machining Machining is a manufacturing process where a desired shape or part is created using the controlled removal of material, most often metal, from a larger piece of raw material by cutting. Machining is a form of subtractive manufacturing, which util ...

, tool wear is the gradual failure of

cutting tool Cutting is the separation or opening of a physical object, into two or more portions, through the application of an acutely directed force. Implements commonly used for cutting are the knife and saw, or in medicine and science the scalpel an ...

s due to regular operation. Tools affected include tipped tools, tool bits, and drill bits that are used with

machine tool A machine tool is a machine for handling or machining metal or other rigid materials, usually by cutting, Boring (manufacturing), boring, grinding (abrasive cutting), grinding, shearing, or other forms of deformations. Machine tools employ some s ...

s. 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 In mathematics, orthogonality (mathematics), orthogonality is the generalization of the geometric notion of ''perpendicularity''. Although many authors use the two terms ''perpendicular'' and ''orthogonal'' interchangeably, the term ''perpendic ...

cutting this typically occurs where the tool temperature is highest. Crater wear occurs approximately at a height equalling the cutting depth of the material. Crater wear depth () = cutting depth * Notch wear which happens on both the insert rake and flank face along the depth of cut line causing localised damage to it primarily due to pressure welding of the chips. The chips literally get welded to the insert. * built-up edge in which material being machined builds up on the cutting edge. Some materials (notably

aluminium Aluminium (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has ...

and

copper Copper is a chemical element; it has symbol Cu (from Latin ) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orang ...

) 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 shine 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. *Edge Rounding, Edge rounding refers to the radius increase of cutting edge of the tool due to material removal. Edge rounding combines wear contribution from both flank face and rake face. Edge rounding is mostly found in machining of composite, i.e. Carbon Fiber Reinforced Plastics (CFRP), hybrid composite, metal-CFRP stack like CFRP-Ti stack. Edge rounding is reported for both hard ceramic-coated, and uncoated cutting tool.

Effects of tool wear

Some general effects of tool wear include: * increased cutting forces * increased cutting temperatures * poor surface finish * decreased accuracy of finished part * May lead to tool breakage * Causes change in tool geometry Reduction in tool wear can be accomplished by using lubricants and coolants while machining. These reduce friction and temperature, thus reducing the tool wear. A more general form of the equation is :

V_c T^n \times D^x S^y=C

where *

V_c

=cutting speed *''T''=tool life *''D''=depth of cut *''S''=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.

Energy considerations

Energy Energy () is the physical quantity, quantitative physical property, property that is transferred to a physical body, body or to a physical system, recognizable in the performance of Work (thermodynamics), work and in the form of heat and l ...

comes in the form of heat from tool

friction Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. Types of friction include dry, fluid, lubricated, skin, and internal -- an incomplete list. The study of t ...

. 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.

Multi-criteria of machining operation

Malakooti and Deviprasad (1989) introduced the multi-criteria metal cutting problem where the criteria could be cost per part, production time per part, and quality of surface. Also, Malakooti et al. (1990) proposed a method to rank the materials in terms of machinability. Malakooti (2013) presents a comprehensive discussion about tool life and its multi-criteria problem. As an example objectives can be minimizing of

Total cost In economics, total cost (TC) is the minimum financial cost of producing some quantity of output. This is the total economic cost of production and is made up of variable cost, which varies according to the quantity of a good produced and includ ...

(which can be measured by the total cost of replacing all tools during a production period), maximizing of

Productivity Productivity is the efficiency of production of goods or services expressed by some measure. Measurements of productivity are often expressed as a ratio of an aggregate output to a single input or an aggregate input used in a production proce ...

(which can be measured by the total number of parts produced per period), and maximizing of quality of cutting.

Tool Condition Monitoring

Monitoring tool wear has become increasingly important for ensuring product quality, preventing equipment damage, and optimizing productivity and cost efficiency in manufacturing processes, and in recent years to address this challenge, several experts have proposed an efficient deep learning framework and integrated other techniques to accurately predict tool wear in high-speed CNC milling operations.

References

* Malakooti, B; Deviprasad, J (1989). "An Interactive Multiple Criteria Approach for Parameter Selection in Metal Cutting". Operations Research 37 (5): 805-818. * 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. * K. Kadirgama et al. 2011, "Tool Life and Wear Mechanism" "http://umpir.ump.edu.my/2230/" * Malakooti, B. (2013). Operations and Production Systems with Multiple Objectives. John Wiley & Sons * Malakooti, B., Wang, J., & Tandler, E. C. (1990). "A sensor-based accelerated approach for multi-attribute machinability and tool life evaluation".The International Journal of Production Research, 28(12), 2373-2392.

External links

Tool Wear Prediction and Verification in Orthogonal CuttingStudy of tool wear and surface roughness in machining of homogenised SiC-p reinforced aluminium matrix composite
{{DEFAULTSORT:Tool Wear Metalworking