STATE OF THE ART OF ADVANCED CNC MACHINING TECHNIQUES USING SPECIAL CUTTING TOOLS
by Adrian Mester and Cosmin Cosma
Published onJun 06, 2024
STATE OF THE ART OF ADVANCED CNC MACHINING TECHNIQUES USING SPECIAL CUTTING TOOLS
STATE OF THE ART OF ADVANCED CNC MACHINING TECHNIQUES USING SPECIAL CUTTING TOOLS
Adrian Mester, Cosmin Cosma
Technical University of Cluj-Napoca, Faculty of Industrial Engineering, Robotics and Production Management, B-dul Muncii nr. 103-105, 400641 Cluj-Napoca
Current advancements are underway within the industry, requiring ongoing evolution in production methodologies to improve machining processes, time and minimize the costs. For example, the automotive industry is witnessing significant growth, marked by the gradual transition from conventional combustion engines to electric propulsion systems. Such parts in manufacturing demand entail a multitude of intricate operations subsequent to the casting phase. As industries advance, so do cutting tools, adapting to the changing demands of modern production. As a result, engineers are continuously pushing the boundaries of innovation in this field. At this point, only imagination is the limit.
1. INTRODUCTION
In today's rapidly evolvoing industrial ladscape, the need to enhance efficiency and precision in manufacturing processes has become crucial. This paper dives into the topic of Computer Numerical Control (CNC) machining, specifically focusing on the utilization of special tools equipped or not with indexable inserts, made only for some specific operations of the process, so they can not be used as conventional tools such as mills, drills or reamers by other manufacturers. As industries such as automotive shifts towards electric engines, the demand for specific machining operations post-casting has intensified, as being large series production items.
Nowadays, more and more people choose to purchase a car, and most families own at least 2 cars, and not to talk about car enthusiasts with huge collections. Even if some of us love the bursting sound of a v12 combustion engine, or the gasoline smell, due to increasing air pollution and for a better enviroment, everything has to change. Slowly, old cars begin to be replaced, about 2 in 3 new cars being either electric or hybrid ones. Also, as the reliability of electric propulsion systems continues to improve, surpassing that of conventional ones, there emerges a pressing need for a larger-scale production of electric engines. Unlike their predeccesors, electric cars have fewer moving parts, leading to reduced wear and tear and thus, increased longevity. This highlights the necessity for scaling up the production of electric engines to accommodate the growing demand for reliable, long-lasting transportation solutions.
To meet these evolving demands, cutting-edge advancements in cutting tools have emerged, featuring indexable inserts that offer enhanced precision (2 or 3 microns) and versatility. This paper aims to explore the application of these advanced machining techniques within the context of CNC operations.
2. METHODOLOGY
Computer Numerical Control (CNC) is a computer-assisted processing method that directs general machines using instructions generated by a processor. CNC programs are usually stored on memory systems such as USB sticks or disks and consist of lines written in "G" code (e.g., G00 is used for Rapid Positioning, G01 for Linear Interpolation, and so on), interpreted by the machine. Initially used on conventional metalworking machines like mills, boring machines, and drills, CNC has since expanded to various applications including robotics, grinders, welding and laser cutting, among others. The primary goal of CNC machining is to be more cost-effective and to reduce the process time, leading to improvements such as decreased skill requirements for precision components, reduced setup time, increased product uniformity, longer cutting tool life, and decreased fixturing and tooling storage costs.
There are two types of control variations: Three-Axis Controls; and Four and Five-Axis Controls. The tool moving programming can be done in two different ways. For straight – cutting linear milling, for example, we can tell the machine to move in Absolute or Incremental Dimension Coordinates. In the first case, the machine shaft is always moving from absolute part zero and all the features are dimensioned directly from the same zero point in all axes, while the other one is done from point to point, like a “virtual resetting” of the zero point [1].
Figure 1: Parts of a CNC Milling Machine [2]
The process may include various operations such as milling (figure 1), drilling, turning, and grinding, depending on the requirements of the part being produced. Throughout the machining process, monitoring and quality control measures are implemented to ensure accuracy and consistency in the final product [3].
2.1. Cutting tools and inserts
A cutting tool (Figure 2) is a device or implement used in machining operations to remove material from a workpiece. Cutting tools are typically made from hard materials such as high-speed steel, carbide, or ceramic, and are designed to withstand the high forces and temperatures generated during cutting.
There are various types of cutting tools, each designed for specific machining operations and materials. Some common types of cutting tools include: End mills, drills, turning tools, inserts, reamers, taps and so on.
Cutting tools are crafted from a diverse array of materials, such as:
Steels - These are the most used types of materials and includes Carbon steels (the first material used to make tools; we can find an increased concentration of carbon in their composition; it must not reach the temperature of 250°C), Alloy steels for cutting tools (elements such as chromium, vanadium, manganese, tungsten were used alongside steels, coming in help of carbon steels for an increased stability, allowing a higher cutting speed; the temperature can go above 250°C, but no more than 350°C) and High–speed steels or HSS (an optimization for the previously mentioned steels, which ensure stability up to 650°C). Every category can be reinforced by using some thermal treatments.
Ceramic materials – Widely used in cutting tools due to their excellent hardness, wear resistance and high-temperature stability, these materials include Alumina (Al2O3), Silicon Nitride (Si3N4), Cubic Boron Nitride (CBN), Sialon (SiAlON) and Whisker-Reinforcement Ceramics.
Metal Carbides – Sintered metal carbides are obtained from metal carbides such as tungsten, tantalum, vanadium, titanium, chromium, bound together by a cobalt binder. This binding is achieved through sintering.
Polycristalline diamond (PCD) – Diamond, which constitutes the cutting component of the tool, is the hardest natural mineral, making it the best option for processing other materials. It possesses extremely high hardness and has very sharp cutting edges when processed appropriately. Diamond can scratch any other raw mineral, but no raw mineral can scratch diamond. The diamond crystals are sintered together with a hard metal round under high temperature and pressure, obtaining a round insert.
Cutting inserts (Figure 2, bottom) were made for easily changing the cutting edge without changing the entire tool. Indexable inserts are standardized according to ISO no. 1832 (1977, 1985 and updated in 2005). Usually, cutting inserts are made from carbides and processed through sintering, for example, the WC inserts (tungsten-cobalt, its content being around 85% - 95% tungsten carbide alongside 5% - 15% cobalt, used as a binder) [4].
Figure 2: Cutting tools and inserts [5]
There are some important tool manufacturers in the industry, and one of the greatest is Gühring. Hollfelder department, within this company, designs lots of extremely intriguing custom tools adapted to the needs of customers (Figure 3), resulting in assemblies that are difficult to even imagine, but extremely effective and impressive [6].
2.2. Machining using cutting tools with special geometry
To further reduce machining durations and streamline production processes, manufacturers are opting for specialized tools. To illustrate this enhancement, let’s consider an example. We have a shaft (like an electric engine case), and let’s say it has three different diameters and two different types of chamfers. This “engine case” is produced in large series. Typically, an end mill serves as the conventional choice for material removal from the workpiece. However, its utilization necessitates a comprehensive CNC program encompassing each surface operation. Moreover, due to inevitable tool wear, the program must be periodically changed so the final product won’t be a scrap. To make it easier, tool manufacturers come with a solution.
We can order a special turning tool with indexable inserts that “covers” the workpiece and does all these operations in one pass, so the CNC programming will be much simple than before. It can be said that the tool only moves up and down the workpiece length, and the final product is done. Furthermore, the cutting inserts are affixed within cartridges (Figure 4), which are subsequently mounted onto the tool. This configuration makes the insert-cartridge assembly adjustable, enhancing precision within micron tolerances during the machining process. Additionally, even as the inserts undergo wear, the ability to adjust them facilitates longer lifetimes. Subsequently, when the inserts reach the end of their operational lifespan, they are replaced individually, rather than necessitating the replacement of the tool body [7].
Figure 3: Examples of Hollfelder special tools [8]
In the context of electric engine production, the presence of numerous diameters, chamfers, radii, and intricate shapes necessitates the utilization of specialized tools.
Figure 4: Insert-cartridge assembly [9]
Despite the potentially higher cost associated with these tools, their adoption significantly reduces production time by consolidating multiple operations into a single pass. Moreover, the use of such tools enhances the precision of part manufacturing, obviating the need for complex CNC programming.
3. DISCUSSION
This study reviews choosing the best options in CNC machining process for making it more productive. Key findings highlight advancements in cutting tool and cutting inserts design, materials and applications. Special tool geometries have demonstrated enhanced precision and efficiency in machining processes over the time. Overall, these insights contribute to a deeper understanding of modern manufacturing practices.
4. CONCLUSION
In conclusion, using special tools in advanced CNC machining in the large series production, through a brief review, it is evident that specialized tools play a crucial role in enhancing efficiency, precision, and cost-effectiveness in modern manufacturing. Despite initial investment costs, these tools offer substantial time savings and improved part precision, without relying on complex CNC programming (making it easier for every manufacturer). Embracing technological advancements in CNC machining is essential for meeting the evolving demands of industrial production, ensuring optimal performance, and maximizing productivity.
5. REFERENCES
[1] James Madison. (1996). CNC Machining Handbook: Basic Theory, Production Data, and Machining Procedures, ISBN: 978-0831130640
[4] Oyekola Morufu Oduola, Charles Arienrhi Ikutegbe, Kunle Akinluwade. (2016). Cutting Tool Materials and Wear Mechanisms in Metal Cutting: Toughness, hot hardness and wear resistance constitute the prime properties for cutting tool materials in manufacturing, ISBN: 978-3330019461
GuangDong ARCiNTU Intelligent Technology Co,. Ltd. (28.06.2023). “What are the most successful marketing strategies for businesses in the industrial machinery industry?”
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