MMC Magazine

Kotaro Sakaguchi: Prototype Operator / Joined in 1998
Toshiya Matsumoto: Production Operator (former Prototype Operator) / Joined in 2004
Takayuki Azegami: Development Staff / Joined in 2006
Takahiro Misono: Production Technology Staff / Joined in 2006

Exchangeable Head End Mills「iMX」

Innovative Fastening Mechanism Produced by Craftsmen

The development of exchangeable head end mills started as far back as 2001. As with any long term development the end product turned out to be quite different from the first prototype. Mitsubishi Materials engineers considered the double face contact of the cemented carbide part of the system to be a critical aspect to satisfy the needs of maximum strength, rigidity and reliability; however, new technology was needed to achieve this. For this article, four engineers involved in the process were interviewed; two that specialise in development and production technology and two prototype machine operators.

Q: Please tell us about the background of the development.

Azegami: "There are two different end mill types: solid and exchangeable head types. End mills with exchangeable heads are very economical because they can be easily changed for different requirements which makes them suitable for a wide range of applications. Solid end mill bodies are as the description suggests, manufactured from one solid piece and this ensures high rigidity and precision. Therefore combining the merits of both types to better satisfy customer needs was the thinking behind the start of development in 2001. The original fastening mechanism supported the head through contact with the tapered surface alone, which didn’t provide the strength and rigidity that was needed. In a process of repeated trial and error the conclusion was reached that using a double-face contact of the cemented carbide parts to the fastening mechanism would greatly improve performance. Frankly speaking this was very challenging and we were not sure at that time if it was possible to turn the idea into an actual product."

Misono: "We found that cemented carbide screw threads tended to break when tightened. This meant that we had to develop technology that would allow us to insert steel screws into cemented carbide."

Q: Is double-face contact with the cemented carbide parts really so difficult?

Azegami: "Yes. The double-face contact applied to the iMX series is formed by facilitating the elastic deformation properties in the tapered parts to create a strong contact between the end surface of the head and holder. While cemented carbide is super hard, it can also be brittle. What I mean by this is that cemented carbide used for cutters has an extremely small capacity for elastic deformation, so there is a high possibility that the holder will break when the head is tightened. To address this we used a tougher grade of cemented carbide, which is durable but not the same type commonly used for cutters."

Matsumoto: "When we made a prototype of the holder, the end surface of the holder was gradually ground in 1μm increments to find the perfect tolerance. After finishing the holder, we conducted a fastening experiment and confirmed that elastic deformation allowed the outer diameter of the holder to increase by just a few μm in the double-face contact state. We were very excited with the results."

Misono: "For the mass production of the double-face contact type fastening mechanism, we needed to develop a new technology that would allow us to set the strict dimensional tolerances needed, something that was thought to be impossible at that time for mass production. We looked at a wide range of fields, including inspection and measurement devices, machine tools and the overall process method before finally establishing the mass production technology we needed."

Sakaguchi: "When we first established the mass production system we had to respond to ever more difficult requests from the development section. The relationship between the manufacturing and development section was frayed for a while."

Everyone: (Laughs)

Q: Please tell us about the joint structure technology.

Misono: "The iMX series uses a special joint structure from steel and cemented carbide that effectively utilises the characteristics of both materials. For manufacturers that produce cemented carbide and high-speed steel tools, it had been a long-term goal to establish technology that would allow a stable and strong joint between cemented carbide and steel. Technology for the joining of shanks and cutting heads made of different materials for the mass production of cutting tools was already being applied, but it was extremely challenging for us to adjust this existing technology. At the Akashi Plant, we started by looking at new machines and setting up an infrastructure we had little experience with. Smooth mass production also called for modification of existing hardware that required significant effort."

Azegami: "It was a process of trial and error. We were selecting different materials for the steel and cemented carbide parts and conducting repeated joint and tensile tests on hundreds of units before we were able to produce the strength that was required. It was a great feeling when the test operator finally signed off on product performance."

Sakaguchi: "It was important that after all the different phases of a long development process, something new and innovative was launched during JIMTOF 2012. We believe the final product reached that innovative target because we created a series of tools that would benefit our customers."

Q: Do you have anything you would like to say to our customers?

Azegami: "Since the iMX series was introduced to the market in 2012, customers that have changed from solid end mills have been very satisfied with the results. With the outstanding strength and convenience that comes with the exchangeable head technology, I am confident that more and more customers will be looking at implementing iMX series."

Misono: "We will continue working on the development of precision manufacturing technologies to meet customers’ needs with high quality products. Our products feature the most advanced technology and I am sure that we’ll be seeing expanded use of them in the market place as their popularity spreads."

Sakaguchi: "The iMX series development now focuses on responding to customers’ needs, and I know the market is also looking forward to seeing our new products."

Matsumoto: "Due to our prompt response to customers'requests for special as well as standard products, the popularity of the iMX series is certain to grow."