final report perfect

8/19/2019 Final Report Perfect

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National Institute of Technology, Warangal Dept. Of Mechanical Engineering

Computer Integrated Manufacturing Page 1

CHAPTER 1

INTRODUCTION

Material removal is one of the major and oldest shaping processes for the economic

production of machine components. Because of the wide use of engineering materials and

alloy steels with high hardness in the aerospace industry, fast and precise machining problems

have attracted much attention in manufacturing. Rapid failure of cutting tool leads to

deterioration of the work piece surface integrity, loss of geometrical tolerances and increase

of machining times.

Consideration of cutting tool life suggests that the following conditions of tool

performance would be highly desirable when attempting to cut metal at a high rate of cutting

speed. [4]

1. A large effective rake angle in so far as the shear process is concerned, a

small actual rake angle from the stand point of strength and heat flow.

2. Positive means for carrying the fluid to the tool point at high cutting speeds as in

the case of journal bearing.


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3. The possibility of increasing chip velocity without necessitating a corresponding

increase in cutting speed.

The first item could be accomplished by means of inclination of the tool relative to the

work velocity vector. The second two items can be achieved by providing a sidewise motion

of the tool relative to the work

One of the main features of any material removal process is that a significant portion

of the mechanical energy generated by the interaction of the tool and the workpiece is

converted into heat. In metal cutting, this energy is mainly created by shearing and friction

and is dissipated through conduction of heat into the tool, the workpiece and the chip. This

results in an increase in tool temperature which accelerates the tool wear. Tool wear is not

desirable because both tool life and the accuracy of the machined surface are adversely

affected.

Several methods have been investigated by researchers in order to lower the tool

temperature. In particular, the use of cutting fluids that serve as both a heat transport

mechanism and as a lubricant at the tool-chip interface has been studied and used in practice

today. However, in some cases, its effectiveness is limited by its inability to penetrate the

tool-chip interface. Furthermore, these days, the use of cutting fluids is less desirable because

of its adverse effect on the environment. Some investigations have reported that exposure to

particles generated by evaporation of cutting fluids can cause breathing trouble and skin

irritation.

A novel method to get the sidewise motion is to use a rotating cutting edge in the form

of a disk. This type of device is known as a rotary tool and it provides a rest period for the

cutting edge thereby allowing for the edge to be cooled and a continuously fresh portion of

the edge to be engaged with the workpiece. This enables the tool to getkinematically induced inclination angle and it is the predominant variable that controls

performance of rotary machining operation.


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Fig 1-1: Self Propelled Rotary Cutting Process. [6]

Though there is a rapid development of advanced aerospace materials like titanium and

composite materials with improved properties such as strength to weight ratio, the difficulties

in machining of these materials economically and effectively are limiting their applications.

As the development of new cutting tool materials are reaching an optimum level, the attention

of manufacturers all over the world is focused on novel tool designs. One such development

is the rotary tool machining operations i.e. self-propelled rotary tool turning and self-

propelled rotary tool milling operations in which the tool life increases enormously and

aerospace materials can be machined at a faster rate at lesser tool cost than that of

conventional machining operations.

Radial rake angle is considered to be inclination angle in rotary milling cutter which

has great importance while dealing with the mechanics of rotary machining. In face milling

operation lead angle has importance in chip thinning action and this lead angle is variable due

to the circular edge of the insert and depends upon the depth of cut provided.

Fig 1-2: Variation of effective lead angle and average chip thickness with variation in

depth of cut while using round inserts.


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However, the lead angle of a round insert cannot be truly defined. The effective lead

angle will change throughout the cutting depth. A 3/4-inch diameter (inscribed circle) insert is

shown in Fig 1-2 at a depth of cut of 0.375, 0.250 and 0.125 inch respectively.

As the lead angle changes, the cutting forces are also changing. Where the insert is at

the maximum depth of cut (one half the insert diameter), the axial and radial forces are

balanced. When the depth of cut is reduced, the radial forces decrease and the axial forces

increase. At a very light depth of cut, the forces would be almost totally in the axial direction.

Thus, depending on the setup and part parameters, maximum productivity can be gained with

a round insert cutter by selecting the optimum depth of cut that best controls the cutting

forces.

Ceramic inserts are preferred for rotary milling cutters where ceramic inserts are

capable of machining hardened steels at much higher speeds than conventional carbide cutting

tools due to its high melting point. Rotary milling cutters are built for security and

repeatability at ceramic milling speeds. Modern whisker-reinforced ceramics have a melting

point of more than 2000o C, which means that ceramic inserts can operate at speeds well

beyond the point where carbide tools fail. In fact, whisker-reinforced ceramics work better

above the melting temperature of carbide inserts. Coolant is not recommended for hard

milling applications with ceramic inserts. Ceramic inserts have more strength in compression

and weak in tension due to its high brittleness and it is suggested to provide negative axial

rake angle

Fig 1-3: Rotary milling cutter with single inclination angle [17]

(Rotary Technology Corporation, U.S.A)


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In DRDL extensive research has been carried out [16] on the performance of rotary

milling operation using the single inclination commercial milling cutter having inclination

angle of 18.5 degrees. Models are predicted and established for the forces and surface

roughness using the milling cutter show in fig 1-3. Inclination angle of the rotary insert is the

major parameter which governs the cutting forces, surface roughness and chip flow direction.

Models can be predicted for the cutting force and surface roughness accurately if we take the

variation of inclination angle in to consideration.

In this thesis an attempt has been made to design and develop a rotary milling cutter

having a provision to accommodate four inclination angles such as 20°, 30°, 40° and 50° for

the catridge assembly carrying circular insert. Cutter was designed to machine difficult-to-cut

materials like titanium alloys and hardened steels.


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Chapter 2

LITERATURE REVIEW

2.1. Generalities

Generally, rotary tool turning is a cutting process in which the cutting edge of a round

insert rotates about its axis, so that a continuously indexed cutting edge is fed into the cutting

zone. Compared to a conventional stationary tool or non-rotating circular tool, rotary tool

allows each portion of the cutting edge to be cooled between engagements and makes use of

the entire circumference of the edge which has a positive influence on lowering overall tool

temperature.

Insert rotation can be either externally driven (Driven Rotary Tool) or generated by a

self-propelling action induced by chip formation (Self-Propelled Rotary Tool). Venuvinod et

al. (1981) [25] studied the mechanics of the DRT process. Shaw et al. (1952) [4] investigated

the DRT process and measured the average tool-chip interface temperatures using the tool-

work thermocouple technique. Armarego et al. (1994) [10]

investigated the mechanics of both DRT and SPRT processes theoretically and

experimentally.

Like conventional cutting processes, the rotary tool cutting process is classified as

orthogonal or oblique depending on whether the workpiece velocity is perpendicular to the

rotary tool cutting edge or not, respectively. The DRT can be both, whereas the SPRT


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requires the cutting edge to be at an oblique angle to the cutting speed in order to derive its

motion. The insert rotation about its axis is derived from the cutting force parallel to the

workpiece velocity. Consequently, the static inclination angle i must be non-zero for the tool

to rotate.

In self-propelled tool cutting process, another way to explain the reduction of

temperature could be given. Indeed, in metal cutting the temperature in the tool-chip interface

depends on the balance between the generation and the dissipation of heat. In conventional

cutting, the consumed power is largely converted into heat. In rotary tool cutting, some energy

is required to drive the tool and is turned into kinetic energy. Thus, the heat generation is

reduced.

2.2. Kinematics

Like stationary tools, two motions are important in a rotary tool turning process:

• Cutting motion, rotational speed of the workpiece.

• Feed motion of the tool into the work piece.

The main feature of a rotary tool is that the cutting insert also rotates. Thus, a third

motion, i.e. rotational speed of the tool, Nr occurs in this process. The consequences of this

characteristic concern the kinematics and the mechanics of the chip formation process.

Indeed, it is obvious that the spin of the round insert deviates the chip flow velocity vector.

Also, the effect of feed rate Vf can be ignored because its value is much smaller than thecutting speed Vw and Vr. Thus, the following relations between the different velocities can be

derived.

V = Vw – Vr

Vcr = Vc – Vr


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Consequently, the mechanism is studied in the frame of the tool where the cutting

edge is assumed to be a straight line since the tool radius is large compared to other geometric

parameters (Fig 2-1).

Fig 2-1: Rotary cutting process as observed from fixed point (a) in space,

(b) on tool. (Armarego et al., 1994) [10]

Armarego et al. (1994) carried out investigations in order to understand the

fundamentals of the rotary tool cutting processes. Studying operations for machining a tube,

they related rotary tool processes to the better known orthogonal and oblique cutting

processes and developed mechanics of cutting models for these new processes. They

performed a theoretical investigation and validated their model trough experimental

investigation. When the rotary tool and the tube diameters are large compared to the tube

thickness and the feed speed is negligible compared to the cutting speed, the rotary tool can be

represented by a straight cutting wedge tool of constant normal rake angle.

As pointed out earlier, all rotary tool processes can be classified into three basic types:

driven orthogonal rotary operation, driven oblique rotary operation and selfpropelled rotary

operation. If the angle between the cutting velocity Vw and the normal plane Pn (called static

inclination angle) is equal to zero then it is called orthogonal otherwise, it is called oblique.

Thus, there exists only one way to get a driven orthogonal rotary operation, i.e. the

tool has to be on centre. For the self-propelled, there are two possibilities. On one hand, the

tool can be tilted. On the other hand, it can be set above or below centre. For the driven

oblique process, the tool is not inclined but is set above or below centre. The different cases

are presented in Figure 2-2, 2-3 and 2-4.


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2.2.3. Self-propelled oblique rotary tool cutting process

Contrary to the former process, this process has to be oblique in order to allow the

rotation of the tool. As pointed out earlier, one way to get tool motion is to set it above or

below centre. If the rotary tool is free to rotate and is set above centre so that is not equal to

zero, the cutting action will result in a force along the cutting edge which will propel the tool

counter-clockwise (negative Vr) until an equilibrium position is achieved where no side force

acts along the tool edge (assuming the rotary tool axis can rotate freely with no friction and

chip transportation requires no additional energy). This condition occurs when the relative

velocity V lies in the normal plane (inclination angle is zero) as shown in Fig 2-6. Thus, the

equivalent process is a classical orthogonal process. When the tool is set below centre, the

static inclination angle is becomes negative, the inclination angle i is zero, and the tool is

propelled clockwise.

The other way to propel the tool is to give an effective negative rake angle to the

tool. Thus, the tool is again driven by the chip in a counter-clockwise direction. This tilted

position of the tool is similar to the one where it is set above centre. Also, some tools are

inclined in two directions, around the workpiece axis and around the axis normal to the latter

(effective negative rake angle).

Table 2-1: Rotary tool and corresponding equivalent classical processes.

Rotary tool processes Driven oblique Driven OrthogonalSelf-propelled

(Oblique)

Corresponding

Oblique;equivalent classical Oblique Orthogonal

Orthogonal if Vr=0cutting processes


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2.3. Machining of Difficult-To-Cut Materials

Conventional methods of machining hardened materials usually involve rough

machining of the annealed workpiece followed by heat treatment, grinding and superfinishing

or honing. The main issues with this multi-step process are obviously its high cost and time.

Also, this process requires several machines for each operation. Hard turning refers to single

point machining of materials approximately 45 HRC and higher using extremely hard, wear-

resistant cutting tools such as polycrystalline cubic boron nitride (PCBN) or ceramics. This

process can yield material removal rates close to rough machining and surface characteristics

comparable to grinding, using a single machine tool. This provides an attractive alternative to

the conventional machining sequence because the number of operations is reduced and the

entire machining process can be performed after heat treatment. Moreover, machine tools

used for hard milling are typically cheaper than those used for grinding and chips generated

during hard milling are easier to recycle than grinding swarf. Therefore, hard machining

provides cost savings and environmental advantages when used as a replacement for grinding

operations.

Titanium alloys are considered to be difficult-to-cut materials. Properties of EN24 (alloy

steel) like low specific heat, and tendency to strain-harden and diffuse between tool and work

material, give rise to certain problems in its machining such as large cutting forces, high

cutting-tool temperatures, poor surface finish and built-up- edge formation and EN24 at

hardened state, above 40 HRC considered as difficult-to-cut material.

2.4. Importance of Round and Ceramic Inserts

The shape of an insert has a major influence on the impact resistance of the carbide.

The weakest section of a milling insert is the corner, which is exposed to constant interrupted

cuts and extreme heat changes. Since a round insert has no corners, it is more secure than any

other shape.

Consider the tremendous forces that are placed on a milling insert in a typical cut. As

the insert enters the cut, it is subjected to a large compressive load. The initial contact

between the cutting edge and the workpiece may be very unfavorable depending on the position of the cutter in relation to the workpiece. As the insert moves through the cut, the


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chip thickness is constantly changing, varying the radial and axial cutting forces. Finally, as

the insert leaves the workpiece, it is subjected to tensile stresses that break down the carbide.

The chip bending away from the insert places large tensile or "ripping" stress on the face of

the carbide.

One major reason for the success of the round insert in so many applications is that the

axial and radial cutting forces can be managed by changing the axial depth of cut. A high

radial cutting force can cause vibration and chatter. Conversely, a high axial force can cause

the workpiece to move in its fixturing and cause poor tolerances. With the use of traditional

milling cutters, the lead angle dictates the kind of cutting force produced.

Another reason the round insert cutter is so widely used is the high table feeds that can

be attained. This is due to the chip thinning effect of the round cutting edge. Chip thinning is

what happens when you increase lead angle of the tool. The greater the lead angle, the thinner

the chip since it is distributed over a greater length of the cutting edge. Therefore the insert

load will be reduced allowing for higher feeds per tooth and superior metal removal rates. In a

tool with no lead, the chip thickness is equal to the feed per tooth. Round insert cutters, like

all lead angle cutters, have a change in chip thickness when feed per tooth is changed. But

unlike other lead angle cutters, the chip thickness for a round insert is also affected by a

change in depth of cut. High velocity milling cutters are built for security and repeatability at

ceramic milling speeds. Modern whisker-reinforced ceramics have a melting point of more

than 2000o C, which means that ceramic inserts can operate at speeds well beyond the point

where carbide tools fail. In fact, whisker-reinforced ceramics work better above the melting

temperature of carbide inserts. Coolant is not recommended for hard milling applications with

ceramic inserts.

Ceramic inserts are capable of machining hardened steel at much higher speeds than

conventional carbide cutting tools. Combine the higher operating speed with the proper

feedrate and a healthy step-over and the shop can achieve some impressive metal removal

rates. Another key factor in increased production rates when hard milling is the cutter density.

Every additional tooth in a cutter increases the cross feedrate. Higher speed and more feed

add up to lower cycle times.


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The surface finish achieved by rough milling with ceramics leaves less work for a

finish milling operation, and reduces finishing and polishing time. Milling at relatively light

feedrates in hardened steel with carbide usually leaves a good finish, but many times with

ceramic inserts the rough finish is even better than the required finish. In some cases,

additional milling, grinding and polishing can be eliminated.

2.5. Hard Milling with Ceramic Inserts

Proper application of speed and feed for the material hardness are critical factors for

good tool life when hard milling with ceramic inserts. Unfortunately, depth- and width-of-cut,

as well as cutter lead angle, are commonly overlooked. A basic understanding of how these

factors influence tool life can make a huge difference in metal removal rates. If a tool is

running with the incorrect chip load or at inefficient speeds and feeds, it not only sacrifices

tool life, but productivity as well. When considering all of the factors, productivity increases

and decreases can be astounding with small changes in cutting parameters. [11]

2.5.1. Cutting speed

The cutting speed necessary for successful hard milling with ceramics is based on the

actual material hardness, usually in the 45–65 Rockwell C hardness range. At elevated

temperatures the metal being machined becomes plasticized, or softened, which lessens the

cutting forces, and aids in chip separation. To take advantage of the strength and hardness of a

whisker-reinforced ceramic insert, it is necessary to run at a surface speed

high enough to create sufficient heat in the cutting zone, which may be as much as five times

the cutting speed of conventional carbide.

Successful cutting with ceramic inserts demands high surface speed coupled with

balanced feed rates. High speed cutting is necessary to generate the high heat within the

cutting zone and to assure that the heat propagates into the workpiece immediately ahead of

the cutter.

This is not to suggest that hard milling with ceramic inserts requires a new high-speed

machining center with 50 horsepower and the latest advanced processor. The speed necessary


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for milling hardened materials with ceramics is within the range of many of the machines in a

modern shop. The horsepower consumption is actually quite low due to the low cutting forces

being generated.

In general, a conservative approach to cutting speeds and feeds is the single largest

contributor to process failure when trying to implement ceramic cutters. When cutting speeds

are too slow, insufficient heat is generated. Because heat cannot be transferred ahead of the

cutter, in effect, to anneal the already hardened workpiece, cutting forces become too high and

insert failure occurs.

2.5.2. Feed

Before programming a hardened part, it is important to consider the factors that

influence the difference between the programmed feedrate per tooth and the actual thickness

of the chip being formed. The feed per tooth specified in the program can be dramatically

reduced by the cutting conditions. The actual thickness of a chip being formed is affected by

the depth- and width-of-cut as well as the insert radius or the lead angle of the tool.

Actual chip thickness is a crucial factor for heat dispersion (i.e., the chip must have

enough mass to carry away a majority of the heat). When the depth- and/or width-of-cut is

below an acceptable level, the chip generated will not be thick enough to carry away all of the

heat being produced by the cut. Heat that is not absorbed by a thin chip has to go somewhere.

It will be pushed into the part, the inserts, the cutter and the fixture. It is much more efficient

to send the largest portion of the heat away with the chips.


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2.6 Different Angles in Face Milling and their Importance

Table 2-2: Function and effects of different angles in face milling

Type of Angle Function Effect

Axial Rake Angle Determines chip disposal

Positive: Excellent machinability. direction.

Radial Rake Angle Determines sharpness. Negative: Excellent chip disposal.

Corner Angle Determines chip thickness.Large: Thin chips and small cutting impact.

Large back force.

Positive (large): Excellent machinability.

True Rake Angle Determines actual sharpness. Minimal welding. Negative (large): Poor

machinability. Strong cutting edge.

Cutting Edge Determines chip disposal Positive (large): Excellent chip disposal.

Inclination direction. Low cutting edge strength.


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2.6.1. Lead angle

The lead angle of a round insert cannot be truly defined. When the tool is used at

different depths of cuts, the lead angle changes with the depth of cut. The lead angle can be

measured at the depth-of-cut line.

Fig 2-8: Variation of cutting forces and effective lead angle

with variation in depth of cut while using round inserts

As the lead angle changes, the cutting forces are also changing. Where the insert is at

the maximum depth-of-cut (one half the insert diameter), the axial and radial forces are

balanced. When the depth of cut is reduced, the radial forces decrease and the axial forces

increase. At a very light depth of cut, the forces would be almost totally in the axial direction.

Thus, depending on the setup and part parameters, maximum productivity can be gained with

a round insert cutter by selecting the optimum depth of cut that best controls the cutting

forces.

2.6.2. Radial rake angle

Generally more radial rake angles are provided to the rotary milling cutters and climb

Milling is especially desirable with milling cutters having a high radial rake angle. The high

radial rake angle weakens the tooth because it is relatively thin. The forces imposed on the

tooth during conventional milling are in a direction that will cause the tooth to deflect because

it has no support to oppose the forces. On the other hand the forces imposed on the insert

during the climb milling are in a direction more parallel to the tooth body, thus giving added

support to prevent deflection to the cutters designed for high metal removal rates.


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2.7. Rotating Inserts

Rotating inserts have been around for fifty years or so. The inserts are mounted on

thrust and radial bearings, which allow them to rotate freely. This rotation creates a slicing

action that, combined with the continuous change of the cutting edge zone exposed to the

metal-removal process, leads to lower temperature, improved tool life resulting from

distribution of tool wear around the entire insert circumference, lower machining forces and

power requirements, and better surface finish. [13]

Limitations of the tooling have been reliability issues arising from the bearing system,

excessive size of the insert-holding cartridges, higher initial cost of the cutter and inserts, and

a lack of effective analytical tools for cutting tool design.

Fig 2-9: Rotating Insert [13]

Rotary Technologies' development is a compact cartridge system for housing the

bearings consisting of a stator surrounded by a thrust bearing and needle roller bearing. The

bearings allow the rotor to rotate under the action of cutting forces. Inserts are mounted on the

rotor and locked in place using a lock nut. A dovetail on the bottom of the stator enables the

cartridge to be guided in the tool and locked in place using a clamping mechanism. Cartridges

are sealed using O-rings that prevent contamination of the bearings by cutting fluids or chips.

The advantages of rotary-insert tools depend entirely on the fact that the insert rotates

during the cutting process, propelled by forces generated during the machining process.

Rotary-insert tool design is complicated by the fact that the machining forces creating the

insert torque are a complex function of a number of variables and need to be high enough toovercome the friction inherent in the cartridge bearings.


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2.8. Geometrical Analysis of Rotary Machining and Influence of

Inclination Angle

2.8.1.

Effect of feed rate on the chip cross-sectional area

Feed

r

Depth of cut

Fig 2-10: Model to demonstrate the effect of

feed rate on the chip cross-sectional area [2]

The feed rate influences the both cutting force and feed force components

significantly. An increase in the maximum cutting and feed forces with increasing feed rate is

analogous to the traditional relationship during machining with stationary tools [2]. It could

be due to an increase in the cross-sectional area of the uncut chip. In Fig 2-10 variation of

uncut chip cross-sectional area with feed rate was demonstrated.

2.8.2. Effect of depth of cut on surface irregularities

Rotary insert

Machined surface

Depth of

cut=1mm

Height of surface Feed Depth of cut = 0.5mm

irregularities

Fig 2-11: Model to demonstrate the effect of depth of cut on surface irregularities


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The influence of depth of cut can be explained with the help of a model for surface

irregularities shown in Fig 2-11. As evident from the model, a change in depth of cut does not

contribute directly to the change in height of surface irregularities and hence the surface

roughness [7], but increase in depth of cut after certain limits will lead to vibrations during

machining and deteriorates the surface finish significantly.

2.8.3. Differences in the cutting action of stationary and rotary inserts

The rotary inserts differ from that of the stationary inserts on three accounts.

1. Geometry of insert

2. Geometry of the cutter

3. Insert rotation

1. Geometry of insert: The diameter of the round insert used in a rotary tool operation is

analogous to the tool nose radius of a stationary insert. Usually, the diameter of a round insert

is very large (27 mm) as compared to the tool nose radius (usually of the order of 0.8 mm). It

changes the geometry of cut and the lead angle on the milling cutter and consequently

influences the cutting forces. [3]

2. Geometry of cutter: The rake angle provided on the round insert is analogous to the axial

rake angle on a stationary insert. Similarly, the inclination angle of a round insert is analogous

to the radial rake angle on a stationary insert. It also changes the geometry of cut andconsequently the cutting forces.

3. Insert rotation: It changes the nature of friction at the tool-chip and tool-work interfaces

and hence the cutting forces. In rotary tools, as the insert rotates, the rake surface is

continuously moved under the chip unlike the stationary rake face in a conventional milling

cutter. Similarly, at the tool-work interface, a rotary insert has two relative motions, one, due

to the rotation of milling cutter and the other due to the insert rotation. In the case of

stationary inserts, the second motion is not present.


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2.8.4. Effect of inclination angle on the magnitude of cutting forces

It is observed from the schematic in Fig 2-12 that the inclination angle influences two(Fx and Fy) of the three force components. The third force component, Fz remains unaffected.

Therefore, the modified equations to predict cutting forces after incorporating effect of

inclination angle are given as below: [3]

--------------- ( i )

The instantaneous X, Y and Z-force components at the cutter (considering only

one round insert) will now be given as:

-------------- ( ii )

By substituting Eq. ( i ) in Eq. ( ii ) we will get a set of basic equations to predict cutting

forces, which includes the effect of inclination angle.

FT*

FR Rotary Insert

FR *

Y

FT i X

Z

Fig 2-12: Effect of inclination angle on cutting forces in rotary face-milling


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Chapter 3

MODELING OF ROTARY MILLING

CUTTER ASSEMBLY

3.1. Conceptual Design

Inclination angle is the major parameter to study the rotary milling performance

profoundly and inclination angle is equal to the radial rake angle in face milling insert

geometry. Four inclination angles 15, 25, 35 and 45 degrees are considered and a model is

proposed as follows. Cutter body has to hold a round insert which is able to rotate around its

own axis. Initially milling cutter body model is proposed to accommodate four inclination

angles without considering provision to hold the rotary inserts.

Fig 3-1: Proposed model with different inclination angles


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This model has to hold the rotating catridge assembly designed by rotary corporation

technology [17]. Model proposed is changed to suit the catridge assembly by providing the

dove tail slot and v-groove. These dimensions are extracted from the commercial rotary

milling cutter by inspecting it under flash microscope and coordinate measuring machine in

metrology department. Cutter body model concept is designed by considering the importance

of different inclination angles and radial distance of the cutting tip from the centre (55mm).

Pockets are provided on the cutter to get some similarities and uniform ness in slot

dimensions for the clamps. Axial rake angle of 4.5° was provided on the catridge and fixed.

Internal bore diameter was fixed by considering the weight of the cutter and it is designed to

suit Ø40mm morse taper shank.

3.2. Components of the Rotary Milling Cutter Assembly

Rotary milling cutter body has to hold the catridge assembly which requires two

clamps, front clamp and rear clamp respectively having internal left hand threads. Studs with

left hand and right hand M6 threads on respective sides are provided to make sure the clamps

are tightly holding the catridge by locking mechanism. Front clamp is designed to push the

catridge towards the cutter body to overcome the inevitable play in dovetail slot and rear

clamp will hold the catridge tightly. Rotary corporation technology designed the catridge

assembly with advanced bearing materials which assures negligible wear inside the bearing

system.

1. Cutter body

2. Front clamp rear clamps

3. Studs (2)

4. Catridge Assembly

3.3. Pro-E Model

Pro-E is the modeling software used to develop the 3-D models of the cutter assembly

components. All the components are modelled according to the designed dimensions and

assembled. Components are assembled with 10-2microns to ensure the gluing operation should

be done during stress analysis. Care was taken during model cutter body to ensure the cuttingtip should be at constant radial distance from the center.


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Proper planes are created and slots are made to ensure the forces on to the clamps

should be axial and minimum bending moment occurs. Threaded holes are drilled to the

maximum possible deep. All the manufacturing drawings for the cutter body are extracted

from this model and for other components manufacturing drawings drawn in AUTO

CAD2010. Catridge assembly is modeled to replicate the original catridge. Rotary milling

cutter assembly model is shown in Fig 3-2 and exploded view was shown in Fig 5-7.

3.4. Work Material for the Cutter Components

EN24 (BS 970 817M40) (SAE 4340)

EN24 is a high quality alloy steel and it combines high tensile strength, shock

resistance, good ductility and resistance to wear at defined hardness. It is supplied as black

round shape in annealed condition and readily machineable and hardness of the raw material

is around 20 HRC. It is nickel chromium molybdenum steel with high strength and toughness

used for heavy duty gears, axles and high strength studs. Due to its extreme resistance to

impact loads at 32 HRC we choose it as work material for cutter components.


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3.4.1. Composition

Table 3-1: Composition of EN24

Table 3-2: Strength and impact values of EN24 at different hardness values

Tensile Strength Yield Stress Impact Izod (J) Impact KCV (J) Hardness HB

( N/mm2) (N/mm²)

850/1000 654 40 35 248/302

850/1000 680 54 50 248/302

925/1075 755 47 54 269/331

1000/1150 850 47 42 293/352

1075/1225 940 40 35 311/375

1150/1300 1020 34 28 345/401

1550 1235 10 9 444

Milling cutter should have resistance to impact loads and EN24 is having maximum

resistance to impact at the hardness around 32 HRC according to the table 3-2. Heat treatmentcycle for EN24 was hardening followed by tempering to 32 HRC and it requires through

hardening process to attain uniform hardness throughout the volume.

3.4.2. Through Hardening

Through Hardening is a process used to produce high strength and good toughness

when the entire part needs to be hardened. In through hardening, the metal is heated to form


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austenite, and then quenched to transform the austenite to martensite, which has a much

harder microstructure. Then the part is tempered to the defined temperature to attain the

required hardness. Tempering between 250°C-375°C is not recommended as this can

seriously reduce the steels impact value.


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Chapter 4

STRESS ANALYSIS OF MILLING CUTTER ASSEMBLY

Rotary milling cutters are designed to machine difficult-to-cut materials and for

intermittent cutting operations. Impact loads coming on to the cutter are significant.

Theoretically basic rotary machining operation is studied for rotary milling cutters and forces

are calculated using standard values of the specific cutting energy values (Appendix-1) of the

different materials. Cutter assembly model in CATIA V5 is imported to ANSYS9 and stress

analysis was carried out. Stress analysis was carried out in static condition of the cutter body

and factor of safety six to seven is provided. All the dimensions are fixed to minimize the

weight of the cutter and it is 4.2 kg.

Specifications of Milling Cutter

1. Outside diameter 150 mm2. Effective diameter 110 mm

3. Bore diameter Ø 40 mm

4. Thickness 52 mm

5. Insert diameter 28 mm

6. Inclination Angles 15°, 25°, 35° and 45°


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Work material EN24

Young’s modulus 2.12e5 MPa

Poison’s ratio 0.3

Tensile strength of the material 1050 MPa

Yield stress 755 MPa

Fig 4-2: Meshed view of rotary milling cutter using Hypermesh.

4.2.1. Boundary Conditions

All degrees of freedom for the surfaces coming into direct contact to the milling shank

are fixed i.e. surfaces on the shank which are taking load from cutter body.


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4.2.2. Load Conditions

Fc = 2550 N

Fr = 1785 N

Fa = 1020N

Where,

Fc = Force Component Perpendicular to Insert,

Fr = Force Component Tangential to Insert,

Fa = Force Component Perpendicular to Fc & Fr

4.2.3.

Maximum Load Conditions

Initially a set of experiments are conducted using the imported rotary milling cutter

developed by Rotary Technologies Corporation. The experiments are conducted based on

minimum and maximum levels of cutting speed and feed, keeping depth of cut constant. The

experimental values of various cutting forces are shown below in the table

The experiments are performed using the rotary and vertical milling machining centre (VMC).

The radius of the rotary insert considered is 14 mm (nearly).

Experiment

No.

Speed

(rpm)

Feed

(mm/min)

Depth of cut

(mm)

Force Fx

(N)

Force Fx

(N)

Force Fz

(N)

1 40 40 0.9 2157 1561 1358

2 40 80 0.9 3946 2758 2355

3 100 40 0.9 1161 871 827

4 100 80 0.9 2039 1504 1363

From the table it can be observed that maximum cutting forces obtained for Fx, Fy and

Fz are 3946 N, 2758 N and 2355 N respectively. Hence the maximum cutting forces are

Fx = Ft = 3946 N

Fy = Fr = 2758 N

Fz = Fa = 2355 N


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By comparing both theoretical and practical load conditions, it is clear that the maximum

load conditions from experiments are higher. So we take these forces into account while stress

calculations in our ansys analysis.

4.2.5. Stresses in cutter body (Von-mises stresses)

Maximum Stress = 119.28MPa

4.2.6. Stresses in front clamp (Von-mises stresses)

Maximum stress= 12.16 MPa

Maximum stress = 83.78 MPa


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4.2.7. Stresses in stud (Von-mises stresses)

Maximum stress= 14.26MPa

4.2.8. Stresses in Pin (Von-mises stresses)

Maximum stress= 14.19MPa


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The maximum stress developed on the cutter body with single rotary cartridge was

very minimum and found to be around 120 MPa where as the yield strength of the cutter

body material is 755 MPa. Hence the design of cutter is having a factor of safety of about 6.3

and the design is found to be very safe.


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Chapter 5

MANUFACTURING OF ROTARY MILLING CUTTER

COMPONENTS

Rotary milling cutter is designed and modeled to hold the catridge assembly at

different inclination angles. Manufacturing drawings (APPENDIX-2) are extracted from the

model by freezing the model at different stages and close tolerances were provided. Sequence

of operations (APPENDIX-3) prepared according to the different stages of manufacturing.

Rotary milling cutter assembly comprises cutter body, catridge assembly, rear clamp, front

clamp and studs.

Generally milling cutter is subjected to impact loads and cutter components should

have enough resistance to impact loads. EN24 (SAE 4340) is the work material and it is a high

quality alloy steel supplied readily in machineable condition. It combines high tensile strength,

shock resistance, good ductility and resistance to wear after proper heat treatment. We can

achieve required hardness more precisely and accurately.


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Machine tools allotted in process plan

1. Center Lathe

2. Vertical milling machine

3.

Surface grinding machine4. Cylindrical grinding machine

5. Universal milling machine

6. Vertical machining center (VMC)

7. CNC milling machine

8. Schaublin CNC lathe

9. Wire electric discharge machine (WEDM)

10. Jig grinding machine

11. Conventional milling machine

12. Copy milling machine

Different Stages of Manufacturing:

5.1.1 Stage one operations

Operations Involved: Turning, Facing, Taper Turning, Drilling,

Reaming, Boring, Counter Boring, Slot Milling,

Surface Grinding and Cylindrical Grinding


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5.1.2 Stage two operations

Operations Involved: pocket milling using mastercamon

bridgeportVertical machining Center

5.1.3

Stage three operations

Operations Involved: Drilling, End Milling, Flat Drilling,

Reaming and Tapping


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5.1.4 Stage four operations

Operations Involved: Wire EDM Using AUTOCAD Drawing,

Welding and Jig Grinding

5.2 Important Machining Operations

5.2.1 Vertical Machining Centre: End milling operation was done on this machine

using Mastercam to produce the pockets. 4-pockets on the component don’t have any proper

references to do manually. Model of the component is given at this stage and uploaded to the

computer connected to the VMC.

Fig 5-1: Model given to the shop floor for pocketing operation

Pocket


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Program was developed using mastercam and after positioning the component on the

table similar to the position of model in computer by dialing the bore & reference holes

provided on the component machining was done.

5.2.2 Universal Milling Machine: All 8-slotted holes are radially at different angles

and different offsets. Each hole is at different offset from radial axis. On universal milling

machine we can do this operation by swiveling the table about both the axes.

Fig 5-2: Threaded hole and slot whose axis is offset to the radial axis.

Fig 5-3: Cross section of the cutter body


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5.2.3 Heat Treatment Cycles: Milling cutter should have resistance to impact loads

and EN24 is having maximum resistance to impact loads at the hardness around 32 HRC

according to the table 3-1. Heat treatment cycle for EN24 was hardening followed by

tempering to 32 HRC and it requires through hardening.

Through Hardening is a process used to produce high strength and good toughness when

the entire part needs to be hardened. In through hardening, the metal is heated to form

austenite, and then quenched to transform the austenite to martensite, which has a much

harder microstructure. Then the part is tempered to the defined temperature to attain the

required hardness.

Heat Treatment Cycle for EN24 to get 32 HRC

• Hardening:

Heat the component to 840/860°C in electric furnace. Soak the component for two hours to

attain uniform temperature. Quench in oil. Now it is in martensite state and material has

extreme brittleness and hardness. Internal holes and slots should have to fill with chalk

powder to avoid oxidation during heat treatment. Furnaces are controlled by digital process

controllers to ensure accurate process temperatures and reproducible results.

• Tempering:

Heat the component to 600°C temperature and hold the temperature for two hours to attain

uniform hardness. Take out the component from the furnace and allow the component to cool

in standstill air to attain ambient temperature. Pickling operation is carried out to clean the

oxides formed on the surface of the components.

5.2.4 Wire Electric Discharge Machine (WEDM): Wire cut operation is next to heat

treatment to avoid inevitable distortions to the dove-tail slot which suits the standard catridge

assembly. Profile of the wire cut path in Auto CAD file was uploaded to the machine

according to the true scale. Component is positioned on the frame of the WEDM similar to

the position in uploaded drawing by dialing the internal bore and reference holes.


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Fig 5-4: Slot produced in wire cut operation

During wire cut speed of the wire is in the range of (0.35-0.80) mm/minute. For each slot

it took 3 to 4hrs. Accuracy depends upon the position of the component clamped respective to

the position of the input drawing.

5.3 Manufacturing of Clamps and Studs

EN24 is the work material for the components. Round Ø30 × 40 mm work pieces are

machined on FN2 milling machine to get the size 20×12×36 mm for the clamps and Round

Ø10 × 120 mm size directly taken for the studs.

Clamps 2-D profile is given as the path of the tool in program and uploaded to the

machine. 6mm end mill is used for the machining. After machining the required height of the

clamp, left hand tap is rotated. Remaining part of the block is removed from the clamp using

saw in fitting shop and surface is grounded on the surface grinding machine. For rear clamp v-

groove is suited to the drawing in fitting shop.

Studs are having left hand and right hand threads on respective side. Initially

workpiece is machined to size of outer diameter of the threads on precision lathe. Studs are

designed to uniform strength and hence remaining length in between the RH & LH threads

machined to inner diameter of threads. Using the standard 1mm pitch special purpose insert,


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threads are machined on schaublin CNC lathe by uploading the program and are matched with

the standard M6 thread gauges. Slot on the stud is machined on the copy milling machine

using 2mm end mill.

Rear Clamp Front Clamp Stud (LH/RH)

Fig 5-5: Rear clamp, Front clamp and Stud.

5.4 Milling Cutter Assembly and Components

Fig 5-6: Exploded view of the rotary milling cutter assembly


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5.5. Scheme of Measuring the Inclination Angle (i) on CMM

In rotary face milling operation inclination angle (i) is defined as the angle between

cutting velocity vector and axis of rotation of the insert. Cutting velocity vector is tangential

to the effective diameter of the cutter at the tool workpiece contact point. Geometrically this

inclination angle is equal to the angle between the plane containing the cutting edge and radial

axis passing through the point of intersection of plane containing cutting edge and axis of

insert rotation as shown in Fig. Inclination angle was measured for the 30° slot in fabricated

rotary milling cutter using Coordinate Measuring Machine (CMM).

Axis of Insert Rotation

i = Inclination Angle

Fig 5-7: Inclination angle in rotary face milling cutter

Step1: Selection of reference plane. By touching the probe on different points of the grounded

surface of the cutter body reference plane was selected.


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Step2: Location of vertical axis of cutter body. By touching the different points on the inner

bore of the cutter axis was located.

Step3: Location of insert rotating axis. By touching the different points on cylindrical part of

the catridge body axis was located.

Step4: Location of cutting edge plane. By touching the probe on different points on the

circular cutting edge, plane containing cutting edge was located.

Step5: From the plane of cutting edge and axis of insert rotation intersection point was

located. Vertical axis passing through this point is the axis to change the inclination angle of

the insert. This is the neutral axis for all slots to guide catridge assembly and passing through

the pitch circle of 110mm diameter.

Step6: Inclination angle was measured between the plane of cutting edge and radial line

passing through the intersection point of cutting edge plane and axis of insert rotation.

Measured Inclination Angle (i) on CMM for 30° slot = 29 degrees 34 minutes

Error in inclination angle (e) = (30°) - (29°34’)

= 26 minutes

This error in inclination angle is due to the off-set of the plane containing the cutting edge

in model. The cutting edge plane is measured roughly and model built for catridge assembly,

that error causes the variation in inclination angle and was geometrically demonstrated.


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CHAPTER 6

CONCLUSIONS AND SCOPE OF

FUTURE WORK

6.1. Conclusions

Concepts of rotary milling are studied profoundly and it is clear that inclination angle

is the predominant variable to study the performance of rotary milling operation and directly

it will effects the chip formation and surface roughness produced. A model of rotary milling

cutter with different inclination angles was proposed and developed.

Physical and mechanical properties of different materials are studied and alloy steel

EN24 (SAE 4340) was chosen as the work material for cutter components and it combines

high tensile strength, shock resistance, good ductility and wear resistance.

Solid model was developed using CATIA V5 to suit the catridge assembly

manufactured by rotary technology corporation. Theoretically forces are calculated to

machine difficult-to-cut materials like alloy steels, hard cast iron and titanium alloys. Using

ANSYS9 stress analysis was done under static conditions on milling cutter model and cutterdimensions are optimized to minimize the weight.


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Manufacturing drawings and process plans were prepared and machining carried out

in shop floor at different stages to complete the components. Components are heat treated to

32 HRC where EN24 will get the maximum resistance to impact loads. Scheme of measuring

inclination angle on CMM was explained and inclination angle for 30° slot was measured and

it is 29°34’. This error is due to the offset of cutting edge plane in model from the original

catridge assembly. Models can be predicted for cutting forces and surface roughness

accurately in rotary milling using the cutter fabricated.

6.2. Scope of future work

Rotary tools application in face milling has received limited attention and research

work is going on to study the performance of rotary milling. Using the cutter developed we

can predict models for cutting forces and surface roughness and we can optimize the process

parameters more precisely.

Mathematical models for rotary face milling are not yet developed appropriately and it

requires lot of attention to develop a mathematical model for rotary face milling.

Machining with rotary milling cutter using ceramic inserts is different from using

carbide inserts due to the differences in cutting velocities and mechanics of machining. There

is need to optimize the process parameters separately.

Depth of cut has different and significant role in machining with round inserts due its

variable lead angles at different depth of cuts. It will be interesting if we consider the

variations in lead angles while predicting the models for cutting forces as it causes the

variations in the ratios of force components.

Chip formation in rotary face milling is the another scope to study as chip control has

the special importance in modern automated manufacturing due to its direct effect on the productivity and quality of the produced surface.


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APPENDIX-1

Table: A-1 Specific cutting energies of materials during face milling operation at different

feeds

Tensile Strength

Specific Cutting Pressure KFs

(N/mm2)

Work Material (Mpa) & Hardness

0.1mm/tooth 0.2mm/tooth 0.3mm/tooth 0.4mm/tooth 0.6mm/tooth

Mild Steel 520 2200 1950 1820 1700 1580

Medium Steel 620 1980 1800 1730 1600 1570

Hard Steel 720 2520 2200 2040 1850 1740

Tool Steel 770 2030 1800 1750 1700 1580

Cr Mn Steel 630 2750 2300 2060 1800 1780

Cr Mo Steel 730 2540 2250 2140 2000 1800

Ni Cr Mo Steel 940 2000 1800 1680 1600 1500

Ni Cr Mo Steel 352 HB 2100 1900 1760 1700 1530

Cast Iron 520 2800 2500 2320 2200 2040

Hard Cast Iron 46 HRC 3000 2700 2500 2400 2200

Gray Cast Iron 200 HB 1750 1400 1240 1050 970

Brass 500 1150 950 800 700 630

Light Alloy 160 580 480 400 350 320

(Al-mg)

Light Alloy 200 700 600 490 450 390

(Al-Si)


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2. Mechanics of machining of face-milling operation performed using a self-propelled round

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3. Modeling of cutting forces in a face-milling operation with self-propelled round insert

milling cutter. Pradeepkumar Baro, Suhas S.Joshi, S.G.Kapoor. International Journal ofMachine Tools & Manufacture xx (2005)1-9

4. Metal cutting principles by Milton C.Shaw; CBS publishers and distributors,1992

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Hill edition, 1973

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steel, A thesis presented to the academic faculty by Vincent Dessoly. Georgia Institute of

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propelled round inserts milling cutter Uday.A.Dabade, S.S.Joshi, N.Ramakrishnan;

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8. A model for cutting forces generated during machining with self-propelled rotary tools.

L.Li, H.A.Kishawy. International Journal of Machine Tools and Manufacture. Article in

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9. Introduction to physical metallurgy, Sidney H Havner, second edition, Mc GRAW-HILL

editions. Material science and metallurgy series 1974

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Machine Tools and Manufacture. Vol.34, No. 6, pp. 785-801, 1994

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benefits of hard milling with ceramics. Ran Malone.

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temperature alloys, Manufacturing Engineering, Society of Manufacturing Engineers,

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Manufacturing Engineering, Society of Manufacturing Engineers, January 2002, Vol. 128

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14. Mitsubishi, Technical information, Function of tool features for face-milling, Function of

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final report perfect

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