BOARD EXAMINATIONS – OCTOBER 2019 ANSWER KEY

COURSE : MECHANICAL ENGINEERING MAXIMUM MARKS : 75 SEMESTER : V SEM QUESTION PAPER CODE : 678 SUBJECT : PROCESS PLANNING AND COST ESTIMATION

Part-A

1. What is line balancing? Line balancing is a process of assigning tasks to work stations in such a way that the workstations have

approximately equal time requirements.

2. Define machine capacity and illustrate the types of capacity. Machine capacity may be defined as the time available for work at a machine, expressed in machine

hours. If overtime is worked, these extra hours per week should be added to the machine capacity to find the

planned machine capacity.

Types : Capacity Management. Capacity Strategy. Capacity Utilization.

3. State the applications of micro motion study. Micro motion study is one of the most accurate techniques of work analysis used for work improvement.

4. What is work measurement? Work measurement is concerned with the determination of the amount of time required to perform a

unit of work. Work measurement is very important for promoting productivity of an organization.

5. Define i) set up time ii) economic lot size.

I)Definition of setup time:

Period required to prepare a device, machine, process, or system for it to be ready to function or accept a

job.

II)Economic lot size:

Quantity at which ordering and inventory carrying costs are minimized for a group of inventory items.

6. Define tool approach and tool over travel. Tool approach:

Tool approach is the distance a tool is fed from the time it touches the work piece until it is cutting to the full depth. Tool over travel

Over travel is the distance the tool is fed while it is not cutting. it is the distance over which the tool idles before it enters and after it leaves the cut.

7. What are the factors for the selection of cutting speed? • Material of the cutting tool. • Rate of feed and depth of cut. • Tool geometry. • Size of the tool flank.

• Cutting fluid used. (ANY 2) 8. How will you select jigs and fixtures for the process?

• Production of jigs and fixtures with minimum number of parts; • Set up time reduction; • Reduction of lead time • Easy disposal of chips; • Enhanced flexibility. (ANY 2)

PART –B

9. Briefly explain the concept of process planning

Process planning is a systematic determination of the methods by which a product is to be manufactured

economically and competitively. The engineering drawing of the component is interrupted in terms of the

manufacturing process to be used. This step is referred to as process planning and it is concerned with the

preparation of a route sheet. The route sheet is a listing of the sequence of operations which must be performed

on the component. It is called a route sheet because it also lists the machines through which the part must be

routed in order to accomplish the sequence of operations.

Concept of Process planning determines: • The operations involved in the manufacture of each product. • The machines on which operations are to be done. • The tools, jigs and fixtures required. • The material requirements including scrap. • The speed and feed to be used. • Type of labour required. • Time required for each operation.

10. Briefly explain the manual process planning.

In traditional process planning systems the process plan is prepared manually. The task involves

examining and interpreting engineering drawings, making decisions on machining process selection, equipment

selection, operation sequence and shop practices. Therefore, the manual process plan is very much dependent on

the skill judgement and experience of the process planner. That’s why if different planners were asked to develop

a process plan for the same part, they would probably come up with different plans. 11. Briefly explain about technological choice in process selection.

Selection of process based on technology is of two types namely:

• Major technological choice • Minor technological choice

• Major technological choice

To Identify the Major technological choice the following facilities are to be considered: • Does technology exist to make the product. • Are there competing technologies among which we should use. • Should the technology be developed in the country itself or to be licensed from foreign countries.

• Minor technological choice To Identify the Minor technological choice the following facilities are to be considered:

• Once the major technological changes are made, there may be a number of minor technological process alternatives available. The operations manager should be involved in evaluating alternatives for costs and for consistency with the desired product and capacity plans.

• Should the process be continuous which carried out for 24 hours a day in order to avoid expensive start ups and shutdowns as used by steel and chemical industries.

• An assembly line process on the other hand, follows the same series of steps as production but need not run for 24 hours a day.

• Job shop processes produce items in small lots, perhaps custom made for a given customer.

(ANY 3 POINTS EACH) 12. What are the objectives of method study?

• To improve the processes and procedures. • To improve the design of plant and equipment. • To improve the plant layout.

• To improve the use of men, materials and machine. • To standardize the methods. • To improve safety standards. • To achieve efficient material handling. (ANY 3)

13. What is SIMO Chart? What is its application? A SIMO Chart is a chart, often based on film analysis, used to record simultaneously on a common

time scale the therbligs or groups of therbligs performed by different parts of the body of one or more

workers. It is used to identify the micro level work performed in work area. 14. List the principal elements of metal machining and explain any one. Elements of metal machining:

• Cutting Speed • Feed • Depth of cut

Factors considered to select cutting speed: • Metal removal rate • Rigidity of machine and tool • Flow of cutting fluid • Condition of material • Continuity of cut

Factors considered to select feed : • Type of tool • Surface finish • Power available • Rigidity of machine • Strength of workpiece

Factors considered to select depth of cut : • Cutting speed • feed

15. Explain how cutting time for reaming(forming) is estimated Time for reaming = 𝑙𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑐𝑢𝑡

(𝑓𝑒𝑒𝑑/𝑟𝑒𝑣) × (𝑟.𝑝𝑚)

16. A cutter will cut for 5 hours before it needed resharpening. It takes 20minutes to change the tool. If the tool can be sharpened 12 minutes before it is discarded, determine the unit tool change time per cycle.

Tk = 5 Hours = 300min Tc = 20 min T = 12 x 5 = 60 hrs =3600 min t = Tc x Tk/T 20 x 300/ 3600 t = 1066 min

PART-C 17 a) Explain the automated process planning with the help of neat sketches. state its

advantages. Computer-aided process planning: Computer Aided Process Planning is a process, that is done by using the

computer. Computer-aided process planning (CAPP) is nothing but to produce a design that needed for

manufacturing like instruction, specifications etc.

This used to give a complete information to manufacture a product. To perform this operation it should be

well coordinate with CAD/CAM. this is an important technique used in the manufacturing industry.

This is widely used due to the quick response and more flexibility in manufacturing firms.

This used to set standard timings in operation and helps in improving process planning.

Types of CAPPsystems:

1. Retrieval type of CAPP system. 2. Generative CAPP system.

1. RETRIEVAL TYPE:

In Retrieval type, manufactured parts are used to divided into part families, this is done by manufacturing

characteristics. after this, we used to store the plane about to establish a standard process plan for each part

family. This plan can be retrieved at any time to use for the same family. after this, we need to give a code

number to it by this CAPP program used to find the required family matrix and compress it. in this modification

is done when there is a same code number in the file is founders and make it to the new design by retrieving

from operation sequence and standard machining routing. By using a process plan format, the paper document

is prepared.

2. GENERATIVE TYPE:

Generative process planning may be defined as a system that synthesis process information in order to

create a process plan for new component automatically. In generative approach, a process plan is created from

scratch for each part without human intervention. These systems contain the logic to use manufacturing

database and suitable part description schemes to generate process plan for particular part. In this generative

approach the computer is used to generate each individual process plan automatically and without reference to

any prior plan. Some of the generative systems used in practice are CPPP, AUTAP, APPAS, TIPPS, EXCAD, SIPP

and TOM.

OPERATION OF GENERATIVE CAPP SYSTEM

• The generative CAPP system uses a branch of artificial intelligence called expert system. • Expert system is a computer program that is capable of solving complex problem. • The problem solving procedure by using an expert system is termed as inference engine. • The technical knowledge of manufacturing and logic used by successful process planners are captured

and coded into programs, these programs are called knowledge base. • By using this knowledge base and inference engine, the CAPP system synthesis new process plan from

scratch for new part.

17. (B) Suguna industry is manufacturing 1,24,000 pump sets per year.one of the components of pump set

is purchased for 10 rupees from outside. Engineering department says that it can be manufactured

in the factory itself. The following data are available. Fixed cost if component produced Rs 80,000,

additional labour cost Rs 1,50,000. Overhead cost will increase by 20% which is now 7,00,000.

Increase in material cost Rs 7,00,000. Decide whether the industry will buy or make the component. How much will be gain or loss, if manufactured?

SOLUTION: Total cost of purchase = Rs 1,24,000x10

= Rs 1,240,000

Total cost of manufacture = fixed cost + variable cost

Fixed cost = 80,000

Variable cost = labour cost + material cost + overhead

= 1,50,000 + 7,00,000 + (0.2x7,00,000)

= 1,50,000 + 7,00,000 + 140,000

Variable cost = Rs 990,000

Total cost of manufacture = Rs 1,070,000 As the projected cost of manufacture is lesser than the cost of buying, it can be decided to make. 18. a) How will you determine the man, machine and material requirement of an industry to a particular

product?

a)Determination Man Power Requirement

In general one day means eight hour. If worker works for one hour, it is called as one man hour. In the

process selection, man hour plays an important role. Therefore it is necessary to calculate the man hour as

follows:

1. Number of man hours required for load on hand = H1 hours 2. Number of man hours required due to new load = H2 hours 3. Allowances for leave, absents, etc. = H3 hours 4. Total man hour required = H1 + H2+ H3 5. Available man hours = H4 hours 6. Additional man hours required = (H1+H2+H3)-H4

(Assume 8 hours x 5days x 5 weeks = 2000 man hour/year) 7. No of additional man hour required = ( H1+H2+H3)-H4/2000

b) Determination Machine Requirement

While determining the machine requirement, we have to consider the following: 1. Accuracy 2. Rate of output 3. Cost

The requirement of machinery is calculated as follows: Load on machines due to work on hand – h1 hours New load on machines based on process sheet - h2 hours Total load on machines = h1+h2 Time required for maintenance = h3 hours No. machine hour /year /machine = h hours No.of machines required (n1) = h1+h2+h3/h Available machine = n2 Additional machine required = n1-n2

DETERMINATION OF MATERIAL REQUIREMENT

The selection of materials depends upon the types of material shape and size. Material should be of write quality and chemical composition as per the products specifications, shape and size of material should reduce the scrap. While calculating the material requirement we have to consider the following: 1. Material required for work already on hand – q1

2. Material required for new work - q2

3. Total material requirement = q1+q2

4. Material available in stores –q3

5. Additional material to be purchased = (q1+q2)-q3

The selection of jig fixtures extra will give higher production rate, reduce the cost of production per piece and reduce production time.

18. b) SOLUTION

Total cost = F1+Q1 V1 = 500+(800X2)

a) Capstan lathe total cost = Rs 2100 Total

cost = F2+Q2 V2 = 1600+(800X0.5)

Automatic lathe total cost = Rs 2000 = 500+(700X2)

b) Capstan lathe total cost = Rs 1900 Total

cost = F2+Q2 V2

= 1600+(700X0.5) Automatic lathe total cost = Rs1950

We select capston lathe as the total cost is less F1+Q1 V1 = F2+Q2 V2

Break even point = 733 units.

19. a) State the principles of motion economy. briefly explain them.

A. Use of Human Body: 1. The two hands should begin and complete their motion at the same time. 2. Arm movements should be symmetrical, simultaneous and in opposite directions. 3. Hand and body motions should be confined to lowest classification to perform the work satisfactorily. 4. The two hands should not be idle at the same time (except during rest). 5. Momentum should assist the worker (otherwise reduce to minimum). 6. Smooth continuous and curved movements preferable over straight-line movement with sharp changes

in direction. 7. Ballistic movements are (easy fast and accurate) preferred over controlled movements. 8. Arrange work to provide natural rhythm where possible. 9. Eye fixations should be as few and as close together as possible.

B. Arrangement of Workplace:

1. Make definite and fixed place for all tools and materials. In other words there should be a place for

everything and everything at its place. 2. Locate tools materials and controls as close to the place, of use as possible. 3. Gravity feed the material to the point of use (though bins and containers). 4. Locate materials and pools to permit best sequence of operations. 5. Good illumination for satisfactory visual perception. 6. Use drop delivery where possible. 7. Arrange work place height to permit alternate sitting and standing at work. 8. Provide chair of suitable type and height to permit good posture.

C. Design of Tools and Equipment:

1. Relieve hands if the work can be economically done by jig, fixture or pedal. 2. Combine two or more tools where possible. 3. Pre-position tools/materials where possible. 4. When fingers are loaded divide work with according to the capabilities of the fingers. 5. Locate levers and handler to permit work with least change in body posture and greatest mechanical

advantage.

19. b) SOLUTION NORMAL TIME = OR/SRXOT

1) 0.99 2) 0.96 3)1.17 4)1.1 5) 1.1 6)0.63 7)0.96 8)0.91 9)0.9 10)0.88 Total normal time =

9.32 min Total allowance = 30%x total normal time (0.3x9.32) Total allowance = 2.796 min Standard time = normal time +allowances(9.32+2.796) Standard time 12.116 min

20 a) What are the different methods of apportioning the overheads?. Explain any two with ecamples.

Overheads are business costs that are related to the day-to-day running of the business. Unlike operating

expenses, overheads cannot be traced to a specific cost unit or business activity. Instead, they support the

overall revenue-generating activities of the business.

For example, a vehicle retail company pays a premium rent for business space in an area with adequate space to accommodate a showroom. The premium rent is one of the overhead costs of the business. A business must pay its overhead costs on an ongoing basis, regardless of whether its products are selling or not.

Types of Overheads There are three main types of overhead that businesses incur. The overhead expenses vary depending on the

nature of the business and the industry it operates in.

1. Fixed overheads Fixed overheads are costs that remain constant every month and do not change with changes in business

activity levels. Examples of fixed overheads include salaries, rent, property taxes, depreciation of assets, and government licenses.

2. Variable overheads Variable overheads are expenses that vary with business activity levels, and they can increase or

decrease with different levels of business activity. During high levels of business activity, the expenses will increase, but with reduced business activities, the overheads will substantially decline or even be eliminated.

Examples of variable overheads include shipping costs, office supplies, advertising and marketing costs, consultancy service charges, legal expenses, as well as maintenance and repair of equipment.

3. Semi-variable overheads Semi-variable overheads possess some of the characteristics of both fixed and variable costs. A

business may incur such costs at any time, even though the exact cost will fluctuate depending on the business activity level. A semi-variable overhead may come with a base rate that the company must pay at any activity level, plus a variable cost that is determined by the level of usage.

Examples of semi-variable overheads include sales commissions, vehicle usage, and some utilities such as power and water costs that have a fixed charge plus an additional cost based on the usage.

20. b) SOLUTION

Total sharpening time t = tkxtc/t Total sharpening time t =0.20 min/casting Checking time = 1.25 min/casting Total time = 39.55 min/casting

Time for 100 casting = 3955 min

Set up time = 225 min Total estimate time = 4180 min Total actual time = estimated time x performance factor (4180 x 1.4)/60 Total actual time = 97.53 hrs Total labour cost = total actual time x direct labour cost(Rs 10)

Total labour cost = Rs 975.33

21. a) SOLUTION N = 1000 x S/3.14X D time T = L/f x N mins Machining time = 1.04 min Mounting time =50 sec/60 =0.833 min Total time = Machining time (1.04 min) + Mounting time(0.833 min) Total time = 1.89 min

21. b) SOLUTION

N = 1000 x S/3.14X D TABLE FEED =feed/tooth x no.of teeth x rpm table feed = 212 mm/min table cutter travel =length of job +added table travel = 250+2√Dd-d2 table cutter travel = 301 mm machining time = total table travel/feed per min machining time = 1.14 min

Prepared By Mr. S Shanmuga Sundaram HoD I/C Automobile Engineering PSG Polytechnic College Coimbatore - 641 004