ISO 8688-2:1989 フライス盤での工具寿命テスト—パート2：エンドミル加工 | ページ 5

7.5.1 逃げ面摩耗（VB）の測定

逃げ面摩耗の測定は、摩耗ランドの表面に平行に、元の刃先に垂直な方向で実行されます。たとえば、元の切れ刃から元の逃げ面と交差する摩耗ランドの限界までの距離です。逃げ面の大部分の逃げ面摩耗ランドは均一なサイズであるかもしれませんが、工具プロファイルとエッジチッピングに応じて、逃げ面の他の部分での値にばらつきがあります (7.3 を参照)したがって、逃げ面摩耗測定の値は、測定が行われる刃先に沿った領域または位置 (図 8 を参照) に関連するものとします (7.2 および 7.3 を参照)

9.1 目的

テストの主な目的は、被削材、工具材料、工具形状、または切削油の比較 (またはランキング) です。その他の目的には、切削条件の推奨事項を作成するのに役立つデータの確立、工具にかかる力、機械加工された表面の特性、切りくずの形状などの機械加工特性の研究が含まれる場合があります. ただし、これらの目的のために、ISO 8688 のこの部分に記載されている特定の推奨事項を含めることができます。テストの特定の要件または目的に合わせて変更する必要があります。そのような変更は報告されなければならない。

10.1 一般的な考慮事項

多刃工具を使用したエンドミル加工による劣化試験結果の評価は、次のガイドラインを使用して実施する必要があります。

• 試験の目的は、0 節または 9.1 節に従って確立するものとする。
• テスト結果は、適切に計画されたテスト プログラムから得られる必要があります (9.2 を参照)
• 試験技法の原則を適用する必要があります（9.4 を参照）。

7 Tool deterioration and tool-life criteria

7.1 Introduction

In practical workshop situations the time at which a tool ceases to produce workpieces of the desired size or surface quality usually determines the end of useful tool life. The period up to the instant when the tool is incapable of further cutting may also be considered as the useful tool life. However, the reasons for which tools may be considered to have reached the end of their useful tool life will be different in each case depending on the cutting conditions, etc.

To increase reliability and comparability of test results it is essential that tool life be defined as the total cutting time of the tool to reach a specified value of tool-life criterion.

In order to produce test values which are reliable and comparable with test values produced from a variety of sources, it is necessary to identify and classify tool deterioration phenomena in accordance with 7.3 and to recommend those, together with their limiting values, which should be used to determine the end of useful tool life in accordance with 7.4.

Depending on where the deterioration occurs at the cutting edges, different values can be accepted.

This part of ISO 8688 recommends that tool deterioration in the form of wear be used for determining tool life. Since other modes of tool deterioration may determine the end of useful tool life, the definitions given in 7.2 take into account cracks, chipping and deformation.

Each type of deterioration will progress or occur in a variety of ways depending on the cutting conditions. Where more than one form of deterioration becomes measurable, each should be recorded, and when any one of the deterioration phenomena limits has been attained, the end of tool life has then been reached.

The numerical value of tool deterioration used to determine tool life governs the quantity of testing material required and the costs of testing.

If the limiting value if too high, the cost of establishing results may exceed the worth of these results. If the limiting value is too low, the established result may be unreliable since it may be determined during the initial stages of deterioration development under the test conditions.

Many types of tool deterioration phenomena are listed in this clause. Some of them may occur only occasionally under the testing conditions recommended in this part of ISO 8688.

7.2 Definitions

For the purposes of this part of ISO 8688, the following definitions apply.

7.3 Tool deterioration phenomena

Wear on end milling cutters and slot drills is illustrated in figure 8.

7.4 Tool deterioration phenomena used as tool-life criteria

In order to be able to determine tool life and to compare the influence of different test parameters it is necessary to select one defined type of deterioration of the cutting part as a criterion.

The tool-life criterion can be a predetermined numerical value of any type of tool deterioration which can be measured. Where more than one form of deterioration becomes measurable, each should be recorded and when any one of the deterioration phenomena limits has been attained, the end of tool life has been reached.

The type of deterioration that is believed to contribute most to the end of useful tool life in a specific series of tests shall be used as a guide to the selection of one of the tool-life criteria specified. The type and value of the criterion used shall be reported.

7.4.1 Recommended tool-life criteria

Tool-life criteria which can be defined as a predetermined numerical value of specific types of tool wear are recommended.

A certain width of the flank wear land (VB) is the most commonly used criterion.

The following tool life end points are recommended:

• Uniform wear: 0,3 mm averaged over all teeth.
• Localized wear: 0,5 mm max. on any individual tooth.

7.4.2 Other tool-life criteria

In cases where none of the recommended criteria applies, it may be possible to obtain meaningful data by using one of the following criteria.

• A certain depth of the face wear (KT) is sometimes used as a criterion.
• Chipping (CH) is a criterion which may be used.
• When chipping occurs it is to be treated as localized wear using a VB 3 value equal to 0,5 mm (see figure 8) as a tool-life end point.
• Chipping (CH) in a very heavy form and flaking (FL) are forms which exceptionally could be used as criteria.

Catastrophic failure (CF) can occur inadvertently and should not be used as a primary criterion for the tool-life end point.

Cutters with small diameters (usually less than 12 mm) sometimes break owing to clogging or increasing wear of various types before wear measurements can be recorded. This type of deterioration is not recommended as a tool-life criterion.

7.5 Assessment of tool deterioration

Measurement of tool wear and brittle deterioration using appropriate equipment (see 8.2 and 9.3.5) at intervals determined by the test plan (see 9.2) should be recorded on the data sheets and plotted on diagrams (see 10.4 and annex B).

When there is evidence of built-up-edge (BUE), built-up-layer (BUL), or other debris of work material on the surface of the cutting tool, such observations should be reported since accurate measurement of the deterioration phenomena may be impeded by such deposits. Although mechanical techniques for the removal of deposits from tool surfaces are not recommended, it may be permitted to remove BUE or BUL using a soft material such as a"thumb nail", piece of plastic or wood, with a minimal risk of damaging the tool. Chemical etching may be used only when the cutting tool material is very different from the work material. If deposit removal is undertaken, the method used shall be reported in detail.

7.5.2 Measurement of face wear (KT)

Face wear KT 1 is evaluated by the crater depth which is measured from the original face of the tool in a direction perpendicular to the original face. Since the depth of the crater will vary along its length, the position of the depth measurement in relation to the original cutting edge should be recorded together with the position of the section considered for measurement in relation to some reference point on the tool faces (see 7.2 and 7.3.2.1).

Face wear KT 2 is measured as the distance between the worn edge and the original cutting edge in a direction perpendicular to the original face (see 7.2 and 7.3.2.2).

7.5.3 Assessment of chipping (CH)

Chipping should be measured both on the flank and on the face parallel and perpendicular to the original cutting edge. The position along the cutting edge where chipping occurs should be indicated.

7.5.4 Assessment of cracks (CR)

Cracking is evaluated by counting the magnification of 8X) and by measuring between two consecutive cracks. The should be reported.

8 Equipment

8.1 Machine tool

The milling machine on which the tests are to be conducted shall have sufficient power and physical capacity, be of stable design and be in such condition that abnormal vibrations or deflections are not observed during the test. Cutting conditions which cause chatter should not be used. However, if chatter does occur it may be reduced significantly or eliminated by a small change in cutting speed without varying other cutting parameters.

The spindle axis orientation, vertical or horizontal, shall be recorded.

The accuracy of the milling machine shall be in accordance with ISO 1701.

The feed speed under load shall be constant.

The traverse required for a test should not exceed 0,75 times the limit of motion of the axis.

8.2 Other equipment

Table 5 lists equipment which is necesary and recommended for carrying out the tests specified in this part of ISO 8688.

9 Procedure

9.2 Planning

Planning of the test programme should take into consideration which of the following types of tests should be used to achieve the purpose of the test.

• Type A: One single test point for a particular combination of test variables.This type of test is intended for the determination of, for example, differences between two or more batches of work materials, groups of tools, etc. (see 10.3.1).
• Type B: One vT curve, with the cutting speed as a variable for a particular combination of other cutting variables (see 10.3.2).
• Type C: Tool life as a function of cutting speed and feed (see 10.3.3).
• Type D: Tool life as a function of cutting speed, feed, and axial and radial depths of cut (see 10.3.3).
• Type E: Machining characteristics such as cutting forces, machined surface and chip formation.

When planning the tests outlined above, the likely scatter in test results and the need for a minimum number of tests, which may be determined from previous experience or from statistical considerations (see clause 10), should be considered.

Care should be exercised when assessing the material quantity requirements for completing the entire test programme (see tables 6 and 7). Guidance in the selection of the cutting speed range, the feed values and the desirable time intervals between successive assessments of the amount of tool deterioration, taking into account the expected progression of tool deterioration, may be obtained from preliminary tests.

9.3 Preparation of material, tools and equipment

Prior to the commencement of any single experiment constituting part of a test programme the following preparatory steps should be taken.

9.3.1 Workpiece

All types of surface scale should be machined away. Individual specimens of appropriate size should be cut from the bars or billets and clearly stamped to identify the parent bar or billet, and the position and orientation within that bar or billet originally occupied by the specimen.

Visual inspection and hardness tests should be carried out on each test piece and details recorded before commencing the cutting test (see 3.1). Where a specimen has been used previously, the machined surface generated under the test conditions may have to be considered as"scale" and removed by clean-up cuts with a fresh tool before a new experiment is started.

9.3.2 Tool geometry and cutting edges

Tool geometry should be inspected and recorded (see 4.2, 4.3 and 7.4.1 ). The cutting edges should be marked, inspected and compared with recommended cutting edge conditions at a minimum magnification of 8X and checked for cutting defects such as burn marks, chipping and cracking. The cutting edges shall have neither burrs nor feather edges. The defects shall be corrected, if possible; otherwise the tool shall not be used.

9.3.3 Tools and tool holders

The chuck should be checked for damage. The machine spindle and chuck should be cleaned immediately prior to mounting the chuck. The axial and radial runout of the tool should be measured, after it has been mounted in the chuck, using an indicator, graduated to 0,001 mm and having a flat anvil, and the values recorded for each edge. Recommended limiting values of runout are given in 4.5.

9.3.4 Machine tool

Since spindle speeds and feed speeds quoted on machine tools may be nominal values, the actual spindle speeds and feed speeds should be measured and recorded under load conditions which are representative of the test conditions. Before any testing is commenced, the machine tool should be warmed up by running the spindle for a minimum period of 30 min at a speed of 0,7 times the maximum available spindle speed or at the speed to be used in the test. At 5 min intervals during this period the feed motion should be engaged to cause an axis movement at least equal to that required for the test, in the region to be used for testing, and the axis then returned at rapid traverse.

Clamping devices should be checked to ensure the best possible workpiece stability.

9.3.5 Equipment for assessment of tool deterioration

The availability and quality of suitable equipment for measuring tool deterioration phenomena should be ensured (see 8.2). This information should be recorded on suitable data sheets (see annex B).

9.3.6 Personnel

Machine operators and other persons involved in the test programme should be adequately instructed as to the purposes of the tests and the test procedure.

9.4 Test techniques

Complete information concerning the tests should be recorded on suitable test data sheets (see annex B).

Before starting the actual tests, a check should be made to ensure that the cutting conditions have been chosen to be compatible with the cutting tools, the tool holder, the machine tool, the clamping device, etc., and that the estimated tool life will be obtained.

Tool or spindle overhang should be kept to a minimum.

Successive passes should always be made in the same feed direction and the tool should be returned to the starting point for a pass, ensuring that there is no possible contact between the cutting edges and the workpiece during the return motion.

Successive cuts in the same slot, in the axial direction of the tool, should not be allowed and for slotting tests (see figure 1 ) the slot should not be allowed to break out from the workpiece.

The walls between slots shall have a thickness equal to a quarter of the depth of cut and shall be not less than 3 mm.

The length of the pass is considered to be equal to the length of the workpiece or, if this is not relevant, the cut length corresponding to the feeding distance with the tool in full engagement with the workpiece.

Prior to commencing a new test run, the workpiece shall be"cleaned up" using a fresh tool (see 9.3.1).

9.5 Measurements and recording of tool deterioration

At time intervals determined by the test plan all edges should be examined. Measurements of tool deterioration should be carried out and the observations recorded on the data sheets together with details of any deterioration (see annex B).

These measurements should be made with the tool mounted in the machine (see 7.1 and 7.2). The measurements should be made on the most deteriorated edge. It may be acceptable to measure the cutter after removal from the machine tool spindle, provided that the cutter can be reinserted in the spindle and realigned in the same position after measurement.

The tool deterioration measurement values should be treated in accordance with clause 10.

10 Evaluation of results

10.2 Treatment of test values/observations

The individual edges of the same tool used in a given test run are not independent of each other. Consequently, the test values from measurements or other observations of tool deterioration on individual edges shall be regarded together as the result of a specified test run with one tool.

In tests where a specific type of deterioration is expected and measured or studied (see 7.3 to 7.5) any early or sudden occurrence of an unexpected deterioration phenomenon shall be carefully observed and recorded. If this unexpected deterioration is likely to have an influence on the test results, the test run shall be disregarded in the calculations of the total result.

Unexpected and very serious deteriorations should normally cause a rejection of the test run. The reasons shall be investigated. In the case of repeated failure, a change of the test conditions shall be considered.

10.3 Number of test runs

Regardless of the purpose of the test or the type of test undertaken (see 9.1 and 9.2) the accuracy of the results which can be achieved or might be desired is always a function of the number of test runs.

The desired accuracy of the test results shall be balanced against the limitations given by the consumption of material, tools, time and money (see 7.5).

For the study of machining characteristics such as chip formation, surface characteristics, etc. (test type E, see 9.2), one test run of limited size for each test condition will normally be sufficient.

When comparing cutting tool materials, cutting fluids, etc. (see 9.1), experienced personnel may be able to establish with sufficient accuracy the significance of differences in the test results from a very small number of test runs.

For test procedures the purpose of which is to determine the tool life, edge deterioration phenomena are measured directly (see 7.4.1 and 7.5) or indirectly by observations of surface finish, dimensions of the workpiece or other machining results.

In these cases a number of test runs for each cutting condition is recommended to give an acceptable accuracy from a practical point of view and from the basis of experience and statistical considerations.

10.3.1 Test type A

For test type A (see 9.2) a minimum of three repeated test runs is needed. However, if the differences between batches of materials, groups of tools, etc. are small, the use of the statistical methods given in annex C will show that more test runs may be needed in order to determine whether the results are significant.

10.3.2 Test type B

To plot the tool life (see clause 7) as a function of the cutting speed ( vT diagram) it is necessary to have at least five data points corresponding to five cutting speed values (see figure 9).

Starting with a cutting speed giving a tool life of not less than 5 min, the cutting speed should be decreased for each data point, if possible using a constant ratio such that the maximum tool life during testing is not less than 25 min.

A tool life of less than 5 min will be unreliable. However, a tool life in excess of 25 min may be costly in terms of material and time.

The actual cutting speeds used depend on the speeds available on the machine tool and the requirement for stable cutting, and they should be reported.

Two or more types of deterioration may occur in the same test. If it is not clear which type of deterioration will dominate, it is possible to use two (or even more) criteria (I and II in figure 10). This can be carried out in two different ways as follows.

• a) Determination of the tool life for criterion I for all tests in a specific series and subsequent determination of the tool life for criterion II, also for all tests in the series.When tool life is plotted for both criteria as a function of a variable (e.g. the cutting speed) then two different curves will be obtained (see the example given in figure 10).
• b) Combined criteria are adopted and, in this case, the tool life will be considered to be ended when either criterion I or criterion II is reached. When tool life is plotted as a function of a variable (e.g. the cutting speed) this will usually result in a"broken" curve (see the example given in figure 10).

10.3.3 Test types C and D

For test type C (see 9.2) the minimum number of data points is seven, obtained in seven test runs. For test type D (see 9.2) the minimum number of data points is nine, obtained in nine test runs.

10.4 Diagrams

Tool deterioration values of any type (see 7.3) obtained in a test run and treated as a group of dependent values from all the edges on the same cutter can be plotted over the effective cutting time (see 9.5). The data points on the curve may be the individual measurement values (see figure 11), the arithmetic mean values (see figure 12) or the maximum and minimum values (see figure 13). The arithmetic mean values and the maximum and minimum values are calculated statistically as described in annex C.

The tool life is obtained from the point or the field of intersection of the curves mentioned above and the horizontal line representing the limiting deterioration value determined as the"tool-life criterion" (see 7.4.). For repeated test runs, the tool life values can be treated statistically to calculate the arithmetic mean value, the standard deviation, the maximum and minimum values and the confidence interval.

Figures 11, 12 and 13 show a variety of curves which intersect the tool-life criterion level. It is essential, when plotting tool life against any cutting parameter or when reporting tool-life values, that it is made clear whether tool life is based on the values from one single test run, from the arithmetic mean value of a number of test runs or from the statistically determined maximum or minimum value.

Tool-life values obtained as described above can be plotted against any independent factor, e.g. cutting Speed (sec 9.2 types B, C or D), in Order to give a vT diagram (sec figure 9). lt is common to plot VT diagrams with logarithmic scales. The vT curve thus obtained will, under normal conditions, be represented by a straight line. This line should be fitted to the data points in such a manner that the sum of the squares of the vertical distances between the line and the actual points is as small as possible. Experienced personnel may well be capable of constructing a line through the test points"by eye" with sufficient accuracy. Guidance on statistical calculations for this purpose are found in ISO 3685, and other references are given in clause 2.

It should be noted that the deterioration may change in character when cutting properties are changed, e.g. an increase in cutting speed. Consequently any diagram representing tool life as a function of changing cutting data shall be based on one specified deterioration phenomenon and one tool-life criterion. If this is not possible, the actual conditions shall be specially recorded.

10.5 Statistical interpretation

The use of statistical methods in the evaluation of test results from cutting operations needs great care with regard to the number of test values and the quality of the test results. If these demands cannot be met, statistical methods should not be used.

Guidelines for statistical calculations of arithmetical mean values, standard deviations, maximum and minimum values and confidence intervals are given in annex C.

The determination of significant differences between results from two or more cutting conditions is also described as an example in the same annex. The recommended calculation method is based on Student's t distribution.

Guidelines for the statistical calculations which can be used for determining tool-life diagrams of type B, C or D (see 9.2) are found in ISO 3685 and other references given in clause 2 and in the bibliography.

Bibliography