Lab Report - Part 2

1 - Lab Report introduction. Objective and introduction
* Objectives
Operate the CNC milling machine using G-codes, M-codes in a CNC program. * Equipment: Minitech CNC machine (Series 2)
* Machine introduction
Most CNC milling machines are computer controlled vertical mills with the ability to move the spindle vertically along the Z-axis. This extra degree of freedom permits their use in die sinking, engraving applications, and 2.5D surfaces such as relief sculptures. When combined with the use of conical tools or a ball nose cutter, it also significantly improves milling precision without impacting speed, providing a cost-efficient alternative to most flat-surface hand-engraving work. CNC machines can exist in virtually any of the forms of manual machinery, like horizontal mills. The most advanced CNC milling-machines, the multiaxis machine, add two more axes in addition to the three normal axes (XYZ). Horizontal milling machines also have a C or Q axis, allowing the horizontally mounted workpiece to be rotated, essentially allowing asymmetric and eccentric turning. The fifth axis (B axis) controls the tilt of the tool itself. When all of these axes are used in conjunction with each other, extremely complicated geometries, even organic geometries such as a human head can be made with relative ease with these machines. But the skill to program such geometries is beyond that of most operators. Therefore, 5-axis milling machines are practically always programmed with CAM. 2. Principles and practice

* Principle
Milling operates on the principle of rotary motion. A milling cutter is spun about an axis while a work piece is advanced through it in such a way that the blades of the cutter are able to shave chips of material with each pass. Milling processes are designed such that the cutter makes many individual cuts on the material in a single run; this may be accomplished by using a cutter with many teeth, spinning the cutter at high speed, or advancing the material through the cutter slowly. Most often it is some combination of the three. The speed at which the piece advances through the cutter is called feed rate, or just feed; it is most often measured in length of material per full revolution of the cutter. As material passes through the cutting area of a milling machine, the blades of the cutter take swarfs of material at regular intervals. This non-continuous cutting operation means that no surface cut by a milling machine will ever be completely smooth; at a very close level (microscopic for very fine feed rates), it will always contain regular ridges. These ridges are known as revolution marks, because rather than being caused by the individual teeth of the cutter, they are caused by irregularities present in the cutter and milling machine; these irregularities amount to the cutter being at effectively different heights above the work piece at each point in its rotation. The height and occurrence of these ridges can be calculated from the diameter of the cutter and the feed. These revolution ridges create the roughness associated with surface finish. * Procedure

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1. Power on and initialization
2. Load the program and simulate the code
3. Set up the origin and do a dry run
4. Run the machining operation
3. Design and results

Fig. 3-1 CAD print of the Design

Our design is as shown in Fig.3-1, which is originated from 2008 Beijing Olympic cycling icon. It includes 2 linear interpolations and 5 arc interpolations (1 semi-circle, 1 quater-circle and 3 full circles) We first sketched the design in CAD, to make sure it fits in the 3*5 square inch area. Then, we used “dimention mark” to find out coordinates of all the line end points and arc center points. Unlike the WEDM lab, which use the difference between arc center points coordinates and arc interpolation starting points coordinates to code, CNC machining lab use the absolute values of arc center points coordinates, which is the distances relatively to our chosen origin (We set the left bottom conner of the work piece as the origin). With the coordinates settled, we programmed and debuged the G-code and M-code for CNC machining. The finished product is as shown in Fig.3-2.

Fig. 3-2 finished product

4. Conclusion and recommendations
By preparing for the lab, we have learned the working principles of Minitech CNC milling machine. We have also learned how to make a satisfactory workpiece design for CNC machining, such as never fully occupying the available working surface on work piece, in case that the miller end would hit hit the clamps. Moreover, we have practiced programming in G-code and M-code for a desined workpiece to fufill its manufacturing process by CNC machining. In the process of doing the lab, we have learned practical operations of Minitech CNC milling machine, including manually set the origin on work piece by moving the miller end, till it touches both work piece and clamp, in order to set “zeros” for Y and X axises, and then move the miller end all the way down till it touches the top surface of the work piece, to set the “zero” for Z axis. We have also learned that it is always a good idea to lift up miller end above work piece surface before actual milling, to let the miller end go a “vacant run”, in order to observe if the tool path matches the countour in design.


Codes for workpiece:

N1 G90 G49
N2 M8
N3 M3 S2000 F5
N4 G00 Z0.5
N5 X3.01 Y2.37
N6 G01 Z-0.15?
N7 G02 X3.37 Y2.37 I3.19 J2.37
N8 G02 X3.01 Y2.37 I3.19 J2.37
N9 G01 X1.65
N10 G03 X1.65 Y1.65 I1.65 J2.01
N11 G02 X1.83 Y1.47 I1.65 J1.47
N12 G01 X1.83 Y 1.216
N13 G02 X0.81 Y0.584 I1.32 J0.9
N14 G02 X1.83 Y1.216 I1.32 J0.9
N15 G00 Z0.5
N16 X2.581 Y2.37
N17 G03 X3.097 Y1.449 I3.34 J2.19
N18 G02 X3.631 Y3.752 I3.34 J0.9
N19 G02 X3.097 Y1.449 I3.34 J0.9
N20 G00 Z0.5
N21 X0 Y0
N22 M02

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