Star Micronics Co., Ltd. opened its doors in 1950 as a small parts factory with only six employees. The company began with the manufacture of precision parts for watches using automatic lathes from Switzerland and Japan. To produce higher quality precision parts, the company shifted to manufacturing its own machine tools for in-house use. The shift was driven by the founder’s desire to develop an automatic lathe. The company touted its product as “Made by machinists for machinists” and soon began receiving orders for automatic lathes from other companies.
“We have been manufacturing a wide range of precision parts using machine tools that we have developed internally. Our Development Division takes feedback on the usability and reflects it to the development and improvement of new and existing products. This is a major strength that we have,” said Fumio Masuda, Executive Manager, Sales & Marketing Department, Machine Tools Division.
Star Micronics started global expansion of its automatic lathe sales with exports to England in 1962. Currently, they have established production, sales and service structures in Europe, the United States and Asia. They do not rely on distributors and sales agencies, instead they send employees directly to customers to provide thorough before and after sales service of their products. Such close attention has been highly regarded by the market, and their Swiss-type automatic lathes have now captured around a 30% share of the global market, establishing their position as the leading automatic lathe manufacturer. Their Swiss-type automatic lathes have also been used in the manufacture of bone screws, artificial tooth implants, auxiliary material for joints and much more.
The combination of long thin geometries and difficult-to-cut materials that comprise a lot of medical components, means that they are difficult to manufacture without Swiss-type automatic lathes. This is why Star’s products have been chosen by the medical industry as the machine tools of choice. “Additionally, because bone screws and other parts used in medical treatment are placed inside our body, they must conform to extremely high standards, conform to blood compatibility and be corrosion resistant. To meet these demanding requirements, they are manufactured from difficult-to-cut materials such as titanium alloys and also require extremely high geometrical accuracy,” said Noriaki Ozeki, Manager, Technical Sales Support Section, Sales & Marketing Department, Machine Tools Division.
Swiss-type automatic lathes have designs and specifications that respond to such exacting requirements and are highly regarded by medical device manufacturers.
“When developing Swiss-type automatic lathes, we focused on machine rigidity. We utilised a slant-bed structure with trapezoidal sliding dovetail type surfaces. In this structure, fixed and movable parts are constructed in a way that brings the ball screw centre closer to the cutting point and therefore reduces the moment load during cutting. This reduces the vibration caused by cutting resistance and improves accuracy. This makes it possible to maintain smooth, stable machining accuracy even when significant changes of the cutting depths are required,” said Daisuke Suzuki, Executive Manager, Development Department, Machine Tools Division.
In addition to the dovetail slant bed, the application of a wide range of structures, including a spindle sleeve sliding surface that supports the cutting load on the spindle during processing increases machine rigidity. They also elaborated on a wide range of ingenious designs to realize an even higher degree machining precision.
“For example, artificial teeth for dental implants sometimes require the drilling of a hole 80 mm deep, but only 1.8 mm in diameter. Drilling such holes on the main side of a machine is a problem due to limitations in length; therefore, we fit an attachment on the spindle on the back side that can drill up to 100 mm hole depth,” said Ozeki, Technical Sales Support Section Manager. Also, in order to restrain thermal displacement, a unique design has been applied that makes it possible to measure and predict heat changes and to adjust the machine accordingly. “Medical professionals sometimes visit us to observe the manufacturing process. Therefore, we also focused the design on building a simple structure that prevents oil leakage, this in turn helps cleanliness,” added by Fumio Masuda, Executive Manager, Sales & Marketing Department. Meanwhile, the Star motion control system was developed for superior overall control. This system changes spindle speed at the most appropriate timing and ensures smooth movement throughout the cycle to achieve a significant reduction in non-cutting time. During preparation for subsequent steps, the system reduces cutting feed to allow adjustments at predetermined locations and timing. This helps to reduce vibration and increases accuracy.
Many metal cutting companies employ highly-complex manufacturing appli-cations, such as forming cylindrical bars into squares or other shapes. Lathes with low rigidity frequently fail to meet the desired geometrical standards for these types of product, therefore, the improved surface finishes and accuracy of Swiss-type automatic lathes are of great benefit for companies that have encountered such problems.
The partnership between Star Micronics and Mitsubishi Materials started in the early 2000s. At that time, the materials being processed by automatic lathes were shifting from free-machining steels to stainless steels. This material change was used increasingly for injector systems for automobile engine, and use of SUS316 and titanium materials in medical device parts also increased. While chip control is important in stainless steel machining, tool life is a major factor for automatic lathes. However, they tend to use oil coolants that are not as effective for stainless steels. Furthermore, difficult-to-cut titanium materials are used often to manufacture medical device parts, and this means greater challenges when drilling. To address these challenges, smaller diameter drills with through coolant holes, coated with high heat resistant coatings were required. As a solution, Mitsubishi Materials developed the MWS drill using a VP coating with an extremely high heat resistance. Since its launch Mitsubishi Materials and Star Micronics have used the MWS high-performance drill for test applications and also included them as part of turnkey package tooling. Keiichi Kuroda, who was in charge of sales in 2000, looked back that time and said, “We used a wide range of small-diameter long drills for various in-house applications, and this led us to recommend these drills for deep hole processing.” We asked Mr. Ozeki what his impression of Mitsubishi Materials was at that time. He said, “The tools we used to process aircraft parts had high durability, and even when the feeds and speeds were increased, the tools continued to produce high-precision parts. When I was assigned to China, we started to use Mitsubishi Material tools for medical parts due to previous experiences when manufacturing aircraft components. Overall, I was impressed with the quality of the tools.”
At Star Micronics exhibitions in Europe and the United States in 2016, we tested a solid carbide spot/chamfer drill that was under development on a Swiss-type automatic SR series lathe. It provided excellent performance, and this led to use of the DLE spot/chamfer drill at exhibitions both at home and abroad in FY 2018. In June that year, the DLE series of drills was introduced to the market. Drills Development manager Shoichi Fujisawa, (Drill, CBN & PCD Products Development Center, Tools R&D Group, Mitsubishi Materials Corporation) explained the characteristics of this new drill: “Existing spot drills had sharp edges, which were often chipped during the machining of hard-to-cut stainless materials. Making many prototypes to ensure the strength of the edge solved this problem; and after repeated inspections, we decided to apply a double-angle point geometry. We also combined this with point thinning that realised low resistance to reduce the load on the machine tool.”
Mr. Masuda said, “Machine tool compatibility is important for improved processing accuracy. We would like tool manufacturers to carry out development from a wide range of perspectives, including feed, speed and chip control, to develop tools that allow maximum performance for individual machines.” “Hiroaki Ohara, Sales Division, Fuji Sales Office, Mitsubishi Materials said, “The development of this new spot drill is a prime example of our commitment to deliver ever better tools for our customers.”
Mr. Ozeki, Technical Sales Support Section Manager told us about their future vision, “We are planning to expand the sales of products related to the medical industry in India and other regions with large populations. It is essential for us to consider measures to reduce costs and for us to develop not only Swiss-type automatic lathes, but also fixed-type automatic lathes that respond to the increasing demand in the United States for spinal plates. Our main job, though, is addressing customer feedback regarding technical issues. Along with providing solutions we also want to make proposals that lead to better results for customers.” Mr. Suzuki, Development Department Executive Manager, continued, “We have been working for more than three years on developing structures for each module that are compatible with other machines to reduce costs. The most important priority for machine tools is development, and this is something that will always remain true. We felt great responsibility to design products that satisfy customer needs, and we maintain a particular focus on improving machine rigidity.
They also want to develop machine tools capable of processing hardened steels for high-precision parts, and hope that tool manufacturers can develop inserts that support this goal. Mr. Fujisawa, Tools R&D Group, Mitsubishi Materials Corporation strongly said, “The strength of our group is in the manufacture of materials and tools, and we excel at development and manufacture of tools for hardened steels. We will continue responding to customer needs using high-performance tools developed to satisfy an ever wider range of material applications.
The challenges manufacturers face change significantly over time. Mr. Masuda, Star Micronics Sales & Marketing Department Executive Manager said, “It is predicted that the spread of electrical vehicles in the future will reduce the number of automotive parts. However, demand for the small-size precision parts that we manufacture will increase along with the trend of minimisation and the need for precision in final products. Using our position in such a growing industry, we will continue innovating to ensure that our products satisfy customer needs.” Mitsubishi Materials will continue working with Star Micronics as we move into the future to fulfill our mission to contribute to further growth in the medical industry around the world.