Basic knowledge of APS production scheduling system-data model

APS is the abbreviation of Advanced Production Planning and Scheduling System. The basic principle of APS is to schedule according to the process model, and the model is maintained by the user. This article introduces the main model data required for APS operation, as well as the key points and difficulties in the model. After reading this article, you will understand what data needs to be prepared to import APS, the processes and main constraints that the current APS system can support, and what are the difficulties in scheduling.

Preface

Usually we say that the APS system is common to all industries, and the scheduling logic is determined by the customer’s process model. In principle, as long as the production process can be accurately defined, it can be automatically scheduled. Although the system functions provided by various manufacturers vary, they all require user-defined process models.

With PlanMateAPS as the column, users can use Excel to collect models. The APS system provides model maintenance tools and imports models into the system by defining the data file format. If it is a small amount of modification, it can also be modified in the user interface provided by the software.

Rules that are too flexible and unprincipled will make it difficult for the system to automatically optimize and implement them. This part needs to be compensated for by flexible user interfaces that allow user intervention.

It needs to be understood that APS cannot solve all the problems of the enterprise. Insufficient production capacity, suppliers’ inability to deliver on time, on-site equipment abnormalities, order changes, etc. These problems have plagued enterprises for a long time, and the planning department is often in a state of firefighting. Many people will think that APS is only suitable for companies with stable orders and material status and few exceptions. In fact, on the contrary, by importing APS?, it can help enterprises alleviate problems to a certain extent:

1. Although production capacity cannot be increased, forecasts can be accurately assessed, allowing companies to prepare in advance. Need to add equipment? Order molds in advance? Ready to ship out? If outsourcing is required, APS can help you determine when to outsource, which products and work orders need to be outsourced, so that cooperating vendors can prepare in advance.
2. Supplier problems are partly caused by companies giving delivery dates that are inaccurate, too vague or change frequently. APS can help companies make more accurate plans, thereby providing suppliers with more accurate and stable delivery dates, long-term tracking, and improving delivery status to a certain extent.
3. Due to on-site abnormalities and order changes, the traditional manual modification of plans is not only troublesome but also causes confusion in the plan. Especially in companies with multiple production processes, inserting orders will cause a lot of conflicts. The rapid rescheduling provided by APS can help companies quickly modify plans.

APS production process model:

1. Production equipment, the equipment here refers to the equipment that needs to be independently prepared for production planning. If you have a production line with multiple machines connected, you only need to define the production line, and there is no need to define each machine separately. In APS we call it the main resource. There are the following attributes that need to be noted for the main resource:

Production mode: In discrete manufacturing, main resources include two main production modes: flow production and batch production.

• Flow production: SMT production lines, mechanical processing equipment, molding equipment, etc. Products are produced one by one. This is flow production.
• Batch production: Heating furnaces, magnetron sputtering machines, and large containers are used for cleaning. These equipment are produced in batches. For example, if a heating furnace is used for annealing in mechanical processing, a certain number of products must be heated at the same time each time, and cannot be produced one by one. This is batch production equipment.

Whether it can be interrupted: There is an important parameter that needs to be paid attention to in the above equipment, whether it can be interrupted. In flow-type production, when shifts change and the time is discontinuous, the machine can stop and wait for the next day to continue. The heating furnace type equipment cannot be stopped. As long as it is started, it must be completed continuously. This cannot be interrupted.

Work calendar: For production resources, in addition to the types and parameters that need to be defined above, its work calendar also needs to be considered. The work calendar uses the week as the basic cycle, including the number of shifts per day, the working hours of each shift, and rest days. The definition of working hours also takes into account meal breaks, which may be interrupted for a period of time. The work calendar also needs to define holidays. In PlanMateAPS, the work calendar of each main resource can be different.

2. BOM: Product list and material consumption structure. There are two types of BOM in APS

• Material BOM: Same as the BOM in ERP, the material consumption structure is defined according to the material number
• Process BOM: The production of a product requires multiple processes. Materials can be added at different process points and do not need to be added uniformly in the first process. This is the process-level BOM in APS. If the entire production cycle of a product is long, the process BOM can delay the material demand time and greatly reduce the material inventory level.

3. Product production process: Each product will go through multiple production processes, and there is a certain relationship between these processes.

Process sequence: The production process of some products is determined. For example, in PCBA, we will go through laser engraving, SMT BT sides, wave soldering or selective soldering, assembly and testing. Each product is carried out in a fixed order, and the production line equipment allowed to be used in each process is different.

In addition, some products may have multiple optional processes, which are more common in machining. An advanced CNC equipment can complete multiple processes such as turning, milling, and drilling at one time, and only needs to be scheduled once. These processes can be replaced by two or three single-function equipment, forming parallel optional processes.

In addition to parallel processes, in the machining industry, the decomposition of processes is not fixed. For example, the processing of a hexahedron can be divided into 6 processes, with each device processing one side, or it can be divided into 3 processes, with each device processing two sides, or simply let one device do it all. Process decomposition can be based on experience so that the processing time of each work order is appropriate, the buffer connection between processes is easy to manage, and the equipment can be fully utilized.

Buffering between processes: In the definition of product processes, in addition to process sequence and equipment selection, we also need to pay attention to the relationship between processes and buffer parameters.

Considering the impact of transportation on product quality and production efficiency, regional and workshop restrictions should be considered. In PlanMateAPS, multi-level areas are defined. The main resources include factory area, workshop, and equipment location parameters. It can be defined that production processes should be prioritized in the same workshop and factory area. For example, the BT sides of SMT are strictly limited to production in the same workshop. From SMT to wave soldering, board cutting, etc., priority is given to production in the same workshop.

There are generally two types of process relationships:

ES: The process can only start after all the previous processes are completed.

EE: Pre-process and post-process can partially overlap

For buffering between processes, different production processes will have different requirements.

• For flow production, transportation time, transportation tools and the quantity carried in each transportation need to be taken into consideration. There will be some delays in front-end production, so there needs to be a certain buffer. Buffering methods can be defined by time or by product quantity.
• The process transfer of combined furnace production is more complicated, because a work order may be divided into multiple furnaces, or several work orders may be merged into one furnace, and cooling time is required after the furnace is released. Special attention must be paid when defining the process buffer. I won’t go into details here, you can communicate with the supplier.

The equipment and production cycle required for the product process:

Products go through multiple production processes, and the equipment allowed to be used in each process needs to be defined. Even in the same process, the equipment allowed for each product is different. Among the allowed equipment, there will be different priorities and cycle times. For example, in SMT, the cycle time varies greatly due to different line configurations.

In the molding industry, product selection molds, mold selection equipment, and the machines that can be used for each mold have certain requirements. For example, a mold can be used on a 60- or 80-ton machine. As long as delivery is not affected, priority should be given to using small-tonnage machines to save costs.

The rhythm of flow production:

Takt time is calculated by how long it takes to produce a product. Some companies define production capacity in terms of output per hour. Takt time =3600s/output per hour.

In the molding industry, we take each mold release as the cycle time. If there are multiple holes on the mold, the cycle time should be divided by the number of holes.

Cycle time=Mold ejection cycle/number of product holes

Furnace production cycle time and quantity:

For the furnace production method, the production time cannot be calculated based on a single product, but the total time required for each furnace must be defined, and the switching time between furnaces must also be considered.

In the combined furnace production mode, we also need to consider the total capacity of each furnace. Due to different sizes of products, the allowed processing quantities of different products are also different. It can be defined as follows:

Define the furnace capacity with standard size products, and then define the size for each product. It can be a multiple of the standard size (decimals are allowed). When scheduling products of different sizes, you need to calculate the number of products allowed to be scheduled each time based on the product size.

Another situation is that production requires the use of special fixtures. It is necessary to define the number of fixtures that each furnace can accommodate, the total number of fixtures for various product specifications, and the corresponding relationship between products and fixtures, which will create constraints on the schedule.

In furnace production scheduling, it is also necessary to consider the production time of different products, the materials to be used, etc. Only products with the same processing time and materials can be combined into one furnace.

Supporting resources:

Auxiliary resources have a constraining effect on production schedules, including various types of jigs, fixtures, molds, and steel mesh in SMT. In processes that mainly rely on manpower, workers are also an auxiliary resource.

In PlanMateAPS, auxiliary resources are divided into several types:

Tools: steel mesh, jigs, fixtures, testing instruments, etc. This type of auxiliary resources only plays a constraining role in scheduling and does not affect the production cycle time. When switching products, the switching time between work order tasks will not be affected.

Mold category: mainly refers to molds in the molding industry. Molds are different from ordinary auxiliary resources. Molds are related to main production resources and determine the production cycle time. In addition, there are issues such as multiple cavities in one mold and multi-product molding, which all need to be defined in the APS process model.

Workers: In some industries, workers are the main resource affecting production. For example, finished product assembly, garment making, etc. Because workers have different operating skills, the total number of workers cannot be completely constrained. Assume that the workshop has two main processes A and B. There are 100 workers in total. 50 of them can only operate process A, 30 people can only operate process B, and 20 people can operate process AB. We can divide the workers into 3 groups. 1:50 people, 2:30 people?, 3:20 people, of which the 20 people in group 3 can operate both processes AB.

In processes such as assembly, there are two situations that need to be considered:

1: The number of workers required for the production of each product is fixed, and the total number of workers determines which products can be produced at the same time.

2: The number of workers has a certain range. For example, 8-12 people are needed to produce a product, but the number of people will have an impact on the production rhythm (more people will make things faster). In this case, the model must also define the impact of different manpower on the production rhythm. . When APS performs optimization, it needs to calculate the working time of the task based on manpower.

In order to simplify labor management, it is best to queue tasks that require the same manpower together in the same assembly line. However, the actual situation is difficult to meet. If the manpower keeps changing, it will make workshop management more difficult. PlanMateAPS provides a good solution for this situation, providing manpower changes and equipment replacement tables to help the workshop manage human resources.

Product attributes and switching:

Product attributes can have an impact on scheduling or simply be used as a reference in reports. The main attributes can include: machine model, product category, customer, transportation method, color, main material, etc.

The optimization of switching is also an important function of the APS system. Mainly includes: product switching optimization for the same product, the same mold, and the same attributes. In PlanMateAPS, you can optimize switching according to product attributes. For example, for molding colors, products of the same color or the same color number but different shades are arranged together to reduce the waste of toner. Similar models can be defined in SMT, and similar models can be prioritized together to reduce switching time.

Summarize:

The above is the process model required by the automatic scheduling system. Each product may have some differences. You can communicate with the supplier when the system is imported.

These data are also needed in the manual scheduling mode, but in the manual mode, there is no clear definition and unified management requirements. Instead, it is managed by the planner himself, or becomes the planner’s personal experience. Sometimes when planners take leave or leave, this data is lost causing scheduling chaos.

Some customers will say that we have not organized the data well and have difficulty importing it into APS. Let’s think about this problem in reverse:

The reason why no one organizes it is: if there is no compulsion to do a job, no one will do it seriously.

Failure to carefully organize process data is a management flaw. APS forces companies to manage their own process data and helps companies improve management and accumulate process data. If the process model is accurate, there will be no confusion in the plan due to new employees not understanding it when old employees take leave or resign. The long-term accumulation of process data is also conducive to process improvement.

Another benefit of introducing APS is that the production line is scheduled according to standard production capacity, eliminating randomness. The production efficiency of the production line can be accurately evaluated, reducing the waste of equipment man-hours, which is of great help in improving production efficiency throughout the day.