Seminar and Technical Writing for Friction and wear of cutting tool.

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1. TOPIC:- Friction and Wear of Cutting Tool PRESENTED BY:- JAGRIT SAHU ROLL NO.:- 120CR0650              PRESENTED TO:- Prof. DEBASISH SARKAR       SEMINAR AND TECHNICAL WRITING

2. Contents.. Introduction: Tool Wear Modes of Cutting Tool Failure Classification of Frictional Tool Failure- Crater, Flank and Nose wear Tool wear Mechanisms  Control of Tool wear

3. INTRODUCTION Wear is loss of material on an asperity or micro-contact, or smaller scale, down to molecular or atomic removal mechanisms. It usually progresses continuously. 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 bit that are used with machine tools. Gradual failure of cutting tools due to regular operations is also known as tool wear . Tool failure implies that the tool has reached a point beyond which it will not function satisfactorily until it is re-sharpened.

4. Relation between Friction and Wear in Cutting Tools Friction causes wear: When a cutting tool interacts with a workpiece, friction between them generates heat and removes material from the tool surface, leading to wear. Heat accelerates wear: Friction generates heat at the tool-workpiece interface, which increases the rate of wear processes such as abrasion, adhesion, and diffusion. Wear affects surface: As wear progresses, the tool surface undergoes changes such as microstructural alterations, surface roughening, and formation of wear debris, influencing frictional behaviour. Abrasive wear induced by friction: High frictional forces can cause abrasive wear, where hard particles in the workpiece or tool chip away at the tool surface, further exacerbating wear.

5. MODES OF CUTTING TOOL FAILURE      FRACTURE FAILURE: This mode of failure occurs due to mechanical breakage due to excessive forces and shocks at the tool point causing it to fail suddenly by brittle fracture. Also known as mechanical chipping. Such kind of tool failure is random and catastrophic in nature, results in premature loss of tool and hence is extremely detrimental.       TEMPERATURE FAILURE: This failure occurs when the cutting temperature is too high for the tool material, causing the material at the tool point to soften, which leads to plastic deformation and loss of the sharp edge. This type of failure also occurs rapidly, results in premature loss of tool and is quite detrimental and unwanted.       GRADUAL WEAR: Gradual wearing of the cutting-edge causes loss of tool shape, reduction in cutting efficiency, an acceleration of wearing as the tool becomes heavily worn, and finally tool failure in a manner similar to a temperature failure. Gradual wear is preferred because it leads to the longest possible use of the tool, option of changing the tool before the final catastrophic loss of the cutting edge occurs, with the associated economic advantage of that longer use.

6. Number of pieces of work machined. Total volume of material removed. Total length of cut. Limiting value of surface finish. Increase in cutting forces. Dimensional accuracy. Overheating and fuming. Presence of chatter.   WAYS OF MEASURING  TOOL LIFE

7. Type of tool material and its hardness Type and condition of work piece material Dimensions of cut (Feed and depth of cut) Cutting speed Tool geometry Tool temperature (function of cutting speed, feed and depth of cut) Type of cutting fluid  TOOL WEAR   DEPENDING    FACTORS

8. The tool wears are classified into the following types: Crater wear on tool face Flank wear Localized wear such as the rounding of Cutting edge (Nose wear/Corner wear) Chipping of the cutting edge

9. CRATER WEAR It consists of a cavity or concave section on the tool face/rake face formed and grows from the action of the chip sliding against the surface. High stresses and temperatures characterize the tool-chip contact interface, contributing to the wearing action. The crater can be measured either by its depth or its area. Crater wear affects the mechanics of the process increasing the actual rake angle of the cutting tool and consequently, making cutting easier.  At the same time, the  crater wear weakens the tool wedge and increases the possibility for tool breakage. This wear predominates at high speed. In general, crater wear is of a relatively small concern. KM=Distance to middle KB=Width KT=Depth KL=Distance to Start

10. CAUSES OF CRATER WEAR :-    The crater wear is mainly caused due to :- The presence of friction between the chip-tool interface, o The abrasion action of microchips present at the chip- tool interface. The abrasive action of fragments of Built up Edge (BUE) at the chip-tool interface and diffusion wear. The diffusion wears, due to the atomic attraction between the tool and work the atoms of the tool material will get diffused and deposited over the work piece called diffusion wear.

11. FLANK WEAR It occurs on the tool flank as a result of friction between the machined surface of the work piece and the tool flank. Flank wear appears in the form of so-called wear land and Is measured by the width of this wear land, VB. Flank wear affects to the great extend the mechanics of cutting. An extreme condition of flank wear often appears on the cutting edge at the location corresponding to the original surface of the workpart . This is called notch wear. occurs because the original work surface is harder and/or more abrasive than the internal material, which could be caused by work hardening from cold drawing or previous machining, sand particles in the surface from casting, or other reasons. As a consequence of the harder surface, wear is accelerated at this location. Cutting forces increase significantly with flank wear. If the amount of flank wear exceeds some critical value (VB > 0.5~0.6 mm) then the excessive cutting force may cause tool failure. This wear predominates at low speed.

12. CAUSES OF FLANK WEAR         The flank wear is mainly caused due to: The presence of friction at the tool work interface. The abrasive action of microchips or powdered particles present at the tool work interface and diffusion wear. The diffusion wears, due to the atomic attraction between the tool and work the atoms of the tool material will get diffused and deposited over the workpiece called as diffusion wear.

13. It occurs on the tool corner. It can be considered as a part of the wear land and respectively flank wear since there is no distinguished boundary between the corner wear and flank wear land. We consider corner wear as a separate wear type because of its importance for the precision of machining. Corner wear actually shortens the cutting tool thus increasing gradually the dimension of machined surface and introducing a significant dimensional error in machining, which can reach values of about 0.03~0.05 mm. CORNER WEAR OR NOSE WEAR

14. TOOL WEAR CURVE The general relationship of tool wear versus cutting time is shown in figure. Although the relationship shown is for flank wear, a similar relationship occurs for crater wear. Three regions can usually be identified in the typical wear growth curve. The first is the break-in period, in which the sharp cutting edge wears rapidly at the beginning of its use. This first region occurs within the first few minutes of cuttina . The break-in period is followed by wear that occurs at a fairly uniform rate. This is called the steady-state wear region. In our figure, this region is pictured as a linear function of time, although there are deviations from the straight line in actual machining. Finally, wear reaches a level at which the wear rate begins to accelerate. This marks the beginning of the failure region, in which cutting temperatures are higher, and the general efficiency of the machining process is reduced. If allowed to continue, the tool finally fails by temperature failure.

15. The rate of tool wear strongly depends on the cutting temperature; therefore,  any measures which could be applied to reduce the cutting temperature would reduce the tool wear as well. Use of cutting fluids, lubricants is another method. Additional measures to reduce the tool wear include the application of advanced cutting tool materials, such as coated carbides, ceramics, etc. The figure shows the process parameters that influence the rate of tool wear. CONTROL OF TOOL WEAR

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