MR4 Turning Process
Unit Process Life Cycle Inventory
Dr. Devi Kalla, Dr. Janet Twomey, and Dr. Michael Overcash
August 19, 2009
Turning process summary ................................................................................................... 2
Methodology for unit process life cycle inventory model .................................................. 4
Turning Process Energy Characteristics ......................................................................... 4
A. Parameters affecting the energy required for turning .................................................... 8
Turning Energy ............................................................................................................... 8
Idle Energy .................................................................................................................... 11
Basic Energy ................................................................................................................. 12
B. Method of Quantification for Mass Loss ..................................................................... 17
Lci for Material Mass Loss Calculations ...................................................................... 17
Lci for Cutting Fluid Waste Calculations ..................................................................... 18
Lci for Lubricant Oil Waste Calculations ..................................................................... 19
Cutting tool usage ......................................................................................................... 19
Case Study on Turning...................................................................................................... 19
Product Details: ............................................................................................................. 20
Cutting Parameters ........................................................................................................ 21
Machining Process: ....................................................................................................... 21
Time, Power, and Energy calculations ......................................................................... 22
Lci Material mass loss calculations .............................................................................. 24
Lci for Cutting fluid waste calculations ........................................................................ 24
Summary: .......................................................................................................................... 24
References Cited ............................................................................................................... 24
Appendices ........................................................................................................................ 25
Manufacturers Reference Data ..................................................................................... 25
1
Turning process summary
Turning is a frequent unit process in manufacturing as a mass reduction step, in
which the major motion of the single point cutting tool is parallel to the axis of rotation of
the rotating workpiece thus generating external surfaces. Facing is a special case of
turning in which the major motion of the cutting tool is at right angles to the axis of
rotation of the rotating workpiece. Hence this life cycle heuristic is to establish
representative estimates of the energy and mass loss from the turning unit process in the
context of manufacturing operations for products. The turning unit process life cycle
inventory (uplci) profile is for a high production manufacturing operation, defined as the
use of processes that generally have high automation and are at the medium to high
throughput production compared to all other machines that perform a similar operation.
This is consistent with the life cycle goal of estimating energy use and mass losses
representative of efficient product manufacturing.
Turning is a cutting process in which material is removed by a rotating workpiece
across which a point cutting tool removes material, typically aided by cutting fluids. The
workpiece is usually held in a workholding device such as a chuck, and the tool is
mounted in a tool post. In turning, the tool progressively generates a surface by removing
chips from a workpiece rotated and fed into a cutting tool and these chips are swept away
by the rotation of the workpiece. The turning process is used to produce cylindrical
external surfaces and flat surfaces during facing operation. The turning process requires a
turning machine or lathe, workpiece, fixture, and cutting tool. Turning is also commonly
used as a secondary process to add or refine features on parts that were manufactured
using a different process. Consequently, chip disposal in turning and the effectiveness of
cutting fluids are important. An example turning machine is given in Figure MR4.1,
while the turning mechanism is illustrated in Figure MR4.2.
Figure MR4.3 shows an overview of the developed environmental-based factors
for turning operations. For a given workpiece (illustrated in Figure MR4.2) the life cycle
analysis yields energy use and mass losses as byproducts or wastes.
Figure MR4.1. Computer numerical control (CNC) turning machine with 3-axis control
(Photograph from Haas Automation, Inc. California, USA)
2
Figure MR4.2. Process Schematic (Todd et al., 1994)
Figure MR4.3. LCI data for turning process
3
Methodology for unit process life cycle inventory model
In order to assess a manufacturing process efficiently in terms of environmental
impact, the concept of a unit operation is applied. The unit process consists of the inputs,
process, and outputs of an operation. Each unit process is converting material/chemical
inputs into a transformed material/chemical output. The unit process diagram of a turning
process is shown Figure MR4.4.
The transformation of input to output generates five lci characteristics,
a. Input materials
b. Energy required
c. Losses of materials (that may be subsequently recycled or declared waste)
d. Major machine and material variables relating inputs to outputs
e. Resulting characteristics of the output product that often enters the next unit process.
Machine tool, Fixing, Cutting Fluid
Work Piece
Process parameters
Cutting Tools
Cutting Fluid
Energy
Turning
Product with
desired shape
Chips
Noise
Waste Coolant
Scrap
Mist
Figure MR4.4. Input-Output diagram of a turning process
Turning Process Energy Characteristics
Because high production turning is a semi-continuous process, there are a variety
of CNC turning machines, ranging from a simple two-axis lathe to a multi-axis
machining center. The main parts of the CNC turning centers are the bed, headstock,
cross-slide, carriage, turret, tailstock, servomotors, ball screws, hydraulic and lubrication
systems, and the machine control unit. These machines are classified as horizontal,
vertical or universal based on the spindle orientation. The uplci is based on a
representative operational sequence, in which
1) Work setup generally occurs once at the start of a batch in production. The setup
time is composed of the time to setup the turning machine, plan the tool
movements, and install the fixture device into the turning machine. All drawings
and instructions are consulted, and the resulting program is loaded. Typical setup
times are given in Table MR4.1 (Fridriksson, 1979). The total setup time must be
divided by the size of the batch in order to obtain the setup time per component.
The energy consumed during this setup period is divided by all the parts
processed in that batch and is assumed to be negligible and is discussed in the
example below.
2) The power consumption during a batch for positioning or loading each new piece
into the turning CNC machine, with respect to tool axis is low. Time is required to
load the workpiece into the turning machine and secure it to the fixture. The load
4
3)
4)
5)
6)
time can depend on the size, weight, and complexity of the workpiece, as well as
the type of fixture. This is at the level of Basic energy and is labeled Loading.
Relative movement of the cutting tool and the workpiece occurs without changing
the shape of the part body, referred to as Idle Energy and is labeled Handling.
This is the time required for any tasks that occur during the process cycle that do
not engage the workpiece. This idle time includes the tool approaching and
retracting from the workpiece, tool movements between features, adjusting
machine settings, and changing the tools.
Cutting of a workpart for desired shape occurs and is labeled Tip Energy. The
time required is for the cutting tool to make all necessary cuts in the workpiece
for each operation.
The piece is repositioned for subsequent cutting, thus the energy and mass loss
will be repeated. (Idle Energy for Handling and then Tip Energy for turning)
When the final shape is attained, the piece is unloaded and typically sent forward
to another manufacturing unit process. This is at the level of Basic Energy and is
labeled Unloading.
Table MR4.1. Set-up times for machining operations (Fridriksson, 1979)
Basic setup time (h)
Additional setup per tool (h)
Machine tool
Horizontal band saw
0.17
---
Manual turret lathe
1.2
0.2
CNC turret lathe
0.5
0.15
Milling machine
1.5
---
Drilling machine
1.0
---
Horizontal-boring machine
1.3
---
Broaching machine
0.6
---
Gear hobbing machine
0.9
---
Grinding machine
0.6
---
Internal grinding machine
0.6
---
Machining center
0.7
0.05
In this representative unit process, the life cycle characteristics can be determined
on a turning per piece basis or on a full piece (with one or more cuts) basis. Since this is a
high production process, the start up (at the beginning of a batch or shift) is deemed to be
small and not included. In this uplci, there are three typical power levels that will be used,
Figure MR4.5. Each power level, kw, is the incremental power not the absolute total
5
power. Thus if electrical measurements are made, the kw during the tip measurement
must have the idle and basic power (kw) values subtracted to obtain this tip power (kw).
Correspondingly, there are times within the turning sequence from which these three
power levels are used, Figure MR4.5. The overall time per piece is referred to as cycle
time and is generally consistent in a batch. Each power level is a reflection of the use of
various components or sub-operations, of the CNC machine, Figure MR4.6.
Power
Spindle and Coolant
motor Startup
Idle Energy
Tip Energy
Basic Energy
Pturning
Pidle
Pbasic
tturning
Time
tidle
tbasic
Figure MR4.5. Determination of power characteristics and energy requirements of
machine tools.
The steps 2), 3), 5), and 6) are estimated as representative values for use in this
unit process lci and energy required of removing material by turning, 4), is measured
using specific cutting energy values.
The system boundaries are set to include only the use phase of the machine tool,
disregarding production, maintenance and disposal of the machine. Moreover, the
functioning of the manufacturing machines is isolated, with the influence of the other
elements of the manufacturing system, such as material handling systems, feeding robots,
etc. covered in other uplci reports.
The energy consumption of turning is calculated as follows.
6
Etotal = Pbasic * (tbasic) + Pidle * (tidle) + Pturning * (tturning)
(Basic energy) (Idle energy) (Turning energy)
(1)
Servo Motors
Fan
Oil pump
Chiller System
Main Spindle
Automatic tool changer
Rapid Axis Movement
Cutting fluid pump
Machine Tool idle power
Machine Tool basic power
Unloaded Motors
Chip Generation Zone
Tip Energy
Numerical control
Lighting
Way lube system
Figure MR4.6. System boundary of the machining process
7
A. Parameters affecting the energy required for turning
An approximate importance of the many variables in determining the turning
energy requirements was used to rank parameters from most important to lower
importance as follows:
1. Workpiece Material properties
2. Feed rate
3. Cutting speed
4. Diameter of the workpiece
5. Turning time
6. Depth of cut
7. Coolant
8. Part holding fixture
9. Tool wear
10. Geometry and set-up
From this parameter list, only the top 6 were selected for use in this unit process life
cycle with the others having lower influence on energy. Energy required for the overall
turning process is also highly dependent on the time taken for idle and basic operations.
Turning Energy
Turning time (tturning) and power (Pturning) must be determined for the turning energy
and are calculated from the more important parameters given above. Turning process time
is used to calculate a part of the energy for this unit process and based on a turning area
(tool in contact with workpiece).
The total turning process is illustrated in Figure MR4.7. The cutting speed, V (m/min),
is the peripheral speed of the workpiece past the cutting tool. The rotational speed of the
spindle, N, (rev/min) (set on the machine), N = V/ (π*Di). Where V = cutting speed,
mm/min and Di = Initial diameter of the workpiece, mm. Feed, f (mm/rev), for turning is
the distance that a tool advances into the workpiece during one revolution of the
headstock spindle. V and f are estimated from the material properties, Table MR4.2 and
Table MR4.3. The feed rate, fr (mm/min) is the rate at which the cutting tool and the
workpiece move in relation to one another. The feed rate, fr (mm/min), is the product of
f *N. The volume removal rate has been defined as the expected cut area multiplied by
the rate at which the material is removed perpendicular to the area. For turning, the area
removed is an annular ring of initial diameter Di and finished diameter Df. Thus, the
expected cut area is
(Di2 -Df2)/4. The rate at which the tool is fed, fr (in unit distance per minute), is f * N.
Therefore, the volume removal rate (VRR) for turning is:
VRR = ( (Di2 -Df2)/4) * fr (mm3/min)
Difference between the initial and final diameter is the depth of cut. The actual
turning time is the turning length, divided by the feed rate, fr.
Time for turning tturning = (l)/f*N = l/fr = l /[f*(V/π*Di)]
(2)
8
Where l = Length of the surface to be machined, mm.
f – Feed, mm/rev.
N- Spindle speed, rpm
fr - feed rate, mm/min
V – cutting speed, m/min
Figure MR4.7. Schematic diagram of turning process
The turning energy is thus E (Joule/cut) = turning time*Pturning,
E = turning time*(volume removal rate)*(specific cutting energy, Up, W/mm3/sec)
(3)
Eturning (Joule/cut) = tturning *VRR*Up = tturning * Pturning
With a given material to be cut, the specific cutting energy, Up, is given in Table MR4.2.
Then for that material a representative cutting speed, V is selected from Table MR4.2. V
and Di are used to calculate N. Then N and f are used to obtain fr.
The turning energy is then calculated from equation 3. Thus with only the material to be
cut, and the depth of cut, one can calculate the lci turning energy for a single cut. This
then must be added to the idle and basic energies, see below.
9
Table MR4.2. Average values of energy per unit material removal rate and recommended
speeds and feeds (Erik, 2000; Hoffman, 2001; Joseph, 1989; Kalpakjian, 2008; 9, 10)
Hardness
[Brinell
hardness
number]
Specific
cutting
energy,
Up
[W/ mm3
per sec]
(Hp/ in3
per min)
Cutting Speed, V
(m/min, ft/min)
125 - 175
2.98 (1.1)
24 - 46, 80 - 150
125 - 175
3.67 (1.35)
11 - 43, 70 - 140
125 - 175
3.94 (1.45)
18 - 54, 60 - 175
250 - 375
35 - 40
3.26 (1.2)
3.80 (1.4)
21 - 49, 70 - 160
12 - 18, 40 - 60
High
temperature
nickel and
cobalt
200-360
6.8 (2.5)
Aluminum alloys
30 -150
0.68 (0.25)
56, 184
182 - 244, 600 800
Plain cast iron
150 -175
0.82 (0.30)
45 - 60, 148 - 196
176 - 200
0.90 (0.33)
35 - 50, 115 - 165
201 - 250
1.14 (0.42)
25 - 40, 82 - 132
251 - 300
1.36 (0.50)
18 - 32, 60 - 105
150 - 175
0.82 (0.30)
36 - 76, 120 - 250)
176 - 200
1.14 (0.42)
24 - 46, 80 - 150
201 - 250
1.47 (0.54)
18 - 37, 60 - 120)
150 - 175
150 - 175
176 - 200
201 - 250
100
225
1.14 (0.42)
1.69 (0.62)
1.82 (0.67)
2.18 (0.80)
0.68 (0.25)
2.72 (1.0)
60 - 120, 200 - 400
40 - 150, 130 - 500
26 - 125, 85 - 410
20 - 80, 65 - 265
100, 330
30, 100
145 -240
2.26 (0.83)
2.26 (0.83)
90 - 180, 300 - 600
76 - 152, 250 - 500
Material
Low carbon
alloy steels
Medium carbon
alloy steels
High carbon
alloy steels
Titanium
Alloys
Steels
Alloy cast iron
Malleable iron
Cast steel
Zinc alloys
Monel
Brass
Bronze
Feed (f)
(mm/rev,
inch/rev)
0.18 - 0.75,
0.007 - 0.030
0.18 - 0.75,
0.007 - 0.030
0.13 - 1.52,
0.005 - 0.06
0.13 - 1.27,
0.005 - 0.05
0.2, 0.007
0.18, 0.007
0.18 - 0.64,
0.007 - 0.025
0.5 - 0.89, 0.02
- 0.035
0.38 - 0.64,
0.015 - 0.025
0.3 - 0.56,
0.012 - 0.022
0.254 - 0.52,
0.010 - 0.020
0.38 - 0.64,
0.015 - 0.025
0.3 - 0.56,
0.012 - 0.022
0.254 - 0.52,
0.010 - 0.020
0.254 - 0.52,
0.010 - 0.020
0.25, 0.01
0.20, 0.007
0.15, 0.005
0.4, 0.15
0.18, 0.007
0.38 - 0.64,
0.015 - 0.025
0.38 - 0.64,
Density
(kg/m3)
7480-8000
7480-8000
7480-8000
4500
7850
8900
2712
6800-7800
6800-7800
6800-7800
6800-7800
6800-7800
6800-7800
6800-7800
6800-7800
6800-7800
6800-7800
6800-7800
7140
8830
7700-8700
8900
10
Copper
125-140
2.45 (0.90)
30 - 90, 100 - 300
0.015 - 0.025
0.127 - 1.27,
0.005 - 0.05
Magnesium
alloys
Lead
150
80 -100
0.73 (0.27)
0.6
80, 275
45, 150
0.38 - 0.64,
0.015 - 0.025
0.4, 0.015
8930
1810
11,350
Table MR4.3. Recommended speeds and feeds for turning plastics (Terry and Erik, 2003)
Turning Single Point (H-S Steel)
Material
Thermoplastics
Polyethylene
Polypropylene
TFE fluorocarbon
Butyrate
ABS
Polyamides
Polycarbonate
Acrylics
Polystyrenes, low
and medium impact
Thermosets
Paper
and cotton base
Homopolymers
Fiber glass,
and graphitized
Asbestos base
Cutting Speed, V
m/s
Feed, f , mm/rev
Depth of cut, mm
0.8 - 1.8
1.5 - 2.0
1.0 - 2.0
1.5 - 3.8
1.2 - 1.8
2.5 - 3.8
3.8 - 5.0
3.8 - 5.0
2.5 - 3.8
2.5 - 3.8
0.25
0.05
0.30
0.40
0.38
0.25
0.05
0.05
0.19
0.02
3.8
0.6
1.5
3.8
3.8
3.8
0.6
3.8
3.8
0.6
2.5 - 5.0
5.0 - 10.0
2.0 - 2.5
1.0 - 2.5
2.5 - 5.0
3.2 - 3.8
0.30
0.13
0.30
0.30
0.13
0.30
3.8
0.6
3.8
3.8
0.6
3.8
Idle Energy
Energy-consuming peripheral equipment included in idle power are shown in
Figure MR4.6. In the machining praxis it is known as “run-time mode” (Abele et al.,
2005). The average idle power Pidle of automated CNC machines is between 1,200 and
15,000 watt*. (* This information is from the CNC manufacturing companies, see
Appendix 1). The handling power characterizes the load case when there is relative
movement of the tool and the work-piece without changing the shape of the body (e.g.
rapid axis movement, spindle motor, coolant, tool changer) - Handling.
11
The idle time (tidle) is the sum of the handling time (thandling) and the turning time
(calculated above as tturning, equation 2), see Figure MR4.5. For CNC turning machines,
the handling times are the air time of cutter moving from home position to the location at
the start of the cut, the approach to the actual cut, the overtravel, then retraction after
turning to the next cut at this location, and traverse, if needed to cut at another location on
the same work piece. Approximate Handling time will vary from 0.1 to 10 min. We can
calculate the idle times and energy as follows.
Idle time = [timehandling + timeturning]
(4)
A cutting tool moves from the home position to the location of the start of the cut
at a horizontal traverse rate, HTR and is defined as the air time1. This distance would be
in the range of 5 to 30 mm. During the turning process, the total travel of the cutting tool
is larger than the length of the workpiece due to the cutter approach and overtravel
distances and this time can be defined as air time2. The approach and overtravel
distances, l1 and l2 respectively, can be assumed to be 2 to 10 mm, enough for the cutting
tool axis to clear the end of the part. During this time the cutting tool moves with the
constant feed rate, fr. After reaching the overtravel point, the tool retraces back to an
offset position, but at a faster rate called the vertical traverse rate, VTR.
Time for handling is
Air time1 + Approach/overtravel times + retraction times = thandling
(5)
To this idle time must be added the time to traverse to the next cut (if needed) and
this is (cut spacing)/transverse speed, HTR, as given by the CNC manufacturer. The
example given later in this uplci lists such traverse speed data for use in any
representative turning scenarios.
From these calculations the idle energy for a single cut is
E (Joule/cut)idle = [thandling + tturning]* Pidle
(6)
Thus with just the information used in calculating tturning, and the representative
idle power (1,200 – 15,000 watts), one can calculate the idle energy for this turning unit
process.
Basic Energy
Turis the demand under running conditions in
The basic power of a machine tool
ning
“stand-by mode”. Energy-consuming peripheral equipments included in basic power are
Con movement between the tool and the workshown in Figure MR4.6. There is no relative
ditio
piece, but all components that accomplish the readiness for operation (e.g. Machine
ns motors, pumps) are still running at no load
control unit (MCU), unloaded motors, servo
Feed
power consumption. Most of the automated CNC machine tools are not switched off
rate power. The average basic power P
when not turning and have a constant basic
basic of
Turand 8,000 watt* (* From CNC manufacturing
automated CNC machines is between 800
ning
companies the basic power ranges from
1/8th to 1/4th of the maximum machine power,
dept
h
Cutt
12
ing
spee
d
(see Manufacturers Reference Data in Appendix). The largest consumer is the hydraulic
power unit. Hydraulic power units are the driving force for motors, which includes chiller
system, way lube system and unloaded motors.
From Figure MR4.5, the basic time is given by
Tbasic = tload/unload + thandling + tturning
(7)
where thandling + tturning = tidle as determined in equation 4.
An exhaustive study of loading and unloading times has been made by
Fridriksson, 1979; it is found that these times can be estimated quite accurately for a
particular machine tool and work-holding device if the weight of the workpiece is known.
Some of Fridriksson, 1979 results are showed in Table MR4.4, which can be used to
estimate machine loading and unloading times. For turning representative work-holding
devices are chuck, Collet, clamps, face plate, independent chuck and three jaw chuck etc.
To these times must be added the times for cleaning the workholding devices etc.
Table MR4.4. Sum of the Loading and Unloading Times (sec) versus Workpiece weight
(Fredriksson, 1979) (load and unload times are assumed equal)
Workpiece Weight
Holding Device
0-0.2
0-0.4
0.2-4.5
0.4-10
4.5-14
10-30
14-27 (kg)
30-60 (lb)
Crane
Angle Plate
27.6
34.9
43.5
72.1
276.5
Between Centers,
with dog
25.6
40.2
57.4
97.8
247.8
Between Centers,
no dog
13.5
18.6
24.1
35.3
73.1
Chuck, universal
16.0
23.3
31.9
52.9
--
13
Chuck, independent
(4 jaws)
34.0
41.3
49.9
70.9
--
Clamp on table
(3 clamps)
28.8
33.9
39.4
58.7
264.6
Collet
10.3
15.4
20.9
--
--
Faceplate
(3 clamps)
31.9
43.3
58.0
82.1
196.2
Fixture, horizontal
(3 screws)
25.8
33.1
41.7
69.4
274.7
14
Fixture vertical
(3 screws)
27.2
38.6
53.3
--
--
Hand-held
Jig
1.4
25.8
6.5
33.1
12.0
41.7
---
---
Magnet table
2.6
5.2
8.4
--
--
Parallels
14.2
19.3
24.8
67.0
354.3
15
Rotary table or
Index plate
(3 clamps)
28.8
36.1
44.7
72.4
277.7
“V” Blocks
25.0
30.1
35.6
77.8
365.1
Vise
13.5
18.6
24.1
39.6
174.2
Thus the energy for loading and unloading is given by
Basic energy, tbasic = [timeload/unload + timeidle ]*Pbasic
(8)
Where timeidle is given in earlier sections and timeload/unload is from Table MR4.4. Pbasic is
in the range of 800 to 8,000 watts.
16
Thus the uplci user must add some reasonable value from Table MR4.4 for the
load/unload times and can then use the timeidle to determine the Basic energy
In summary, the unit process life cycle inventory energy use is given by
Etotal = Pbasic * (tbasic ) + Pidle * (tidle) + Pturning * (tturning)
This follows the power diagram in Figure MR4.5. With only the following
information the unit process life cycle energy for turning can be estimated.
1. Material of part being manufactured
2. Volume material removal rate
3. Turning time
4. Table MR4.4
(9)
B. Method of Quantification for Mass Loss
The mass loss streams in turning process, identified with the associated process
performance measures, are depicted in the Figure MR4.11 below.
Turning


Cutting fluid mist
Dust (dry machining)

Chips, worn tools

Spent cutting fluids
Gas/Aerosol
Waste
Stream
Solid
Liquid
Figure MR4.11. Waste Streams in turning process
Lci for Material Mass Loss Calculations
The workpiece material loss after turning a cross sectional area can be specified
as chip mass (ms). Metal chips are accumulated, and cutting fluid is separated from these.
The chip mass (ms) can be calculated by multiplying the volume of material removed
(Vremoval) by the density of the workpiece material ρ.
Density of the material can be attained from the material property list as shown in Table
MR4.2, kg/m3.
  ( Di 2  D f 2 ) 
* l  [mm3]
Volume of the material removed = Vremoval  
(10)


4


Where
l = Length of the workpiece to be machined in mm,
Di = Initial diameter of the workpiece in mm.
Df = Final diameter of the workpiece in mm.
Chip mass (ms) = Vremoval * ρ * (1 m3/1 E+09 mm3) [kg]
(11)
17
Lci for Cutting Fluid Waste Calculations
For turning operations, cutting fluids can be used to allow higher cutting speeds,
to prolong the cutting tool life, and to some extent reduce the tool - work surface friction
during machining. The fluid is used as a coolant and also lubricates the cutting surfaces
and the most common method is referred to as flooding (Wlaschitz and Hoflinger, 2007).
Table MR4.5 shows the recommended cutting fluid for turning operations. Cutting fluid
is constantly recycled within the CNC machine until the properties become inadequate.
The dilution fluid (water) is also supplied at regular intervals due to loss through
evaporation and spillage.
Table MR4.5. Cutting fluid recommendations for turning operation
(Hoffman et al., 2001)
Material
Aluminum
Alloy Steels
Brass
Tool steels and Low carbon
Steels
Turning (most of these
cutting fluids are
aqueous suspensions)
Mineral Oil with 10% fat
or soluble oil
25 Percent sulfur base oil
with 75 percent mineral
oil.
Mineral Oil with 10
percent of fat
25% land oil with 75%
mineral oil
Copper
Monel Metal
Cast iron
Soluble Oil
Soluble Oil
Dry
Malleable Iron
Soluble Oil
Bronze
Soluble Oil
Magnesium
10% Land oil with 90%
of mineral oil.
The service of a cutting fluid provided to one CNC machine tool for one year was
considered as the functional unit. It is assumed that the number of parts produced per unit
18
time will not vary depending on the cutting fluid replacement. The turning time
associated with one year of production was based on the schedule of 102 hr of
turning/week for 42 weeks/year from one of the most comprehensive cutting fluid
machining studies (Andres et al., 2008). From (Andres et al., 2008) a single CNC
machine using cutting fluid required an individual pump to circulate the fluid from a 55
gallon (208L) tank to the cutting zone. The 208L/machine is recycled within process until
it is disposed of after two weeks. Assuming cutting fluid is used 204 hr/ 2 weeks, then the
cutting fluid loss is 208L/ (204*60) per minute. Which is 0.017 L/min or about 17 g/min
as the effective loss of cutting fluid due to degradation. The coolant is about 70wt% - 95
wt% water, so at 85wt% water, the coolant oil loss is 15wt% or 2.5 g cutting oil/min.
With the machining time for turning a cross sectional area the mass loss of coolant oil can
be calculated.
There is also be a fugitive emissions factor here that could account for aerosol
losses. Wlaschitz and Hoflinger (2007) measured aerosolized loss of cutting fluid from a
rotating machining tool under flooding conditions. For a cutting fluid use of 5,700 g/min,
the aerosol oil loss was about 0.0053 g/min and water loss of 0.1 g/min. Other losses
from spills and carry off (drag-out) on workpieces were not included at this time.
Lci for Lubricant Oil Waste Calculations
Lubricant oil is mainly used for a spindle and a slide way. Minute amount of oil is
infused to the spindle part and the slide way at fixed intervals. From the CNC
manufacturing companies it is found that lubricant oil is replaced only 2-3 times of the
life of the machine. It is assumed that the life of the machine is around 20 years. Since it
is negligible lubricant oil loss is not considered for this study.
Cutting tool usage
Turning processes often require regular replacement of cutting tools. The tool life
is a time for a newly sharpened tool that cuts satisfactorily before it becomes necessary to
remove it for regrinding or replacement. Worn tools contribute significantly to the waste
in the form of wear particles and a worn tool at the end of tool life. The wear particles
usually are carried away by the cutting fluid. From an environmental perspective the
cutting tools remaining at the end of the tool life are of importance as they are often
disposed off and hence are a burden to the environment. The worn tool can be identified
by the process performance in terms of the cutting forces, energy consumed, and surface
finish. For simplification regrinding of the tools are not considered.
Case Study on Turning
In this report we analyze the detailed energy consumption calculations in the
turning process. The machining process is performed on Jeenxi Technology 4-axis CNC
machine (JHV – 1500). The machine specifications are listed below:
19
Table MR4.6. Specifications of JHV – 1500 CNC Machine
Model
TRAVEL
X axis Travel (mm)
Y axis Travel (mm)
Z axis Travel (mm)
Distance from the table to spindle nose (mm)
TABLE
Table dimensions, mm
Max. load of table (kg)
SPINDLE (rpm)
Spindle Taper
Spindle Speed (rpm)
Spindle Drive
Spindle Motor (kw)
Spindle Cooling
FEED RATE
Rapid Traverse (X,Y) (m/min), HTR
Rapid Traverse (Z) (m/min), VTR
Cutting Feed rate (mm/min), fr
3 Axes motor output (X, Y, Z) (kw)
A.T.C
Magazine Type
Tool Magazine Capacity (pcs)
Max. Tool Diameter (mm)
Max. Tool Length (mm)
Max. Tool Weight (kg)
Tool Selection
OTHER
Maximum Power Consumption (KW)
Floor Space (L x W x H)
Machine Weight (kg)
JHV - 1500
Liner
1500
750
700
120 – 820
1650 x 750
1000
8000
BT - 40
8000, 10000
Belt type
7.5 / 11
BT - 40
10000, 12000, 15000
Direct type
7.5 / 11
Oil Cooler
30
24
1 – 15000
4.0 / 4.0 / 7.0
Carosel
16
100 / 150
300
7
Fixed type
Arm
24
80 / 150
300
7
Random
30
4100 x 2640 x 2810 mm
11000
Product Details:
For this example we are assuming a low carbon alloy steel as the work piece. The
work piece is a cylindrical bar that is 3 in. (76.2 mm) diameter and 10 in. (254 mm) long,
where 0.2 in. (5.1 mm) is to be removed up to 3 in. (76.2 mm) length from the end of the
bar. The objective of the study is to analyze the energy consumption in turning process.
The product dimensions are shown in Figure MR4.12. From the dimensions and the
density from Table MR4.2, the weight of the workpiece is 9.26 kg (assuming density as
8000 kg/m3).
20
Figure MR4.12. Dimensions of the Work piece
Cutting Parameters
The machining conditions and the cutting parameters are listed in Table MR4.7.
Table MR4.7. Cutting Parameters for Example Case
Cutting Conditions
Workpiece Diameter (Di)
76.2 mm
Cutting Speed (V), Table MR4.2
40 m/min
Feed (f), Table MR4.2
0.5 mm/rev
Spindle Speed (N) = V/πDi
168 rpm
Feed rate (fr) = f *N
84 mm/min
Length of the surface to be machined
76.2 mm
(l)
depth of cut (d)
5.1 mm
Finish workpiece Diameter (Df)
71.1 mm
VRR = ( (Di2 -Df2)/4) * fr
49,536 mm3/min
Rapid Traverse (horizontal, X,Y)
30
(m/min), HTR
Rapid Traverse (vertical, Z) (m/min),
24
VTR
Machining Process:
Before turning on the work piece in a CNC machine, it is important to set the coordinate axes of the machine with respect to the work piece. The direction along the
length and breadth are taken as positive X and Y axis respectively. The vertical plane
21
perpendicular to the work piece is considered as the Z-axis. During the machining
process the tool is considered to be at an offset of 10 mm above the work piece. Every
time while turning the tool comes down from a height of 10 mm to the approach distance,
5 mm, from the workpiece. Because the end of the cut is a flat surface there is no
overtravel. It goes back to the home position at transverse speed. The feeds and speed are
stated in Table MR4.7.
Time, Power, and Energy calculations
The total processing time can be divided into the 3 sub groups of basic time, idle
time, and turning time.
Turning Time:
The time for turning is determined by
tturning = (l)/fr
(min)
Where l is the length of the workpiece to be machined in mm, fr is the feed in mm/min.
Time for turning a cross section cut will be,
tturning = (76.2)/ 84
= 0.907 min/cut = 54 sec/machined
Machining Power for each cut,
pm = VRR * Specific cutting energy
VRR from Table MR4.7 = 49,536 mm3/min and specific cutting energy, Up, from Table
MR4.2 = 2.98 W/mm3/sec
pm = 49,536 * 2.98/60 = 2.46 kW
Tip Energy required per cut is em = pm * tturning = 2.46 * 54 = 133 kJ/cut
Handling Time:
Time required for the cutter to move from offset position to position prior to cutting (10
mm) is essentially turning in air. The air time of the approach is
ta1 = 10/ (transverse speed)
ta1 = 10/ 24000 mm/min
= 0.0004 min = 0.0025 sec (neglect)
After reaching the approach distance 5 mm from the workpiece it reaches the workpiece
at feed rate, fr (84 mm/min. When not cutting the workpiece, the approach distance,
(Approach)/fr
ta2 = (15)/84 mm/min
= 0.06 min = 4 sec
Retract time ta3 = (76 + 5)/24000 = 0.2 sec
Idle power of the machine can be calculated based on the individual power specifications
of the machine.
Pidle = Pspindle + Pcoolant + Paxis
The assumed values are
22
Pcoolant = 1 kW (~1.5 hp); Pspindle = 4 kW (~5 hp); Paxis = 5 kW (~7 hp)
(These assumed values are from the CNC manufacturing companies, see Appendix 1)
To convert a horse power rating (HP) to Watts (W) simply multiply the horsepower
rating by 746
Idle power for the process is
Pidle = Pspindle + Pcoolant + Paxis
=4 + 1 + 5
= 10 kW
Total Idle time for cut t idle = ta + tturning = 4 + 0.2 + 55
= 59 sec
Total Energy during the idle process is,
eidle = Pspindle * tidle + Pcoolant* tidle + Paxis*tidle
= 10*59
= 590 kJ/cut
Load/unload Time:
The total basic time can be determined based on the following assumptions for this
example:
 The workholding device used for clamping the workpiece is a 4-jaw chuck,
independent, Table MR4.4.
 The total time required to mount the work piece on the vise manually is assumed
to be 49.9/2 = 25 sec.
 After completing the turning process on a single workpiece, the machine is
cleaned using pneumatic cleaners or air blowers. The time required to clean the
machine is assumed to be 0.4 min (25 sec).
 The machined part has to be removed manually from the fixture. The time
required to remove the material from the fixture is assumed to be 49.9/2 = 25 sec.
Therefore, basic processes time for this study is,
Tb = loading time + cleaning time + unloading time
= 25 + 25 + 25
= 75 sec
Basic power of the machine can be assumed as the 25% of the machine maximum in the
manufacturer specifications. Therefore the power consumed during the basic process is,
Pbasic = 7.5 kW
Energy consumed during this process is,
Ebasic = Pbasic * ttotal
The basic time for the process can be taken as the sum of idle time (which contains
machining time) and load/unload times, i.e.
Tbasic = Tb + tidle
= 75 + 59
= 134 sec
ebasic = 7.5* 134 = 1,000 kJ per cut
Total Energy required for turning can be determined as,
23
eprocess = em +eidle + ebasic
=133 + 590 + 1,000
= 1,723 kJ/ cut
Power required for machine utilization during turning is,
Pmtotal = eprocess / ttotal
= 1,723/134 = 12.8 kW.
Lci Material mass loss calculations
Volume of the material removed for a given crossectional area =
  ( Di 2  D f 2 ) 
Vremoval  
* l  [mm3]


4


= 44,936 mm3
Chip mass (ms) = Vremoval * ρ [kg]
ms = 44,936 * 8,000 * 10-9
= 0.359 kg/cut
Lci for Cutting fluid waste calculations
From (Andres et al., 2008) a single CNC machine using cutting fluid required an
individual pump to circulate the fluid from a 55 gallon (208L) tank to the cutting zone.
The 208L/machine is recycled within process until it is disposed of after two weeks.
Assuming cutting fluid is used 204 hr/ 2 weeks, then the cutting fluid loss is 208L/
(204*60) per minute, which is 0.017 L/min or about 17 g/min. The coolant is about 96
wt% water, so at 96wt% water, the coolant oil loss is 4wt% or 0.68 g cutting oil/min.
Turning time per cut tm = 54 sec
Mass loss of the coolant = 0.68*54/60 = 0.61 g cutting oil/cut
The fugitive loss is 0.1 g cutting oil/min or 0.09 g cutting oil/cut
Summary:
This report presented the models, approaches, and measures used to represent the
environmental life cycle of turning unit operations referred to as the unit process life
cycle inventory. The five major environmental-based results are energy consumption,
metal chips removed, cutting fluid, lubricant oil, and cutting tool. With only the
following information the unit process life cycle energy for turning can be estimated.
1. Material of part being manufactured
2. Volume material removal rate
3. Turning time
4. Table MR4.4
The life cycle of turning is based on a typical high production scenario (on a CNC turning
machine) to reflect industrial manufacturing practices.
References Cited
24
1. Abele, E.; Anderl, R.; and Birkhofer, H. (2005) Environmentally-friendly product
development, Springer-Verlag London Limited.
2. Clarens, A.; Zimmerman, J.; Keoleian, G.; and Skerlos, S. (2008) Comparison of
Life Cycle Emissions and Energy Consumption for Environmentally adapted
Metalworking Fluid Systems, Environmental Science Technology,
10.1021/es800791z.
3. Dahmus, J.; and Gutowski, T. (2004) An environmental analysis of machining,
Proceedings of IMECE2004, ASME International Mechanical Engineering
Congress and RD&D Expo, November 13-19, Anaheim, California USA.
4. Erik Oberg. (2000) Machinery’s Handbook, 26th Edition, Industrial Press.
5. Fridriksson, L. Non-productive Time in Conventional Metal Cutting, Report No.
3, Design for Manufacturability Program, University of Massachusetts, Amherst,
February 1979.
6. George, F.S; and Ahmad, K. E. (2000) Manufacturing Processes & Materials, 4th
Edition, Society of Manufacturing Engineers.
7. Groover, M.P. (2003) Fundamentals of Modern Manufacturing, Prentice Hall.
8. Hoffman, E.; McCauley, C.; and Iqbal Hussain, M. (2001) Shop reference for
students and apprentice, Industrial Press Inc.
9. http://www.engineeringtoolbox.com/metal-alloys-densities-d_50.html
10. http://www.mapal.us/calculators/turning/CalculatorTurning.htm
11. Joseph R. Davis. (1989) Machining Handbook, Vol. 16, American Society for
Metals international.
12. Kalpakjian, S.; and Schmid, S. (2008) Manufacturing Processes for Engineering
Materials, 5th Edition, Prentice Hall.
13. Piacitelli, W.; Sieber, et. al. (2000) Metalworking fluid exposures in small
machine shops: an overview, AIHAJ, 62:356-370.
14. Schrader, G.; and Elshennawy, A. (2000) Manufacturing Processes & Materials,
4th Edition, Society of Manufacturing Engineers.
15. Terry, R.; and Erik, L. (2003) Industrial Plastics: Theory and Applications, 4th
Edition, Cengage Learning.
16. Todd, R.; Allen, D.; and Alting, L. (1994) Manufacturing processes reference
guide, Industrial Press, New York.
17. Wlaschitz, P. and W. Hoflinger. (2007) A new measuring method to detect the
emissions of metal working fluid mist, Journal for Hazardous Materials,
144:736-741.
Appendices
Manufacturers Reference Data
The methodology that has been followed for collecting technical information on
CNC machines has been largely based in the following:
The documentation of the CNC machine and the technical assistances collected
from the manufacturing companies through internet. Several interviews with the
service personnel of the different CNC manufacturing companies have been carried
out. After collecting the information from the different companies it has been put
25
together in the relevant document that describes the different approaches the different
companies have regarding the technical information on the CNC machines.
Telephone conversations allowed us to learn more about basic power and idle power.
Companies that involved in our telephone conversations are Bridge port, Fadal, Hass
and Jeenxi. These companies’ manufactures different sizes of CNC machines, but this
report shows the lower, mid and highest level of sizes. For our case study we picked
machine at the highest-level.
Specifications
Model Number
Spindle Speed
Spindle Drive
Spindle Motor
Rapid Traverse (X,Y)
Rapid Traverse (Z)
Cutting Feed rate
3 Axes motor
output(X,Y,Z)
Power Consumption
Specifications
Model Number
Spindle Speed
Spindle Drive
Max Torque
With Gearbox
Spindle motor max
rating
Axis Motor max thrust
Rapids on X-axis
Rapid on Y & Z Axes
Max Cutting
Power
Consumption(min)
Specifications
Model Number
Spindle speed (Belt)
Spindle speed (Gear)
Rapid Traverse (X, Y)
Rapid Traverse (Z)
Cutting feed rate
Spindle drive motor
JEENXI TECHNOLOGY
JHV – 850
JHV – 1020
JHV – 1500
8000 rpm
8000 rpm
8000 rpm
Belt/Direct type
Belt/Direct
Belt/Direct type
5.5/7.5 kw
7.5/11 kw
7.5/ 11 kw
30 m/min
30 m/min
30 m/min
20 m/min
20 m/min
24 m/min
1 – 15000 mm/min
1 – 15000 mm/min
1 – 15000
mm/min
1.8/ 1.8/ 2.5
1.8/ 1.8/ 2.5
4.0/ 4.0/ 7.0
20 KVA
20KVA
40 KVA
VF- 7
7500 rpm
Belt/Direct type
HAAS
VM - 2
12,000 rpm
Inline direct drive
75 ft-lb@1400
250 ft-lb@ 450
20 hp
75 ft-lb@1400
30 hp
MDC
7,500 rpm
Direct speed belt
drive
75 ft-lb@1400
20 hp
3400 lb
600 ipm
600 ipm
500ipm
200 – 250 VAC
380 – 480 VAC
3,400 lb
710 ipm
710 ipm
500 ipm
200 – 250 VAC
380 – 480 VAC
2,500 lb
1,000 ipm
1,000 ipm
833 ipm
200 – 250 VAC
380 – 480 VAC
VMC – 850
8000 rpm
4000/7000 rpm
590.55 ipm
472.44 ipm
236.22 ipm
7.5/ 10 hp
KAFO
VMC – 137
8,000/10,000 rpm
4000/7000 rpm
787.4 ipm
787.40 ipm
393.7 ipm
15/ 20 hp
VMC - 21100
6000/8000 rpm
4000/7000 rpm
393.7 ipm
393.7 ipm
393.7 ipm
15/20 hp
26
X,Y,Z axis drive motor
Power consumption
Specifications
Model Number
Spindle Speed(Belted)
Fanuc Motor Power
Heidenhain Motor
Power
Spindle Speed(Directly
coupled)
Fanuc Motor Power
Heidenhain Motor
Power
Rapid Traverse (X,Y)
Rapid Traverse (Z)
Cutting Feed rate
Power
Specifications
Model Number
Spindle Speed
Spindle Drive
Rapid Traverse (X,Y)
Rapid Traverse (Z)
Cutting Feed rate
Motor Power
Air Pressure Required
Specifications
Model Number
Spindle Speed(Belted)
Spindle Motor Power
X Axis Motor Power
Z Axis Motor Power
Coolant Pump Motor
Power
ATC Motor Power
a12, a12, a12
20 KVA
XR 760
9000/15000 rpm
25/25 hp
28/28 hp
a22, a22, a30
25 KVA
BRIDGE PORT
XR 1270 HP
-
a30, a30, a30
35 KVA
XR 1500 HPD
-
15000 rpm
15000 rpm
30 hp
33 hp
40 hp
34 hp
375 – 7500 rpm
(Gear Box)
40 hp
40 hp
1692 ipm
1417 ipm
787 ipm
30 KVA
1417 ipm
1417 ipm
787 ipm
40 KVA
1417 ipm
1417 ipm
787 ipm
40 KVA
VMC 4020
FADAL
VMC 6030
10 - 10,000 rpm
Automatic
Mechanical Vector
Drive
900 ipm
700 ipm
600 ipm
10 hp
80 – 120 psi
10 - 10,000 rpm
Automatic
Mechanical Vector
Drive
400 ipm
400 ipm
400 ipm
14.7 hp
80 – 120 psi
TTC-630
4000 rpm
15/20 KW
2.8 KW
2.8 KW
TTC
TMC 500
6000
5/7 KW
15000 rpm
1 KW
40 hp
XR 1500 HPD
375 – 7500 rpm
(Gear Box)
40 hp
12.6 KW
34 hp
40 hp
VMC 6535
HTX
6000 rpm
Automatic
Electric Vector
Drive
900 ipm
700 ipm
600 ipm
29.5 hp
80 – 100 psi
27
Rapid Traverse (X,Y)
Rapid Traverse (Z)
Total Driving Power
Hydraulic Pump
197 mm/min
630 mm/min
40 KW
1.1 KW
1417 ipm
1417 ipm
787 ipm
40 KVA
1417 ipm
1417 ipm
787 ipm
40 KVA
28