Sales throughput: throughput
Throughput is calculated by deducting the total amount of invoiced sales and purchases relating to raw materials, transport or subcontracting. The calculation formula is T = Sales - Material costs.
The inventory corresponds to the investments made on the production line: equipment, maintenance, premises, etc. It also includes stocks valued at their purchase value. The formula for calculating the inventory is I = Investments + Stocks.
Expenses for band database transforming throughput into inventory: operating expenses
Operating expenses include all the expenses necessary to transform stocks into throughput. These include personnel costs, rent, taxes and duties. Operating expenses can be summarized by the following formula: OE = Sum of expenses - T.
The use of the theory of constraints in the OPT method
Definition of the OPT method
The OPT method , Optimized Production Technology, makes it possible to meet three objectives:
The OPT method is based on the following paradigm: the global optimum is not constituted by the sum of local optima.
The theory of constraints at the heart of the OPT method
The OPT method is deployed for production flow management. It naturally includes the theory of constraints. Its goal is to identify bottlenecks to eliminate unnecessary stocks in a production line.
The essence of the OPT method is to ensure an optimal lean flow through the production line so as not to create additional stocks and therefore unnecessary costs. Within a factory, not all machines have the same output capacity. Bottlenecks appear.
These bottlenecks negatively impact the manufacturing flow. The size of intermediate stocks is then likely to increase. The OPT method proposes to size production volumes based on the potential of the machines to avoid creating bottlenecks responsible for the creation of unnecessary stocks.
The critical chain method
The Critical Chain Method (CCPM) is a parallel to OPT, as it includes the theory of constraints. It was developed in the previously cited work by Eliyahu M. Goldratt. The critical chain method takes into account the task dependencies of a production system. It also takes stock of the resources required to complete the project.
These resources are subject to constraints whose origins are variable and more or less controllable upstream. In order to overcome these hazards, the critical chain method mobilizes so-called buffer resources. When they are used, they make it possible to deal with unforeseen events.
There are several types of buffer resources :
Buffer resources are material resources that can be mobilized in the event of a request from the critical chain. They include additional employees, auxiliary equipment, the use of external service providers, etc.
Buffer times are the additional time planned for a project. Adding them to the schedule helps anticipate delays on the traditional chain.
Buffer project deadlines are defined as the additional time planned between the final task and the project end date. This additional time allows for the final tasks to be completed before final delivery.
The critical chain method focuses attention on the due date of a project or the completion of tasks. The success of the chain is assessed based on the rate at which buffer resources are used. As long as the production team does not request additional resources, the project is considered to be on track. The critical chain is part of a process of continuous improvement.