This document is a project report submitted by Ramani Hardik V. and Bhesdadiya Parag M. to their professor V.B. Patel at U.V. Patel College of Engineering. The report examines quality control issues related to chip impressions causing rejection of gears during manufacturing at Mahindra Gears & Transmission Pvt. Shaper.Rajkot. The document includes an introduction of the company, definitions of gear terminology, descriptions of gear manufacturing processes like hobbing, and analysis of rejection data through tables and Pareto charts to identify sources of chip impressions.

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A REPORT ON
“QUALITY CONTROL BY REDUCING REJECTION DUE TO CHIP INPRESSION”
Prepared By:
RAMANI HARDIK V. (08 ME 58)
BHESDADIYA PARAG M. (08 ME 03)
MECHANICAL ENGINEERING DEPARTMENT
U.V.PATEL COLLEGE OF ENGINEERING
GANPAT UNIVERSITY
GANPAT VIDYANAGAR
KHERVA.

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2012
A REPORT ON
“QUALITY CONTROL BY REDUCING REJECTION DUE TO CHIP INPRESSION”
A PROJECT REPORT SUBMITTED IN PARTIAL FULFILLMENT OF
THE REQUIREMENTS FOR THE DEGREE OF
BACHELOR OF TECHNOLOGY
(MECHANICAL ENGINEERING)
BY
RAMANI HARDIK V. (08 ME 58)
BHESDADIYA PARAG M. (08 ME 03)
UNDER THE GUIDANCE OF
PROF. V.B. PATEL
AT THE
MECHANICAL ENGINEERING DEPARTMENT
U.V.PATEL COLLEGE OF ENGINEERING,
GANPAT UNIVERSITY

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CERTIFICATE
This project work is the bonafide work done by following students of VIII semester of Mechanical Engineering Department of U. V. Patel College of Engineering, under the guidance of Prof.V.B.Patel towards the partial fulfillment of the requirements for the Degree of Bachelor of Technology (Mechanical Engineering) of Ganpat University, Ganpat Vidyanagar in the year 2012.
NAME : EXAM NO.
(1) RAMANI HARDIK V. 5059
(2)BHESDADIYA PARAG M. 5002
Guide : ______________________________
Internal Examiner: ____________________
External Examiner: ____________________
Head of Department: ___________________
(ME/MC Dept.)

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INDEX
INTRODUCTION OF COMPANY
INTRODUCTION TO GEAR

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INTRODUCTION OF THE COMPANY
 MAHINDRA GEARS&TRANSMISSION PVT. SHAPER.RAJKOT
 Company Established in 1987
 ISO/TS-16949:2002 Certification (2003) from TUV SUD Management service GmbH.
 Recertification in 2005.
 M&M acquired this company in Jan’05
 Capacity to produce more than 250,000 components a month, Module range from 1.5-8 &
Diameter 25-400 mm
 Conforming to German specification DIN 7 (soft) to DIN 8/9 (fully finished) class of accuracy.
SALES HISTORY
0
2
4
6
8
10
12
14
16
2002-03 2003-04 2004-05 2005-06 2006-07 2007-08 2008-09 2009-10
3.7
4.9
8.2
10.2
11.7
13.56
15.78 16

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INTRODUCTION TO GEAR
Gears are used extensively for transmission of power. They find application in: Automobiles, gear boxes, oil engines, machine tools, industrial machinery, agricultural machinery, geared motors etc. To meet the strenuous service conditions the gears should have: robust construction, reliable performance, high efficiency, economy and long life. Also, the gears should be fatigue free and free from high stresses to avoid their frequent failures. For fulfil the purpose, it is necessary to manufacturing gear in proper way.
PRODUCTS OF MAHINDRA GEARS

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Law of Gearing
The law of gearing states the conditions which must be fulfilled by the gear tooth profiles to maintain a constant angular velocity ratio between two gears. It states that the common normal at the point of contact of the two teeth should always pass through a common pitch point.

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Classification of Gears
Gears can be classified according to the relative positions of their shaft axes.
Parallel Shafts
Regardless of the manner of contact, uniform rotary motion between two parallel shafts is equivalent to the rolling of two cylinders, assuming no slipping. Depending upon the teeth of the equivalent cylinders i.e. straight or helical, following are the main types of gears to join parallel shafts.
a) Spur Gears
They have straight teeth parallel to the axes and thus are not subjected to axial thrust due to tooth load (Fig. 3.8.a). At the time of engagement of the two gears; the contact
extends across the centre width on a line parallel to the axes of rotation. This results in sudden application of the load, high impact stresses and excessive noise at high speeds.In an internal spur gear, the teeth are formed on the inner surface of an annulus ring. An internal gear can mesh with an external pinion (smaller gear) only and the two shafts rotate in the same direction.
b) Spur Rack and Pinion
Spur rack is a special case of a spur gear where it is made of infinite diameter so that the pitch surface is a plane (Fig. 3.9). The spur rack and pinion combination converts rotary motion into translatory motion, or vice-versa. It is used in a lathe in which the rack transmits motion to the saddle.

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Spur Rack and Pinion
c) Helical Gears or Helical Spur Gears
In helical gears, the teeth arc curved, each being helical in shape. Two mating gears have the same helix angle, but have teeth of opposite hands (fig 3.10) .At the beginning of engagement, contact occurs only at the point of leading edge of the curved teeth. As the gears rotate, the contact extends along diagonal line across the teeth. Thus the load application is gradual which results in low impact stresses and reduction in noise. Therefore, the helical gears can be used at higher velocities than the spur gears and have greater load-carrying capacity.
Helical Gears or Helical Spur Gears
Helical gears have the disadvantage of having end thrust, as there is a force component along the gear axis. The bearings and the assemblies mounting the helical gears must be able to withstand thrust loads.
d) Double-helical and Herringbone Gears

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A double-helical gear is equivalent to a pair of helical gears secured together, one having a right- hand helix and the other a left-hand helix. The teeth of the two rows are separated by a groove used for tool run out. Axial thrust, which occurs in case of single-helical gears, is eliminated in double- helical gears. This is because the axial thrusts of the two rows of teeth cancel each other out. These can be run at high speeds with less noise and vibrations. The left and the right inclinations of a double-helical gear meet at a common apex and there is no groove in between, the gear is known as herringbone gear.
Terminology of Gear Tooth
A gear tooth is formed by portions of a pair of opposed involutes. Most of the terms used in connection with gear teeth are explained in Fig.
Base Circle. It is the circle from which involute form is generated. Only the base circle on a gear is fixed and unalterable.
Pitch Circle. It is an imaginary circle most useful in calculations. It may be noted that an infinite number of pitch circles can be chosen, each associated with its own pressure angle.
Pitch Circle Diameter (P.C.D.). It is the diameter of a circle which by pure rolling action would produce the same motion as
the toothed gear wheel. This is the most important diameter in gears.
Module. It is defined as the length of the pitch circle diameter per tooth. Thus if P.C.D. of gear be D and number of teeth N, then
module (m)=D∕N . It is generally expressed in mm.

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Diametral Pitch. It is expressed as the number of teeth per inch of the P.C.D.
Circular Pitch (C.P.). It is the arc distance measured around the pitch circle from the flank of one tooth to a similar flank in the next tooth.
.’. C.P. = ΠD∕N=Πm
Addendum. This is the radial distance from the pitch circle to the tip of the tooth. Its value is equal to one module.
Clearance. This is the radial distance from the tip of a tooth to the bottom of a mating tooth space when the teeth are symmetrically engaged.
Dedendum. This is the radial distance from the pitch circle to the bottom of the tooth space.
Dedendum =Addendum + Clearance =m+0.157 m=l.157 m.
Blank Diameter. This is the diameter of the blank from which gear is a t. It is equal to P.C.D. plus twice the addenda.
Blank diameter =P.C.D.+2m. =mN+2m = m(N+2).
Tooth Thickness. This is the arc distance measured along the pitch circle from its intercept with one flank to its intercept with t le other flank of the same tooth.
Normally tooth thickness.=½ C.P.=Πm∕2
But thickness is usually reduced by certain amount to allow for some amount of backlash and also owing to addendum correction.
Face of Tooth. It is that part of the tooth surface which is above the pitch surface.
Flank of the Tooth. It is that part of the tooth surface which is lying below the pitch surface.

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Line of Action and Pressure Angle. The teeth of a pair of gears
in mesh, contact each other along the common tangent to their base circles as shown in Fig. This path is referred to as line of action. As this is the common generator to both the involutes, the load or pressure between the gears is transmitted along this line. The angle between the line of action and the common tangent to the pitch circles is therefore known as pressure angle ø.

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SPUR GEAR MANUFACTURING PROCESS
GEAR HOBBING PROCESS
 Hobbing is the process of generating gear teeth by means of a rotating cutter called a hob. It is a continues indexing process in which both the cutting tool & work piece rotate in a constant relationship while the hob is being fed into work.
 Each hob tooth cuts its own profile depending on the shape of cutter ,but the accumulation of these straight cuts produces a curved form of the gear teeth, thus the name generating process.
 For in route gears, the hob has essentially straight sides at a given pressure angle. The hob and the gear blank are connected by means of proper change gears. The ratio of hob& blank speed is such that during one revolution of the hob, the blank turns through as many teeth. The teeth of hob cut into the work piece in Successive order & each in a slightly different position. Each hob tooth cuts its own profile depending on the shape of cutter, but the accumulation on the shape of cutter, but the accumulation of these straight cuts produces a curved form of the gear teeth, thus the name generating process. One rotation of the work completes the cutting up to certain depth.

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HOB CUTTER
Fig. illustrated front & side view of the Hob cutter.
TYPE OF HOBBING :-
1) Axial hobbing :-
This type of feeding method is mainly used for cutting spur or helical gears. In this type, firstly the gear blank is brought towards the hob to get the desired tooth depth. The table side is them clamped after that, the hob moves along the face of the blank to complete the job. Axial hobbing which is used to cut spur & helical gears can be obtained by ‘climb noting’ or ‘conventional hobbing!
2) Radial hobbing :-
This method of hobbing is mainly used for cutting worm wheels. In this method the hob & gear blank are set with their ones normal to Each other. The gear blank continues to rotate at a set speed about its vertical axes and the rotating hob is given a feed in a radial direction. As soon as the required depth of tooth is cut, feed motion is stopped.
3) Tangential hobbing:-
This is another common method used for cutting worm wheel. In this method, the worm wheel blank is rotated in a vertical plane about a horizontal axes. The hob is also held its axis or the blank. Before

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starting the cut, the hob is set at full depth of die tooth and then it is rotated. The rotating hob is then fed forward axially. The front portion of the hob is tapered up to a certain length & gives
the fed in tangential to the blank face & hence the name ‘Tangential feeding’.
DEFINATION OF THE PROBLEM
WHAT IS CHIP IMPRESSION?
It is the impression of the chip on the spur gear during Hobbing & Deburing operations. Due to chip impression, damaging surface of the spur gear so, the customer reject such pieces. It effect on plant productivity.

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During the manufacturing of gears, in locator of the hobbing machine some chip are remains so that this chip causes impression on next gear.
The effect of this impression causes screeches on gear.
PARATO CHART
What is a Pareto Chart?
 The Pareto Chart is named after Vilfredo Pareto, a 19th century economist who postulated that a large share of wealth is owned by a small percentage of the population. This basic principle translates well into quality problems.
 A Pareto Chart is a series of bars whose heights reflect the frequency or impact of problems. The bars are arranged in descending order of height from left to right. This means the categories represented by the tall bars on the left are relatively more significant then those on the right. This bar chart is used to separate the “vital few” from the “trivial many”.
 These charts are based on the Pareto Principle which states that 80 percent of the problems come from 20 percent of the causes.
 Pareto charts are extremely useful because they can be used to identify those factors that have the greatest cumulative effect on the system, and thus screen out the less significant factors in an analysis. Ideally, this allows the user to focus attention on a few important factors in a process.
Why should a Pareto Chart be used?
 You can think of the benefits of using a Pareto Charts in economic terms. A Pareto Chart breaks a big problem down into smaller pieces, identifies the most significant factors, shows where to focus efforts, and allows better use of limited resources.
 You can separate the few major problems from the many possible problems so you can focus your improvement efforts, arrange data according to priority or importance, and determine which problems are most important using data, not perception.
 A Pareto Chart can answer the following questions:
What are the largest issues facing our team or business?
What 20% of sources are causing 80% of the problems?
Where should we focus our efforts to achieve the greatest improvements?

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When should a Pareto Chart be used?
 A Pareto Chart is a good tool to use when the process you are investigating produces data that are broken down into categories and you can count the number of times each category occurs. A Pareto diagram puts data in a hierarchical order, which allows the most significant problems to be corrected first. The Pareto analysis technique is used primarily to identify and evaluate nonconformities, although it can summarize all types of data. It is the perhaps the diagram most often used in management presentations.
 Making problem solving decisions isn’t the only use of the Pareto Principle. Since Pareto Charts convey information in a way that enables you to see clearly the choices that should be made, they can be used to set priorities for many practical applications. Some examples are:
 Process improvement efforts for increased unit readiness
 Skills you want your division to have
 Customer needs
 Suppliers
 Investment opportunities

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DATA ANALYSIS
TABLE-I
Sr No.
Part no.
Total part
Rejected part
1
320/03131
1397
447
2
2523-31
1270
203
3
5501541
1415
184
4
320/08030
1365
177
5
2154-32
1350
135
6
1936-30
1314
92
7
8882428
1360
39
8
751-10141
1250
25
9
750-10121
1916
19
10
5198545
950
19
11
751-13982
500
5
12
8875881
400
4
13
1503-31
400
4
14
320/06637
300
3
15
4302242
200
2
16
10008695AA
200
2
Table show the number of parts and the types of parts which are being investigated.There are several part which have large no. of rejection, but the part no. 320/03131 has maximum rejection. So for reducing the rejection of the whole lot, focuses should be on that part.

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TABLE-II
No.
Part No.
Percentage
Cumulative Percentage
1
320/03131
32%
32%
2
2523-31
16%
48%
3
5501541
13%
61%
4
320/08030
13%
74%
5
2154-32
10%
84%
6
1936-30
7%
91%
7
88824288
3%
94%
8
751-10141
2%
96%
9
750-10121
1%
97%
10
5198545
2%
99%
11
751-13982
0
99%
12
8875881
0
99%
13
1503-31
0
99%
14
320/06637
1%
100%
15
4302242
0
100%
16
10008695AA
0
100%
 Find the cumulative percentage.
Each category’s cumulative percentage is the percentage for that category added to the percentage of the category of the larger category before it.
Here, largest percentage is 32% .So, cumulative percentage for this part is 32%.
 For second part, we can find out cumulative percentage by adding cumulative percentage in to individual percentage.
For example,
For 3edpart it is,
Cumulative percentage is=highest cumulative percentage+ percentage of that part

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PARATO CHART
From the analysis of the parato chart, we can conclude that the maximum rejection from the inspected lot is due to part no.320/03131.
Principle of the parato chart give advice us to concentrate on such things that contain large share of the rejection. So, we have scope of improvement by reducing rejection of that part. Thus, parato chart give direction to our quality improvement task.
447
203
184
177
135
92
39
25
19
19
5
4
4
3
2
2
33
48
61
74
84
91
94
96
97
99
99
99
99
100
100
100
0
10
20
30
40
50
60
70
80
90
100
0
200
400
600
800
1000
1200

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PART NO.320/03131
PART SPECIFICATION
 Gear No. -MG001250GC
 Cast alloy –wrought iron
 Module of the Gear-(d/Z)=(1.9)
 Coating material-Alcrona
 Hardness-(.05hv)
 Maximum service temperature-1100 c
 Dryness fraction -.35

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CAUSE & EFFECT DIAGRAM
What is Cause & effect Diagram ?
 A cause and effect diagram is “a fish-bone diagram that presents a systematic representation of the relationship between the effect (result) and affecting factors (causes).”
 Solving a problem in a scientific manner requires clarification of a cause and effect relationship, where the effect (e.g., the result of work) varies according to factors (e.g., facilities and machines used, method of work, workers, and materials and parts used). To obtain a good work result, we must identify the effects of various factors and develop measures to improve the result accordingly.
When is it used and what results will be obtained?
 A cause and effect diagram is mainly used to study the cause of a certain matter. As mentioned above, the use of a cause and effect diagram allows clarification of causal relation for efficient problem solving. It is also effective in assessing measures developed and can be applied to other fields according to your needs.

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CAUSE & EFFECT DIAGARM-1
This diagram shows rejection in Deburing operation due to following causes.
First cause is that lack of inspection during Deburing process. Due to lack of inspection by the operator. So, operator should concentrate on cleaning of teeth after each cycle.
Second cause is that temperature increase during Deburing operation. So, the material become soft chip removed from the blank is directly impressed on the same blank during gear cutting.
Third cause is that improper locator when blank is mounted on the locator; contact area, between more so whatever chip is removed from the blank, that chips are not properly removed so there is chances of chip impression on the gear blank. For the remedies change in design of the locator is necessary. It has less contact with the gear blank and hence change in design of the locator. In the new locator bearing are is lesser so that chip impression probability is less.
Forth cause is that burst remain on the surface of the of the material due to high speed of the rotation of the gear. Rotary speed of the gear tooth is high so bursts are not properly removed from the gear teet. Thus the speed of the rotation of gear should optimum.

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CAUSE & EFFECT DIAGARM-2
 This diagram shows causes of chip impression during VMC operation .First cause is that lack of hydraulic clamping in VMC operation. If clamping is mechanically so its handling done by manually. There is chances of loose clamping is more so metal remove from blank is not perfectly. Chip is not perfect there is scratching on the gear blank due to this reason.
 Second cause is that improper locator when blank is mounted on the locator; contact area, between more so whatever chip is removed from the blank, that chips are not properly removed so there is chances of chip impression on the gear blank. For the remedies change in design of the locator is necessary. It has less contact with the gear blank and hence change in design of the locator. In the new locator bearing are is lesser so that chip impression probability is less.
 Third cause is manual error in programming. It means that when program for the gear cutting on blank is prepared by programmer there is chance of manual error in program. That causes part comes in rejection due to incorrect input data. So that reference, taken automatically, is according to program and that is not desirable. So there is chance of chip impression due to value of feed, depth of cut and improper co-ordinate.
 Forth cause is that the speed of the spindle. Speed of the spindle appropriate for each part and its specification. That vary accordingly types of material. For hard material gear speed is high and vice versa.

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CAUSE & EFFECT DIAGARM-3
 This diagram shows sub causes of the rejection due to chip impression during hobbing operation. First cause is that temperature increase during hobbing operation. So, the material become soft chip removed from the blank is directly impressed on the same blank during gear cutting.
 Second cause is that improper locator when blank is mounted on the locator; contact area, between more so whatever chip is removed from the blank, that chips are not properly removed so there is chances of chip impression on the gear blank. For the remedies change in design of the locator is necessary. It has less contact with the gear blank and hence change in design of the locator .In the new locator bearing are is lesser so that chip impression probability is less.
 Third cause is insufficient dwell period in which operator have less time changes between sub sequent parts. So operator can’t clean the locator properly. Therefore somewhat portion of the chips remain on the locator due to this reason chip impress on the next gear blank.
 Fourth cause is unskilled labor. Operator is not trained so, he has not practice for the gear cutting operation. There is not proper attention in gear cutting process. So, by him mistake chip impression on the gear blank.
 Fifth cause is extreme pressure of the cutting tool on the gear blank. When pressure is more on the gear blank at that time temperature is high so impression of tip of the tool on the gear blank. Sixth cause is long cutting tool contact means the speed of the hob cutter should optimum. So, temperature is maintained due to this reason impression on the gear blank.

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CAUSES WISE REJECTION
1
Chips impression on face during hobbing operation due to operator indiscipline- approx.36%
2
Chip impression during deburring operation due to improper deburing fixture-approx.27.5%
3
Heavy chip impression during VMC operation due to improper chips cleaning after every cycle.- approx-16%
4
Heavy chips impression during VMC due to improper fixture-approx.-20%

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ACTIONS IMPLEMENTED
BEFORE
MAXIMUM CONTACT AREA
As shown in fig., during hobbing operation the gear blank is held on this locator. The contact area is very large. Due to pressure applied on the gear blank by clamping, the bearing stress is applied on the blank. Also at high temperature, due to chip melting, there is possibility of adhere chips on the gear blank. This causes face of the gear dull.

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AFTER
MINIMUM CONTACT AREA
As shown in fig., gear in new locator the contact area between gear blank and locator is reduced. So that possibility of adhering chip with the gear is less and problem of chip impression on gear is reduced at somewhat level.

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Display Notification

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BEFORE
The problem of chip impression is due to chip present between locator and gear blank during machining process. Thus if there is no chip then there is not any problem of chip impression, ultimately we can say that “prevention is better than cure”
Fig. shows that present locator is not appropriate for rapid cleaning of chip in dwell period.So, there is scope of change in shape of the locator such that rapid cleaning possible.

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AFTER
The new locator serve the purpose of rapid cleaning of chip removal and also the contact area is also reduced. Due to counter shape of the locator, it is easy for operator to remove chip by passing highly pressurised air for