Cost reduction through value engineering case study on tap switch control assembly

This section summarizes the VE study carried out on tap switch control Assembly used on distribution transformers, as illustrated in fig. The objectives of study were to bring down cost, simplify design and find an alternative to high cost material, without detriment to quality and reliability.

1. The problemTransformer is one of the major products manufactured in a wide range, in national and international markets. In order to improve market and continue to have profit in the high inflation word, VE study was carried out on “tap switch control assembly”, used on distribution and power transformers. The main function of this unit is to facilitate the adjustment of turn ratio of primary to secondary windings of the transformer. Fig 1 shows the present design of the tap switch control assembly.

2. The objective The objectives of this study were to bring down cost, simplify design, and to find alternatives to high cost material, without detriment to quality and reliability.

3. The teamAs value engineering is inherently a team task, a group was formed consisting of personnel from all disciplines, such as design, manufacturing, quality assurance, marketing and value engineering to achieve the set goal. Team members were given training to enable them to use value-engineering techniques more effectively and meticulously during the study.

4. The methodology The value engineering study was carried out in a systematic and organized way, as per VE job plan, consisting of information phase, functional analysis phase, functional-cost-worth analysis, creative phase, evaluation phase, recommendations and implementation. These are now discussed.

a. Information phase In this phase, team members collected all the relevant information about the items under study. The study of drawings, material specifications, designs, and processes cost, procurement and

Fig 1. Transformer tap control switch – before value analysis

quality problems, as also in-house and field complaints were made in detail. The tap switch control assembly is a subassembly used in all distribution and power transformers. It is often required to change the turn ratio of primary to secondary windings of transformers, to adjustb. Functional analysis phaseThe results of a value engineering exercise, generating good alternatives for achieving the desired functions at optimum cost, mostly depends on how well the functional analysis done. The functional requirement of the tap switch assembly as a whole is analyzed and recorded as below:

Verb Noun Basic/Secondary Facilitates Tap change Basic Transmits Rotation BasicPrevents Leakage BasicIndicates Position SecondaryFacilitates Locking SecondaryPrevents Rusting Secondary

Further, the details of the functions of each component in the assembly were analyzed and listed (annexure B).c. Function-cost-worth analysisIn this phase, the team found the worth of each item of the subassembly. After identifying the desired functions of each item, the team established the worth of each item, depending on its essential function. While establishing the worth, the definition of value, i.e., the lowest price one has to pay to reliably accomplish a given function, was used as the basis.

The estimated worth was also based on other on other factors such as: State of art The accuracy of the available information Thoroughness of the functional analysis of the item An uncommon amount of commonsense The experience and subject knowledge of team membersCritically examining the present design, the following points can be made:1. The basic function of oil-tight gland (switch boss assembly) is to prevent oil leakage and

provide support to the spindle (shaft).2. Item 12, “switch boss”, is welded to the transformer tank. It is bigger in size, because it

has to accommodate brass plug which has lesser worth (see fig.).3. Item 13, “plug” is made out of brass. Its function is to position the oil seal. The cost of

the brass plug is about 40 % of the total cost of the subassembly. When compared to its basic function, the worth of the plug is much less.

4. The stopper provided on anodized aluminum plate is made out of brass material to resist corrosion.

5. Spindle is machined in order to get smooth surface where the oil seal comes into contact with it.

With the above information the team members analyzed function cost worth of each item of the subassembly and arrived at the value gap in each item, as given in annexure C.

d. Creative phase The poor value (hidden cost) areas, identified earlier, were subjected to brainstorming, to find out alternative ways of accomplishing the functions. Criticisms and evaluation are avoided in the brain storming session, to prevent the premature death of potentially good ideas. Even wild ideas were noted down in line with basic VF principles.

During the brain storming session, a large number of ideas were generated for each item to perform the same function. Help was taken from experts who were involved in similar design and process. Vendors were contacted to contribute alternative ideas. In all, 35 ideas were generated for items of the subassembly; these are listed in annexure D.e. Evaluation phaseThe alternative ideas suggested during the creative phase were refined and analyzed with a view to ascertain, whether they could achieve the desired functions. This was carried out in two stages: In the first stage, all suggestions were studied and those, which could not be adopted because of quality, reliability or other basic reasons, were eliminated, and the others were shortlisted.In the second stage, the ideas shortlisted after first evaluation were critically studied and discussed with the concerned personnel, for feasibility and practicability of production. Thus, the ideas were further shortlisted after first evaluation were critically studied and discussed with the concerned personnel, for feasibility and practicability of production. Thus, the ideas were further shortlisted and assigned for feasibility ranking matrix.

For judging the ideas, the following designs were considered:A functionB costC maintainabilityD quality and reliabilityE space

Each of these design criteria was given a weightage factor. This was carried out as follows: each of the above criteria was compared with others, and depending on their relative importance, three categories were formed, viz. major, medium, and minor. A score of 3,2and 1 respectively was assigned to each of the levels. The details are as follows:

Weight age analysis PointsMajor difference 3Medium difference 2Minor differences 1

Paired comparisonB C D E SCORE

A B2 A2 A1 A3 6B B2 B1 B3 8

C D2 C2 2D D3 5

E 1

Example:Note that the function A and quality D are closely connected with the weightage factor 3.Weightage for each criterion

A: function 6

B: cost 8 C: maintainability 2 D: quality and reliability 5 E: space 1

The following short listed ideas for the brass for the brass plug were taken for evaluation:a. M.S. cover plate instead of plug to hold oil sealb. Nylon plugc. Internal circlip to hold oil seald. Handle itself as coverplate for oil seal

Feasibility ranking

A B C D E Score Rank Design ideas

6 8 2 5 1

A 1/6 2/16 1/2 1/5 3/3 32 IVB 3/18 2/16 2/4 2/10 1/1 49 IIC 1/6 2/16 2/4 1/5 2/2 33 IIID 2/12 3/24 3/6 2/10 3/3 55 INote: 2/16 means score of 16 is achieved as 2 x 8 in row of a column of B. Similarly, the shortlisted ideas for other components were also evaluated.

f. Recommendations based on the feasibility ranking of ideas, team members made the following recommendations:

eliminate brass plug, and its function has to be obtained by redesigning the handle suitably.

Standard bright bars of shorter length to be used without machining O.D. for spindle. Switch boss has to be redesigned to lesser width. Stopper to be redesigned with internal thread and to be made out of aluminium rod.

Fig.2 Transformer tap control switch – after value analysis

g. ImplementationFig 2 shows the proposed design of the tap switch control assembly.

One prototype was built, as per VE team recommendation and tested for its performance and reliability. Based on the test results, thorough discussions were held with the concerned department, i.e., production shop, design office, quality assurance and sales and servicing, and their comments were obtained. Five more assemblies were made as per the proposed design and sent for field trails. After successful field trials and ensuring that quality and reliability were unaffected, the proposed designs were introduced in regular production.

Benefits of value engineering

1. Cost benefits a. Cost of subassembly before value engineering Rs 165.00 b. Cost assembly after value engineering Rs 85.00 (ref. Annexure E for cost benefit on each item) ____________ c. Savings per subassembly Rs 80.00 d. Expected annual savings Rs. 96,000.00

2.Other benefitsa. simplified designb. reduction in assembly timec. reduction of components and less inventory

Annexure A: Bill of materialComponent No. per

assemblyBought or made

material Cost per piece

Cost per assembly

Handle 1 B.O Aluminium casting

20.00 20.00

Spindle 1 B.O Steel bright bar 12.00 12.00Brass plug 1 B.O Brass (Hex) 67.00 67.00Switch boss 1 B.O Mild steel 26.00 26.00Dial plate 1 B.O Aluminium

plate16.25 16.25

Switch stopper 2 B.O Brass 4.00 8.00Oil seal 1 B.O Rubber 12.00 12.00Hardware - B.O Steel 3.75Total 165.00

Annexure B : function analysisComponent Basic function-

verb Basic function- noun

Secondary function-verb

Secondary function-noun

Handle Changes Provides Transmits

Position Grip Rotation

Prevents Locates

Rust Handle

Spindle TransmitsConnects

RotationMechanical

Prevents Locates

Rust Handle

Plug Positions Oil seal Provides Prevents Guides

Support Rust Spindle

Switch boss Guides Spindle Connects Mechanical

Holes Oil seal Prevents Holds

Leakage Dial plate

Dial plate Indicates Position Facilitate Holds Prevents

Locking Stopper Rust

Switch stopper Restricts Over travel Prevents Rust Oil seal Prevents Leakage Reduces Friction Hardware Connects

Withstands PartsOperative forces

Prevents Rust

Annexure C : function-cost-worth analysisComponent Present

cost Functions

-verb

Functions-Noun

Functions-BS

Worth(Rs)

Value gap

Handle 20.00 Transmits ChangesProvides

Rotation Position Grip

BB

15.00 5

Spindle 12.00 Transmits Locates

RotationHandle

BS

8.00 4

Brass plug 67.00 Holds Prevents

Oil sealRust

BS

6.00 61

Switch boss 26.00 Holds Seats

Spindle Oil seal

BB

16.00 10

Dial plate 16.25 Indicates Holds Facilitates

Position Stopper Locking

BS

15.00 1.25

Switch stopper 8.00 Restricts Over travel B 2.00 6Oil seal 12.00 Prevents Leakage B 12.00 0Hardware 3.75 Connects

Prevents Parts Rust

BS

3.75 0

Annexure D : Through brainstormingItem Ideas generated Handle 1. Cast iron handle

2. Extended boss in handle for positioning the oil seal3. M. S. fabricated handle, with plating4. Spindle and handle one piece made of aluminium or cast

iron5. Spindle and handle one piece made of DMC or polymer

Spindle 1. Standard bright bar for spindle2. Short length spindle3. Made out of DMC4. Aluminium rod

5. Polymer rod6. Bakelite rod

Brass plug 1. M.S. coverplate instead of plug to hold oil seal2. M.S. plug with plating3. Plastic plug4. Nylon plug5. Internal circlip to hold oil seal6. Die cast aluminium7. Hard rubber plug8. Spring loaded pressure plate9. Handle itself as coverplate for oil seal10. Threaded wooden plug11. Eliminate brass plug from the assembly12. Dial plate itself as coverplate

Switch boss 1. Lesser boss width2. Cast iron switch boss3. Put switch outside the oil

Dial plate 1. Fibre reinforced plastic or plastic painted plate2. Sticker on tank wall instead of displate3. Bakelite plate with engraving

Switch stopper 1. Mold steel plated stopper2. Internal threaded stopper3. Internal threaded aluminium stopper4. Small dia. Stopper5. Steel screws instead of special stopper6. DMC with metal inserts

Annexure E : Benefits Of Value Engineering

Tap switch control assemblyItems Before VE – Rs. After VE – Rs.Handle 20.00 22.00Spindle 12.00 8.00Brass plug 67.00 -Switch boss 26.00 16.00Dial plate 16.25 16.25Switch stopper 8.00 2.00Oil seal 12.00 12.00Hardware 3.75 3.75Total 165.00 80.00