Some companies use IT systems to manage production and run smoothly; some companies can also arrange production in an era without IT systems. It can be seen that the puzzle of planning management is not caused by methods and tools, but by the consistency between the logical calculation method of the plan and the actual production scene.
01
The purpose and realistic conditions of the production plan
The main purpose of production plan management is to use, combine, and adjust the existing production resources of the enterprise to meet the needs of customers for timely delivery while at the same time the lowest cost. Production resources refer to operators, production equipment, production materials, working hours, etc. used for production. Why does a “reasonable” production plan always appear chaotic or unreasonable in actual implementation? There are several reasons.
First, market demand is fluctuating, while production resources are fixed values in the short term, which creates a difference between production capacity and demand. Pre-production and inventory are used to make up for this difference, and often because the production is scheduled according to forecast, it causes inventory backlog, and there is still no reserve for the actual production needs.
Second, various abnormalities will always occur in the production process, which can be avoided as much as possible through improvement, but it is impossible to eliminate it to “zero”. The various “zeros” in the Toyota Production System are the ideal state it pursues to lead continuous improvement. TPS in reality hides a lot of “buffer resources” to deal with abnormalities.
Third, production is an interdependent process, and any abnormality in any link will affect the output of the system.
Fourth, the existing production resources are often relatively simple in function, and market demand is changing, which leads to the total production capacity seems to be sufficient, but for specific orders, the capacity is often insufficient.
The above four questions let us rethink the function of production planning and lead the direction of production improvement from the perspective of planning.
02
Resolve conflicts between supply and demand
To resolve this contradiction, we must learn from Toyota’s total leveling mechanism. After the “World War II”, Toyota Motors faced the domestic market demand for multiple varieties and small batches. If we produce according to actual demand every day, we must prepare production resources according to the upper limit of market fluctuation, which will result in a waste of capacity. Therefore, Toyota accumulates the total market demand (exact orders + market forecast) in the next month, and then allocates the total demand evenly to each working day, and production resources (equipment, personnel, inventory) are prepared according to daily demand. In this way, it not only ensures the balance of supply and demand within a month, but also minimizes the occupation of production resources.
The total leveled data can be completed in the form of virtual orders using the ERP system. The calculated data is only used for the preparation of production resources to form a “Production Capacity Preparation Plan”, which determines the number of shifts, equipment, number of operators, and the number of varieties of raw materials (previous to suppliers).
Do not produce or purchase raw materials according to the forecast data, as there is a big risk; prepare according to the forecast, even if there are more preparations, there will be no side effects.
In reality, there is a lot of excess capacity in the society, and there is no need for companies to purchase more equipment (except for high-precision and sophisticated). Just level the total amount and do a good job in resource development. The development and sharing of resources is not limited to production capacity, such as equipment spare parts, raw materials, and operating staff can be developed and shared. If resource development is taken as a strategic decision, the production of enterprises will be more comfortable.
03
Scheduling and locking
The actual production scheduling plan is based on the actual order: the daily production volume is determined based on the CT or beat of the bottleneck process; the production cycle is measured based on the intermediate quantity and process abnormalities; based on the current production task, the start of the new order is determined time. The data of the production scheduling plan needs to be adjusted manually according to the actual situation, and the IT system only needs to provide the basic formula.
Under the premise that demand forecasts are transformed into production resource preparations, because production according to forecasts is strictly prohibited, a planned lock-in period must be inverted based on the order date of production, so that suppliers have time to produce the required raw materials, parts, and production. And transported to the production site of the enterprise.
For reusable raw materials or parts, you can set a certain amount of inventory, use the inventory to supply production, and use inventory consumption to drive purchases. Even if all the raw materials are in stock, a short plan lock-up period is required for internal production preparations. Therefore, according to the actual production schedule, a “production preparation plan” should be compiled. The status of production preparation and the monitoring of production progress can be realized by MES.
04
Abnormal response strategy
Abnormalities in production (equipment failure, poor quality, raw material supply, etc.) are uncertain. When scheduling production, additional resources (buffer) must be considered to digest abnormalities. Therefore, if the buffer is not used well, the cost may be wasted.
Buffer can be divided into material buffer (safety stock), time buffer (relax time), capacity buffer (reserved equipment capacity and operator). Which buffer is most suitable? Can calculate costs and benefits. Time buffering (relaxing time) directly extends the production cycle, delays capital turnover, and reduces the sensitivity to market changes. Material buffering indirectly prolongs the production cycle, delays capital turnover, reduces sensitivity, and increases capital occupation. The capacity buffer is the most reasonable. Reserve a certain amount of equipment capacity, which only increases the capital occupation.
Reserve more personnel (excellent ones temporarily leave the operating post), and when they are not required to operate, they can make various improvements, multi-functional training, work standards and so on. You can also arrange for them to go to positions such as deputy squad leader, engineer assistant, etc., to complete the transactional work of the principal, and exchange a “low-paid deputy” for a “high-paid engineer”.
The reserves and investment of human resources are value-added. Attrition to the extreme, material buffer and time buffer must be used to deal with abnormalities.
05
Goal-on time
Through rolling demand forecasts, a “Production Capacity Preparation Plan” can be formed to guide the development of excess capacity in society. You can schedule production according to actual orders, calculate the production date, and determine the plan lock-up period to implement the “production preparation plan.” At the same time, use flexible capacity buffers (especially manpower) to cope with uncertainties.
It is difficult for us to achieve “on time” as Toyota did in the short term, but with the support of the above strategy, we can achieve “on time JIT (D) on working days” within a few months, that is, weekly demand leveling, three The level of daily plan lock-in, production scheduling by order, and daily settlement.
The optimization of the production planning system must also follow the principle of continuous improvement, and must not pursue one-step completion.
