KESEIMBANGAN LINI KESEIMBANGAN LINI PRODUKSIPRODUKSI

((PRODUCTION LINE PRODUCTION LINE BALANCINGBALANCING))

(Bagian 1)(Bagian 1)

1

Assembly Systems andLine Balancing

Assembly involves the joining together of two or more separate parts to form a new entity, called a subassembly, an assembly or some similar name.

Three major categories of processes used to accomplish the assembly of the components:1. Mechanical fastening2. Joining methods3. Adhesive bounding

1. Mechanical fastening: A mechanical action to hold the components together.Includes:

2

Threaded fasteners: Screw, nuts, bolts, etc. Very common in industry. Allow to be taken apart if necessary.

Rivets, crimping, and other methods: he fastener or one of the components is mechanically deformed.

Press fits: The two parts are joined together by pressing one into the other. Once fitted, the parts are not easily separated.

Snap fits: One or both of the parts elastically deform when pressed together. Commercial hardware such as retainers, C-rings, and snap rings may be used.

Sewing and stitching: Used to assemble soft, thin materials such as fabrics, cloth, leather, etc.

3

2. Joining methods: Includes welding, brazing, and soldering. Molten metal is used to join two or more components together. Common feature of welding techniques is that fusing and melting occur in the metal parts being joined.In brazing and soldering, only the filler metal becomes molten for joining. The metal components do not melt. Not as strong as welding.

3. Adhesive bonding: Involves the use of an adhesive material to join components. Two types of adhesives: thermoplastic and thermosetting. Thermosetting adhesives are more complicated to apply, but are stronger and capable of withstanding in high temperature.

4

Assembly SystemsThe methods used to accomplish assembly

processes:1. Manual single-station assembly: Generally

used on a product that is complex and produced in small quantities. One or more workers are required depending on the size of the product. Ex: machine tools, industrial equipment, aircraft, ships, etc.

2. Manual assembly line: Consist of multiple workstations. One or more workers perform a portion of the total assembly work on the product.

3. Automated assembly system: Uses automated methods at the workstations rather than human beings. 5

Manual Assembly LinesUsed in high-production situations where the

work can be divided into small tasks (work elements) and the tasks assigned to the workstations on the line.

By giving each worker a limited set of tasks repeatedly, the worker becomes a specialist in those tasks and perform more quickly.

Transfer of Work Between Workstations1. Nonmechanical Lines: Parts are passed from

station to station by hand. Problems are:Starving at stationsBlocking of stations

As a result, cycle times vary. Buffer stocks are used to overcome.

6

2. Moving Conveyor Lines: Use a moving conveyor (ex. A moving belt, conveyor, etc.) to move the subassemblies between workstations. The system can be continuous, intermittent (synchronous), or asynchronous.Problems of continuously moving conveyor:StarvingProducing incomplete items

In the moving conveyor line, production rate may be controlled by means of feed rate.

= feed rate = conveyor speed (feet per minute or

meters per second) = spacing between parts

7

pf

cV

pSp

cp SV

f

Raw workparts are launched onto the line at regular intervals.

The operator has a certain time period during which he/she must begin work before the part flows past the station. This time period is called the tolerance time.

= tolerance time = length of the station

Model VariationsIt is highly desirable to assign appropriate

amount of work to the stations to equalize the process or assembly times at the workstations.

This brings the line balancing problem and the three different types of lines.

8

tT

sLc

st VL

T

1. Single Model Line: Specialized line dedicated to the production of a single product.

2. Batch-model Line: Used for the production of two or more models with similar sequence of processing or assembly operations.

3. Mixed-model Line: Several models are intermixed on the line and are processed simultaneously.

These cases may be applied to both manual flow lines and automated flow lines.

Type 2 and 3 are easier to apply to manual flow-lines.

The problem of line balancing becomes more complicated when going from type 1 to type 3.

9

The Line Balancing ProblemIt is to arrange the individual processing and

assembly tasks at the workstations so that the total time required at each station is approximately the same.

Very difficult to achieve perfect balance in most practical situations.

If workstation times are unequal, the slowest station determines the overall production rate of the line.

TERMINOLOGYMinimum Rational Work Element. The smallest

practical indivisible tasks into which the job can be divided.

= Time required to carry out this rational work element.

Considered to be constant. In fact it varies in a manual station.

Assumed that they are additive. In fact it changes when two are combined at one station

10

tT

Assembly Line BalancingThe General Procedure

1. Determine cycle time by taking the demand (or production rate) per day and dividing it into the productive time available per day

2. Calculate the theoretical minimum number of work stations by dividing total task time by cycle time

3. Perform the line balance and assign specific assembly tasks to each work station

11

Product-Oriented Floor Plan

12

1 3

2

4

5

WorkWork

OfficeOffice

Belt ConveyorBelt Conveyor

Work Work StationStation

Note: 5 tasks or operations; 3 work stationsNote: 5 tasks or operations; 3 work stations

Work StationWork Station

StationStation

Total Work Content. ( ) Sum of the time of all the work elements to be done on the line.

= Number of work elements that make up the

total work or job.

Workstation Process Time. ( ) The sum of the times of the work elements done at the station.

n= number of stations

Cycle Time. ( ) Ideal or theoretical cycle time of the flow line. The time interval between parts coming off the line.

13

wcT

en

jejwc TT

1

en

n

i

n

jejsi

e

TT1 1

siT

cT

p

c RE

T sic TT max ejc TT

Precedence Constraints. (Technological sequencing requirements)

The precedence requirements that restrict the sequence in which the job can be accomplished. There are also other constraints which concern the restrictions on the arrangement of the stations. Position constraintPosition constraint. When the product is too large for one worker to perform work on both sides, operators are located on both sides of the flow line. Zoning constraintZoning constraint. May be either positive or negative. According to positive zoning constraint, certain work elements should be placed near each other. A negative zoning constraint indicates that work elements should not be located in close proximity since they might interfere with one another.

Precedence Diagram. Graphical representation of the sequence of work elements. Nodes may be used to symbolize the work elements, and arrows connecting the nodes for the order.

14

Balance Delay. (balancing loss) (d) Measure of the line inefficiency.

The balance delay d will be zero for any values n and that satisfies the relationship

Minimum number of workstations required to optimize the balance delay for a specified may be found by

15

c

wcc

nTTnT

d

cT wcc TnT

cT

c

wc

TTintegersmallest theisn minimum

ReferensiIE462 Introduction to Manufacturing

Systems

16