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720ADVANTAGES AND THE FUTURE OF CNC MACHINES
Alisher Mamadjanovich Mamadjanov
Tashkent State Technical University
Sardorbek Marufovich Yusupov
Fergana Polytechnic Institute
Shokhrukh Sadirov
Fergana Polytechnic Institute
ABSTRACT
This article examines the knowledge of the CNC machining process, various CNC machining operations and their required equipment, advantages and future of CNC machining and some of the considerations that may be taken into account by manufacturers and machine shops when deciding whether CNC machining is the most optimal solution for their particular manufacturing application.
Keywords: CNC machining, machine tools, subtractive manufacturing, designs, computer-aided design, computer-aided manufacturing, tolerance, file conversion, CNC program.
INTRODUCTION
CNC machining is a term commonly used in manufacturing and industrial applications. But exactly what is CNC? And what is a CNC machine?
The term CNC stands for 'computer numerical control', and the CNC machining definition is that it is a subtractive manufacturing process which typically employs computerized controls and machine tools to remove layers of material from a stock piece—known as the blank or workpiece—and produces a custom-designed part [1-5]. This process is suitable for a wide range of materials, including metals, plastics, wood, glass, foam, and composites, and finds application in a variety of industries, such as large CNC machining, machining of parts and prototypes for telecommunications, and CNC machining aerospace parts, which require tighter tolerances than other industries. Note there is a difference between the CNC machining definition and the CNC machine definition- one is a process and the other is a machine. A CNC machine is a programmable machine that is capable of autonomously performing the operations of CNC machining.
METHODOLOGY
Subtractive manufacturing processes, such as CNC machining, are often presented in contrast to additive manufacturing processes, such as 3D printing, or formative manufacturing processes, such as liquid injection molding. While subtractive processes remove layers of material from the workpiece to produce custom shapes and designs, additive processes assemble layers of material to produce the desired form and
formative processes deform and displace stock material into the desired shape. The automated nature of CNC machining enables the production of high precision and high accuracy, simple parts and cost-effectiveness when fulfilling one-off and mediumvolume production runs.
While each type of manufacturing process has its advantages and disadvantages, this article focuses on the CNC machining process, outlining the basics of the process, and the various components and tooling of the CNC machine (sometimes incorrectly known as a C and C machine). Additionally, this article explores various mechanical CNC machining operations and presents alternatives to the CNC machining process [611].
Overview of CNC Machining Process
Evolving from the numerical control (NC) machining process which utilized punched tape cards, CNC machining is a manufacturing process which utilizes computerized controls to operate and manipulate machine and cutting tools to shape stock material—e.g., metal, plastic, wood, foam, composite, etc.—into custom parts and designs. While the CNC machining process offers various capabilities and operations, the fundamental principles of the process remain largely the same throughout all of them. The basic CNC machining process includes the following stages:
- Designing the CAD model;
- Converting the CAD file to a CNC program;
- Preparing the CNC machine;
- Executing the machining operation.
CAD Model Design
The CNC machining process begins with the creation of a 2D vector or 3D solid part CAD design either in-house or by a CAD/CAM design service company. Computer-aided design (CAD) software allows designers and manufacturers to produce a model or rendering of their parts and products along with the necessary technical specifications, such as dimensions and geometries, for producing the part or product.
Designs for CNC machined parts are restricted by the capabilities (or inabilities) of the CNC machine and tooling [12-17]. For example, most CNC machine tooling is cylindrical therefore the part geometries possible via the CNC machining process are limited as the tooling creates curved corner sections. Additionally, the properties of the material being machined, tooling design, and workholding capabilities of the machine further restrict the design possibilities, such as the minimum part thicknesses, maximum part size, and inclusion and complexity of internal cavities and features.
CNC Machining Tolerances Tables
When specifying parts to a machine shop, it's important to include any necessary tolerances. Though CNC machines are very accurate, they still leave some slight
variation between duplicates of the same part, generally around + or - .005 in (.127 mm), which is roughly twice the width of a human hair. To save on costs, buyers should only specify tolerances in areas of the part that will need to be especially accurate because they will come into contact with other parts. While there are standard tolerances for different levels of machining (as shown in the tables below), not all tolerances are equal. If, for example, a part absolutely cannot be larger than the measurement, it might have a specified tolerance of +0.0/-0.5 to show it can be slightly smaller, but no larger in that area.
Table 1: Linear Tolerances in CNC Machining
Dimension Fine (F) Medium (M) Coarse (C) Very Coarse
Range (mm) +/- +/- +/- (V) +/-
0.5-3 0.05 0.1 0.2 --
3-6 0.05 0.1 0.3 0.5
6-30 0.1 0.2 0.5 1
30-120 0.15 0.3 0.8 1.5
120-400 0.2 0.5 1.2 2.5
400-1000 0.3 0.8 2 4
1000-2000 0.5 1.2 3 6
2000-4000 -- 2 4 8
Table 2: Angle Tolerances in CNC Machining
Dimension Fine (F) Medium (M) Coarse (C) Very Coarse
Range (mm) +/- +/- +/- (V) +/-
0-10 1o 1o 1°30' 1o
10-50 0°30' 0°30' 0°30' 0°30'
50-120 0°20' 0°20' 0°30' 0°30'
120-400 0°10' 0°10' 0°30' 0°30'
400 0°5' 0°5' 0°30' 0°30'
Table 3: Radius and Chamfer Tolerances in CNC Machining
Dimension Fine (F) Medium (M) Coarse (C) Very Coarse
Range (mm) +/- +/- +/- (V) +/-
0.5-3 0.2 0.2 0.4 0.4
3-6 0.5 0.5 1 1
6 1 1 2 2
CAD File Conversion
The formatted CAD design file runs through a program, typically computer-aided manufacturing (CAM) software, to extract the part geometry and generates the digital
programming code which will control the CNC machine and manipulate the tooling to produce the custom-designed part [18-21].
DISCUSSION
CNC machines used several programming languages, including G-code and M-code. The most well-known of the CNC programming languages, general or geometric code, referred to as G-code, controls when, where, and how the machine tools move— e.g., when to turn on or off, how fast to travel to a particular location, what paths to take, etc.—across the workpiece. Miscellaneous function code, referred to as M-code, controls the auxiliary functions of the machine, such as automating the removal and replacement of the machine cover at the start and end of production, respectively.
Once the CNC program is generated, the operator loads it to the CNC machine.
Machine Setup
Before the operator runs the CNC program, they must prepare the CNC machine for operation. These preparations include affixing the workpiece directly into the machine, onto machinery spindles, or into machine vises or similar workholding devices, and attaching the required tooling, such as drill bits and end mills, to the proper machine components.
Once the machine is fully set up, the operator can run the CNC program.
Machining Operation Execution
The CNC program acts as instructions for the CNC machine; it submits machine commands dictating the tooling's actions and movements to the machine's integrated computer, which operates and manipulates the machine tooling. Initiating the program prompts the CNC machine to begin the CNC machining process, and the program guides the machine throughout the process as it executes the necessary machine operations to produce a custom-designed part or product.
CNC machining processes can be performed in-house—if the company invests in obtaining and maintaining their own CNC equipment—or out-sourced to dedicated CNC machining service providers [22-24].
Types of CNC Machining Operations
CNC machining is a manufacturing process suitable for a wide variety of industries, including automotive, aerospace, construction, and agriculture, and able to produce a range of products, such as automobile frames, surgical equipment, airplane engines, gears, and hand and garden tools. The process encompasses several different computer-controlled machining operations—including mechanical, chemical, electrical, and thermal processes—which remove the necessary material from the workpiece to produce a custom-designed part or product. While chemical, electrical, and thermal machining processes are covered in a later section, this section explores some of the most common mechanical CNC machining operations including:
- Drilling;
- Milling;
- Turning.
Table 4 - Characteristics of Common CNC Machining Operations
Machining operation Characteristics
Drilling • Employs rotating multi-point drill bits • Drill bit fed perpendicular or angularly to workpiece • Produces cylindrical holes in workpiece
Milling • Employs rotating multi-point cutting tools • Workpiece fed in same direction as cutting tool rotation • Removesmaterialfromworkpiece • Produces broader range of shapes
Turning • Employssingle-pointcuttingtools • Rotatesworkpiece • Cutting tool fed along the surface of the workpiece • Removesmaterialfromtheworkpiece • Produces round or cylindrical parts
Advantages of CNC
CNC-numerical software allows you to carry out the process of manufacturing parts on various industrial machines in automatic mode. In addition, the software constantly monitors each production phase - the operator of such machines can only change the workpiece in time, check the parameters of the finished part and, if necessary, make adjustments to the program [25].
As a rule, CNC machines are used in serial and mass production of the same type of parts. Software can be equipped with almost all types of machine tools - it is installed on lathes, milling, grinding, presses, metal-cutting machines and even grinding machines.
RESULTS
At enterprises, the CNC allows you to achieve a lot of advantages in the production of products:
First, the speed of production of parts increases almost twice. This is achieved by processing the part from one or two installations. In addition, the tool change time is reduced - as a rule, CNC machines are equipped with an automatic turret head, which
can change the cutting tool during operation. This tool holder can accommodate up to 12 tools for various purposes [26-28].
Secondly, the accuracy of the processing of parts. Computer control of the machine eliminates as much as possible the negative consequences of interference in the processing of the human factor. The machining of parts on CNC machines is carried out with an accuracy of up to microns.
Third, the purity of the processing. The hydraulic drive, under the precise control of the machine software, moves at a given speed so smoothly that, under certain settings, the finished part looks like polished.
Fourth, on CNC machines, it is possible to quickly process parts of complex configurations. The machine methodically, step by step, works out each point of the program entered into it - only a damaged tool or suddenly lost electricity can become an obstacle on the way to achieving the goal.
Fifth, CNC machines make it possible to use fewer people in production. The normal approach to automated production is considered to be the maintenance of two to four machines by one operator-it all depends on the duration of the part processing. If the complete processing cycle of the product lasts for 10-15 minutes, the operator is quite able to maintain 2-3 machines.
But the most significant advantage of CNC machines is the ability to combine them into a complex production conveyor, which, due to the use of machines for different purposes, allows you to organize the production of complex products from beginning to end [29].
The Future of CNC Machining
Computer numerical control (CNC) has helped revolutionize design and manufacturing industry tremendously since it was first introduced in the 1960s. Since automation and high-precision are the critical advantages of CNC, it has changed the way parts are designed and made. With such exponential growth, many are thinking, what does the future hold for CNC technology?
Leaders in the manufacturing industry have questioned if the current programming of CNC machining services will still be available in the future. Or something new will emerge and replace the CNC machines [30]. One prediction is that the human programmers will be less in demand in the future because the machining process is knowledge-based, highly adaptive, and closed-looped. And the feature recognition is becoming more progressive each day. If CNC machining went in this direction, there would be a drastic change in the programmer-oriented field.
CNC and Robotics
The concept of CNC has limited the functions of CNC programs to the control of the machines that form part of the manufacturing process. However, through time, manufacturers have moved towards centralized systems that manage the resources and
tracks the productivity of the machines. One example of this system is the Enterprise Resources Planning software.
Another development that manufacturers are adopting is an interconnected system that will simplify the CNC machines and integrate it with other procedures and machines. Enter robotics. Typically, the CNC machine and robots are paired on the shop floor. The CNC machines in charge of processing the raw materials while the robots are moving and packing the produced parts.
In the future, CNC developers, machine designers, and robot manufacturers can create a straightforward programming language to have a better interaction between the robots and the CNC machines. Recent development includes an interface that enables the CNC operator to control in a single panel both the robots and the CNC machines. With more collaborations, the goal towards a more progressive CNC and elevating its efficiency will not be far-fetch. Digitalization
Remember the Tron movie? Yes, the film where the movements are simulated in the virtual world. Digitalization is precisely like that. In digitalization, the process or object in the virtual world is simulated to get a better insight. It is now a growing trend in many industries, and soon it will find its way into the shop floor.
The machine and tool industry will not be left behind when digitalization sets in. In fact, when the real and digital world is linked, it can open significant possibilities. As a result, it will boost productivity and develop fresh business models.
CONCLUSION
Involved in digitalization is the massive collection of data on temperatures, forces, and vibrations. These data will then go to the cloud for processing, analysis and transforms them into a working replica. When you have more data, it can create a more accurate virtual twin. The virtual twin will be able to provide a more precise and real simulation. The design engineers will use the results of the simulation to plan the machining process, maximizing the machine's accuracy and efficiency, and producing parts with less waste.
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