Developing an Experimental Set

Up for Measurement of Cutting

Temperature in Turning

OperationPresented By:

1. AMIT KUMAR

2. ANKIT RAIPURIA

3. ARPIT KUMAR GAHLOT

4. HIMANSHU KUMAR SINGH

Motivation

In machining process, the importance of knowledge of the tool temperature in cutting

tools is well recognized as temperature has a critical influence on tool life and work

piece surface integrity.

High temperature generated leads to many problems like built-up-edge formation,

reducing the shear strength, dimensional inaccuracy of the work piece, surface damage

by oxidation, rapid corrosion and burning, rapid tool wear which reduce tool life.

Problem Definition

Developing an experimental set up for measurement of cutting temperature in

turning operation

Goal Statement

To accurately predict the temperature in turning operation.

Performance Specifications

Common thermocouple parameters are:

Coating Material

Operating Range

Thickness of coating

Sensor Parameters:

Rise time

Setting time

Heating at tool tip during cutting operation using single-point cutting tool depends upon the

following factors:

Feed Rate

Depth of cut

Cutting Velocity

Friction

Sources of error:

Chatter at tool tip

Cutting fluids

Chip formation

Literature reviewThe main techniques used to evaluate the temperature during machining (tool–chip

thermocouple, embedded thermocouple, and thermal radiation method) are shown in figure.

Thermocouples have always been a popular transducer used in temperature

measurement. Thermocouples are very rugged and inexpensive and can operate over a wide

temperature range.

Standard thermocouples embedded in the cutting tool or workpiece material can be used to

measure the temperature at a single point or at different locations to establish the

temperature distribution in the tool.

Thermocouple

• A Thermocouple is a sensor used to measure temperature. Thermocouples consist of two

wire legs made from different metals. The wires legs are welded together at one end,

creating a junction. This junction is where the temperature is measured. When the

junction experiences a change in temperature, a voltage is created. The voltage can

then be interpreted using thermocouple reference table to calculate the temperature.

• There are many types of thermocouples, each with its own unique characteristics in terms of

temperature range, durability, vibration resistance, chemical resistance, and application

compatibility. Type J, K, T, & E are “Base Metal” thermocouples, the most common types of

thermocouples. Type R, S, and B thermocouples are “Noble Metal” thermocouples, which are

used in high temperature applications

We will use type K thermocouple due to following

reasons • High temperature measuring range

• Type K thermocouple are inexpensive

• Type K thermocouple are accurate

• Type K thermocouple are reliable

Specification of type K thermocouple

Temperature Range:

• Thermocouple grade wire, –454 to 2,300F (–270 to 1260C)

• Extension wire, 32 to 392F (0 to 200C)

• Melting Point, 2550°F (1400°C)

Accuracy (whichever is greater):

• Standard: +/- 2.2C or +/- .75%

• Special Limits of Error: +/- 1.1C or 0.4%

• Chromel {90% nickel and 10% chromium}

• Alumel {95% nickel, 2% manganese, 2% aluminium and 1% silicon}

Composition of type K thermocouple

Schematic and ConstructionSequence of coating-substrate

thermocouple fabrication, (a)

part of coating was removed

and two pieces of wire were

adhered (different wires are

used) (b) to fix the coating-

substrate thermocouple on tool

holder

Mica is used for insulation.

Much research has been

done on proper coating to be

used for thermocouples.

However, proper prediction of

temperatures is an incumbent

challenge.

Experimental Setup

Schematic representation of the coating-substrate thermocouple

The cutting experiment is performed

with a turning lathe. A general overview

of the experimental setup is shown in

alongside. Tool and work piece are

insulated from the machine tool. The

coating-substrate thermocouple is

mounted on the tool holder. The

electric signals can be translated from

the sensor to computer through the

amplifier and A/D convertor. This

experiment is an oblique cutting test.

SolidWorks Model

Thermocouple

Ease of experimental

setup

Capable of notifying

temperature at various

points without changing

setup

Can be used for

processes like grinding,

drilling, milling, etc.

Temperature of surface

cannot be measured

directly.It is a

destructive technique

Cannot be used for

processes like grinding,

drilling, milling, etc.

For making observation

at different point, setup

is required to be

rearranged after

stopping the machining

Tool-Work Transverse Embedded

Use of thermocouples1. Tool-work thermocouple has always been a

popular tool to be used in temperature measurements

during metal cutting

2. Thermocouples are conductive, rugged and inexpensive and can operate

over a wide temperature range.

3. In machining applications, a thermoelectric emf is generated between

the tool and the work piece. With these method, the

entire tool is used as a part of the thermocouple and the

work piece as the other part.

4. The cutting zone forms the hot junction while a cold part of the tool and the work

piece forms the cold junction. This technique is easy to

apply but only measures the mean temperature over the

entire contact area of tool and work piece.

Factors in temperature measurement

For HSS tools, during machining of steel

based alloys, O’ Sullivan and Cottrell

found that an increase in cutting speed

resulted in a decrease in cutting forces

and machined surface temperatures.

This reduction in temperature was

attributed to the higher metal removable

rate which carried more heat being carried

away by the chip

Kurimoto cut low alloy engineering steel using

cemented carbide tool over a range of speeds. The

results showed that the chip-tool interface

temperature increased with increasing cutting

speed during machining. Cutting fluids reduced

the mean chip-tool interface temperatures in relation

to the dry cutting

The friction on the

flank face has a big influence on the heat

generated

Cutting often employs various lubricants

such as wet and dry type, emulsifiers and

SAE-oils.

Graph of temperature variation during

cutting and cooling for HSS cutting tool

Graph of temperature variation during cutting

and cooling for carbide cutting tool

Prototype componentsCutting tool material - heat treated Iron

tool signature –

10, 20, 7, 6 ,8 ,15 ,1/32

Thermocouple used - type k

Binding agent - mica strip coating

MAXIMUM TEMPERATURE RANGE

Thermocouple Grade

– 328 to 2282°F

– 200 to 1250°C

Datasheet of type K thermocouple

Tool-Thermocouple Interface

Insertion of thermocople hot junction: Since this must be as close as possible to the insert tool, generally a small hole is made in th holder through which wire penetrates. In case of single attachment tools, an external insert is necessary.

Insulation of thermocouple junction from other metallic contact: This is usually done by providing insulation with mica or ceramic. Certain industrial glues have sufficient strength to be used for directly attaching the junction. For example, the glue DB5015, has thermal resistane within temperatures from -40 °C to 1220 °C. The DB5015 glue is a composite of silver powder and abio-aluminate. The shear strength of the glue is 7.42 MPa.

Cold-junction contact with workpiece: A popular method in literature is using mercury baths with a wheel attached to the spindle for maintaining electrical contact during motion of workpiece.

Instead, we propose to use Hall-Effect sensors during machining. Hall Effect sensors are routinely used as very accurate sensors for proximity sensing. They generate small currents/emf when some object with corresponding mating magnet comes very close. We propose using a metal junction and a magnetised T-slot. As the workpiece will move ahead, the cold junction will remain at nearly constant potential. A small battery powered external electricity source is necessary.

There are three main challenges to thermocouple setting:

Analysis and Limitations

Data Aquisition and Plotting

FEM is the most popular method for modelling heat affected zones.

A sampling rate of 5-10 per second is minimum requiremnet for precise readings

Thermocouples do not work properly with alloys and materials with low

conductivities.

Calibration of tool-work piece pair is difficult.

Limited transient response time

Concluding Remarks

The tool-work thermocouple measurement technique is an economic and fairly accurate technique

of temperature measurement. However, this technique is not universal and has its limitations.

An IR pyrometer can be used in conjugation with the above apparatus to obtain better results.

Thermocouples are prone to stress , strain and corrosion, particularly as they age.

These thermocouples used generally suffer from a standard error of Standard: ± 2.2C% or ±.75%

The chromel element is subject to what is known as "green rot." When this happens, the chromium

becomes oxidized and turns green and corroded. This occurs in reduced oxygen environments from

815° to 1,040°C. Such depleted-oxygen environments are called reducing, and K-type

thermocouples should never be used in either reducing or cyclically oxidizing and reducing

atmospheres e.g presence of carbon and graphite in coolant. In such cases, tool-work type of setup

is not accurate. Embedded sensors are preferred in such circumstances.