Production Planning

9) a) Draw a flow chart to explain the procedure to schedule ‘n’ jobs on two machines: Ans: The following are the ten steps involved to schedule ‘n’ jobs on two machines: Step 1) Prepare list of the jobs to be processed on the two machines. Step 2) Estimate processing time for each job on each machine. Step 3) Construct a job array, called sequencing matrix. To construct the matrix the jobs to be processed are recorded row head wise, the machines to be employed to process the jobs are recorded column head wise and the processing time of each job is recorded against the under the respective machine. Step 4) Scan the job array and identify the smallest processing time. Step 5) If the smallest time appears: i.

On the first machine, A, assign the corresponding jobs as close to the beginning of the job sequence as possible. ii. On the second machine, schedule the corresponding job as close to the end of the job sequence as possible. iii. If there is a tie of minima for both machines i.e., if the smallest element occurs on both machines, (one minimal element on each machine), select among the tied up jobs the one with the smallest time on the first machine and schedule it as early in the job sequence as possible. iv. If the tie of the minima occurs among the elements of the first machine, select among the tied up jobs the one with the smallest time on the second machine and schedule it as early in the job sequence as possible. v. If the tie for the minima occurs among the elements in the second machine, select among the tied up jobs the one with the smallest time on the first machine and schedule it as late in the sequence as possible. Step 6) Delete from the array the jobs scheduled and its corresponding processing times. Step 7) Repeat steps 4, 5, 6 and 7 for remaining processing times, placing the jobs next to first or next to last until all jobs are scheduled. Step 8) Calculate the total elapsed time to process all jobs through the two machines. Step 9) Calculate the idle time for machines A and B.

Fig: Flow chart for”n jobs: 2 machines” sequencing model START Construct a sequencing matrix with n jobs and two machines (A & B)

Scrutinize processing time of all jobs on both machines and select the smallest time

Does the smallest time occur on first

No

Yes Schedule the job corresponding to the smallest time as close to the beginning of the job sequence as possible.

Delete the job scheduled and its corresponding processing times

No

Have all jobs been scheduled

Yes Calculate start and finish time of each job on machine A

Calculate start and finish time of each job on machine B

Determine total elapsed time to process all jobs though two machines

Calculate idle time of each machine

STOP

Schedule the job corresponding to the smallest time as close to the end of the job sequence as possible

b) Five jobs A, B, C, D and E are required to be processed on two machines M1 and M2. Each job has to be processed on machine M1 and then on machine M2. The order of the completion of jobs has no significance. The processing time hours for five jobs on the two machines is as under: Job Machine

A

B

C

D

E

Machine #1

4

17

14

9

11

Machine #2

5

7

12

2

6

Ans: The smallest time in the job array is 2 hours and it appears for the first stage. The corresponding job D therefore is scheduled last and its entry is made in the last cell of the sequencing bar. D Delete the corresponding job schedule leaves us 4 jobs in the array. The next smallest time is 4 hrs and it occurs on the job A which is present in the sequence of Machine #1. Therefore the entry is made in the first cell of the sequencing bar. D

A

Deleting the job schedule leaves us with 3 more entries in the array. The next smallest time is 6 and is present in the job E, which is present in the sequence of Machine #2. Therefore the entry is made in the last but one cell of the bar. A

E

D

Deleting the job schedule leaves us with 2 more entries in the array. The next smallest time is 7 and is present in the job B, which is present in the sequence of Machine #2. Therefore the entry is made in the 3rd cell of the bar. A

B

E

D

Since the last job is left unscheduled, it is therefore placed in the empty cell: Therefore the optimum sequence, therefore is A, C, B, E & D A

C

B

E

D

2. What is Production Planning and Control? What are its key functions? How does PPC contribute to the two basic objectives namely “long term growth of business” and “Profit of the company”? Ans: Introduction: Production Planning is a centralized activity (normally conducted in the office) and includes such functions as order preparation, material control, process planning, tools control and scheduling. Production control, on the contrary, a diffused activity (usually conducted in the shops) and includes such functions as dispatching, progressing and expediting. Functions of Production Planning & Control:

1)

2)

3)

4)

Control Functions Order Preparation includes activities like1. making of work orders, converting work orders into shop orders, preparing auxiliary orders, and releasing such orders to shops to authorize manufacturing activity. Materials control concerns preparation of materials estimates indenting non-stick2. materials, ascertaining availability of materials purchased to stock, continual follow-up with purchase and store for timely receipt of materials, advising store to allocate required quantities of available materials (alternatively on their receipt) against specific shop orders. Processing Planning or Routing concerns fixation of method of manufacture operations and their sequence, machine tools for each3. operation, jigs and fixtures, measuring instruments and gauges etc to enable shops to produce goods of the right quality at the lowest cost. Tools Controls concerns preparation of4. estimates of cutting tools (Standard as well as non-standard tools), gauges and measuring instruments including jigs & fixtures, indenting non-stock tooling, follow-up with tool room for timely manufacture of jigs & fixtures, periodical replenishment of worn-out-non-consumable tooling (e.g. work aborts, collets, copying masters, Allen keys, spanners. etc.)

Optional Functions Cost Estimation concerns preparation of preproduction cost estimates to be used by sales department for quotation purposes. (Alternatively this function may be assigned to costing department or industrial engineering dept) Work Measurement concerns fixation of time to be allowed to a qualified workman to carryout a specified task, under specified conditions and at the defined level of performance. Work measurement employs scientific, well-known techniques like time study, analytical estimating etc (Alternatively, work measurement work may be assigned to industrial engineering dept.) Sub Contract concerns off-loading of work on outside vendors for economic reasons or to augment existing manufacturing facilities. Sub-contract work alternatively may be handled by Materials/Purchase Dept. Capacity Planning concerns estimation of requirements of men and machines as the basics of decision making to meet the firm’s increased volume of business (Some companies prefer to assign this function to engineering dept)

5) Scheduling concerns preparation of machine 5) Demand Forecasting concerns making loads, fixation of calendar dates of various projection of company’s product market, operations to be performed on a job, coordination though, long term forecasts are given by sales with sales to confirm delivery dates of new items department but short term forecasts required for and periodical preparation of dispatch schedules materials planning, machines loading, or regular items. subcontracting etc, may be prepared by PPC departments. 6) Dispatching concerns preparation and distribution of shop orders and manufacturing instructions to be concerned department as their authority to perform the work according to the predetermined schedule. 7) Progressing concerns collection of data from manufacturing shops, recording of progress of work, and comparing progress against the plan. 8) Expediting concerns intensive progress chasing to identify delays and interruptions which may hold up production, devising cures from time to time to keep rate of production in line with the schedule communicating possible failure in delivery commitments to sales department.

b) Long term Growth of business and Profit of the Company: Long term growth of business and profitability are the two basic objectives of an organization. For long term growth, the company must have enough orders and for enough orders it must have large number of satisfied customers. Five essentials to achieve customers’ satisfaction are: 1) 2) 3) 4) 5)

Timely delivery Advance communication in case of expected late shipments Short lead time in emergency Consistent and good quality of products Competitive price.

Good production planning and control is necessary to meet these essentials of customers’ satisfaction. Good PPC system is also necessary to minimize waiting time costs, overtime costs, inventory costs and other manufacturing overheads. Goods PPC system helps to improve utilization or resources morale of the employees.

3) (a) How does Production Planning differ from Production Control? Ans: Production Planning: It is the determination, acquisition and arrangement of all facilities necessary for future production of items. In other words, production planning is essentially a pre-production activity, associated with the design of the production system. Production Control: It is the corollary to short term production planning or scheduling and is quite simply concerned with the implementation of production schedules. Production Planning Versus Production Control PLANNING (Planning the Work)

CONTROL (Working the plan)

1) Planning involves collection and maintenance of1) data regarding time standards, materials and their specifications, machines and their process capabilities, drawing and operational layouts etc. 2) Planning is seeing that requirements-tools,2) machines, men, instructions, authorizations and the like-well be available at the right time and in the right quantities and are of proper quality. 3) Planning involves preparation of load charts and3) fitting various work orders into uncommitted time available on the company’s facilities (men or machines). 4) Planning involves preparation of all necessary4) forms and paper work 5) Planning involves designing suitable feedback5) as to what may happen. 6) Planning involves forward thinking as to the remedial action to be taken if the job fails6) behind schedule.

Control involves dissemination of data, preparation of reports regarding output, machine and labour utilization, labour efficiency, percentage defectives etc.

Planning therefore, is a centralized activity (in the office) and includes such function as materials control, tools control, preprocess planning and scheduling.

Control is thus a diffused activity (in the shops) and includes functions such as dispatching, progressing and expediting.

Control is seeing that the requirements are actually made available at the right place in the right quantities. Control involves actual seeing that the jobs are started and completed as per schedule prepared by scheduling cell of the PPC. Control involves actual issue of forms and paper work. Control involves keeping track of what is happening and collecting information as to what has happened. Control involves suggesting remedial action when the job is falling behind schedule.

(b) What type of information is necessary for efficient functioning of PPC department? Which department in the organization originates this information? Ans: Introduction: The efficiency of Production Planning and Control department depends upon the information it gets from other departments and the accuracy of such information. To prepare load and schedule chat, it must know the preventive maintenance schedule. To give realistic delivery date, it must know the work content of each job. Production Planning and Control department generally requires the following information: Information Concerning

Details

Source

Department originating indicated Information

1. Production programme.

1. Quantity to be manufactured. 2. Delivery date.

Sales order or Order Acceptance

Sales

Drawings/Bill of Material Stock Cards

Drawing Office

2. Production materials

1. 2. 3. 4.

3. Tooling 4. Quality Standards

5. Operation Methods. 6. Path of Materials.

Kind and quality of material. Quantity of material required Stock on hand and reservations Lead time required for procurement. 1. Standard and special tooling 1. 2. 3. 4.

Dimensional requirements. Finish requirements Tolerance requirements Hardness desired.

1. 2.

Operations and their sequence. Machine tool for each indicated operation Jigs and fixtures needed Speeds & Feeds.

3. 4.

1 List of Operations and their Sequence 2. Alternatives possible

7. Operation time. 1. Setup time and standard time for each operation

Stores Purchase Tool Card P.P.C Drawings Customer’s feedback Process sheets Capacity charts

PPC PPC

Experience Route sheets

PPC

Plan layout Industrial Engineering Work Measurement data

8. Scheduling

P.P.C 1. Starting and finishing dates.

9. Progress of Work.

Drawing office Sales Department

Machine Load & Scheduled charts Production

1. Work Completed as on date.

Daily production reports/Time ticket/Perforated slips

4) How do the following management decisions influence design of the PPC system? (i) (ii) (iii) (iv)

Plan for meeting occasional increase in demand. Status of the PPC department in the organization Degree of centralization Internal structure of PPC department.

Ans: PLANNING MEETING SEASONAL OR OCCASIONAL INCREASE IN DEMAND: This influences greatly the production planning and control system which the company should have. Alternatives available to the company and associated activities are as under: i)

Having factors of production for the peak demand and utilizing extra capacity to manufacture products of non-seasonal nature or taking up subcontract work etc. Having factors of production for the least demand and meeting requirements of extra capacity by overtime or by holiday working or by hiring capacity or by sub-contracting etc. Production planning and control and the purchasing function under such a situation assumes very important role in the company.

ii)

STATUS OF THE PPC DEPARTMENT IN THE COMPANY: The status of PPC department in the company depends upon the company’s manufacturing processes. If the work is highly repetitive and the number of workmen is not very large, the work of planning may be performed directly by the line staff, there being thus no formal PPC department in the company. And in manufacturing units where plant and machinery is laid out as per sequence of operations and there is little difference in machine capacity for different products, the PPC may be sub-division of the manufacturing department. In firms, where either the product variety is very large or where machine capacities are different for different products, or where plant and machinery is laid out as per function in different departments not related to each other, PPC should be set up as an independent department with the head of the department responsible to the managing director, General manager, or works manager, depending upon the magnitude and complexity of the planning functions and the size of the firm. DEGREE OF CENTRALISATION: Degree of centralization implies extent to which planning activities are performed by PPC. Two systems in general are available: i) ii)

Centralized Planning where the functions of production planning is controlled centrally by staff specialist (s). Decentralized Planning where planning is carried out by line executiveforemen-who direct normal work in their respective departments.

Both types of planning, centralized as well as decentralized planning, have their relative advantages and disadvantages, the centralized planning takes away the burden of planning from the line staff thus leaving free to handle men and machines more effectively. Decentralized planning gives line staff sense of participation and opportunity to use their experience but it takes away lot of their valuable time in performing planning functions The trend today is towards the blend of “Centralized” and “Decentralized” system, called semi-centralized planning. It combines the merits of both the systems and it especially gives better results in a large industrial complex. Under semi-centralized planning, the scheduling of operations within the pre-fixed period and allotment of work to men and machines is done by line staff while overall coordination of materials ordering, sub-contract work planning, progressing and follow-up, capacity planning man power planning, maintenance planning etc, is done centrally by the staff specialists. THE INTERNAL STRUCTURE OF THE PPC DEPARTMENT Internal structure implies the functions to be assigned to PPC which depends on the nature of industry the size of the company and the management policies. Different companies assign different functions to the PPC department. It is common practice to assign following functions to PPC department: i) ii) iii) iv)

Order Preparation. Materials Control Tools Control Process planning

v) vi) vii) viii)

Scheduling Dispatching Progressing Expediting.

Few companies assign following four areas to PPC department: i) Cost Estimation iii) Sub-Contracting ii) Work Measurement iv) Capacity planning The functions actually to be assigned depend on the size of the company. This aspect also considers assigning of various functions of production control to different cells which again depends on the size of the company. In a medium or large sized industry there may be following important cells in PPC department: i) ii) iii) iv) v)

Materials Control Cell Tools Control Cell Process Planning Cell Scheduling Cell Dispatching Cell

vii)

vi) Progressing Cell Cost Estimation Cell viii) Sub-Contract Cell ix) Work Measurement Cell

Each cell may be headed by a senior engineer and supported by planning assistant(s) and clerk(s).

A representative production planning and control department of a medium size firm is illustrative in the following figure.

General Manager

Development Department

Order Preparation

Factory Production

Material Control

Process Planning

Production Planning & Control

Tools Control

Inspection & Quality Control

Scheduling

Plant Maintenance

Dispatching

6) (a) “Data given on the process sheet can be put to lot many uses in the organization” Discuss. Ans: Introduction: Process planning is the process of establishing the shortest and most economical path that each part is to follow from the point it is received as raw materials until it leaves as furnished part or a finished product. Process planning indicates operations to be performed and their sequence; specified the machine tool for each indicated operation; shows the necessary tooling (jigs and fixtures, cutting tools, cams and templates, measuring instruments, and gauges) for each indicated operation; gives manufacturing data such as speeds and feeds; sometimes the specifications of the skill for each operation. The document which incorporates this vital information is called process sheet or route sheet. Text: The information contained in the process sheet can be put to a variety of uses: (i)

Scheduling: The scheduling cell of PPC can obtain for each operation the setup and the processing time. This information helps them to prepare load and schedule charts

(ii)

Materials Movement: The Shop supervisor and the dispatch clerk can know where the jobs require to be sent for the next operation.

Progressing

(iii)

Cost Reduction and Cost Control: A process sheet gives an idea of the tooling (standard tools, jigs and fixtures, templates, gauges and measuring instruments) which could be arranged prior to the starting of the operation. This cuts down set-up time and reduces labour cost and overheads.

(iv)

Costing: Costing group can use the information to determine pre and post production cost of each component.

(v)

Method of Working: Method study engineer without going on the shop floor can know as to how presently the part is being manufactured.

(vi)

Requirement of manpower and machines: Set up times and processing times given in different route sheets may be consolidated machine wise into total man-hours or machine-hours required to enable the management to take decisions concerning requirements of manpower and machines.

(vii)

Shop efficiency: Operation wise time data given in the process sheet is also helpful to the shop personnel to know whether the shop performance is in line with the expected performance.

(b) A Small pump shaft is to be manufactured from a round bar on four machines in a workshop. It is first cut to length on a power hack-saw which can produce 12 pieces per hour. The cut pieces are then “faced to length” and “centered” on a special facing and centering machine. Once this machine is set-up (taking 30 minutes), the operator can complete 30 pieces per hour. Faced and centered pieces are next moved to the copying lathe. It takes 45 minutes to set up the copying lathe and 3 minutes to turn each piece. The final operation is cutting of the keyways on a special purpose key-way milling machine. It takes 8.50 minutes to cut hey-way on each piece. 8.0 minutes are required to set-up the hack-saw and 10 minutes to set-up the key-way milling machines. After cutting the key-ways the parts are debarred and inspected. Draw up a process sheet for the manufacture of this part. Though tooling and gauges do not require to be indicated yet their relative position on the process sheet should be shown. Sol:

PTO

Part Name: Pump Shaft Part No. : P0401125

Process Sheet

Set Up Time

Op. No. 1

Operation Description

Cutting it to Length

2

Faced to length & Center

3

Power Hack Saw Spiral Machine Lathe Machine

Copying Lathe

4

Machine

Cutting Keyways

Checked by (Signature & Date)

12 30

Key way milling Machine

REVISION Prepared by (Signature & Date)

Tooling Set up Std min 80

60

30

60

45

3

10

8.50

DATE: KALLURI ENGINEERS HYDERABAD - 500070.

7 (a) Why is it necessary to record the progress of work? What different methods are available to collect information? Ans: Introduction: Progressing is the process of checking actual performance against the production plan and reporting exceptional deviations to the concerned authorities for the corrective action. Progressing function consists in keeping a watch on flow of materials, recognition of delays and interruptions, taking steps to rush up the remaining operations and communicating possible delays to the customer (wherever necessary) It is sometimes argued that progressing is only a substitute for poor planning. Should a driver take his hands off the steering wheel because the road is straight? Should a pilot divert his attention from the control board because the weather is fine? No! They can’t do this, similarly, progressing is required even if the material control and process planning functions are discharged satisfactorily, scheduling is done properly, manufacturing orders are released. There are usually a number of factors which tend to push the schedules off the mark. Some of the notable ones are as under: • • • • • •

Delay in receipt of material from vendor(s) Excessive absenteeism (more than the normal) Machines breakdowns Excessive spoilage Errors in drawings Strikes and acts of Gods.

The need for progressing is also created when the customers do the follow up on their own to know the status of their orders. Methods to collect information: (i) (ii) (iii) (iv) (v)

Physical Count Daily production report Job Card Perforated route sheet Detachable sheet

(b) Explain with a diagram any two methods to collect data on progress of work. Ans: Daily Production Report: It is prepared by the supervisor, this is another method of obtaining feedback. A daily production report contains fixed space to record:       

Operator’s Name and Token number Machine on which he worked Time spend Quantity produced Quantity checked by the patrolling inspector Results of the inspection Idle time and its reasons.

This report may be prepared either by the shop supervisor or the patrolling inspector and is collected at the end of the shift or the next day by the progress clerk of the PPC department. This method is best suited for large workshop having a process type of layout producing number of non-standard parts.

DAILY PRODUCTION REPORT Machin e

Operator’s Name Code

507

A.R. Yande

508

-do-

509

Manjit

208/1

R. B. Kale

208/2

-do-

Part Name & No. Double Gear: 29 teeth Cam Shaft Gear (Op. No. 80) Idler Gear

SECTION DATE SHIFT

Hours Worked

: : :

Gear Shop 12.11.04 First Shift

From To 7AM 3.30 PM

Qty. First Inspection Tole produc Qty. OK OK Rej Code ed 78 20 20 -

7AM 3.30 PM

42

18

17

1

E

7AM 3.30 PM

60

15

15

-

G

Axle Shaft (Op. No. 90)

7AM

3.30PM

Agro Control Shaft (Op. 120)

7AM

3.30PM

½ Hr

20

20

-

-

-

6

6

2

2

G

1 Hr

It is a useful method of production feed back/collecting data on progress of work. The route sheet for each job carries part number, product or assembly number it is in, list of operations to be performed, and the necessary information. The route sheet is handed over to the supervisor or is tied to the product. As soon as each operation is completed, the operator or the supervisor signs the lower portion of the route sheet, detaches it, and returns to the progress section for their analysis. This method is suitable for tool rooms, jobbing shops or workshops producing one or few numbers of a component.

OPERATION DESCRIPTION Inspect Grind Chamfer Thread Grind Grind OD Grind total length Grind bore and face Heat treat Inspect

½ Hr

34

Perforated route sheet:

SHOP ORDER OP. NO. NO. 2002 130 2002 120 2002 110 2002 100 2002 90 2002 80 2002 70 2002 60

Idle Hours _

DATE OF SIGN COMPLETIION

2002 2002 2002 2002 2002

50 40 30 20 10

Cut keyway Finish blank Rough blank Drill 50 hole Saw off

Fig: Perforated route sheet for manufacture of a thread roll 10 (a) What are the steps involved in solving an assignment problem. Ans: Introduction: Hungarian method is the most efficient method for solving an assignment problem involving minimum objective. Though its standard procedure is for balanced problems, minimization problem, free from restrictive, but it can be applied to even special situations by adopting additional steps.

Basic Principles: The Hungarian method is based on the following properties: (i) (ii)

If a constant element is added or subtracted from every element of any row or column in the given cost matrix, an assignment that minimizes the total cost in the original matrix also minimizes the total cost in the revised matrix. In an assignment matrix, solution having zero total cost is the optimal solution.

Assumptions: (i)

Each facility is capable of performing each task

(ii)

Tasks differ in their work contents and facility in their capabilities

(iii)

Only one task can be assigned to each facility

(iv)

As only one task can be assigned to each facility, the assignment matrix must be of n x n size. (In case the matrix is not square, dummy rows or columns, equal to the difference, are added).

Procedural steps to solve standard assignment problems: A standard assignment problem is a balanced assignment problem (i.e., number of tasks equal number of facilities), incorporates no restriction in allocation and involved minimization objective, Hungarian method to solve such problem requires following steps: Step 1: Express the problem into n x n assignment matrix Step 2: Select the smallest element in each row and subtract it from every element of that row. Step 3: Select the smallest element in each column of the reduced matrix obtained from step 2 and subtract it from every element of that column. Step 4: Cover all zero elements by minimum number of straight lines (horizontal and vertical lines only). If the number of lines drawn is equal to n(number of rows/columns), the solution is optimal and proceed to Step 7. if the number of lines drawn is smaller than n, go to step 5. Step 5: Select the smallest uncovered element (i.e., smallest element not covered by the lines), subtract it from all uncovered elements including itself, and add it to the elements covered twice (i.e. elements located at the intersection of any two lines), and reproduce other elements (i.e. elements through which only one line passes) as they are.

Step 6: Repeat steps 4 and 5 until an optimal solution is obtained. Step 7: Given the optimal solution make the job assignments as follows: (a) Examine the rows one by one starting with the first row until a row with an exclusive zero (i.e. row with exactly one zero) is found. Mark the zero by enclosing it in a square indicating assignment of the task to the facility. Cross out all zeroes (if any) in the column as they cannot be used to make other assignments. (b) Examine next the columns for any mutual exclusive zero and mark each as above, crossing out the remaining zeroes in that row. (c) Repeat steps (a) and (b) successfully until either of the following conditions occur: i. All zeros have been marked / crossed and each row contains one marked zero. This means that the optimal solution has reached. ii. All zeros have not been marked / crossed. The remaining unmarked zeros lie at least two in each row and column. This means that more than one optimal solution exists. (b) A drawing office incharge has four tasks and equal number of draught men. His estimate of time for each job – draught men combination is given (in hours) in the following matrix: Draughtmen Processing time (Hours) Jobs

D1

D2

D3

D4

J1

25

25

20

15

J2

35

20

15

20

J3

25

15

20

18

J4

30

10

25

20

Find out the optimal assignment. Sol: Step1: “Express the problem into n x n assignment matrix”. This step has already done in the case problem. Step2. “Subtract the smallest element in each row from every element in its row so as to obtain atleast one zero in each row.” 15, 15, 15 & 10 are the smallest in 1st, 2nd, 3rd and 4th rows respectively. Subtraction of the smallest element in the row from every element in its row gives rise to an assignment matrix shown in the following table.

Draughtmen Processing time (Hours) Jobs

D1

D2

D3

D4

J1

10

10

5

0

J2

20

5

0

5

J3

10

0

5

3

J4

20

0

15

10

Step 3. Subtract the smallest element in each column of assignment matrix obtained in step 2 from every element in its column. This step gives rise to yet another assignment matrix…

Draughtmen Processing time (Hours) Jobs

D1

D2

D3

D4

J1

0

10

5

0

J2

10

5

0

5

J3

0

0

5

3

J4

10

0

15

10

Connect all zeros in the assignment matrix obtained in step 3 by minimum number of straight lines. Min 4 straight lines are required to connect all zeros. Step 4. (a) “Examine the rows one by one, starting with the first row until with an exclusive zero (i.e. row with exactly one zero) is found. Mark the zero by enclosing it in a square indicating assignment of the task to the facility. Cross out all zeros in the same column as they cannot be used to make other assignments. (b) Examine next the columns for any mutual exclusive zero and mark each as above, crossing the remaining zeros in that row. Here… 1) Row J1 has two exclusive zeros which occur at Junction J1 D1 and J1 D4 hence the allocation of task J1 is postponed for the time being. 2) Row J2 has 1 exclusive zero which occurs at junction J2 D3 hence Job J2 is assigned to D3. 3) Row J3 has two exclusive zeros which occur at Junction J3 D1 and J3 D2 hence the allocation of task J1 is postponed for the time being. 4) Row J4 has 1 exclusive zero which occurs at junction J4 D2 hence Job J2 is assigned to D2. 5) With the allocation of J2 and J4 we have 2 jobs left out unassigned. Looking at the matrix again, we see that the Under J3 there are 2 zeros out of which the position D2 is already assigned to J4 and cannot be reassigned to J1 as this is a

mutual exclusive zero assignment matrix. So the only position left out is J3D1. Hence the job J3 is assigned to D1. 6) With the allocation of Job J3 to D1 we are left out with J1. Considering the exclusive assignment matrix. The Job J1 can only be assigned to D4. Hence J1D4. So the Optimal assignment matrix is the following

Jobs

Draught Men Processing Time

J1

D4

15

J2

D3

15

J3

D1

25

J4

D2

10

Total Processing Time:

65 Hours

11 (a) what is critical ratio scheduling? What advantages does this technique have over other technique? Ans: Introduction: Critical ratio scheduling is a technique for establishing and maintaining priorities among the jobs-be it in a production control department for the purpose of scheduling or expending in a purchase department for the purpose of “Purchase order follow up” or in any other department of the company. The technique utilities concept of ratios called Critical ratios which provide time relationship between when a product/part/material is required and when it can be made available/supplied. Definition: A Critical ratio in its simplest form, may be stated as the ration of “time when a product is required“to the “time when the product can be supplied”. I.e. Critical Ratio =

Time when a product is required Time when the product can be supplied

For E.g., Critical Ratio = The Product is required in 20 days. The product can be made available in 10 days =

2.

A critical ratio of 2 implies that the time available to deliver the product is twice the time required to manufacture the product, similarly, a critical ratio of ½ will mean that the time available to deliver the product is half of the time required to manufacture the product. This also suggests that the processing time must be reduced to half of the normal expected time otherwise the product will not be delivered on time. Interpretation of critical ratios: Critical ratios have the following significance: A critical ratio of (i)

Greater than one means that there is sufficient time and job can be completed ahead of the schedule.

(ii)

Equal to one implies that job is just on schedule and requires to be closely watched.

(iii)

Less than one suggests that the job is critical and needs to be expedited to complete it on schedule.

In general, the smaller the critical ratio, the more critical the job is from delivery point of view. Advantages: This technique of critical ratio scheduling helps to:  Determine the relative job priorities for scheduling.  Make automatic adjustment in the shop schedule when there are changes in demand and job progress.  Reduce dependence on expeditors since a properly designed critical ratio system, coupled with necessary progress reporting, identifies critical jobs.  Compare both stock and made to order jobs on a common basis.  Prevent crises in scheduling of production  Exercise control by exception. Critical ratio scheduling, when applied to activities of production control department helps in establishing and maintaining priorities among the jobs and when applied to purchase follow up on pending orders. The technique helps to identify components/parts/ materials which require expediting of their pending quantities from their suppliers.

The technique utilizes the concept of ratios called critical ratios which provide a time relationship between a product / part /material is required and when it can be made available / supplied.

(b) Write few typical critical ratios and explain what they signify? Ans: 1) A total of 20 work orders completed over last one quarter were analyzed and following data on ineffective timer per operation (days) was obtained: 2.0 0.8 3.2 4.9

2.5 1.20 5.80 2.06

6.0 3.5 3.4 1.6

3.0 2.7 4.9 0.6

2.8 1.8 2.3 0.9

Calculate (i) (ii)

The average time per operation the component stayed on the shop floor due to waiting queuing, hunting, job splitting, change in priorities, power failure, machine break down etc. What total lead time should be considered for component with the following details?

Batch quantity = Total set up time = Total processing time = No. of operations = Average labour efficiency = against performance standards

300 no.s 12 hrs 18 min 5 80 %

N.B: The Company works two shifts per day, each shift of 8 hrs duration. Sol: (a) Expected ineffective time per operation is EIT

=

N ∑ 1

Xi,

P(Xi)

The computational process is given in the table below:

Probability P(Xi) that ineffective time per operation shall be Xi

Xi .P (Xi)

0.15

0.15

0.075

4

0.20

0.20

0.300

2.5

////// 7

0.35

0.35

0.875

3–4

3.5

//

2

0.10

0.10

0.350

4–5

4.5

//

2

0.10

0.10

0.450

5-6

5.5

//

2

0.10

0.10

0.550

Range of ineffective time per operation (days)

Mid value

Frequency Tally Total

Xi

Marks

Upto 1

.5

///

3

1–2

1.5

////

2–3

Relative frequency

20

Total: 2.600

Therefore, expected value of ineffective time per operation = 2.60 days

(b) Total Lead time is given by the formula N TLT

=

P

+

∑ 1

N (W + T)

+

∑ 1

S+QR HXE

Where, P W

T

=

= Order preparation time = 7 days (assumed) Expected value of ineffective time per operation x No. of

Operations = = = =

2.60 x 5 13 days Transit time between operations x No. of operations 0 (Transit time assumed to be insufficient)

And N ∑ 1

S+QR HXE

=

12 +

18 / 60 X 16 X 0.80

=

7.97 days

+

7.97

300

Therefore, TKT

=

7

+

13

=

28 days.

2) National Engineering Company utilizes critical-ratio-scheduling technique for the purpose of scheduling and expediting. The status of few made-tostock items is given in the table below.

S.No

Stock-on hand

Safety stock

Average daily consumption

Average lead time remaining (to complete remaining operations) (days)

1 2 3 4

1320 480 520 785

840 120 80 235

60 30 40 50

4 15 10 30

Calculate critical ratio for each of the items and decide on the action to be taken. Sol: Critical Ratio =

Lead time available (LTA) Lead time required (LTR)

For made to stock items LTA

=

LTR

=

(Stock on hand) – (Safety stock) Average daily consumption Lead time required to the complete remaining operations

=

This has been given in the problem

Critical ratios for above items have been calculated in the table below:

S.No

Lead time available (LTA

Lead Time required

Critical ratio

1

1320 - 840 / 60

= 8

4

8 / 4 = 2.00

2

480 - 120 / 30

= 12

15

12 / 15 = 0.80

3

520 - 80 / 40

= 11

10

11 / 10 = 1.10

4

785 - 235 / 50

= 11

30

11 / 30 = 0.37

From the above critical ratios, we can conclude that progress of item (i) (ii) (iii) (iv)

At serial 1 is more than satisfactory. The item is likely to get completed on time and not much of attention is required to be paid to it. At serial 2 is unsatisfactory. The item has become critical either because its consumption has risen above its average or the job has been delayed. In any case, its progress must be accelerated to avoid potential stock out. At serial 3 is just satisfactory. The item needs to be closely monitored At serial 4 is extremely critical. Every possible avenue should be explored to expedite the remaining operations.

12 (a) What are make or buy decisions? What costs are considered while finding the cost to make and cost to buy? Ans: Introduction: Make or buy decisions generally concern items required to the company’s own design. No firm can manufacture each and every item of its product. It is neither possible nor desirable. Items which do not form the company’s product line are always purchased from outside. An automobile firm for example requires to purchase raw materials, forgings, castings, tyres, tubes, bulbs, wires, bearings, automotive wheels, etc, from others. Similarly, an engineering firm needs to buy grinding wheels, oils and greases; tools etc., since the manufacture of these items require totally a different manufacturing process. Items which require specialized technical knowledge or procurement of special equipment are generally sub-contracted. A small firm for example normally gets its items heat-treated, surface coated (zinc plating, or galvanizing, or phosphating) from outside to get benefit of low price. The exclusion of the above categories of items leaves the firm with items which require to be manufactured to its design either at the home plant or to be purchased from outside

suppliers. The decision whether to make the item at the home plant or buy it from outside vendors is referred to as “make-or-buy” decision. Costs to be considered while making a make or buy decision: Cost analysis refers to the determination of cost to make the item and cost to buy it. A complete and correct assessment of the various elements of the cost is essential to make sound economic decisions. The following data needs to be collected and analysed. Particulars Raw materials Landed cost of the item being cub-contracted Weight of raw materials/ Casting/forgings Weight of finished component Present utilization of company’s facilities Methods of manufacture (Route sheet) Set up times and operational times Machine hour cost and labour hour cost

Departments originating the information Purchase Purchase or sub-contracting Purchase/Production Planning & Control Production Planning & Control Production Planning & Control Production Planning & Control Industrial Engineering Costing/Industrial Engineering / Sales/Finance

The analysis is based on annual requirements of components against the following elements: (a) Raw Material: The raw material cost consists of cost of raw materials less value recovered during to the sale of scrap like turnings, borings, end pieces etc. The raw material cost is considered towards the cost to make. However, if the raw material is supplied to the vendor free of cost, the cost of such materials also required to be considered towards cost to purchase. (b) Labour cost: Labour cost implies the wages and costs of other benefits (Provident fund, E.S.I., bonus, gratuity etc.) payable to the workmen engaged on the job. This cost however, requires to be considered only when additional labour force needs to be employed while production capacity is available. (c) Tooling cost: Jigs and fixtures generally require to be made if the item is to be machined at the home plant. The jigs and fixtures once made maintain their accuracy only for certain quantity, say “n” pieces, after which again a new set of jigs and fixtures require to be made. The cost of tooling thus requires to be amortized over “n” pieces and the annual cost of such tooling requires to be added to “cost to make”. At times, when an item is purchased from outside vendors, certain special cutting tools (broaches, hobs, shaping cutters etc.) and jigs and fixtures require to be

supplied to the vendor free of cost. The cost of such tooling, therefore, requires to be considered separately as tooling cost towards “cost-to-buy” (d) Overhead cost: the bulk of cost associated with a make or buy decision is the cost of production capacity. This is the area where most often mistakes are made. These costly errors can be avoided by keeping a single fact in mind that the costs which influence make or buy decisions are just the incremental costs the costs which will be incurred if the part currently made is purchased or vice versa. (e) Recoupment cost: Recoupment cost implies the setup costs (if the item is to be manufactured at the home plant) or the procurement cost (if the item is to be purchased). Set-up cost is the “preparation cost” of the machines and it varies depending upon the number of production runs in a year. The procurement cost is the cost of raising a purchase order and processing the deliveries from the vendor(s) and it varies depending upon the frequency of receipts of the item from the vendor(s). (f) Outside operations cost: The item manufactured at the home plant may require sub-contracting of certain operations such as rough blanking, heat treatment, plating etc. The cost of such operations requires to be considered separately towards “cost to make” (g) Purchase cost: Purchase cost includes the price given to the vendor, packing and forwarding, excise, sales tax, transport cost, control etc. (h) Capacity cost: Capacity cost implies the cost of capacity rendered idle if the item currently being manufactured is purchased. Such a cost requires to be added to “cost to buy”. 1.

“Production Planning and Control department is called the nerve center of a production unit” Discuss.

Ans: Introduction: Good production planning and control system is a must for a firm to enable it to make reliable promises and then to stick to them. It is also essential to devise methods which will ensure selection of right equipment, right tooling and enable the shop to make the job in the simplest but in the fool proof way. The following costs can be controlled / avoided through better production, planning and control, which make it the nerve center of a production unit. (a)Waiting time: “Time waste is the easiest of all wastes and yet the hardest to correct because it does not litter the floor” remarked Henry Ford once. This statement is as true as death. Excessive waiting time is really a big hazard – a big expense. A closer look around the department can enable us to spot some of these time leaks. We will find some of our workmen waiting at that tool crib. Some may be waiting for raw materials. Other may be waiting for the tools to be sharpened. Yet there may be

some waiting for prints and instructions for the next job. These little time leaks, if considered in isolation, do no mean much but too many of these can certainly add to a large amount, may be larger than few big ones. To reduce waiting time, each supervisor must know as to when the job in hand must be completed and when next job should get started so that necessary tools. Gauges, prints, materials, etc. for the next job can be kept ready. (b) Hunting Time: “An Operative in an engineering concern spends more than 2% of his time in wandering or looking for the things he needs to do the jobs” we will find them sharing their tools with other operators. Lot of operative’s time is wasted in searching for straps, clamps, bolts, nuts and washers.” We can reduce this ineffective time by fixing right place for everything and providing our men a set of everything they need well in advance of starting of the job. Good production planning and control can convert some of these time leaks into useful production hours. (c) Stalling: “Workers usually try to coincide the end of their jobs with the end of the day by stretching the jobs in hand”. A worker usually tends to delay the completion of job so that he does not need to start a fresh job towards the end of the day. “why start now, I wont be able to finish it in my shift” is the commonest attitude among our workmen. We can somewhat avoid this by setting the system where by each workman knows when he is expected to complete the job-in-hand and what is his next work assignment. Scientific scheduling can do this! (d) Interrupted workloads: “Unplanned over lapping of operations lead to idle machines and job split-ups”. Interrupted work from the previous operation not only results in partial utilization of the next machine but also seriously undermine morale of the shop. Careful production planning can prevent such unnecessary losses of time. (e) Costly overtime: “Poor planning is the common cause of overtime.” Prolonged overtime is not merely the extra strain on the finance of the company but means much more. Excessive overtime and hence extra time earnings make the workers accustomed to a new standard of living and any action on the part of the management to reduce or discontinue overtime is disliked by the workers. It is just not palatable to them. The mere knowledge that the company intends to do away with the overtime make the workers slow down their pace and thus the company is forced to overtime working. It then becomes a vicious circle and once caught in it the company cannot come out of it. The result is of anybody’s guess. The workers go on getting overtime day after day and month after month and thus worsening the already worsened situation. The overall effect is thus the lowering of efficiency – firstly because of accumulation of fatigue and secondly because of slackering of pace to get overtime. The need for overtime arises due to:  Unrealistic delivery dates without there being any leeway for unforeseeable.  Acceptance of too many rush orders.  Frequent delays in receipt of materials  Excessive machine breakdowns

 Lack of qualified workers  Insufficient manpower or machines. The majority of the causes cited above can be avoided by proper planning (f) Unproductive time of the machines: “Productivity of factors of production to a large extent depends on the quality of supervision”. The prime responsibility of the supervisory staff is to ensure that the company’s machines work for maximum time and the loss of time due to different reasons is kept at minimum. The production time of the machines is lost due to weaknesses in one or more of the following supervisory functions:  Operators’ unauthorized absenteeism and the failure of the supervisor to make substitute arrangement  Enforced idle time of the machine for want of smooth movement of materials on the shop floor  Lack of effective supervision which cause idle time of the machines since operators merely shop around, visit unnecessarily places of personal needs, steal longer tea breaks, resume work 5-10 min late in the beginning of the shift and after lunch break and close work 10-15 min prior to lunch break and the end of the shift.  Idle time of the machines due to delayed action by the supervisor to trace defects to the source and stoppage of the machines by the workmen until then.  Wastage in factors of production enumerated above occurs not only because of poor quality of supervision but also when the supervisory staff gets burdened with routine functions namely materials planning, tools planning, movement of materials on the shop floor, machine loading, expediting etc. PPC relieves supervisory staff from clerical functions and thereby enable them to spend more time for training of workmen, proper allocation of work to workmen, trouble shooting and maintaining shop discipline. (g) Higher overhead costs: Since production planning anc control relieves supervisory staff from a number of clerical responsibilities, they get more time for training of workmen, troubleshooting, maintaining shop discipline and improvising methods of work. At the same time they can handle more workmen and more machines, which reduce supervisory overheads. (h) Poor labour efficiency: “Workmen who get accustomed to working intermittently never work continuously”. This is no exaggeration. It is a fact based on human physiology and it holds good not only for workmen but also for supervisory personnel. Many a times in large companies, jobs get delayed due to irregular deliveries of materials, interruptions from the supervisors, improper loading and scheduling, lack of sufficient volume of work etc. and as a result workmen are either rendered idle or are utilized for part of the time. And if such delays are frequent, workmen get accustomed to partial working and thus the efficiency of the shop floor suffer a set back. They even do not work continuously when sufficient work is available.

PPC can prevent such a situation by exercising better control on availability of tools and materials monitoring a close control on work-in-progress on the shop floor, reallocating jobs from other machines by shifting idle operators to other machines, changing the route, ensuring smooth movement of materials from and into the different shops, and reporting cases of idle time of men and machines to enable the scheduler to release new jobs. (i) Investment in inventories: Good production planning and control can help the firm to ensure continuity in production with minimum inventory investment. Stock outs and higher inventory investment result if the requirements of materials are not indented on time and also if materials on receipt are not allowed properly to the work orders as per job priorities. Shop personnel can neither do forward planning of materials nor can they keep track of receipts and issues of materials. Only a centralized agency such as PPC can co-ordinate the activities of shops, stores department and the buying department. Timely deliveries

Quick feedback on job status

Lower capital investment

Better availability

Better co-ordination between production, sales & stores.

PRODUCTION PLANNING & CONTROL

Effective supervision

Better job satisfaction

Cost reduction & cost control

Effective utilization of factors of production

Good return on investment

Fig: Effect of production planning and control on the firm’s operations (j) Lowered morale: A department plagues by rush orders, broken deliveries, uneven work loads, frequent revisions in process, costly overtime, excessive machine breakdowns and the like can hardly be expected to have good morale. An integrated approach to production, planning and control can go a long way to eliminate or atleast minimize the occurrences of the above mentioned losses. Certainly production, planning and control is the nerve center of a production unit.