The Know-How of Line Balancing

“Good line balancing with small stocks in the sewing line has to be drawn up to increase the efficiency and quality of production”

In garment industry, line balancing is a method of levelling the workload for all processes in a line in order to remove the bottleneck operation and excess production. Bottleneck operation refers to those operations which reduces the productivity of rest of the operations in a line. Hence it can be stated that bottleneck operations decide the output of a line.

The objectives of line balancing are to

• Ensure regular flow of material throughout the line
• Maximize the use of manpower and machine capacity
• Minimizing the process time
• Maximizing the output at the desired time without affecting the quality of the materials produced
• Reduce the production cost

“In order to balance the sewing line as well as to increase the efficiency of the line, at first a detailed work and time study has to be carried out to calculate task durations” (Niebel, 1976).

But before those are conducted, one need to understand the two types of line balancing which are usually done, namely

• Pre- Load Balancing

This balancing is done when the operation breakdown for a style is made. After all the operations which are needed to produce a garment is jotted down, the I.E. receives list of machines available along with the number of operators available. After both the lists are received, the I.E. allocates the machine to the operators in such a way that minimum operators and machines produces maximum target output.

The target output is usually set according to the daily required target output which meets the shipment date of the order.

After the initial balancing is done, the line in-charge goes to the line and further observes the set process. The process flow after pre- load balancing is stated below:

Hence if the need arises, the line in-charge does the dynamic line balancing.

• Dynamic Balancing

Dynamic balancing is done during production. The line in-charge goes to the line and he looks at the operations being done. By looking at the operators having high WIP he then rearranges the input available in order to keep up with the output demand.

In dynamic line balancing, firstly the I.E. finds output of each operator and then finds the bottleneck and overproducing operations. Then a graph is made with target output as constant.

The bottleneck and overproducing operations are then analyzed, and checked if there is any problem with the method. If there is need, then method improvement activities are done.

For example in the graph shown on next page one can see the typical line output of polo neck t-shirt:

If we observe, we can see that our first major bottleneck is at operation number 3.

Here Operation 2 produces 240 pieces per hour

Operation 3 produces 142 pieces

Hereby we can first start balancing the line by managing operation 2 & 3

After studying the capacity of individual operations, the next process of balancing will be to observe the output of operations against the capacity. This step is called capacity study of operation.

Tools required:

• Stop watch
• Spread sheet or Calculator

Step 1: Capacity study: List down all operations (with operator name) as per operation sequence in a paper. Using stop watch, calculate cycle time (time study) for each operation for five consecutive cycles. With average cycle time calculate hourly capacity of the operators. (For e.g., if operation cycle time is 30 seconds and total allowances is 20% then capacity is 100 pieces per hour). Draw a line graph with per hour capacity data.

Step 2: Target setting: With the above capacity data, check current hourly operator production report. Draw a straight line with target output data on the line graph.

Step 3: Identification of bottleneck areas: Now we compare the output of operators with the target output. Each individual operator whose output is less than the target output is bottleneck operation for the line.  For example as mentioned in the case in previous section, operation number 3, 6, 10 and 11 seems to be major bottlenecks of the line

Step 4: Then bottlenecks from the line are removed using following methods:

• Operation sharing is done between the overproducing and the bottleneck operations. For this, both the operations should have same machines and attachments (if any). Preferably the machines should be within range of 4 machines to each other.
• Club operations where possible. Where there is higher output than the target output, give that operator another operation with less work content. Considering machine type and sewing thread colors.
• Deskilling devices are used to assist the operator in handling parts during sewing, positioning cutting and disposing finished task
• Shuffle operators: Operations that have low work content use low performer there. And where work content is higher use high performers. This usually is done during the preload balancing using skill matrix.
• Add more operators at bottleneck operations. Before adding one more machine, compare the cost-benefits of putting additional machine into the line. It can be simply compared by estimating machine productivity in both cases.
• In order to reduce or make the WIP, line supervisor can make the operator work overtime.

Taking above pointers in mind, let’s try to balance the line mentioned in example in last section.

In this example, we have tried to club the operation of Box placket making (no. 3) with Placket top stitch (no. 2) operation. This action will however, reduce the output of operation 2 to 180 from 240, but it is still helpful as bottleneck at operation 3 means no matter how much operation 2 can produce, it cannot push its output across operation 3 (whose output is only 142). So, even if output of operation 2 drops to 180, it will not affect the output of the line.

Hence effectively after balancing, the output after 3^rd operation will improve from 142 to 180.

Similarly, from many methods mentioned above there can be many other possibilities to further balance the line in next operations

So, in a gist, the process flow of dynamic line balancing can be stated by a basic process flow diagram as displayed below:

Conclusion

Line balancing doesn’t have a single standard process to achieve better result. But there are set of possibilities which can be tried by supervisors from the options mentioned in previous section depending on the constrain he/she has in hand. For e.g., if he has no extra machine to spare for the line, then increasing a machine at bottleneck is not possible and he then has to look for work sharing as an effective tool.

For an effective balancing results it is very much required that a supervisor has the real-time data in his hand (Output rate, pitch time, and WIP level being few of such important KPIs). The problem with most of our manufacturing setups is that we are unable to capture these data correctly. And even in cases where we somehow manage to get these data, it’s already too late to take any action as these results are accessible only after end of each hour or two where any balancing method will take its own time to show results. So, virtually all our efforts are as good as shooting arrows in dark. What we need is a system which gives pulse by pulse data from workstations so that we can identify our bottlenecks when they arise and take effective actions which show visible results real-time.

Our primitive form of data collection (like operator to operator manual data fetching) are not only inefficient but also not cost effective in longer runs. Solutions like NFC, RFID or barcode based tracking are being explored in few of the cases. But then, without any software based networking and reporting tools, these solutions prove to be more of cosmetic. Today Software solutions are desperately needed which can analyze the data coming from each workstation and give logical suggestions of line balancing to supervisors, based on algorithms of decision making criteria specific to the factory demands. Visit here to know about such software solutions.

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Source:  ThreadSol