The Okuma Double Column Machining Centre (DCMC) range of CNC machines has without doubt earned the tag of ‘benchmark’, underpinned by a long-time cultural ethic at Okuma for continuous improvement. Since 1966, Okuma DCMCs have been outclassing rival machines around the world, achieving phenomenal success in the field with thousands of DCMCs in operation today that bear the Okuma name.
In October 1981, the first Okuma DCMC for the Australian and New Zealand markets was completed and installed. That first machine, an MCV-A model delivered to a customer in Christchurch, New Zealand 37 years ago, is still in active use to this day.
Okuma DCMCs are defined by their basic construction. Often referred to as bridge construction, Okuma prefers the DCMC description. The machines have fixed columns either side of a table that moves underneath an elevating cross rail (W Axis). The table is connected to the two columns, along which the Y-axis/main-spindle headstock travels. This is actually similar to the MB-V/Genos M Vertical Machining Centre (VMC) range, another market-leading product line for Okuma.
The key for the DCMC is its five-face machining ability using a choice of angular, extended or high-speed attachments. For example, an NC B and C-axis tilting, rotating head attachment along with three other chosen vertical or angular attachments can be stored, all of which are automatically exchanged using an automatic attachment changer (AAC) by program command. All can accept cutting tool holders that are also automatically exchanged with an automatic tool changer (ATC), irrespective of the attachment selected. It’s not uncommon to add a fourth-axis CNC rotary table arrangement and even two pallets.
Okuma’s DCMCs are, by design and quality, machines that stand the test of time in longevity and that remains critical when analytical investigations into specifications, prices and delivery are a key focus. According to Okuma, there are four key factors that always surface in discussions about the DCMC with potential customers: high levels of accuracy; reliability; usability; and ongoing support, not just from the local distributor, but from the manufacturer.
Accuracy
Okuma has now been producing DCMCs since 1966, when the MDB model was released. In a classic case of “if it ain’t broke, don’t fix it” the Double Column concept has stood the test of time, with real improvements coming from modernised casting techniques, more efficient machining of components, materials used, and – perhaps above all else – ever-improving electrical and electronic components and software developments.
The slideways of a DCMC cannot just be machined. They must be ground. Massive investment is made in Waldrich Coburg grinders that can and must be able to grind the full length of the individual large components, such as slideways, columns and beds, to within single-digit microns for flatness and straightness. These are the parts that guide the moving table, cross rail and the headstock, and upon which the whole aspect of squareness and overall accuracy depends.
As for the vertical axes, there are two. The elevating cross-rail W-axis can be continuously CNC-controlled or preset with high accuracy at any one of ten positions. Attached to the elevating rail is the Y axis saddle, to which the second vertical movement axis, the Z-axis is attached. It is of square ram-type construction and supported by proper slideways for superior rigidity.
Okuma’s unique combination slide/roller guideway system on all main axes allows spritely axis feeds without significant thermal change. The thermal stability of the whole machine itself is controlled these days by Okuma’s Thermo Friendly Technology, which in simple terms is a negative of the thermal map developed under machining conditions of every machine individually. This global award-winning technology has revolutionised the control of part repeatability over long machining times and integrates ambient temperature changes as well.
Every Okuma DCMC is built to order. There is no stock specification. Every Okuma DCMC is manufactured and assembled completely as per the customer’s specification at Okuma’s factory, in the giant Kani 5 DCMC assembly hall where around 35 of the machines can be assembled simultaneously. The machine is then vigorously tested to ensure compliance with Okuma’s stringent accuracy standards, in most cases with the customer present as a witness. The machine is then disassembled for packing and shipping. Typical accuracies for an average MCR BIII 30 x 65 DCMC (with 3.0m between columns and 6.5m of table length)are as follows:
- Parallelism: Better than 0.03mm – usually 0.02mm.
- Straightness: Better than 0.02mm/ metre – usually 0.10mm/metre.
- Squareness: Better than 0.03mm/500mm – usually 0.015mm/500mm.
- Bidirectional repeatability: X axis, Y axis, Z axis and W axis: All <0.010mm
Despite these figures, accuracies can be a dynamic matter and are often best achieved in the set-up and levelling process at installation time, and they will vary from machine to machine. The point is Okuma consistently produces large machines with impressive performance outcomes, upon which the company’s global benchmark status in DCMC manufacture is founded.
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Reliability
Okuma holds a prominent position in the market for reliability. This stems from its longstanding internal culture of continuous improvement, enshrined in its values since 1898. A young Eichi Okuma explained to his staff 120 years ago that: “Trust is important. To obtain trust, you must satisfy the customer.”
This was not just about selling machine tools. It was about trust: in the machine for reliability and accuracy, in the manufacturer, in the supplier, in the support chain including spares and service, in the management of the supplier.
Where the most trust is created is in the simple fact that Okuma makes the lot – machine and control – and is the sole source for support. In addition, Okuma aims at lifetime support for parts, which in the case of DCMCs, are rarely needed. It’s a key reason why, for example, the New Zealand MCV-A has earnt its place in that shop, with the investment paid off financially many times over during its 37-year life so far. This support-based trust doesn’t come automatically. It’s evolutionary and Okuma’s 120 years of experience is crucial to how reliably and effectively any glitch will be corrected. The DCMC build program by Okuma has been active for more than 50 years and the documented experiences inside Okuma provides a massive platform for experienced troubleshooting.
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Usability
The same Okuma OSP controller, language and architecture that is used on Okuma’s MB-V vertical machining centre (VMC) for small tool rooms is used on the massive MCR-C 35 x 120 DCMC. All DCMCs offer straight ISO or Okuma’s own conversational formats. So there is a consistency of operation criteria that will allow an operator to confidently switch between large and small Okuma machines.
These days, however, there are several more application-based options that are designed to provide more user-driven outcomes. Machining Navi will seek the optimum machining conditions of speed and feed rate, while Servo Navi AI offers intuitive acceleration and deceleration variability against the mass of the part. In addition there are all manner of gauging options, laser surface hardening and metal deposition, machine condition analytical monitoring, Super NURBS, physical dimension compensations, Servo Vibration Auto Adjustment, Collision Avoidance Systems, power-conscious ECO options for idling stop and monitoring, not to mention Inductosyn scale feedback, NC-W and NC Rotary table axes, and a wide array of attachment heads.
For an investment that is generally large, there needs to be a comprehensive set of features that assist the perfect outcome of what can often be a one-off job that simply has to be right first time.
Support
Of the 40-plus DCMCs that have been installed in Australia over the years, some are old. The average age of the machines in the Australian market is 21 years. Every single one is operating today.
Owners can look forward to remarkable reliability in a sturdy machine with a second-to-none support program that involves local applications, and mechanical service and electrical service employees who are well experienced on all models because all Okuma DCMCs follow a generally common design criteria. In addition, for every DCMC installation, Okuma factory engineers will attend to take charge of the complete assembly and commissioning process.
Okuma Double Column Machining Centres are a major part of the Okuma machine range that includes vertical and horizontal-spindle CNC lathes, vertical and horizontal-spindle machining centres, multifunction turning centres and five-axis machining centres, cylindrical and internal grinding machines, robotic handling equipment, and the full scope of the OSP Control including motors, drives, encoders and software.