The Japanese are famous for concepts like ‘kaizen’ that promote excellence in manufacturing, but the term ‘monozukuri’ is less well known and has no direct translation; the essence of its meaning is ‘the art of continuous improvement in making things through perfection in craftsmanship, backed by technology and processes that integrate development, procurement and production.’

Yoshimaro Hanaki — president and CEO of Okuma Corporation, which is represented in the UK by NCMT Ltd, Thames Ditton (www.ncmt.co.uk) — says achieving such improvement is only possible if the manufacture of premium Japanese machine tools remains in Japan, which is why the company is committed to expanding and improving production at its plants in Oguchi and Kani, near Nagoya. Mr Hanaki made the comment during the recent annual Okuma Machine Fair, held at the company’s Oguchi headquarters in November.

Okuma’s policy of domestic manufacture is in contrast to that of some other large machine tool producers, which build factories in different parts of the world to be near key global markets, the aim being to reduce the cost of transportation and improve competitiveness; as shipping typically adds up to 8% to the cost of a machine tool, the rationale is understandable. However, to maintain top quality, Mr Hanaki believes it is essential to base production of Okuma machines in Japan, despite the strong yen and the high cost of shipping machines thousands of miles. He says the company’s machine-building skills, experience and tradition, which are deeply embedded in its 115-year history, reside in the Aichi and Gifu prefectures and are not reproducible elsewhere.

Multiple FMSs

The latest manifestation of Okuma’s manufacturing philosophy was the opening of a new factory — Dream Site One (DS1) — at the company’s Oguchi complex. Construction was started in August 2012; it involved demolishing an original manufacturing facility and erecting a new building with a 20% larger floor area. The cost was 8 billion yen (£48 million), and the factory entered full production in May 2013.

Driving the investment is the Japanese manufacturer’s desire to introduce lean manufacturing to allow it to compete more effectively with European producers of high-added-value machine tools. It will also help to combat the threat from emerging countries that take advantage of low wages rather than efficiency to compete on price.

The automated facility undertakes the machining of a large variety of components in low volumes on a 24/7 basis, followed by the assembly of medium-to-large multi-tasking machines and lathes. It has doubled productivity and increased production capacity by 30% to 120 units per month, worth 3 billion yen (£18 million). Moreover, lead times have been halved, shortening delivery times. Manufacturing costs have also been reduced, making the company more competitive; this is largely because the high level of unattended machining has allowed the head count in the factory to be reduced by a third.

Mr Hanaki said: “Provided that the world economy continues on its current path of steady recovery, I anticipate that DS2 and DS3 will be started in 2014 and completed within two years. These facilities will be for the assembly of larger and smaller machines. An additional investment of around 12 billion yen will be required to complete our Dream Site initiative in Oguchi, which is designed to streamline production of high-added-value products in Japan and cement
our position at the top of global machine tool manufacture.”

Factory details

The 23,600m2 DS1 site comprises a machine shop incorporating a spindle production area, linked to a just-in-time assembly hall which includes inspection and shipment areas. Both main parts of the factory are temperature-controlled. Compared with traditional factory units, DS1 takes 30% less power from the grid, as electricity is generated by banks of solar panels on the outside walls and roof. Furthermore, LED lighting, wall insulation and other ‘green’ measures contribute further to reducing the carbon footprint.

Four lines of Okuma horizontal machining centres of various sizes, plus washing machines, form the centrepiece of the new machine shop. The production stations in each line are linked to form flexible manufacturing systems (FMSs) using automated multi-level storage and retrieval systems for machine pallets from the Finnish company Fastems.

The largest FMS comprises double-column machining centres and produces cast-iron machine beds and bases; the other FMSs are devoted to headstocks, saddles and columns. There is also a cell (served by robots) for producing spindle components and housings for multi-tasking machines and vertical machining centres, and another cell for producing cylindrical grinder parts. Three Waldrich Coburg twin-head grinders have been imported from Germany and retrofitted with Okuma OSP controls for high-precision machining of slideways, several at a time. Overall, 40 production units are in use at the factory, and most have a high degree of
automation.

Extensive use is made of virtual modelling throughout DS1, from monitoring the order-driven production control system for prioritising work flow to simulating machining cycles for ensuring ‘right first time’ metal-cutting. The whole factory operates on the established, continuous quality improvement model known as PDCA (plan-do-check-act).

Large machines such as double-column machining centres as well as cylindrical and internal grinders are produced in a separate complex nearby at Kani; this has five factory buildings totalling over 105,000m2 and has also seen much improvement over recent years.

Increasing exports

Mr Hanaki says it is Okuma’s aim to increase its exports from the current level of 63% of production to 70% in the next financial year. Europe and the USA are particular targets for growth (they currently consume 28 and 13% of its output respectively), as well as China and emerging markets. Industry sectors expected to support the increase in export sales are aerospace (nearly 30,000 new aircraft worth US$4.4 trillion will be needed globally over the next 20 years), automotive, energy, infrastructure and medical.

Okuma says it is the only single-source CNC machine tool manufacturer in the world: the machines, drives, motors, encoders, spindles and PC-based open-architecture OSP control are all produced in-house to ensure that all elements of a machine are “perfectly complementary and without compromise”.

CNC lathes represent 29% of turnover by value. Machining centres account for 45% and include vertical, horizontal and double-column models. In the latter category, Okuma had nearly half of the domestic market last year. The company is particularly strong in five-axis CNC machining centres, with 10 new models introduced in the past 18 months. Multi-tasking turn-milling machines represent 21% of turnover; the company also produces grinders as well as wheel-manufacturing machinery and other specialised equipment.

Technical developments

Some 2-3% of turnover is invested annually in research and development — an activity that involves 200 people based mainly in Oguchi. The latest advance was the introduction last year of an auto-tuning system for Okuma five-axis vertical and horizontal machining centres and multi-tasking machines.

It replaces the manual tuning process, which can take 5hr or more. The five-axis auto-tuning system performs measurements and compensation in real time and allows adjustments to compensate for geometric errors to be made in just 10min — without a high level of operator skill. The system automatically measures the machine and compensates for up to 13 geometric errors, including volumetric accuracy.

Other initiatives in Okuma’s ‘Intelligent Technology’ suite of performance-enhancing capabilities include its Thermo-friendly Concept, whereby symmetrical machine design and other measures eliminate the need for a temperature-controlled machine tool environment (top accuracy is maintained by restricting dimensional changes to within 8µm over an 8°C temperature variation).

Advanced collision avoidance built into the Okuma OSP control provides real-time monitoring of the entire machining area, including tool, holder, spindle, spindle head, component, fixture, slideways and guarding. Moreover, it does this during an automatic machining cycle, as well as in manual mode.

Meanwhile, ‘Machining Navi’ in the OSP control avoids chatter and consequent inaccuracies by choosing the optimal spindle speed. If chatter is detected (by a factory-fitted sensor or retrofittable microphone) in a machining centre, the frequency is analysed and settings to eradicate it are displayed. They are applied either automatically or manually by the operator. Okuma says suppressing chatter for lathes requires a different approach, especially when turning at lower speeds; its preferred method is automatic spindle speed variation within pre-set limits.