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Comprehensive analysis report on the multi-product, small-batch production model: The complexity and scale of production management in aerospace enterprises have also changed significantly; it is necessary to be able to respond swiftly to the diverse and uncertain demands of the market, and to deliver products that meet customer needs quickly. “\"Short, flat, fast\" became an important characteristic of production sites during this period. Delivering products that met customer needs on time, with high quality and in the required quantities, at minimal cost, became the goal of production management. However, due to constraints such as a limited number of skilled workers and insufficient equipment, it seemed increasingly difficult to keep things on schedule. In practice, the author introduced a constraint management mechanism (the core idea of such constraint management is that every system has at least one constraint, and the output of the constrained resources determines the overall productivity of the system; any improvements to non-constrained resources are futile unless the production capacity of those constrained resources is increased). It aims to provide some references and insights for advancing production management. I. Main characteristics The main characteristics of multi-product, small-batch production include the following: simultaneous production of multiple products. Since aerospace products involve producing multiple items for a single customer. Different products have different requirements, and a company’s resources are allocated across multiple products. Resource sharing. Every task in the production process requires resources, yet the resources available in practice are very limited. For example, during the production process, the problem of equipment conflicts often occurs, which is caused by the sharing of project resources. Therefore, finite resources must be allocated appropriately to meet the project’s requirements. Uncertainty in project outcomes and production cycles. Due to the strict requirements regarding the quality and stability of aerospace products, newly developed products cannot guarantee success from the first design attempt; there are many areas that need to be improved and refined throughout the subsequent process. If the results of a particular task are not satisfactory, other related tasks also need to be adjusted accordingly, which increases the number of iterations in the process and poses new challenges in terms of resources. Due to the instability of customer demands and inconsistencies in the timing of various elements such as personnel, machinery, materials, methods, and environment compared to the planned milestones, the production cycle is often uncertain. Projects with insufficient time frames require more resources, thereby increasing the difficulty of production control. The production process remains largely unchanged. Since the types of products handled by various aerospace companies remain essentially unchanged, this determines that the critical path of the products, as well as the Gantt chart representing the network with various tasks as nodes, are also largely consistent. In the process of manufacturing the chassis, almost all steps involve design drawings – manufacturing methods – production of the main beams – fabrication of the frame – and final assembly and testing. II. Constraints 1. Unstable technical condition and poor scalability of processing methods. Although the products developed at present offer significant reference value in terms of their technical characteristics compared to previous products, the adaptability of these new products to the entire new system is an important indicator for assessing their technical condition. Often, a single product is adapted to create a new product, but the process of developing this new one involves further exploration. To ensure production schedules, aerospace companies have adopted a production management approach that involves developing products while simultaneously finalizing their design and starting mass production. However, the repeated processes resulting from changes in product status, as well as the need to address quality issues that arise from such changes, consume resources and lead to disruptions in production planning. Due to the differences in process adaptability between newly developed products and those produced in bulk, and since it is not possible to add new production lines in the short term, adjustments must be made using existing resources for process planning. When equipment capacity approaches its limit, it is only possible to rely on the skills of the operators, which makes it difficult to ensure the stability of product processing quality. The increasing number of product repairs, reworkings, and reprocessing after scrapping, along with frequent adjustments to production plans, further increases the difficulty of control. 2. Virtual manufacturing is widely used. Virtual manufacturing refers to the process of starting with product design, creating technical documents, and then entrusting external manufacturers with the production tasks. These manufacturers process and assemble the components to form complete assemblies; after passing quality inspections during the production process, they are sent to the factory for final product assembly. Aerospace products are characterized by system integration. Over the course of their long-term development, although aerospace companies have built up certain manufacturing capabilities, the design and production of many key individual products still take place outside these companies. There is a large amount of product procurement and outsourcing, and to monitor the status of these products, track their progress, and ensure quality control, companies need to establish external control systems. This requires significant resources and also increases the complexity of production management and control. 3. Material control and balanced production are challenging. Zero inventory is a material management system for enterprises based on the JIT (Just In Time) model; it is a low-cost material management approach adopted after an enterprise has established a stable supply chain, and it is based on bulk ordering, low costs, and timely delivery. In the production management process of product development, repeated orders for small batches or even single products, along with short delivery cycles, significantly affect the timeliness of suppliers and the stability of the entire supply chain system. Issues such as reluctance to accept orders, inability to meet deadlines, and unstable product quality that lead to repeated orders increase the difficulty of ensuring a complete set of components, thereby hindering the smooth progress of production. In the production of multi-product, small-batch items, multiple projects proceed in parallel. The similarity between these projects leads to high demands for resources such as equipment and labor at certain times, resulting in conflicts; whereas as the product production process moves forward, these strained resources become idle at other times. This fluctuating usage of resources disrupts balanced production. 4. Locality of critical path control: The current production management processes primarily rely on critical path control. By establishing production plans for products, identifying the key and essential techniques, and determining the critical path that affects a particular batch of products, active support is provided in terms of resource utilization to ensure the smooth production of those products and thus maintain the overall progress of the batch. However, with the simultaneous introduction of multiple batches of products, conflicts arise in the critical paths for each batch. For example, there is a situation where CNC gantry milling machines have to wait in line during production, and sometimes it is necessary for management to make a decision on which product should be processed first. Since the critical paths for each batch all converge on the same machine, any delay on the critical path for a particular batch’s products will result in the inability to meet the production schedule; the localized nature of critical path management affects the overall progress of the production process. III. Countermeasures: Due to the environment of multi-batch, small-volume production, the aforementioned constraints arise. To overcome the impact of these constraints during the production process, efforts can be made in the following areas. 1. Strengthen horizontal design management and the research on diversified processes. Current design work is based on a vertical structure, with projects proceeding from top to bottom, involving a single product, a single design, and single production. In reality, aerospace products share similarities to some extent; there are parallels in terms of structural design, electrical design, and even the theoretical requirements of the entire system. Turning these similarities into interconnections can greatly reduce the complexity of production management. This requires the establishment of a horizontal design management system for the development of “basic modules”. For example, in the design and manufacturing process of chassis, companies usually focus their efforts on the design of a specific model of chassis. In reality, although different models of chassis have similar overall functions, they still possess some structurally similar parts and components. For instance, the steering system components used in different chassis models may differ only in terms of their external dimensions or the location of certain holes in those components. At the mold design stage, if a vertical design approach is adopted, a separate mold must be designed for each component; whereas with a horizontal design approach, only one set of molds is needed, and the excess dimensions can be removed through machining. It is necessary to conduct diverse research on processing methods to ensure that there are multiple possible approaches for producing a given product at the manufacturing site. For example, under current manufacturing concepts, in order to increase the production speed of products, it is common to use machining centers to achieve one-time shaping of the products. However, if the precision of conventional equipment is sufficient, then when resource constraints arise, the most reliable solution is to reallocate some of the products to handle the additional workload. Of course, it is not possible to wait until a product reaches a certain stage in the production process before considering alternative processing methods; rather, alternative approaches should be proposed ahead of time. This helps to mitigate resource conflicts significantly and facilitates the orderly progress of production. In addition, it is necessary to strengthen research on group technology, so that similar modules of different models can be processed in batches or groups to ensure processing efficiency and quality. For example, tooling is a means used to process products; it is usually designed to meet the processing requirements of a specific product. If the processing needs of multiple products are similar, producing tooling that can be used for these various products in advance of starting production will yield better results with less effort. 2. Focus on the key elements: The various problems arising from virtual manufacturing are mainly reflected in the fact that quality and timing cannot fully meet the requirements. During the process, only design technical specifications are considered; once the product is designed and manufactured, it becomes difficult to conduct acceptance checks due to the lack of mastery of the core aspects. Sometimes, even if the acceptance tests are passed, the product still fails to meet the required standards for use. Therefore, to ensure that virtual manufacturing meets the requirements, it is necessary to gain a deeper understanding of the relevant technologies. After designers submit their design specifications, the inspection personnel must conduct a thorough analysis of the products and physical prototypes, identifying the key data and acceptance criteria. If this cannot be done in a short period of time, it is necessary to monitor the virtual manufacturing process to determine those key data points, thereby ensuring that the products meet the requirements and improving the suitability of virtual manufacturing. 3. Create a virtual inventory space. Strengthen outsourcing and planning management; getting involved in advance is the best way to ensure timely supply of materials. Under the current circumstances, if material managers can understand in advance the composition and key properties of the products, they can identify the critical factors that affect production and make the necessary preparations ahead of time. It is common practice for designers to prepare a long-term material inventory list at the start of the design process, but the demand for other materials (those that are not critical yet important) emerges relatively later. However, such materials have a high degree of substitutability and are used across multiple models; therefore, considering the establishment of a virtual inventory is feasible. An analysis of such materials is carried out on an annual and quarterly basis; orders are placed based on the common characteristics of different models, and a detailed list of the materials is prepared. The delivery schedule is planned in stages. Once the official design drawings are available, material management can be conducted through a balanced planning approach, thereby reducing the costs and management complexities associated with small-scale, individual orders and ensuring timely supply of the materials. The biggest problem posed by parallelizing multiple projects is the bottleneck of resource drift over a certain period of time. Based on annual and quarterly planning as well as capacity balancing, different projects remain balanced in the long term. However, if a technical, quality, or management issue arises in one of the projects, it can cause changes in the timelines and milestones of various critical paths, thereby altering the existing resource bottlenecks – this is what is known as the problem of resource bottleneck drift. At this point, even with full utilization of equipment and human resources, the demands cannot be met, and it is not possible to replenish these resources in the short term; outsourcing can significantly alleviate the challenges posed by resource constraints. Therefore, to ensure balanced production, it is necessary to strengthen external cooperation management, make full use of market resources, and ensure coordination among all stages in order to meet production demands. In outsourced management, it is essential to pay close attention to the basic conditions of the market environment and its changes, to ensure that goods can be delivered out and brought back. Another issue that gives rise to bottleneck drift constraints is the delivery date. The current practice* is to start the process before the New Year, going through stages such as design, manufacturing, and production. Since the procedures are generally similar, the time it takes to reach the production site is roughly the same. There may be little production activity during one period, while another period sees a peak in activity. Therefore, the timing of starting production also needs to be determined based on the importance of the batches of products and various deadline requirements, in order to ensure smooth progress without interference between different tasks and to maintain balanced production. 4. To transform the critical path into a critical chain, it is first necessary to analyze the points of overlap between various production tasks. For example, if the key products of models A and B require the same production resources and are both located at critical nodes, then in practice it is essential to rank the importance of tasks A and B first, identify the priority tasks, and include them in the critical chain. However, for the scheduling of priority tasks, the available utilization rate of resources can only be set at 70%, with the remaining 30% designated as a buffer. As the node requirements for Task B and even Task C change, the buffer value is continuously adjusted to ensure that there are sufficient resources to meet the needs of multiple tasks (tasks outside the critical path). If a delay in the production of tasks B or C does not affect the demands for those tasks, then the buffer can be set to the critical value of 0, delaying the start of tasks B and C in order to avoid the impact of task interleaving. During the execution of tasks, it is crucial to update promptly the progress of each task as well as the level of buffer usage. If a critical step in task A has not yet been completed while all the buffers have been used up, it is necessary to add resources to replenish the buffers. To address the issue of a shortage of production equipment, it can be compensated for through outsourcing production and working overtime in shifts. The critical point of buffering is not easy to reach; process control involves determining the allocation of resources based on the ratio of the completion degree of various task chains within the entire production system to the level of buffer consumption, especially in situations where there is a shortage of resources for key equipment such as CNC gantry mills. Companies will give priority to products that require less time, while projects that take longer will be put on hold to ensure the rational use of resources. Production management is a management process for complex systems; the absence of any single component can affect the proper functioning of the entire system. When constraints arise, it is important to strengthen management and provide guidance in order to ensure the proper operation of the entire production management system. This article is authorized for reproduction. 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