Increased abrasion resistance with the advancement of coolant-driven technology
The need for high-efficiency machining for difficult-to-cut materials has been increasing in the aircraft and other industries; and now, tools capable of performing under advanced machining conditions for extended periods of time are also required. For difficult-to-cut material machining, the use of turning tool holders using high-pressure coolant has gradually increased. Although proven to be effective in controlling chips, another goal, tool longevity, has yet to become stable. Special equipment is also required for high-pressure coolant. Therefore, machine shops have longed for standard tool holders that can be used on different machine tools while they improve abrasion resistance. In this feature, we interviewed three Mitsubishi Materials employees who have developed extremely effective coolant technology in cooperation with Professor Toshiyuki Obikawa from the University of Tokyo.
Takahashi: The significant characteristic of our new coolant-driven technology, “Jet Tech Holder,” is the placement of an L-shape nozzle that we developed at the edge of the holder to provide a powerful jet of coolant from the flank face of the insert to the cutting edge. Coolant is generally supplied from the insert rake face or to the flank face in reverse tool holder use. However, when supplied from the flank face, as shown in Fig. 1 (left), chips can interfere with the flow. Even when supplied from the rake face, the coolant does not enter the narrow, high-temperature, high-pressure space where the tool’s rake face and the surface of a target material; which is rotating at high speed, come into contact. The end result is that coolant does not always effectively reach the edge that needs to be cooled. As shown in Fig. 1 (right), Jet Tech supplies high-pressure, high-speed coolant from the flank face to the edge to prevent it from becoming too hot. This makes effective edge cooling possible, which improves insert abrasion resistance. We also confirmed that this technology can prolong tool life by approximately 30 to 50% when compared general external coolant supplied from the rake face.
Shimizu: We were working to address the significant deterioration of tool life experienced during the machining of difficult-to-cut materials, but we felt we lacked the in-house resources we needed to ensure the competitiveness of the new products that were under development. For this reason, we sought outside cooperation. We met with Professor Toshiyuki Obikawa of the University of Tokyo, who had been engaged in research on extending the life of taools used for difficult-to-cut materials. Professor Obikawa was investigating the effect of a system that directed air for cooling from the flank face to the edge. Impressed with the potential of this method to extend tool life, we began joint research in 2008.
Takahashi: Japanese tool manufacturers were not interested in coolant-driven technology at that time. Mitsubishi Materials was also not really enthusiastic about it then either. When I learned about this joint research, I thought it looked promising; but I was also worried about whether commercialization would be practical and whether the concept would sell.
Shimizu: In developing tools and technology, our Advanced R&D Group looks five to ten years into the future; but specific product development focuses on introduction to the market within two to three years. I knew commercialization would be a challenge, but I felt this coolant-driven technology had potential. Besides, our group is named, “advanced R&D,” and I felt coolant-driven technology was just that.
Takahashi: The biggest turning point during development was choosing between an air-assisted method to emit coolants, or direct acceleration of the coolant. After a great deal of discussion, we decided to prioritize ease-of-use under a wide range of environments and application of it to the different cutting tools employed in the market. This led to our choice of coolant rather than an air assist type. After this decision, we set to work on important details such as determining the most effective form and size of the hole that would emit the coolant and the amount of flow, etc. During this phase of development, Professor Obikawa’s fluid analysis was extremely helpful. Because my knowledge of fluid analysis was rusty, I broke out my textbooks from college and brushed up on it. Through these efforts, we were able to complete the basic design concept for Jet Tech, which allowed us to start full-scale development for mass production and commercialization. We put Imai in charge of the most important aspect of the development, design!
Imai: I had just finished a large product development project. To tell the truth, a turning tool holder development requires more effort, so it’s difficult to get people motivated. Unlike the development of milling tools, which are popular projects, nobody looks forward to being involved in turning tool development. However, Takahashi’s description of the basic concept of Jet Tech hooked me, so I signed up to the project. The basic effects had been verified, so I felt that I could concentrate on commercialization.
Takahashi: He says so now, but I still remember that when I told him about the project, he looked disappointed and clearly less than happy about the idea. In the end though, asking Imai to take charge of design for this product was the right move.
Imai: I love development and working on difficult-to-solve problems fits my personality.
Imai: The most difficult part was the form of the port that would emit the coolant because it should not be produced by machining.
There were no tool holders that had a coolant port around the edge, and mass production of such a tool holder via machining was not possible. In other words, it was necessary to make an independent part. Since I wanted to do something that no one had done before, I set to work.
Shimizu: In fact, seeing an obstacle to manufacturing this design with the existing equipment, we gave up on machining the port and asked Imai to create the part.
mai: First, we had to decide what material we should use for the prototype. Since a resin 3D printer was being used in other product development, we went with resin. Coolant emission was fine; but as might easily be expected, when we put it to the test in actual machining, the heat of chips quickly damaged it. We decided to make another prototype, this time using metal. We found a company handling 3D printers for metal and placed the order for the prototype parts.
Takahashi: At the beginning of development, we designed the part to be effective under normal water pressure. Some customers however, use high-pressure coolant and under such conditions, the nozzle would fly right off. Therefore, we needed to change the design to accommodate both normal and high pressure conditions. We also found that the screws that fix the part to the tool bent under high pressure, so we had to improve those as well.
Imai: At that time, Takahashi was coming at me with one request after another. We had our share of difficult discussions, usually based on, “This is not what you were asking for last time!”
Takahashi: Every time I asked Imai to change specifications, he told me, “This is completely different from what you were talking about before!” He was right, but my motive was to ensure that the part would satisfy customer needs. Difficult as it was, Imai and I kept at it.
Imai: The advantage of making prototypes with a 3D printer is that we can perform tests with them and evaluate the results for improvement. The advancement of 3D printers has reduced the development period not only in the tool industry, but in just about every area of manufacturing.
Takahashi: After determining the final design, we verified the part under different machining conditions by changing coolant type and flow. Finally, we were ready to make a presentation to other companies at an exhibition held last year. The conference room was filled to capacity. We were asked many questions and felt a high level of interest among customers. Many asked us if the part functioned as well under normal pressure. I felt that people were very interested in the fact that a Japanese tool manufacture was working on new coolant technology. I was very pleased that we had kept at this without giving up.
Takahashi: We first started sales with the ISO C-type geometry, and expanded to W, D, S, T and V-geometries. We are planning to apply this technology to products other than turning tool holders.
Shimizu: This technology should be used more broadly, even by other companies as an excellent way to increase service life. Indeed, it should be seen as an industry standard that contributes to reduced production costs for customers. Really, this technology represents an improvement for the entire machining industry. I also feel that industry-university-government collaboration should be enhanced. Compared with activity overseas, Japan is not taking advantage of this nearly as much as it could. I want to follow this approach more and more.
Imai: What I imagine becomes reality. My imagination is commercialized and makes customers happier. This is fantastic. Being engaged in development means doing something completely new. We may fail and encounter difficulties but our ability to work on, in spite of setbacks leads to our ultimate success. That ability is nurtured in no small part by our more experienced colleagues who encourage us to see failure as a learning opportunity and difficulties as a challenge. This comfortable environment is a key to the creation of something new.
Takahashi: I’ve been in development for 16 years. I put plans into final shapes and validate theory. When the theory and actual product match perfectly, it’s a great thrill. Development is great fun for me because I am pursuing a goal that no one has reached yet. It may be the world’s first, the world’s best or even the only one in the world, and I am very proud to be doing such work. I will continue working on the development of new products to make our customers happier.
University of Tokyo Professor Toshiyuki Obikawa is a leading expert in machining. He started research on machining when he was studying for his master’s degree. The topic of his research was the effects of manganese sulphide (MnS) contained in free-cutting steel. We interviewed Professor Obikawa about the joint development of Jet Tech Holders with Mitsubishi Materials.
Obikawa: Around 1980, when I became an assistant, machining targeted steel only. Difficult-to-cut materials such as titanium alloys and nickel-based heat-resistant alloys were extremely expensive and hard to obtain. However, I felt that Japanese machining technology for the aerospace industry was behind other countries, so I chose difficult-to-cut materials for my research. Machining generates heat and that heat causes significant deformation; but analyzing data to clarify this was very difficult. Analytical theories described in the technical manuals at that time were not about large deformation, but about stress. It was very difficult to analyze deformation.
Obikawa: When I became a professor, MQL machining was popular as an environmentally friendly method. The use of a small amount of oil mist rather than a large amount of lubricant was the standard at that time and it had spread quickly since it reduced power consumption and machining costs. In the late 1990s, an automobile manufacturer reported that replacing the coolant pump could cut energy consumption by approximately 40%. I also examined the effects of MQL machining, investigating various points by using fluid analysis. When I was watching MQL machining tools that emit oil mist from both flank and rake faces, I wondered what would happen if compressed air were emitted from the ports in regular wet cutting. My experiments yielded favorable results. This is the Air Jet Asist (AJA) method. Using air however, cost a lot more than I had expected; and this led me to the idea that we should instead use coolant and emit oil mist from a smaller port. Next came the idea that we should emit compressed air only and then follow with a coolant.
Obikawa: Using the AJA machining method, we thought we could push coolant by air. The flow speed of coolant is about 1 to 2 meters per second while the flow speed of compressed air is about 100 to 200 meters per second, which is quite a difference. We knew that MQL emitted air effectively, and we thought we would be able to use it. I was very lucky because the initial data in all of the research showed extremely good results. Often, unfortunately, if we obtain discouraging data at the beginning, we tend to abandon the idea.
Obikawa: First we examined the best size and form for the port. However, it is very difficult for students to freely adjust the size and form of the ports on prototypes. To address this we made an adaptor with ports on the edge of the nozzle, changed the diameter of the ports and measured both flow and speed. As the diameter becomes larger, the flow increases; but past a certain size, the speed drops. We discovered that approximately a 2mm2 cross-sectional area yielded the best flow and speed, and we set that as the standard for design. Although I felt that emitting machining lubricant from both flank and rake faces would be ideal, I finally decided on the flank face only to prevent a decrease in speed with the increase of flow.
- What impressed you most about Mitsubishi Materials?
Obikawa: They helped our research immeasurably. The cross-sectional area of the port for the machining lubricant on the Jet Tech Holder was larger than the port for the air employed in the AJA machining method, so some ports were filled with adhesive. When we emitted the machining lubricant, the adhesives were softened by the lubricant and finally destroyed. We changed from circular to L-shaped ports, which also differ depending on the edge of each insert. I know that it must have been very difficult for Mitsubishi Materials to make and verify different forms for actual use.
Obikawa: I agreed with the idea of emitting coolant from the flank face and worked together with Mitsubishi Materials through a process of trial and error to complete the product. When I saw the final product, I felt it was simply beautiful. Tool holders are high added value products. When roughly calculated, 1 gram of an airplane costs about 200 yen and 1 gram of the most advanced hybrid automobile costs about 2 yen. One gram of an insert on the other hand, costs about 50 yen; and inserts are disposed of after a few milligrams of wear, which makes them extremely costly. I would like to continue research that expands the potential of cutting tools.