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Lab 8. Introduction to MasterCAM

CNC machines use a special programming language called GN-code (technical name: RS274). MasterCAM

is a software that allows users to create GN-code programs that can be used to cut different geometric

shapes on CNC machines. Here we study MasterCAM for CNC Milling machines.

The main functions are:

(i) Describe the geometry of the part to be machined.

(ii) Create a tool database – this DB carries information about the available milling tools.

(iii) Create the GN-code program to cut the part.

(iv) Simulate the machining of the part (for visual verification of the program).

(v) Upload the program to the CNC machine controller.

Step 1. Describe the geometry of the part to be machined

You can create the geometry in one of two ways:

(a) by using the graphical design interface provided by MasterCAM

(b) by making the design in a CAD software, e.g. CATIA, Pro/Engineer, SolidWorks, and saving it in

a format that MasterCAM can import (safest format to use: IGES; other possible formats include

STL, STEP)

Method (a) is useful if you want to cut a simple shape; although MasterCAM provides some functions to

generate 3D curved surfaces, defining the geometry in this environment is not convenient. So: if you want to

make a part where the entire shape is defined using volumes made by sweeping 2D profiles normal to the

plane of the geometry, use method (a). If you have access to any CAD system, use method (b).

Method (b)

Here, we will assume that we have designed the following part using a CAD system, and saved it as in the

IGES format.

[0] Design the part (in, e.g. CATIA or SolidWorks). It is best if you already create the part such that the

surfaces to machine are in the correct orientation and position for the machine. That is, the machining surfaces

should be accessible from –Z direction, and the part should be located such that the covering, rectangular

stock should be in the positive octant of the coordinate frame, with the corner at the origin.

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[i] Import the part into MasterCAM

MAIN MENU File Converters IGES Read File in the file browser, select file OK.

The part will display in the main window. If you can’t see it, fit it into the screen by clicking Screen fit

Click on MAIN MENU to start the next step.

[ii] ONLY IF Step 0 did not locate the part properly: Rotate, and then Translate the part to correct location.

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To Rotate: The main way to use this function is to use it in a principal view (namely TOP VIEW, to rotate

about the Z-axis; FRONT VIEW to rotate about Y-axis, SIDE VIEW to rotate about X-axis).

Below, I illustrate how to rotate about Z-axis.

MAIN MENU Xform Rotate All Entities Done [the entire model is selected,

changes color] [select the point around which you want to rotate] in the Rotate window: Operation:

Move; Number of steps: 1; Rotation angle: <enter the angle> OK.

To translate: It is convenient to use the standard views only. For example, to move the part in the XY plane:

MAIN MENU Xform Translate All Entities Done [the entire model is

selected, changes color] Between Pts [define the move by clicking the start point, then the end point]

in the Translate window: Operation: Move; Number of steps: 1 OK.

NOTE: the Xform functions are more useful if you are defining your part geometry using the user-interface

provided by MasterCAM; you can ignore them if you import the part from a CAD system.

Step 2. Create the Stock

This step defines the block from which you will cut the final part. It is essential to create the cutting plan.

MAIN MENU Toolpaths Job Setup in the Job Setup window, Click Bounding Box

[Window will vanish], MasterCAM will prompt you to select the entities:

All Entities Done

Job setup window re-appears, and the size of the bounding box is displayed in the correct boxes OK.

You will see the bounding box around the part (different colored lines)

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Step 3. Working with the Tool Database

The tool database describes the geometry of tools available for use in the workshop. The path that a tool

travels in order to cut a shape depends on the size of the tool; some other information about the tool is also

important – for example, the length of the cutting teeth on a drill or an end mill constraints the depth of the

hole these can cut. The main functions for the tool database are:

(i) Look for an existing tool that you may want to use

MAIN MENU NC Utils Def. Tools Library

The Tools Manager window comes up, listing all available tools. Suppose we want to look for a flat end-mill

of small diameter (e.g. less than 6mm). We can use the filter as follows:

Click Filter. In the Tools list Filter window, click Endmill1 Flat (top left icon) [if you leave the mouse cursor

above the icon, its name appears] Tool diameter: [less than] value: 6 Unit masking: metric OK.

The tools Manager window will show all tools that match these criteria.

NOTE: by default, ALL TOOL TYPES are selected; you must click on each icon to DE-SELECT it.

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The figure below shows that my search gave five tools matching my criteria; If I want to use a 5mm end mill,

double click on this tool, and its details will be shown in a Define Tool window.

If the search results in no existing tool, and you would like to enter the data of a tool you have into the

library: RIGHT-CLICK within the Tools Manager window Create new tool. This also pops up the Define

Tool window; type the data for the new tool, and click Save to library...

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Step 4. Creating GN code (machining plan) for the part

There are many different options and settings in generation of the tool path. I will not describe all possibilities

here; you can experiment with some during the lab.

NOTE: The version of MasterCAM we have is somewhat buggy, and if something goes wrong, it may be

either due to user-error, or software error (see example below).

Since the geometry we have has corners of radius 2.5mm, therefore the largest tool that can cut the entire

shape is a 5mm diameter end mill. If you use a larger tool the software should leave some corners without

cutting.

We will use a 5mm diameter end mill.

MAIN MENU Toolpaths Surface will give the following menu:

Click on the Surf/Solid option until you get option ‘A’ (which tells the software to use all surfaces in

computing the tool path).

Rough Pocket the Surface Pocket Rough window should pop up; RIGHT-CLICK in white area Get

tool from library…

Now use the filter to find the 5mm diameter flat end mill.

The tool will show as an icon in the Surface Pocket Rough window. Using the Tool parameters tab, you can

set the Spindle speed, Feed rate and Plunge rate; if you know the values, enter them; otherwise just use the

default – you can modify these when you actually machine the part, on the CNC machine.

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In the Surface parameters tab, set the clearance: 20; Retract: 10, and make sure the box “Prompt for tool

center boundary” is OFF. Smaller retract and clearance are ok since our workpiece is flat.

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In the Rough pocket parameters tab, select Zigzag; Stepover percentage: 75%; set the Finish box as ON –

this will generate a finish cut pass (when the tool takes a very small depth of cut, and also moves along the

boundaries to provide better surface finish and remove any small under-cut areas.

Hit OK, and if all goes well, the software will generate the tool path for you, and display it. Notice that the

tool path where it is cutting is shown in different color than when it is moving up or down, and moving

between pockets. Also notice how the tool path for removing the region inside the pocket is zig-zag, but the

tool path also goes once around the contour of each pocket.

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You can see a 3D animation of the cutting by the following:

MAIN MENU Toolpaths Operations The operations Manager window pops up; Verify, and then

click the Machine button on Verify: simulation window. You can speed up the simulation by moving the

slider to the right: (slow) (fast)

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After the simulation is over, the machined part is displayed.

Another try: MAIN MENU Toolpaths Surface Rough Pocket; and selected: Parallel Spirals style

of pocket machining in the Rough pocket parameters tab. All other parameters are the same. The resulting

cutting plan generated by MasterCAM did not clear out the inside of the middle pocket (maybe software bug)

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Step 5. Save the GN-code file

The tool path generated by MasterCAM has all information required to control a CNC machine tool to cut the

part. However, different CNC machines use slightly different versions of GN-code. The conversion of the

machining data to the GN-code specific for a particular CNC machine is called Post-Processing. The exact

format of the GN-code is stored in different post-processing files, and the system will use whichever post-

processing format you select.

MAIN MENU Toolpaths Operations

The operations manager is a useful interface for MasterCAM. It allows you to store different plans for the

same part (e.g. to be machined on different machines, or using different cutting style, parameters, tools etc.).

In the figure below, the Operations manager window shows two Surface Rough Pocket operations (1: for

zigzag, 2: for parallel spirals). We shall use the zigzag path (it’s the one selected in the figure below) for Post-

processing. Click Post.

You can use the Change Post button to select the correct post-processor. Click the Save NC file ON OK.

Save the NC file; you can open this file with any text editor, e.g. Notepad, to read the GN-code.

Step 6. Upload the program to the CNC machine controller

Click the Send to machine box ON Comm..; the Communications window pops up. You can set the

communications settings for your CNC machine controller, and if your PC is connected to the CNC machine

controller, the program will be uploaded to the CNC machine. Use ASCII format; the port, baud-rate, parity,

data bits and stop bits will be specified to you by the machine technician in the lab.