axis. The tool penetration conditions are normal. The operating mode of the instrument is unstressed.
The design of the part makes it possible to process a number of surfaces with tool sets. It is not possible to reduce the number of processed surfaces, since the accuracy and roughness of a number of surfaces of the part cannot be ensured at the stage of obtaining the workpiece.
There is no single technological base for the part. During processing, reinstallation will be required to drill the M12 hole, and also control of alignment will require the use of special devices for basing and securing the part. No special equipment is required to manufacture the housing.
Thus, the structural form of the part as a whole is technologically advanced.
2.2.3.Analysis of the dimensional description of the part.
The design dimensional base of a part is its axis, from which all diametrical dimensions are specified. This will make it possible to ensure the principle of combining the bases when using the axis as a technical base. This can be realized during turning using self-centering devices. Such a technological base can be implemented with external cylindrical surfaces of sufficient length or a hole with a cylindrical length of Ø108 and a hole of Ø90H11 with a length of 250 mm. In the axial direction in the dimensional description, the designer used the coordinate method of specifying dimensions, which ensures the implementation of the principle of combining bases during processing. For surfaces machined with a dimensional tool, the dimensions correspond to the standard tool size - eight M12 threaded holes.
Analyzing the completeness of the dimensional description of the part and its service purpose, it should be noted that it is complete and sufficient. Accuracy and roughness correspond to the purpose and operating conditions of individual surfaces.
General conclusion. Analysis of the manufacturability of the “Body” part showed that the part as a whole is manufacturable.
2.3.Analysis of the basic technological process of processing the hull.
The basic technological process includes 25 operations, including:
Operation No. | Operation name | Process time |
Quality Control Control. Storage area for workpieces. | ||
Horizontal boring. Horizontal boring machine | 348 minutes |
|
Quality Control Control | ||
Moving. Electric overhead crane. | ||
Locksmith's shop. | 9 minutes |
|
Quality Control Control. | ||
Moving. Electric overhead crane. | ||
Marking. Marking plate. | 6 minutes |
|
Quality Control Control. | ||
Screw-cutting lathe. Screw-cutting lathe. | 108 minutes |
|
Quality Control Control. | ||
Moving. Electric overhead crane. | ||
1.38 minutes |
||
Moving. Crane beam Q -1t. Electric car Q -1t. | ||
Quality Control Control. | ||
Marking. Marking plate. | 5.1 minutes |
|
Milling, drilling and boring. IS-800PMF4. | 276 minutes |
|
Adjustment of IS-800PMF4. | 240 minutes |
|
Moving. Crane beam Q -1t. | ||
Locksmith's shop. | 4.02 minutes |
|
Hydraulic tests. Hydraulic stand T-13072. | 15 minutes |
|
Moving. Crane beam Q -1t. | ||
Marking. Mechanic's workbench. | 0.66 minutes |
|
Quality Control Control. | ||
Total labor intensity of the basic technological process. | 1013.16 minutes |
Operations of the basic technological process are performed on universal equipment, using standard tools and equipment, with reinstallation and change of bases, which reduces the accuracy of processing. In general, the technological process corresponds to the type of production, but the following disadvantages can be noted:
For conditions of serial and small-scale production, the annual product production program is not carried out all at once, but is divided into batches. Lot of parts– this is the number of parts 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 requires a uniform supply of ordered products. Another factor is the reduction of work in progress: if, for example, 1000 gearboxes need to be assembled, then manufacturing 1000 No. 1 shafts will not allow for the assembly of a single gearbox until at least one set is available.
The batch size of the parts affects:
1. On process performance and him cost price due to the share of time of preparatory and final work (T p.z.) per product
t pcs. = t pcs + T p.z. / n , (8.1)
Where t pcs. - piece-calculation time for a technological operation; t pcs – piece time for a technological operation; n– batch size of parts. The larger the batch size, the shorter the unit costing time for the technological operation.
Preparatory-final time (T p.z.) is the time for performing work to prepare for the processing of parts at the workplace. This time includes:
1. time to receive the task from the site foreman (operational card with a sketch of the part and a description of the processing sequence);
2. time to familiarize yourself with the task;
3. time to obtain the necessary cutting and measuring tools, technological equipment (for example, a three-jaw self-centering or four-jaw non-self-centering chuck, a drill chuck, a rigid or rotating center, a fixed or movable rest, a collet chuck with a set of collets, etc.) in the tool room pantry;
4. time to deliver the required workpieces to the workplace (in case of non-centralized delivery of workpieces);
5. time to install the required devices on the machine and align them;
6. time to install the required cutting tools on the machine, adjusting to the required dimensions when processing two to three test parts (when processing a batch of parts);
7. time for delivery of processed parts;
8. time to clean the machine from chips;
9. time to remove fixtures and cutting tools from the machine (if they will not be used in the next work shift);
10. time to hand over fixtures, cutting and measuring tools (which will not be used in the next work shift) to the tool storeroom.
Typically, the preparatory and final time ranges 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 size of the workshop: The larger the batch, the more space required for storage.
3. To the cost of production through work in progress: The larger the batch, the larger the work in progress, the higher the cost of production. The higher the cost of materials and semi-finished products, the greater the impact of work in progress on production costs.
The batch size of parts is calculated using the formula
n = N´ f/f , (8.2)
Where n– batch size of parts, pcs.; N– annual production program for all parts of all groups, pcs.; F– number of working days in a year; f– the number of days of stock for storing parts before assembly.
Thus, N/F– daily graduation program, pcs. Number of days of stock to store parts before assembly f = 2…12. The larger the size of the part (more storage space is required), the more expensive the material and manufacturing (more money is required, more loans are required), the lower the number of days of stock for storing parts before assembly is set ( f = 2..5). In practice f = 0.5...60 days.
For continuous production, the starting cycle and release cycle are characteristic.
t h =F d m/N zap, (8.3)
Where t z – start stroke, F d m– actual equipment time fund for the corresponding work shift m, N zap – program for launching blanks.
The release cycle is determined similarly
t V =F d m/N issue, (8.4)
Where N issue – parts production program.
Due to the inevitable occurrence of defects (from 0.05% to 3%), the launch program must be more program release for the appropriate share.
Mechanical engineering production is characterized by output volume, product release program, and production cycle.
Product output volume- this is the number of products of certain names, standard sizes and designs manufactured or repaired by an enterprise or its division during a planned period of time (month, quarter, year). The volume of output largely determines the principles of constructing the technological process.
Installed for of this enterprise a list of manufactured or repaired products indicating the volume of production and deadlines for each item for the planned period of time is called production program .
Release stroke is the time interval through which products or blanks of a certain name, standard size and design are periodically produced.
Release stroke t, min/piece, is determined by the formula:
t = 60 F d / N,
where F d – actual time fund in the planned period (month, day, shift), h; N – production program for the same period, pcs.
The actual operating time of equipment differs from the nominal (calendar) time fund, since it takes into account the loss of time for equipment repair.
The actual operating capacity of the equipment, depending on its complexity and the number of days off and holidays with a 40-hour work week and working in two shifts in engineering production ranges from 3911 to 4029...4070 hours. The worker's time fund is about 1820 hours.
Depending on production capacity and sales opportunities, products at the enterprise are manufactured in various quantities - from single copies to hundreds and thousands of pieces. In this case, all products manufactured according to design and technological documentation without changing it are called product series .
Depending on the breadth of the range, regularity, stability and volume of product output, three main types of production are distinguished: single, serial and mass. Each of these types has its own characteristic features in the organization of labor and in the structure of production and technological processes.
Type of production is a classification category of production, distinguished on the basis of breadth of product range, regularity, stability and volume of production. In contrast to the type of production, the type of production is distinguished based on the method used to manufacture the product. Examples of types of production are foundry, welding, mechanical assembly, etc.
One of the main characteristics of the type of production is transaction consolidation ratio K z.o., which is the ratio of the number of all different technological operations O, performed or to be performed during the month, to the number of jobs P:
With the expansion of the range of manufactured products and a decrease in their quantity, the value of this coefficient increases.
Single production characterized by a small volume of production of identical products, the re-production and repair of which, as a rule, is not provided for. In this case, the technological process of manufacturing products is either not repeated at all, or is repeated at indefinite intervals. Unit production includes, for example, large hydraulic turbines, rolling mills, equipment for chemical and metallurgical plants, unique metal-cutting machines, prototypes of machines in various branches of mechanical engineering, etc.
Unit production technology is characterized by the use of universal metal-cutting equipment, which is usually located in workshops on a group basis, i.e. broken down into sections of turning, milling, grinding machines, etc. Processing is carried out with a standard cutting tool, and control is carried out with a universal measuring tool. A characteristic feature of unit production is the concentration of various operations at workplaces. In this case, one machine often performs complete processing of workpieces of various designs and from various materials. Due to the need for frequent reconfiguration and adjustment of the machine to perform new operation share of main (technological) time in general structure The standard processing time is relatively small.
Distinctive Features unit production lead to relatively low labor productivity and high cost of manufactured products.
Serial production characterized by the manufacture or repair of products in periodically repeating batches. In mass production, products of the same name or the same type in design are manufactured according to drawings that have been tested for manufacturability. Series production products are machines of an established type, produced in significant quantities. These products include, for example, metal-cutting machines, internal combustion engines, pumps, compressors, equipment for food industry etc.
Serial production is the most common in general and medium-sized mechanical engineering. In mass production, along with universal, it is widely used special equipment, automatic and semi-automatic, special cutting tools, special measuring instruments and devices.
In mass production, the average qualification of workers is usually lower than in individual production.
Depending on the number of products in a batch or series and the value of the consolidation coefficient, operations are distinguished small-scale, medium-scale and large-scale production . Such a division is quite conventional for various branches of mechanical engineering, since with the same number of machines in a series, but of different sizes, complexity and labor intensity, production can be classified as different types. The conventional boundary between the varieties of serial production according to GOST 3.1108-74 is the value of the coefficient of consolidation of operations K z.o. : for small-scale production 20< К з.о < 40, для среднесерийного – 10 < К з.о < 20, а для крупносерийного – 1 < К з.о < 10.
IN small-scale production, close to a single unit, the equipment is located mainly by type of machine - a section of lathes, a section of milling machines, etc. Machines can also be located along the technological process if processing is carried out according to a group technological process. Mainly universal means of technological equipment are used. The production batch size is usually several units. In this case, a production batch is usually called items of labor of the same name and standard size, launched into processing within a certain time interval, with the same preparatory and final time for the operation.
At the initial stage of development of the machining technological process, the batch size of parts can be determined using the following simplified formula:
where N is the number of parts of the same name and size according to annual program release of products;
t – required stock of parts in the warehouse in days; for large parts t=2...3 days; for average t=5 days; for small parts and tools t=10...30 days;
F – the number of working days in a year, is taken to be 305 days with one day off and a working day of 7 hours. and 253 days with two days of rest and a working day of 8 hours.
Conventionally, parts weighing up to 2 kg can be classified as small (or light), parts weighing up to 2 kg can be classified as medium, parts weighing from 2 to 8 kg can be classified as large (or heavy), over 8 kg.
In medium-scale production, usually called serial production, equipment is located in accordance with the sequence of workpiece processing stages. Each piece of equipment is usually assigned several technological operations, which makes it necessary to re-adjust the equipment. The production batch size ranges from several tens to hundreds of parts.
In high-volume, near-volume production, equipment is typically arranged in a process sequence for one or more parts that require the same machining process. If the product production program is not large enough, it is advisable to process workpieces in batches, with sequential operations, i.e. After processing all the blanks of a batch in one operation, this batch is processed in the next operation. After finishing processing on one machine, the workpieces are transported as a whole batch or in parts to another, while vehicles use roller tables, overhead chain conveyors or robots. Processing of workpieces is carried out on pre-configured machines, within the technological capabilities of which readjustment to perform other operations is permissible.
In large-scale production, as a rule, special devices and special cutting tools are used. Limit gauges (staples, plugs, threaded rings and threaded plugs) and templates are widely used as measuring tools, which make it possible to determine the suitability of processed parts and break them down into size groups depending on the size of the tolerance zone.
Serial production is much more economical than individual production, since equipment is better used, allowances are lower, cutting conditions are higher, jobs are more specialized, the production cycle, interoperational backlogs and work in progress are significantly reduced, a higher level of production automation, labor productivity increases, sharply decreases labor intensity and cost of products, simplifies production management and labor organization. In this case, the reserve is understood production stock blanks or components products to ensure uninterrupted execution of the technological process. This type of production is the most common in general and medium-sized engineering. About 80% of mechanical engineering products are mass-produced.
Mass production characterized by large volumes of production of products that are continuously manufactured or repaired over a long period of time, during which one work operation is performed at most workplaces. Parts are usually made from blanks, the production of which is carried out centrally. The production of non-standard equipment and technological equipment is carried out in a centralized manner. The workshops, which are an independent structural unit, supply them to their consumers.
Mass production is economically feasible when producing enough large quantity products, when all material and labor costs associated with the transition to mass production quickly pay off and the cost of the product is lower than in mass production.
Mass production products are products of a narrow range, unified or standard type, produced for wide distribution to consumers. These products include, for example, many brands passenger cars, motorcycles, sewing machines, bicycles, etc.
In mass production, high-performance technological equipment– special, specialized and aggregate machines, multi-spindle automatic and semi-automatic machines, automatic lines. Multi-bladed and stacked special cutting tools, extreme gauges, high-speed control devices and instruments are widely used. Mass production is also characterized by a steady production volume, which, with a significant production program, provides the opportunity to assign operations to specific equipment. At the same time, the production of products is carried out according to the final design and technological documentation.
The most advanced form of organizing mass production is in-line production, characterized by the arrangement of technological equipment in the sequence of operations of the technological process and a certain cycle of product release. The flow form of organizing the technological process requires the same or multiple productivity in all operations. This makes it possible to process workpieces or assemble units without backlogs at strictly defined time intervals equal to the release cycle. Bringing the duration of operations to a specified condition is called synchronization, which in some cases involves the use of additional (duplicate) equipment. For mass production, the coefficient of consolidation of operations K z.o. = 1.
The main element of continuous production is the production line on which the workplaces are located.
To transfer the subject of labor from one workplace to another, special vehicles are used.
In a production line, which is the main form of labor organization in continuous production, one technological operation is performed at each workplace, and the equipment is placed along the technological process (along the flow). If the duration of the operation at all workplaces is the same, then work on the line is performed with the continuous transfer of the production object from one workplace to another (continuous flow). It is usually not possible to achieve equality of piece time in all operations. This causes a technologically inevitable difference in equipment loading at work stations on the production line.
With significant output volumes during the synchronization process, the need most often arises to reduce the duration of operations. This is achieved through differentiation and time combination of transitions that are part of technological operations. In mass and large-scale production, if necessary, each of the technological transitions can be separated into a separate operation if the synchronization condition is met.
In a time equal to the production cycle, a unit of product leaves the production line. Labor productivity corresponding to the allocated production site(line, section, workshop), is determined by the rhythm of production. Rhythm of release – This is the number of products or blanks of certain names, standard sizes and designs produced per unit of time. Ensuring a given rhythm of production is the most important task when developing a technological process for mass and large-scale production.
The flow method of work provides a significant reduction (tens of times) in the production cycle, interoperational backlogs and work in progress, the possibility of using high-performance equipment, reducing the labor intensity of manufacturing products, and ease of production management.
Further improvement of flow production led to the creation of automatic lines, on which all operations are performed with a set clock cycle at workstations equipped with automatic equipment. Transportation of the subject of labor to positions is also carried out automatically.
It should be noted that at one enterprise and even in one workshop one can find a combination various types production. Consequently, the type of production of an enterprise or workshop as a whole is determined by the predominant nature of technological processes. Production can be called mass production if most workplaces perform one constantly repeating operation. If the majority of workplaces perform several periodically repeating operations, then such production should be considered serial production. The absence of frequency of repetition of operations at workplaces characterizes unit production.
In addition, each type of production is also characterized by the corresponding accuracy of the initial workpieces, the level of refinement of the design of parts for manufacturability, the level of automation of the process, the degree of detail in the description of the technological process, etc. All this affects the productivity of the process and the cost of manufactured products.
The systematic unification and standardization of mechanical engineering products contributes to the specialization of production. Standardization leads to a narrowing of the range of products with a significant increase in their production program. This allows for the wider use of in-line work methods and production automation.
The characteristics of production are reflected in the decisions made during technological training production.
