Consideration of certain aspects oftool wear during high speed machining

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Authors Dumas, Walter Arthur, 1925-

Publisher The University of Arizona.

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CONSIDERATION OF CERTAIN ASPECTS OF TOOL WEAR ■ ■ : DURING HIGH SPEED MACHINING "

byWalter A. Dumas

A Thesis Submitted to the Faculty of the DEPARTMENT OF MECHANICAL ENGINEERING

In Partial Fulfillment of the Requirements ; For the Degree of '

\ ; 'MASTEROF' SCIENCE ' ’-V

In the Graduate CollegeTHE UNIVERSITY OF ARIZONA

1 9 6 1

STATEMENT BY AUTHOR

This thesis has been submitted in partial fulfillment of requirements for an advanced degree at The University of Arizona and is deposited in The University Library to be made available to borrowers under rules of the Library.

Brief quotations from this thesis are allowable without special permission, provided that accurate acknowledgment of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major depart­ment or the Dean of the Graduate College when in their judgment the proposed use of the material is in the in­terests of scholarship. In all other instances, however, permission must be obtained from the author.

This thesis has been approved on the date shown below:

SIGNED

APPROVAL BY THESIS DIRECTOR

B. S. MESICK Professor of Mechanical Engineering

B. S. MESICK / DATE/ DATE

11

ABSTRACT

The experiments by the Lockheed Aii’eraft Corpora- tIon for the United States Air Force provide interesting observations on tool wear at machining speeds above 30,000 surface feet per minute. Present tool wear theory assumes that the majority of the wear on the flank of a tool is the result of friction and erosion. Results of the experi­ments indicate that tool wear decreases at high velocities.

This thesis reviews the present theories of tool , wear and shows that the currently popular theories must be changed to.explain the decrease of wear as veloeitles in­crease „ The theory advanced assumes surface melting of small asperities in a surface layer less than .0003 inches: thick. Correlation between tool wear and temperatures and velocities, although not,conclusive, indicate that the melting theory has some basis in fact. Analysis is confined to a given tool-wdrk pair in a limited range of cutting velocities,

ACKNOWLEDGMENT

The author’ wisttes to express gratitude Tor She. assistance given to him in the preparation; of this thesis by Professor A„ G. Poster and Professor B„ S. Mesick of The University of Arizona. Professor Foster has been the person responsible' for the background • knowledge fn ; machining■and cutting theory that the author obtained as an undergraduate-and graduate student. Dr. Mesick is responsible for keeping the author on a converging course in the .preparation of this thesis .' . : ,

iv

TABLE OF CONTENTS

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OE , TABLES e o o » o e # o o 0 6 ‘ e o e e e o e o V0F F1CTJBES 6 . . . i -;.- , , . , „ . . . « vii

Chapter ' ' . :X o BX STOBY # 6 « e D O o ' & O O 0 . 0 o 0 6 6 0 O 0 O X

XIV BAGKCROm© . . . . . . . . . . . . . . . . . . 8III LOCKHEED EXPERIMENT . . . .• .. , . .. . . . . . . 26IV, .CORRELATION AND ANALYSIS '; V, : CONCIDSIONS ‘"' ' ’ ’'VI.• RECOMMENDATIONS FOR.FURTHER STUDY . . . . . . . 52

EXPERmENTAL DATA . 'V V . V .' . v . , ' V . r"; . . . ; 5458

v

LIST OF TABLES

Table . ■I. Wear Measurements with Model 0 Tool HolderII. Wear .Measurements with Model D Tool Holder

111., Cutting Force Measurements . . . . . . .IV. Temperature Measurements . . . . . . . .

EEST OF HGTOES

Figure , Page1.1 Dr. Salomon’s Data Plotted in English Measure , 72.1 Tool Nomenclature . . . . . . . . . .... , . . . 92.2 Types of Wear . , . . .. . . , ' . . . . . .. . , 112.3 Typical Wear Lands on Tool Flank . . . . . . . . 142.4 Correlation, Wear Rate and Length of Cut . . . , 152.5 Interlocked Asperities .. . . . . , , . . . . . 173.1 Effective Wear . „ . . . . . . . . . . - . . . .' 344.1 Correlation, Plank Wear and Cutting Velocity . .... 374.2 • Correlation> Plank5 Wear and Cutting Velocity ", , 384.3 Correlation, Plank Wear and Velocity . . . , / 39.4.4 Correlation, Horizontal Force and Flank Wear . . •404.5 Correlation, Vertical Force and Plank Wear , . . ' 4 14.6 Correlation, Temperature and Velocity . . .. . 43. 4.7 Temperature -wear Correlation ., . . . , . . . 444.8 Correlation, Flank Wear and Velocity . . . , . 464.9 Correlation Test, Quadrant Sum Method . . . . . 47

vii.

CHAPTER I

INTRODUCTION AND HISTORY

The development; of the *’space age” high strength* heat resistant metals has introduced serious problems_into the machining industry. These new alloys are forcing in­dustry to machine at much slower speeds than are used for "ordinary" metals* resulting in machining times comparable to those associated with metals twenty years ago. This slowdown has stimulated Industry and government to inves­tigate new methods and techniques in order to maintain production capacity., Two alternatives appear to solve the production bottleneck that is being caused by the new "space age” metals: ; ’ -

a ., Invest additional capital to procure additional ■ machine tools:

b. Develop more rapid and more efficient methods for cutting and forming the difficult alloys being introduced.

This thesis is concerned with the second of these alternatives> that.of more rapid, metal removal methods and more specifically* the resulting tool Wear. The increase of the metal removal rate is based on greatly increased

omttimg velocities, velocities that have been obtained in the laboratory but as ,yet are impossible to achieve on an economical production basis * These cutting velocities' are included in the ultra high speed range, with velocities from 20,000 surface feet per minute |sfpm), just beyond velocities now being used in industry, to velocities approach ing 300,000 sfpm. These advanced cutting speeds move us into an area where existing theory has. not been confirmed, and where present theory apparently cannot be used to predict tool wear with accuracyI No investigation into the ultra high speed range would be of value without. first understand­ing the basic theories of metal cutting and tool wear in the normal range of speeds. These will be reviewed in Chapter II, The only experiments to date utilizing cutting veloci­ties in the ultra high speed range have been those performed by Lockheed Aircraft Corporation under contract to the . United States Air Force, Therecorded results of these experiments will be used in this thesis to analyze tool wear at. ultra: high velocities and to obtain correlation between the tool wear and some other parameter of the process or the materials involved. Present knowledge cannot be used to :. explain why tools wear at apparently different rates,at high velocities than at low velocities. To datej correlation of data has been hampered by the lack of adequate and accurate temperature data at critical points on the cutting tool.

Unfortunately, the Lockheed.. experiments did not produce the necessary temperature data for positive correlations„

It will be obvious, throughout the discussion in this thesis, that the ultra high speed machining apparatus is not yet in the configuration necessary for practical use on the production line in industry, Mo claims will be made that ultra high speed machining will cure the ills that beset the industry when cutting the high strength, heat resistant alloys„ It is quite obvious' that much is yet to be learned about cutting metals and tool wear at all velo­cities. Present machines and cutting tools are inadequate , for the application of the knowledge gleaned from the far too few experiments in the ultra high speed range, although it would appear that machines and tools using these veloci­ties can be.produced* Cutting speeds of 5,000 sfpm, common today, would have astonished manufacturing engineers in 1900,

Ihe machine tool industry has advanced rather slowly in the past 050 years, and the basic machine tools used in industry today are very similar to those found in the 18th century. Studies of the mechanics of :the. metal cutting process were initiated in the mid-l800s, and by 1900, considerable progress had been made in understanding the basic shearing processes involved. Modern cutting tools were made possible by Frederick if. Taylor, who introduced the High Speed Steel (HSS) tool to the metal cutting industry

in 1897. This tool, made from an alloy containing 18$ tungsten, 4^ chromium, and .37^ vanadium, possessed red hardness, allowing turning speeds to he doubled. The HSS ... tool also had an increased tool life over the then used carbon steel tool, a real economic advantage, Taylor also - introduced his well known tool life formula, VT = C, about this time, a formula used today with only minor modifications. Taylor's original High Speed Steel has been modified through the years, and is now known as 18-4-1 tool steel.

The introduction of the HSS tool was as great a development in its time as the jet engine was to the air­craft industry in the 1940s. The permissible speeds using HSS tools rose through the years as the alloy was improved, but cutting velocities were still quite limited due to tool wear. Harder, stronger, and .tougher tools were needed, and the introduction of the sintered (or cemented) carbides in the early 1930s partially filled this need. Cutting speeds measured in the hundreds of surface feet per minute became routine with the carbide tool, and helped make possible the huge expansion of industry during World War II, These tools ... are made from the carbides of tungsten, titanium, and tantalum, using either the individual carbides or alloys of them. In turn the carbides were followed quickly by the cast non-ferrous tools, the Stellites, and more recently, the oxides and the ceramics. ; With these last tools, cutting

velocities of 15,000 surface feet per minute are entirely possible and are used in industry today to machine certain of the non-ferrous alloys having high maehinability ratings.

As cutting velocities increased through the years,, so did the problems of tool wear. It was readily apparent that temperatures had a major effect on tool wear, and that as temperatures rose, tool life decreased. Tool life was a major problem, as worn tools forced operators to stop machines for tool replacement, losing valuable production time. The exact relationships between tool wear and temperatures are not yet entirely understood.

Dr. Karl Salomon, in 1923 in Germany, made a series of experiments concerning the relationship of velocity and temperature, using a circular saw blade mounted in a variable speed drill press. Brass and aluminum plates were fed by hand into this blade, using velocity as a variable, the chips impinging onto a wax covered board. Results showed that the temperature of the ehips ihcreased to a certain value, then decreased, as evidenced by chips either bouncing off the board or melting the wax |1). ip to this time, it had. been thought that chip temperature would increase with ' velocity until melting points were .reached, Later analysis of Dr .'. Salomon ’ s work by E» Tangerman (2 ) revealed that there might be. a Hforbidden zone" in the velocity range where HSS tools couid not be used because of unknown factors,

whereas the tool might be quite satisfactory at velocities above or below the critical or "forbidden” zone„ This zone is marked on the.graph of Salomon's data (Figure 1.1).

Early interest by lussian engineers in tool wear at high velocities is evidenced by the work in this, field done at the Serbian-Fhysico Technical Institute prior to World War II by Professor ¥„ P. Kuznetzov. (3)« Experiments were conducted; with continuous and interrupted cutting with cutting velocities to 10,000 sfprn slow today, but fast at that time. Unfortunately., the conclusions drawn from the work are not of value, although it was found that a milling cutter would cut marble; at 1Q>00Q .sfpm without evidence of tool wear. Gurrent Russian literature, not readily avail­able in this country, contains many articles on high speed machining processes and basic research into tool wear. The engineers and researchers in the European countries, in general, appear to be more interested in tool wear research than those in the United States. .

7

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/M d ,____985. 197C 2955 ^94C

212

200Cutting Velocity (feet per minute)

Dashed lines are estimates*

Dr. Salomon's Data Plotted in Dnglish Measure (From 1951 Patent)

Figure 1.1

cmPTia ii

BACKGROUND ■

Although there has been a considerable amount of research performed In the past twenty years on the subject of tool wear and the mechanics of the cutting process, no theory existing today is in complete accord with the exist­ing data, and it is probable that no satisfactory theory will be forthcoming until such time as more complete experimental data Is available (4). Although cutting action and tool wear can be explained using present knowledge of dislocations and imperfections on the atomic scale, the dislocation theories are not yet advanced to the point that deformation and wear phenomena can be predicted. It is evident from experience that there is large variation in tool life when using identical tools and materials, a range of 30^ being normal in repeated tests(5). This would Indi­cate that there are a large number of variables not yet appreciated or accounted for properly in the metal cutting process.

Today's industrial cutting tools are manufactured from a great variety of ferrous and non-ferrous materials, and in a variety of shapes and sizes„ The geometry of the

9tool is described in a set manner, this description being termed the "signature" of the tool. This thesis is con­cerned with a single shape of tool, one with a 0° back rake angle and 5° end or flank clearance angle. This geometry is as shown in Figure 2.1. This tool shape closely approxi­mates a tool used in a shaper, and is used in many of the qualitative studies of the cutting process in order to make certain simplifications and assumptions.

Toolshank

ChipFace

Shearzone

Cuttingedge

Flank

Backrakeangle

End clearance angle

-* Direction of cut

Figure 2.1--Tool nomenclature

The major assumption has been that of orthogonal cutting with a type II chip. This assumes that the cutting edge of the tool, or the intersection of the flank and the face, is perpendicular to the axis of the cut; that a single

straight cutting edge is involved in the cutting process; and that the chip flows from the.work in a continuous ribbon. Included in the orthogonal cutting process is the assumption that there; is no side cutting action to be con­sidered . The orthogonal cutting process is best achieved in the 'laboratory by cutting thin walled tubing on a lathe With a wide tool* using the, longitudinal feed mechanism to provide constant depth of cut. The same type of cutting would be possible in a shaper by machining the. edge of a relatively thin plate. Provided the speed of the cutting tool in relation to the work is sufficiently fast.; a con­tinuous chip will be produced. This chip, defined as a type 11 chip, is the normal.chip,produced when machining ductile materials at production speeds (6), When the cutting velocity is slow, a built-up edge (BUI) tends to form in the front of the tool, insulating the tool edge from actual con­tact with the work. The built-up edge is a mass of highly compressed metal and becomes welded to the cutting edge> periodically breaking away from the tool. These pieces are readily discernable, and when they are carried away by the .Workpiece, produce a rough surface on the work. The BUI type of cut produces a type 111 chip, and is very undesirable, not because of the rough -surface normally produoed, but be­cause of the aceeiefated fool wear caused by the BUE carry- . ing,away part of the tool, A type I chip is an intermittent.

11discontinuous type of chip, the normal type produced when machining cast irons or other brittle materials and result­ing from periodic fracture instead of continuous shear in the shear zone. This study will be confined to the type II chip, the type normally found at high cutting velocities.

Wear patterns vary with the various types of tools, wear being a function of geometry, composition, velocity, and physical properties of the tool and material. With the carbide tools, crater wear is normally severe, whereas HSS tools usually fail because of flank wear. Face wear, occurring in all tools, is not normally a primary reason for failure, except perhaps, in the ceramic tools where chipping of the edge is a primary cause of failure. The various types of wear are indicated on Figure 2.2. On a given tool, all three types may be seen simultaneously, although flank wear usually determines tool life.

Directionof

cutting

Face Flank Cratering

Figure 2.2--Types of wear

. ■ : : v... . "■ ■■■■ ^The basic causes of the three types of wear are not

entirely understood although it is known that heat is a major factor in all tool wear. Oratering is apparently the result of a chemical diffusion-of atoms from the chip■into the face of the tool. Investigations of this type of wear have indicated that certain atoms diffuse into the tool material, where new,.relatively weak, alloys are formed, the process being aided by the high temperatures present at the tool-chip interface (7, 13), These temperatures have been measured and found to be as high as 2000° F. (8),Tests have shown that the diffusion process is selective and the composition of the tool has a definite bearing on the amount of eratering possible (9).

Face wear is the result of heat and friction, the face being one of the two significant heat producing areas. These two areas are the face of the tool, adjacent to the cutting edge, and the shear zone in the workpiecev The first area, that on the face of the tool, produces heat as a direct result of the chip rubbing, along the face, and it is'in this area that face wear is evident. Artificial reduction of the tool chip contact area on the face of the topi has been shown to result in longer tool life, and decreased power consump­tion (10), The shear zone is that area where severe plastic deformation of the workpiece takes place (see Figure 2.1) and where the chip is sheared from the work. This very

narrow zone 'produces an estimated 70$ of the heat released ... in the cutting process .

; The wear on the flank of a cutting.tool is the least understood of the three types of tool wear. The factors influencing flank wear have almost been ignored in the in­vestigations of tool wear, not because they are understood any better, but because of the inherent difficulties of investigation in the laboratory. Experiments into the wear of cutting tools by- Hans Optiz of Germany (11) indicate that when metal is cut, an electric current is produced, the current leaving the workpiece and .entering the tool.. The introdUctidn of a compensating, current, through the tool into the work increases tool life by as much as 200$, this reduction "taking place at the cutting edge and the flank of the tool, but not in,the crater area. This significant finding confirmed earlier conclusions that flank wear was a different type of wear than wear on the face and crater, and that flank wear should be'investigated separately. It should be remembered, at this point, that flank wear is used as a parameter to determine tool life in industry, Excessive flank wear produces rough surfaces, and requires additional power for.a given cut.

Plank wear appears in the form of a land or wear area on the flank of the tool, this land not being uniform. Often, long grooves are found extending back from the wear

14

Length

Directionof

Cutting

Figure 2 .3--Typical wear lands on tool flank

land, complicating the problem of determining the length of the land in order to determine the wear on the tool. Nor­mally, the grooves are ignored as they will not cause gross failure of the tool, and the wear pattern is measured using the average length of the land. The grooves are an indica­tion that wear does not proceed in a uniform manner. Japa­nese investigators have concluded that the length of the extreme groove, divided by two, will produce the best wear land length to use in determining tool life, but western in­vestigators disagree, the latter disregarding any grooves (5).

Wear rates, difficult to determine, are definitely related with machining time as indicated on Figure 2.4 (12). The initial wear rate is large, taking place in the "wear- in" period. Subsequently, the wear rate decreases, and the curve for HSS tools is often concave downward in this region.

15

Toolwearrate

After a certain critical time period, wear proceeds in an accelerated manner, and if the tool is not reground, becomes catastrophic. This wear rate pattern is not accepted by all investigators (34, 5), but the differences probably could be resolved if all experimental conditions were standardized. The non-linear pattern of Figure 2.4 is the presently accepted concept.

The theories of dry friction are of primary interest to anyone studying wear of cutting tools as they furnish the basic explanation of flank wear. It has been shown that at surface speeds over 400 sfpm the use of cutting fluids or lubricants serves only to increase the temperature gradient

Highcuttingspeeds

Low cutting speeds

Length of cut

Figure 2.4--Correlation, wear rate and length of cut

: : . . , 16 In the outtlng ■tool, as the fluid, cannot penetrate Into the critical areas of the workpiece-tool-chip interfaces' (l4). Various Investigators hare arrived at different conclusions, concerning the causes.and results of dry friction, probably resulting from different surface preparations and different experimental methods. Bowden, working under laboratory conditions, has shown that chemically clean surfaces will weld on.contact, producing extremely high coefficients of friction when members of a,sliding pair (15). His experi­ments, carried out with contrdlied atmospheres, showed that the oxide films on the metal surfaces act as lubricants at low speeds. This has been confirmed by studies conducted by the National Advisory Committee for Aeronautics (16) anfl -others ( 1 7 \ ■. v . . .. . .. y ) ,: Friction is explained by Feng in the Journal of Applied Physics (l8) as the result of the interlocking of two deformed asperity surfaces. ' In this theory, the tips of the microscopic surface asperities that are present on any surface, no matter how fine a finish it might have, make contact. The small asperities are deformed as the normal load is increased, some asperities being deformed elastically, and others plasticallyo The interfaces of those asperities that are deformed plastically are roughened by the action of the slip planes and the interface becomes interlocked, as shown in Figure 2.5. ’ .

17

Figure 2.5--Interlocked asperities

Tangential forces applied to one of the members will cause one of the interlocked asperities to shear, the location of the shear plane being somewhat random. As the asperity shears, energy is released, sometimes visible as a blue flash, resulting in heat. This heat aids a diffusion and adhesion process at the interface, and if conditions are right, can cause welding of the surfaces.

If the heat is insufficient, the sheared portion is free and can interact with other asperities, causing addi­tional wear. These loose particles are believed by some to be the principal cause of accelerated and catastrophic wear. Feng’s theory states that the interlocked asperities may shear at the plane of the oxide film, resulting in no loss of metal by either of the sliding pair, and in a lower co­efficient of wear. If shear takes place at some other plane

18than the plane of the oxide film, no welding takes place because of the contamination of the surfaces in contact, and a free particle is produced. Welding will take place only if the normal force 'is sufficient to rupture and break the oxide film. High speeds can also cause the breakdown of the oxide film, and increased wear effects would be evident, ting and hucek (19) have shown that asperities do deform plastically and elastically, and that both welding and adhesion are involved in the wear process.

Krafft (20). has proposed, as a resuit of experimen­tal data, that friction at Very high speeds involves some melting at the sliding surfaces, He suggests that at high speeds heat transfer is reduced because of the length of time available for_ transfer, and that an adiabatic process takes place, The heat produced by the friction actually melts the tips of the surface asperities, producing a liquid film, and reducing friction. This theory minimizes the effects of surface films as the films would be molten prior to the time the metals melt. Using ballistic velocities, he found evidence of melting to a depth of 1,3 x 10“ cm (,0003 inches) when using A1SI 4340 steel as a target material. Similar melting was found in static tests when the AISI 4340 steel surface was held at a temperature of 1500° 0. for 24 microseconds. The projectiles Krafft used in his experiments were of harder material than the target

v>/-. ■ 19material, and also showed evidenee of melting after the surface contamination had been taken off by abrasion in the penetrating process.

Bowden and Bidler (21), as a result of experiments at moderate speeds, found that melting took place on the surface asperities of one member of a sliding pair, the melting being on the metal with the lowest melting point. Another investigation has shown that sulfide inclusions in metals tend to smear “ at certain critical speeds, reducing .friction by providing a certain amount of lubrication be­tween a sliding pair (22). These;experiments have all been performed in laboratory conditions, and indicate that any meItihg that takes place is confined to a very narrow sur­face layer. Bowden in commenting on a paper by Trent (33) stated that he had observed temperatures of 1832® P. on sliding metals at velocities of 3 meters per second, the duration of the temperature being less than 1 microsecond.

There is some doubt that oxide films are'present in the metal cutting process' as performed at ultra high velo­cities. Several of the recent qualitative analyses assume ; that the surfaces involved in friction' and Wear are chemi- ,• cally clean, with no oxide films or other contamination possible. Other analyses assume that a vacuum is not possible at the point of metal shear, and that some oxida­tion is inevitable. Owethrney. Smith, and Leidhauser (16)

Goncluded that the formation of an oxide film is dependent on the processes of diffusion and electron transfer. . Electron transfer. In turn,- is dependent on the electrical conductivity of the oxide film, and on the emission of elec­trons „ As with so many other theories of metal cutting, the basic facts cannot be determined at the present time with existing methods.

Flank wear, in addition to being influenced by tem­perature, is affected.by the abrasiveness of the workpiece material. Hard inclusions in the work, such as aluminum oxides, appear to cause the grooving seen in the typical flank wear pattern. Sther factors to be considered include vibrations, bulging, and thermal effects. Vibrations are very damaging to the carbide and ceramic tools, causing edge chipping and rapid failure. High Speed. Steel tools are less sensitive to vibrations and shock, and therefore can be used successfully for intermittent cutting operations.

Bulging of the tool has been found to occur as a result of high cutting forces and elevated temperatures. Gutting forces td-4,®Oi()©0 psi have been measured and tool temperatures of over 2000° F. are believed to exist under severe cutting.conditions. The tip of the tool is deformed elastically, and is then subject to additional wear. Ther­mal cracking has been found in HSS and carbide tools as a result of thermal shocks, but investigators believe that in

many cases, these cracks are "self iXealing.11 The self heailng" process occurs when continued heat causes migra­tions of atoms, closing the thermal cracks. Failures from thermal'cracking are rare In ESS tools.

The effect of .temperature on tool wear has been analyzed and has been found to be the dominant factor.One Investigator has computed that tool life. Is Inversely proportional to the 20th power of the'absolute temperature of the cutting edge (23). If this is so, a very small change In cutting edge temperature would have a drastic effect on tool life. It Is not surprising that the major oil companies of the United States spend millions of dollars annually in the development of coolants for the cutting tool industry I Trigger and Ohao have stated that with a. given tool-work pair, the temperature of the tool-chip interface is the governing factor in the rate of tool wear (24),Their results show the logarithm of the wear rate is propor­tional to the absolute interface temperature. Although . current investigators disagree on exact relationships be­tween tool life and temperature, all agree that temperature is important in all tool wear. . .

. Recent attempts to analyze the mechanics of metal cutting and tool wear show that there are many variables involved, many of which are in turn functions of temperature, Bisacre and lisaere, noted British engineers, list 14

V .: ' ; . ' ; _ ' • . . 22 ;variables affecting tool wear (25), while D„ C» Drucker and H. Ekstein list 16 variables affecting the cutting action, and these 16 do not include the additional variables necessary to analyze tool wear (26)„ Dr. Orowan (27) has stated that thermal diffusivity is an important, parameter in the metal cutting process, as this parameter is a measure of the ability of the tool and material to dissipate heat from the cutting edge and heat producing . areas„ In his analysis, he developed the following two .parameters t .

■= q , = ^a v *

in which u is the specific cutting force and A the cross sectional area of the chip prior to cutting. The term appearing in Qg is the reciprocal of thermal diffusivity, the same term as appears in Fourier1s equation for tempera­ture distribution in a body in the unsteady state,

3© _ Jk f 2>*6 . d 6 \dt ^Cp + + JIt should be noted that the product of the specific heat and the density appears in both of the Q, terms developed by Dr. Orowan. Tests conducted at Lockheed show that the re­lationship of the two terms, Q^and Qg, is a straight line with slope of .22 when plotted on double log paper. It can thus be, shown that the temperature is dependent on the quantity (/Pcp-4), and that temperature varies about as the

sqtiare root of tills term (28) „ Calculations by the author using Buckingham'sFi theorem reveal that thermal diffusi- vity appears in many of the developed parameters„ The vari­ables considered significant by investigators using dimensional analysis methods include i.

a. Densities of work and toolb. Thermal conductivity of work and tool c„ Cutting velocity

. d„ Specific heat of tool and work -e. Specific cutting force f . Area of contact ..

. ; go Hardness of tool and materialh. Yield stress of tool and work .i. Modulus of elasticity•J. Melting points of tool and work k. Tool geometry1. Coefficient of friction on tool-chip interface Unfortunately j, the results of dimensional analysis

cannot -be confirmed because of the difficulty of obtaining adequate experimental data, as mentioned earlief„f'Tempera­tures at critical points on the:topi are needed to verify the theories advanced regarding tool wear, but no process tried thus far has yielded satisfactory data .. Methods attempted have included the use of thermal sensitive paints, which show only the.surface temperatures, and which possess

a large delay time of reaction. Thermocouples have "been Imbedded In the tool, and In the work, but these are inher­ently Inaccurate because of. the size of the cavity required, ,and they further show only average values at the tool-chip or work interfaces. Radiation detectors using lead sulphide cells have been psed,, but again these .merely show surface conditions, and do not give accurate indications of tem­peratures at the cutting edge, which is not visible during the cutting actions Dr. V. Paschkis (29) has attempted to determine temperatures using an electric analogy, but the required simplifications make accuracy of the results doubt- . ful. Many investigators have attempted qualitative- analyses to find critical temperatures, ' bpt again, in order to make necessary mathematical manipulations, sweeping simplifications have had to be made, resulting in data that leave much to bedesired. Heat balance methods have peratures, showing neither maximums

resulted in average tern- nor distributions, both

essential for the understandlhg of tool wear. A number ofthe qualitative analyses involve the use of the 11 thermal

, ft ■ .number," , where V is cutting velocity, t is the thiok-' ' h ■■ .V. ■■■.ness of the chip before removal, and h^ is thermal diffus-

ivlty (30). The influence of the thermal number on toolwear has not been determined entirely and is a fertile fieldfor further work.

It is obvious that until further experimental data

are ©btaineci,, additional work on tool wear will consist largely of empirical work with tz»ial and error methods.For this reason, the United States Air Force authorisedlockheed.Aircraft Corporation to proceed in a very inter-' ' ' ' ' ■ ' ..esting experiment that has resulted in new tool wear data. This experiment provides the data that will be used in the remainder of this thesis.

CHAPTER III

, ^ V: $HEvW6KEira IXPlRllEMTSv /. E ., ; ;

lia 1958# as a r-esult of eertaih preliminary studies into the theories of plastic deformation, the United States Air Force awarded the Lockheed.Aircraft Corporation a con­tract to determine the feasibility of Tnachining high strength materials at high speeds. The stated objective was: : ' V ; ' : ,

’■to 'investigate and determine the feasibility of utilizing ultra high speed machining in the approxi­mate range of 30,000 to 50,000 plus surface feet per minute, to the newer high strength thermal resistant materials, which will be used in the design, fabrica­tion and construction of the advanced types of weapon systems under development for the Air Force," (28)

Previous, .'Studies had indicated that each material has a critical velocity in impact, which, if exceeded, will cause the material to fall in a brittle manner under tension. It had been concluded that if the brittle fracture fange did exist, it would be possible to change the normal relation­ships in the machining process by exceeding the critical ' velocity. Further, the rates of temperature rise and tool wear found at normal cutting speeds would change.

The Lockheed study was conducted using a gun-type accelerating device and a fixed tool. The workpiece was,,

■ . ■ • , ' .. 27in fact» a projectile^ shot f3?©m a modified gun barrel, past the. tool^ into a target. The apparatus was so ar­ranged, tha-t the tool would take a given cut on the work­piece, and all applicable parameters could be measured and recorded. All the experimental work was performed "at the Lockheed Missile and.Space Bivision’s Santa-Gruzfest Base, California. ' . '’ ' '

, ;• The gun-type device was chosen as it appeared to bethe best device that could efficiently and economicallyimpart the hecessary high ivelQCities to the projectiles.The gun barrel was a 20mm cannon barrel bored to .855— .866 inches, thereby removing the lands. Rotation was not desired as rifling marks would have hampered the examination of spent projectiles. Both ends of the barrel were modified in order to mate with special muzzle and breech mechanisms. The chamber of the barrel was re-machined to provide for the special projectiles used/

The breech device was a single shot device, con­taining a firing pin driven by a squib assembly. The basic block was made of AISI 4130 steel, with extra heavy walls to permit the firing of projectiles with the relatively large; propelling charges necessary to achieve the high velo­cities desired in the study.

, The muzzle fixture consisted of a heavy extension to the barrel and provided a mounting platform for the tool•

. ; ■ . asand the test instrumentation. Machined from AISI 4130 steel, the fixture was approximately 3 inches in diameter and 8 inches long„ k flat was milled on the top for the tool holder> and holes were drilled radially to receive the con­tactors that were to provide the timing signals„ A small hole, | inch in diameter, was drilled horizontally through the fixture, providing a "window" through which the actual cutting action could be photographed, 3he fixture was bored out to match the bore of the barrel and thus provided a guide for the projectile during the cutting action, pre- . venting deflection of the projectile, ' The fixture was press fitted onto the barrel and the bores were checked to insure ■ concentricity.

Glutting tools for the study were various commercial type tools, although the High Speed Steel tools of SAE T-8 cpmposit ion'.were used for the majority of the tests. These tools contain the following alloying elements:

14 fo Tungsten4 . fo Chromium# # Vanadium5 fo Cobalt

Carbon„7f> Molybdenum

Balance IronSAE T-8 cutting tools are recommended for intermittent cutting of tough, abrasive, materials at high temperatures (32). Other types of tobla were" used (Carbide's and Stel- lltes), but were used in so few shots that insufficient

information is available for analysis. . The tools wereground with a 0° back rake angle and a 5° end relief angle.In order to assure standard test conditions, new. tools wereutilized for each shot.

The workpieces, or projectiles, were made from fivedifferent high strength, heat resistant metals, but again,only one metal, M S T 4340.steel, was tested sufficiently toprovide adequate data. All workpieces were from the sameheat, and had the following compositiont

.4 % Carbon 1,8 % Hickel .8 % Chromium .7 # Manganese .3 # gilioon .230 Molybdenum _

The workpieces were cylindrical in shape and varied in length from 1.5 to 6 Inches, the variation being necessary to achieve the range of velocities desired in the study. . In eertain eases, wdrkpieces were partially drilled out to lessen Weight, and in all cases, projectiles had a circulargroove turned in the blind end. This groove was used toseat a plastic "0 ring” that acted primarily as a ’gas seal.The ring had a copper wire helix wound around it to provideelectrical contact with the barrel and the contactors pro­truding into the barrel. By replacing the "0 ring,11 the projectile could be used in subsequent shots. .Workpieces used in the tests were selected to provide the maximum pos­sible length of cut arid yet attain the required velocities.

, . ■ ' - • ' ' ; ' • - - . : ' . • 30. •Data used in this thesis were obtained using drilled out projectiles„ tapered on the leading end to lessen Impact effects on the tools« Both propellent charges and pro­jectile weights were varied to obtain a spread of veloci­ties. Projectiles were.fired Into bunkers filled with soft materials, enabling test personnel to recover the undamaged projectiles quickly„ provisions were also made to recover the chips for detailed study „ ■.

The most difficult part of the test setup was the instrumentation required to obtain data for evaluation and analysis. Velocities were measured using the pin contactors in the muzzle fixture and break wires beyond the muzzle fixture The pin contact or s were actually the mechanisms from finellne mechanical pencils which were inserted into ' insulated.holders in the muzzle fixture. The leads were extended into the barrel and-were contacted by the projectile.' as it passed through the muzzle fixture, making electrical contact . . The use of the pencil mechanisms assisted in the preparation of subsequent tests as,the leads merely had to be screwed'out further'after each shot, Photographic coverage of the tests was provided using the contactors in. the muzzle fixture for timing purposes', and using the "win- ’ dow" in the muzzle fixture to photograph the actual cutting action. & high speed camera capable of taking 22,000 pic­tures per second was used to obtain timed Sequences, from r

which chip velocities were computed„ Pictures obtained, clearly show the cutting action from the time of original

. tool-projectile contact to the time when the projectile passed the tool and. the propelling gases clouded the window. Projectiles were fired through the barrel in a,M r y " condition after it was found that barrel lubricants were responsible for erratic operation of timing devices.

Several different types of tool holders were utilized in the early stages of the Lockheed study, from which two types were finally refined and used. The Model 0 tool holder was a rigid holder, made from heavy structural parts, not capable of being instrumented for force measurements.This holder provided a groove for the unhampered escape of the chips and wire connections for the use of thermocouples on the •cutting tool. It was engineered to eliminate excess tool overhang so as to minimize deflection and cantilever action of the tool when struck: Initially by the workpiece.The tool was inserted vertically and was adjusted for a cutting depth of .025 inches. The Model D tool holder, used in many of the tests, was an instrumented tool holder, equipped with strain gages to'measure horizontal and verti­cal forces on the tool. With this tool holder, the tool was wedged into place and was on an angle of 6o°, although the tools were ground to maintain, the standard 0° back rake angle and 5° relief angle. Both the tool holders. Models C

and D, were carefully calibrated using a standard compression test machine. Both holders were engineered to Insure mini­mum cantilever action and uniform results when subject to like' pressures, .with, the result that data obtained from

. tests with the Model 0 tool holder can be compared and ana­lyzed with the data from the Model 6,

Exact temperature measurements were not obtained because of the difficulty of attaching thermocouples at the cutting edge of the tool, Attempts were made to attach thermocouple materials to the tool'by plating and through the.use of epoxy cements, but the final results in both cases were failures. Temperature measurements were finally obtained on the, f lank ofvthe tool, at distances of 3/16 and 1/4 inch from the cutting edge, by welding thermocouples to the flank,; The wires 'oh the tool were coated with, a By sol epoxy to insulate the wires and protect them from the pro­pellent gases, ' ''/ I I-V

The propellents used in the tests were loaded into standard 20 mm cartridge cases, which were in turn assembled with the projectiles, producing the equivalent of a round of ammunition. At the higher velocities, propellent charges were too large to fit into the standard cartridge cases, and cardboard extensions were provided between the cartridge case and the projectile, •.

A total of.2lS shots were fired in. the course of the

Lockheed study, 211 of them using AISI 4340 projectiles with SA1 T-S•HSS tools„ The remainder of the shots used a variety of other "space ageM metals. Including titanium, magnesium, aluminum, and nickel alloys. In these latter tests, tool materials were varied, as well as tool geometry Bata obtained from the tests which used AISI ,43 0 projec­tiles are listed on Tables I through IV,

The limitations, of the Lockheed experiments must be realized before an worthwhile analyisis is made using, the,reported data, Because of the very nature of the shots the depth of cut for each run was fixed, but could not be adjusted to close tolerances. It should be noticed that the depth of cut for each shot varied considerably, and the resulting weight of metal removed also varied, the latter being a function of the depth of cut, All the cuts made during the experiments were cuts involving only a portion of the width of the tool edge, with no side effects on the tool as such. This is a somewhat different type of cut than found in the normal mabhlnlng process. Only data obtained from 6 inch workpieces are reported in this thesis as the longer projectiles were least affected by impact. Velocities reported in the results are, in fact, average . velocities and not necessarily the exact velocity at the time of the cuttihg action. No data are available on the change of velocity during the actual cutting process.

34although personnel conducting the experiments reported that the change was less than 5 feet per second. In view of the rather large velocities involved, this change would have a negligible effect and can be disregarded.

In making their conclusions, the engineers at Lock­heed have used what they term "effective wear" as a criteria for tool wear.

7Face wear

j Eff.

Figure 3.1--Effective wear

This is not, as previously explained, the industrial stand­ard for tool wear, and the results must be adjusted accord­ingly. It may be that the present industrial wear standard is fallacious at ultra high speeds, but any discussion of this is outside the scope of this thesis.

Bart__I Flank

wear

CHAPTER IV

AHALYSiS AND CORRELATION

The'only results of the Lockheed experiments that will be.considered In this chapter are those resulting from the heat treated AISl4340 steel projectiles used In con­junction with SAl T-S HSS tools, ' Both the Model. C and the 'Model B tool holders were used during these tests, -and '. although some differences in'the results were noticed, the significant results using the two tool holders appear to be

: in general agreement. The heat treated projectiles, as opposed to annealed projectiles, were chosen for analysis as more data were avaiiabie concerning the heat'treated projectiles.,. Further, the normal cutting problems are more difficult when using heat treated steels than when using

' annealed steels„ ; - . & V- 1 -'A A". , ' . ' ■'As predicted, tool wear was definitely affected as

cutting velocities.were increased (Tables l;and II), The change was not, however, what could be easily expected from low speed experiences. In the velocity range of 500 to 2000sfps, flank wear decreased until a critical velocity ofabout 1900 sfps was reached, when flank wear apparently

... began to increase, The least amount of flank wear occurred

when the projectiles were machined at velocities of approxi­mately 1900 sfps, fhese trends are particularly evident with the results from the Model 0 (rigid) tool holders (Figure 4.1). The trend of flank wear is seen in Figures 4«2 and 4„3 as reported by the Lockheed Corporation.

As the tolerances in the test apparatus were such as to allow the amount of metal removed per shot to vary, the use of flank wear alone as a.parameter is misleading. Some indication of the amount of metal removed, depth of cut, or metal removal rate is necessary to give a true pic­ture of the wear process and the correlation with process parameters. For this reason!, flank wear is plotted on the various graphs in this chapter in conjunction with some other parameter indibatihg a measure of the,metal removed.The use of this type of parameter already has been seen in Figure 4.1. '

Thermal cracking was apparent on the tools when the shorter projectiles were fired at the higher velocities.These short projectiles had not been tapered, but after several failures, were modified,. A short taper, turned on the leading end of the projectiles, was sufficient to elimi­nate cracking due- to impact, although thermal cracking was not affected and was still visible. Thermal cracking was not apparent with the longer 6 inch projectiles, lending credence to the theory that thermal cracks are "self healing.

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38It is believed that the additional time at elevated tempera­tures afforded by the longer projectiles was sufficient to promote 'self healing.” Thermal cracking did not cause tool failure during any of the tests.

s-Flank wear 4 ■

Wt. of metal removed 3'inches/ x 10-2 2 -/gram

/ 1 1 &—/ooo Zooo 3 0 0 0

Cutting velocity (feet per second)

Figure 4.2--Correlation, flank wear and cutting velocity

Forces on the tools were measured using the instru­mented Model D tool holder and the results are tabulated on Table III. Plots of the average horizontal and vertical forces with flank wear per gram of metal removed are not indicative of close correlations between forces and flank wear (Figures 4.4 and 4.5). The horizontal force appears to increase as flank wear per gram decreases, but the avail­able data are insufficient for accurate analysis. It must

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C orrelation , Flank Wear and V elo c ity

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42be remembered that the forces involved in the cutting process are used primarily to overcome the resistance of the metal to shear and to friction at the tool-chlp interface. Forces required to overcome the friction at the tool flank are minor forces compared to those required and found at the shear zone and the tool-chip interface.

Temperature has been reported to be the dominant factor in tool life, and thus some correlation should be evident between temperature and tool wear. The temperatures used in Figures 4.6 and 4.7 are the peak temperatures on the tool flank, 3/l6ths of an inch behind the original cutting edge. As discussed before, the values reported are average values for a certain area of the flank, and should be considered as “indicators” of true tool temperatures, not as exact temperature measurements at a specific point. A straight plot of temperature with flank wear shows nothing of real significance, although from a plot of temperature and velocity we can obtain some correlation. A graph of this type. Figure 4.6, indicates that temperature increases as velocity increases, reaching an apparent peak when the cutting velocity is approximately 2000 sfps. The importance of this peak temperature will be indicated later. The re­lationship between temperature and the flank wear per gram of metal removed is shown on Figure 4.7. It is obvious from the graph that the peak temperatures will rise if flank

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45wear is decreased.

Using only that data obtained when using 6 inch projectiles. Figure 4.8 indicates the excellent correlation obtained between flank wear per gram of metal removed and cutting velocity. Using the quadrant sum test for correla­tion, a confidence level of over 99% is obtained (Figure 4.9).

Surfaces of expended workpieces and tools were examined by metallurgists at Lockheed for evidence of metal­lurgical changes. Results of these examinations indicated that some changes in hardness and phase had taken place on both the flank surfaces of the tools and the machined sur­faces of the workpieces. All workpieces showed evidence of surface and subsurface heating, indicated by partial trans­formation of the metal to slightly tempered or untempered martensite. These transformations increased as velocities increased, reaching a maximum at velocities of about 2400 sfps. A depth of less than .005 inches was involved, and gross melting was not observed. For these transformations to have taken place, temperatures greater than 1515 F., the critical temperature for steel, must have been present. Melting would have required temperatures of at least 2700° F.

Tools showed metallurgical changes to a depth of less than .0002 inches. The same type of transformations occurred in the tools as occurred in the surface of the work­piece, in addition to evidence of partial solution of

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48of carbides. Tool hardness was not significantly affected.

If flank wear had occurred In accordance with the theories of dry friction as presented in Chapter II, the results should show that flank wear increased rapidly as the velocity was increased. The high velocities would have caused the surface asperities to weld: together as only chemically clean surfaces were involved. According to friction theory, the[clean surfaces would cause large in­creases in the surface friction coefficient and flank wear.If the critical impact theory is considered, one might rationalize that the asperities struck each other with such high velocities that they were sheared off in a brittle manner, producing free particles, in turn causing additional wear. The only theory that can explain the REDUCED wear is Krafft's melting theory, in which melting takes place, on the tips of- the asperities. This melting would aid the reduction of wear by providing a film of molten mdtal which would act as a lubricant between the sliding members.

If-this.theory is to be confirmed, the results of the Lockheed experiments should provide data to fit the theory. Using data from Figure 4.4, the temperature reached a maximum at about 1900 sfps, the velocity at which flank wear per gram of removed metal is reported to be the lowest (Figures 4.2 and 4.3). It can be postulated, then, that at approximately 1900 sfps, the melting of the asperities is

; . _ 49at the maximum for minimum friction and tool wear. Figure 4.7 confirms that temperature.Eincreases as flank wear decreases. Figure 4.2 shows that at 1900 sfps,■when the temperature is the highest, the flank wear per gram is the lowest 1,. ,■ v;: •-' ■ : ' ; I . . -

• It should be noted that there are serious short­comings to the ultra high speed process. Flank wear, at best,'- is extremely severe when it is remembered that present standards consider a tool worn out if the flank wear reaches .060 inches. This wear was exceeded, in the majority of eases, after the tool had been in contact with the work less than 6 inches. By present standards, this is catastrophic wear.

GOHeyjSlOMS ‘

It has been shown that machining at ultra high speeds is entirely possible> if not practical, and that favorable tool wear trends exist in at least one velocity range. Temperatures did not decrease as predicted by Salomon, although no evidence was found that, temperatures would rise indefinitely„ The flank wear data have confirmed that the theories advanced for flank wear at low velocities cannot be extrapolated blindly into the ultra high speed range. The dry friction theories apparently do not extend into this area, and the melting theory advanced by Bowden and ICrafft seems ,to be correct»- The evidence that tempera­tures are still rising in the 500-2000 sfps range assists in explaining why flank wear decreases and reinforces the theory that the surface asperities of both metals are molten at ultra high velocities,

Plank wear is definitely affected by temperature, as found at the lower velocities^ although the temperatures at the ultra high velocities act in the opposite manner than they do at low velocities. At the high velocities, the high temperatures appear to aid in the reduction of flank

wear, rather than the increase of wear,■as at low velocities.Definite, critical temperatures can be found for the

topi-work;pair studied in this theSis„ Changes in the rate .' offlank wear are found at approximately 500 sips and 2000 sfps. These critical velocities have not been examined closely and no explanation is offered for their existence„

Correlation studies indicate that flank wear at ultra high velocities is closely related to velocity, temperature, and some parameter indicative of the amount of metal removed.

lieSElNBAflSMS FOR ITOTHEH STEET

She ultra high speed machining process has provided data indicating that much is yet to be learned about the basic machining processes and cutting actions„ ■ Tool wear in general is a field of study that needs.further research in order to obtain full utilisation from present and future machines and tools„ - The research performed in the course of preparing this thesis uncovered■numerous areas of study that have been neglected and that'.could be profitably examined . ' . \

■ The following specific areas are recommended for v further study and examinations

a.l The use of compensating currents to reduce tool ' - wear .1 - . ' , ■" b . The influence of atmospheric contamination on

; c. The effect of sliding friction on flank wear,d . The existence df. asperity melting as described

by Krafft when machining at conventional speeds.e . . The'' detefmination of a criteria - Pf tool life to '

V i■ use at the ultra high speeds. -\

; ■: .■ ■ ■ : \ ■. : ^ - 53. f,, The postmlation of dry wear theories applicable

to the cutting process and topi wear, g , The determination of actual tool temperatures

using analog computer methods

TABLE IWEAR MEASUREMENTS WITH MOSEL 0 TOOL HOLDER

TestNo,

Velo­city (sfpm)

Wt, ofMetal

Removed(grams)

DepthofOut(in.)

FaceWear(in.)

FlankWear(in.)

Effec­tiveWear(in.)

6”; Heat Treated AISI 4340 Projectiles, Model 6 Tool Holder

102 437 .63 .015 .026 . 121 .010103 437 .63 .015 .028 .133 .006104 469 .72 .015 ,055 . . 145 .006126 472 .53 .010 .035 ,150 .016178 957 .36 .011 .25 .145 .015109 990 .64 .014 .30 .125115 1623 . 1.02 .015 ,037 , 110 ,0086116 1652 .79 .014 ,033 _ .115 .010124 1975 I.08 . 016 .048 ,105 ,0083120 2160 \i.i6 \'":' ',.0.16 .-:. ,, f :.052 ' ,107 .009

12 11 ■ ? D ; 2 •Seat Treated A1SIv4340 Projectiles, Model © Tool Holder

144 ; 1593 185 .Oil .043 ,060 .005180 1 1993 .84. ,016 .050 ,1.15 ,003145 -2033 .47 .011 .035 ,141 .013179 2047 .48 .. .013 .052 .100 .010147 2715 .50 o-- ,014 .058 .100 .007183 2727 : .32 .005 .175 .015

aTJltn?a High Speed Machining Test Bata, Lockheed Aircraft Corporation, extracted from AM© Tech Report 60-7-635(1).. .

v ': ' f I B I S I I ' .' ' ' '

WEAR MEASUREMENTS WITH MODEL D TOOL HOLDER3-

Test No. .

Velo­city(sfpm)

Wt. of Metal

Removed (grams)

Depth of Cut (in.)

PaceWear(in.)_

Flank Wear (in.)

Effec­tiveWear(in.)

6”, Heat Treated AISI 4340 Projectiles, Model. D Tool Holder

155 3S9 .34 .005 .055 .127 . . 018134 ’ 466 .62 .010 .048 .123 .025133 474 : ' .49 .010 .045 . 122 ,023136 . 991 .80 .020 .040 .141 .010156 IO44 .47 .015 .048 . 127 .013138 1536 .56 .017 .042 .130 .010140 ' 1933 .73 .017 .053 . 125 .008

3 % Heat Treated AISI: 4340 Project1les. Model D Tool Holder

174 1104 > .30 .018 .040 .090 .010169 ; 11637 V;>; >64'.-'' ; . .018 .040 .083 .007 .148 1532 :7 '' .94 7 .020 .053 .058 .005150 1961 .99 .022 .056 .070 . 008173 1942 .80 .020 .053 ,058 .005168 2089 ; .42 .011 .052 .117 .015153 2705 .89 .018 .071 .128 .007157 2920 .82 .019 .072 .125 .008

aUltra High Speed Machining Test Data, Lockheed Aircraft Corporation, extracted from AMO Tech Report60-7-635(1).

W f H M FORGE MEASUREMENTS3,

Test Velo- Gutting Forcesj, pounds FlankNO. cxry

(sfpm) Vertical Horizontal wear(in.)

Av. Peak Av. Peak

155 329 • 5300 7300 660 3200 .127134 466 5316 8793 ; 2884 5243 • .123136 991 7510 12991 4052 7150 .141156 1044 , 6400 IO634 5975 6700 .127138 1536 4796 12421 1595 3850 .130140 1935 ; 7647 I556I . 5400 9448 . .125

174 T" ; 1104 3866 7200 1854 306o .090169' 7 1163 . 1700 2700 1083148 . . ■ 1532,, 7300 2600 38OO O Ml GO

173 1942 3640 v 5120' - 1153 2600 00S

150 . 1961 4400 6700 1500 2700 .070168 2089 .v .117153 - 2705 v; 38 b© 7300 / 3900 8200 .128157 2920 1900 3200 .125

aUltra High Speed Eaehining Test Bata, Lockheed Aircraft Corporation, extracted from AMC Tech Report 60-7-635(1). (Note;.Above data obtained from an oscillo­scope) . '

TMMM IV 'TEMPERATURE MEASUREMENTS3-

TestNo.

Velo­city

Temperature3/16 in. from Cutting Edge .

measurements^ in. from Cutting Edge

Flank Wear (in.)

Time(milii-sec.)

PeakTemp.m . )

Time PeakTemp.

156 1044 . 10 113 18 105 .127140 1935 10 117. 13 113 .125

174 1104 21 ■ ■ 86 19.5 92.7 .090169 1163 13 99.1 33 83,6 .083148 A Tib;,,':'•:>/27 7', 101 . .058173 ' 1942 . 4 , 128.2 119.3 G

O8

150 1961 ; 117 20 105 .070168 . .. 2089 95.5 2.5 ;180C' .117153 2705 ; :; 'io 119 . 10 83 .128157 2920 18 92 28 105 .125

aUltra High Speed Machining Test Data, Lockheed Aircraft Corporation* extracted from AMO Tech Report 60-7-635(1). . :

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