Coated CBN material for high-hardened steel turning BC81 SERIES

The challenge of the CBN/PCD team in developing high-performance, long-life CBN materials

The team embarked on the development of the BC81 Series (BC8110, BC8120) in 2011. To develop a new CBN series for high-hardened steel that would outstrip other companies, a completely new technology needed to be developed. Below is an interview with six development and manufacturing members who tackled this goal.

Q: Tell us how the BC81 Series came to be developed.

Yumoto: In recent years, the automotive and machine industries have entered a growth trend and there has been an increase in demand for CBN (cubic boron nitride) tools that could be used for machining high-hardened steel parts. Mitsubishi Materials launched BC8020, a coated CBN material for general cutting of high-hardened steel in 2010, but in some cases it lagged behind the products of our competitors. Taking this disappointment to heart, we drew fully upon the strengths of new technologies and developed the BC81 Series coated CBN material for machining high-hardened steel.

Q: Tell us about the development of BC8110.

Yumoto: BC8110 was developed as a coated CBN material for continuous cutting of high-hardened steel. In our development process, we committed ourselves particularly to pursuing "what customers seek." By having our entire team focus on user-oriented product development rather than on technology-driven development, we were able to proceed towards the same goal without going off track.

Maekawa: When starting our development we exhaustively investigated "what needs to be improved" in comparison with competitors' products. The result pointed to an improvement of wear and chipping resistance, so we set our eyes on developing as our main concept "a CBN base material with excellent chipping resistance and a coating with superior wear resistance."

Q: How was the development actually carried out?

Yumoto: First of all, to develop "a CBN base material with excellent chipping resistance," we single-mindedly worked to improve the toughness of the CBN base material. However, all sintered CBN materials, including those of our competitors, had the same type of composition, so it was evident that CBN base material produced in the ordinary way would only provide the same level of performance in the final analysis. Therefore, to achieve a toughness that outstrips our competitors, we invented the new "ultrafine binder" technology.
Owing to this technology, we were able to make the BC8110 binder much finer than our previous and competitors' products and succeeded in developing a ceramic binder with improved toughness. We were thus able to achieve extremely good resistance to chipping.

Maekawa: Following the development of the base material, we embarked on the development of "a coating with superior wear resistance." Generally speaking, coatings do not adhere as easily to CBN tool material compared to other carbide tool materials.
So what needed to be done to achieve both adhesive strength and wear resistance? As a result of examining the issue in various ways, we decided to modify our company's unique Miracle coating technology so that it could be applied to CBN. This involved what seemed to be an endless series of trials and errors to find the appropriate conditions, this was because carbide tools and CBN tools differ completely in the way a coating adheres to them. We also introduced new facilities to the manufacturing stage and added a new process after coating.
There were bound to be disadvantages to increasing the number of work processes, but a comprehensive review needed to be performed, beginning with the manufacturing stage in order to achieve the performance we desired.

Okada: Frankly, as a member in charge of manufacturing, I doubted whether increasing the number of work processes would make any difference. However, seeing one of our members passionately explain the need to increase the number of processes to achieve the goal, I had to believe in him. In the end it led to good results, although there is still more room for improvement.

Yasuda: In the product testing stage, we performed repeated field tests with the cooperation of our customers. By proposing a new perspective to the customer at this stage, they came to value our product more than our competitors, especially as we ultimately succeeded in extending tool life.

Maekawa: Customers who cooperated in the testing requested to buy the product before its release, even if it was a special-purpose product. Receiving such high commendation before a product's release has left a very strong impression on us.

Q: Tell us about the development of BC8120.

Yumoto: BC8120 is a successor of the BC8020 coated CBN grade for general cutting of high-hardened steel, which was released in 2010. Some application problems arose with BC8020, such as degradation in dimensional precision due to delamination of the coating and also when chipping occurred during continuous cutting. When developing BC8120, we therefore aimed to resolve these problems and to develop a material that delivers greater intermittent performance compared to competitors' products.

Yasuda: BC8020 lagged behind our competitors' products in some areas, so we knew that we would fall further behind if we were to spend four to five years developing something new. For this reason, it was essential to develop our next product in a short period of time. As a matter of fact, it took us only a year or so to further improve our CBN base materials and coatings.

Yumoto: It was necessary to increase the chipping resistance of the CBN base material.
We initially thought we could enhance toughness to a certain degree by applying the ultrafine binder technology to BC8120 that had been developed for the CBN base material, but this was no easy task. Due to limited time, we even worked over the weekends making sample after sample and ultimately succeeded in applying the ultrafine binder to develop a dedicated CBN base material for BC8120.

Maekawa: For the coating our main objective was to control delamination. We began by considering film compositions and applied a new technology that would control residual stress in order to enhance adherence strength. As a result, we achieved greater adherence strength than ever before.

Q: Were any special efforts made in manufacturing the BC81 series?

Kodera: Because the BC81 series is a new type of material, we began searching for processing methods only after gaining a thorough understanding of the material. It was a tremendous challenge to produce samples in a short time without any disruption to regular production.

Yumoto: Mr. Kodera is a specialist, so he would make a sample three times faster than other people. That is why we always ended up asking him to make a sample (laughs). Having someone like Mr. Kodera on the manufacturing staff is an enormous support to production development.

Kodera: The result was achieved not only by me, but by the cooperation of the manufacturing staff. The members of the CBN/PCD team are extremely cohesive and tend to want to help whenever someone needs it (laughs).

Kubota: On the production floor, we hear our customers' appreciation and words that they are awaiting our product and this motivates us to make greater efforts. In hindsight, I think that our wish to "make outstanding CBN/ PCD products" created a solidarity beyond the bounds of departments and roles. This is because we had a relationship of mutual trust that we were able to realize our product goals.

Q: Please say a few words to your customers.

Yumoto: We have absolute confidence in the BC81 series, particularly considering all the struggles we have gone through. We will actively engage in cutting tests and PR activities and hope customers will try our products.

Maekawa: This fiscal year, BC8105 coated CBN material for finishing high-hardened steel and the BC8130 coated CBN material for continuous cutting of high-hardened steel are scheduled to be released. However, we will also focus our efforts on further developments, so please look forward to our future lineup of products.

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