Chapter -1 Introduction

In recent years, the RMG has emerged as one of the biggest industrial sector in Bangladesh .Now a days the apparel industries in Bangladesh require to increase the productivity to meet the customer demand which is growing in a large scale domestically and internationally .With the rapid increase of the demand the apparel industries are trying to raise their promotional activities to compete with their market rival .As productivity measures how well the resources are utilized to produce maximum amount of output ,researches have been done to improve the productivity through various tools and techniques or performance parameters .These are designed to monitor and improve the performance or productivity to a desired level .

1.1 Productivity

productivity is the relationship between the output generated by a production or service system and input provided to create this output .In RMG sector productivity improvement is defined as to improve the production time and reduce the wastage .Sometimes specific problems such as setup time ,machine changing time ,operator skill and efficiency also effect the probability to improve the plant productivity .productivity improvement is not just doing things better ,more importantly, it is doing the right thing better .

Among many techniques for improving productivity ,time study , motion study ,line balancing can be used to raise the productivity to a certain level by monitoring the performance of the system .

Chapter -2 Tools and Technique

2.1 Line balancing Line balancing is an optimum distribution of the workload evenly across all the processes in a cell or a sequence of activities needed to produce specific goods to remove bottleneck or excess capacity . Assembly line balancing helps an industrial engineer to know how task are assigned to workstation and achieve their desired goal .The main goals of assembly line balancing are minimization of the workstation and maximization of the production rate .Line balancing is one of the most common optimization technique which is used to allocate task of workers in different workstation in order to increase productivity . Historically ,line balancing is designed for high volume production of single item or similar family of items .The first movable assembly line was created by "Ford "to manufacture automobiles which is known as Ford model . Then Adam Smith and Alfred Alan ( general motors' ) enhanced Ford's work .In 1970 s Japan expanded worker involvement to handle a variety of manufacturing process .

2.2 Types of assembly line :

single model assembly line mixed model assembly line multi model assembly line 2.2.1 Single model assembly line : single model represents a type of assembly line where product is assigned in the same direction from the certain set up and won't variant it's setup .This assembly system is called single model assembly line .The goal of single model assembly line are minimizing the cycle time and minimizing the number of station.

sleeve hemmingsleeve hemmingsleeve hemming

Fig: single balancing for sleeve hemming in a RMG industry.

2.2.2 Mixed model assembly line : During1960 Thompoulos was the first to develop mixed model assembly line by the help of heuristic model . A mixed model assembly line produces several items belonging to same family. In contrast single model assembly line produces one type of product with no variation but mixed enables a plant to achieve both high volume production and product variety .However, it complicates scheduling and increases the need for good communication about the specific parts to be produced at each station .

Side seamingBack hemmingSleeve hemming

Fig: An example of mixed model assembly for RMG sector .sometimes mixed model assembly can be developed by the application of computer heuristic solution methodology called COMSOAl. This is generally applied to the constrained resource application problem. COMSOAl means computer method of sequencing operation for assembly line. It was first developed by De Puri .

2.2.3 Multi model assembly line : It is the combination of simple and mixed model assembly line. In this model the uniformity of the assembled products and the production system is not that much sufficient to accept the enabling of the product and the production levels. To reduce the time and money this assembly is arranged in batches, and this allows the short term lot-sizing issues which made in groups of the models to batches and the result will be on the assembly levels.

represents machine set up time .

Fig: Multi model assembly line for RMG sector .

2.2.4 Unequal time assignment and u shaped line : The line balancing method sometime s causes an unequal time assignments .The U shaped layout which is assigned by standard task helps to solve these unequal time assignments situations .In line balancing U shaped cells avoid constant displacement to the start of the line and solve money of the distribution problem . 2.2.5 Heuristic method for choosing the eligible task :Heuristic procedures generally allow for a broader problem definition but do not guarantee optimal solution. Optimizing procedure generally have used more narrowly defined problems but ensure the optimal solution.Heuristic method is a simple rule that propose two selection criteria .The second criteria will only be used if there are several tasks that coincide in the first criteria .The obtained solution can be compared by analyzing the idle time shared among the workstations . The two criteria are

among the eligible tasks choose the task that has the largest total number of following task .

If two or more task coincide select the task with longest time .

2.2.6 Terms used in line balancing : 1.cycle time : cycle time is the maximum amount of time allowed at each station .This can be found by dividing required units to production time available per day .production time available per dayCycle time = units required per day

2.Lead time : Summation of production time along the assembly line .Lead time = Production time along the assembly line . 3.precedence :It can be represented by nodes or graph .

4.Idle time :Idle time is the time specified as period when system is not in use but fully functional at desired parameters .

5.Productivity : Defined as the ratio of output over input . outputproductivity = labor production time /day

6.minimum number of workstation =( task time /cycle time)7.Efficiency = Task time / (actual no workstation largest assigned cycle time )8. Line balance loss percentage = {( n T max - t ) /(n Tmax)} *100%where , n= number of workstation T max = Value of the highest cycle time . t = Total cycle time

2.2.7 Time study : Time studyis the application of ascientific method of determining process times using data collection and statistical analysis. This study is concerned with the establishment of time standards for a worker to perform a specified job at a defined level of performance .It was originally proposed by Fredrick Taylor and was modified to include a performance rating adjustment . Taylor used the most qualified worker to

establish the standard working time and Educating the rest of workers to carry out the

tasks in the same manner . Taylor decided to include two kinds of allowances which are

related to the workers fatigue and Regarding variations among various worker

capabilities. Time study is considered to be one of the most widely used

means of work measurement .

The times that are calculated through a scientific study are used for various initiatives such as:

Establishing accurate productivity goals Compiling objective data that compares automation/methods Identifying non-value-added time percentages Determining current staff utilization and identifying opportunities Quantifying gains through layout and/or method changes Reducing labor costs

2.2.8 Procedure of time study, Data analysis and calculation :

Time study leads to the establishment of work standard . Development of time standard involves computation of 3 times .Such as 1.Observed time 2. Normal time 3. Standard time Steps of time study :1.Job selection : First select the job to be studied .Breakdown the work content of the job into smallest possible elements .Then inform the worker and define the best method .2.Determine the no of cycle : Observe the appropriate no of cycles .3.Determine the average cycle time : CT =( times /No of cycles )4. Determine the normal time : NT =CT(PR) where PR is the performance rating .

5.Establish the standard time : ST =NT (AF) and AF = {1/(1- %allowance ) , where AF is the allowance factor ./

Another process of establishing standard time is WORK SAMPLING . Work sampling is also a technique for establishing standard times of activities . This method was introduced By LHC Tippet in 1934 .This method is suitable for analyzing group activities and repetitive activities which take longer duration. If a given individual performs more than the time standard for each activity may be computed using this method .

Steps of work sampling :1.Job selection: This step includes 1. inform the workers about the method study , 2. Prepare detailed list of activities .2.Decide the Total duration of observation : Total duration of observation = (No of hours /shift) (No of shifts/day)No of days .3. Decide the no f observations to be made .4.record the performance rating of the worker .5.Determine the percentage of working on a given task using the following formula .6. Determine the acceptable no of units produced during the period .7.percentage of working = (Frequency of performance of a task /total no of observation ) 1008.Determine the normal time , NT = {(Total time) (% of working ) PR}/ no of acceptable units produced.9. Determine the standard time (ST) ST= NTAF/

2.2.9 Important terms related to Time study :

Standard minute value and standard allowed minute(SAM &SMV): is used to measure task or work content of a garment. This term is widely used by industrial engineers and production people in manufacturing engineering . General Sewing Data (GSD) has defined set of codes for motion data for SAM calculation. There is also other methods through which one can calculate SAM of a garment without using synthetic data or GSD. In American published books SAM is mentioned, while in European published books SMV is mentioned. Similarly, factories in Asia which are under the influence of European consultants use the term SMV, while factories in South America which are under the influence of American consultants use the term SAM. When SAM is used as an extension to SMV, i.e. it is the allocated time for a task rather than the measured time./ Standard allowed minute (SAM) of an operation is the sum of 3 different parameter, i.e. machine time, material handling (with personal allowances) time and bundle time. Material handling and bundle time is calculated by motion analysis.

steps of calculating SAM using synthetic data :1. Select one operation2. Study the motions of that operation.3. List down all motion sequentially.4. Standard allowed minutes (SAM) = (Basic minute + Bundle allowances + machine and personal allowances).

Sample SAM value (assumed) for some product :

productSAM (AVG)SAM ( Range)

Crew check T shirt8 6-12

Polo T shirt15 10-20

Formal full sleeve T shirt21 20-25

Sweat shirt 45 35-55

suit101 70-135

/Predetermined motion time system(PMTS): is frequently used to set labor rates in industry by quantifying the amount of time required to perform specific tasks. The first such system is known as Methods-time measurement, released in 1948 and today existing in several variations, commonly known as MTM-1, MTM-2, MTM-UAS, MTM-MEK and MTM-B. Obsolete MTM standards include MTM-3 and MMMM (4M). The MTM-2 standard has also largely been phased out by the organization, but is still used in some commercial applications.Performance rating : Performance = ( total units / operating time )/ ideal run rate . performance rating is the step in the work measurement in which the analyst observes the worker's performance and records a value representing that performance relative to the analyst's concept of standard performance.

Bottle neck and sewing line efficiency : A sequence of operations is involved in making a garment. In bulk garment production, generally a team works in an assembly line (Progressive Bundle system) and each operator do one operation and give it other operator to do next operation. In this way garment reached to end of the line as a completed garment. In the assembly line after some time of the line setting, it is found that at some places in the line, work is started to pile up and few operators sit idle due to unavailability of work. This type of situation is known as bottleneck. So , bottleneck can be defined as delay in transmission that causes slow production rate.steps of Bottleneck study :1.Capacity study 2. Target setting 3. Locate bottleneck areas4. Eliminate bottlenecks from the line .Pitch time : In industrial Engineering, Pitch time is a ratio of total SAM of garment and number of operations to be set for the style. pitch time = Garments SAM / No of operation. Pitch diagram : A graphical presentation of individual operations time (SAM) and pitch time on a same chart is called pitch diagram.Pitch diagram is used for line balancing in an assembly line. To make a pitch diagram on operators capacity Vs line target collect information as following. First conduct a capacity study for all operators and find out how many pieces operators are making at each operation. Where more than one operator is doing same operation, sum up their capacity for that particular operation.

sample pitch diagram ( assumed ) : Actual capacity v/s Target Fig: Pitch diagram

Takt time : Takt time is the allowable times to produce one product at the rate of customers demand.

2.2.10 Layout:

Layout is the most effective physical arrangement of machines ,processing equipment and service departments to have greatest Co-ordination and efficiency of man ,machine and material in a plant .Product layout :Machines are grouped according to the product manufacturing sequences . A layout that organizes resources by the product production sequences. It is a layout in which workstation or departments are arranged in a linear path. This strategy is also known as line flow layout .This type of layout often follow a straight line and layout can be L,O,S or U shaped .This layouts are called manufacturing or assembly line .Advantages :1.production time is lower .2.total material handling cost is lower .3.smaller floor area /unit of production.4.Production control is simpler

Disadvantages:1.Duplication of the processing equipment and m/c tool .2.investment cost more . In most of the readymade garments product layout is used . other types layouts are 1.process layout 2.group technology layout3.fixed position layout But those types of layouts are not suitable for RMG sector in Bangladesh .In this perspective U shaped product layout can be used to improve material flow across the entire production line .Material flow :Flow pattern can be classified as 1.straight line 2.u shape flow pattern3.convoluted type .4.circular type 5. zigzag type Tools and techniques of layout:operation process chart Flow process chart Flow diagramstring diagramform to chart Assignment model

1. Cyclone Appliances has developed a new European-style convection oven that will be made on an assembly line. The schedule requires 80 ovens in an 8-hour day. The assembly includes seven tasks. The table below indicates the performance time and the sequence requirements for each task.

TaskPerformance Time (minutes)Task must follow Task listed below

A1

B2A

C3B

D2B

E4C, D

F1E

G2F

a.What is the cycle time for this assembly operation?b.What is the minimum number of workstations? c.Draw the precedence diagram

Answer :

a)The cycle time is 480 minutes per day / 80 ovens = 6 minutes/oven. b) The sum of all task times,15 minutes

cycle time, 6 minutes; 15 / 6 = 2.5 or 3 = no of workstations.

c) The precedence diagram appears below.

Reference:[1]APPLYING GENETIC ALGORITHMS TO THEU-SHAPED ASSEMBLY LINE BALANCING PROBLEMDebora A. AjenblitRoger L. WainwrightMathematical and Computer Sciences DepartmentThe University of Tulsa600 South College AvenueTulsa, OK 74104-3189, USArogerw@penguin.mcs.utulsa.edu

[2] Productivity Improvement through Line Balancing in ApparelIndustriesMd. Rezaul Hasan Shumon, Kazi Arif-Uz-Zaman and Azizur RahmanDept. of Industrial Engineering and ManagementKhulna University of Engineering and TechnologyKhulna, Bangladesh[3] IMPROVING PRODUCTIVITY THROUGH LINEBALANCING - A CASE STUDYLim Chuan PeiMasine Md. TapFaculty of Mechanical Engineering,Universiti Teknologi Malaysia,81310 UTM SkudaiJumal MekanikalDisember 2002, Bil. 14, 48 62[4] Assembly Line Balancing: A Review of Developments andTrends in Approach to Industrial ApplicationBy Naveen Kumar & Dalgobind MahtoGreen Hills Engineering CollegeGlobal Journal of Researches in EngineeringIndustrial EngineeringVolume 13 Issue 2 Version 1.0 Year 2013Type: Double Blind Peer Reviewed International Research JournalPublisher: Global Journals Inc. (USA)Online ISSN: 2249-4596 Print ISSN:0975-5861