ASTM E618-81(1996)
(Test Method)Standard Method for Evaluating Machining Performance of Ferrous Metals Using an Automatic Screw/Bar Machine
Standard Method for Evaluating Machining Performance of Ferrous Metals Using an Automatic Screw/Bar Machine
SCOPE
1.1 This method covers a production-type test for evaluating the machining performance of ferrous metals as they are used in single-spindle or multiple-spindle automatic screw machines. It is based on producing parts of a standard design in such machines to uniform levels of quality with respect to surface roughness and size variation. The standard test piece, designed for this test, is machined from bars using a specified number of tools in a specified sequence. Nothing in this method should be construed as defining or establishing limits of acceptability for any grade or type of metal.
1.2 This standard may involve hazardous materials, operations, and equipment. This standard does not purport to address all of the safety problems associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: E 618 – 81 (Reapproved 1996) An American National Standard
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Reprinted from the Annual Book of ASTM Standards. Copyright ASTM
Standard Test Method for
Evaluating Machining Performance of Ferrous Metals Using
an Automatic Screw/Bar Machine
This standard is issued under the fixed designation E 618; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
This test method was written to fill a requirement for a standard test for determining the
machinability of ferrous metals using automatic screw/bar machines. (Hereafter, these machines will
be referred to as automatic screw machines.) Although a variety of short-time laboratory tests have
demonstrated different machining characteristics among ferrous metals, it has been difficult to apply
the resulting data to commercial automatic screw machine practice.
In this test method a standard test piece is machined using tools and machining operations typical
of automatic screw machine practice.
Through the use of this test method, the relative machining performance of a metal can be evaluated
even though different automatic screw machines are used. Further, comparisons can be made among
different lots of the same grade or different grades to determine relative machining performance.
1. Scope the surface roughness per set of samples is the average of the
roughnesses recorded as in 3.1.5.1 for the six test pieces per
1.1 This test method covers a production-type test for
set. A test set is described in 9.3.
evaluating the machining performance of ferrous metals as
3.1.2 calculated hourly production rate (in pieces per
they are used in single-spindle or multiple-spindle automatic
hour)—3600 s/h divided by the cycle time in seconds per
screw machines. It is based on producing parts of a standard
piece. (Unit: pieces per hour.)
design in such machines to uniform levels of quality with
3.1.3 cycle time—the time in seconds per piece from bar
respect to surface roughness and size variation. The standard
feed-out to bar feed-out, or from cutoff to cutoff, during
test piece, designed for this test, is machined from bars using
uninterrupted operation of the machine. It includes all stock,
a specified number of tools in a specified sequence. Nothing in
machine, and tool movements.
this test method should be construed as defining or establishing
limits of acceptability for any grade or type of metal. 3.1.4 surface speed—the product of the original bar circum-
1.2 This standard does not purport to address all of the ference (in feet or metres) and the spindle speed in revolutions
safety concerns, if any, associated with its use. It is the per minute. (Unit: ft/min or m/min.)
responsibility of the user of this standard to establish appro- 3.1.5 surface-roughness average value (R )—the surface-
a
priate safety and health practices and determine the applica-
roughness average value is the mean reading around which the
bility of regulatory limitations prior to use. needle tends to dwell or fluctuate under small amplitude when
a continuously averaging meter is used. (Refer to 3.8.1.1 in
2. Referenced Documents
ANSI B46.1). The surface-roughness value obtained by a
2.1 American National Standard:
continuously averaging digital readout meter is acceptable.
B46.1 Surface Texture
3.1.5.1 The surface-roughness recorded for each surface on
3. Terminology the test piece is the maximum of the surface-roughness average
values measured on that surface at a minimum of four places
3.1 Definitions of Terms Specific to This Standard:
equispaced around the circumference and measured as de-
3.1.1 average surface roughness (per set of samples)—for
scribed in 3.1.5.
each surface (the major and minor diameter formed surfaces)
3.1.6 surface-roughness range (per set of samples)—the
lowest and highest values of the surface roughnesses recorded
This test method is under the jurisdiction of ASTM Committee A-1 on Steel,
for each surface as in 3.1.5.1 for each set.
Stainless Steel, and Related Alloys and is the direct responsibility of Subcommittee
A1.15 on Bars.
3.1.7 surface-roughness range (per test)—the lowest and
Current edition approved March 27, 1981. Published July 1981. Originally
highest values of surface roughnesses recorded for each surface
published as E 618 – 77 T. Last previous edition E 618 – 77 T.
2 as in 3.1.5.1 during the test.
Available from American National Standards Institutes, 11 West 42nd Street,
13th Floor, New York, NY 10036. 3.1.8 theoretical hourly production rate (in pieces per
E 618
hour)—3600 s/h divided by the cycle time in seconds per piece 3.2.3 Hourly rate of production as described in 3.1.2 or
diminished by: (1) the indexing time or high-speed time in 3.1.8.
seconds per piece for a multiple-spindle machine, or (2) the 3.2.4 A test sample set is described in 9.3.
time in seconds per piece when no tools are cutting for a
4. Summary of Test Method
single-spindle machine.
3.1.9 tool feed rate—the distance traveled by the tool at a 4.1 A standard test piece, shown in Fig. 1, is machined from
uniform rate divided by the number of spindle revolutions bar stock in an automatic screw machine.
during which this travel occurs. (Units: decimal inch or 4.2 Specified tools are used in a standard sequence to shape
decimal millimetre per revolution.) the test piece. Drills and form tools are used simultaneously to
3.1.10 tool life (for a form tool)—the hours of machine time provide a typical machining condition during the test.
determined from the calculated hourly production rate and the 4.3 Cutting speed and tool feed rate for the metal being
total number of test pieces produced from the start of the test tested are varied from one test run to another to determine the
to the earliest point at which the average of the recorded maximum rate at which test pieces can be produced for the
surface-roughness average values or the average of sizes of the specified length of time without exceeding the specified limits
test pieces in a sample set consistently exceed either the for surface roughness and size dimensions.
4.4 When measured as specified, the level of and changes in
surface-roughness limits or the size limits specified in 9.7.1,
9.7.2, and 9.7.3 for the piece diameter produced by that tool. surface roughness and the size of pieces produced are used to
evaluate the machining performance of the metal being tested.
3.2 Machining performance in this test method is evaluated
by the following criteria:
5. Significance and Use
3.2.1 Tool life as described in 3.1.10.
3.2.2 Cutting speed and tool-feed rate as described in 3.1.4 5.1 This test method can be used to evaluate the machining
and 3.1.9. performance of a single grade or type of metal or to compare
FIG. 1 Details of the ASTM Machinability Test Specimen and the Relative Positions of Form Tools
E 618
one grade or type with another. size test piece provided that the material removed and the
5.1.1 The machining performance of the test metal is material remaining is in the same cross-sectional proportion as
measured by the maximum rate at which test pieces can be in the test piece shown in Fig. 1. When a different bar size is
produced within specified surface roughness and dimensional used a proportionate change is made in all dimensions, except
limits for a specified length of time and also by the cutting that both formed surfaces must be at least ⁄8 in. (9.5 mm) long.
speed and tool feed employed to attain that rate. This is to ensure accurate surface-roughness measurements.
5.1.2 The relative machining performance of the various
7.3 When a different size test piece is used the bar size and
metals tested using this test method may be evaluated only at test piece dimensions shall be recorded on the test report.
operating conditions that produce test pieces of like quality
with respect to surface roughness and dimensional limits for 8. Procedure for Machine Setup
comparable periods of machining time.
8.1 Since there is a difference between automatic screw
machines as to how movement is conveyed to the end and side
6. Apparatus
working tools, cams must be designed or selected to provide a
6.1 Automatic Screw Machine:
uniform rate of tool feed for a distance greater than that
6.1.1 A single-spindle automatic screw machine with a six-
necessary to remove the required metal. This will ensure a
or eight-hole turret, with adequate spindle capacity, and with
uniform feed rate throughout the cut.
sufficient feed, speed, and power to machine a 1-in. round bar
8.2 Feeds and speeds on the initial test run should be
of free-machining, alloy or high-strength steel, or
selected on the basis of experience or general guide lines for a
6.1.2 A multiple-spindle automatic screw machine with a
ferrous metal of similar composition and condition.
spindle capacity and with sufficient feed, speed, and power to
8.2.1 The positive stop pressure maintained during the test
machine 1-in. round bars of free-machining, alloy or high-
shall be that which is recommended by the machine tool
strength steel simultaneously at all spindles.
builder.
6.2 Metal-Cutting Tools—On the basis of current use for
8.3 Place the cutting tools so they cut in the following
general applications for automatic screw-machine production,
sequence. The form tools and drills shall cut at the same time.
two tool-steel grades (M7 for drills and M2 for form tools) are
8.3.1 Spot drill (optional).
suggested in 6.2.1 through 6.2.5. This is not intended to
8.3.2 Rough form and drill to depth with ⁄8-in. (15.88-mm)
preclude the use of other grades. This test method does require
diameter drill.
that the use of tool materials, other than those suggested, be
8.3.3 Finish form to 0.875-in. (22.22-mm) outside diameter
recorded and reported together with the reason(s) for the
11 3
and drill ⁄32 in. (8.73 mm) deep with the first ⁄8-in. (9.52-mm)
change.
diameter drill.
6.2.1 A ⁄4-in. (19.05-mm) diameter or larger spot drill with
8.3.4 Drill ⁄32 in. (8.73 mm) deep (through the cutoff) with
a 90° included point angle may be used.
the second ⁄8-in. (9.52-mm) diameter drill.
3 5
6.2.2 Two ⁄8-in. (9.52-mm) diameter and one ⁄8-in. (15.88-
8.3.5 An optional sequence of tooling for a single-spindle
mm) diameter drills ground as specified in 8.6.
automatic machine uses only three drills in the turret; namely,
6.2.3 Either a dovetail or a circular rough-form tool of M2
5 3
one spot drill, one ⁄8-in. (15.88-mm) drill, and one ⁄8-in.
steel designed as shown in Fig. 2.
(9.52-mm) drill with double indexing of the turret between
6.2.4 A flat, circular, or dovetail finish-form tool at least ⁄16
successive drilling operations.
in. (14.29 mm) wide made from M2 steel as shown in Fig. 3.
8.3.6 Cut off the finished piece.
6.2.5 A cutoff tool as described in 8.5.
8.4 Form Tool Conditions:
6.3 Stylus-Type Standard Commerical Surface-Roughness-
8.4.1 Using the most rigid cross-slide, set the rough-form
Measuring Instrument, capable of measuring surface rough-
tool so that the part of the tool forming the 0.615 to 0.620-in.
ness in microinches arithmetic average (AA) and having a
1 (15.62 to 15.75-mm) or minor diameter will cut on center.
stroke of at least ⁄4 in. (6.35 mm).
8.4.2 Set the finish-form tool to cut the rough-formed 0.900
6.3.1 In all cases an electric cutoff of 0.030 in. (0.8 mm) is
to 0.905-in. (22.86 to 22.99-mm) or major diameter on center
used. The stylus and skids of the tracer head must be
and remove 0.030 in. (0.76 mm) from that diameter to form the
compatible with a 0.030-in. (0.8-mm) cutoff. (See 3.6.2 in
0.870 to 0.875-in. (22.10 to 22.22-mm) diameter. When a
ANSI B46.1 for a definition of cutoff.)
different size test piece is used, proportionately more or less
6.3.2 The length of trace is the maximum possible on the
metal will be removed by the finish-form tool.
surface being measured but must be at least 0.150 in. (3.81
8.4.3 Grind and mount all form tools in the machine with an
mm).
effective positive top rake angle of 10°, a front clearance angle
6.4 Micrometer(s), capable of indicating to 0.0001 in. or
of 5 to 12°, and, for the rough-form tool, a side-clearance angle
0.002 mm.
of 2 to 4°. Note any deviation from these angles found
6.5 Toolmaker’s Microscope or equivalent.
necessary and record the reason.
6.6 Commercially Available Coolant.
8.4.4 When the side-clearance angle for the rough-form
7. Test Specimen
tools is obtained by a tilted tool holder, it is recommended that
7.1 The test specimen detailed in Fig. 1 shall be machined the rough-form tool be reground in a tool holder or fixture
having an identical angle of tilt.
from 1-in. (25.4-mm) diameter bars.
7.2 Different bar sizes may be used to produce a different 8.4.5 All form tools must be hardened to 63 minimum HRC.
E 618
FIG. 2 Details of the Tool Edge for the ASTM Rough-Form Tool
8.5 Cutoff Tool—An appropriate commercial tool shall be 8.6.2.3 Use a split point on the drills with 135° included
used. angle.
8.6 Drills: 8.6.2.4 All drills shall have the helix angle which is standard
for the manufacturer of the drills.
8.6.1 Use solid two-flute standard length or screw-machine
8.7 Direct the coolant to flood the test pieces and the tool
length high-speed steel twist drills. Note any deviation that is
cutting edges during machining.
found necessary to conduct the test and record the reason.
8.6.2 Included (point angles) angles shall be 118° for all
9. Test Method
metals except stainless steels and high-strength metals, when a
135° included angle shall be used.
9.1 Determine the reliability of machining-performance
8.6.2.1 The lip clearance angles shall be 14 6 2° for the data to be expected on any given machine by running machine-
⁄8-in. (9.52-mm) drill(s) with 118° included angle; 12 6 2° for
capability tests prior to a test program to determine the
the ⁄8-in. (15.88-mm) drill with 118° included angle; 12 6 2° tolerance limits within which the machine is capable of
for the ⁄8-in. drill(s) with the 135° included angle; and 10 6 2°
producing the test piece. A method for doing this is described
for the ⁄8-in. drill with 135° included angle. in Appendix X1. Machine-capability tests should be performed
8.6.2.2 Web thinning may be necessary when resharpening each time a variance pattern of sizes develops which departs
drills with 118° included angle. from the norm pre
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