JP2005293303A - Manufacturing method and system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make a manufacturing instruction to an upstream process with no drastic change for supplying a component to a downstream process without any excessive stock even when component consumption in the downstream process is leveled or when orders from a customer fluctuate greatly. <P>SOLUTION: In this manufacturing system constructed of the upstream process S and the downstream process T, a work instruction board Km for a component is returned to the upstream process S when the component is consumed in the downstream process T, and component manufacturing based on the work instruction board Km is carried out in the upstream process S. In this process, an upstream process work instruction board Ks, which is used for instructing component manufacturing and circulates only the inside of the upstream process S, is issued on the basis of a stock criterion for the component, and the work instruction board Km returned to the upstream process S is replaced by the upstream process work instruction board Ks circulating inside the upstream process, while the upstream process work instruction board Ks replaced by the work instruction board Km is returned to the head process in the upstream process. The component is manufactured even when the work instruction board is not returned to the upstream process. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a production method and a production system when production is performed in a production process including a pre-process and a post-process.

  When production is performed in which the production of a part is a pre-process and the assembly process of the part is a post-process, the work instruction board for that part is returned to the pre-process when the part is consumed in the post-process. It is generally done that parts are produced and the produced parts are sent to the subsequent process together with the work instruction board. However, when returning the work instruction board to the previous process, the convenience of the previous process is not considered. Even if it is normal and considered, excessive parts inventory is requested in order to avoid running out of parts, and as a whole, it is difficult to maintain optimum inventory standards and achieve proper production.

On the other hand, if the target is a product that cannot be stable in order production, it will be difficult to deliver parts to the subsequent process itself, and it will be difficult to realize the production instructions for the previous process based on the consumption of parts in the subsequent process. is there. For this reason, it is necessary to have a lot of delivery times to customers, or it is necessary to have parts inventory ready for disposal.
JP 2001-202442 A Japanese Patent Laid-Open No. 2001-325016

  The present invention has been invented in view of the above-described conventional problems, and even when the amount of parts used in the subsequent process is leveled or the order fluctuation from the customer is large, the production instruction to the previous process is abruptly fluctuated. It is an object of the present invention to provide a production method and a production system that can supply parts to a subsequent process in a timely manner without involving excessive inventory.

  In order to solve the above-mentioned problems, the production method according to the present invention comprises a pre-process and a post-process, and when the parts are consumed in the post-process, the work instruction board for the part is returned to the pre-process and the work instruction is issued in the pre-process. In the production process where parts production based on the board is performed, a work instruction board for the previous process that is used for the production instruction of the above part and circulates only in the previous process is issued based on the inventory standard of the above part and returned to the previous process. The work instruction board is replaced with the work instruction board for the previous process circulating in the previous process, and the work instruction board for the previous process replaced with the work instruction board is returned to the first process in the previous process. Yes. Even when the work instruction board has not returned to the previous process, the part is produced by the work instruction board for the previous process issued based on the inventory standards of the parts.

  In this case, the work instruction board returned to the previous process is replaced with the work instruction board for the previous process that circulates in the previous process, which is located closest to the subsequent process, thereby supplying parts to the subsequent process. Can be done most promptly.

  The above inventory criteria can be determined by ranking according to the predicted number of orders in the future, and based on the ranking result and the ratio to the total number of orders, as well as based on trends in the predicted number of orders in the future By performing the ranking and determining based on the ranking result, it is easy to maintain and manage the appropriate inventory level.

  If there are multiple previous processes related to the same part, determine the return destination of the work instruction board to be returned to each previous process according to the number of work instruction boards staying in each previous process. It is possible to give instructions in consideration of the production capacity of

  And if it increases from the previous value when the inventory standard is changed, it can be dealt with by issuing a new work instruction board, but if it decreases from the previous value, the product number is attached according to the difference from the previous value. Issuing a sampling instruction card according to the work instruction board and the work instruction board for the previous process, extracting the work instruction board to be returned to the previous process according to the instruction of the sampling instruction card, and circulating in the previous process If the instruction board is extracted according to the instruction of the extraction instruction card, the management man-hour for the work instruction board can be reduced.

  Set the minimum inventory standard based on the inventory standard and its rank, and when the work instruction board in the subsequent process falls below the minimum inventory standard, send the production priority instruction of the corresponding part to the previous process, If the maximum stock standard is set on the basis of the above and the work instruction board in the previous process exceeds the maximum stock standard, a production priority instruction for the corresponding part is transmitted to the previous process, so that the parts can be prevented from running out.

  In addition, it is possible to improve forecast accuracy by correcting future sales plans based on the correlation between past sales plans and actual sales results, and determining inventory standards based on these corrected sales plans. Therefore, the validity of the inventory standard can be increased.

  Further, the degree of stay of the work instruction board for the previous process at a plurality of inventory points in the previous process is obtained, and production is performed based on the work instruction board for the previous process having a large degree of stay at the inventory point close to the subsequent process. The accuracy of inventory standards can be increased by reducing the inventory standards for parts and increasing the inventory standards for parts produced based on the work instruction board for the previous process that has a low retention rate at inventory points close to the subsequent process. .

  The production system according to the present invention includes a pre-process and a post-process, and when the parts are consumed in the post-process, the work instruction board for the part is returned to the pre-process, and the parts production based on the work instruction board is performed in the pre-process. A production system that includes an inventory standard determination unit that determines an inventory standard for a part and a board issue management unit. The board issue management unit is configured based on the inventory standard determined by the inventory standard determination unit. Issue a work instruction board for the production instruction and a work instruction board for the previous process that is used for the production instruction of the part and is replaced with the work instruction board that circulates only in the previous process and is returned to the previous process. In addition, it is characterized by managing these issued boards. Even for production processes with large order fluctuations and production processes where the load balance between the preceding and following processes is not balanced, by issuing the work instruction board for the previous process, it is possible to supply parts to the subsequent process in a timely manner, and the parts inventory for the entire preceding and subsequent processes. Can be controlled.

  In the present invention, even when the work instruction board has not returned to the previous process, in order to produce the part by the work instruction board for the previous process issued based on the parts inventory standard, the parts supply to the subsequent process is timely performed. In addition, since the work instruction board for the previous process is issued on the basis of the inventory standard, it does not cause excessive inventory. Even when there is a large change in order from, the production instruction to the previous process is not accompanied by a sudden change.

  Hereinafter, the present invention will be described based on an embodiment shown in the accompanying drawings. FIG. 1 shows an example of a production process according to the present invention, S is a process for manufacturing a part, and T is a process for assembling the part. Yes, T corresponds to the post-process, and S corresponds to the pre-process. The pre-process S in the illustrated example is composed of three processes, that is, a part manufacturing S1, a part process inspection S2, and a part shipment inspection S3. Immediately after each of these three processes S1, S2, and S3, inventory points P1, P2, and P3 are included. Is present. Further, P0 in the figure is a point immediately before the part manufacturing S1 process, and P4 is an inventory point existing immediately before the assembly manufacturing T1 process in the subsequent process T.

  In such a process, when production management is performed using the work instruction board Km, when a part is used in the assembly manufacturing T1 process of the subsequent process T, the part with the work instruction board Km attached to the inventory point P4. At this time, the work instruction board Km is collected and returned to the point P0 in the previous process S. Here, when issuing the work instruction board Km for instructing the production of a certain part, Based on the above, a work instruction board Km and a work instruction board Ks for the previous process are issued. Both of them instruct the manufacture of the same part. The former work instruction board Km is returned to the previous process S when the parts are consumed in the subsequent process T, whereas the latter work instruction board Ks for the former process is used. It circulates only in the previous process S.

  The work instruction board Km is returned from the post-process T to the point P0 of the pre-process S, but here, since there is a part manufacturing based on the instruction of the pre-process work instruction board Ks, When returning the work instruction board Km to the process S, the presence or absence of the work instruction board Ks for the previous process is checked from the inventory point P3 closest to the subsequent process T among the plurality of points P0 and the inventory points P1 to P3 in the previous process S. Then, if there is a work instruction board Ks for the previous process at the stock point P3, the work instruction board Ks is replaced with the work instruction board Ks, allocated with the parts after the parts delivery inspection, and collected. Returns to point P0. If there is no work instruction board Ks for the previous process at the inventory point P3, it is checked whether there is a work instruction board Ks for the previous process at the inventory point P2. Then, the collected pre-process work instruction board Ks is returned to the point P0. When there is no work instruction board Ks for the previous process at the inventory point P2, it is checked whether there is a work instruction board Ks for the previous process at the inventory point P1, and if there is, it is replaced and allocated with the parts after the parts are manufactured. And return the collected pre-process work instruction board Ks to the point P0. If there is no work instruction board Ks for the previous process at the stock point P1, the work instruction board Km is returned to the point P0, which means an express production instruction.

  FIG. 2 shows a flow of the above operation. It should be noted that the parts manufacturing instruction based on the work instruction board Ks for the previous process that is collected by replacement with the work instruction board Km and returned to the point P0 is an instruction with low priority, and it is not always necessary to start manufacturing. By performing component manufacture according to the instruction from the process work instruction board Ks, it is possible to smoothly supply components to the post-process T.

  Here, the number of issuance of the work instruction board Ks for the previous process (the number of parts for which production is instructed) and the number of issuance of the work implied board Km are determined based on the inventory standard (the number of inventory standards) as shown in FIG. However, as shown in FIG. 4, the inventory reference number is calculated by comparing the ratio of the number of orders by product number to the total number of orders and the reference inventory days by rank in the inventory reference rank master. Now, if there is an order table having the contents shown in FIG. 5 (a), and the contents of the stock standard rank master are the contents shown in FIG. 5 (b), the order number corresponding to rank B is 80%. Since A has a standard inventory days of 2 weeks and an order quantity of 10000, it is multiplied by ½ to make 5000 the standard inventory quantity. Similarly, since the product number B with the order quantity of 20000 is rank A, the standard inventory number is multiplied by 1 week and the standard inventory quantity is multiplied by ¼ to be 5000.

  As shown in FIG. 6, the above-mentioned inventory standard rank master obtains the number of orders by product number and calculates the rank, and rank A with an order high percentage of 0 to 70% is produced once a week, more than 70 If the production method of rank B, which is ˜90%, is produced once every two weeks, and that of rank C, which is more than 90 to 100%, is produced once a month, the post-process reference inventory days are shown in FIG. As shown in (a), rank A is 1 week, rank B is 2 weeks, and rank C is 1 month.

  Also, as shown in Fig. 7 (a), the maximum fluctuation width of the three-month average of the number of orders is calculated, and as shown in Fig. 7 (b), the deflection ratio is calculated by aggregating the fluctuation width with respect to the three-month average. As shown in FIG. 8B, the pre-process reference stock days are set to 1 week for rank A, 1 week for rank B, and 2 week for rank C. For this reason, the number of stocks in the back process is 3 months average x back process standard stock days, the product number A of rank B is 20000 × 1/2: 10000, the product number B of rank A is 40000 × 1/4 = 10000, The number of processes in stock is 3 months average x previous process reference inventory days, rank B product number A is 20000 × 1/4 = 5000, and rank A product number B is 40000 × 1/4 = 10000. FIG. 9 shows a flowchart relating to this point.

  The inventory standard may be determined based on a ranking result by ranking based on a tendency of the predicted number of orders in the future. The flow chart in this case is shown in FIG. 10, and the number of orders and their trends are calculated (see FIG. 11 (a)) for three months (current month, next month, next month), as shown in FIG. 11 (b). The inventory reference days are calculated by comparison with a previously determined inventory reference rank master. FIG. 11C shows the calculation result in this case.

  The inventory standard for parts may be determined based on the predicted number of orders in the future by product number and the manufacturing / inspection lead time per unit time. When the number of orders for the current month by product number is as shown in FIG. 13 (a) and the daily production capacity of each process is as shown in FIG. 13 (b), the number of consecutive production days in the subsequent process is shown in FIG. 13 (c). If there is a capacity difference, calculate the safety stock days for each product number (see Fig. 13 (d)), calculate the capacity difference between the previous process and the back process. The sum of the product multiplied by the difference and the safety stock multiplied by the daily average sales number is the stock standard (assembly stock standard). If there is no capacity difference, the safety stock multiplied by the daily average sales number is the stock base. To do. A flowchart is shown in FIG.

  It is also preferable to determine the inventory standard based on the estimated number of orders in the future by product number and the relationship among equipment, molds, and inspection lines. That is, as shown in FIG. 14, the calculation of the number of orders for the current month by product number, the calculation of the daily production capacity of each process, the calculation of the number of continuous production days of the subsequent process, and the calculation of the safety stock days by product number are shown in FIG. The mold master information shown in Fig. 1 is acquired, and the part number / mold with which the mold is in contact is calculated. If there is a contact, the number of days required for production of the corresponding part number is calculated and the pre- and post-process operations are performed. The number of continuous production days is calculated from the ratio with the number of days. After this or when there is no exchange, the standard stock days are determined in consideration of the capacity difference in the safety stock days.

  As shown in FIG. 15 (a), when product numbers B and C are in contact with each other by using a common mold in steps S1, S2 and S3, and the post-process T can be produced in each line, In the case of the order table, the process daily capacity master, the continuous production day master, and the safety stock day master shown in FIG. Therefore, the product number A that is not in contact is 5 × (1000−500) + 3 × 500 = 4000, whereas the product number B that is in contact is 20000 in the process T10 days. S3 is 6.7 days and 13400 (remaining 3.4 days is 0), 2000 and 1340 per day, and 10 x (2000-1340) + 3 x 1000 = 9600 as the assembly inventory standard. The generated product number C is 100000 in the process A 20 days, 166500 in the 13.3 days of the process S3 (0 in the remaining 6.7 days), 5000 and 3325 per day, and 20X (5000-3325) + 3 × 5000 = 48500 is assembled. It is based on inventory standards.

  The distribution of the work instruction board Km and the pre-process work instruction board Ks may be changed at any time according to the shipping tendency. As shown in FIG. 16, the number of weekly orders by product number (see FIG. 17 (a)) is acquired, and the post-process reference rank master and the pre-process reference rank master (see FIGS. 8 (a) and (b)) are acquired. Based on these, the stock standard (standard) is calculated for each product number and an inventory master is created, and then the post-process stock standard number is calculated based on the ratio of the average number of orders per week and the number of weekly orders. In addition, the calculation of the pre-process inventory reference number based on the post-process inventory reference and the standard inventory reference total number is repeated until there is no more readable product number.

  The standard post-process / pre-process inventory master is as shown in FIG. 17 (b) (the pre-process inventory standard is calculated by the ratio of the excess order quantity and the pre-process inventory quantity, and the difference between the total inventory quantity and the pre-process inventory is calculated. (However, the upper limit of the post-process inventory standard is not exceeded.) 2000, which is twice the order number 1000 of the first week of product number A, does not exceed the upper limit of the post-process inventory standard of 5000, so 2000 is adopted. The difference 5500 from the total upper limit 7500 is set as the previous process inventory standard. As a result, the post-process inventory standards are standard 5000 for the product number A, 2000 for the first week, 4000 for the second week, 5000 for the third week, 5000 for the fourth week, and 5000 for the product number B, 5000 for the first week, and 5000 for the second week. 2000, 3rd week 2000, 4th week 5000. The pre-process inventory standard is 2500 for the product number A, 5500 for the first week, 3500 for the 2nd week, 2500 for the 4th week, 2500 for the 4th week, and 5000 for the product number B, 5000 for the first week, 8000 for the second week, The third week is 8000 and the fourth week is 5000.

  By the way, when there are a plurality of pre-processes for the same part, especially when there are pre-processes for the same part outside the company and in the company, as shown in FIG. It is preferable to determine the return destination of the work instruction board to be returned to each previous process according to the number of work shop display boards. When the order / arrangement allocation table for the internal / external pre-process is as shown in FIG. 19 (a), the internal / external inventory standard as shown in FIG. 19 (b) is referred to the inventory standard rank master. Create a table and compare the number of work instruction boards staying in the previous process at the current time (see Fig. 19 (c)) so that the ratio is as close as possible to the level of the inventory standard table. The return destination of the instruction board is distributed.

  Moreover, when changing an inventory standard, it is preferable to process as follows. That is, when the inventory standard is increased from the previous value, a new work instruction board is issued. When reducing the inventory standard from the previous value, issue a sampling instruction card with a part number for work instruction board Km and for work instruction board Ks for the previous process according to the difference from the previous value. When the work instruction board Km is returned from the post-process T to the pre-process S, if there is an extraction instruction card for the work instruction board Km, the work instruction board Km is extracted. If not, the work instruction board Km is returned to the previous process S and replaced with the previous process work instruction board Ks as described above, and the replaced previous process work instruction board Ks is returned to the point 0. At this time, if there is an extraction instruction card for the work instruction board Ks for the previous process, the work instruction board Ks for the previous process is extracted. In this case, management of the work instruction board Km and the pre-process work instruction board Ks is facilitated.

  In addition, the minimum inventory standard is set based on the inventory standard and its rank, and when the work instruction board in the subsequent process falls below the minimum inventory standard, the production priority instruction for the corresponding part is sent to the previous process, It is also preferable to set a maximum stock standard based on the rank, and to send a production priority instruction for the corresponding part to the previous process when the work instruction board in the previous process exceeds the maximum stock standard. The former flowchart is shown in FIG. 21, and the latter flowchart is shown in FIG. An example of the minimum inventory standard (MIN inventory standard) master is shown in FIG. 23B, and an example of the maximum inventory standard (MAX inventory standard) master is shown in FIG. The inventory reference number and the minimum inventory reference number / maximum inventory reference number are obtained for each product number from the order table (see FIG. 23 (a)), the minimum / maximum inventory reference master, and the above-mentioned inventory reference rank master. If the instruction board Km cuts the minimum inventory standard or the work instruction board Km in the previous process S exceeds the maximum inventory standard, the production priority instruction is given to the previous process.

  The flowchart shown in FIG. 24 is a case in which work is started by comparing storage space information of a plurality of inventory points and work instruction board unoccupied occupation rate by product number, and an inventory status table (FIG. 25) and evaluate the retention point for each product number, and for the most retained product in the product number, calculate the retention status for each process and determine whether the occupancy of the later process is low If it is low, a production instruction to be sent to the subsequent process is transmitted, and if it is high, the part number of the process with the highest occupancy is extracted in the process with the most stagnation. In addition, about what is determined to be low at 0 to 30%, supply is performed from the previous process, and about what is determined to be normal at 30 to 70%, the difference between the preceding and subsequent processes. If it is determined that the occupation rate is 70 to 100% and is high, it is determined whether or not it should be sent based on the difference from the later process. 25, the product number A is supplied from the point P0 and the stock point P2, since the stock is 0 at the stock points P1 and P3, and the product number B is half of the stock point P3, so there is no rush. Since C has a lot of points P0, it is judged to be rushed, and the stock point P1 should be supplied from the previous process because the occupancy rate is low, and the stock point P2 is in the later process because the occupancy rate is high The stock point P3 to be sent is determined to be received because the occupation rate is normal and the previous occupation rate is high.

  Also, as shown in the flowchart of FIG. 26, it is also preferable to store the arrival date of the work instruction board and manage the staying days so as not to exceed a predetermined number.

  In addition, regarding demand forecasts for determining inventory standards, future sales plans are corrected based on the correlation between past sales plans and actual sales results, and inventory standards are determined based on these corrected sales plans. It is preferable to do. A sales plan / actual history table as shown in FIG. 27 is created, and for example, the past plan 3 months ÷ the past plan 3 months is applied to the future plan as a correction value. In this case, the product number A shown in FIG. 27 is not corrected, the product number B is corrected to the 70% minus side, the product number C is corrected to the 80% plus side, and the product number Z is corrected to the 50% plus side. FIG. 28 is a flowchart regarding the correction.

  From the standpoint of keeping the inventory standard, especially the pre-process inventory standard, appropriate, the following is also preferable. That is, the degree of stay of the work instruction board for the previous process at a plurality of inventory points in the previous process is obtained, and production is performed based on the work instruction board for the previous process having a large degree of stay at the inventory point close to the subsequent process. The inventory standard for parts is reduced, and the inventory standard for parts produced based on the work instruction board for the previous process having a small stay at the inventory point close to the subsequent process is increased. If the total of a certain part is 100, the stock at the point P0 and the stock points P1, P2, P3 is 0, 10, 20, 70, respectively, and if 70% of the threshold is always at the stock point P3, the stock standard is overstocked. Reduce. If the stock at the point P0 and the stock points P1, P2, P3 is 70, 20, 10, 0, respectively, and if 70% of the threshold value is always at the point P0, the stock standard is increased as the stock is insufficient.

  As shown in FIG. 30, the degree of delivery of the work instruction board to the subsequent process is calculated, and the part number that can be delivered immediately reduces the inventory standard of the previous process due to excessive inventory, and delivery takes more than a threshold (for example, 3 days). In this case, the stock standard may be increased due to a shortage of stock.

  FIG. 31 shows a main configuration in a production system capable of carrying out the above production method. Sales plan data, post-process inventory standard data, work instruction board number data, pre-process inventory standard data, pre-process work instruction board Storage unit M for storing number-of-sheets data, pre-process work instruction board location data, work instruction board location data, etc., post-process inventory standard decision process, work instruction board issuance management, pre-process inventory standard determination process, for pre-process Location monitoring for monitoring the location of the order processing input unit Q1 and the work instruction board, which includes a processing unit CPU responsible for work instruction board issuance management, pre-process work plan process, post-process work plan process, work instruction board replacement process, and the like Device Q2, sales forecast information input unit Q3, etc. are connected, and work instructions for the post-process described above The command issue management unit and the work instruction board issue management unit for the previous process are used for the production instruction of the part and the production instruction of the part based on the inventory standard determined by the inventory standard determination processing unit. In addition, a work instruction board for a previous process which is replaced with a work instruction board which is circulated only in the previous process and returned to the previous process is issued and these issued boards are managed. In FIG. 32, an arrow a indicates a signal, a mouth indicates a flow of the work instruction board for the previous process, and c indicates a flow of the work instruction board for the post process.

It is explanatory drawing of an example of embodiment of this invention. It is a flowchart same as the above. It is a flowchart regarding stock standard determination same as the above. It is a flowchart regarding stock standard determination same as the above. (a) is explanatory drawing of an example of an order prediction table, (b) is explanatory drawing of an inventory standard rank master. It is explanatory drawing of an example of an order table. (a) is an explanatory diagram of an example of the order fluctuation width, and (b) is an explanatory diagram of the fluctuation rate. (a) is explanatory drawing of a back process stock reference | standard rank master, (b) is explanatory drawing of a front process stock reference | standard rank master. It is a flowchart regarding calculation of an inventory standard rank master. It is a flowchart of the other example regarding determination of an inventory standard. (a) is explanatory drawing of an example of an order table, (b) is explanatory drawing of an inventory standard rank master, (c) is explanatory drawing of the determined inventory standard. It is a flowchart of the further another example regarding stock standard determination. (a) is an explanatory diagram of an example of the above order table, (b) is an explanatory diagram of the process daily capacity master, (c) is an explanatory diagram of the continuous production days master, and (d) is an explanatory diagram of the safety stock days master. is there. It is a flowchart of another example regarding stock standard determination. (a) is an explanatory diagram of the same mold master, (b) is an explanatory diagram of an example of distribution. It is a flowchart of another example regarding stock standard determination. (a) is explanatory drawing of a weekly order table, (b) is explanatory drawing of a standard post process / pre process inventory master. It is a flowchart regarding work instruction board return destination determination. (a) is an explanatory view of an order / arrangement distribution table, (b) is an explanatory view of an inventory standard table, and (c) is an explanatory view of a stay work instruction board number table in the previous process. It is a flowchart of the other example regarding work instruction | indication board retention cancellation. It is a flowchart of the further another example regarding work instruction board retention cancellation. It is a flowchart of another example regarding work instruction board retention cancellation. (a) is an explanatory diagram of an order table, (b) is an explanatory diagram of a minimum inventory standard master, and (c) is an explanatory diagram of a maximum inventory standard master. It is a flowchart of the other example regarding work instruction board retention cancellation. It is explanatory drawing of an inventory condition table. It is a flowchart of the further another example regarding work instruction board retention cancellation. It is explanatory drawing of an example of a sales plan / result log | history table. It is a flowchart regarding order prediction. It is a flowchart regarding stock standard evaluation. It is a flowchart of the other example regarding stock standard evaluation. It is a flock figure of a production system. It is a schematic diagram same as the above.

Explanation of symbols

S Pre-process T Post-process Km Work instruction board Ks Pre-process work instruction board

Claims (11)

  In a production process that consists of a pre-process and a post-process, and that the work instruction board of the part is returned to the pre-process when the part is consumed in the post-process, and parts production based on the work instruction board is performed in the pre-process, A work instruction board for the pre-process that is used for production instructions and circulates only in the previous process is issued based on the inventory standards for the above parts, and the work instruction board returned to the previous process is for the pre-process that circulates in the previous process A production method wherein the work instruction board is replaced with a work instruction board, and the work instruction board for the previous process replaced with the work instruction board is returned to the first process in the previous process.   2. The production method according to claim 1, wherein the work instruction board returned to the previous process is replaced with a work instruction board for the previous process that is circulated in the previous process and that is located closest to the subsequent process. .   3. The production method according to claim 1, wherein the stock standard is determined based on a ranking based on a predicted number of orders in the future and a ratio of the ranking result and the total number of orders.   The production method according to claim 1, wherein the inventory standard is determined based on a ranking result obtained by ranking based on a tendency of a predicted number of orders in the future.   When there are a plurality of previous processes related to the same part, the return destination of the work instruction board to be returned to each previous process is determined according to the number of work instruction boards staying in each previous process. Item 5. The production method according to any one of Items 1 to 4.   A new work instruction board is issued when the stock level changes from the previous value when it increases from the previous value, and when it decreases from the previous value, a sampling instruction card with a part number is placed in front of the work instruction board according to the difference from the previous value. Issued according to the work instruction board for the process, the work instruction board returned to the previous process is extracted according to the instruction of the extraction instruction card, and the work instruction board for the previous process circulating in the previous process is extracted according to the instruction of the instruction instruction card The production method according to claim 1, wherein the production method is extracted.   2. A minimum inventory standard is set based on the inventory standard and its rank, and a production priority instruction for a corresponding part is transmitted to the preceding process when the work instruction board in the subsequent process falls below the minimum inventory standard. The production method of any one of -6.   The maximum stock standard is set based on the stock standard and its rank, and when the work instruction board in the previous process exceeds the maximum stock standard, a production priority instruction for the corresponding part is transmitted to the previous process. The production method of any one of -7.   9. The future sales plan is corrected based on the correlation between the past sales plan and the actual sales performance, and the inventory standard is determined based on the corrected sales plan. 2. The production method according to item 1.   Obtain the degree of retention of the work instruction board for the previous process at multiple inventory points in the previous process, and the parts produced based on the work instruction board for the previous process with a large retention degree at the inventory point close to the subsequent process The inventory standard is reduced, and the inventory standard of parts produced based on the work instruction board for the previous process having a small retention at an inventory point close to the subsequent process is increased. The production method according to item.   A production system comprising a pre-process and a post-process, and when a part is consumed in the post-process, the work instruction board for that part is returned to the pre-process and parts are produced based on the work instruction board in the pre-process. The board issue management unit includes a work instruction board for instructing production of the parts based on the inventory standard determined by the inventory reference determination unit. And a work instruction board for the previous process which is used for the production instruction of the part, is circulated only in the previous process and is replaced with the work instruction board which is returned to the previous process, and these issued boards are managed. Production system characterized by being.

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