CNC Lab - Professor Samardzic PDF

Preview

Summary

Professor Samardzic...

Description

1

MECHANICAL ENGINEERING LABORATORY NEW JERSEY INSTITUTE OF TECHNOLOGY

Report Submitted by

Emily Carvalho

Date Performed

2/06/20

Course & Section

ME215-004

Experiment No.

Date Submitted Instructor

2/19/20 Professor Veljko

COMPUTER NUMERICAL CONTROLLED MACHINING

Performed by Group

Group Members

001A

With TA

Paul Mamauag (Leader) Mohamed Diab Kai Cha Ramazan Uku

Yassine

3A

2

TABLE OF CONTENTS Abstract

3

Introduction Objectives Background and Importance

3 3 3

Procedure

3

Original Data Sheet

5

Results and Calculations

9

Discussion

9

Conclusion

10

Questions and Answers

10

References

11

3

Abstract This laboratory is focused on introducing CNC machining to students. The purpose of the lab is to expose students to the programming codes responsible for moving the machine so they can be understood and applied. We were split up into groups and given the task of writing the CNC sequence, cycle time, and the manuscript for part P-34. The method we used to do this was by first analyzing the CNC sequence, cycle time, and the manuscript for the Plate and then using what we observed from this to create the CNC programming for P-34. The result of this lab was an understanding of the basics of CNC machining and a use of the Haas Mini Mill, vise, parallels, calipers, cutting tools, and a USB flash drive.

Introduction This laboratory gives students a demonstration of the different functions and tools of CNC machines and an application of this new knowledge to write the g-code for two different parts. Objectives The main objectives of this lab was to 1) familiarize students with CNC machinery, 2) understand how to write CNC code, 3) write the CNC sequence, cycle time, and manuscript for part P-34, 4) simulate the g-code written for P-34 on the CNC simulators, 5) write the CNC sequence, cycle time, and manuscript for the tension specimen Background and Importance In the 1950’s NC machines were created, using punch cards to communicate to the machine what cuts and movements it should be making. Not long after they were upgraded to CNC machines, which made accuracy, repeatability, quality, and production times all improve. CAD programs write g-code automatically so the user only needs to develop tool path instructions in order to create their part. This lab is extremely important for future engineers because CNC machines are widely used in the industry and a solid understanding of how it works is vital in moving forward with their career.

4

Procedure Week 1 1. Familiarize yourself with the basics of CNC programming 2. Analyze the drawing of the Plate in Figure 2.5 and the corresponding CNC sequence, manuscript, and cycle time in Table 2.1, 2.2, 2.3, respectively. 3. The TA will discuss the Plate with the class more in depth 4. Analyze the drawing of P-34 in Figure 2.6 and fill out Tables 2.4-2.6 5. Write all the names of the group members on page 30 and get approval from the TA that Tables 2.4-2.6 were completed correctly 6. As an individual, prepare for week 2 by using the template provided to create a program for P-34. Save it as a text file (.txt) on to a USB drive and bring it to class so it can be used in a CNC simulator. Week 2 1. Plug your usb into the CNC simulator, run your g-code, and compare it to your lab partners. 2. Analyze the drawing of the Tension Specimen in Figure 2.7 and fill out tables 2.7-2.9

5

Original Data Sheet

6

7

8

9

Results and Calculations

10

When our g-code for P-34 was plugged into the simulator we received this output, where you can see the starting point in the bottom left, the 3 holes drilled, and a slot, which corresponds correctly with the drawing of the part we were given.

Discussion This laboratory was extremely informative on exposing us to CNC machining and the steps on how to properly utilize it. We learned how to visualize the coordinates for cuts of the part and properly write them in G-code for the machine. We were able to successfully write the CNC sequence, manuscript, and cycle time for part P-34 and the tension specimen. To do this, we had to have a firm understanding of the different g-codes, feed rate, speed, tools, and how the tool and table moved in relation to each other. To reiterate, the main objectives of this lab were to 1) familiarize students with CNC machinery, 2) understand how to write CNC code, 3) write the CNC sequence, cycle time, and manuscript for part P-34, 4) simulate the g-code written for P-34 on the CNC simulators, 5) write the CNC sequence, cycle time, and manuscript for the tension specimen. We accomplished all of these objectives when we wrote the code for part P-34, and then again a week later when we were able to recall what we learned and write the code for the tension specimen. A source of error we encountered was in using our g-code in the CNC simulator. Out of our lab group, only one of us was able to get the correct simulation, which means the rest of us had small mistakes that messed up how our part was cut.

Conclusion In conclusion, the lab was successful in teaching us how CNC machines read code and how to write the corresponding code to create parts. We were also taught about the different tools and parts that go into the machine and a brief overview of how everything works. The purpose of this lab was to expose us to the programming codes responsible for moving the machine so they could be understood and applied to models given in the lab. We were able to accomplish all our objectives and work cohesively as a group to teach ourselves how to write and understand gcode.

Questions and Answers 1) Explain the difference between numerical control and computer numerical control. The difference between numerical control and computer numerical control is that for NC machines the input was punch cards that told the machine what to do whereas CNC machines use G-code to control the movement of the machine. CNC is more accurate and easier to modify because everything can be done on the computer. 2) What is the first step in preparing the program on a NC machine? The first step in preparing the program on a NC machine was to have a drawing of the model and convert the dimensions/coordinates for the punch sheet. 3) What do the following expressions mean?

11

a) N100 G01 G81 Z-1.5 F2100 Line number 100, Linear Interpolation Motion, Drill Canned Cycle, Tool moves to -1.5, Feedrate of 2100 in/min b) N55 G00 G91 X0 Y0 M3 Line number 55, Rapid Positioning Motion, Incremental Positioning Command, Table moves to (0,0), Rotate spindle 4) Why is compressed air required for the CNC mill in the lab? Compressed air is required for the CNC mill because during the machining process chips and debris fly everywhere and for a tool change to occur, the air is used to make sure no shavings get inside the tool compartment, which would alter the positioning of the tool and consequently the accuracy. 5) 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 fac ecycle. The depth is 0.195 inches and the feed rate is 10 inches per minute. N5

G00 G90 X-1

Y-1

N10

S1500

T1

M3

Z.05

N15

G00

X2.125

N20

G01

Z-.195

N25

G00

Z.05

N30

G00

X-1

Y1.625

Y-1

F10

M30

6) Assume a 0.750 in wide and 1.000 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 a 0.750 in diameter. a) Based on the data provided in Figure2.10find 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 recommended speed and feed for a HSS end mill is 80-140 fpm and . 003-.010 feed per tooth (Black & Kosher, 2017) b) Ns = 12(80)/pi(.75) = 407.44 rpm Ns = 12(140)/pi(.75) = 713.01 rpm The corresponding rpm of the spindle is 407.44 - 713.01 rpm c) fm = (4)(407.44)(.003) = 4.889 fm = (4)(713.01)(.010) = 28.52 The corresponding feed rate is 4.889-28.52 inches per minute

12

d) Volume removed = .375^2(pi)(1) = 0.4418 in^3 Tm = (1)/4.889 = 0.205 min Tm = (1)/28.52 = 0.0351 min hp = (.58 hp-min/in^3) * (.4418in^3)/(.205) = 1.25 horsepower hp = (.58 hp-min/in^3) * (.4418in^3)/(.0351) = 7.30 horsepower Since the mill only has 5 horsepower available, the lowest recommended feed rate of 4.889 requires 1.25 horsepower which means 4 passes can be made (5/1.25 = 4). The larger feed rate of 28.52 would require 7.3 horsepower, which the mill cannot accomplish.

References Black, J., & Kosher, R. (2017). DeGarmo's Materials and Processes in Manufacturing(12th ed.). Hoboken, NJ, USA: Wiley....