Cutting tool material

The influential parameter for selection of cutting fluid in machining processes is the cutting

tool material. Various cutting tool materials are commercially available for all kind of

machining processes. High speed steel cutting tools can be used with all type of cutting

fluids. However waterless cutting fluids are preferred when difficult-to-cut materials are

machined. In case of the tungsten carbide (WC) cutting tools application, more cooling

characteristics from cutting fluids are required. This is because of high generated heat in the

interface of cutting tool and work piece material. The negative effect of generated heat during

machining with WC cutting tools causes rapid tool wear. Hence tool life will be shorter and

surface finish quality falls. Ceramic and diamond cutting tools can also protect their

characteristics at high temperatures. They are generally used in finish machining operation. In

using ceramic cutting tools, air is sprayed into the cutting zone. The water based cutting

fluids must be used when diamond type cutting tool materials are used.1

Carbide tool

Nowadays Carbide tools have replaced instead of high-speed steels in most applications.

These carbide and coated carbide tools cut about 3 to 5 times faster than high-speed steels.

Ceramic cutting tools are harder and more heat-resistant than carbides, but more brittle.

The proper choice can double tool life or double the cutting speed of the same tool. Coated

tools should be considered for most machining applications because of their longer life and

faster machining.

Super hard tool

Super hard tool materials are divided into two categories: Cubic boron nitrate (CBN) and

polycrystalline diamonds (PCD) cutting tools have been found important place in machining

processes. However, these cutting tools are expensive and they can protect their

characteristics in high temperature machining conditions. They are generally used in finish

machining operation to obtain high dimensional accuracy and excellent surface finish quality.

The application of cutting fluids is not necessary when machining operations are carried out

with these cutting tool materials. Cubic boron nitride is used for machining very hard ferrous

materials such as steel dies, alloy steels and hard-facing materials.

All cutting tools are “perishable,” meaning they have a finite working life. A stronger carbide

grade, different edge preparation, or lead angle change may eliminate chipping. Built-up edge

is a deposit of work piece material adhering to the rake face of an insert. These deposits can

break off, pulling out pieces of carbide from the tool.3

Cutting tool coatings

The major categories of hard carbide include tungsten carbide, titanium carbide, tantalum

carbide, and niobium carbide. Each type of carbide affects the cutting tool’s characteristics

differently. A higher tungsten content increase wears resistance, but reduces tool strength. A

higher percentage of cobalt binder increases strength, but lowers the wear resistance.2

Work piece material

The main factor for selection of suitable cutting fluids in machining processes is the type of

work piece material. The application of cutting fluids should provide easy machining

operation in all materials. Cast iron cast group of material s are brittle during machining they

break into small size chips. The friction between cutting tool and chip is less due to small size

chip formation. It was proposed that using emulsion cutting fluids increases surface finish

quality and prevents dust formation during machining. The concentration of emulsion cutting

fluid should be kept around 12% – 15% to decrease oxidation.

In steel machining operation, generally the high pressure containing and additive cutting

fluids are used. In stainless steel machining, high pressure cutting oils should be selected.

Work-hardening properties in some steels would cause some problems during machining

operation. However using sulphur added oils for this kind of steels machining leave stain

over machined surface. For machining of heat resistant and difficult-to-cut steel alloys, water

based cutting fluids are preferred, because temperature becomes higher in cutting area. The

mixture ration of water based cutting fluids changes between 1/20 – 1/40. In some machining

operations, using sulphur added mineral cutting oils is possible.

During machining of aluminium and aluminium alloys, high temperatures do not occur

Waterless cutting fluids prevent the formation of “built up edge”, however this type of cutting

fluids must be non-active (leaving no stain).

Machining of copper and copper alloys poses similar problems. The application of emulsion

cutting fluids or thin mineral oils should be selected for copper and copper based alloys

machining. High pressure additive cutting oils are preferred for brass machining.

In the machining of nickel and nickel alloys, the machining operation should be carried out as

dry or using cutting fluids. Higher cutting speeds and feed rates should be selected when

cutting fluids are used in the machining of these materials. Generally sulphured mineral oil as

cutting fluid is preferred. Water based cutting fluids are used in turning with high cutting

speed, milling and drilling operations. The applications of synthetic cutting fluids are possible

in drilling and broaching operations.

In machining of the difficult-to-cut materials such as titanium alloys, high temperature

becomes an influential factor for selection of cutting fluid. Therefore the application of

cutting fluid would eliminate the effect of generated heat during machining process. The

selected cutting fluid must have both cooling and lubricating characteristics. The cooling

factor of cutting fluid is more important in machining of titanium alloys due to high heat

generation during machining operation. This would also induce to use higher cutting speeds.

It is observed that lubrication properties of selected cutting fluids are preferred when low

cutting speeds are selected. Emulsion oil can be selected in the machining of titanium alloys

when cutting speeds are used; chlorine additive cutting oils are preferred when high cutting

speed is selected.

In the machining operations of composites that used commonly nowadays, using cutting

fluids is recommended. In particular the using cutting fluid has positive influence on the

surface roughness quality.1

Effect on work piece material properties

Some research found that when alloys were subjected to cryogenic cooling, the hardness

increased retaining most of their mechanical properties, making them a very good choice as

cutting material. However, some other researchers have noted little difference when the same

cryogenic treatment is applied on high-speed steels and other cutters. Some researchers

agreed that different treatment attempted by different researchers has contributed to the

difference in the results of material properties being reported. Further recommended that the

best approach is by having simultaneous cooling of both work piece and cutting tools would

be an ideal effective cryogenic cooling strategy.4

Die and mould material

Our research focus is on the Die and mould manufacturing industries. Die and mold makers

deal with steel in wide ranges of hardness, from low (HB 200 and less) to high (HRC 63).In

line with the main field of application there are six general and two special-purpose classes of

tool steels, from which the following are the most popular in the die and mold industry:

• Cold- work tool steels including A series (air-hardening medium-alloy), D series (high-

carbon high-chromium) and O series (oil hardening)

• Hot-work H series

• Water hardening W series

• Plastic mold P series

• Shock resistant S series

• Special-purpose L series (low-alloy).

In die and mold design, the main properties of tool steels are strength, wear resistance,

corrosion resistance, etc. However, while for a die and tool maker dealing with the material,

which has already been specified by designers, more important properties are: hardness,

machinability, polish ability and dimensional stability. Consequently, in die and mold

making process, hardness of tool steel (even the Same grade) can vary within a wide range

from HB 200 and less (soft steel) to HRC 63 (hard steel). Therefore, steels can be divided

into the following conditional groups depending on their hardness.

Soft annealed to hardness to HB 250

Pre-hardened of two grades:-HRC 30-37 – HRC 38-44

Hardened of three grades: - HRC 45-49 – HRC 50-55 – HRC 56-63 and more

Hard to cut metals

Machining performance on hard to cut metals should be done with properly designed hard

tools and this would cost much higher than soft metal machining. Materials especially

tailored for extreme conditions and environments, which are resistant to very high or very

low temperatures are becoming increasingly important in a variety of industrial fields. Such

materials are difficult to cut.

Moreover difficult to cut materials such as special cast iron (ADI), Aerospace Titanium- or

Sandwich materials, Inconel alloys, hard AISI 440 C stainless steel and hard SCM 440 alloy

steels and organic matrix composites (OMC) are more extensive used in different mechanical

industrial fields. These require a greater use of specialized fluids and tools; both of which

incur a high cost to the final product and also a series of environmental and health problems.5

Hard martensitic stainless steel is found that from the research it produced saw tooth chips in

all operating parameters which increased the cutting forces. There was a research conducted

study on cutting AISI 420 steel using PCBN tool. In this research, two work materials are

used and they are hard AISI 440 C martensitic stainless steel and SCM 440 alloy steel. AISI

410, 420 and 440 A, B, C is all considered as martensitic stainless steel and can be hardened

like other alloy steels. AISI 440 C is widely used in aerospace industries for bearings, steam

and water valves, pumps, turbines, compressor components, shafting, cutlery, surgical tools,

plastic moulds, nuclear applications etc. which demand high strength and high resistance to

wear and corrosion. It has high viscosity, poor thermal conductivity, low corrosion, high

work hardening rate and tendency to form built up edge (BUE) at tool edge. AIST 440 C has

high chromium and high carbon content and possesses high mechanical strength. The SCM

440 material is best known as Cr-Mo alloy steel. This grade steel is used in high tensile

applications where wear resistance is of prime importance.

Chemical Properties of materials Operating parameters

Alloying elements AISI 440C SCM 440

Carbon 0.95-1.20 0.35-0.43 Cutting velocity -

m/min

100,125,150,175,200

Manganese 1.00 0.75-1.00 Feed rate - mm/rev 0.10, 0.20 and 0.30

Chromium 16-18 0.75-0.80 Depth of cut 1.00

Molybdenum 0.75 0.15-0.25

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Chemical properties of materials and Operating parameters

Hard to cut metals have been selected

AISI D2

AISI D2 is a high-carbon, high-chromium tool steel alloyed with molybdenum and vanadium

characterized by:

• High wear resistance

• High compressive strength

• Good through-hardening properties

• High stability in hardening

• Good resistance to tempering-back.

Typical

analysis

C

1.55

Si

0.3

Mn

0.4

Cr

11.8

Mo

0.8

V

0.8

Standard

Specification

AISI D2 W-Nr 1.2379

Delivery

Condition

Soft annealed to approx. 210 HB

Color code Yellow / White

Applications

AISI D2 is recommended for tools requiring very high wear resistance, combined with

moderate toughness (shock-resistance). AISI D2 can be supplied in various finishes,

including the hot-rolled, pre-machined and fine machined condition.

PropertiesPhysical Data

Temperature68 °F (20°C)

390°F (200°C)

750°F (400°C)

Densitylbs/in^3 0.277 0.276 0.275kg/m^3 7700 7650 7600Coefficient of thermal expansionlow temperingPer °F from 68°F 6.8*10^-6Per °C from 20°C 11.2*10^-6high temperature temperingper °F from 68° F 6.2*10^-6 6.7*10^-6per °C from 20°C 11.2*10^-6 12810^-6Thermal conductivityBtu in/ft^2h°F 139 146 159W/m °F 20 21 23Modulus of elasticityksi 30 450 29 000 26 100Mpa 210 000 200 000 180 000Specific heatBtu/lb°F 0.11J/kg°C 460

Properties of hard to cut materials

AISI P20

Mechanical properties:

As normally delivered in the hardened and tempered state, hardness is normally 32HRC. No

hardening risks, no heat treatment, no distortion to tools. Can be further nitride or flame

hardened, locally. Heavier sections can be supplied pre machined saving on weight and less

machining.

Physical Properties:

Density          0.284 lb/in3 (7861 kg/m3)Specific Gravity              7.86Modulus of Elasticity

        30 x 106 psi (207 GPa)

Thermal conductivity

        24 Btu/ft/hr/°F  41.5 W/m/°K

Machinability         60-65% of a 1% carbon steel

Coefficient Of Thermal ExpansionTemperature   ºF in/inº F x106 Temperature  ºC mm/mm ºCx106

70-200 6.7 21-93 12.070-500 7.2 21-260 12.970-1000 7.6 21-538 13.7

Tempering:

  Temperature            P20 tool steel   ºF  ºC                   HRC  400  204                 48 – 49  600  316                 46 – 47  800  427                 43 – 441000  538                 39 – 401100  593                 33 – 341150  621                 30 – 31

P20 is chrome - moly tool steel made specifically to fill the requirements for the machined

cavities and forces used in zinc die casting and plastic molding. It is delivered fully quenched

and tempered to approximately Brinell 300. Other hardness levels may be obtained through

additional heat treatment. P20 is the standard mold steel for machine - cut plastic molds and

zinc die casting dies. P20 is usually supplied in the pre hardened condition, about 300 Brinell,

for injection molds and zinc die casting dies. While in the pre hardened condition, P20 can be

nitride for greater wear resistance. It can also be textured in the pre hardened state. P20 is

also available at an annealed hardness of about 200 Brinell. It can be hardened or carburized

up to a higher hardness of 50/60 RC when used for compression or transfer work. Pre

hardened P20 is used in cavities and cores of zinc die -casting dies, in plastic - molding dies,

and in other mold parts which do not require high surface hardness or high temperature

operation. When carburized, P20 is used for compression, transfer, and other types of molds

requiring high surface hardness.

Machinability - In the pre hardened condition, P20 has a machinability rating of 65 as

compared with a rating of 100 for a 1 percent carbon tool steel. Dimensional Stability -When

quenched in oil from a hardening temperature of 1550 F, this grade normally expands 0.003

in./in. However, as with all liquid quenching analyses, dimensional changes during heat

treatment are greatly influenced by the size and shape of the piece. Strict observance of good

heat treating practice is essential for minimum distortion.

References

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[1] A. Yardimeden, T. Ozben, E. Kilickap O. Çakīr*, "Jornal of Achievements in Materials," Selection of cutting fluids in machining process, vol. 25, p. 4, December 2007.

[2] Dr. Neil Canter, "The possibilities and limitations of dry machining".

[3] www.sme.org.

[4] Zahari Taha1 and Indra Putra Almanar2 Aznijar Ahmad-Yazid1*, "A review of cryogenic cooling in high speed machining," January 2010.

[5] Italy) ,TECOS Celje (Slovenia),Gazela d.o.o. (Slovenia) Wolframcarb SpA (Piedmont. (2007) www.manunet.net.

[6] S.Thamizhmanii and Sulaiman Hasan, "Machinability Study using Chip Thickness Ratio on Difficult to Cut," p. 6, Feb 2012.

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