Cutting mode in turning: elements and the concept of cutting

2024 Author: Henry Conors | [email protected]. Last modified: 2024-02-12 02:55

One of the multifunctional methods of metal processing is turning. With its help, rough and fine finishing is carried out in the process of manufacturing or repairing parts. Process optimization and efficient quality work is achieved by rational selection of cutting data.

Process Features

Turning finishing is carried out on special machines with the help of cutters. The main movements are performed by the spindle, which ensures the rotation of the object fixed on it. The feed movements are made by the tool, which is fixed in the caliper.

The main types of characteristic work include: face and shaped turning, boring, processing of recesses and grooves, trimming and cutting off, threading. Each of them is accompanied by the productive movements of the corresponding inventory: through and thrust, shaped, boring, cutting, cutting and threading cutters. A variety of machine typesprocess small and very large objects, internal and external surfaces, flat and bulky workpieces.

Basic elements of modes

The cutting mode in turning is a set of parameters for the operation of a metal cutting machine, aimed at achieving optimal results. These include the following items: depth, feed, frequency, and spindle speed.

Depth is the thickness of the metal removed by the cutter in one pass (t, mm). Depends on the desired cleanliness and corresponding roughness. With rough turning t=0.5-2 mm, with finishing - t=0.1-0.5 mm.

Feed - the distance of movement of the tool in the longitudinal, transverse or rectilinear direction relative to one revolution of the workpiece (S, mm / rev). Important parameters for its determination are the geometric and qualitative characteristics of the turning tool.

Spindle speed - the number of revolutions of the main axis to which the workpiece is attached, carried out over a period of time (n, rev / s).

Speed - the width of the passage in one second with the specified depth and quality, provided by the frequency (v, m/s).

Turning force - an indicator of power consumption (P, N).

Frequency, speed and force are the most important interrelated elements of the cutting mode in turning, which set both the optimization indicators for finishing a particular object and the pace of the entire machine.

Initial data

From the point of view of a systematic approach, the processturning can be considered as the coordinated functioning of the elements of a complex system. These include: lathe, tool, workpiece, human factor. Thus, the effectiveness of this system is influenced by a list of factors. Each of them is taken into account when it is necessary to calculate the cutting mode for turning:

• Parametric characteristics of the equipment, its power, type of spindle rotation control (step or stepless).
• Method of fastening the workpiece (using a faceplate, faceplate and steady rest, two steady rests).
• Physical and mechanical properties of the processed metal. Its thermal conductivity, hardness and strength, the type of chips produced and the nature of its behavior relative to inventory are taken into account.
• Geometric and mechanical features of the cutter: corner dimensions, holders, corner radius, size, type and material of the cutting edge with appropriate thermal conductivity and heat capacity, toughness, hardness, strength.
• Specified surface parameters, including its roughness and quality.

If all the characteristics of the system are taken into account and rationally calculated, it becomes possible to achieve maximum efficiency of its work.

Turning performance criteria

Parts made using turning finishing are most often components of critical mechanisms. Requirements are met based on three main criteria. The most important is the maximum performanceeach one.

• Correspondence of the materials of the cutter and the object being turned.
• Optimization between feed, speed and depth, maximum productivity and quality of finish: minimum roughness, shape accuracy, no defects.
• Minimum resource cost.

The procedure for calculating the cutting mode during turning is carried out with high accuracy. There are several different systems for this.

Calculation methods

As already mentioned, the cutting mode during turning requires taking into account a large number of different factors and parameters. In the process of technology development, numerous scientific minds have developed several complexes aimed at calculating the optimal elements of cutting conditions for various conditions:

• Math. It implies an exact calculation according to existing empirical formulas.
• Graphographic. Combination of mathematical and graphical methods.
• Tabular. Selection of values corresponding to the specified operating conditions in special complex tables.
• Machine. Use of the software.

The most suitable one is chosen by the performer depending on the tasks set and the mass character of the production process.

Math method

Cutting conditions are analytically calculated during turning. Formulas exist more and less complex. The choice of system is determined by the features and the required accuracy of the resultsmiscalculations and the technology itself.

Depth is calculated as the difference between the thickness of the workpiece before (D) and after (d) processing. For longitudinal work: t=(D - d): 2; and for transverse: t=D - d.

Admissible submission is determined step by step:

• numbers that provide the required surface quality, S_cher;
• tool-specific feed, S_p;
• value of the parameter, taking into account the features of fastening the part, S_det.

Each number is calculated according to the corresponding formulas. The smallest of the received S is chosen as the actual feed. There is also a generalizing formula that takes into account the geometry of the cutter, the specified requirements for the depth and quality of turning.

• S=(C_sR^yr^u): (t ^xφ^{z2), mm/rev;}
• where C_{s is the parametric characteristic of the material;}
• Ry – specified roughness, µm;
• ru – turning tool tip radius, mm;
• tx – turning depth, mm;
• φz – angle at the top of the cutter.

Speed parameters of spindle rotation are calculated according to various dependencies. One of the fundamental:

v=(C_vK_v): (T^mt ^xS^{y), m/min where}

• C_{v – complex coefficient summarizing the material of the part, cutter, process conditions;}
• K_{v – additional coefficient,characterizing the features of turning;}
• Tm – tool life, min;
• tx – depth of cut, mm;
• Sy – feed, mm/rev.

Under simplified conditions and for the purpose of making calculations available, the speed of turning a workpiece can be determined:

V=(πDn): 1000, m/min, where

n – machine spindle speed, rpm

Equipment used capacity:

N=(Pv): (60100), kW, where

• where P is the cutting force, N;
• v – speed, m/min.

The given technique is very time-consuming. There is a wide variety of formulas of varying complexity. Most often, it is difficult to choose the right ones in order to calculate the cutting conditions during turning. An example of the most versatile of them is given here.

Table method

The essence of this option is that the indicators of the elements are in the normative tables in accordance with the source data. There is a list of reference books that list the feed values depending on the parametric characteristics of the tool and the workpiece, the geometry of the cutter, and the specified surface quality indicators. There are separate standards that contain the maximum allowable restrictions for various materials. The starting coefficients necessary for calculating the speeds are also contained in special tables.

This technique is used separately or simultaneously with the analytical one. It is comfortable and accurateapplication for simple serial production of parts, in individual workshops and at home. It allows you to operate with digital values, using a minimum of effort and initial indicators.

Graphographic and machine methods

The graphical method is auxiliary and is based on mathematical calculations. The calculated results of the feeds are plotted on a graph, where the lines of the machine and the cutter are drawn and additional elements are determined from them. This method is a very complicated complex procedure, which is inconvenient for mass production.

Machine method - an accurate and affordable option for experienced and novice turners, designed to calculate cutting conditions when turning. The program provides the most accurate values in accordance with the given initial data. They must include:

• Coefficients characterizing the material of the workpiece.
• Indicators corresponding to the features of the tool metal.
• Geometric parameters of turning tools.
• Numerical description of the machine and how to fix the workpiece on it.
• Parametric properties of the processed object.

Difficulties may arise at the stage of numerical description of the initial data. By setting them correctly, you can quickly get a comprehensive and accurate calculation of cutting conditions for turning. The program may contain work inaccuracies, but they are less significant than with the manual mathematical version.

The cutting mode during turning is an important design characteristic that determines its results. Along with the elements, tools and coolants and lubricants are selected. A complete rational selection of this complex is an indicator of the experience of a specialist or his perseverance.