What is Plant Layout in Operations Managment ?

Plant lay­out is the phys­i­cal arrange­ment of machines, equip­ment, depart­ments, work areas, stor­age spaces and ser­vice areas inside a fac­tory or ser­vice facil­ity. It decides where each resource sits and, as a result, how mate­ri­als, peo­ple and infor­ma­tion move through the build­ing.

Lay­out mat­ters because it qui­etly shapes daily per­for­mance. A well-planned lay­out short­ens move­ment, reduces han­dling, uses space prop­erly and keeps peo­ple safe. A poor one cre­ates back-track­ing, crowd­ing, delays and acci­dents that no amount of hard work can fully can­cel. Once machines are fixed to the floor, chang­ing the arrange­ment is costly, so it pays to plan it well.

Why plant lay­out is impor­tant

Con­sider a small bak­ery. It must decide where to keep flour stor­age, the mix­ing machine, the oven, the pack­ing table and the counter where cus­tomers col­lect orders. If these fol­low the order of work, bak­ing becomes quick, walk­ing is reduced and out­put rises. If the oven is at one end, the mixer at the other and pack­ing in between, staff waste time and the risk of acci­dents grows. The same logic applies to a car plant, a hos­pi­tal or a bank branch.

A good lay­out there­fore:

• reduces mate­r­ial han­dling cost and move­ment of work­ers;
• cuts pro­duc­tion time and work-in-progress;
• uses floor space and height effi­ciently;
• improves super­vi­sion, coor­di­na­tion and com­mu­ni­ca­tion;
• makes the work­place safer and more com­fort­able;
• allows changes and expan­sion with­out major dis­rup­tion.

Objec­tives of plant lay­out

Smooth flow of work

Mate­ri­als should move for­ward from one oper­a­tion to the next with­out back-track­ing or cross­ing paths.

Min­i­mum mate­r­ial han­dling

Han­dling adds cost but no value, so the dis­tance and num­ber of moves should be as small as pos­si­ble.

Bet­ter use of space

Floor area should be used with­out wastage or con­ges­tion, includ­ing the ver­ti­cal space above machines.

Bet­ter coor­di­na­tion

Related depart­ments should be close so that super­vi­sion and com­mu­ni­ca­tion are easy.

Safety and com­fort

Work­ers need safe aisles, ade­quate light and ven­ti­la­tion, clear fire exits and guard­ing around haz­ardous machines.

Flex­i­bil­ity

The lay­out should allow changes in prod­uct design, vol­ume and meth­ods at rea­son­able cost.

Reduced pro­duc­tion time

Less wait­ing and less move­ment shorten the total time from raw mate­r­ial to fin­ished prod­uct.

Prin­ci­ples of a good plant lay­out

1. Prin­ci­ple of inte­gra­tion – men, mate­ri­als, machines and sup­port­ing ser­vices are com­bined into one effi­cient work­ing unit.
2. Prin­ci­ple of min­i­mum move­ment – mate­ri­als and peo­ple travel the short­est prac­ti­cal dis­tance.
3. Prin­ci­ple of smooth flow – work moves in a steady for­ward direc­tion, avoid­ing back-track­ing and bot­tle­necks.
4. Prin­ci­ple of cubic space util­i­sa­tion – both floor area and height are used, for exam­ple with over­head con­vey­ors and racks.
5. Prin­ci­ple of safety and sat­is­fac­tion – the arrange­ment pro­tects work­ers and gives them a com­fort­able envi­ron­ment.
6. Prin­ci­ple of flex­i­bil­ity – the lay­out can be rearranged cheaply when require­ments change.

Types of plant lay­out

Process lay­out (func­tional lay­out)

Sim­i­lar machines and activ­i­ties are grouped together in depart­ments: all lathes in one area, all drilling machines in another, all paint­ing in a third. Each job fol­lows its own route through the depart­ments it needs. A gen­eral engi­neer­ing work­shop, a hos­pi­tal (with sep­a­rate X-ray, lab­o­ra­tory and surgery depart­ments), a uni­ver­sity and a repair shop are typ­i­cal exam­ples. It suits job and batch pro­duc­tion with a wide vari­ety of prod­ucts in low vol­umes.

Advan­tages:

• Han­dles a wide vari­ety of prod­ucts and cus­tom orders.
• Needs fewer machines because gen­eral-pur­pose equip­ment is shared.
• A break­down of one machine does not stop the whole plant.
• Work­ers develop spe­cialised skills and super­vi­sion within a depart­ment is easy.

Dis­ad­van­tages:

• Mate­r­ial han­dling is long and costly because jobs criss-cross the floor.
• Work-in-progress and wait­ing time are high.
• Pro­duc­tion plan­ning, rout­ing and con­trol are com­plex.
• Skilled labour is needed, so labour cost is higher.

Prod­uct lay­out (line lay­out)

Machines are placed in the sequence of oper­a­tions needed for one prod­uct, so mate­r­ial moves in a straight line from start to fin­ish. Car assem­bly lines, bot­tling plants, cement and sugar fac­to­ries, and a cafe­te­ria serv­ing line are exam­ples. It suits mass or con­tin­u­ous pro­duc­tion of stan­dard prod­ucts in high vol­umes.

Advan­tages:

• Smooth, fast flow with min­i­mum mate­r­ial han­dling, often by con­veyor.
• Low work-in-progress and short through­put time.
• Sim­ple pro­duc­tion con­trol; semi-skilled work­ers can be used.
• Low cost per unit at high vol­ume.

Dis­ad­van­tages:

• High invest­ment in spe­cial-pur­pose machines.
• Inflex­i­ble: a change in prod­uct design may require rear­rang­ing the line.
• A break­down at one sta­tion can stop the entire line.
• Repet­i­tive work can be monot­o­nous for work­ers.

Fixed posi­tion lay­out

The prod­uct stays in one place because it is too large or heavy to move, and work­ers, mate­ri­als and equip­ment are brought to it. Ship­build­ing, air­craft assem­bly, bridge and build­ing con­struc­tion, and dam projects use this lay­out.

Advan­tages: very flex­i­ble for design changes; the costly job of mov­ing a huge prod­uct is avoided; work­ers take pride in com­plet­ing a whole unit.

Dis­ad­van­tages: mov­ing peo­ple and equip­ment to the site is costly; space at the site can become con­gested; sched­ul­ing many trades on one spot is dif­fi­cult; equip­ment may sit idle between jobs.

Com­bi­na­tion (hybrid) lay­out

Most real plants mix the basic types. A fac­tory may machine parts in a process lay­out and then assem­ble them on a prod­uct line. A hos­pi­tal may have func­tional depart­ments but a line-like flow in its pathol­ogy sam­ple han­dling.

Advan­tage: it takes the ben­e­fits of each type where they fit best. Dis­ad­van­tage: it is harder to design and con­trol.

Cel­lu­lar lay­out (group tech­nol­ogy)

Mod­ern text­books add the cel­lu­lar lay­out. Machines that make a fam­ily of sim­i­lar parts are grouped into a small cell, often U-shaped, where a team makes the part from start to fin­ish. It com­bines some of the flex­i­bil­ity of process lay­out with the smooth flow of prod­uct lay­out, and it reduces han­dling and through­put time.

Process lay­out ver­sus prod­uct lay­out

A sim­ple way to remem­ber it: process lay­out groups machines by type; prod­uct lay­out arranges machines by sequence.

Design­ing a process lay­out: load-dis­tance analy­sis

In a process lay­out, depart­ments with heavy traf­fic between them should be placed close together. The usual mea­sure is the total load-dis­tance:

$$\displaystyle \text{Load-distance} = \sum (\text{trips between two departments} \times \text{distance between them})$$

Worked exam­ple: com­par­ing two arrange­ments

Sup­pose a small work­shop has four depart­ments, Receiv­ing (R), Machin­ing (M), Paint­ing (P) and Ship­ping (S), laid out in a row of four bays 10 metres apart. The daily trips between depart­ments are: R–M 100, M–P 80, P–S 60, R–P 20 and M–S 30. Two arrange­ments are pro­posed: Lay­out 1 in the order R, M, P, S and Lay­out 2 in the order R, P, M, S.

Lay­out 1 needs 3,400 trip-metres a day against 4,500 for Lay­out 2, so Lay­out 1 is bet­ter. If mov­ing one load one metre costs ₹0.50, Lay­out 1 saves $(4{,}500 - 3{,}400) \times 0.50$ = ₹550 per day. The les­son is to keep the busiest pairs, here R–M and M–P, next to each other.

Design­ing a prod­uct lay­out: line bal­anc­ing

In a prod­uct lay­out the tasks must be grouped into work­sta­tions so that each sta­tion has roughly equal work and the line meets demand. This is called line bal­anc­ing. The main for­mu­las are:

$$\displaystyle \text{Cycle time } (C) = \frac{\text{Available production time per day}}{\text{Required output per day}}$$

$$\displaystyle \text{Minimum number of stations} = \frac{\sum t}{C}\ \text{(rounded up)}$$

$$\displaystyle \text{Efficiency} = \frac{\sum t}{n \times C} \times 100$$

where $\displaystyle \sum t$ is the total task time and $n$ is the actual num­ber of sta­tions.

Worked exam­ple: bal­anc­ing an assem­bly line

Sup­pose a line must pro­duce 240 units in an 8-hour (480-minute) day. Seven tasks, A to G, must be done in that order, with times of 50, 40, 30, 60, 20, 70 and 30 sec­onds.

1. Cycle time: $\displaystyle C = \frac{480 \times 60}{240} = \frac{28{,}800}{240} = 120$ sec­onds per unit.
2. Total work con­tent: $\displaystyle \sum t = 50 + 40 + 30 + 60 + 20 + 70 + 30 = 300$ sec­onds.
3. Min­i­mum sta­tions: $\displaystyle \frac{300}{120} = 2.5$, rounded up to 3.
4. Assign tasks in order with­out exceed­ing 120 sec­onds: Sta­tion 1 takes A, B, C (120 s). Sta­tion 2 takes D and E (80 s); adding F would make 150 s, so F moves on. Sta­tion 3 takes F and G (100 s).
5. Effi­ciency: $\displaystyle \frac{300}{3 \times 120} \times 100 = 83.33$ per cent. Total idle time is $360 - 300 = 60$ sec­onds per unit, so the bal­ance delay is 16.67 per cent.

Fac­tors affect­ing plant lay­out

• Nature of the prod­uct – small light items can move on con­vey­ors; huge items need a fixed posi­tion lay­out.
• Vol­ume of pro­duc­tion – high vol­ume favours prod­uct lay­out; low vol­ume favours process lay­out.
• Sequence of oper­a­tions – a fixed sequence suits a line; var­ied routes suit func­tional group­ing.
• Type of machines – heavy, noisy or vibrat­ing machines need spe­cial foun­da­tions and posi­tions.
• Mate­r­ial han­dling needs – con­vey­ors, cranes and fork­lifts need aisles and space.
• Space avail­able – the shape and size of the build­ing limit the options.
• Safety require­ments – fire exits, aisles, ven­ti­la­tion and haz­ardous-area sep­a­ra­tion.
• Future expan­sion – room to add machines or lines later.

Char­ac­ter­is­tics of a good lay­out

• Min­i­mum han­dling and short, straight flow paths.
• Effi­cient use of floor and cubic space.
• Clear aisles and good vis­i­bil­ity for super­vi­sion.
• Safe, well-lit and well-ven­ti­lated work­ing areas.
• Ser­vice areas such as stores, tool­rooms and main­te­nance placed close to where they are needed.
• Flex­i­bil­ity for change and room for growth.

Lay­out, mate­r­ial han­dling, pro­duc­tiv­ity and safety

Mate­r­ial han­dling

Lay­out and mate­r­ial han­dling are planned together. The lay­out fixes the dis­tances; the han­dling sys­tem (con­vey­ors, trol­leys, cranes, fork­lifts) fixes how loads cross them. Straight or U-shaped flow, unit loads and grav­ity-fed chutes all reduce han­dling cost.

Pro­duc­tiv­ity

A good lay­out raises pro­duc­tiv­ity by cut­ting walk­ing and wait­ing, reduc­ing idle machine time, low­er­ing work-in-progress and mak­ing the flow vis­i­ble. A bad lay­out low­ers it through con­ges­tion, repeated han­dling, delays and con­fu­sion.

Safety

Safe aisles, guard­ing, sep­a­ra­tion of haz­ardous processes, fire exits and good light­ing are part of lay­out design, not addi­tions after it.

Flex­i­bil­ity

Mov­able machines, mod­u­lar benches and util­ity con­nec­tions placed at reg­u­lar inter­vals make it cheaper to rearrange the floor when prod­ucts or vol­umes change.

Key terms

Plant lay­out

The phys­i­cal arrange­ment of machines, depart­ments, stor­age and ser­vice areas in a facil­ity.

Process lay­out

A lay­out that groups sim­i­lar machines or func­tions together; suited to job and batch pro­duc­tion.

Prod­uct lay­out

A lay­out that arranges machines in the sequence of oper­a­tions; suited to mass pro­duc­tion.

Fixed posi­tion lay­out

A lay­out in which the prod­uct stays in one place and resources are brought to it.

Cel­lu­lar lay­out

A lay­out that groups dis­sim­i­lar machines into cells, each mak­ing a fam­ily of sim­i­lar parts.

Load-dis­tance

The sum of trips mul­ti­plied by dis­tance between depart­ments, used to com­pare process lay­outs.

Cycle time

The max­i­mum time allowed at each work­sta­tion, equal to avail­able time divided by required out­put.

Line bal­anc­ing

Assign­ing tasks to work­sta­tions so that each has nearly equal work and idle time is min­imised.

Com­mon ques­tions

Which lay­out suits a hos­pi­tal?

Mainly a process lay­out, because patients need dif­fer­ent com­bi­na­tions of depart­ments such as radi­ol­ogy, lab­o­ra­tory and surgery. Some areas, such as a vac­ci­na­tion drive, may run as a line.

Why is a prod­uct lay­out called inflex­i­ble?

Its spe­cial-pur­pose machines are arranged for one prod­uct sequence, so a design change or a new prod­uct often needs the line to be rebuilt.

What is the dif­fer­ence between plant loca­tion and plant lay­out?

Loca­tion decides where the facil­ity is set up; lay­out decides how resources are arranged inside it. Loca­tion is decided first and changed rarely.

How is line effi­ciency cal­cu­lated?

Divide total task time by the num­ber of sta­tions mul­ti­plied by the cycle time, then mul­ti­ply by 100. In the exam­ple above, $\displaystyle \frac{300}{3 \times 120} \times 100 = 83.33$ per cent.

Why do most fac­to­ries use a com­bi­na­tion lay­out?

Because parts are often made in batches, which suits func­tional group­ing, while final assem­bly is repet­i­tive, which suits a line. Com­bin­ing the two gives the ben­e­fits of each.

Ref­er­ences

1. Muther, R. (1973) Sys­tem­atic Lay­out Plan­ning. Cah­n­ers Books.
2. Heizer, J., Ren­der, B. and Mun­son, C. Oper­a­tions Man­age­ment: Sus­tain­abil­ity and Sup­ply Chain Man­age­ment. Pear­son.
3. Steven­son, W. J. Oper­a­tions Man­age­ment. McGraw-Hill Edu­ca­tion.
4. Chary, S. N. Pro­duc­tion and Oper­a­tions Man­age­ment. McGraw-Hill Edu­ca­tion (India).
5. Pan­neer­sel­vam, R. Pro­duc­tion and Oper­a­tions Man­age­ment. PHI Learn­ing.

Related read­ing

• Loca­tion Analy­sis in Oper­a­tions Man­age­ment
• Pro­duc­tion Sched­ul­ing in Oper­a­tions Man­age­ment
• Pro­duc­tion Plan­ning and Con­trol (PPC) in Oper­a­tions Man­age­ment