DiGiannoCNC lab

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New Jersey Institute Of Technology *

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Mechanical Engineering

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Jan 9, 2024

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Mechanical Engineering Laboratory New Jersey Institute of Technology Report Submitted by Michael F. DiGianno Experiment No. 2 Date Performed 9/26/23-10/3/23 Date Submitted 10/10/23 Course & Section ME215-101 Instructor Naruemon Suwattananont Computer Numerical Controlled Machining Experiment Title Performed by Group 101b With TA Md Sojib Kaisar Group Members Michael D Bauly S Yahia Elmanier Marta D Stephen M Jonathan G Braeden G

Table of Contents Abstract 3 Introduction 3 Objectives 3 Background and importance 3 Procedure 4 Original Data Sheet 5 Results and Calculations 6 Discussion 12 Conclusion 12 Questions and Answers 13 Appendix A 14 2

Abstract This is the lab report for experiment two, known as computer numerical controlled machining. This two week lab revolves around the computer numerical control machine or “CNC”. The purpose of the lab was to introduce the students to the inner workings, set up, and usage of the CNC machine. The students first developed an understanding of g-code. G-code is the programming language that is used for CNC machines. Once prepared, they had the CNC machine demonstrated and wrote out a second g-code program by hand. Students should have completed this lab with a deeper understanding of how a CNC machine is operated and its uses. Introduction This laboratory module is broken down into two weeks. In the first week students will familiarize themselves with the syntax and function of g-code. They will then learn the relevant calculations that are brought out of the g-code such as spindle speed, feed rates, and time required. Then in week two, they will receive a demonstration of the mill. This should resolve many questions that they may have about the function and uses of the CNC mill. They will attempt to analyze the g-code they made at home, and finally test their knowledge with a more difficult piece to calculate. Objectives Students participating in this lab should be able to develop an understanding of CNC machines. They should be able to write g-code, as well as perform the required calculations that are derived from the g-code. Aside from this, they should be able to identify the functions of a CNC machine as well as how it works. Background and importance Computer numerically controlled machining, or CNC machining is a fairly modern method of manufacturing that involves using a computer to control the movements of a machine. This is commonly associated with machines that have three axes of movement like mills, lathes, and 3d printers. That said, two axis movement machines such as laser cutters and water jets can run on the same programs and principles. The actual process varies based on the machine, but usually follows the flow of a source such as calculations or a model, which gets put through some kind of conversion. This can be a slicer software, CAM (computer aided manufacturing) simulator, or g-code compiler. The output (Commonly g-code) is then loaded into the machine which carries out the instructions provided to it. 3

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Procedure Lab module two is split into two weeks. During the first week the students were introduced to the concepts of CNC milling and g-code. The students learned and began practicing with the syntax of g-code. They practiced with a part (Figure 1); through this part, they provided the g-code, its description, and relevant calculations (Tables 2.7, 2.8, and 2.9). After week one, they were asked to convert their written g-code into a runnable program. The second week of the lab started with a demonstration of the CNC mill. A small piece was milled (Figure 2). Students observed how the machine was operated, moved, and ultimately used to create the final product. The students then attempted to analyze their g-code prepared the week before. They attempted to have the analysis machine recreate the toolpath of their program (Figure 3). Once this was done, they were to write out the g-code, description, and relevant calculations for a new piece (Figure 4/5). This information is logged in tables (Tables 2.4, 2.5, and 2.6). Once they had this, and their sheets signed, the lab concluded. 4

Original Data Sheet 5

Results and Calculations Table 2.7 (P-34 toolpath description) 6

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Table 2.8 (P-34 g-code) 7

Table 2.9 (P-34 Calculations) 8

Table 2.4 (Tension specimen toolpath description) 9

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Table 2.5 (Tension specimen g-code) 10

Table 2.6 (Tension specimen calculations) 11

Discussion To restate, the main objectives of this lab module are to familiarize students with g-code and its syntax. As well as the function and uses of the cnc mill. During week one we were asked to write g-code and calculate values like machining time, spindle speed, and feed rate. The writing of code went well. Some group members struggled at first, which is understandable as they did not have any previous coding experience. That said, it smoothed out quickly as we finished the g-code and descriptions. The second week was slightly turbulent. It seems there was a series of miscommunications. During week one we were instructed to turn in one g-code, description, and calculation sheet. This left several group members without g-code to digitize. Several other members didn’t own a usb flash drive. In total the group was able to produce two unique flash drives with code. The week started with a demonstration of the CNC milling machine. The operator went slow and showed each function and movement to the class. The finished product is shown here (Figure 2). Once the demonstration concluded, the operator took questions and moved the students to the next section. The analysis machines were not very user friendly, but it was manageable. We were able to navigate through the buttons and menus, and eventually simulated our code (Figure 3). Neither of our codes produced a visible toolpath, although it was evident that the machine was attempting. This leads us to believe that there is something wrong with the z or vertical position of our code. The leading theory is that the bit is simply simulating the motions above the workpiece. The main trouble started when the tension specimen was to be written up. We started working with the instructions given, but later on Prof. disagreed with our current course of action and requested that we start over with a different approach. Overall, there was much confusion over instructions, but we eventually worked out all relevant papers and concluded the lab. Conclusion In conclusion, we now have a better understanding of CNC machining and the code that runs it. It's unfortunate that our code did not simulate correctly. That said, with the limited amount of time that we have, it's hard to tell exactly what the problem was. We understand the syntax of g-code and the reasons that one might use a CNC mill during machining or prototyping. 12

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Questions and Answers 1. Position the tool to cut the hole shown in Figure 2.12, use 3 axis x, y, z motion. The starting point is labeled “S” in the Figure. Write the instruction for positioning, in absolute mode, for spot drilling using the spot face cycle. The depth is 0.195 inches and the feed is 10 inches per minute. n5 g00/g90 x-1 y-1 s1500 t1 m3 n10 z0.5 n15 g00 x2.125 y0.625 n20 g01 z-0.195 f10 n25 g00 z0.5 n30 g00 x-1 y-1 m30 2. What do the following expressions mean? a) N100 G01 G81 Z-1.5 F2100 b)N55 G00 G91 X0 Y0 M3 A.) Line 100, Linear motion, drilling canned cycle tool moves to z -1.5, feed rate =2100in/min B.) Line 55, Rapid motion, incremental positioning, table homes to (0,0), Spindle rotates 3. Explain the difference between numerical control and computer numerical control. The difference is that computer numerical control machines are operated with a computer and g-code. NC machines used punch cards that let the machine do simple calculations as the holes on the punch cards represented numbers that could be used for various calculations. 13

4. Assume a 0.750 in wide and 1.650 in deep slot is to be milled into a 6 in cubic block of plain carbon steel with a Brinell Hardness (BHN) of 125 and carbon content of 0.15%. You may assume a HSS (high speed steel) end mill will be used that has 4 cutting teeth, and has a0.750 in diameter. a) Based on the data provided in Figure 2.10 find the recommended speed and feed for this particular material. b) What is the corresponding rpm of the spindle? c)What is the corresponding feed rate for the table? d) Assuming that the mill to be used only has 5 horsepower available, how many passes are needed? A.) The table (figure 6) suggests using 80-140 rpm B.) N1=12(80)/pi(0.75)=407.5 Rpm N2=12(140)/pi(0.75)= 713rpm C.)F1= 4*407.5*0.003=4.89 F2=4*713*0.01= 28.52 5. Why is compressed air required for the CNC mill in the lab? Air is used to clear chips and shavings away from the workpiece. This is especially important during a tool change when the bit will leave the relevant chucking device making its cleanliness vital 6. What is the first step in preparing the program on a NC machine? To prepare the program for the NC machine (Punch card), you must have an accurately dimensioned drawing of your desired model. This will let you assign number holes correctly to the card. Appendix A. Figure 1: Part P-34 14

Figure 2: Milled example 15

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