Last Updated on 16 September 2023
When creating products in a production line it is usual to run different the processes as fast as you can. This can be measured by cycle time, which is the time it takes for one part to be processed by that station. Variances in the cycle time will cause bottlenecks and stock buildup, leading to waste. You can use line balancing to reorganize the production line to remove this waste and the bottlenecks.
What are we trying to achieve?
The main purpose is reorganizing the resources and workloads of the production line processes to remove bottlenecks and excess capacity that harm efficiency. This is achieved by equaling the cycle times (running speeds) of the different processes. The aim is to equal them all at the takt time, which is the speed needed to meet customer demand.
What does line balancing do?
You will want to do perform this for any system that has inventory building up or processes waiting for another one to catch up.
As it increases efficiency, you can use it as part of the Improve phase of Six Sigma DMAIC, or as part of a lean improvement project such as part of kaizen or as a kaizen event. If you’re not managing to meet customer demand or you find a lot of waste in your organization, line balancing can help improve the situation.
It is often one of the tools you will use after creating a value stream map to improve the efficiency of the process you have mapped.
What are the benefits?
When the different processes are running at different cycle times, it can cause you major issues such as bottlenecks and processes not keeping up with demand. Sortingthese out will bring you several benefits:
Reduce waiting waste
When production is uneven, the processes will spend a lot waiting, when they previous station can’t keep up. When people are waiting for a job to do, you are gettingvirtually all of the costs of operations but none of the revenue, causing huge amounts of waste. With even production, there will be a constant supply of work, removing this waste.
Reduce inventory waste
When you have bottlenecks (which occur without line balancing), inventory will build up at the slower processes. This inventory ties up your working capital, and takes up space to be stored, getting in the way and increasing production costs. There is also increased risk of stock obsolescence and stock losses in case of issues (such as floods; it’s happened to me!).
Meet customer targets
Customers often want their deliveries quickly, and they sometimes can even fine you if you get it to them late. Missed deadlines upset your customer, losing you sales. When you level out your production, your waiting time will greatly reduce, improving your lead times.
Your products will go from order to being with your customer a lot quicker, improving your reputation with your customers, often leading to improved sales.
With uneven production, you will have bottlenecks in your production where a slow process will be holding back production. As your product needs to go through every station, you are only as fast as your slowest part. Balancing out your production virtually always increases the speed of your slowest part. This will increase the number of products you can make.
Reduce production costs
Optimized production will have your cycle times all at the same level. Where you currently have processes running faster than takt time, these can be slowed down, saving resources as you can use less machinery and staff time, saving power, depreciation and wages.
If your processes are running at different speeds, the slowest will often need more time to ‘catch up’. Assuming you want the other processes to be running all day so you don’t have workers waiting around, you will catch up using overtime, which can be expensive as you’ll need the operations to be open and running, supervisors there, security, power etc. and enhanced pay to keep staff there longer. It may even prevent you from adding extra shifts, as it will run operations into that time. Leveling out your operations keep overtime to a minimum, and so remove all these actual and opportunity costs.
How do we improve efficiency?
When the processes are running at different speeds, you end up with waste; line balancing can help you remove this. The aim is to make the cycle times of all of the processes equal to the takt time.
The best way to do this is using operator balance charts. These are a graphical representation of the cycle times for the different processes compared to the takt time, which is the target production speed.
Step by step guide:
1. Calculate your takt time
There will be a level of output that is needed to be met in order to meet customer demand. This can best be shown by the ‘takt time’, which shows the cycle time (time per item made) required to meet current demand levels. If cycle time is running slower than this for any station, we won’t meet customer demand. This can mean deadlines will be missed, revenue will decrease and even fines for your organization.
The takt time is calculated by a simple formula:
Takt time = number of units of demand / amount of time available
It is the amount of time that you have available to make each unit to meet your customer orders.
2. Work out your production chain
You need to know what production chain you’re analyzing. In simple organizations, this may be obvious, but it in complicated operations making a process map is usually the best option. A value stream map will serve this purpose and provide most of the metrics you need, making it a good option for line balancing.
3. Calculate the cycle times
The cycle time is the measurement of how fast the process is working, or to be more exact the length of time it takes to produce one unit. The formula is:
Cycle time = number of units produced / time in production
Calculate these for all of the processes in the production line, and write them on your process map.
4. Operator balance charts
The operator balance charts are a bar diagram of the different cycle times that you are trying to balance. You also add a line for the takt time, which is the cycle time all of the processes need to meet to make customer demand.
We can use this to see where we have spare capacity, and which processes are not going fast enough to meet demand. The aim is to have all of the cycle times running at the same speed as each other, preferably above the takt time.
5. Rearrange resources
You want to move your resources around so that all of the cycle times meet the line. The most obvious method is to move operators from one with excess capacity to one that is struggling. If your stations have more than one worker at them, you can often speed up one station (reducing cycle time) and slow down another (increasing cycle time) by moving an operator from one station to another, for either part of or the whole shift.
This can be a very quick and easy method of line balancing, but if that doesn’t work there are more options:
6. Split your tasks
Process 2 looks like it’s one big task, but it often isn’t. Most processes will have several tasks that they need to do before they can pass the product to the next station. Split your tasks into subsections and it’s more likely that your graph looks something like this:
Time the individual tasks and split them up on your operator balance chart.
7. Moving tasks
With your newly split chart, you can line balance through rearranging the tasks between the different processes. You can even print and cut out the different bars to see how different combinations look!
An option in this example is moving task 1 of process 2 to the end of process 1. Your graphs will end up like this:
We’re still not meeting the takt time, but the flow through the system will be much improved, greatly reducing the waste in the system.
8. Balancing through investment
You can’t always balance the different production lines through rearranging your current resources, such as if there is only one operator at each station doing a single task each. The solution for these situations often then needs added investment. This can involve adding resources (such as extra operators or machinery) to one of the stations or even adding parallel stations that work at the same time.
Adding resources is usually the cheapest and easiest option of investing in new capacity. Often you can reduce the cycle time of a process by adding operators, or automating part of the operation.
You can ‘move the goalposts’ by increasing the time available through overtime or adding an extra shift. This will reduce the height of the takt time line, making it easier to achieve. In the example above, adding 25% overtime to the time available would move the takt time above all three bars, meeting customer demand.