APS solution for sheet metal workshop of injection molding machine enterprise


Abstract: For the production plan and schedule of the sheet metal workshop of an injection molding machine manufacturer. Analyze the shortcomings of the original method of directly using the material requirement planning (MRP)/calculation result of the enterprise management solution (SAP) as the shop floor plan. It is proposed to use Advanced Planning and Scheduling (APS) technology, according to the characteristics of sheet metal parts production of injection molding machine enterprises, programming to establish a resource model, and integrating the input data of the SAP system. Achieve fine process scheduling at the hour level of each equipment, and collect completion feedback information by scanning the bar code on the dispatch order. It is used for rolling re-arrangement of the workshop operation plan, and finally the APS scheduling result is delivered to the basic management of the sheet metal workshop in the form of an interactive equipment-process Gantt chart for manual intervention.

1 Subject background
Injection molding machine is the main molding equipment for the production of various plastic products, which are widely used in all aspects of life. A certain company produces precision high-end injection molding machines with a steady stream of customer orders, but the production plan management method is relatively primitive, resulting in a high rate of order delays, which seriously affects customer satisfaction.

The production of sheet metal parts is a major problem for the company, because sheet metal is the last big part of the complete machine, leaving very little buffer time for sheet metal, and in order to maintain the company "maximum meeting the individual needs of customers" The core competitiveness of the sheet metal parts, the number of new drawings per month for sheet metal parts, and the complex conditions of production materials, all rank first in each production department, but the on-time lean supporting ability of the sheet metal workshop is the weakest in the entire enterprise.

While increasing the resource capacity of the sheet metal workshop. The author noticed that the current extensive production planning management method has great internal potential to be tapped. The workshop planner directly uses the basic start time of the dispatch order calculated by the material requirements planning (MRP) in the enterprise management solution (SAP) as the time to put into production, but the date in SAP is actually fixed according to the material in the bill of materials (BOM) Inferred from the lead time, if the workshop directly puts all the dispatch orders with the basic start time of the day to the first station, and let the section leader decide to arrange production independently, it will cause the section leader to do his own work and only the workers of the section. The working hours are full of consideration, ignoring the overall coordination and overall optimization. During production operations, workers tend to prioritize production with materials placed closer to each other, resulting in poor production coordination and increased product inventory.

Advanced planning and scheduling (APS) technology can cope with the operation plan of the company's sheet metal workshop, fill SAP's blind spots, consider the multiple resource capacity constraints of the production process, and does not require a unique fixed process route, and the lead time can be dynamically calculated. According to the selected production scheduling method, the production scheduling plan is quickly and automatically generated, and the workshop operation plan is accurate to each process, each equipment, every hour or even every minute. This rapid rearrangement capability can cope with the constraints of limited production capacity. Make frequent plan changes or insert orders.

The difficulty of using APS technology is whether it can be combined with the actual situation of the enterprise, that is, it is difficult to apply it in practice. The author will introduce in detail the four-stage process of applying APS technology in the sheet metal workshop of an injection molding machine enterprise to improve the workshop operation plan.

2 planning stage
2.1 Current planning method
After the MRP calculation, the SAP system master production plan releases the sheet metal processing order with the basic start time and basic end time information to the sheet metal workshop, as shown in Figure 1.

The basic end time of MRP is determined by pushing an offset value before the approximate demand date of the corresponding complete machine assembly order. After determining the basic end time, push one lead time forward to get the basic start time. The most important lead time is the fixed attribute value entered when the sheet metal material number is created. This lead time is fixed and will not change with the increase or decrease of the quantity of materials in the order. Some sheet metal materials do not have a maintenance lead time, so there is an unreasonable situation: the basic start time and the basic end time in the SAP order are the same. After receiving these production orders, the sheet metal workshop directly chooses the SAP basic start time to be the same day, and puts it on the station where the first process is located.

Analyzing this planning method, there are the following problems and shortcomings.
(1) Poor enforceability, too extensive and simple, and unscientific. The original method is not a scheduling method with limited capacity, and it does not consider the production capacity of the work center after loading other production dispatch orders. Nor does it consider the issue of sequence optimization under the established production pressure, nor does it consider the establishment of an objective function to evaluate the pros and cons of multiple scheduling methods.

(2) Poor coordination and unbalanced load. There is no detailed plan at the process level, blindness in the production process, and uneven availability of equipment personnel. Since employees do not have a mandatory production sequence during production operations, it will also lead to an increase in product inventory between processes.

(3) The predictability is poor and the plan is not transparent enough. The urgent task of inserting orders will affect a series of other normal production conditions, and it is impossible to make accurate and effective assessments.

2.2 Put forward directions and methods for improvement
If MRP formulates the production plan from the perspective of the BOM structure, then APS focuses on the production plan based on the process and actual working hours. Based on this, the author proposes to change the original method based on the basic start time of MRP to use the calculation result of APS to formulate the workshop operation plan.

2.3 Develop an improvement plan
In order to successfully achieve the above improvement goals, the following process plan has been formulated. First, promote the compilation of process route data and the measurement of standard working hours; secondly, determine the target indicators before improvement with the financial personnel, and propose the expected effect after the improvement; then introduce the APS concept in the sheet metal workshop and conduct the training of lean production methods; finally start Implementation and application of APS technology.

3 execution phase
3.1 Build a data model
According to the technological process of the sheet metal workshop of the injection molding machine enterprise, collect and organize the data of the process, personnel, equipment and shifts. The established APS data model is shown in Table 1.

3.1.1 Establish a process model
The overall process of the sheet metal workshop of the injection molding machine enterprise is shown in Figure 2. According to the characteristics of full tooling, there is no need to consider constraints such as tools and fixtures when building the model. Therefore, the main constraints are divided into two categories: equipment constraints and manpower constraints. The first four procedures in the sheet metal workshop are equipment constraints, and the technological processes are: laser cutting, plate shearing, electronic punching, and bending. The latter two processes-welding and powder spraying are manpower constraints.

3.1.2 Establish equipment model
When defining equipment, the same type of equipment that can process the same process is summarized as an equipment group, and the equipment group is associated with a certain process. The equipment in the same equipment group can be replaced with each other and adjusted automatically according to the capacity and load situation. The equipment group also corresponds to the SAP work center.

Because of the characteristics of the laser cutting machine equipment, it is necessary to use typesetting software to cut sheet metal parts of different shapes on a fixed specification of the raw material sheet. Therefore, the laser cutting machine is defined as a non-exclusive equipment when modeling. Other machine tools are defined as exclusive equipment because they need to set specific parameters or install specific mold fixtures for processing certain sheet metal parts.

3.1.3 Establish personnel model
People are organized in teams. Define the skill matrix and daily production capacity of each person in the team. The squad consists of equipment and manpower. Some machine tools in the sheet metal workshop of injection molding machines (such as bending machines) require two people to operate. This person has a specific labor skill matrix collocation relationship. Teams like this are equipment-type teams. The manpower team is mainly in the welding section and the painting and powder spraying section. At the same time, the fixed ratio of working hours is maintained in the shift table, which is used to settle employee wages.

3.1.4 Establish time model
Establish a factory calendar for APS to automatically avoid non-working days. Then maintain the shift data for each equipment, define the starting time of each equipment shift, and import the scheduled maintenance time plan.

3.2 Determine the integration method of APS and SAP
Use ABAP programming tool to write RFC interface program in SAP. The original functions ORDER_GET_LIST and ORDER_GET_DETAIL in SAP are enhanced, and the enhanced interface function information is shown in Table 2.

The APS software developed by the author transfers SAP order and process data automatically by calling the interface program in SAP through SAPnc03.0. The program refers to sapnco in nc03. 0 when writing. dll and sapnco_utils. dll these two dynamic link libraries, and manually add the following references: using SAP. Middleware. Connector is in app. The connection information of the SAP server is written in the config configuration file, including user name, password, server Internet Protocol address (IP), client number, etc. Finally, execute the RFC function call in the C# program to obtain the order header information and order content information, and save them in the Oracle database of APS.

3.3 Choose to execute scheduling algorithm
According to the order process route obtained from the SAP interface in the foregoing steps, a scheduling algorithm is selected. At present, the commonly used scheduling algorithms in the APS field can be roughly divided into the following categories.
(1) Optimization algorithm based on system simulation or simulation.

(2) Algorithms based on mathematical programming or operations research.

(3) Optimized production scheduling algorithm based on the theory of constraints-restraint-oriented management method (TOC-DBR);

(4) Use genetic algorithms or various swarm intelligence algorithms;

(5) Heuristic rule-based algorithms.

Combined with the actual situation of the sheet metal workshop of the injection molding machine enterprise, the heuristic rule algorithm with lower difficulty was finally selected. Use the measured actual work hours of each process for each part, combined with the production order process route and the required delivery date, to determine the planned start time and planned end time of each process. Then arrange a processing object for each production resource according to the time course. The production resource here can be a bending machine tool or a worker responsible for welding. The processing object refers to a certain process of a certain order. When arranging, select the job with the highest priority from the to-be-selected jobs for processing, and the priority rule is selected in advance by the user. The rules that have been developed and implemented include three types: delivery date, first-come, first-served, and shortest production time. This rule base can be increased. The result is a set of hypothetical initial production schedules. As shown in Figure 3.

3.4 Adjust the APS results. Rolling rearrangement plan
According to the initial scheduling plan generated by the above steps, use c# programming to realize the interactive equipment process Gantt chart, and arrange each process of each order to a certain time of each equipment. The system can also analyze the scheduling plan. Carry out graphical interactive modification, and handle emergency order insertion events. The prepared process operation plan is transferred to the equipment section for execution, and the barcode is scanned after completion, and the execution result is fed back to APS, as shown in Figure 4. Update the actual completion time of the previous process plus the logistics time
Changing the estimated start time of the next process can form a closed-loop and repeatedly rolling rearrangement plan.

4 inspection stage
4.1 The feasibility of the internal self-inspection APS plan
  According to the automatic calculation of APS, the workshop operation plan is obtained, although it is much better than the original plan formulation method of the sheet metal workshop of the injection molding machine enterprise. However, because the constraints of the actual workshop production are intricate, in order to facilitate the modeling calculation, it is impossible to take all the key constraints to participate in the APS calculation. In order to make the plan obtained by the APS calculation closer to the actual production status of the workshop, it is also necessary to reasonably combine the experience and knowledge of the front-line grassroots managers, give play to the subjective function of the workshop managers, and make inspections and manual adjustments to the APS plan.
4.2 External review of the improvement effect of APS
  Sort out various data, check and determine the accuracy of the workshop operation plan generated by APS. At the same time, check the improvement effect scheduled by the financial staff at the beginning of the project. The sheet metal parts are finally delivered to the complete machine assembly branch. After the delivery branch's logistics department and the group's financial staff review and confirm, the APS optimized production scheduling method is used on the premise of not increasing labor costs and equipment and not affecting product quality. The on-time delivery rate of orders in the sheet metal workshop increased by 10%.

5 correction phase
5.1 Summary and promotion
  Based on the above process, the author summarized the experience of using APS to improve the workshop operation plan in the enterprise sheet metal workshop, wrote a group-wide proposal improvement report, and vigorously promoted the principles, methods and value points of APS, and trained promotion personnel. The process of publicity and promotion made APS's viewpoints and concepts gradually accepted by other branch workshops of the group. Facilitate the gradual promotion to other branches and workshops within the group.
5.2 Propose unresolved problems
  The improvement process described by the author is aimed at the operation plan of the sheet metal workshop of the injection molding machine enterprise, so the model constraints are greatly simplified. Only the most concerned equipment and manpower constraints are considered, and the constraints are defined relatively simply. The scheduling algorithm uses heuristic rules. Using the model of lean pulling before and after the process, did not try to use more advanced genetic algorithms. Or APS technology based on simulation. There is still a lack of consideration for the control of the inventory of the work-in-process in the workshop, and it is temporarily unable to deal with the business scenarios of the complex workshop.
  In the process of program design and implementation, the C#ADO method is used to connect to the Oracle database. The interaction between the program and the database is relatively frequent, and the calculation mode of resident memory is not adopted, which results in the slower calculation speed of the APS rearrangement plan.
  The methodology of the application planning, execution, inspection, and correction (PDCA) cycle must be cycled to achieve the effect of continuous improvement. Therefore, the above-mentioned legacy problems that occurred during the application of APS technology in the sheet metal workshop of injection molding machine companies should be reflected in the next PDCA In the cycle, in order to facilitate continuous improvement.

6 total language
  The MRP method that combines order requirements and inventory calculations with a BOM structure is suitable for processing master production plans. However, because of the lack of consideration of the limited capacity constraints of on-site elements, it is not suitable for direct use in the formulation of workshop operations plans. The author summarized the implementation process of applying APS technology in the sheet metal workshop of the injection molding machine company. During the project implementation, the integration method with the SAP system was explored. The basic functions of the injection molding machine company APS were also realized through C# programming, which can partially replace the expensive foreign APS software. . The final proof of practice: in the business environment described by the author. APS technology can be used to continuously improve the shop floor plan.