CVD Coated Cemented Carbide for Steel Turning "MC6100 Series"

Performance has been drastically improved by using manufacturing technologies, feedback and thoughts of customers, together with the staff at the Central Research Institute.

CVD Coated Cemented Carbide for Steel Turning

Kenichi Sato, Coating Development Section, Materials Development Department, Tsukuba Plant / Masakuni Takahashi, General Manager,  Materials Development Department, Tsukuba Plant / Takuya Ishigaki, Manager, Coating Development Section, Materials Development Department, Tsukuba Plant

With automobile parts at the top of the list, the material specified for these parts by manufacturers have become harder. Along with this tendency, cutting tools are therefore required to have greater wear resistance. However, increasing wear resistance leads to a greater frequency of tools becoming chipped, this in turn leads to defects in products, making it impossible to guarantee stability in production. Collaborative development in response to requests from customers to solve this problem had to begin. Based on findings at the Central Research Institute, Tsukuba Plant worked on tool development in close cooperation with the Plant Engineering Group. As a result, a solution was provided that significantly improved wear resistance and tool-edge stability.

Originated from customer requests

– First of all, please tell us what was behind the development of the new product.

Takahashi:   The rationale behind new product development can be classified into two main categories. One is requests from customers, and the other is the need to develop new technology. MC6100 series development began with a request by an overseas customer; but this request also aligned quite closely with new technology that was already under development.

Sato:  The request from the customer, an automobile parts manufacturer, was for longer tool life. In addition, the customer also wanted to increase machining efficiency, which required the improvement of tool performance. In this case, one thing was different, and that was the complete coordination with the customer during development. Work on new product development is usually done purely in-house, so this was an unusual case.

– Even if customers make requests, it’s not easy to move ahead without the technology that can respond to them, is it?

Ishigaki:  Yes. Responding to the request for extended tool life meant increasing wear resistance. Mitsubishi Materials has products coated with CVD technology. CVD stands for Chemical Vapor Deposition, which is a method of forming a thin film made with a wide variety of substances. Our CVD coating technology is excellent and the CVD thin film coating has outstanding wear resistance; however, it needs to be controlled precisely to prevent peeling. Fortunately, we had been working on the development of technology that prevents peeling to maximize high wear resistance.

Sato:  The materials that can be used for hard coatings are limited. Considering ways to achieve both wear resistance and tool-edge stability in possible combinations and under different conditions is an eternal pursuit. We have accumulated technologies to increase wear resistance, and one of these is Super Nano Texture Technology.

Originated from customer requests

Super technology to increase wear resistance

– Why did you add “Super” to the existing Nano Texture Technology?

Ishigaki:  Nano texture technology is one of the Central Research Institute’s areas of research. We have been developing technology to increase wear resistance by unifying the direction of crystal growth, and have acquired patents since 2000. Since we significantly improved such technologies for this case, we decided to add “Super” to the name. In terms of technological improvement, grain size and direction of growth in Al2O3 crystal grains were uneven in the initial technology. Therefore, we tried to improve the evenness of the grain size. This is called Nano Texture Technology. Additionally, we improved the evenness of the direction of crystal growth. This is called Super Nano Texture Technology. Ensuring greater precision and evenness in crystal growth significantly improved wear resistance.

Takahashi:  I’m sure that Mitsubishi Materials now has the top-class technology needed to optimize crystal growth. The reason that we could achieve such high technological development is because we, the development group, and the Central Research Institute always cooperated to accumulate know-how. The elemental technology of Super Nano Texture Technology was developed by the Central Research Institute.

– However, it is not always the case that the development of new elemental technology imme­diately leads to commercialization, is it?

Sato:  Yes, that’s correct. Customers want us to use our elemental technology to develop cutting tools capable of outstanding performance under their machining conditions. In other words, customers want the development group to develop the technology and tools that provide them with stability and superior quality. The ability to commercialize elemental technology is necessary for that next step.

Super technology to increase wear resistance

From micro to macro – Issues caused by the difference in scale

– I wonder if it’s difficult to apply the technology developed at the Central Research Institute to mass production.

Takahashi:  This is why the Development Center exists. Even if we are confident that the elemental technology developed at the lab will be successful, we need the manufacturing technology to mass produce it. Developing that type of manufacturing technology is our role.

Sato:  Until three years ago, I was working at the Central Research Institute on basic technology development for CVD coatings, and learned about the control of crystal growth direction at the Central Research Institute. After that, I was transferred to the Tsukuba Plant, where I started work on the MC6100 series. However, the preconditions for micro-scale experiments performed at the lab and macro-scale mass production are quite different. Fortunately, what I learned about basic technology at the Central Research Institute was very helpful for me in understanding phenomena I observed during testing for mass production.

– Since MC6100 series development was based on a customer request, did you feel pressure to move quickly?

Ishigaki:  Exactly. But that pressure didn’t mean that we could take shortcuts. We proceeded through a steady and deliberate process of repeated trial and error, identified problems through testing, and made adjustments accordingly until we were confident that we could not only meet, but exceed the customer’s expectations. It is also important that the PDCA cycle be applied efficiently at a high rate of speed. This is because the scale of production between lab testing and mass production is different, we see phenomena in the production phase that differ from those seen in the lab. And to establish an efficient mass production system, we needed close cooperation from the coating staff during the production technology and manufacturing phases to advance development. The more specialized staff involved in a project, the greater the need is to move forward quickly.

Takahashi:   It’s important in the PDCA cycle to follow the rules and principles. If we follow the rules and principles, it is easier for us to find the parameters where problems occur.

– The parameters may influence changes in lab scale.

Sato:  The distribution of some parameters may change due to changes in scale. In such cases, it is also necessary to return to the basic principles, establish a hypothesis, and then test that hypothesis through experiments. We communicate closely with the staff responsible for production technology about the process to ensure that everyone is moving in the same direction when establishing a hypothesis based on the changes in parameters using calculated data provided by the Central Research Institute.

Overcoming difficulties through exceptional approaches and close cooperation with customers

Overcoming difficulties through exceptional approaches and close cooperation with customers

– What was your biggest challenge in develo­ping the MC6100 series?

Ishigaki:  Because this began with a request from the customer, we worked together with that customer from the initial stage. We talked at length to understand exactly what they actually wanted. Then, we examined prototypes made using machining equipment on the actual production line at the customer’s workshop. We were unaccustomed to responding to customer’s pin-point needs, and this was an extremely challenging shift in our approach.

Sato:  When testing on the customer’s production line, our staff visited the site. Standing next to the actual machine being tested, our staff listened carefully to the operator’s opinions. In addition, the staff and salespersons from Mitsubishi Materials talked with the customer’s engineers to determine the direction of improvement. Repeating these processes, we continued improving wear resistance. Just as we reached a level that we felt was very close to our goal, however, we encountered a final problem that was difficult to solve.

– What was the problem you encountered?

Takahashi:   In a certain mode, the test machine at the customer caused specific damage. If we solved this problem, we would achieve the goal. Try as we might, though, trial and error using our equipment failed to replicate the damage that was being observed on the customer’s line.

Sato:  According to our theoretical discus­sions on the causes of the problem, one idea occurred to us. We thought that the damage might be occurring during an early stage of machining. If we could identify the cause at that stage, we would be able to address the issue. However, to test our hypothesis, we had to use the customer’s machining equipment and shut it down in the middle of the operation to check the tool edge. For the customer, it was out of the question to stop machining in the middle of the process. However, we explained how stopping the process would allow us to better understand the problem and how this would bring us closer to a solution.

– And how were you able to solve the problem?

Ishigaki:  The results of the experiment confirmed our hypothesis. Because of the fact that damage occurred in an early stage of machining, we could identify a solution to reduce it. We tested an improved prototype, and we were successful. This success, along with the required wear resistance that we had already achieved, made the customer very happy.

Adding two new technologies increased stability

– I understand that in addition to the Super Nano Texture Technology, other new technologies were applied to the MC6100 series.

Sato:  Yes, one of these was the reduction of sudden fracturing, which was solved by using the advice of a customer. CVD coating is formed at a high temperature, and tensile stress occurs in the coating layer during cooling. Machining with an unstable tool edge during that time creates uneven impact wear and cracks tend to become larger because the tensile stress is unable to reduce the expansion of cracks. This is how fracturing occurs. The challenge is to mitigate the tensile stress to solve the problem.

Takahashi:  How we mitigated the tensile stress is a secret, but the solution came through a deliberate process of repeated trial and error. We also applied the PDCA cycle.

– What is the other technology, Super TOUGH-Grip?

Ishigaki:  Mitsubishi Materials had already developed the TOUGH-Grip technology, which firmly bonds two different coating layers. Specifically, it is used to bond the Al2O3 (aluminum oxide) layer and the TiCN (titanium carbon nitride) layer, which is the base of the Al2O3 layer. Making the crystal grains finer increased the adhesive surface of the Al2O3 and TiCN layers, and enhanced the adhesive strength between the coating layers. In other words, this new technology more effectively reduced the peeling of coating layers compared with the existing technology. The peeling resistance test for the Super TOUGH-Grip showed that adhesive strength increased 1.6 times.

Sato:  To bond Al2O3 and TiCN, which have different crystal structures, we needed to first learn as much as we could about the basic characteristics of each crystal structure. With such knowledge, we could work on increasing adhesive strength. During the specific development processes, cooperation from the members of the Plant Engineering Department allowed us to conduct repeated experiments using the actual coating furnace.

Takahashi:  Our development team and Plant Engineering Department proceeded through every step of the process in close communication. The entire staff at the Tsukuba Plant frequently exchanged opinions with the aim of maintaining a clear focus on the goal. One of our major strengths is this emphasis on cooperation.

Wear and defect resistance are eternal themes

Wear and defect resistance are eternal themes

– The outcome of these new technologies is the MC6100 series, isn’t it?

Ishigaki:  The MC6115 is for high-speed cutting. Applying a thick Al2O3 film made using Super Nano Texture Technology makes it possible to achieve excellent wear resistance during machining when tool edge temperature tends to become high, similar to the conditions found during high-speed cutting and high-efficiency machining. As for MC6125, adding the Ti-based substances or Al2O3 lamination layer to the Super Nano Texture Technology Al2O3 layer, we achieved a level of machining performance capable of responding to a broader range of applications.

– How have customers reacted?

Sato:  What satisfied customers most was the extension of tool life. Since conditions such as processing and machining speeds could be improved, we hear from customers that productivity has also improved. We are extremely happy because such achievements were the goal of development. Another thing we did was to use gold for the outer colour. During development, the customer wanted a distinctive tool edge to show its status as “used or unused.” When we deliver the MC6100 series to customers, most of the customers seem to be impressed with the colour. The colour also seems to help negotiations. It’s only a small thing, but we are glad that we chose it.

– How about the cost of the new technologies including the gold coating?

Ishigaki:  Prices are at almost the same level as existing tools. Cost was a priority issue from the mass production stage, so we checked aspects of the production lines, including the flow of each item through plant-wide coope­ration. Costs are determined by the time in production. However, because customer sales have been going so well, production according to the initial specifications has also been smooth without a need for changes.

– What direction do you think you’ll be moving to now?

Takahashi:  Improving wear and defect resis­tance are eternal themes for cutting tools, so we will continue working on these areas. We also need to consider changes in automobile engines. We have to observe how customer needs change as automobile production shifts entirely to electric vehicles. Changes in their needs directly influence the direction of technological development. Considering needs in quality and machining speed as well, we will continue striving to meet customer expectations.