Using CNC for Mercedes Benz Logo Design

Contents

Abstract

Acknowledgements

Declaration

1 Introduction
1.1 Coordinate system
1.2 Advantages and disadvantages of CNC machining
1.2.1 Advantages
1.2.2 Disadvantages
1.3 Motivation
1.4 Objectives
1.5 PRODUCT REQUIREMENT SPECIFICATIONS
1.5.1 Requirements
1.6 Concept
1.6.1 Concept Motivation
1.7 Design Modification
1.8 3D drawing
1.8.1 Engineering drawing
1.8.2 G - Code
1.9 Methodology
1.9.1 Procedure and Modelling
1.9.2 Programming
1.9.3 Machining
1.9.4 Precautions
1.10 OBSERVATIONS AND RESULTS
1.11 Discussion
1.12 Conclusion

Appendices

Appendix A CNC machine and G-Code used 13

A.1 G-code 13

List of Figures

1.1 Mill Axes for a Typical Vertical Machining Center. Note: ar- rows show table motion in positive g-code direction. (Author’s own work)

1.2 5-Axis Mill With Trunion Table (Author’s own work)

1.3 Mercedes Benz logo (MEYERS and O’DONOHUE, 1973) . . .

1.4 3-D model of the Mercedes Benz logo (Author’s own work) . .

1.5 Machining pattern (Author’s own work)

1.6 Engineering drawing of the Mercedes Benz logo (Author’s own work)

1.7 cylindrical base (Author’s own work)

1.8 Upper finish (Author’s own work)

A.1 Machine utilized (Author’s own work)

List of Tables

1.1 CNC system components

1.2 G-functions

Abstract

This report covers the work that was carried out by a group of researchers¹ on CNC (Computer Numerical Control) programming and machining. The task was to choose and design a creative item to be machined using CNC machining, which then required to write a code using CNC language. Prior to the machining process, we did a Computer Aided Design (CAD) draw- ing of the Mercedes Benz logo. The logo was further modified with the final model drawn using Auto Desk Inventor. We used foam for our model and a 10 diameter end mill tool. The main problem that was experienced was the cutting time; the model took longer to be complete. The cutting time was affected by the complexity of the design, chosen tool size and the cutting technique. We learnt from the demonstration that the shorter the constructed code the more robust it is, using a bigger tool is more efficient in terms of saving energy and time, and that if the code is correct the CNC machine model becomes identical to that of the product Design.

Chapter 1 Introduction

According to Jacobs and Haberman (2017), Computer Numerical Control (CNC) machining is a process that involves the use of computers to control machine tools. This process is mostly used in manufacturing industries. A computer numerical control system is made up three components:¹

Table 1.1: CNC system components

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The Part program Set of instructions produced to produce a part.

Machine tool The hardware that receives instructions from the Machine Control.

The part program contains a set of instructions (G-code) written using a CNC machining language to control various features of the machine tool such as location, coordination, speed and input parameters such as the feed rate, depth of cut and so forth (Shin et al., 2007). The table with the vice holding the work-piece follows the coordination system while the cutting tool remains stationary - the cutting tool can only move in the vertical direction. A machine unit is a small computer used for storing and for executing the G-code (Shin et al., 2007). Shin et al. (2007) argued that, machine tools such as lathe, grinder, router and mill are programmable using such a language.

1.1 Coordinate system

Each machine come up with its own specific axis orientation which we should become familiar with. Here are some common types:

‘Z’, ‘X’ and ‘Y’

‘A’, ‘B’ and ‘C’ are the rotary axis of motion ‘XY’, ‘XZ’ and ‘YZ’ are planes of operation

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Figure 1.1: Mill Axes for a Typical Vertical Machining Center. Note: arrows show table motion in positive g-code direction. (Author’s own work)

Much more complex configurations are possible when we have more axes. Note that in Figure 1.2 bellow, we have added two rotational axes to the basic mill diagram to provide an A-Axis and a B-Axis. In general, A, B, and C are rotational axes that rotate around axes formed by the X, Y, and Z respectively. For instance, Figure 1.2 is a 5-axis setup. CNC machine can operate in either absolute (X, Y, Z) or incremental coordinates (U, V, W).

1.2 Advantages and disadvantages of CNC machining

1.2.1 Advantages

CNC machines produce quality products at a high speed with high level of accuracy. CNC systems are easy to operate, people with little experience can operate them unlike with manual milling/lathe machine which require people with high skill set. Modern CNC machines can be used constantly without

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Figure 1.2: 5-Axis Mill With Trunion Table (Author’s own work)

switching them off. This means that the machine can run 24 hours a day, all year round as long as routine maintenance checks are done. Due to the fact that CNC machines are computerized, they can replicate an original design of a product and machine thousands of products of the same design with precision.² Fewer people are needed to operate CNC machines. Companies will save a lot of money as few operators will be employed, without there being any reductions in the level of product rate and quality.

1.2.2 Disadvantages

CNC machines are expensive compared to conventional machinery. Most CNC machines take up a lot of space when compared to conventional machine and therefore purchasing the machine might not be a good idea for smallmedium enterprises (SME’s) where space is limited. The introduction of CNC machines has resulted in a decline in the need for skilled manual lathe workers and therefore people losing their jobs.

1.3 Motivation

- To get an appreciation of the friendly-use of the CNC machine and to obtain the experience of using the machine.
- To develop the skill of programming and understand the language of the machine.
- To familiarize to the activities with the implementations from a design and the effects it may implicate on production such as wastages.

1.4 Objectives

This project aims at:

- Producing designs that allow CNC milling programming.
- Developing understanding on how CNC machining works.

1.5 PRODUCT REQUIREMENT SPECIFI- CATIONS

1.5.1 Requirements

- The design chosen must be creative.
- An engineering drawing of the design must be produced.
- A CNC program must be written and verified with the CNC laboratory.
- Use M and G functions to write the CNC program.
- The design must be CNC machined

1.6 Concept

1.6.1 Concept Motivation

Founded in 1926, Mercedes Benz (‘best or nothing’) is a global manufacturer of automobiles. The brand is known for the manufacture of luxury vehicles, trucks, buses and coaches. The design chosen for this project was inspired by the Mercedes Benz logo.

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Figure 1.3: Mercedes Benz logo (MEYERS and O’DONOHUE, 1973)

1.7 Design Modification

Mercedes Benz employs the technique of molding to produce the logo (MEY- ERS and O’DONOHUE, 1973). This gives them the advantage to produce unique 3D features which cannot the achieved with a three axis CNC machin- ing. Modifications were developed from the original Mercedes Benz logo in order to produce a feasible and appealing result. The changes are as follows:

- Removed outer circle - considering that the cutting tool rotates, the contact between the points and the outer circle would have been com- promised.
- Add circular base - attempts to sustain the effect of the outer circle removes, protruding the logo to a higher level from the base; also includes application of circular interpolation.
- No 3D surface - the original design has a pointy finish on the surface that cannot be achieved with a three axis CNC.

1.8 3D drawing

1.8.1 Engineering drawing

1.8.2 G - Code

In writing the G-code for CNC machining, Table 1.2 was used as guidance and the G-Code for this part is in APPENDIX.

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Figure 1.4: 3-D model of the Mercedes Benz logo (Author’s own work)

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Figure 1.5: Machining pattern (Author’s own work)

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Figure 1.6: Engineering drawing of the Mercedes Benz logo (Author’s own work)

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#G00,G01,G02,G03 G00,G01,G02,G03 01 positionning , interpolation

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- G90, G91 03 Absolute/incremental programming

Table 1.2: G-functions

1.9 Methodology

1.9.1 Procedure and Modelling

- Make a Computer Aided Design (CAD) drawing of the Mercedes Benz logo using Auto Desk Inventor.
- Click the Smart Dimensions tab and add dimensions to the drawing.
- Click save.

1.9.2 Programming

- Using the G-functions and the G-code format, write a G-code with co-ordinates that match those on the CAD drawing.
- Save and print the G-code.
- Use online G-Code simulator³ to validate the code and the Cutviewer software to simulate the machining process.
- Take the G-code to the laboratory demonstrator for verification.

1.9.3 Machining

- Load the G-code onto the computer in the CNC machining room at North West Engineering laboratory.
- Machine the Mercedes Benz logo.
- Collect machined part.

1.9.4 Precautions

- Each line is for one instruction.
- Add points to coordinate values.
- Add a G function for every instruction.
- Compensate on the G-Code coordinates.
- Submit code to instructor before operation.
- Wear PPE before entering lab.

1.10 OBSERVATIONS AND RESULTS

Figure 1.7 and 1.8 demonstrate the precision offered by the machine. The machining took long because it required a significant removal of material. Only T2 (dia 10mm) was used for machining. The cutting tool only moved vertically during machining while the XY coordination was handled by the table. The control unit interface displayed steps according to operation to allow debugging. However, Waste was difficult to control.

[...]

¹ Roland Kalonji and Mike Nkongolo

¹ http://wings.buffalo.edu/academic/department/eng/mae/courses/460-564/Course- Notes/CNC-20notes.pdf [Accessed 13 March 2017]

² http://www.lowrancemachine.com/news/advantages-and-disadvantages-of-cnc- machining [Accessed 10 March 2017]

³ (https://nraynaud.github.io/webgcode/)