In order to maximise output, increase profits or to remain competitive, firms must continually look out for ways to maximise efficiency. One of the ways in which organisations can increase efficiency is through line balancing. Line balancing ensures that workers and machinery work together in a balanced way. That way no worker or machine is overburdened or idle. By minimising downtime line balancing reduces waiting waste.
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What is Line Balancing
Line balancing refers to balancing the production or assembly line. It is a production strategy concerning the balancing of operator and machine time. It involves levelling the workload across all processes in a cell or value stream so that bottlenecks and excess capacity are removed. The objective of line balancing is to match the production rate after all wastes have been removed to the takt time (the rate at which products must be produced in order to meet customer demand). The line is perfectly balanced when production time equals the takt time. If not, bottlenecks and excess capacity may hold up production. Also, an optimal production rate is achieved when labour and machinery are balanced.
Line Balancing Example
In this simplified example, suppose that a production line has 2 machines that produce 2 different parts of a product:
Machine X, producing the first part, manufactures 5 per hour,
Machine Y, producing the second part, manufactures 10 pieces per hour,
Since Machine X has minimum capacity, producing only 5 pieces per hour, machine Y will remain idle for 50% of the time indicating that the line is unbalanced. One way to balance the line is to assign 2 machines of type X to machine Y or to assign another task to machine Y so that it doesn’t remain idle. That way tasks are evenly distributed over the workstations so that idle time and excess capacity of both men and machinery are minimised. Line balancing is used to group tasks and workers in an efficient pattern to enhance an efficient flow of production. Tasks can be grouped in such a way that total time taken is equal to or less than the time available at each workstation.
Methods of Line Balancing
In order to solve problems that arise from an unbalanced line several methods can be applied. For intermittent flow systems and where problems are complex, heuristic methods are applied because of their low costs. When the system is continuous with high volume production linear or dynamic programming will be suitable although the methods are costly and time consuming. Heuristic methods give the most likely solutions whilst linear and dynamic programming give optimum solutions.
Heuristic methods are experimental methods used to develop solutions for product layout problems. These are:
- Incremental Utilisation heuristic
Tasks are added, one at a time, to each workstation in the order of task precedence until utilisation is at 100%. This method of line balancing applies when the time taken by one or more tasks is equal to or greater than the cycle time.
- Longest task time heuristic
This method of line balancing also add tasks one at a time to each workstation in the order of task precedence. If a decision has to be made between 2 or more tasks the task that takes the longest time to complete is added first so that those that take less time are used to determine the optimum solution.
Linear programming is a mathematical tool that is applied when solving minimisation or maximisation problems. It is characterised by linear functions and constraints that can be written as inequalities. In line balancing, linear programming is used to determine the exact number of workstations that are needed together with the tasks that should be assigned to each workstation. Equations are used to represent the constraints, for example, cycle time and task constraints can be formulated with the aid of inequalities.
Dynamic programming is another method of line balancing. It is applied to find the fastest route from start to finish in assigning tasks to each workstation, that is finding optimum scheduling. Dynamic programming can be used to find the best solution using optimum solutions to sub problems, which are determined by optimum solutions to the sub, sub problems. The constraints that slow a process down can be removed.
Benefits of Line Balancing
There are various advantages of line balancing, and these are outlined below.
- Reduction waiting time
Waiting time is regarded as waste time, and this can occur in an instant when a worker waits for a machine or another person to complete a task. Machine downtime is another type of waste time that occurs when equipment is not operating. Any idle time that occurs when operations are not in sync can be reduced by line balancing.
- Reduction in inventory waste
Line balancing reduces inventory waste by ensuring that there is minimum work in progress. By standardising production build ups or surplus inventory can be reduced. Also, on time delivery is guaranteed by bringing production time closer to takt time.
- Absorption of irregularities
A balanced production line is stable and flexible. If takt time changes as a result of customer demand fluctuations, production can be readjusted quickly through line balancing.
- Increase in Profit
With the help of line balancing, no operator or worker is paid for remaining idle. All resources can be utilised to their full potential. That way, costs are minimised, and profits will increase.
- Identifying bottlenecks and excess capacity
Line balancing can assist in identifying bottlenecks and excess capacity. Late deliveries or high transport costs can be discovered by increases in takt time. excess capacity can be observed from workstations that take less than takt time. if the constraints can be discovered through line balancing resources can be reallocated appropriately.
Disadvantages of Line Balancing
- Rebalancing may cause disruptions to production and loss of production time
- Changes to production lines may lead to out of balance flows
- The investment and training costs for line balancing are high
- Production, planning and control is generally challenging
- With regards to linear programming, a specific objective function and the various constraints may be difficult to determine
- Sometimes the constraints in line balancing cannot be expressed as linear inequalities