Introduction
The company under study is producing cosmetics. Its sales have dropped recently. The main reason for this is the failure to deliver on time. Recognizing the issue, the company is determined to enhance its on-time delivery rate as a strategic initiative to subsequently boost sales.
The problem lay in excessive waste in the packaging process. This led to increasing lead time and cycle time, which resulted in low productivity, affecting the on-time delivery rate and sales of the company. Therefore, the company sought to reduce both cycle and lead time in order to improve on-time delivery rate.
Value stream management (VSM), a well-structured methodology, has been used to solve the problems with the objective of reducing waste, thus reducing production lead time, reducing production cycle time to meet takt time.
The current state value stream map (CSM) was constructed, and the current performance indexes were assessed. Lean tools, including single minute exchange of die (SMED), Job Design, Line Balancing, Kanban, and first in first out (FIFO), were used to construct the future state value stream map (FSM), and the future performance indexes were assessed. Comparing the CSM and the FSM, both the lead time and cycle time were reduced, and the cycle time met the takt time.
Literature review
VSM was used to improve the production processes in LED manufacturing (1), in PCB manufacturing (2), and in trolley-bag manufacturing (3), in production processes (4), and in warehouse operation processes (5) by using tools, including SMED, Work Design, Line Balancing, Kanban, and FIFO.
SMED is a tool developed by Shigeo Shingo for changeover reduction (6). Job Design is a lean tool used for reducing workstation cycle time (7). The two-hands method is often used to remove non-value-added operations and arrange value-added operations properly. In addition, some physical tools are designed to reduce operation times. Line Balancing is a lean tool that evenly distributes the work elements within a value stream to meet takt time (7). The main objective of line balancing is to distribute the task evenly over the workstations so that the idle time of man of machine can be minimized (8).
Kanban is a lean tool that performs pull principle of lean thinking to control in-process inventory by using supermarket concept and pull signal (7). The Kanban system is an inventory stock control system that triggers signal for production of product based on actual customer requirement (9). FIFO is also a lean tool for control in-process inventory (7). FIFO is simpler than Kanban: inventory is brought in at one end and removed from the other end of FIFO lanes.
Research methodology
In this paper, the research methodology includes the following steps:
1. Choose the value stream
2. Map the current state
3. Map the future state
The step of choosing the value stream includes the following sub-steps:
1. Collect data on the number of products consumed
2. Use Pareto chart to identify the product to be researched
3. Use suppliers inputs process outputs customers (SIPOC) to define the process to be researched
The step for mapping the current state includes the following sub-steps:
1. Identify all workstations of the value stream
2. Collect data on the workstation attributes
3. Collect data on the available production time, customer daily demand
4. Collect data on the inventories of the value stream
5. Calculate times in process of the inventories
6. Map the current state value stream
7. Assess the current performance indexes
The step for mapping the future state includes the following sub-steps:
1. Draw the current balanced chart
2. Use SMED to increase the workstation takt times
3. Use Job Design to reduce the workstation cycle times
4. Use Line balancing to balance the line and meet workstation takt times
5. Use Kanban and FIFO to control inventories in the value stream
6. Map the future state value stream
7. Assess the future performance indexes
8. Assess the lean improvement
With review from (7), the SMED procedure used in this research includes the following steps:
1. Identify and classify internal and external activities
2. Separate internal from external activities
3. Convert internal activities to external activities
4. Eliminate internal waste to minimize internal activities time
The Job Design procedure (7) used in this research includes the following steps:
1. Identify and classify left- and right-hand operations
2. Eliminate all waste in left- and right-hand operations
3. Design physical tools to reduce operations time
4. Allocating operations evenly to left and right hands
Line balancing evenly distributes the work elements among workstations within the value stream to meet workstation takt time by the following sub-steps:
1. Identify work elements and workers of the current workstations
2. rearrange work elements and workers to future workstations
The work elements and workers are rearranged to balance the work between stations so that the new workstation cycle times do not exceed workstation takt times.
The Kanban and FIFO systems are constructed by the following sub-steps:
1. Define the positions of the Kanban and FIFO systems
2. Collect data and calculate the numbers of Kanban cards
3. Collect data and calculate the sizes of the FIFO lane
After collecting data to estimate daily demand D of back workstation, lead time L of front workstations, safety parameter α, and container size Q, the numbers of Kanban cards N are calculated by the following model.
After collecting data to estimate of cycle time mean M, and standard deviation SD of front and back workstations, and station down time DT of front workstations, the sizes S of the FIFO lanes are calculated by the Christoph Roser model in (10).
Choosing the value stream
The company produced many products. The data for the number of products consumed in 6 months were collected. The pareto chart for the number of products sold in 6 months is shown in Figure 1.
Figure 1. The Pareto chart of products sale in 6 months.
From the Pareto chart, the product of Riori Whitening Body Lotion was selected for further research. The SIPOC diagram of the chosen product is shown in Figure 2, in which, the packaging process included 7 workstations.
Figure 2. The SIPOC diagram of Riori whitening body lotion.
Current state mapping
All the workstations in the stream are shown in Table 1.
Table 1. Workstations in the value stream of Riori Whitening Body Lotion.
The workstation attributes including cycle time CT, lead time LT, change over time COT were collected and shown in Table 2.
Table 2. The workstations’ attributes.
The company worked 1 shift per day, 8 h per shift. The total break time per day was 90 min. The available production time was calculated as follows.
The customer average daily demand DD was collected as follows.
The process takt time was calculated as follows.
The number of inventories I of raw materials (RM), work in process (WIP) between workstations and finish good (FG) were collected and are shown in Table 3. The corresponding times in process (TIP) were calculated from the number of inventories I and the above daily demand (DD) and are also shown in Table 3.
Table 3. Inventories and time in process.
From all the above data, the CSM was drawn from the supplier to the customer as shown in Figure 3. with inventory I (units), number of workers N, cycle time CT (sec), changeover time (COT) (sec), value added time VAT (sec), non-value added time NVAT (day).
Figure 3. The current state map CSM.
From the map, the current performance indexes, including process lead time LT, and process cycle time CT were as follows.
The lead time LT of 42.4 h was much longer than value added time VAT of 149 s. Besides that, the process cycle time (32 s), did not meet the process takt time (23.4 s). Lean tools needed to be applied to reduce lead time and reduce cycle time to meet takt time.
Future state mapping
With the available production time APT of 23400 (s), the daily demand DD of 1000 products, workstation takt times TT were calculated from changeover time COT and are shown in Table 4.
Table 4. Workstation takt times.
The balance chart with workstation cycle time CT and workstation takt time TT is shown in Figure 4.
Figure 4. The balance chart of the value stream.
Some workstation cycle times exceeded the corresponding workstation takt times. SMED should be used to reduce workstation changeover times to lift up workstation takt time TT. After using SMED, the workstation COTs were reduced, then workstation TT were changed as in Table 5.
Table 5. Workstation takt times after SMED.
The balance chart after using SMED is shown in Figure 5.
Figure 5. The balance chart after SMED.
After using SMED, some workstation cycle times still exceeded workstation takt times. Job Design was used to reduce workstation cycle times CTs. The results are shown in Table 6.
Table 6. Workstation CTs after Job Design.
The balance chart after using Job design is shown in Figure 6.
Figure 6. The balance chart after Job Design.
Looking at the chart, the cycle times of workstations 4 and 6 still exceeded takt times. On the other hand, the value stream was unbalanced. Line balancing needed to be applied to balance the stream and to meet takt time. After using Line Balancing, there were 6 news stations in the value stream with cycle times CT, changeover time COT, takt time TT shown in Table 7.
Table 7. The cycle times CTs of the 6 news stations after using Line Balancing.
The balance chart after using Line Balancing is shown in Figure 7.
Figure 7. The balance chart after Line Balancing.
The number of workers was reduced from 7 to 6. All the workstations then met their takt times, but the value stream was still unbalanced. In order to reduce lead time, inventories needed to be reduced and controlled. Raw materials would be reduced to 3000 and finished goods would be kept at the level of 500. Kanban and FIFO systems needed to be installed to control WIP inventories.
With review from (7), dual kanban systems were placed between stations 1 and 2, stations 4 and 5, as shown in Figure 8.
Figure 8. The positions of Kanban systems.
After collecting data, daily demand D of back workstation, front workstation lead time L (day), safety parameter α and container size Q were estimated and are shown in Table 8. The numbers of Kanban cards N were calculated and are also shown in Table 8. There were 3 cards in the supermarket between W1 and W2, and 2 cards in the supermarket between W4 and W5.
Table 8. The calculation of number of Kanban cards between stations.
FIFO lanes would be placed between stations 2 and 3, stations 3 and 4, stations 5 and 6 as shown in Figure 9.
Figure 9. The positions of FIFO lanes.
After collecting data, the cycle time means M, and standard deviations SD of front and back workstations, and station down time DT of front workstations were estimated and are shown in Table 9. The sizes S of the corresponding FIFO lanes were calculated by the supporting software provided by Christoph Roser in (10) and the results are shown in Table 9.
Table 9. The calculation of FIFO lane size.
From all the above data, the FSM from the supplier to the customer was drawn and shown in Figure 10, with inventory I (units), number of workers N, cycle time CT (sec), changeover time COT (hours), value added time VAT (sec), non-value added time NVAT (hours).
Figure 10. The future state map FSM.
From the map, the future performance indexes, including process lead time LT, and process cycle time CT were as follows.
In order to assess the lean improvement, the critical performance indexes of the maps CSM and FSM are shown in Table 10.
Table 10. The results of the implementation.
From the table, we see that the number of workers was decreased from 7 to 6, the process lead time was reduced by 46.23% from 42.4 to 22.8 h, the process cycle time was reduced 31.25% from 32 to 22 s, meeting the TT.
Conclusion
The paper applied the VSM methodology to improve the production process of the company with the objective of reducing process lead time and process cycle time to meet takt time. The current state map (CSM) was constructed, and the current performance indexes were assessed. The future state map (FSM) was constructed using lean tools of SMED, Job Design, Line Balancing, Kanban, and FIFO systems. From the map, the future performance indexes were assessed.
The results showed that the objectives were achieved. The process lead time was reduced by 46.23% from 42.4 to 22.8 h, the process cycle time was reduced 31.25% from 32 to 22 s, meeting the TT. These positive results would lead to an improvement of on-time delivery rate. On the other hand, the number of workers was decreased from 7 to 6.
However, the paper also has some limitations. The data were collected in a short duration, not enough for better parameter estimations to make better results. The future state map hasn’t been experimented to validate the real improvement. Future research would have new vistas that overcome these limitations.
Conflict of Interest
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
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