For processing graphite Diamond coated end mill (For Finishing) DF End mill series "DF2XLBF"

A CVD coating with the perfect balance for sharp edged materials

For processing graphite Diamond coated end mill (For Finishing) DF End mill series

Launched in 2016, DF2XLBF was developed as a special product for a specific customer. The development goal was to prolong the life of tools used in the processing of hard composite resin materials to approximately twice that of existing products. Although the in-house small-lot test on the prototype revealed favorable results, the medium lot test at the customers’ site was disappointing.

Their tireless efforts, however, led to unexpectedly long tool life. It was the determination of young staff that brought success.

The evaluations

– Would you please give us the background of DF2XLBF development?

Tominaga:  Mitsubishi Materials already had a CFD diamond coated end mill for machining graphite. This new DF2XLBF is used for finishing and the letter “F” actually stands for “finish”. It was originally developed as a special product ordered by a customer in the medical industry, and we later expanded sales to all customers.

Hosokawa:  We were initially asked by the customer in November of 2014 to manufacture the tool. They wanted to improve tool life on hard composite resin materials. The goal was to double the existing tool life. Although this was extremely difficult, we began making and testing prototypes and by the next summer, our customer reported that our product had passed in-house inspection and we began receiving orders. To be honest though, the real development started from that point.

– Did you have any trouble after delivery of the product?

Tominaga:  When the customer started using our tool at its manufacturing sites, there was a significant deterioration of tool life. Of course, we made improvements each time a problem was found and we tested quality through in-house inspections to confirm the basic performance before delivery; but actual performance at the manufacturing sites varied and was altogether unsatisfactory.

Hosokawa:  The customer was irritated one day and said we should think about stopping development. We suspected that there must be a fundamental problem somewhere, so we asked the customer to allow us to visit their site. The customer’s attitude toward our request was very severe: “It has been taking too much time for inspection and development, and the results have been completely unacceptable. We feel we can do without Mitsubishi’s tools.” When we examined the manufacturing processes, however, we noticed something important. The individual parts they manufactured had slightly different forms. In other words, the machining load differed depending on the part. We considered the difference in the form of each part and quickly improved the cutting edge geometry. We were confident that the improvement would solve the problem and asked the customer for just one more chance to test the new edge geometry.

– What made you so confident in the result?

Tominaga:   It was simply the optimization of the coating and edge geometry. Hard composite resin materials cause serious abrasion, but they are not iron metals that tend to react with carbon. Therefore, we used CVD diamond coating, which has extremely high abrasion resistance. In general, CVD coating film tends to be thick, which makes it hard to create sharp edges. However, the tool we developed was for finishing and so required sharp edges. So, we optimized the coating to be thin enough to enable sharpness, but thick enough to resist abrasion.

Hosokawa:  We also improved the neck diameter and cut length. Increasing rigidity and tool life generally requires a larger neck diameter and shorter cut length, but we needed an end mill with a smaller diameter for insertion into the deeper sections of components because of the characteristics of their forms. This meant that we needed a smaller neck diameter and a longer cut length. We considered what neck diameter would be rigid enough but not cause interference during machining. We decided that a diameter change from 1.90 mm to 1.86 mm might suffice. Although it was such a slight difference, we were excited to see if this would solve the problem.

The evaluations

Last test determines our destiny

– What was the customer’s reaction?

Hosokawa:  The customer agreed to allow us one more chance to test the tool, but with certain conditions. Under the same processing environment, that is work materials, cutting conditions and machines, we were required to machine a designated number of parts within a set time limit with favorable results before conducting a final test at the customer’s site. We started test machining, knowing this would be the last chance for Mitsubishi Materials. During this process, Ms. Ikuta was key.

Ikuta:   It was my first year after joining Mitsubishi Materials, and I was very nervous about being assigned to such an important project. We took pictures of the tool edge and components and checked them after machining one batch of five parts. One part took 30 minutes. Therefore, one batch took around three hours. We repeated the process every day until we finished 40 batches (200 parts). We sent 10 batches to the customer, who then checked the results.

– When did you start feeling that you would be able to achieve good results?

Hosokawa:  It was around the time that we had finished processing about 150 parts. My concern changed to confidence and after completing 200 parts, we reported our results to the customer. The customer conducted tests at each manufacturing site and achieved an average of four times the tool life of the existing tool. The results had significantly exceeded the original goal, and the customer was visibly pleased. Our in-house testing could be conducted successfully within such a short period of time because of Ms. Ikuta’s efforts.

Ikuta:  I just continued machining as much as possible. I was fully aware of the project’s importance for Mitsubishi Materials, so I concentrated on moving forward.

Tominaga:  The key to success in this case was two young employees of the project team. Employees with experience like us are often quick to decide that a request is impossible. Both Mr. Hosokawa and Ms. Ikuta, however, were new enough not to let a request that seemed impossible get in their way and were eager to make this work. They were positive and not worried about failure.

– Do you have a message for our readers?

Hosokawa:  We are very proud of the DF2XLBF. Its price, tool life and cost performance ratio are excellent. We recommend this tool for the processing of materials to which CVD diamond coating can be applied.