Background
Lean Manufacturing/TPS has been spreading its philosophy and concepts across industries worldwide over the last two decades. By now, most practitioners have come to a broad consensus on the advantages of implementing One Piece Flow, which is widely recognized as a core Lean concept and considered the heart of a Lean process.
The biggest successes achieved by implementing flow manufacturing have happened in assembled products. Assembly and packing operations are known to be the most amenable to single piece flow and typically many of these already are already manufactured in such lines. The identification of bottleneck operations through process observation and reducing the cycle time of such operations through tools such as Operations Analysis and Line Balancing have given significant results in terms of productivity and throughput increase.
But is One Piece Flow the only and the best way for an assembled product to be manufactured?
Does it always deliver the highest value-adding ratio, leading to the most effective resource utilization?
These two small cases show us that there is one other option which can be more effective than One Piece Flow in certain circumstances.
Case 1 – Moulded Plastic Toy
The toy industry is seasonal in nature, with peak sales during the festival seasons, and the manufacturing level fluctuates accordingly, with even zero production for 3–4 months. The manufacturing team was working to ramp up productivity and throughput for a high-demand toy. The current output had peaked at 800 units per day on an assembly and packing line with 11 people and a running conveyor to transfer the product from station to station.
While the maximum cycle time recorded was 30 seconds per toy, a major muda at each workstation was the act of picking up the toy from the conveyor and placing it back after completing the work. This pick-and-place activity took around 5–6 seconds and often interfered with the operator’s concentration. The team brainstormed and came up with two improvement options, and both of these were tried out.
Option A – Line Balancing and Improvement
The belt conveyor was removed, and tables were reoriented so that operators stood side by side in the order of the operation sequence. One person was redeployed as a material feeder to supply all the parts in front of the respective workstations. During the production trial, the output increased to 1000 units per day with the same team of people.
Option B – Single-Person Workstation
Two single-person workstations were set up next to each other. All six assembly operations were done by the first person, and all four packing-related operations were performed by the second person. Each station had all the required tools. For example, the first station had two different fixtures, two pneumatic screw guns, and all the assembly parts arranged in the order of the assembly sequence. The cycle time achieved was 75 seconds per toy in each station, which translated into an output of 260 toys per day for the two-person cell.
In summary, the existing productivity of 72 toys per person per day increased to 90 toys in Option A and a much higher 130 toys using Option B. However, the team felt they were more comfortable with Option A and went ahead with standardizing and sustaining it.
Case 2 – Electronic Product
The unit manufactures electronic products against customer orders, mainly through government tenders. Hence, the business is again fluctuating in nature, with peaks and troughs depending on tender opening timelines and government priorities. While the business had tripled within a couple of years, margins were low and further eroded due to higher conversion costs.
The team was working on how to increase productivity and lower costs so as to remain competitive. In the final assembly and packing line, 12 operators worked to deliver 2000 units per day. There were 8 such lines working in the company. The maximum cycle time was 12 seconds, but this varied anywhere from 6–10 seconds for the other operations. In this case as well, the team decided to try out two alternative methods.
Option A – Line Balancing and Workstation Arrangement
Operators sat side by side in a long line in the existing process. The team made a U-shaped line, modifying one of the existing tables so that people could stand on both sides. After line balancing, a smooth single-piece flow was established, delivering an output of 2000 units per day utilizing only 8 people.
Option B – Two-Person Workstation (Cell)
A small table was cut out from the existing long table, and two workstations were created, one on each side. The first operator did all the assembly work and slid the assembled unit to the second operator, who then completed the packing of the unit, accessories, and instruction cards. One such cell was able to deliver an output of 700 units per day.
In this case, the original productivity of 170 units per person per day increased to 250 in Option A, while Option B delivered 350 units. The team decided to run one line using Option A, one cell using Option B, and continued running the other lines in the existing process. After a month, the teams met and concluded that Option B was the best. Within the next month, they dismantled all existing assembly lines and replaced them with two-person workstations.
In both the above cases, the single-person workstation or two-person cell proved to be superior to the balanced One Piece Flow line. However, one team decided to stick to the tried-and-tested flow, while the other team took the leap and completely changed the face of their manufacturing operations. This begs a few questions.
Why did these decisions happen?
When can and should we apply each of these alternate concepts?
What are the pros and cons of each?
…To be continued.
