The Mother Machine: The Machine that Creates Machines

Yasuhiro Kakinuma (Associate Professor, Department of System Design Engineering)

1. Foundational Technology Supporting Japanese Manufacturing: The Ultimate Machines in Pursuit of Precision and Efficiency

Dear readers, are you familiar with machine tools? The machines that have quietly supported Japan's proud manufacturing—from automobiles and aircraft to cameras, watches, and even the smartphones you are holding right now—are machine tools. As the name suggests, machine tools are "machines for crafting," capable of automatically cutting metal into any shape, bending it, drilling holes in electronic circuit boards, or polishing surfaces to a mirror-like shine. Because they are machines that create things, they are called "mother machines."

Here, let's consider the precision of the mother machine itself and the machine parts created by it. In the case of humans, a child can sometimes surpass their parents' abilities and become more accomplished. However, this is not the case with machines. Since parts cannot be machined with greater precision than the mother machine, the resulting machine parts will never exceed the precision of the mother machine. This is called the "Coping Principle" (Figure 1). In other words, without superior mother machines, superior products cannot be created.

Japan's machine tool technology is world-class, and the country has brought to market mother machines that achieve extremely high machining precision and efficiency. As evidence of this, Japan's machine tool production value held the top spot in the world for over 20 years. (*Although China has surpassed Japan in production value since 2009, Japan and Germany still lead in terms of technological capability.) It is no exaggeration to say that Japan's manufacturing industry has achieved dramatic growth, supported by these superior mother machines. If this technology had not been world-class, the growth of Japan's manufacturing sector, including its automotive industry, would have been impossible. Maintaining foundational technologies, including machine tool technology, at a world-class level is nothing less than creating the foundation for new industries in Japan's future.

2. Why Machine Tools Are So Precise

Machine tools can be seen as robots for manufacturing, but let's compare their performance with that of industrial robots. While the positioning accuracy of industrial robots is limited to the order of ten micrometers due to their structure, machine tools can achieve sub-micrometer positioning. This is because the ball screws used in the drive systems of machine tools are designed to prevent lost motion (a momentary stop when motion reverses, which is an issue related to motion accuracy), and they employ feedback control (fully closed-loop control) that measures both the position of the drive stage and the motor's rotation (Figure 2). Furthermore, when efficiently cutting or polishing metal, very large forces are applied to the machine tool, causing the machine to deform. To minimize this, high rigidity and damping are achieved through the optimal design of mechanical structures like ribs and the use of high-damping cast iron for the frame (*which are actually called columns and beds). In addition to this, thermal and vibration design make it possible to machine parts with an accuracy of a few micrometers. State-of-the-art machine tools are truly a crystallization of technologies combining manufacturing science, mechanical engineering, and control engineering. As someone who studied in the Department of System Design Engineering, this is a supremely fascinating field of research.

Today, thanks to non-contact drive technologies like linear motors and hydrostatic guideways, machine tools can now achieve nano-precision manufacturing (machine tools capable of nano-precision machining are called ultra-precision machines). A familiar example that demonstrates the dramatic improvement in machining precision is plastic models. When I was in elementary school, building a plastic model required nippers, a file, glue, and putty. When you removed the parts by hand, they would have burrs, so you had to cut them off with nippers and then file the cut areas to clean them up. Next, you would glue the parts together, but gaps would form between them, which had to be filled with putty. What about today's plastic models? Even when you snap the parts off by hand, there are almost no burrs. You don't need glue to assemble the parts, and there are no visible gaps between them. Here, we can see the dramatic progress of machine tools. Plastic models are made by pouring molten resin into a "mold" and letting it cool and solidify. In other words, the precision of the plastic model is determined by this mold. This mold is made by machining, and its precision is vastly different today compared to the past.

3. The Evolution of Mother Machines and the Goal of Becoming Global Number One

Machine tools, which have long pursued precision and efficiency, are now on the verge of further evolution. One of these trends is "intelligentization." The development of technology is underway that allows the machine tool itself to assess the machining status and perform stable machining accordingly (e.g., avoiding vibrations and collisions, and performing appropriate tool changes). This concept has existed for a long time, of course, but recent advances in MEMS technology, measurement technology, sensor technology, and control technology have made practical application possible. Another contributing factor is the analysis of vibration phenomena based on theoretical models of the machining process and the systematization of theories to suppress it.

In addition to theory, the intelligentization of machine tools also requires on-site experience in design and development, the intuition of engineers, and information from the user side. To further advance the world-leading technology that Japan has cultivated and to aim for "Global Number One" machine tool technology that leaves other countries behind, I feel that a serious collaboration leveraging the respective strengths of industry and academia is needed right now. And surely, the systematization of a new academic discipline that includes tacit knowledge from the factory floor will be required.

I would be delighted if reading this has sparked even a little interest in understanding the importance of foundational technologies, including machine tool technology, as a source of national strength, and in developing and elevating this technology to be the best in the world.