Analysis of machining operation with a Planer cutting tool

Analysis of machining operation with a Planer cutting tool

Case1

Objective: To simulate the machining operation on a rectangular specimen and find out the effect of changing the velocity of the planer (cutting tool) on the Equivalent Stress, Total Deformation and Temeperature generated in the process. The simulation will be carried out in the Explicit Dynamics module of Ansys Workbench.

Geometry: The model consists of a rectangular workpiece 14.8755mm*6.8mm*1.47mm which is almost in contact with a planer i.e. the cutting tool. The cutting edge of the planer is positioned 0.374mm from the top surface of the specimen.

Material Definition: The planer is assigned structural steel as the working material. Its behaviour is set to \"Rigid\".

Particulars	Magnitude	Unit
Density	7.85E-06	Kg/mm3
Young’s Modulus	2.00E+05	MPa
Shear Modulus	76923	MPa
Bulk Modulus	166670	MPa
Poisson’s Ratio	0.3
Yield Strength	250	MPa
Ultimate Strength	460	MPa

The workpiece is assigned \"Steel 1006\" as the working material from the Explicit Materials list found in Engineering Data Sources.

The workpiece material contains the Johnson Cook failure model as well as the Linear EOS Shock model included in its properties.

Connections: No contacts are defined for the simulation. Instead a Body Interaction is introduced, the parameters of which are set as per the table below:

Meshing: The planer is meshed by \"Patch Confirming Method\" using Tetrahedron elements. The workpiece is meshed by defining 10 elements along its thickness.

Analysis Settings: The simulation is run for 7.5E-04s with the maximum number of cycles set to 1E+07.

The energy error is limited to 10% of the energy at reference cycle. The time step safety factor is left to its default value of 0.9.

Boundary Conditions: Two boundary conditions are imposed in this model-a fixed support at the bottom surface of the workpiece and a velocity of 20000mm/s in the positive X-direction for the planer.

Case2

For this case, the feed velocity of the planer is dropped to 15000mm/s. Since the feed velocity is reduced, the velocity with wihich the workpiece gets removed also decreses. This drops the overall energy of the specimen at the set refrence cycle. The energy error now forms a greater fraction (more than 10%) of the reference cycle energy. To avoid the simulation from throwing up an error and stopping the simulation, the Maximum Energy Error is increased to 0.14 or 14% of the reference cycle energy.

The rest of the setup remains exactly the same as Case1.

Results:

The Total Deformation, Equivalent Stress and Temperature generated for the two cases have been tabulated below

SR No	Particular	Case1	Case2
1.	Total Deformation (mm)	29.259	23.175
2.	Equivalent Stress (MPa)	492.74	675.12
3.	Temperature Generated (degree Celsius)	376.95	363.51

1) Total Deformation: With a higher cutting speed the specimen exhibits a higher deformation or displacement of elements from their initial positions in the model.

Case1

Case2

The green, blue and red lines in the graph indicate the respective maximum, average and minimum deformations recorded during the run.

2) Equivalent Stress: Higher stress values are recorded in the second case, where the cutting velocity has been reduced.

Case1

Case2

The green, blue and red lines in the graph indicate the respective maximum, average and minimum Von-Mises Stress recorded during the run.

3) Temperature Generated: The temperature generation is almost the same in both the cases with Case1 recording a slightly higher temperature (about 7 degree celsius higher) than Case2.

Case1

Case2

The green, blue and red lines in the graph indicate the respective maximum, average and minimum temperatures recorded during the run.

Inference:

Both the simulations terminate successfully with the energy errors being within the designated targets of 10% and 14% of reference cycle energy for Case1 and Case2 respectively.

From the results obtained, the follwoing inferences can be drawn:

• Run time being constant, a reduction in the feed velocity reduces the the amount of material removed from the workpiece. This is evident from the Total deformation/displacement recorded for the planer, which displaces 15mm in case1 and only 11.25mm in case2.

• Failure occurs in the model if the stress at any point in the model exceeds that computed by the Johnson Cook failure model:

The co-efficients, exponents, reference strain rate and melting temperature have been defined in the material card itself.

• Case1 records a higher temperature than case2. This is on account of the higher material removal and consequently higher strain and internal energy (28653mJ in case1 and 22726mJ in case2) developed in the specimen in case1.

Energy Summary of Case1

Energy Summary of Case2

• Von-Mises stress is lower in case1 as the planer has already removed the intended amount of material from the specimen (due to high feed velocity). The stress that can be observed on the leftover specimen is actually the residual stress froom the machining. In case2 the planer has traversed just 11.25mm and hasn\'t yet cut the workpiece along its entire length. The high stress can be observed at the base of the curled up part of the removed material. This region experiences stress due to the planer feed as well as its own deformed geometry. Hence the Von-Mises stress in Case2 is higher.