MMC Magazine

Demand for trochoidal milling has been increasing in the aircraft, automobile and other industries. Trochoidal milling combines a circular orbital and a linear motion, which reduces load when deep groove and pocket machining. However, there are certain issues. One of these is the large amount of chips generated. To address this, Mitsubishi Materials developed a unique method that uses the edge geometry of the end mill to break chips. When development started in response to a request from customers in Europe, many competitors had already launched products. Since the competitors had a head start, the Mitsubishi team had to focus on delivering higher performance.

Exciting trials and significant pressure

Would you please tell us your thoughts when you were first asked to develop a unique end mill?

Shikata It wasn’t included in the lineup of conventional products, so I felt at first that it would be an exciting challenge. I started out by checking competitor’s products and found that a few already had similar end mills. This increased the pressure because we had to develop a product that would be superior to the competition, while being very careful not to violate their patents. The Smart Miracle end mill series has superior base materials and coatings, so that was no problem; however, the geometry would be a key challenge. We revolved around a number of ideas based the roughing end mills whose structure is very similar to chip breaker types, and then we asked Niizuma develop 10 prototypes.

Niizuma Shikata always insists on the best results, so I knew from the start that expectations were high. It was a challenge to develop the optimal geometry, but we had the knowledge of the base materials and coatings that we had accumulated through the Smart Miracle End Mill Series, so making samples was not a problem. I wanted to give us enough time for in-house evaluation for the prototypes and worked hard to finish them well before the deadlines.

How was the performance of the first prototype?

Shikata After looking at competitor products, I saw that they had achieved higher performance than I had expected. For the first prototype, I focused on vibration resistance, but I fell short on just about every specification. Having five flutes to improve machining efficiency made it difficult to suppress chatter. Besides the chatter, we also had to improve chip breaking capability, chip discharge and achieve rigidity. The pressure was really overwhelming.

Nagaoka We tested about 10 prototypes for a week to evaluate them. During that time, I could sense Shikata’s disappointment. After repeating three or four evaluation cycles, though, we could see improvement in product quality that was clearly surpassing the competitor’s products already on the market. I was continually surprised at the difference in performance we were achieving with only slight changes in form.

Shikata　We intentionally applied an irregular pitch flute and minimized the clearance angle of the peripheral cutting edge, which helped produce well-balanced performance. Then, we experimented with different groove patterns to identify the most suitable for high-efficiency machining with an eye on a round form with high chip-discharge performance. In the end, high rigidity was also achieved. To break chips, end mills need some notches; however, the smoothness of the finished surface is almost the same as the smoothness produced by square end mills.

Ensuring high usability by maximizing performance

You continued with development even after exceeding the performance of competitor products.

Shikata Both Managers of the Tool Deve­lopment and Cutting Technology Sections provided an ideal environment, giving us a free hand and plenty of time to work with. This made it possible to achieve maximum performance within the range of prototype development.

Nagaoka From that stage, it was my turn to face the challenges. One example is that the prototypes had become more durable, which meant that we had trouble producing defects to evaluate the breakage limit even with very heavy loads. This added significantly to the time required for testing. In addition, during the tests, Shikata, who was always standing behind me, kept thinking of new ideas. He’d take a prototype that we had chosen carefully from all the protypes and come up with more changes that he wanted to try out.

Niizuma Development had kicked off with a request from a customer in Europe. We had originally focused on machining deep grooves in stainless steel. However, Shikata wanted the end mill to have different capabilities and for wider range of purposes. After we succeeded in developing a prototype with specifications that readily exceeded the competition’s products, we began competing with ourselves, trying to surpass our results.

Shikata The three of us worked well together, and this is why we continued developing even better products. During the seventh evaluation cycle, data from the 10 prototypes developed by Niizuma finally showed no significant variation, so I left the final decision to Nagaoka to choose the final product.

Nagaoka During development, I saw myself as the first user of the product. I focused on tiny differences that I picked up on during the repeated evaluations, things such as difference in sound and usability, and evaluated these from the end user’s point of view.

Aiming to expand end mills as a new series

How did customers react to the completed product?

Shikata One comment in particular sticks in my mind: “This is the best tool on the planet right now.” I was also pleased to receive high evaluations when we conducted field tests in Europe during the three or four months before we launched the end mill. Besides the trochoidal milling, they examined shoulder machining, for which data had not yet been acquired. This really demonstrated the product’s great versatility. I deeply appreciated the on-site staff in charge of marketing in Europe for the work they did building good relationships with engineers across a broad range of markets such as the aerospace, plastic mould and semiconductor-related businesses.

Nagaoka Looking at the flagship products that the competition had on the market and comparing the data that we had acquired, showed that the threshold feed rate of our end mill was about two times greater, efficiency was about 1.5 times higher and tool life was about 1.2 times longer. With this in mind, I was confident that customers would be satisfied with our end mills. This turned out to be the case, and it was this that gave me great satisfaction.

Niizuma When we started development of the end mill, there was a mountain of problems to be solved. Therefore, we started on a small scale, developing only two types of end mills. However, since these products have been highly regarded as general-purpose tools, and customers in Europe have made additional requests, we are looking to increase the number of different types. We have already been working on larger diameter and longer end mills and would like to develop a corner radius-type to add to our conventional square-types.