The concept of balancing is based on designing a sequence of operations with the same duration.
in a system just in time, we are looking to set up smoothed and continuous streams to avoid out-of-beat, in-progress stocks… Task balancing is one of the tools to achieve this.
The concept of balancing is based on designing a sequence of operations with the same duration. By doing so, one can produce a Part-by-Part, avoid bottlenecks, and obtain a fluid production to work as close to the Takt Time.
The two approaches to balancing
Approach 1 : All Tasks have the same duration
This first approach is to put in place a perfect balancing of all tasks. This approach is only possible if the processes or demand have very low variability. The specifics of this balancing are :
- The bottleneck, if any, is permanently mobile.
- When a bottleneck appears, it is more difficult to identify it.
- Force to have additional resources in case the demand increases.
- Allows you to have a perfect blend to optimize efficiency.
Approach 2 : A bottleneck is ” forced “
This second approach is to voluntarily create a bottleneck. This is especially adapted to situations where variability in processes or demand is important. The characteristics of this balancing are :
- The neck is known and controlled.
- The Takt Time is adjusted with respect to the neck.
- Management manages the risks more easily because a degree of latitude is given.
- Allows you to manage a load supplement without having to add resources necessarily.
The task Balancing table helps the operational to organize the work. It also highlights opportunities for improvement by making all tasks more visual.
1. Collect Data
The first step in balancing tasks is to collect the entire process data in a table. The table is structured as follows :
In the class column, the process type is identified according to the following classification:
- Value-added task (VA) : These are the tasks that the client is close to paying. They aim to increase the value of the product (Shape, Mechanical property…).
- Essential Task (VAW) : Task with no added value but required. These are in particular tasks of recoveries, adjustments or controls.
- No value Added Task (NVA) : A task that does not change the value of the product. These are tasks Muda That we have to eliminate.
- Optional Task (VAV): The task that depends on the product specification. It can exist or not (for example, a car model can have a GPS or not), or have a variable time depending on the specification (for example, a computer can have 1 or 4 USB jacks).
2. Balancing graph
To help with the analysis of the balancing of operations, we will use a graph named Yamazumi. Literally translated as ” The “Ordered Mountain”, it’s a stacked histogram chart.
- In the X-axis: The different steps with each of them, stacking the subtasks with the associated color code.
- In order: The times associated with Substage.
- Finally, we add a line that corresponds to our Takt Time.
3. Choose the balancing approach
We will choose our balancing approach based on our level of variability in our processes. A 2% threshold variability in operations is a good practice. Thus, if the timings showed variability :
- > 2%: We’ll have to force a bottleneck to balance the line.
- < 2%: We can then aim for a perfect balance between the positions.
4. Choose the balancing option
4.1 In the case of a forced bottleneck approach
For this first approach, there is only one possible option. It consists of having a person who is fixed on the bottleneck Position and one or more others who share the other tasks. We detail an example below :
|Type de distribution||Opérations non équilibrés||Opérations équilibrés|
|Temps total par pièce||180 sec||180 sec|
|Goulot||90 sec||90 sec|
|Production / Hour||40||40|
|Conclusion||Nous avons un gain de 33%. Mais un opérateur court beaucoup.|
This solution allows us to gain in productivity. The downside is that we have a person who “ runs ” A lot, and this can lead to problems of safety and ergonomics.
4.2 Options In the case of a perfectly balanced approach
In this second approach, we have 3 possible balancing options that we describe below :
|Type de distribution||Etat initial : opérations non équilibrées||Option 1 : Plusieurs opérations par employé||Option 2 : Combiner des opérations entre employés||Option 3 : Une opération par employé|
|Temps total par pièces||180 sec||180 sec||180 sec||180 sec|
|Goulot||90 sec||60 sec||90 sec||60 sec|
|Production / Heure||40||40||40||40|
The choice is going to be based on 3 criteria :
- of social criteria: The staff is not versatile enough and does not want to become one, preventing us from having 1 same person in several positions. We will choose option 3.
- of the technical criteria: If the distances between posts are too large, option 1 is not possible. If technically the same Position cannot be combined (not enough space…), one will have to choose option 1.
- Ergonomic Criteria : Depending on the possibilities of combinations or distances, we will not be able to implement certain solutions for ergonomic reasons (distances too large, ” normal ” work plan not suitable for combination with other tasks…).
4.3 The specific case of serial machines
The elements described above work in the case of manual or semi-manual processes. But many processes are only composed of a series of end-to-end machines, connected by conveyors or accumulation tables.
The problem is that a machine represents the bottleneck, and that we cannot change the pace for technical reasons.
This particular case requires the setting up of a V-Graph. It will allow us to do the balancing study and ensure maximum productivity.
The V-graph is a graphic with:
- On the x-axis: The different equipment.
- In order: The pace of the equipment.
The challenge in this case is to build a graph in the Shape of V.
Why the V-Graph?
Let’s take an example of a pharmaceutical packaging line. This line consists of a suite of equipments with in order: The feeding bottle, the filling machine, the Corker, the label, the cartoning machine, the printing case, the Casher and the paletiseur. Most often, the bottleneck will be the Corker because performing a technically complex operation. As a first step, our flux study will give us the following V-Graph:
We will then tend to adjust the machines at a speed equal to or slightly higher than the bottleneck machine at about the speed of the bottleneck, to avoid over-stocks.
However, in order to optimize productivity, it is essential that it is constantly rotating: the basic principle of TOC Planning : It is not necessary to balance the gears but to unbalance them. Thus, in terms of graph, one will obtain a graph one V, the upstream and downstream machines having increasing or decreasing speeds but far greater than the speed of the bottleneck thus allowing:
- Upstream: To ensure that the bottleneck machine is powered.
- Downstream: to ensure that the products of the bottleneck machine are “aspirated“.
We then get the following graph, in the Shape of V:
5. Set up the action plan
With regard to the different data collected and the solutions chosen, we will implement the action plan. It will take depending on the options chosen redesign the posts and work lines, and make the staff more versatile.
6. Balancing Manager
Balancing management will be based on the change in the Takt Time. So :
- Takt Time is maintained : We will keep the operation we have.
- Takt Time decreases : Demand increases, the priority will be to rebalance tasks on the number of operators most important.
- Takt Time increases : The demand decreases, it will be necessary to redistribute the tasks on the number of the lowest operators and position the other people on other positions. An option is however to keep the same number of people as in the initial state, and to allocate the unproductive time to the improvement of the Position (problem solving, ergonomics, productivity…).
In this task balancing study, it is not recommended to have a chart with all process columns just up to the time of Takt. You have to keep a ” ” valve” to avoid overheating of the employees and to the risks of production (increase of demand suddenly, absence…). It is better to have a rate of 95%.
For example, if the Takt time of 10 minutes, the maximum time of the columns will be 9 mn and 30 sec.
B. Townsend (2012) – The Basics line balancing and JIT kitting
J. Niederstadt (2010) – Standardized work for noncyclical processes
O. Fontanille, E. Chassende-Baro, C. De Cheffontaines, O. Frémy (2010) – Reduce losses in design, production and industrialisation