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Tuesday, October 27, 2009

THE MICROMETER

     
The micrometer is a precision measuring instrument, used by engineers. Each revolution of the rachet moves the spindle face 0.5mm towards the anvil face. The object to be measured is placed between the anvil face and the spindle face. The rachet is turned clockwise until the object is ‘trapped’ between these two surfaces and the rachet makes a ‘clicking’ noise. This means that the rachet cannot be tightened any more and the measurement can be read.

















EXAMPLE MEASURE READINGS

Using the first example seen below:

1. Read the scale on the sleeve. The example clearly shows12 mm divisions.

2. Still reading the scale on the sleeve, a further ½ mm (0.5) measurement can be seen on the bottom half of the scale. The measurement now reads 12.5mm.

3. Finally, the thimble scale shows 16 full divisions (these are hundredths of a mm).

The final measurement is 12.5mm + 0.16mm = 12.66


Example :














Ex#2

Read the following 17 micrometer measures. Label your answers with the appropriate units.

Metric Micrometer Readings




























American Standard Micrometer Readings





Solution:

Metric: American:
1. 14.10 mm 1. 0.230 in
2. 10.14 mm 2. 0.364 in
3. 15.29 mm 3. 0.554 in
4. 24.25 mm 4. 0.635 in
5. 18.43 mm 5. 0.608 in
6. 13.18 mm 6. 0.323 in
7. 10.14 mm 7. 0.459 in
8. 13.03 mm 8. 0.803 in
9. 22.18 mm


THE VERNIER CALIPIER

     
The Vernier Caliper is a precision instrument that can be used to measure internal and external distances extremely accurately. The example shown below is a manual caliper. Measurements are interpreted from the scale by the user. This is more difficult than using a digital vernier caliper which has an LCD digital display on which the reading appears. The manual version has both an imperial and metric scale.
Manually operated vernier calipers can still be bought and remain popular because they are much cheaper than the digital version. Also, the digital version requires a small battery whereas the manual version does not need any power source.




HOW TO READ A MEASUREMENT FROM THE SCALES


EXAMPLE 1: The external measurement (diameter) of a round section piece of steel is measured using a vernier caliper, metric scale.

A. The main metric scale is read first and this shows that there are 13 whole divisions before the 0 on the hundredths scale. Therefore, the first number is 13.
B. The’ hundredths of mm’ scale is then read. Only one division on the main metric scale lines up with a division on the hundredths scale below it, whilst others do not. In the example below, the 41st division on the hundredths scale lines up exactly with a division on the metric scale above.
C. This 41 is multiplied by 0.02 giving 0.82 as the answer (each division on the hundredths scale is equivalent to 0.02mm).
D. The 13 and the 0.82 are added together to give the final measurement of 13.82mm (the diameter of the piece of round section stee)l.







useful link :
http://www.physics.smu.edu/~scalise/apparatus/caliper/tutorial/simulation.html





Saturday, October 24, 2009

describes the common machines used in metal cutting.

describes the common machines used in metal cutting.

     
arbor The bar attached to the spindle in a horizontal milling machine. The arbor holds the milling cutter.
automatic bar machine A turning machine that continuously cuts a number of parts from a piece of bar stock, one after another. The bar stock advances through the spindle and is held by the collet during the operation.
axis An imaginary straight line that passes through the center of an object.
backstroke The return motion of a saw blade that cuts with a back-and-forth movement.
band saw A long, continuous cutting blade with serrated teeth that is looped around two or more wheels.
bar stock Raw material purchased from metal manufacturers in the form of long bars.
base The foundation of a machine that supports all the other machine components.
bed The main supporting structure upon which the operating parts of the machine are mounted and guided.
bed-type milling machine A type of milling machine used to mill flat surfaces that has a large bed, which only moves along a horizontal axis.
broach A multi-point cutting tool made of a series of progressively smaller teeth that can both remove metal and finish the surface of a workpiece with one pass of the cutting tool.
broaching machine A machine that uses a multi-point cutting tool to shape and finish either the interior of a hole or the surface of a workpiece.
carbide insert A cutting bit made of hard material that has multiple cutting edges. Once a cutting edge is excessively worn, it can be indexed to another edge, or the insert can be replaced.
carriage The section of the lathe that slides back and forth along the ways and supports the cross-slide and cutting tool.
center The device located in the tailstock that holds in place the end of the workpiece opposite the spindle.
chip An unwanted piece of metal that is removed from a workpiece. Chips are formed when a tool cuts or grinds metal.
chuck A device that holds a workpiece in place as it rotates. The chuck commonly has three or four jaws that can be adjusted to fit various sizes.
circular saw A power saw that cuts with a toothed or abrasive disk rotating at high speed.
CNC machining center A sophisticated CNC machine that can perform multiple machining operations in the same setup with a variety of tools.
CNC turning center A sophisticated CNC machine that specializes in turning, boring, drilling, and threading operations, all at the same location.
collet A slitted device that holds a workpiece in place as it rotates. A collet has a hole through which the workpiece passes, and it is designed to hold specific dimensions. Collets can also be used to hold cutting tools.
column The vertical support, or backbone, of a machine.
column-and-knee milling machine A milling machine with a spindle that is mounted in the column and a worktable that rests on an adjustable knee.
compound rest The part of the lathe on the carriage that allows for angular adjustment of the cutting tool.
contour A cutting process that creates a curved, non-linear dimension.
countersinking The cutting of a beveled edge at the end of a hole so that the head of a screw can rest flush with the workpiece surface.
cutting The use of single- or multi- point tools to separate metal from a workpiece in the form of chips.
drilling The use of a rotating drill in order to cut a round hole into a workpiece.
drive The main device that powers the rotation of the spindle.
end mill A thin, tall mill cutter with cutting edges that wind up the sides. Both the bottom and side of the end mill are used during milling operations. End mills resemble drills.
engine lathe The original and most basic type of lathe.
face mill A flat mill cutter with multiple cutting teeth surrounding the tool. The bottom of the face mill is primarily used during milling operations.
feed handle A handle attached to a machine that controls the movement of the cutting tool.
finishing tool A single-point cutting tool used to make a very light cut for final touches to achieve precise tolerances or improved finishes.
form mill A type of milling cutter that is designed in an irregular shape in order to mill contours.
hacksaw A saw that contains a blade made of high-speed steel, molybdenum, or tungsten alloy steel that cuts in one direction.
head The part of a drill press that contains the spindle and the motor.
headstock The end of a lathe that holds the spindle and the drive that rotates the workpiece.
high-speed steel A material used in cutting tools to machine metals at high cutting speeds. High-speed steel stays hard at high temperatures, has great hardness, and is resistant to abrasion.
keyway A rectangular slot or groove that is machined down the length of a hole.
knee The device supported by an elevating screw that raises and lowers and guides the back and forth motion of the saddle.
lathe A machine tool that holds a cylindrical workpiece at one or both ends and rotates it while various cutting tools remove material. Turning is a common operation performed on the lathe.
leadscrew The long, threaded device that controls the precise movement of the carriage on a lathe.
machine tool A power-driven machine that holds a variety of tools. These tools include cutting tools, workholding devices, punches, and other manufacturing tools.
machining The process of removing metal to form or finish a part, either with traditional methods like turning, drilling, milling, and grinding, or with less traditional methods that use electricity, heat, or chemical reaction.
mill A multi-point cutting tool that is used to remove metal from the surface of a workpiece.
milling cutter A rotary cutting tool with teeth around its periphery that is used on milling machines.
milling machine A machine that uses a multi-point tool to remove metal from the surface of a workpiece.
multiple spindle drill A drilling machine that contains two or more spindles, which perform multiple cutting operations at the same time.
multi-point tool A cutting tool that has two or more cutting edges.
overarm The device on a horizontal milling machine that reaches over the workpiece and supports the spindle or arbor.
plain mill A cutting tool for the milling machine with cutting surfaces on the periphery. It is used to mill flat surfaces.
planer-type milling machine A very large type of milling machine that often contains numerous milling heads.
plate stock A flat piece of raw material that is used to make manufactured parts.
pocket An interior recess that is cut into the surface of a workpiece.
radial drill A drilling machine that can accommodate large workpieces by maneuvering an overarm in place over the workpiece.
reaming The use of a multi-point cutting tool to smooth or enlarge a previously drilled hole.
reciprocating The back-and-forth motion of a hacksaw in which only one motion actually contacts and cuts the workpiece.
rough cutting The quick removal of metal from a workpiece without regard to tolerances or finish.
roughing tool A single-point cutting tool used to make very heavy cuts and remove metal as quickly as possible.
saddle The device supported by the knee that slides back and forth on the knee and guides the left and right motion of the worktable.
saw A multi-point cutting device that is used to rough cut a part to a certain length.
shell mill A type of milling cutter that has cutting edges around its periphery and can be mounted on an arbor.
side mill A narrow type of milling cutter that has cutting edges on both its end and periphery.
single-point tool A cutting tool that has a single cutting edge.
slab broach A flat-shaped broach that is used to remove metal from the workpiece surface.
spindle The part of the machine tool that spins. On the mill, the spindle holds a cutting tool. On the lathe, the spindle holds the workpiece.
stock The raw material out of which manufactured parts are made.
tailstock The part located at the end of a lathe opposite the headstock that supports the end of longer workpieces.
tapping The process of cutting internal threads in a workpiece with a multi-point tool.
tolerance The unwanted but acceptable deviation from the desired dimension.
t-slot cutter A type of milling cutter that is used to machine a portion of a T-shaped slot into a workpiece.
turning A machining operation used to make cylindrical parts. A single-point cutting tool passes along the outer surface of a cylindrical workpiece as it rotates, and gradually removes a layer of material.
turret The component of a lathe that holds a number of cutting tools. The turret rotates to place tools in the cutting position.
turret lathe A lathe with a mounted device that holds multiple cutting tools. The turret rotates to position a specific cutting tool in place.
vise A workholding device with one fixed jaw and one moveable jaw. Vises are often used to hold simple rectangular or cubic workpieces on a mill or machining center.
ways Two precisely measured, parallel tracks that support and guide the movement of the carriage and cross slide.
workpiece A part that is being worked on. It may be subject to cutting, welding, forming or other operations.
worktable The part of a machine tool that supports the workpiece and any workholding devices.


Monday, April 20, 2009

Saturday, April 18, 2009

CUTTING FLUIDS IN MACHINING

CUTTING FLUIDS IN MACHINING

     


Introduction to Cutting Fluids

Cutting fluids are used in metal machining for a variety of reasons such as improving tool life, reducing workpiece thermal deformation, improving surface finish and flushing away chips from the cutting zone. Practically all cutt ing fluids presently in use fall into one of four categories:
  • Straight oils
  • Soluble oils
  • Semisynthetic fluids
  • Synthetic fluids
Straight oils are non-emulsifiable and are used in machining operations in an undiluted form. They are composed of a base mineral or petroleum oil and often contains polar lubricants such as fats, vegetable oils and esters as well as extreme pressure additives such as Chlorine, Sulphur and Phosphorus. Straight oils provide the best lubrication and the poorest cooling characteristics among cutting fluids.

 Synthetic Fluids contain no petroleum or mineral oil base and instead are formulated from alkaline inorganic and organic compounds along with additives for corrosion inhibition. They are generally used in a diluted form (usual concent ration = 3 to 10%). Synthetic fluids often provide the best cooling performance among all cutting fluids.

 Soluble Oil Fluids form an emulsion when mixed with water. The concentrate consists of a base mineral oil and emulsifiers to help produce a stable emulsion. They are used in a diluted form (usual concentration = 3 to 10%) and provide good lubrication and heat transfer performance. They are widely used in industry and are the least expensive among all cutting fluids.

 Semi-synthetic fluids are esentially combination of synthetic and soluble oil fluids and have characteristics common to both types. The cost and heat transfer performance of semi-synthetic fluids lie between those of synthetic and sol uble oil fluids.


Cutting Fluid Application Strategies:

The principal methods of cutting fluid application include:
  • Flood Application of Fluid:

    a flood of cutting fluid is applied on the workpiece



  • Jet Application of Fluid:

    a jet of cutting fluid is applied on the workpiece directed at the cutting zone



  • Mist Application of Fluid:

    cutting fluid is atomised by a jet of air and the mist is directed at the cutting zone

Cutting Fluid Effects in Machining

The primary functions of cutting fluids in machining are :
  • Lubricating the cutting process primarily at low cutting speeds
  • Cooling the workpiece primarily at high cutting speeds
  • Flushing chips away from the cutting zone
Secondary functions include:
  • Corossion protection of the machined surface
  • enabling part handling by cooling the hot surface
Process effects of using cutting fluids in machining include:
  • Longer Tool Life
  • Reduced Thermal Deformation of Workpiece
  • Better Surface Finish (in some applications)
  • Ease of Chip and Swarf handling


Cutting Fluid Selection Criteria:

The principal criteria for selection of a cutting fluid for a given machining operation are:
  • Process performance :
    • Heat transfer performance
    • Lubrication performance
    • Chip flushing
    • Fluid mist generation
    • Fluid carry-off in chips
    • Corrosion inhibition
    • Fluid stability (for emulsions)
  • Cost Performance
  • Environmental Performance
  • Health Hazard Performance


Cutting Fluid Maintenance and Disposal:

Cutting fluid maintenance involves checking the concentration of soluble oil emulsions (using refractometers), pH (using a pH meter), the quantity of tramp oil (hydraulic oil leaking into the cutting fluid system) and the quantity of particulates in the f luid. Action taken to maintain the fluid includes adding make-up concentrate or water, skimming of tramp oil, adding biocides to prevent bacterial growth and filtering the particulates by centrifuging:





The cutting fluid within a coolant system degrades with time due to bacterial growth and contamination with tramp oil and fine metal swarf from the machining operation. When it becomes uneconomical to maintain the fluid by regular make-up operations it is dumped. Prior to letting the fluid flow into a sewer system, it should be treated to bring the fluid composition to safe disposal levels.









>
WHAT IS MILLING?

WHAT IS MILLING?

     

Milling is the process of cutting away material by feeding a workpiece past a rotating multiple tooth cutter. The cutting action of the many teeth around the milling cutter provides a fast method of machining. The machined surface may be flat,angular, or curved. The surface may also be milled to any combination of shapes. The machine for holding the workpiece, rotating the cutter, and feeding

CLASSIFICATION OF MILLING

  • Peripheral Milling

    • In peripheral (or slab) milling, the milled surface is generated by teeth located on the periphery of the cutter body. The axis of cutter rotation is generally in a plane parallel to the workpiece surface to be machined.

    (Kalpakjian S., Introduction to Manufacturing Processes)

  • Face Milling

    • In face milling, the cutter is mounted on a spindle having an axis of rotation perpendicular to the workpiece surface. The milled surface results from the action of cutting edges located on the periphery and face of the cutter.

  • End Milling

    • The cutter in end milling generally rotates on an axis vertical to the workpiece. It can be tilted to machine tapered surfaces. Cutting teeth are located on both the end face of the cutter and the periphery of the cutter body.

    METHODS OF MILLING

  • Up Milling

    • Up milling is also referred to as conventional milling. The direction of the cutter rotation opposes the feed motion. For example, if the cutter rotates clockwise , the workpiece is fed to the right in up milling.

    (Boothroyd G. & Knight W., Fundamentals of Machining and Machine Tools)


  • Down Milling

    • Down milling is also referred to as climb milling. The direction of cutter rotation is same as the feed motion. For example, if the cutter rotates counterclockwise , the workpiece is fed to the right in down milling.

    (Boothroyd G. & Knight W., Fundamentals of Machining and Machine Tools)

    The chip formation in down milling is opposite to the chip formation in up milling. The figure for down milling shows that the cutter tooth is almost parallel to the top surface of the workpiece. The cutter tooth begins to mill the full chip thickness. Then the chip thickness gradually decreases.

    Other milling operations are shown in the figure.

    (Kalpakjian S., Introduction to Manufacturing Processes)

    MILLING EQUIPMENT

    The milling machine is one of the most versatile machine tools in existence. In addition to straight milling of flat and irregularly shaped surfaces, it can perform gear and thread cutting, drilling, boring and slotting operations which are normally handled on machine tools designed specifically for these specific operations.



    The above is a Bridgeport CNC Milling Machine


    Column & Knee type Milling Machines

    Used for general purpose milling operations, column and knee type milling machines are the most common milling machines. The spindle to which the milling cutter is may be horizontal (slab milling) or vertical (face and end milling). The basic components are:

  • Work table, on which the workpiece is clamped using the T-slots. The table moves longitudinally with respect to the saddle.
  • Saddle, which supports the table and can move transversely.
  • Knee, which supports the saddle and gives the table vertical movements for adjusting the depth of cut.
  • Overarm in horizontal machines, which is adjustable to accomadate different arbor lengths.
  • Head, which contains the spindle and cutter holders. In vertical machines the head may be fixed or vertically adjustable.


    Bed type Machines

    In bed type machines, the work table is mounted directly on the bed, which replaces the knee, and can move only longitudinally. These machines have high stiffness and are used for high production work.

    Planer Machines

    Planer machines are similar to bed type machines but are equipped with several cutters and heads to mill various surfaces.

    Rotary Table Machines

    Rotary table machines are similar to vertical milling machines and are equipped with one or more heads to do face milling operations.

    Tracer Controlled Machines

    Tracer controlled machines reproduce parts from a master model. They are used in the automotive and aerospace industries fro machining complex parts and dies.

    Computer Numerical Control(CNC) Machines

    Various milling machine components are being replaced rapidly with computer numerical control(CNC) machines. These machine tools are versatile and are capable of milling, drilling, boring and tapping with repetitive accuracy.

    • Milling Cutters

    A milling cutter is a cutting tool that is used on a milling machine.Milling cutters are available in many standard and special types, forms, diameters, and widths.The teeth maybe straight (parallel to the axis of rotation) or at a helix angle. The helix angle helps a slow engagement of the tool distributing the forces .The cutter may be right-hand (to turn clockwise) or left-hand (to turn counterclockwise).The figure shows a typical end milling cutter.

    Features of Milling Cutters

    Some of the terms used to identify the major features

    of a milling cutter are given in the figure.

    (Olivo C.T., Machine Tool Technology and ManufacturingProcesses, C Thomas Olivo and Associates)

    Types of Milling Cutters





    STEWART PLATFORM as a Machine tool

    VARIAX

    Researchers have been looking at a device called a parallel kinematic link mechanism to replace the conventional base and tower milling machine tool. The analysis showed that the type of motion and forces needed could be provided in large part by a mechanism called Stewart platform- a type of parallel kinematic link mechanism. A number of research labs and a few companies are working at aspects of this design. Giddings and Lewis have designed the VARIAX (shown above) and Ingersoll Milling Co. have designed the octahedral hexapod. These machine tools consist of a lower platform, an upper platform and six legs that connect the two. The top platform (head) contains the machine spindle and the bottom platform (bed) holds the workpiece. The six legs perform the task of positioning the head woth respect to the bed. Since the machine has no prescribed axis, no linear bearings and no ways in which to travel it offers extraordinary machine stiffness. For more on this machine tool look up the following links:

  • A 3 DOF parallel link mechanism is being developed in the SMARTCUTS project at the University of illinois, Urbana-Champaign.
  • Machine Tool Structures page.

    • Miscellaneous Links

  • MIT - NMIS Machine Shop Tutorial
  • Society of Mechanical Engineers
  • Manufacturer's Information Network
  • Thomas Registry
  • TradeWave Galaxy
  • METAL Machining and Fabrication
  • CNC Manufacturing Systems
  • WWW Virtual Library: Mechanical Engineering
  • Precision Machined Products Association Home Page

    • THE SHAPING MACHINE

    THE SHAPING MACHINE

         

    A shaping machine is used to machine surfaces. It can cut curves, angles and many other shapes. It is a popular machine in a workshop because its movement is very simple although it can produce a variety of work.

    Shaping machines come in a range of sizes but the most common size is seen opposite.


    The main parts are indicated below:

    The tool feed handle can be turned to slowly feed the cutting tool into the material as the 'ram' moves forwards and backwards. The strong machine vice holds the material securely. A small vice would not be suitable as the work could quite easily be pulled out of position and be damaged. The vice rests on a steel table which can be adjusted so that it ca be moved up and down and then locked in position. Pulling back on the clutch handle starts the 'ram' moving forwards and backwards.




    EXAMPLE - QUICK RETURN CRANK MECHANISM

    The shaping machine is used to machine flat metal surfaces especially where a large amount of metal has to be removed. Other machines such as milling machines are much more expensive and are more suited to removing smaller amounts of metal, very accurately.

    The reciprocating motion of the mechanism inside the shaping machine can be seen in the diagram. As the disc rotates the top of the machine moves forwards and backwards, pushing a cutting tool. The cutting tool removes the metal from work which is carefully bolted down.


    prob: Draw a diagram of the shaping machine and explain how the quick return mechanism works?


    The tool post and the tool slide can be angled as seen below. This allows the shaper to be used for different types of work





    DIA A: The tool post has been turned at an angle so that side of the material can be machined
    		DIA B: The tool post is not angled so that the tool can be used to level a surface.

    DIA C: The top slide is slowly feed into the material so that a ‘rack’ can be machined for a rack and pinion gear system.










    QUESTIONS:

    1. Draw a diagram to represent a shaping machine and label the important parts.

    2. Describe the type of work carried out by these types of machines.




    >
    Introduction to Heat in Machining

    Introduction to Heat in Machining

         

    Introduction

    Heat has critical influences on machining. To some extent, it can increase tool wear and then reduce tool life, get rise to thermal deformation and cause to environmental problems, etc. But due to the complexity of machining mechanics, it's hard to predict the intensity and distribution of the heat sources in an individual machining operation. Especially, because the properties of materials used in machining vary with temperature, the mechanical process and the thermal dynamic process are tightly coupled together. Since early this century, many efforts in theoretical analyses and experiments have been made to understand this phenomena, but many problems are still remaining unsolved.

    Theoretical Analysis Review


    Assumptions

    Due to the complexity of heat problem in machining, the following assumptions are generally imposed:

    • First, almost all (90%-100%) of the mechanical energy consumed in a machining operation finally convert into the thermal energy.
    • Second, There are three major sources of thermal in orthogonal cutting with a sharp tool: plastic deformation in the so-called primary zone and secondary zone, and the frictional dissipation energy generated at the interface between tool and chip. But if the tool is with a round tip, part of heat may be generated at the interface between tool and workpiece due to friction. In pure theoretical analysis, more assumptions are needed: usually, the plane heat sources at the shear plane and the tool-chip interface are assumed as being uniformly distributed.
    • Third, even with the above assumptions, the problem of estimating the mean temperatures on the shear plane and tool face is complex. This is because part of the thermal energy will convected away by the chip, part will conducted into the workpiece and tool, i.e., a partition criterion is needed.
    • In addition, the geometry of the tool, chip and workpiece,as well as boundary conditions are simplified to some extent.


    Approaches

    The pure analytical approches , in general, came out the average temperature on the shear plane and at the tool/chip interface. The temperature distridution along the shear plane and the tool/chip interface was also obtained some of the following approaches:


    1. Moving Heat Source Method

      Here is the idealized diagram of shear plane moving heat source:

      The temperature distribution along the shear plane was assumed as the same as that along a uniform band source of heat moving obliquely through an infinite solid. Similarly, the temperature distribution or average temperature at the chip/tool interface also can be approximatedly obtained.


    2. Image Source Method

      To avoid giving rise to two different temperature on either side of a same plane due to partition principle, Chao and Trigger approximated the uniform plane heat source at the interface by a grid of point sources. Assuming that the angle between the rake and flank faces was right and that the tool surfaces were insulated, the grid of real and fictious image point sources is shown as follows:

      Then they used an iterative procedure to obtain the final interfacial temperature distribution and later extended their work to include the frictional heat source at the tool/work interface.


    3. Dimensional Analysis

      Kronenberg postulated that the temperature at the tool/chip interface was dependent on the following important variables: chip area, cutting speed, a specific cutting force, a thermal conductivity, and the product of density and specific heat. Applying the principle of dimensional analysis, two dimensionless groups of variables were derived. Then the experimental results were fitted in the following:


    Experiment Retrospection

    Since 1920s, many experimental methods were devised to measure the tool,chip or workpiece temperature and their distribution:

    1. Tool-Chip Thermocouple Technique

      Here is the schematic of tool-chip thermocouple set-up:


      Generally, only the average temperature at the tool/chip interface can be obtained. Sometimes, a tool-work thermocouple was also used.

      The calibration of the tool-chip thermocouple is shown as:

      Some limitations of this methods are mainly:

      1. The elimination of parasitic e.m.f.'s which could affect the thermocouple output.
      2. The calibration of the thermocouple output.


    2. Embedded Thermocouple Technique

      The following is a typical embedded thermocouple setup:


    3. Infrared Radiation Technique

      The first use of this technique was reported by Schwerd who developed a total Radiation Pyrometer for determining the temperature distribution at the surfaces of tool and workpiece.

      Several researchers attempted to access to chip/tool interface by scanning through holes drilled either in the work or tool. Prins' pyrometer arrangement is shown as follows:

      Limitation of the above measurements is that there is considerable interference of the contact zone which must influence the heat flow and the resulting temperature of either the chip or tool surface.

      Infrared Photography technique proposed by Boothroyd can obtain a full temperature field in the chip and workpiece. A calibration strip, which was electrocally heated from one end,was simply used to calculate the real temperature. The following setup was used at that time:

      Today, many disavantages of this technique are overcomed.


    4. Metal Microstructure and Microhardness Variation Measurement

      Under suitable cutting conditions, the metallographic method can be used to determining the temperature gradients in high speed steel cutting tools. The following picture is the etched rake face of tool used to cut nickel in normal dry atmosphere at 46 m/min, 0.25 mm/rev feed for 30 seconds(After E. F. Smart and E. M. Trent):

    5. However, the microstructure, microhardness and other properties change to some extent dependent on temperature and time.


    6. Thermosensitive Painting Technique

      Using the thermosensitive paints for estimating cutting temperature is because that these paints change colors at different temperature.

      Limitations are that there is a relatively long time lag for the colors to change and that small changes in temperature are not easy to be detected.

    7. Temper Color Technique

      This technique is based on the fact that the temper colors of some metals are different at different temperatures. And it wasn't widely used.


    Numerical Simulation

    The numerical methods were successfully applied in calculating the temperature distribution and thermal deformation in tool, chip and workpiece. Especially,the finite element and boundary element methods can deal with very complicated geometry in machining, they have great potential to slove the problems in practice. These methods are listed in the following:


    1. Finite Difference Method

      Generally, the pure theoretical methods only gave us very approximate results, such as average temperature and temperature distribution along the shear plane and the tool/chip interface.

      Finite difference method can be used to calculate the temperature distributions in the chip, tool and workpiece. And better results can be expected because the geometry and boundary conditions of chip, tool and workpiece, as well as the shape of distributed heat sources can be descripted well.

    2. Finite Element Method

      Finite element method(FEM) has great potential to calculate the temperature distributions in the chip, tool and workpiece if the geometry, boundary conditions and the shape of distributed heat sources become very complicate.The following diagram is the mesh used by O. A. Tay:

      In addition, FEM can be used to calculate the temerature distribution in either toolholder or machined parts and then to obtain the thermal deformation.

      Finally, because an accurate distributed heat source model is needed in order to obtain a better result in the temperature distribution. FEM can be naturally coupled with some mechanics model, therefore, predicts the intensity and distribution of the heat sources.

    3. Boundary Element Method

      Boundary Element Method(BEM) was used in calculating the temperature distribution in the tool by O. A. Tay. BEM has great potential in reducing solid modeling to surface modeling. A wide application in this field is undoubtable.


    1. Semi-Analysis

      In this class of methods, some information such as chip surface temperature or temperature distribution in workpiece is first obtained experimentally. Then the temperature distribution and/or thermal deformation in chip, and sometimes in the tool and workpiece as well are calculated analytically. The inverse heat transfer problem in machining is an example of these methods.


    Heat Generation


    1. Heat Generated in Various Machining Operations

      Almost all of the heat generation model were established under orthogonal cutting condition. But in practice, there are various machining operations which cannot satisfy this condition, such as oblique turnning, boring, drilling, milling, grinding, etc.

      Generally, the intensity of heat sources in real machining operations can be determined approximatedly by the external work applied, however, the distribution of the heat sources are hard to obtained by either theoretical or experimental methods.

      The following listed are the simplified heat source model in real operations:

      • Boring: A uniform moving ring heat source.
      • End Milling: An ellipsoidal shape distribution with a distribution of uniform heat flux at milling area.(Heat source not defined by its intensity)
      • Grinding: A circular heat source moving on the surface of workpiece.

    2. Types of Heat Sources

      There are several types of heat source in machining:

      • Plastic work converted to heat.
      • Viscous dissipation transformed into heat if the cut material are viscoplastic.
      • Work done by friction converted to heat.
      • Ambient heat source sometimes need be considered if thermal deformation is concerned.
      • In non-traditional machining, other types of heat sources exist.

    3. Heat Generated in Primary Zone

      Heat generated in this zone is mainly due to plastic deformation and viscous dissipation. But in classical machining theory, the rate of heat generated is the product of the shear plane component, Fs, of the resultant force and the shear velocity, Vs, i.e., the shear energy is completedly converted into heat.

      If heat source is uniformly distributed along the shear plane, the intesity of shear plane heat source, Ip, satisfies the following relation:

      Fs Vs
      Ip = ---------------
      b t1

      where b is the cutting width and t1 the uncut depth.

    4. Heat Generated in Secondary Zone

      In this region, because of the complexity of plastic deformation, this part of heat was ignored in many prevoius theoretical research.

      Boothroyd has shown that the secondary plastic zone is roughly triangular in shape and that strain rate, E., in this region varies linearly from an approximatedly constant value along the tool/chip interface given by

      Vc
      E. = --------------
      dt

      Where Vc is the chip velocity, dt the maximum thickness of the zone.

      Hence the maximum intensity of heat source in this zone is proportional to the strain rate.

    5. Heat Generated at Interface between Tool & Chip

      Heat is generated at the tool/chip interface by friction. The intensity,Ic, of the frictional heat source is approximatedly by

      F Vx
      Ic = ------------
      h b

      where F is the friction force, Vx the sliding velocity of the chip along the interface, and h is the plastic contact length.

    6. program to Calculate Heat Generation

    7. More on Heat Generation

      Heat generation is not well investigated in the following areas:

      • Non-Coulumb Friction
      • Plastic Deformation Work in the Second Zone
      • Temperature Influence on Heat Generation
      • Heat in the Practical Operations

    Heat Transfer


    1. Conduction, Convection & Radiation in Ordinary Cutting Operations

      The three types of heat transfer, conduction, convection and radiation, all exist in the machining operations.

      Heat transfer inside the chip and workpiece, the tool and toolholder is by conduction.

      Heat transfer between coolant/air and the chip/tool/workpiece is by convection.

      Radiation is rarely investigated in traditonal machining operations. But radiation techniques are widely applied in measuring the temperature distribution in various machining operations.

    2. Temperature Distribution near Cutting Zone

      The typical temperature distributions are shown as follows: Here is the isothermal lines for dry orthogonal cutting of free machining steel with a carbide tool.

      (From: Milton C. Shaw, Metal Cutting Principles, Clarendon Press, Oxford, 1984)

      For more plots of temperature distrbutions, please click here.

    3. Cutting Fluids' Effects on Heat Transfer

      Cutting fluids' effects on heat transfer are, in gerneral, classified as:

      • Cutting fluids may reduce the cutting force, such as friction, therefore, heat generation is reduced to some extent.
      • Using cutting fluids, heat generated in machining can be rapidly removed away by convection.
      • Generally, using cutting fluid cannot reduce the maximum temperature at the tool/chip interface, but increase the temperature gradient in both the chip and the tool because cutting fluid is not easy to access the cutting edge.

    4. More About Heat Transfer

      In practice, there are other types of heat source involved in machining, such as ambient heat sources. They may cause some thermal deformation in the lathe and so on.


    Heat Effects


    1. Heat Influences on Cutting Forces

      Heat influence on the cutting forces is mainly because that:

      • The friction coeffient is tightly dependent upon temperature.
      • The properties of cut material also depend on temperature.

    2. Heat Effects on Tool Life

      Heat has great influence on tool life. The following diagram verify this point:

      Variations of tool life with workpiece bulk temperature when milling Cr-Ni-Mo steel at speeds of (1) 150 fpm and (2) 200 fpm. (After krabacher and Merchant 1951)

      (From: Milton C. Shaw, Metal Cutting Principles, Clarendon Press, Oxford, 1984)

    3. Heat Influences on Surface Toughness

      Heat gives rise to thermal deformatiom in the workpiece, which finally takes on the form of surface toughness.

    4. Heat Influences on Thermal Deformation in Lathe

      Thermal deformation in the lathe is the so-called thermal error in precision machining.

    5. Heat Effects on Mass Transfer in Coolant Circulation System

      Interesting? please take a Health issue in Enviromentally Conscious Machining.


    Heat Related Research Issues


    1. Heat Generation Model

      Predictive heat generation models in either orthogonal cutting or other various operations

    2. Convection by Coolant

      Because convection of coolant varies with many factors, such properties of coolant, application conditions, state of coolant flow, and operation conditions, etc, it's required to investigated these corresponding issues.

      A Heat Transfer Performance Module, which can predict the convective heat transfer coeffients of several kinds of coolants used in some typical machining operations, can be accessible.

    3. Simulation of Open Cutting Fluid Circulation System

      A energy and mass flow model of cutting fluid circulation system is a very important issue in environmentally conscious machining. Sometimes, the disposal of chips and coolants needs much more energy than that in real cutting operations. Developing an effective way to utilize energy should be under consideration.

    4. Heat Effects

      Other than research issues mentioned above, there are still some areas listed here:

      • Thermal softening on shear banding formation in the chip
      • Heat influence on chip morphology
      • Heat effect on the carry-off capacity of coolant
      • Thermal and mechanical coupled machining theory


    Links to Other Web Sites





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