Introduction to computer aided manufacturing (CAM)Lesson 3 part 2: CAM+

Tony SchmitzUniversity of Tennessee, Knoxville/ORNL

ace America’s Cutting Edge

This program is funded by the Department of Defense (DoD) Industrial Base Analysis and Sustainment (IBAS) Program from the Office of Industrial Policy.DoD has collaborated with ORNL and IACMI to establish America’s Cutting Edge (ACE), a national initiative for machine tool technology development and advancement.

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Lesson 3: Milling basics

▪ Previously, we programmed a facing toolpath using the lesson 3 instructions.▪ Next, let’s use CAM+ to simulate the machining behavior for this toolpath.

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▪ The toolpath uses Tool #1.▪ Tool #1 is a 2” (50.8 mm) diameter face mill with six teeth.▪ The feed per tooth is 0.00267” (0.068 mm)▪ The axial depth of cut is the distance between the Top Height, which is set to the Stock

top, and the Bottom Height, which is set to the Model top (1” stock Height (Z) – 0.625” part height – 0.2” Stock Bottom Offset = 0.175” remaining on the top of the part).

▪ The step down, or axial depth of cut, is 0.175” (4.45 mm).▪ The radial depth of cut is the full stock width, or 1.75” (44.45 mm).

Radial depth of cut

Axial depth of cut

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Enter these parameters in the CAMPlus_data_v1 spreadsheet. Select Tool 1 and Spindle 1 on the Tools sheet. Save the file.

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Switch to the Cut sheet. Use the 6061-T6 aluminum force model values.

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On the Cut sheet, enter the cut description values. We’ll begin with a spindle speed of 3000 rpm. Save the file.

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In the CAM+ app, calculate the tool tip frequency response function (FRF) for Tool #1 in Spindle #1 using the Tap test button.

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In the CAM+ app, calculate the stability map using the Stability map button.

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In the CAM+ app, simulate the force, vibration, and sound for a 3000 rpm spindle speed using the Simulation button.

3000 rpm spindle speed, 4.45 mm axial depth

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Let’s zoom in on the x (feed) direction force and displacement. This is a stable cut; the force and vibration repeat at regular intervals. The once-per-tooth samples (red circles) demonstrate this repetition. Run the simulation again to hear the sound.

This is a stable cut.

3000 rpm spindle speed, 4.45 mm axial depth

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In the CAMPlus_data_v1 spreadsheet, change the spindle speed to 2400 rpm. Don’t forget to save the file.

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In the CAM+ app, simulate the force, vibration, and sound for a 2400 rpm spindle speed using the Simulation button.

2400 rpm spindle speed, 4.45 mm axial depth

The chatter lamp is lit.

Let’s zoom in on the x direction force and displacement. This is an unstable cut (chatter); the force and vibration do not repeat at regular intervals. The once-per-tooth samples (red circles) demonstrate this variation. Listen to the sound!

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This is an unstable cut (chatter).

The chatter lamp is lit.

We’ve just compared the machining behavior at two spindle speeds: 3000 rpm and 2400 rpm. We saw that the 3000 rpm cut was stable, while the 2400 rpm cut exhibited chatter. This is due to the combination of the tool tip FRF, workpiece material, and the axial and radial depths of cut.

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2400 rpm spindle speed, 4.45 mm axial depthChatter!

3000 rpm spindle speed, 4.45 mm axial depthStable

Switch back and forth between the two spindle speeds and repeat the simulations to hear the difference in sound. For the stable cut, you hear the tooth passing frequency (this is the spindle speed multiplied by the number of cutter teeth). For the unstable cut, however, you hear the chatter frequency. This depends on the FRF.

Stable point is below the boundary.

Unstable point is above the boundary.

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Let’s now switch to Spindle #3 on the Tools sheet. We’ll still use Tool #1. Physically, this means we put the same tool in a new spindle. Save the file.

In the CAM+ app, calculate the tool tip frequency response function (FRF) for Tool #1 in Spindle #3 using the Tap test button.

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The FRF changed with the new spindle!This was the FRF for Tool #1

in Spindle #1.

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In the CAM+ app, calculate the new stability map using the Stability map button.

This was the stability map for Tool #1 in Spindle #1.

The stability map changed with the new spindle!

In the CAM+ app, simulate the force, vibration, and sound for a 2400 rpm spindle speed using the Simulation button.

2400 rpm spindle speed, 4.45 mm axial depth

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This is a stable cut. Changing to a new spindle changed the previously unstable cut to stable.

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Let’s again zoom in on the x (feed) direction force and displacement. For this stable cut, the force and vibration repeat at regular intervals. The once-per-tooth samples (red circles) also repeat.

Stable point is below the boundary.

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Summary▪ We saw that changing the spindle speed for the same radial and axial depths of cut can change the behavior from stable

to unstable (chatter). ▪ We therefore need the stability map to select the best spindle speed.▪ We saw that inserting one tool in two different spindles can give two different FRFs.▪ With the change in FRF, we observed a change in the stability map.▪ A cut that was unstable with a tool inserted in one spindle was stable when the same tool was inserted in a different

spindle.▪ We therefore need the stability map to select the best spindle speed.

▪ You now have the opportunity to explore machining dynamics using the CAM+ app on your own!

Answer the following multiple choice questions in the online quiz.

1. For Tool #1 in Spindle #1, the cut was stable for a spindle speed of 2400 rpm. a) True; b) False.2. For Tool #1 in Spindle #3, the cut was stable for a spindle speed of 2400 rpm. a) True; b) False.

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