By Christian Hillary, managing director, Global Machine Tools Limited
Global Machine Tools Limited, the exclusive distributor of Doosan machine tools in NZ, has announced the launch of a new series of Doosan linear guideway (NHP) and box guideway (NHM) horizontal machining centres.
Doosan is one of the world’s leading and largest machine tool builders and suppliers. These new products represent an important step-change in horizontal machine tool design and construction, and demonstrate that a combined linear/box guideway technology platform, a global first incidentally, delivers improved performance for both types of machines.
Up to the early 1990s box guideways were the preferred route and the technology of choice for horizontal machine tool manufacturers and their customers. During the last 20 years or so, this situation has changed with machines equipped with linear guideways, making their mark and becoming more popular.
Linear guideways are bolted to the machines cast base and are then adjusted, as opposed to being machined, meaning that a single-piece base casting can be used. Box guideway horizontal machines by comparison have a two-piece base casting because it is not possible to grind box guideways 90° to each other.
In a traditional box guideway machine, the column moves in Z (towards and away from the front of the machine), with the spindle mounted on it moving in Y (vertically), while the pallet moves side to side (X).
The machines offer higher levels of rigidity than their linear guideway counterparts but they do have their limitations – slower axis movements, slower pallet and tool-change times, less effective chip control and removal (swarf has to come out the side of the machine). Additionally, there is relatively poor operator visibility, as the column moves past the operator, obscuring his view.
With the single-piece, base casting linear guideway design, the column moves in X, the spindle mounted on it moves in Y, and the pallet now moves in Z (the pallet rotates in B as before).
The benefits linear guideway machines have over the box guideway versions include faster tool and pallet change, improved chip control (due to splashguard designs), improved swarf handling as it can now be taken out the rear of the machine, plus improved operator visibility.
Linear guideway machines have many positive attributes but do not provide the same rigidity of box guideway machines. As a result linear guideway machines tend to be (and are perceived as being) light duty, high speed machines. For many years, through the 1990s and into the new millennium, the two designs existed side by side, with the box guideway machines being typically equipped with 50 Taper spindles and the linear guideway machines in many cases utilizing a 40 Taper spindle.
However, with the advent of the roller type linear guideway, rigidity is greatly improved and the demand for box guideway designs fell away. Many machine tool builders ceased or scaled back production of the box guideway machines below 800mm pallet size. Doosan on the other hand firmly believe that even with the linear technology improving, certain applications still are best suited to box guideway machines and continued to develop designs from the 500mm pallet size and upwards, and became a niche market builder.
Doosan has now developed a series of horizontal machining centres that sees an improved box guideway design – which has not seen fundamental design change for 30 years – alongside a linear guideway series, with a drive for common parts applied to help reduce costs as well as benefitting production efficiency and delivery times.
Global Machine Tools congratulates Masport Foundries on the purchase of the first NHP6300 to be installed in NZ. It is also looking forward to the arrival of the first NHM5000 including Doosan’s newly designed seven-pallet Multi Pallet System for another North Island customer due to arrive at the end of April 2013.