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Rapid machining of hardened AISI H13 and D2 moulds,dies and press tools

Helen Coldwell, Richard Woods, Martin Paul,Philip Koshy, Richard Dewes*, David Aspinwall

School of Engineering Mechanical and Manufacturing Engineering/IRC in Materials Processing,

The University of Birmingham, Edgbaston, Birmingham B15 2TT, UK

Abstract

Tools and dies for the forging, die casting and plastics moulding industries are commonly made from AISI H13, heat treated to 4852 HRC,while the press tool sector predominantly uses AISI D2 at a significantly higher hardness of 6062 HRC. Over the last 10 years, the

introduction of high speed end milling has enabled the direct manufacture of prismatic components in the hardened state. The paper briefly

outlines such techniques and details published machinability data. Following on from this, experimental work is presented on the drilling of

hardened AISI H13 using carbide tooling, together with research on ancillary drilling and tapping operations on hardened AISI D2. When

through drilling AISI H13, it was possible to produce up to 210 holes (16 mm deep), with a cutting speed of 30 m/min and a feed rate of

0.1 mm/rev. Drilling data arealso presented on the use of water-based electrical dischargemachining (EDM) dielectric fluids as a replacement

for a conventional soluble oil cutting fluid to allow hybrid HSM/EDM on one machine tool. When drilling and tapping D2, tool life was low

with six and nine holes, respectively. Finally, case study work is detailed, relating to the production of AISI D2 automotive press tool parts, in

which traditional manufacture is compared with high speed machining (HSM) techniques, using both indexable and solid coated carbide

cutting tools. When producing accurate radii on one component, the manufacturing time was cut by 75% using the HSM approach, despite the

relatively poor tool life performance detailed above.

# 2002 Elsevier Science B.V. All rights reserved.

Keywords: Rapid machining; Moulds; Press tools; High speed milling; Drilling; Tapping; EDM/HSM

1. Introduction

High speed machining (HSM) or high speed cutting

(HSC) is usually associated with end milling at high rota-

tional speeds between 10,000 and 100,000 rpm. It has been

applied to a range of applications in the aerospace industry,

originally for the machining of aluminium alloys and more

recently titanium alloys and nickel-based superalloys [1,2].

HSM has also been employed in the machining of the

copper/graphite electrodes used in electrical discharge

machining (EDM). Over the last decade, HSM has increas-

ingly been used to manufacture moulds/dies made from

hardened tool steels such as AISI H13, P20 and D2, for

the production of a wide range of automotive and electronic

components. HSM compares extremely favourably with the

traditional mould/die-manufacturing route which entails

milling the workpiece in the annealed state, heat treatment

to in-service hardness, EDM, grinding and hand finishing

[3]. In order to fully realise the potential of HSM, however,

other machining operations such as drilling, tapping and

reaming need to be addressed.

The UK mould, die and press tool industry is characterised

by large numbers of small companies employing highly

skilled designersand toolmakers. In the past,it has maintained

its market share by producing products of high quality,

however, with increasing imports from countries such as

Japan (81% of UK press tool imports in 1999 [4]), theindustry

is under pressure to compete on price and lead time. One way

in which it is addressing these issues is by adopting HSM.

Benefits with this approach include significant cost/lead time

reduction (a product manufactured using the traditional route

can take over 20 weeks [5]), through the elimination of

multipleprocesses includinghand finishing.Quality improve-

ments stemming from better component dimensional accu-

racy/surface roughness/surface integrity and the elimination

of distortion due to heat treatment are additional factors.

A wide range of tool steels are employed to produce

machined moulds and dies [69]. In forging and die casting,

Journal of Materials Processing Technology 135 (2003) 301311

* Corresponding author. Tel.: 44-121-414-3541;fax: 44-121-414-3958.E-mail address: [email protected] (R. Dewes).

0924-0136/02/$ see front matter # 2002 Elsevier Science B.V. All rights reserved.

PII: S 0 9 2 4 - 0 1 3 6 ( 0 2 ) 0 0 8 6 1 - 0


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the choice is generally hot work tool steels (AISI Group H

series) which can withstand the relatively high working

temperatures involved, typically 315650 8C. These include

chromium-based (e.g. AISI H13) and tungsten-based (e.g.

AISI H21) compositions. Some alloy steels are also utilised.

Forging dies are mainly employed at a hardness of 4556

HRC, while plastics moulds for thermoplastics and thermo-sets are typically made from cold work tool steels including

AISI P20, AISI P6, AISI O1 (oil hardening) and AISI S7

(shock resisting). Tool steels conforming to AISI Group D

are widely used in the manufacture of blanking and cold-

forming dies and in-service hardness for such steels is in the

range 5862 HRC [10].

In previous studies comparing traditional manufacture

with HSM techniques [11,12] it has been reported that

mould, die and press tool components typically range in

overall size from 60 to 500 mm. Components comprise

critical features such as: internal radii down to 1 mm;

external radii down to 4 mm; and M6M12 tapped holes.

The studies also highlighted the use of processes including

drilling, tapping, reaming, grinding, milling (edge profiling,

cavity production and graphite electrode production), EDM

(die sinking, small hole drilling and wire), hand polishing

and vacuum hardening. Typical values for component sur-

face roughness and dimensional accuracy of 15 mm Ra and

550 mm, respectively, have also been reported [13].

2. Literature survey

An extensive body of literature exists on the HSM of

hardened steels, comprising aspects such as operatingparameters, tool life and workpiece surface roughness. This

has been reviewed comprehensively in [3,14], in which

much of the literature relates to AISI H13 hot work tool

steel. In contrast, there is only limited published infor-

mation available on the machinability of AISI D2 cold

work tool steel, despite its extensive use for cold forming

operations.

Polycrystalline cubic boron nitride (PCBN) has been

used successfully to face mill hot work tool steel AISI

H13 (4850 HRC) at cutting speeds between 100 and

200 m/min, with a feed of 0.1 mm/tooth and 1.0 mm depth

of cut [15]. In addition, it has been shown that at a cutting

speed of 180 m/min, a feed of 0.2 mm/tooth and 1.0 mm

depth of cut, PCBN can be used effectively to face mill coldwork tool steel (60 HRC) [16,17]. More recently, PCBN face

milling work on AISI H13 ($52 HRC) and D2 ($58 HRC)has been conducted [10,18]. In the work reported by Koshy

et al., direct comparisons between results are not possible due

to differences in the mode of operation and the radial depth of

cut employed, however, for AISI H13, the volume of material

removed was 120 cm3 compared with 40 cm3 for AISI D2.

The range of tool materials utilised for ball nose end

milling encompasses cermets (ceramic metal composites),

PCBN and limited use of conventional ceramics (silicon

nitride and whisker reinforced alumina), however, coated

cemented carbide tools predominate [1925]. The majority

of carbide cutters are solid, although indexable insert pro-

ducts are also employed [25]. The advantages of the former

include higher accuracy and tool life (in some cases,

>1000 m cut length when machining hardened AISI H13

[20]), however, the purchase price of such tools can be high

(an 8 mm diameter coated carbide ball nose end mill can cost

60120). In contrast, even complex indexable inserts can

be purchased at significantly lower cost (


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Drilling has been reported by Konig et al. [26] and Konig

and Hoff [27] where PCBN was used to drill 32 mm

diameter holes in AISI D2 with a hardness of 60 HRC. A

cutting speed of 100 m/min and feed rates of 0.012

0.025 mm/rev were employed. Further work published by

Konig et al. [28,29] identified the use of a similar drill to

machine a range of ferrous alloys hardened to$62 HRC at acutting speed of 200 m/min and a feed rate of 0.02 mm/rev.

Cutting lengths of 100 mm for AISI A2, 50 mm for AISI D3

and 20 mm for high speed steel AISI M2 were achieved.

Drills made from coated tungsten carbide have also been

used successfully to machine hardened steels. Arai et al. [30]

experimented with cutting fluid supply when drilling 6 mm

diameter holes 30 mm deep in JIS SKD 11 (AISI D2)

hardened to 46 HRC. Usingconventional low pressure cutting

fluid supply, the flank wear after 10 holes was approximately

0.06 mm, however, somewhat surprisingly a higher level of

wear (0.2 mm) was recorded when using high pressure

(7 MPa/$70 bar) fluid. The use of 10 mm diameter TiAlNcoated carbide drills for machining JIS SKD 61 (AISI H13)

hardened to 52 HRC has also been reported [31]. On average,

over 65 blind holes (20 mm deep) could be produced before

drill replacement was necessary. When drilling Ck 45 (AISI

1045) tempered steel at a cutting speed of 80 m/min anda feed

rate of 0.16 mm/rev, TiAlN coated carbide drills achieved

better results than cermet or uncoated carbide products [32].

With surface hardened steel workpieces, carbide tipped

drills (employing high speed steel shanks) were reported to

give tool lives of 1.1 M and 1.0 M for 16MnCr5E(AISI 5117)

and 31CrMo12 workpiece materials, respectively [28].

Tapping is regarded as one of the most difficult machining

operations. Literature available on the tapping of hardenedsteels is extremely limited, however, a number of cutting

tool manufacturers have recently provided details of TiCN

coated carbide taps which they suggest are suitable for tool

steels hardened to 4963 HRC [3335]. Cutting speeds

range from 3 to 5 m/min and quoted tool life is typically

530 holes, depending on hole diameter and depth.

3. Experimental work

The aim of the present work was to assess the drilling and

tapping of AISI D2 and H13 with carbide cutting tools, in

terms of tool life, workpiece quality, productivity and costs.

A secondary aim was to assess the performance of a number

of water-based dielectric fluids, intended primarily for EDM

operations, against a standard soluble oil cutting fluid, in

order to assess the feasibility of a duplex machining arrange-

ment involving HSM and EDM on one machine tool [36]. In

addition, a number of demonstration components were

produced in hardened AISI D2 employing HSM techniques.

These were partly EDM wire machined and then completed

using HSM techniques, instead of traditional manufacturing

operations involving machining in the annealed condition,

grinding and hand polishing.

3.1. Equipment, cutting tools, workpiece materials

and methodology

3.1.1. Drilling of AISI H13

Drilling tests were carried out in two phases. Phase 1

employed a Matsuura FX-5 vertical HSM centre with a

continuously variable spindle speed of 20020,000 rpm, amaximum spindle power of 15 kW and feed rates of up to

15 m/min, phase 2 tests were conducted on a Bridgeport

VMC1000 vertical machining centre with a maximum

spindle speed of 10,000 rpm, a power output of 11 kW

and feed rates of up to 12 m/min. In all tests, the maximum

flank wear and/or chipping on the flank face was measured

using a CCD video microscope equipped with an XY table

employing Mitutoyo digital micrometers. A Somicronic

Surfascan-3D machine was used to measure the surface

roughness of the holes and a Mitutoyo 3-point micrometer

was employed to assess hole size. Roundness and cylindri-

city were measured using a Taylor Hobson Talyrond 300.

In phase 1 tests, cutting force and torque were measured

using a Kistler type 9273 drilling dynamometer and asso-

ciated charge amplifiers connected to a Gould two-channel

oscilloscope.

All tests employed commercial 8 mm stub length AlTiN

coated solid micrograin carbide drills with a 1358 point

angle and 308 helix angle. Through holes were drilled to a

depth of 16 mm. Swarf packing did not occur, therefore,

pecking was not adopted. Cutting fluid (water-soluble oil at

5% by volume) was applied at a pressure of 70 bar and a flow

rate of 17 l/min via two external nozzles directed down the

flutes of the drill. The workpiece consisted of 16 mm thick

discs, which had been EDM wire cut from a bar of AISI H13hardened to 5455 HRC.

Phase 1 investigated the effect of varying cutting speed

and feed rate, the test matrix is given in Table 2. Tests were

stopped when the maximum flank wear/chipping on the drill

reached 0.3 mm or when breakage occurred. As far as

possible, thrust force and torque were measured for the first,

middle (0.15 mm flank wear) and last hole, together with

corresponding workpiece Ra. Sample measurements were

made of hole cylindricity and out-of-roundness. Using the

parameters established in phase 1 that yielded the longest

tool life (in terms of length cut, i.e. cutting speed of 30 m/

min and feed rate of 0.1 mm/rev), phase 2 tests were under-

taken to compare the performance of a standard water-

soluble oil cutting fluid, coded A (at 5% by volume), with

Table 2

Phase 1 test matrix

Cutting speed (m/min) F eed rate (mm/rev)

0.1 0.2

20 @ @ @

30 @ @@

45 @ @@

@ One test performed.

H. Coldwell et al. / Journal of Materials Processing Technology 135 (2003) 301311 303


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three other water-based fluids, principally intended for use

as EDM dielectrics: these were coded B, C and D. Com-

mercial considerations preclude disclosure of the actual

fluids. Each test was performed either two or three times

in order to gauge process variability, whilst hole diameter,

surface roughness, cylindricity and out-of-roundness was

measured for the first and last holes.

3.1.2. Drilling and tapping of AISI D2

Limited tests were conducted to establish tool life when

drilling and tapping hardened AISI D2 (60 HRC) as a

precursor to industrial use. Drilling tests were carried out

on a Mori Seiki SV-500 vertical machining centre, with a

maximum spindle speed of 20,000 rpm, a power output of

18.5 kW and feed rates of up to 16 m/min. The machine was

equipped with through-the-tool cutting fluid application.

Tapping tests were conducted on the previously mentioned

Bridgeport VMC1000.

Solid carbide drills (short and long series) with diameters

of 6.87.0 mm and a multilayer TiCN TiN coating wereused. These featured holes for cutting fluid supply. Through

holes were drilled to a depth of 28 mm, with a peck at14 mm. A water-soluble oil (10% by volume) was employed

at a pressure of 10 bar. Cutting speeds of 5 and 10 m/min and

feed rates of 0.05 and 0.08 mm/rev were employed, see

Table 3. Each test was performed once. A screech criterion

was used to determine the end point of the test, which

occurred prior to catastrophic failure of the drill. In addition,

the maximum flank wear was measured at the end of tests.

In tapping tests, M8 TiCN coated solid carbide taps were

used at a cutting speed of 3 m/min (rotational speed

120 rpm) with an appropriate oil lubricant. The workpiece

was a 25 mm thick plate. The tapping length was 16 mm and

each test was performed only once. The size of the pre-

drilled through holes was 6.8 mm (test 1) and 6.9 mm (test

2). Tests were stopped when chipping/general fracture wasobserved on the tap. A go/no-go plug gauge was used to

determine thread quality.

3.2. Results and discussion

3.2.1. Drilling of AISI H13

In phase 1 experimental work, the mechanism of tool

failure differed between tests, depending on the combination

of operating parameters. Failure occurred either by small

scale chipping on the flank, progressive wear or large-scale

chipping/fracture at the web. Fig. 1 details tool life results in

terms of length cut. Tool life was significantly better when

operating at the lower feed rate, however, cutting speed

appeared to have little influence over the range tested. The

parameters which gave the longest length cut (42 holes)

were a cutting speed of 30 m/min and a feed rate of 0.1 mm/

rev. Large variations in the thrust force and torque values

were observed between tests, see Figs. 2 and 3 which detail

peak values for the first hole using a new drill. The highest

values were recorded when using the higher feed rate of

0.2 mm/rev. Although not detailed, thrust force and torque

increased with tool wear, however, the difference in thrust

force between the first and last holes was typically only

$20%.

Hole surface roughness (Ra) was in the range 0.140.48 mm. This was better than anticipated, typically drilled

holes in standard steels etc. range between 1.6 and 6.3 mmRa[37]. Cylindricity is a measure of the difference between

the radii of two concentric circles that are centred on the

axis of a hole. Stated values refer to the peak-to-valley

distance, which is the minimum radial separation of these

co-axial cylinders which totally encloses all the data points.

Table 3

Drilling of AISI D2 test matrix

Parameter Test (i) Test (ii) Test (iii) Test (iv)

Cutting speed (m/min) 10 5 5 5

Feed rate (mm/rev) 0.08 0.05 0.05 0.05

Drill type/diameter (mm)a A A B C

a A: short series/6.9 mm diameter; B: long series/6.8 mm diameter;

C: long series/7.0 mm diameter.

Fig. 1. Tool life results in terms of length cut when drilling of hardened AISI H13.

304 H. Coldwell et al. / Journal of Materials Processing Technology 135 (2003) 301311


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Three holes were tested for cylindricity at each of the three

cutting speeds (20, 30 and 45 m/min) when operating at

0.1 mm/rev feed rate. The results were 20.40, 35.45 and

45.30 mm, respectively. Out-of-roundness results ranged

from 2.85 to 17.75 mm. These values are the mean peak-

to-valley height from 10 measurements made at equal

intervals down the drilled hole.

Phase 2 tool wear against length cut results are given in

Fig. 4. The variability in tool wear was too high to provide a

definitive ranking of fluids, however, it was evident that the

water-based dielectrics could be used effectively as a cutting

fluid, operating at a pressure of 70 bar. The tool life results

for phase 2 (up to 210 holes) were much higher than phase 1

and it was confirmed subsequently by the cutting tool

Fig. 2. Peak thrust force against cutting speed when drilling hardened AISI H13.

Fig. 4. Tool wear against length cut when drilling hardened AISI H13 with a cutting fluid and water-based dielectrics. Note: The legend shows cutting fluid

codes and test numbers in brackets.

Fig. 3. Peak torque against cutting speed when drilling hardened AISI H13.



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manufacturer, that the micro grain carbide used for the drills

had been upgraded over the intervening period to an ultra

micrograin product, designed to give superior performance.

Figs. 58 show hole diameter, surface roughness (Ra),

cylindricity and out-of-roundness values for first and last

holes. The hole diameter values were a mean of three

measurements, taken approximately half way down the hole.

The majority of hole diameters were within 5 mm of the

Fig. 5. Hole diameter of first and last hole for each cutting fluid tested when drilling hardened AISI H13.

Fig. 6. Surface roughness of first and last hole for each cutting fluid tested when drilling hardened AISI H13.

Fig. 7. Cylindricity of first and last hole for each cutting fluid tested when drilling hardened AISI H13.



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nominal value. The water-based dielectrics (B, C and D)

were not as effective as the conventional cutting fluid (A) in

producing accurate holes. With respect to surface roughness

values, the range bars in Fig. 6 indicate the 95% confidence

limits. The data show that a lower workpiece surface rough-

ness could be achieved when using a conventional cutting

fluid (i.e. A) rather than a water-based dielectric, however,

cutting fluid C produced a consistently low surface rough-

ness. As in phase 1, hole quality was exceptionally good for

all the cutting fluids tested, fluids A and C, however,

consistently produced the highest quality holes. Cutting

fluid B generally produced holes of highest (worst) cylin-

dricity while cutting fluids A and D produced the best

results. All of the values recorded for the first and last holeswere within the range recorded for the first holes in phase 1.

The range bars in Fig. 8 indicate the maximum and mini-

mum out-of-roundness values recorded at the 10 equidistant

depths. For fluids A, C and D, the out-of-roundness values

were within the range recorded for phase 1, however, higher

values were found when using cutting fluid B.

3.2.2. Drilling and tapping of AISI D2

When drilling AISI D2 hardened to 60 HRC, it was found

that more favourable results were obtained with shorter

series drills, even though they were used to drill to a depth

6 mm over their recommended maximum. Table 4 sum-

marises the results. With the use of through-the-tool cutting

fluid application and a short series drill, it was possible to

obtain a length cut of 0.168 m (six holes). This is compar-

able with published data for the drilling of 10 mm

diameter 20 mm deep through holes in JIS SKD11($AISI D2) hardened to 60 HRC, where an average toollife of six holes (0.12 m length cut) was obtained [31]. In the

present research, the wear observed on the drill land was

higher on the longer series drills (tests (iii) and (iv)) and it

was concluded that this was probably due to tool deflection

as a result of a small core diameter.

When tapping AISI D2, a cut length of 0.08 m (five holes)

was achieved in test 1 before catastrophic tool failure

occurred. All of the tapped holes were within tolerance

and no significant wear/chipping was observed on the toolprior to failure. Increasing the pre-drilled hole size to

6.9 mm in test 2 nearly doubled the tool life to 0.144 m

(nine holes) before chipping occurred, see Fig. 9. Further

validation is obviously required: however, the use of this

technique was shown to be feasible for one-off/modification

work on pre-hardened press tools.

Direct comparisons between the drilling results for AISI

H13 and AISI D2 are not possible due to the differences in

operating parameters employed. Generally, however, tool

performance for H13 was far better than that obtained

for D2. For example, when drilling H13 (50 HRC) tool

life values in excess of 3 m were achieved in comparison

with less than 0.2 m for D2 (60 HRC), despite the higher

Fig. 8. Out-of-roundness of first and last hole for each cutting fluid tested when drilling hardened AISI H13.

Table 4

Results from drilling AISI D2 (60 HRC)

Test

no.

Cut length

(m)

Maximum flank

wear (mm)

Observations

(i) 0.056 $0.1 Wear on the land(ii) 0.168 $0.1 Wear on the land

Some micro chipping

(iii) 0.028 $0.1 Wear on the land(iv) 0.028 $0.1 Wear on the land

Fig. 9. Minor chipping on tap used for test ii after tapping 0.144 m.



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operating levels employed with H13. It is likely that the

difference in tool life reflects material hardness/composition

differences, especially with respect to the significantly

higher carbon and chromium content of D2, which in the

hardened state, has a microstructure containing large chro-

mium carbide inclusions. For H13, the composition (weight

%) is typically 0.320.45 C and 4.755.50 Cr, whereas forD2 the values are typically 1.401.60 C and 11.013.0 Cr

[38].

4. Machining of demonstration components in

hardened AISI D2 (60 HRC)

The following case studies detail the production of press

tool components using traditional and HSM techniques.

After an in-depth data collection study in a press tool

company involving machine times and cost metrics, four

components were chosen as representative of press tool

parts, which could potentially be produced using HSM

techniques, see Fig. 10.

4.1. Equipment, cutting tools, workpiece materials

and methodology

The Bridgeport VMC1000 vertical machining centre was

used to manufacture the component shown in Fig. 10(a). The

other three components, (b), (c) and (d), were machined on a

Deckel Maho Gildemeister DMC125U universal machining

centre with a maximum spindle speed of 8000 rpm, a power

output of 15 kW and a capability of employing feed rates of

up to 10 m/min. The cutting tools used for the experiments

are detailed in Table 5. The AISI D2 workpiece material was

hardened between 58 and 60 HRC.

HSM tests were conducted using a variety of solid and

indexable insert coated-carbide tools operating at cutting

Fig. 10. Hardened AISI D2 demonstrator components.

Table 5Cutting tools employed to machine demonstrator components

Tool

no.

Description Diameter

(mm)

No.

inserts/teeth

Format ISO classification Coating and thickness

1 Round insert face/end mill 20 2 Indexable insert Tungsten carbide (P20) TiCNAl2O3 6 mm TiN2 Ball nose indexable end mill 16 2 Indexable insert Tungsten carbide (P05-P20) TiCN 3mm TiN3 Ball nose indexable end mill 12 2 Indexable insert Tungsten carbide (P05-P20) TiCN 3mm TiN4 Solid ball nose end mill with

negative rake angle

10 2 Solid carbide Tungsten carbide (K10-K30) TiAlN (3 mm)

5 Solid ball nose end mill with

negative rake angle

6 2 Solid carbide Tungsten carbide (K10-K30) TiAlN (3 mm)

6 Short series drill 6.9 2 Solid carbide Tungsten carbide AlTiN

7 M8 machine tap 5 Solid carbide Tungsten carbide (K10/20) TiCN



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speeds of up to 200 m/min and feed rates of 0.1 and 0.2 mm/

tooth. Tool paths with minimum changes in feed direction

were employed as far as possible and down milling/dry

cutting was used throughout. The operating parameters were

based on results from machinability experiments previously

carried out by the authors [10] and on recommendations

from cutting tool manufacturers [39]. Components (a) and(b) in Fig. 10 were form dies used to produce radii of 3 and

5 mm, respectively, on automotive brackets. Overall dimen-

sions of the components were 170 mm 45mm 50mmand 100 mm 75mm 52 mm, respectively. The work-pieces were cut to shape using electrical discharge wire

machining. Traditionally, these radii would be produced by

hand. It was estimated that a skilled toolmaker would take

6 h to grind and polish the radii on component (a) while

component (b) would take 5 h. The HSM test for component

(a) employed cutting tool 3 at a cutting speed of 200 m/min

and a feed per tooth of 0.2 mm. Similarly, for component (b),

cutting tools 3 and 5 were used at cutting speeds of 200 and

100 m/min and feed per tooth values of 0.2 and 0.1 mm,

respectively.

Component (c) was a die used to form a strengthening

web on a bracket for securing electronic components. The

overall dimensions of the component were 107 mm50mm 50 mm. As before, the component was machinedto shape using electrical discharge wire machining. It was

estimated that CNC milling of the notch (workpiece in the

annealed state) would normally take 3 h. The HSM test

involved use of cutting tools 3 and 5 on a hardened work-

piece at cutting speeds of 200 and 100 m/min and feed per

tooth values of 0.2 and 0.1 mm, respectively. Component (d)

was a complex die cavity used to form another mountingbracket. The overall dimensions were 106 mm 100 mm51 mm with a maximum cavity depth of 9 mm. Previously,

the component was machined in the annealed state, which

took approximately 2 h followed by hardening and hand

finishing. Table 6 details the tool numbers, operations

performed and the corresponding cutting parameters for

the HSM test.

4.2. Results and discussion

Figs. 11 and 12 show the times and costs, respectively,

for each component when employing HSM and traditional

techniques. Despite the low tool life demonstrated in

machinability experiments [10], the use of HSM was shown

to be feasible and beneficial for the AISI D2 press tool

components. Overall, it was found that the savings with

HSM were approximately 60%. As the volume of material to

be removed increased, however, the cost and time savings

reduced. For the tooling used with components (a), (b)

and (c), the maximum flank wear did not exceed 0.3 mm.

Fig. 11. Times for traditional and HSM of hardened AISI D2 demonstrator

components.

Table 6

Cutting tools and machining parameters used for component (d)

Operation Roughing

face

Finishing

face

Roughing

cavity

Roughing

cavity

Roughing

cavity

Finishing

cavity

Finishing

radii

Tool no. 1 1 1 2 3 4 4

Cutting speed (m/min) 100 100 60 120 120 100 100

Feed per tooth (mm) 0.2 0.2 0.2 0.1 0.1 0.1 0.1

Axial depth of cut (mm) 2 0.3 0.4 1 0.5 0.2 0.2

Radial depth of cut (mm) 1 0.5 0.2 0.2

Fig. 12. Costs for traditional and HSM of hardened AISI D2 demonstrator

components.



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For component (d), the inserts employed with tool 1 had to

be indexed several times during the machining operation,

which increased the cost of manufacture and resulted in more

modest time and cost savings of 35 and 44%, respectively.

In an associated industrial application, a modification was

made to a component in a progression tool. The component

required the additional drilling and tapping of four blindholes. Using traditional manufacturing techniques, the part

would have been annealed before drilling and tapping by

hand and then rehardened, typically over a period of 5 days.

Using HSM techniques, the part was drilled and tapped in

the hardened state using a solid carbide coated drill and

tap. Cutting tool 6 (see Table 5) was employed at a cutting

speed of 11 m/min and a feed rate of 0.04 mm/rev. Cutting

tool 7 was employed at a cutting speed of 3 m/min. The

modification took less than 2 h to complete, including setup

and programming time and resulted in an estimated cost

saving of 2000.

5. Conclusions

1. The drilling of AISI H13 (52 HRC) was shown to be

successful using AlTiN coated carbide tools with both

soluble oil cutting fluid and water-based dielectrics

applied at high pressure (70 bar). Chipping was the

prevalent mode of failure.

2. The use of water-based dielectrics as an alternative to

standard soluble oil cutting fluid when drilling hardened

AISI H13 was shown to be possible, allowing the use of a

hybrid EDM/HSM machine tool utilising a single fluid.

3. Tool life values when ball nose end milling and drillingof AISI D2 (5860 HRC) were considerably lower than

for AISI H13 tool steel (4855 HRC), due to the

difference in workpiece hardness and microstructure, the

D2 structure incorporating large undissolved chromium

carbide particles. Typically, the lower carbon and

chromium content of H13 results in much finer and

more uniformly distributed carbides.

4. Tool life when drilling and tapping AISI D2 (60 HRC)

was low and unpredictable, however, in one-off produc-

tion situations it was demonstrated to be highly

advantageous.

5. HSM of press tool demonstrator components in AISI D2

(5860 HRC) was shown to be viable for workpieces

requiring a relatively small amount of machining, for

example the production of radii and notch features.

Time and cost savings of$60% were achieved.

Acknowledgements

The authors would like to thank the School of Engineering/

IRCin Materials Processing at the University of Birmingham,

the TCD/DTI/EPSRC, Portway Tool and Gauge Ltd.,

Bridgeport Machines Ltd., Charmilles Technologies Ltd.,

De Beers Industrial Diamonds Ltd., Delcam Plc, GTI

Corporation Ltd., the GTMA, HR Pearce & Co. (Tools)

Ltd., Rolls-Royce Plc, Sandvik Coromant UK, Spark Tec

International Ltd., and TRT Manufacturing Ltd., for the

provision of funding, equipment and consumables. Thanks

also go to Richard Fasham, John Wedderburn, Julian Price,

Bob Aston and Peter Thornton, University Technicians, fortheir help during the experimental work.

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