Optimizing the work of a company, especially a manufacturing enterprise, is one of the most important conditions for the company's existence. Not only does competition require an uninterrupted flow of the production process. Current trends in minimizing the cost of manufactured products suggest first and foremost the elimination of downtime and the consistency of operations.
To solve these problems, a methodology is used to optimize the activity and calculate the timing of work. The developed network schedule allows you to determine the logical sequence of individual operations, the possibility of combining them in time, as well as the timing of the entire production cycle.
One of the methods of effective planning of the activity of a production enterprise is the construction of a network schedule. Initially, it was used in construction and determined not so much the sequence of work as the timing of entry to the construction site teams of workers of different specialties. It is called the "work schedule".
In modern conditions, when large enterprises mass produce products, to simplify and improve productivity, the entire process is divided into simple operations. Therefore, the network schedule "migrated" from construction to virtually all industries.
So, what is displayed in this document? First, all operations necessary for the release of goods (production of services) are listed in the most detailed manner. Secondly, the logical interdependence between them is determined. And, finally, thirdly, not only the timing of each particular work is calculated, but also the time necessary to complete the production process.
Disclosing the internal dependencies of project operations, the network schedule becomes the basis for scheduling the workload of equipment and labor.
The notion of "operation" in network planning
In the network schedule, you can estimate the periods of the beginning (completion) of the work, the forced downtime and, accordingly, the maximum delay in the production of certain operations. In addition, critical operations are identified - those that can not be performed with a deviation from the schedule.
Understanding the terminology of planning, it is necessary to clearly understand what an operation is. Most often, this means an indivisible part of the work, which requires time for execution. Next, we understand that the costs associated with the operation are: time and resources (both labor and material).
In some cases, no resources are needed to perform any actions, only time that takes into account the network schedule is required. An example of this is the expectation of congested concrete (in construction), the time of cooling of rolling parts (metallurgy) or simply the approval (signing) of a contract or permits.
Most often, operations in planning are given the name in an imperative mood (develop a specification); sometimes for names use verbal nouns (specification development).
Types of operations
When drawing up a network schedule, several types of work are distinguished:
- merging - this operation immediately precedes more than one job;
- parallel operations are performed independently of each other and, at the request of the design engineer, can be performed simultaneously;
- a fractional operation assumes that after performing it, you can perform several unrelated works at once.
In addition, there are several more concepts needed for planning. The path is the time for execution and the sequence of interdependent operations. And the most long way of the whole system of works is called the critical way. In the event that some kind of operation on this path is not performed in time, the implementation time of the entire project is disrupted.
And the last: an event. This term usually refers to the beginning or end of an operation. The event does not require resources.
What a graph looks like
Any graph familiar to us is represented by a curve located on the plane (rarely in space). But the form of the network plan is very different.
The network project schedule can look in two ways: one technique assumes the designation of operations in the nodes of the block diagram (OC), the second uses the connecting arrows (OS) for this. It is much more convenient to use the first method.
The operation is indicated by a circular or rectangular block. The arrows that connect them determine the relationship between actions. Since the names of the works can be quite long and voluminous, blocks of operations numbers are placed in the blocks, and a schedule is prepared for the schedule.
Rules for the development of graphics
For correct planning, you need to remember a few rules:
- The schedule is unfolded from left to right.
- Arrows denote the relationship between operations; they may intersect.
- Each simple job must have its own serial number; Any subsequent operation can not have a number less than the previous one.
- The chart can not have loops. That is, any looping of the production process is unacceptable and indicates an error.
- You can not use conditions when a network diagram is built (an example of a conditional order: "if the operation is performed, perform work ... if not, do not take any action").
- To indicate the beginning and end of the work, it is more convenient to use one block that determines the initial (final) operations.
Drawing and analysis of the graph
For each work it is necessary to find out three points:
- The list of operations that must be performed before this work. They are called precedent with respect to the given.
- List of operations that are performed after the specified action. Such works are called the following.
- List of tasks that can be carried out simultaneously with the specified. This is a parallel operation.
All the information obtained gives analysts the necessary basis for constructing logical relationships between operations that are part of the network schedule. An example of the construction of these relationships is given below.
The actual schedule requires a serious and objective evaluation of the production time. The definition of time and its inclusion in the schedule makes it possible not only to calculate the duration of the entire project, but also to identify the most important nodes.
Calculation of the schedule: direct analysis
Estimating the time costs for performing one operation is based on the normative effort. Thanks to the direct or inverse calculation method, you can quickly navigate in the order of performing work and identify critical steps.
Direct analysis allows you to determine the early timing of the beginning of all operations. Reverse - gives an idea of the late term. In addition, using both analysis techniques, you can not only establish a critical path, but also identify time intervals for which you can delay the execution of individual jobs without disrupting the overall timing of the project.
Direct analysis considers the project from start to finish (if we talk about the chart, then the movement is from left to right). During the movement of all the chains of operations, the time for executing the entire set of works increases. Direct calculation of the network schedule assumes that each subsequent operation begins at the moment when all previous ones end. It must be remembered that the next work starts at the moment when the longest of the immediately preceding ones will end. At each step of the direct analysis, the execution time of the settlement operation is added. So we get the values of early start (ES) and early completion (EF).
But one must be careful: the early termination of the preceding operation becomes the early beginning of the subsequent operation only if it is not a merger. In this case, the start will be an early termination of the longest of the previous works.
When reverse analysis takes into account such parameters of the network schedule: late completion and later start of work. The name suggests that the calculation is from the last operation of the whole project towards the first (from right to left). Moving towards the beginning of work, it is necessary to subtract the duration of each action. Thus, the most recent start dates (LS) and endings (LF) of the work are determined. If the project timeframe is not initially set, then the calculation starts from the late end of the last operation.
Calculation of time reserves
Having calculated the network schedule of works in both directions, it is easy to determine the time delays (sometimes use the term "fluctuation"). The total time of possible delay in the operation is equal to the difference between the early and late start of a particular action (LS - ES). This is a temporary reserve, which will not break the general terms of the project.
After calculating all the oscillations, they begin to determine the critical path. It will go through all operations for which there is no temporary downtime (LF = EF, and accordingly LF - EF = 0 or LS - ES = 0).
Practical advice on meeting deadlines for the implementation of projects
Of course, in theory everything looks simple and straightforward. The developed network diagram (an example of its construction is shown in the figure) is transferred to production and is implemented. But what is behind the figures and calculations? How to use possible technological downtimes or, on the contrary, avoid force majeure situations.
Specialists in the field of management propose the appointment of the most experienced employees for performing critical operations. In addition, when evaluating project risks, it is necessary to pay special attention not only to these steps, but also to those that directly affect the critical path. If there is no possibility to control the progress of the work as a whole, then it is necessary to find time to obtain the primary information precisely from operations of the critical path. It is a question of talking directly with the performers of such works.
Network graph - a tool for optimizing the activities of a company
When it comes to using resources (including labor), the head is much easier to dispose of them, if there is a network schedule of works. It shows all outages and the employment of each employee (team). The use of non-employed worker on a single object to implement both allows to optimize the operation of the company as a whole.
Do not neglect and another practical advice. In reality, project managers are confronted with "the desires of higher management" to see the work done "yesterday". In order to avoid panic and the release of marriage, it is necessary to increase resources not so much on critical path operations as on those directly affecting it. Why? Because there are no downtime on the critical path, and it is often impossible to shorten the time of production.