Lean production system design for fishing net manufacturing using lean principles and

simulation optimization

Ilyas HussainP2MFG15006

Introduction

The common challenges that companies face are market com-petition, increased pressure on inventory, increased service levels, and reduced work in process (WIP). Lean manufacturing is one of the approaches that can help companies respond appropriately to these challenges.

The focus of the approach is on cost reduction, by eliminating activities that do not add value by linking and balancing work stages, so that products from one stage are consumed directly by the next stage, until the end of the production line is reached.

Fishing net manufacturing is a high make-to-order (MTO) environment, because net size and type change according to the ocean environment, fish kinds and ship size.

MTO manufacturing need not be a pull production system as there are many (or some) simultaneous orders in the manufacturing process and orders may be different in size and specifications.

Higher WIP and longer cycle times always result in a lower service level and produce lower customer satisfaction in MTO environments.

Through the production procedure the production units become bigger and bigger and the processing time in most steps are quite long.

This provides the motivation for this research, to design a lean manufacturing system for this industry.

The objective of the present study is to model a non-typical production system – a fishing-net manufacturing system – and to propose a lean production system design which is optimized by simulation optimization.

Current State Map of Fishing Net There are various fishing nets each net has a unique

application which is based on the ocean environment, fish type and ship size.

Therefore, the same customer could order nets of different types or different sizes. Each order requires different raw material types, twine sizes, mesh sizes, mesh depths and mesh lengths.

Net cage is one kind of fishing net which is the main product of the case study company.

The general diameter varies from 10 m to 30 m, depth varies from 4 m to 10 m, while mesh varies from 2 mm to 30 mm.

There are six workstations for net cage manufacturing. They

are (1) Twisting, (2) Braiding, (3) Net knitting,(4) Dyeing, (5)

Heating and (6) Suturing. All manufactured net cages follow

the sequence of workstation above, from 1 to 6.

There two options for the width of a net: 1 or 2 m. According

to the specification of the knitting machines in the case

company the standard size can be 10 m × 1 m or 10 m × 2 m.

Every knitting machines can knit one single 10 m × 2 m net or

two 10 m × 1 m nets simultaneously.

Dyeing workstation, a number of nets in standard size can be

dyed together, but the total weight of the nets cannot exceed

the capacity of the dyeing machine.

One single 10 m × 2 m net or two 10 m × 1 m nets can be

heated simultaneously in heating machine.

Finally, the nets with standard size are sutured to form net

cages according to the request of the customers.

According to the current state map, reducing the waiting time

in front of the each workstation is an opportunity to reduce the

lead time and, consequently, to increase the service level.

Two performance indicators, average WIP level and average

service level, are taken into consideration in this case study.

WIP level is defined as the total volume of semi-finished goods

in the production system. Service level is defined as the

percentage of orders that are completed before their

corresponding due date.

As the company did not collect data on service level and WIP,

this research developed a simulation model to evaluate it.

Commercial software, Arena is adopted as the simulator for the

present study.

To evaluate the performance of each scenario, a run length of

750 days with 3–12 replications was adopted for the simulation

model.

The estimated service level and WIP are 68% and 63,971 kg

respectively.

Lean Principles

There are five phase for implementation of VSM. The phases

are (1) selection of product family; (2) current state mapping;

(3) future state mapping; (4) definition of working plan; and

(5) achievement of working plan.

The lean techniques to be used are defined in the third phase

which contains seven guidelines to define the future state map.

Guideline 1: Produce to your TAKT time.• “Takt time” is used to synchronize the pace of production with

the pace of sales. • Takt time = available working time per day /customer demand

rate per day Guideline 2: Develop continuous flow where possible.• Continuous flow refers to producing one piece at a time to

reduce the inventory of WIP and production CT. However continuous flow requires a great deal of creativity to achieve and sometimes it requires plant layout redistribution. In this research, this guideline is not applicable and is not taken into consideration in the case study.

Guideline 3: Use a supermarket to control production where

continuous flow does not extend upstream.

• A “supermarket” is nothing more than a buffer or storage area

located at the end of the production process for products that are

ready to be shipped.

• Supermarkets use a kanban system to fix the inventory level. If

the number of kanbans in a supermarket is too high, it causes

higher inventory cost.

• If the number of kanban in the supermarket is too low the

downstream production process will be subject to delays.

Guideline 4: Try to send customer scheduling to only one

production process.

• The process time is set by one of the production processes.

That process is called the “pacemaker process”. The

pacemaker process synchronizes the pace of the entire

manufacturing process and there are no supermarkets

downstream of the pacemaker process.

• Therefore, selecting different workstations as the pacemaker

process will have an important influence on the performance

of the entire manufacturing system.

Guideline 5: level the production mix.• Leveling the product mix means dividing the volume of all the

product types based on their kanban size, and then producing them evenly over a time period.

• The more level the product mix is, the greater is the ability to respond to different customer requirements with a short lead time.

• For example, if there are three product types and the production sequence can be A-A-A-B-B-B-C-C-C or A-B-C-A-B-C-A-B-C.

• The latter is more level and allows the process to proceed smoothly with smaller supermarkets.

Guideline 6: Level the production volume.

• Leveling the production volume is related to Guideline

number1. It means that production should be based on a fixed

pace, the takt time.

Guideline 7: Develop the ability to make “every part

everyday” in fabrication processes upstream of the pacemaker

process.

Future State Map Optimization

From lean principles we identified five key controllable factors as: (1) production unit size, (2) the pacemaker process, (3) the number of batches for an order split, (4) the production sequence, and (5) supermarket size, to optimize the proposed fishing-net manufacturing system.

According to the guidelines for designing the future state map, the production unit should be as small as possible to level the product mix.

The production unit of each workstation depends on the standard net size and the processing times of the standard net size could be different in every workstation.

As regard the pacemaker process, this research selects

Knitting workstation, Dyeing workstation and Suturing

workstation as the candidates.

Knitting workstation usually has the highest machine

utilization. Dyeing workstation is batch processing. Its

capacity is batch-size dependent. Suturing workstation is the

most labor intensive workstation.

the potential bottleneck could shift among the three

workstations which are thus considered as the candidate

pacemaker locations.

The number of batches to be allowed will decide the transportation volume between workstations.

More batches allow for a more level product mix, but will cause more changeovers. The changeover times between different products are different.

An appropriate production sequence can reduce the total changeover time.

This research selects earliest due date (EDD), first in fist out (FIFO) and shortest process time (SPT) as alternative criteria for designing the future state map.

Four factors (production unit, pacemaker process, number of batches and production sequence) are taken into consideration in the experimental approach to designing the future state map.

For each scenario, Opt Quest is used to find the best super-market size and the corresponding performances are viewed as the performance of each scenario.

The Taguchi method aims to find an optimal combination of parameters that have the smallest variance in performance. The signal-to-noise ratio (S/N ratio, ) is an effective way to find significant parameters by evaluating minimum variance.

A higher S/N ratio means better performance for combinatorial parameters .

Effect of s/n ratio of service level

Effect of s/n ratio of WIP level

A2B1C1D2 is the best design for the future state map to

maximize the service level.

A1B1C2D2is the best design for the future state map to

minimize the WIP.

The optimizing results produced by Opt Quest show that the

design of A2B1C2D2 increases service level from 68% to

90% and reduces WIP from 63,971 kg to 42,269.31 kg.

The non-value adding time reduces from 44% (19.78 days)to

35.46% (13.78 days).

Note that the optimal design of production unit (factor A) is

level 2 (10 × 2 m) which is bigger than level 1 (10 × 1 m).

Although the guideline number 7 encourages the production

unit to be smaller the better.

The size of a final net cage range from 120 to 900 m2.The

smaller production unit would cause more processing time for

suturing process and would deteriorate the suturing

workstation performance.

Conclusion

Lean manufacturing has been applied successfully in many

manufacturing industries. It focuses on cost reduction by

eliminating non-value adding activity. In general, waiting is

the most common non-value adding activity.

Based on the guidelines for implementing lean manufacturing,

some important production factors are selected for designing

the future state VSM.

Using experimental design and a simulation optimization tool,

these important factors are optimized. According to analysis

based on the simulation, the future state map not only

increases service level but also reduces the WIP.

In the case study, the selected factors can be changed to any

level without extra investment. That means the case company

can implement the future state map to achieve lean

manufacturing without any financial pressure. This could be

the first step to achieving lean manufacturing.

Thank you