The project involved the machining analysis of an automotive housing manufactured by Tier-1 automotive supplier. The project involved cost analysis and optimization of machining process for the housing. Solidworks was used for part modeling followed by machining analysis in GibssCAM. Further the cost analysis for the part was performed in two parts, in the first part tool life and cost of tooling was calculated and in the second part machine, material,labor, energy and miscellaneous cost estimation was performed. The simulation was performed by using the recommended feeds, speeds and tooling. Finally the machining process was optimized to reduce the manufacturing cost.
Part Geometry And Cutting Cycle Simulation
The part was created in Solidworks and imported to the GibbsCAM for the cutting simulation. The machine used for the machining operation was the OKUMA 3-AXIS vertical milling machine. The cutting cycle was simulated using face mill, end mill and drill, in which 2 types of end mill and drills were used. The operation summary and part report are generated using GibbsCAM. The simulation resulted in a operation time of 14.6 minutes which include machine time (13.36minutes) and tool changing time(1 minute). The following reports were generated at the end of simulation.
Mill Operation Summary
Part Report In GibbsCAM
Cost and Tool Life Analysis
b. Machining and tool changing time
Machining time obtained using tools (GibBsCAM) = 13.36 minutes
Assumingtool changing time = 1minute
Total time for operation = Machining time + tool changing time = 13.36 + 1 = 14.36 minutes
i. Other cost
These includes cost of maintenance = $ 1 per /part
Total cost for one part = Cost of the stock+ tool cost/part+ Labor cost+ energy cost+Machine cost + Cost of instruments and gauges+ Other cost -Salvage cost
= $18.38 + $9854.26 + $ 7.18 + $ 0.0165 + $ 0.54 + $ 2 + $ 1- $ 0.8975
= $ 9882.479
The tool life and cost analysis was conducted, which helped to determine the major parameters contributing the manufacturing cost.
1. Tool life by Taylor life model
Taylor tool life equation
C =V * T^n
Where
V=cutting speed (surface speed, notfeed speed) [m/min]
T=tool life time [min]
n=Taylor exponent
C=Taylor constant [m-min^(n-1)]
Taking cemented carbide tools
C= 800
n= 0.4
Thevalues are based on the values obtained from the GibbsCAM used for the original run
Operation 1- Tool life for Face Mill operation
RPM = 5000
Tool Diameter = 100 mm
Circumference = π x D = π X 100 = 314.159 mm
Cutting Speed (V) = 5000 x 314. 159 = 1570.796 m/min
800 = 1570.796 x T^0.4
0.509 = T^0.4
T1 = 0.184839 min
Operation 2-Tool life for End mill 1
RPM= 9167
Tool Diameter = 12.5 mm
Circumference = π x D = π X 12.5 = 39.269 mm
Cutting Speed (V) = 9167 x 39.269 mm = 359.9872 m/min
800 = 359.9872 m/min x T^0.4
2.222 = T^0.4
T2 = 7.3597 min
Operation 3-Tool life for End mill 2
RPM= 9167
Tool Diameter = 10 mm
Circumference = π x D = π X 10 = 31.415 mm
Cutting Speed (V) = 9167 x 31.415 mm = 287.981 m/min
800 = 287.981 m/min x T^0.4
2.777 = T^0.4
T3 =12.851 min
Operation 4-Tool life for Drill 1
RPM = 3000
Tool Diameter = 5 mm
Circumference = π x D = π X 5 = 15.707 mm
Cuttingspeed (V) = 3000 x 15.707 mm = 47.121 m/min
800 = 47.121 m/min x T^0.4
16.977=T^0.4
T4 = 1187.5512 min
Operation 5-Tool life for Drill 2
RPM = 3000
C =V * T^n
Where
V=cutting speed (surface speed, notfeed speed) [m/min]
T=tool life time [min]
n=Taylor exponent
C=Taylor constant [m-min^(n-1)]
Taking cemented carbide tools
C= 800
n= 0.4
Thevalues are based on the values obtained from the GibbsCAM used for the original run
Operation 1- Tool life for Face Mill operation
RPM = 5000
Tool Diameter = 100 mm
Circumference = π x D = π X 100 = 314.159 mm
Cutting Speed (V) = 5000 x 314. 159 = 1570.796 m/min
800 = 1570.796 x T^0.4
0.509 = T^0.4
T1 = 0.184839 min
Operation 2-Tool life for End mill 1
RPM= 9167
Tool Diameter = 12.5 mm
Circumference = π x D = π X 12.5 = 39.269 mm
Cutting Speed (V) = 9167 x 39.269 mm = 359.9872 m/min
800 = 359.9872 m/min x T^0.4
2.222 = T^0.4
T2 = 7.3597 min
Operation 3-Tool life for End mill 2
RPM= 9167
Tool Diameter = 10 mm
Circumference = π x D = π X 10 = 31.415 mm
Cutting Speed (V) = 9167 x 31.415 mm = 287.981 m/min
800 = 287.981 m/min x T^0.4
2.777 = T^0.4
T3 =12.851 min
Operation 4-Tool life for Drill 1
RPM = 3000
Tool Diameter = 5 mm
Circumference = π x D = π X 5 = 15.707 mm
Cuttingspeed (V) = 3000 x 15.707 mm = 47.121 m/min
800 = 47.121 m/min x T^0.4
16.977=T^0.4
T4 = 1187.5512 min
Operation 5-Tool life for Drill 2
RPM = 3000
Tool Dia= 7.5 mm
Circumference = π x D = π X 7.5 = 23.561 mm
Cutting speed (V) = 3000 x 23.561 mm = 70.685 m/min
800 = 70.685 m/min x T^0.4
11.317= T^0.4
T5 = 430.853 min
Based on the tool time, tools used per part and number of tools required in year:
Based on the tool time, tools used per part and number of tools required in year:
Total cost of the tools = $ 2956278279
2. Cost Analysis for housing
The cost of housing is sum of the various costs which material, machining, tooling , labor, electricity etc.
2. Cost Analysis for housing
The cost of housing is sum of the various costs which material, machining, tooling , labor, electricity etc.
a. Cost of material required (Aluminum alloy)
Density of cast Aluminum alloy(A380) = 2.71 g/cm^3
Volume of the part = 11.5x 11.8 x 2.5 = 339.25 cm^3
The mass of cast aluminum alloy required - A380 = Density of cast Aluminum alloy(A380) x Volume of the part
= 2.71g/cm^3 x 339.25 cm^3 = 919.3675g
Raw material (stock will be purchasedready-to-machine at $20/kg)
The material cost to produce one part is = Mass of one part x cost of stock
= 919.3675 /1000 x $20/kg
Cost for one part =$ 18.38
Volume of the part = 11.5x 11.8 x 2.5 = 339.25 cm^3
The mass of cast aluminum alloy required - A380 = Density of cast Aluminum alloy(A380) x Volume of the part
= 2.71g/cm^3 x 339.25 cm^3 = 919.3675g
Raw material (stock will be purchasedready-to-machine at $20/kg)
The material cost to produce one part is = Mass of one part x cost of stock
= 919.3675 /1000 x $20/kg
Cost for one part =$ 18.38
b. Machining and tool changing time
Machining time obtained using tools (GibBsCAM) = 13.36 minutes
Assumingtool changing time = 1minute
Total time for operation = Machining time + tool changing time = 13.36 + 1 = 14.36 minutes
c. Tool Cost
Thetooling cost includes cost of End mill (10 mm dia) + End mill (12.5 mm dia) +Face mill (100 mm dia) + Drill (0.187’ dia) + Drill (0.3’ dia)…....................................... The tool cost are taken from www.mcmaster.com
Total cost of the tools = $ 2956278279
Thetool cost per part/year = Total cost of the tool / Volume of the parts
Thevolume of part is 300,000 parts per year
=$ 2956278279 /300000
= $ 9854.26
d. Labor Cost
Labor rate = $ 30 /hr
The operation time = 14.36 minutes
Labor cost to produce one part = Labor rate x Total operation time
Labor cost/ part = 30/60 x 14.36 = $7.18
e. Energy Cost
Energy cost = $0.065 /kWh
Energy required to produce one part = Power/energy required to machine the part xenergy cost
Power/energy required to machine the part = Material removal rate x specific cutting energyof material
Material removal rate = Volume of material removed/ time required for removal
= 339.25 cm^3x 10^3 / (13.36 x 60) = 423.216 mm^3/sec
Specific cutting energyof Aluminum alloys = 0.6 W.s /mm^3
Power/energy required to machine the part = 0.6 W.s /mm^3 x 423.216 mm^3/sec
= 253.929 Watts = 0.2539 kW
Energy required to produce one part = 0. 253929 kW x $0.065 /kWh = $ 0.0165
Thetooling cost includes cost of End mill (10 mm dia) + End mill (12.5 mm dia) +Face mill (100 mm dia) + Drill (0.187’ dia) + Drill (0.3’ dia)…....................................... The tool cost are taken from www.mcmaster.com
Total cost of the tools = $ 2956278279
Thetool cost per part/year = Total cost of the tool / Volume of the parts
Thevolume of part is 300,000 parts per year
=$ 2956278279 /300000
= $ 9854.26
d. Labor Cost
Labor rate = $ 30 /hr
The operation time = 14.36 minutes
Labor cost to produce one part = Labor rate x Total operation time
Labor cost/ part = 30/60 x 14.36 = $7.18
e. Energy Cost
Energy cost = $0.065 /kWh
Energy required to produce one part = Power/energy required to machine the part xenergy cost
Power/energy required to machine the part = Material removal rate x specific cutting energyof material
Material removal rate = Volume of material removed/ time required for removal
= 339.25 cm^3x 10^3 / (13.36 x 60) = 423.216 mm^3/sec
Specific cutting energyof Aluminum alloys = 0.6 W.s /mm^3
Power/energy required to machine the part = 0.6 W.s /mm^3 x 423.216 mm^3/sec
= 253.929 Watts = 0.2539 kW
Energy required to produce one part = 0. 253929 kW x $0.065 /kWh = $ 0.0165
f. Machine cost amortized over 10-year period
The volume of parts produced is 30,000 per year and as it is 2-day shift, the total hours of operation in week will be 16 x 5 = 80 hours, with 52 weeks of operation in year.
The total working hours in year = Number of weeks x hours of operation in week = 52 x 80 = 4160 hours a year
The time required to produce the 300,000 parts = Number of parts x time taken to produce each part = 300,000 x 14.36/60 = 71800 hours
The time required to produce the 300,000 parts is higher than the total working hours in year
The total number of machines required = The time required to produce the 300,000parts / Total working hours in year = 71800 / 4160 = 17.25
Number of machines required = 18
Cost of each machine (roughly) = $ 90,000
Costof 18 machines = $ 1620000
Life of the machine = 10 years
Cost of machine per year = $ 162,000
Machine cost per part = Machine cost per year / Number of parts produced in year
= $ 162,000 /300,000
Machine cost per part = $ 0.54
g. Salvage Cost
Salvage cost is cost related with the scrap
The volume of the scrap = Volume of the stock – Volume of the machines part
= 504.84 cm^3 - 339.25 cm^3 = 165. 593 cm^3
The mass of the scrap = Volume of scrap x density = 165. 593 cm^3 x 2.71 g/cm^3 = 448. 759 g
Cost of scrap = $ 2/Kg
Salvage Cost= 448. 759g/1000 x $ 2/Kg = $ 0.8975
The volume of parts produced is 30,000 per year and as it is 2-day shift, the total hours of operation in week will be 16 x 5 = 80 hours, with 52 weeks of operation in year.
The total working hours in year = Number of weeks x hours of operation in week = 52 x 80 = 4160 hours a year
The time required to produce the 300,000 parts = Number of parts x time taken to produce each part = 300,000 x 14.36/60 = 71800 hours
The time required to produce the 300,000 parts is higher than the total working hours in year
The total number of machines required = The time required to produce the 300,000parts / Total working hours in year = 71800 / 4160 = 17.25
Number of machines required = 18
Cost of each machine (roughly) = $ 90,000
Costof 18 machines = $ 1620000
Life of the machine = 10 years
Cost of machine per year = $ 162,000
Machine cost per part = Machine cost per year / Number of parts produced in year
= $ 162,000 /300,000
Machine cost per part = $ 0.54
g. Salvage Cost
Salvage cost is cost related with the scrap
The volume of the scrap = Volume of the stock – Volume of the machines part
= 504.84 cm^3 - 339.25 cm^3 = 165. 593 cm^3
The mass of the scrap = Volume of scrap x density = 165. 593 cm^3 x 2.71 g/cm^3 = 448. 759 g
Cost of scrap = $ 2/Kg
Salvage Cost= 448. 759g/1000 x $ 2/Kg = $ 0.8975
h. Quality instruments and gauge required
This includes cost of instruments and gauges, assuming it as to be $ 2 per part.
i. Other cost
These includes cost of maintenance = $ 1 per /part
Total cost for one part = Cost of the stock+ tool cost/part+ Labor cost+ energy cost+Machine cost + Cost of instruments and gauges+ Other cost -Salvage cost
= $18.38 + $9854.26 + $ 7.18 + $ 0.0165 + $ 0.54 + $ 2 + $ 1- $ 0.8975
= $ 9882.479
Optimization
The cost estimation showed that the cost for manufacturing the valve is very high. Hence optimization was required to reduce the cost. It was observed that process parameters like tool lifeused was very low. As per the Taylor's tool life equation, tool life was affected by the cutting speed. Hence the optimization involved optimizing the cutting speed. Apart from the cutting speed, the material used for the tool had affect on tool life and eventually the machining cost. Hence optimization also involved optimizing the tool material type.
The initial estimation showed that the manufacturing cost for a single part was $9882.479. The tooling cost was one of the bottle necks. For the first optimization approach, the cutting speed was decreased (1/10 the of the original), for this the manufacturing cost drastically reduced to $ 43.23 , in the second optimization approach the tool material was changed to HSS, which reduced the cost to $ 781.334. It was concluded that keeping the optimal cutting speed results in low cost.
The initial estimation showed that the manufacturing cost for a single part was $9882.479. The tooling cost was one of the bottle necks. For the first optimization approach, the cutting speed was decreased (1/10 the of the original), for this the manufacturing cost drastically reduced to $ 43.23 , in the second optimization approach the tool material was changed to HSS, which reduced the cost to $ 781.334. It was concluded that keeping the optimal cutting speed results in low cost.
Machining On OKUMA
After the simulation, a CNC code file was generated in the GibbsCAM. The code was used for developing the part on the Okuma 3- Axis vertical milling machine (shown below).
Okuma 3 Axis Vertical Milling Machine
