The development from MPS to MRP and MRPII
As the name of MRP (Material Requirement Planning) indicates, it is to calculate the net requirements for planning the procurement of parts and materials in the future by developing products into parts and reserving the inventory, issued manufacturing orders and purchase orders.
In the case of pure MRP function only, strictly speaking, it is necessary to prepare the MPS of the product by oneself with Excel, etc., and MRP only calculates the requirements of work-in-progress and materials by taking into account the inventory allowance and safety stock.
Another MRP is called Manufacturing Resource Planning (MRP II), which includes the process of generating an MPS based on order orders and unofficial notices before the conventional MRP, and includes the process of creating a purchase plan from the material requirements calculated as a result of the MRP.
Normally, the quantity of orders received from customers is variable, so the method of manufacturing only the net requirements of products after reserving the product inventory with the order order order or informal notice as the starting point for MRP calculation is applicable only to the industry where the demand can be predicted to some extent.
This function is similar to MRP II in that it creates MPS by subtracting the product inventory from the order and unofficial notice and considering the minimum inventory, develops parts and calculates the required quantity, creates the manufacturing order as a result, allocates resources in consideration of load leveling, issues manufacturing instructions, and issues a purchase order based on this.
The core of business system (ERP) is MRP II, and the core of MRP II is MRP, in which the creation of MPS is very important, and the distinction is made between products, which are managed by MPS, and materials and work-in-progress, which are managed by MRP.
Lead time staggering
Originally, an MPS is a production plan for a final product that is created with the agreement of the sales department, which emphasizes shipment schedules and forecasts from the perspective of customer service, and the production planning and inventory control department (PPIC), which wants to take into account conditions on the shop floor.
In the case of Indonesia, as far as I can actually see in the field, the MPS is prepared mechanically by the production management department from the notice and shipping schedule received from the sales department, and the sales department does not intervene much in the MPS preparation stage.
The unit of Lead Time (L/T) is in days, and the timing for issuing manufacturing orders is calculated by shifting the L/T in days for each process, which means that the manufacturing L/T is moved forward by one day, whether the order quantity is one unit or 1,000 units.
Making the L/T a daily basis means that we can plan for regular orders rather than small orders such as sample production or large orders that rarely occur.
If a large order is received, it should be handled by load leveling, such as assigning work to multiple machines in parallel, and this is not a problem that MRP can handle.
If you can't deal with this, it means that your capacity planning is wrong in the first place. Or the problem of salesmen taking 100 orders against a capacity of 10 per day.
The purpose of MRP is to create a gross production plan to produce the net requirements in normal production, and the production plan created by shifting the MRP lead time comes into existence only after human efforts such as the coordination ability of the field and production preparation (capacity planning and sales planning).
When these limits are reached, the production plan and capacity plan become unbalanced, and as a result, MRP issues inefficient manufacturing instructions, resulting in unnecessary overtime, holiday work, and intermediate inventory stagnation, even though the production capacity is sufficient.
In order to solve this problem, the introduction of Advanced Planning and Scheduling (APS) with finite capacity without time buckets is being considered.
The MRP process
First, the Production Management Department prepares the daily MPS from the unofficial notice prepared by the sales staff, taking into account the facility capacity.
At this time, if the products with small orders are evenly divided into days, it will take a lot of time to set up, so we make adjustments such as concentrating production at the beginning of the week or the beginning of the month.
When the requirements are expanded and the net requirements are calculated by spreading MRP, the manufacturing order is created without considering the resource capacity, but at the same time, the monthly operating hours required to manufacture the final product or work-in-progress are calculated.
A production order is created directly from the order and a string is attached to the order without the lot consolidation.
Since there is a big difference between MRP and serial number control in terms of whether or not the lot is consolidated in the manufacturing process, it is referred to as "MRP corresponding to serial number control" in the system, even though it is treated as a relative concept in technical books.
MRP capabilities of APS
In the ERP system, after the MRP is turned around, the resource allocation work (scheduling) is done while considering the load leveling of the manufacturing orders, and then the MRP for material procurement is turned around once more, so that it is possible to make a purchasing plan to get the materials in at the timing needed for manufacturing.
The thing that automates this and makes it possible to output manufacturing orders and purchase orders at once from the MPS is the APS and with a production scheduler that has an APS function the process from MPS generation onwards can be automated at once.