Manufacturing Principles: Product Layout, Process Layout, and Just-in-Time Manufacturing, Exercises of Industrial Engineering

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LECTURE NOTES

ON

MET 601 (INDUSTRIAL ENGINEERING & QUALITY CONTROL)

PREPARED BY

MR. MITHUN KUMAR KESHARI,

LECTURER IN MECHANICAL ENGINEERING,

GOVERNMENT POLYTECHNIC PURI

CONTENTS

SL NO CHAPTER NAME PAGE NO

1 PLANT LOCATION AND LAYOUT 1 - 4

2 OPERATIONS RESEARCH 5 - 10

3 INVENTORY CONTROL 11 - 16

4 PLANT MAINTENANCE 17 - 20

5 INSPECTION AND QUALITY CONTROL 21 - 27

6 CONTEMPORARY QUALITY MANAGEMENT CONCEPTS 28 - 33

g) Increase employee morale h) Reduce accidents i) Provide for volume and product flexibility j) Provide ease of supervision and control k) Provide for employee safety and health l) Allow ease of maintenance m) Allow high machine or equipment utilization n) Improve productivity

PRINCIPLES OF PLANT LAYOUT:

(i) Principle of Space Utilization: All available cubic space should be effectively utilized – both horizontally and vertically. (ii) Principle of Flexibility: Layout should be flexible enough to be adaptable to changes required by expansion or technological development. (iii) Principle of Interdependence: Interdependent operations and processes should be located in close proximity to each other; to minimize product travel. (iv) Principle of Overall Integration: All the plant facilities and services should be fully integrated into a single operating unit; to minimize cost of production. (v) Principle of Safety: There should be in-built provision in the design of layout, to provide for comfort and safety of workers. (vi) Principle of Smooth Flow: The layout should be so designed as to reduce work bottlenecks and facilitate uninterrupted flow of work throughout the plant. (vii) Principle of Economy: The layout should aim at effecting economy in terms of investment in fixed assets.

PRODUCT LAYOUT: In this type of layout, all the machines are arranged in the sequence, as required to produce a specific product. It is called line layout because machines are arrange in a straight line. The raw materials are fed at one end and taken out as finished product to the other end.

Special purpose machines are used which perform the required jobs (i.e. functions) quickly and reliably.

Advantages:

1. Reduced material handling cost due to mechanized handling systems and straight flow
2. Perfect line balancing which eliminates bottlenecks and idle capacity.
3. Short manufacturing cycle due to uninterrupted flow of materials

4. Simplified production planning and control; and simple and effective inspection of work.
5. Small amount of work-in-progress inventory
6. Lesser wage cost, as unskilled workers can learn and manage production. Disadvantages:
7. Lack of flexibility of operations, as layout cannot be adapted to the manufacture of any other type of product.
8. Large capital investment, because of special purpose machines
9. If one or two lines are running light, there is considerable machine idleness.
10. A single machine breakdown may shut down the whole production line,

5. Specialized and strict supervision is essential.

PROCESS LAYOUT: In this type of layout machines of a similar type are arranged together at one place. E.g. Machines performing drilling operations are arranged in the drilling department, machines performing casting operations be grouped in the casting department. Therefore the machines are installed in the plants, which follow the process layout.

This layout is commonly suitable for non-repetitive jobs. Same type of operation facilities are grouped together such as lathes will be placed at one place all the drill machines are at another place and so on.

Advantages of Process Layout:

(i) There will be less duplication of machines. Thus total investment in equipment purchase will be reduced. (ii) It offers better and more efficient supervision through specialization at various levels. (iii) There is a greater flexibility in equipment and man power thus load distribution is easily controlled. (iv) Better utilization of equipment available is possible. (v) Breakdown of equipment can be easily handled by transferring work to another machine/ work station. (vi) There will be better control of complicated or precision processes, especially where much inspection is required.

2. OPERATIONS RESEARCH

INTRODUCTION: Operations Research (OR) is a discipline that helps to make better decisions in complex scenarios by the application of a set of advanced analytical methods. It couples theories, results and theorems of mathematics, statistics and probability with its own theories and algorithms for problem solving. Applications of OR techniques spread over various fields in engineering, management and public systems.

Operation research signifies research on operations. It is the organized application of modern science, mathematics and computer techniques to complex military, government, business or industrial problems arising in the direction and management of large systems of men, materials, money and machines. APPLICATION:

1. Allocation and Distribution in Projects
2. Production and Facilities Planning
3. Programme Decisions:
4. Marketing
5. Organization Behaviour
6. Research and Development

LINEAR PROGRAMMING PROBLEM: Linear programming is powerful mathematical technique for finding the best use of limited resources of a concern. It may be defined as a technique which allocates scarce available resources under conditions of certainty in an optimum manner to achieve the company objectives which may be maximum overall profit or minimum overall cost. LP can be applied effectively only if a) The objectives can be stated mathematically

b) Resources can be measured as quantities (no. weight etc)

c) There are too many alternate solutions to be evaluated conveniently

d) The variables of the problem bear a linear relationship i.e. Doubling the units of resources will double the profit. LPP can solved by two methods.

1. Graphical method: when two decision variables are involved. This is simple.
2. Simplex method: useful for any no. of decision variable in the problem and no. of constraints. Graphical method: Simple two dimensional linear programming problems can be easily and rapidly solved by this technique. This method can be easily be applied upto 3 variables. EXAMPLE 1 : A company produces two types of dolls A and B. Doll A is of superior quality and B is of lower quality. Profit on doll A and B is Rs 5 and Rs 3 respectively. Raw material required for each doll A is twice that is required for doll B. The supply of raw material is only 1000 per day of doll B. Doll A requires a special crown and only 400 such clips are available per day. For doll B 700 crowns are available per day. Find graphically the product mix so that the company makes maximum profit.

ANSWER :

Graphical method:

1st step: Formulate the LPM.

Max Z = 20x1 + 40x Subjected to x1 + 4x2 24 (c1) 3x1 + x2 21 (c2) x1 + x2 8 (c3) x1, x2 0 (c4) c1 is constrain no. 1 and so on.

2nd step 2nd steps convert the constraint inequalities temporarily into equations. x1 + 4x2 = 24 (c1) 3x1 + x2 = 21 (c2) x1 + x2 = 8 (c3)

3rd step Axis are marked on the graph paper and labeled with variables x1 & x2.

4th step 4th step is draw straight lines on the graph paper using constraint equations and to mark feasible solution on the graph paper.

Taking 1st constraint equation, x1 + 4x2 = 24 x1 = 0, x2 = 6 x2 = 0, x1 = 24

2. Non critical activities: Such activities have provision (slack or float) so that even if they consume a specified time over and above the estimated time, the project will not be delayed.
3. Dummy activities : When two activities start at the same instant of time, the head events are joined by a dotted arrow and this is known as dummy activity. It does not consume time. It may be non-critical or critical. It becomes a critical activity when its EST = LFT. Critical path : It is that sequence of activities which decide the total project duration. It is formed by critical activities. A critical path consumes maximum resources. It is the longest path and consumes maximum time. It has zero float. The expected completion data cannot be met, if even one critical activity is delayed. A dummy activity joining two critical activities is also a critical activity Earliest start time (EST): It is the earliest possible time at which activity can start and is calculated by moving from first to last event in a network diagram. Earliest finish time (EFT): It is the earliest possible time at which activity can finish. i.e. (EST + D) Latest finish time (LFT): It is calculated by moving backward i.e. from last event to first event of the network diagram. It is the last event time of the head event Latest start time (LST): It is the least possible time by which an activity can start. LST = LFT – duration of that activity Float or slack: Slack is with reference to an event and float is with respect to an activity. It means spare time, a margin of extra time over and above its duration which a noncritical activity can consume without delaying the project. Float is the difference between the time available for completing an activity and the time necessary to complete the same. There are three type of float. 1. Total float: It is the additional time which a non-critical activity can consume without increasing the project duration. TF = LST – EST or LFT – EFT and it can be – ve. 2. Free float: If all the non critical activities start as early as possible, the time is the free float. FF = EST of tail event – EST of head event – activity duration 3. Independent float: It can be used to advantage. If one is interested to reduce the effort on a non-critical activity in order to apply the effort on a critical activity by reducing the project duration. IF = EST of tail event – LFT of head event – activity duration. If IF is negative, then taken as 0.

EXAMPLE:

Construct the network from the information. Activity Time Activity Time 1-2 6 3-5 11 1-6 5 4-5 6 2-3 13 6-7 11 2-4 4 5-8 3 ------ ------ 7-8 15

Critical Path Method: In the critical path method the activity times are known with certainty. For each activity EST and LST are computed. The path with the longest time sequence is called critical path. The length of the critical path determines the minimum time in which the entire project can be completed. The activities on the critical path are called critical activities.

EXAMPLE: A small engineering project consists of 6 activities namely A, B, C, D, E & F with duration 4, 6, 5, 4, 3 & 3 days respectively. Draw the network diagram and calculate EST, LST, EFT, LFT and floats. Mark the critical path and find total project duration?

ANSWER: Critical path = 1-2-3-5- Total project duration = 4+6+5+3 = 18 days

3. INVENTORY CONTROL

INVENTORY:

Inventory is a detailed list of those movable items which are necessary to manufacture a product and to maintain the equipment and machinery in good working order. It represents those items which are either stocked for sale or they are in the process of manufacturing or they are in the form of materials which are yet to be utilized.

INVENTORY CONTROL: It may be defined as the scientific method of finding out how much stock should be maintained in order to meet the production demands and be able to provide right type of material at right time in the right quantities and at competitive prices.

CLASSIFICATION OF INVENTORIES:

1. Raw inventories:

 Raw materials and semi-finished products supplied by another firm which are raw items for present industry.  Raw materials are those basic unfabricated materials which have not undergone any operation since they are received from the suppliers. Ex – round bars, angles, channels, pipes etc

2. Work-in-progress inventories:

 Semifinished products at various storages of manufacturing cycle  The items or materials in partially completed condition of manufacturing

3. Finished inventories:  They are the finished goods lying in stock rooms and waiting dispatch. 4. Indirect inventories:

 The inventories refer to those items which do not form the part or the final product but consumed in the production process. Eg – machine spares, oil, grease, spare parts, lubricants

OBJECTIVES OF INVENTORY CONTROL:

 Purchasing material at economical price at proper time and in sufficient quantity as not to run slow  Providing a suitable and secure storage location  To maintain timely record of inventories of all the items  A definite inventory identification system  Adequate and responsible store room staff  Suitable requisition procedure  To provide a reserve stock

FUNCTIONS OF INVENTORY:

 Meeting customer demand: Maintaining finished goods inventory allows a company

to immediately fill customer demand for product. Failing to maintain an adequate supply of finished goods inventory can lead to disappointed potential customers and lost revenue.

 Protecting against supply shortages and delivery delays: A supply chain is only as

strong as its weakest link, and accessibility to raw materials is sometimes disrupted. That’s why some companies stockpile certain raw materials to protect themselves from disruptions in the supply chain and avoid idling their plants and other facilities.

 Separating operations in a process: Inventory of subassemblies or partially

processed raw material is often held in various stages throughout a process. Work in process inventory (or WIP) protects an organization when interruptions or breakdowns occur within the process. Maintaining WIP allows other operations to continue even when a failure exists in another part of the process.

 Smoothing production requirements and reducing peak period capacity

needs: Businesses that produce nonperishable products and experience seasonal customer demand often try to build up inventory during slow periods in anticipation of the high-demand period. This allows the company to maintain adequate levels during peak periods and still meet higher customer demand.  Taking advantage of quantity discounts: Many suppliers offer discounts based on certain quantity breaks because large orders tend to reduce total processing and shipping costs while also allowing suppliers to take advantage of economies of scale in their own production processes.

TERMS USED IN INVENTORY CONTROL:

1. Demand: It is the no. of items (products) required per unit of time. The demand may be either deterministic or probabilistic in nature. 2. Order cycle: The time period between two successive orders is called order cycle. 3. Lead time: The length of the time between placing an order and receipt of items is called lead time. 4. Safety stock: It is also called butter stock or minimum stock. It is the stock or inventory needed to account for delays in materials supply and to account for sudden increase in demand due to rush orders. 5. Inventory turnover: It the company maintains inventories equal to 3 months consumption it means that inventory turnover is 4 times a year i.e. the entire inventory is used up and replaced 4 times a year. 6. Reorder level: It is the point at which the replenishment action is initiated. When the stock level reaches ROL the order is placed for the item.

Reorder point (B)- It indicates that it is high time to initiate a purchase order if not done so the inventory may exhaust, even reserve stock utilized before the new material arrives. From B’ to D’ it is lead time and it may be calculated on the basis of past experience.

DERIVATION OF EOQ:

Let Q is the economic lot size or EOQ C is the cost for one item. I is the cost of carrying inventory in percentage per period P is the procurement cost associated with one order U is the total quantity used per period. No. of purchase orders to be furnished = U/Q Total procurement cost = No. of orders × cost involved in one order= U/Q X P Average quantity = Q/ Inventory carrying cost = average inventory × cost per item × cost of carrying inventory in %= Q/2 X C X I Total cost (T) = a + b = U/Q X P + Q/2 X C X I To minimize cost, dT/dQ = 0

Or Q = 𝟐𝑼𝑷/𝑪𝑰

PROBLEM 2:

ABC ANALYSIS:

ABC analysis helps in differentiating the items from one another and tells how much valued the item is and controlling it to what extent is in the interest of an organization.

4. PLANT MAINTENANCE

INTRODUCTION:

A plant is a place, where men, materials, money, equipment, machinery, etc are brought together for manufacturing products. Maintenance of facilities and equipment in good working condition is essential to achieve specified level of quality and reliability and efficient working. It helps in maintaining and increasing the operational efficiency of plant facilities and contributes to revenue by reducing operating of production.

OBJECTIVES OF PLANT MAINTENANCE:

 To achieve minimum breakdown and to keep the plant in good working condition at the lowest possible cost.  To keep the m/c in such a condition that permit to use without any interruption  To increase functional reliability of production facilities  To maximize the useful life of the equipment  To minimize the frequency of interruption to production by reducing breakdown  To enhance the safety of manpower

DUTIES, FUNCTIONS AND RESPONSIBILITIES OF PLANT MAINTENANCE DEPARTMENT:

A) INSPECTION:

 Inspection is concerned with the routine schedule checks of the plant facilities to examine their condition and to check for needed repairs  Inspection ensures the safe and efficient operation of equipment and machinery  Frequency of inspections depends upon the intensity of the use of the equipment  Items removed during maintenance and overhaul operation are inspected to determine flexibility of repairs  Maintenance items received from vendors are inspected for their fitness

B) ENGINEERING :

 Engineering involves alterations and improvements in existing equipments and building to minimize breakdowns  Maintenance department also undertakes engineering and supervision of constructional projects that will eventually become part of the plant.

C) MAINTENANCE:

 Maintenance of existing plant equipment.  Maintenance of existing plant buildings and other service facilities such as yards, central stress, roadways.  Minor installation of equipments, building and replacements

 Prevent breakdown by well-conceived plans of inspection, lubrication, adjustments, repair and overhaul.

D) REPAIR:

 Maintenance department carries corrective repairs to avoid unsatisfactory conditions found during preventive maintenance inspection.  Such a repair work is of an emergency nature and is necessary to correct breakdowns.

E) OVERHAUL:

 Overhaul is a planned, schedule reconditioning of plant facilities such as machinery etc.  It involves replacement, reconditioning, reassembly etc.

F) CONSTRUCTION:

 In some organizations, maintenance department is provided with equipment and personnel and it takes up construction job also.  It handles construction of wood, brick and steel structures, electrical installation etc.

G) SALVAGE:

 It may also handle disposition of scrap or surplus materials.  This involves segregation and disposition of production scrap.

H) CLERICAL JOB:

 Maintenance department keeps records of cost, of time progress on jobs, electrical installations, water, steams, air and oil lines, transport facilities.

I) GENERATION AND DISTRIBUTION OF POWER.

J) PROVIDING PLANT PROTECTION

K) ESTABLISHING AND MAINTAINING A SUITABLE STORE OF MAINTENANCE MATERIALS

L) HOUSE KEEPING

M) POLLUTION AND NOISE CONTROL