BY AMT ERP Research Group)
In the 1960s, MRP can calculate the accurate time and quantity of related material requirements according to the relevant data, but it is not perfect, and its main drawback is not considered to consider the existing production capacity and the relevant conditions of the company's existing production capacity and procurement. Therefore, the calculated date of the calculated material is likely to produce due to insufficient equipment and work, or cannot be produced due to insufficient raw materials. At the same time, it lacks the function of adjustment of the plan according to the feedback information of the plan implementation.
It is to solve the above problems, and the MRP system is developed into a closed-loop MRP system in the 1970s. In addition to the material demand plan, closed-loop MRP system also incorporates production capacity demand plan, workshop operation plan, and procurement work plan into MRP, forming a closed system.
1. The principle and structure of closed-loop MRP
The normal operation of the MRP system requires a real-feasible main production plan. In addition to reflecting market demand and contract orders, it must meet the production capacity constraints of enterprises. Therefore, in addition to preparing a resource demand plan, we must also develop a capacity demand plan (CRP) to balance the capabilities of the various work centers. The plan can be started only when the measures are taken to achieve capacity and resources to meet load requirements.
To ensure that the implementation plan is to control the plan. When performing MRP, you should use the MRP to control the priority of the machining, and the procurement priority is controlled by purchasing. In this way, the basic MRP system further develops, and the functionality of the competency plan and execution and control plan is also included, forming a ring loop, referred to as a closed loop MRP, as shown in Figure 1.
Figure 1 Closed loop MRP logic flow diagram
Therefore, closed-loop MRP is a complete production plan and control system.
2. Capacity Requirement Planning, CRP)
(1) Resource demand plan and capacity demand plan in closed-loop MRP, the load balance of key work centers is called a resource demand plan, or called a crude capacity plan, its planned object is an independent demand, mainly the main Production Plan; putting the load balance of all work centers as a capabilities plan, or a detailed capability program, and its planned object is the relevant demand, mainly the workshop. Since there is an internal connection between MRP and MPS, there is also a pulse between the resource demand plan and the capacity demand plan, and the latter is calculated on the basis of the former.
(2) Basis of the Capacity Demand Plan 1 Work Center: It is a collective representation of various production or processing capacity units and cost computing units. For the work center, the size of its capacity is quantified by uniformity. 2 Work Calendar: It is a special form of calendar used to prepare a plan. It is made from a normal calendar to remove a week, holiday, shutdown, and other do not produce days, and expands the date as a sequential form. 3 Process Route: It is a document that reflects a "material" processing method and processing order. It illustrates the process sequence of processing and assembly, the work center used by each process, time and cost of each time, the time and cost of the outer process. 4 The components work plan output by MRP.
(3) The basic goal of the capacity demand plan is the basic goal of MRP, the basic goal of MRP is to meet the needs of customers and markets. Therefore, when the plan is prepared, it always guarantees the planning requirements and then makes the ability plan. After many repetitive operations, the adjustment verification is transferred to the next stage. The arithmetic process of the capacity demand plan is to convert the material demand plan to the number of capacity demand, and generate a capacity demand report. This process can be represented by Figure 2.
Figure 2 Capacity requirements report generation process
Of course, there may be a case where you can have overload or low load in the scheduled period. The closed-loop MRP capability plan is usually reported to the planned person by the form of the report (the histogram is a common tool), but does not perform the automatic balance of capacity load, this work is done by the planner.
3. On-site operation control
After the work center capability is basically balanced, the next step is to focus on how to specifically organize production activities, so that all resources can be reasonably utilized and completed all order tasks on time, and perform objective production activities. The status is timely feedback to the system to adjust and control according to the actual situation, which is the on-site job control. Its work generally includes the following four aspects:
The workshop order is under: the order will be a plan order generated by the MRP, and converted to the next order. Job Sort: It refers to the job order or job priority of the working center from the angle of the work center. Input output control: It is a technical approach to monitoring operation streams (working in work) through the work center. Using investment / output reports, you can analyze the problems in production and take appropriate measures. Job information feedback: It is mainly to track the exercise of the job order in the manufacturing process, collect the actual data of various resource consumption, update the balance of the inventory and complete the MRP closed loop.
