Tool wear


Tool wear

Tool wear describes the gradual failure of cutting tools due to regular operation. It is a term often associated with tipped tools, tool bits, or drill bits that are used with machine tools.

Types of wear include:
* flank wear in which the portion of the tool in contact with the finished part erodes. Can be described using the Tool Life Expectancy equation.
* crater wear in which contact with chips erodes the rake face. This is somewhat normal for tool wear, and does not seriously degrade the use of a tool until it becomes serious enough to cause a cutting edge failure. Can be caused by spindle speed that is too low or a feed rate that is too high. In orthogonal cutting this typically occurs where the tool temperature is highest. Crater wear occurs approximately at a height equaling the cutting depth of the material. Crater wear depth ~ t0t0= cutting depth
* built-up edge in which material being machined builds up on the cutting edge. Some materials (notably aluminum and copper) have a tendency to anneal themselves to the cutting edge of a tool. It occurs most frequently on softer metals, with a lower melting point. It can be prevented by increasing cutting speeds and using lubricant. When drilling it can be noticed as alternating dark and shiny rings.
* glazing occurs on grinding wheels, and occurs when the exposed abrasive becomes dulled. It is noticeable as a sheen while the wheel is in motion.
* edge wear, in drills, refers to wear to the outer edge of a drill bit around the cutting face caused by excessive cutting speed. It extends down the drill flutes, and requires a large volume of material to be removed from the drill bit before it can be corrected.

Effects of Tool Wear

Some General effects of tool wear include:
* increased cutting forces
* increased cutting temperatures
* poor surface finish
* decreased accuracy of finished partReduction in tool wear can be accomplished by using lubricants and coolants while machining. These reduce friction and temperature, thus reducing the tool wear.

Tool Life Expectancy

The Taylor Equation for Tool Life Expectancy provides a good approximation.

: V_c T^n=C

A more general form of the equation is: V_c T^n imes D^x f^y=Cwhere
*V_c=cutting speed
*"T"=tool life
*"D"=depth of cut
*"F"=feed rate
*"x" and "y" are determined experimentally
*"n" and "C" are constants found by experimentation or published data; they are properties of tool material, workpiece and feed rate.

Temperature Considerations

At high temperature zones crater wear occurs.The highest temperature of the tool can exceed 700 °C and occurs at the rake face whereas the lowest temperature can be 500 °C or lower depending on the tool.ram

Energy Considerations

Energy comes in the form of heat from tool friction. It is a reasonable assumption that 80% of energy from cutting is carried away in the chip. If not for this the workpiece and the tool would be much hotter than what is experienced. The tool and the workpiece each carry approximately 10% of the energy. The percent of energy carried away in the chip increases as the speed of the cutting operation increases. This somewhat offsets the tool wear from increased cutting speeds. In fact, if not for the energy taken away in the chip increasing as cutting speed is increased; the tool would wear more quickly than is found.

References

* S. Kalpakjian and S.R. Schmidt. "Manufacturing Engineering and Technology". 2000, Prentice Hall, Upper Saddle River, NJ.
* S. Kalpakjian and S.R. Schmidt. "Manufacturing Processes for Engineering Materials". 2002, Prentice Hall, Upper Saddle River, NJ.

ee also

*machine tool
*tool bit
*tipped tool
*drill bit
*drill press
*honing
*cutting

External links

* [http://nsmwww.eng.ohio-state.edu/6thCIRP_toolwear_Toronto.pdf Tool Wear Prediction and Verification in Orthogonal Cutting]
* [http://www.tech.plym.ac.uk/sme/mfrg315/cuttool1.htm Manufacuturing Process Educational Website]
* [http://gundrillingsolutions.com/Pages/toolwear.html Information Page on Gundrilling tool wear]
* [http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TGJ-4FJKWTY-K&_user=716796&_coverDate=05%2F15%2F2005&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000040078&_version=1&_urlVersion=0&_userid=716796&md5=9735141ec2c84f4ea04e63f11af30d59 Study of tool wear and surface roughness in machining of homogenised SiC-p reinforced aluminium metal matrix composite]


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Tool bit — The term tool bit generally refers to a non rotary cutting tool used in metal lathes, shapers, and planers. Such cutters are also often referred to by the set phrase name of single point cutting tool. The cutting edge is ground to suit a… …   Wikipedia

  • Tool steel — Iron alloy phases Ferrite (α iron, δ iron) Austenite (γ iron) Pearlite (88% ferrite, 12% cementite) …   Wikipedia

  • Tool — For other uses, see Tool (disambiguation). A modern toolbox. A tool is a device that can be used to produce an item or achieve a task, but that is not consumed in the process. Informally the word is also used to describe a procedure or process… …   Wikipedia

  • Wear-Leveling — Ein Solid State Drive (SSD, dt. Festkörperlaufwerk), auch Solid State Disk (dt. Festkörperplatte) genannt, ist ein Speichermedium, das wie eine herkömmliche Festplatte eingebaut und angesprochen werden kann, ohne eine rotierende Scheibe oder… …   Deutsch Wikipedia

  • tool — n 1. the penis. The notion of the male member as an implement is very ancient. The word tool itself appeared in Middle English and by the 16th century had been recorded as a sexual metaphor. It was at first an acceptable colloquialism, but since… …   Contemporary slang

  • tool steel — any of various high carbon steels capable of being hardened and tempered to meet special requirements for machining, etc. * * * Specialty steels that are produced in small quantities, contain expensive alloys, and are often sold only by the… …   Universalium

  • machine tool — machine tooled, adj. a power operated machine, as a lathe, used for general cutting and shaping of metal and other substances. [1860 65] * * * Stationary, power driven machine used to cut, shape, or form materials such as metal and wood. Machine… …   Universalium

  • Machine tool — A machine tool is a powered mechanical device, typically used to fabricate metal components of machines by machining, which is the selective removal of metal. The term machine tool is usually reserved for tools that used a power source other than …   Wikipedia

  • Diamond tool — A close up of the segment of a diamond saw blade A diamond tool is a cutting tool with diamond grains fixed on the functional parts of the tool via a bonding material or another method.[1] As diamond is a superhard material, diamond tools have… …   Wikipedia

  • Cutting tool (machining) — In the context of machining, a cutting tool (or cutter) is any tool that is used to remove material from the workpiece by means of shear deformation. Cutting may be accomplished by single point or multipoint tools. Single point tools are used in… …   Wikipedia


Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.