Technical Resource of the Cutting Wedge is the Foundation of the Machining Regime Determination

Technical Resource of the Cutting Wedge is the Foundation of the Machining Regime Determination

Viktor P. Astakhov (Production Service Management Inc, USA) and Stanislav V. Shvets (Sumy State University, Sumy, Ukraine)
DOI: 10.4018/IJMMME.2020040101

Abstract

This article argues that cutting tool wear is not just a particular case of wear found in general machinery because the whole amount of energy required for cutting is transmitted through relatively small tool-chip and tool-workpiece interfaces causing extremely high contact temperatures and pressures. This article discusses a considerably different approach to the determination of the cutting speed based upon the energy passing through the cutting wedge. Moreover, it discusses that, for a given tool material/geometry, there is a limited amount of such energy that the cutting wedge can sustain before reaching the criterion of tool life. This limit is considered as the technical resource of the cutting tool. The article establishes and verifies the existence of the detect correlation between the works done in the cutting system and in tool wear. Based on this finding, the equations to calculate the cutting speed for a chosen tool life and/or the tool life for a chosen cutting speed are proposed. The concept of the technical resource of the cutting wedge is introduced as the total amount of work done before it fails.
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1. Introduction

Reduction of direct manufacturing costs associated with machining operations is a never-ending challenge for manufacturing plants that have this problem more pressing in recent years. There are a number of reasons for that: (1) increased use of special alloys with enhanced properties; (2) significant tightening of quality requirements for machined parts, (3) increasing global competition, which is changing the environment facing most companies today. In the authors’ opinion, the only proper way for the modern metal-machining industry to progress is to increase the productivity of machining operations.

As known (Astakhov & Outeiro, 2019), the productivity of machining operations where the tool or workpiece rotates is determined by the penetration rate commonly known as the feed rate determined as the product of the cutting feed (mm/rev), f and the rotational speed (rpm), n. As the rotation speed is calculated as IJMMME.2020040101.m01 (v is the cutting speed, m/min; dw is the workpiece diameter in turning or drill diameter in drilling, mm, π = 3.141), the productivity equality depends on both the cutting feed and the cutting speed. It is also known (Astakhov, 2014) that the limit of the cutting feed increase is well-set primarily by two factors: (1) Quality of matching: machining surface integrity including surface roughness, circularity, and straightness of machined holes in drilling operations, lobbing in gear hobbling, and so on. (2) Tool strength, which depends on both the properties of the work and the tool materials. In other words, it is set by the allowable normal stress over the tool–chip interface. When the cutting feed, and thus the normal stress over the tool–chip interface exceeds this limit, the whole rake faces cracks. Therefore, the only feasible option to increase productivity is the cutting speed, which should be optimal for a given application. Increase of the cutting speed to its optimal value actually decrease tool wear in spite of common notions, e.g. the widely-used Taylor’s formula (Astakhov & Outeiro, 2019).

In reality of practical machining, one of the most important steps to make is to determine the optimum cutting speed as the cutting speed directly affects tool life, process productivity, and efficiency. A problem is that there is no a widely accepted methodology of cutting speed determination for a given cutting conditions. The ranges of the recommended cutting speeds given by leading cutting tool manufacturers in their catalogs are based on various experimental studies done by these companies. Let’s consider a few examples.

ISCAR recommends (ISCAR, 2019) for turning of low alloy and cast steels (less than 5% of all alloyed elements) having hardness HB 276, tensile strength 930 MPa (work material group 7) the following cutting speeds: 70 – 130 m/min for tool material IC3028/830, 160 – 280 m/min for IC8250, 110 – 190 m/min for IC9025, 200 – 320 m/min for IC8150, and 220 – 340 m/min for IC5005/428. Walter (2019) recommends for turning of medium-carbon steels having hardness HB 150, tensile strength 500 MPa (ISO material group P2) the following cutting speeds: 200 – 340 m/min for tool material WPV10, and 130 – 200 m/min for WRV20. Kennametal (2018) recommends for turning of low-carbon (0.3% C) steel the following cutting speeds: 180 – 495 m/min for tool material KCP05B/KCP05/KCPK05, and 180 – 460 m/min for KT315/KTP10. Mitsubishi (2019) in its selecting standards recommends for turning of ISO P10 steel the cutting speeds 200 – 400 m/min for tool material UE6105 and 150 – 400 m/min for MC6015. As can be seen, one can select the cutting speeds for the same combination of work/tool materials that differ two times. Moreover, the cutting feed and depth of cut are not accounted for. As a result, some trial-and-error testing is needed to establish the cutting speed for the required tool life.

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