Based in Tianjin, China, Tianjin Betek Machinery Manufacturing Co Ltd (Betek) specialises in the production and processing of mechanical parts for industrial applications. The company’s experience of using machine tools in its manufacturing operations, combined with market research, highlighted significant opportunities in the domestic gear production market.
China has a growing need for CNC gear-cutting machines that combine precision, high processing efficiency and ease of use to replace inefficient mechanical machines. In 2013, Betek decided to diversify into the production of gear-cutting machines and invested some 80 million yuan (about $13 million) in a 25,000m2 purpose-built manufacturing plant and offices. The company’s latest CNC machine tool, the six-axis YK3132Z gear hobber, is now available — less than two years after the start of development.
At the beginning of the project, Betek looked at CNC systems from a number of manufacturers, but it quickly decided to base the machine on NUM’s Flexium+ CNC platform (
www.num.com). Mr Jin Guolin, Betek’s president and general manager said: “Our main reason for choosing a NUM CNC system for our new gear hobber is that, unlike many competitive control products on the market, it has an open architecture. This places no restrictions on our development and customisation work, helping us to reduce costs and shorten time-to-market significantly. We intend standardising on NUM CNC for future machines whenever possible; we are currently developing a new gear grinder that will also be based on NUM’s CNC technology.”
Another factor behind Betek’s choice of CNC supplier was NUM’s extensive experience in gear production applications. The company’s CNC gear-hobbing solutions, based on its NUMgear software, are used by many leading manufacturers of gear production machines. The proximity of a NUM facility in nearby Beijing was also a consideration, allowing Betek to benefit from local applications support and technical service.
Betek’s new YK3132Z six-axis gear-hobbing machine is based entirely on NUM CNC equipment. It uses the latest Flexium+ CNC kernel and high-end NUMDrive X servo drives in conjunction with compact BHX and SHX servomotors; high-resolution encoders and closed-loop control maximise accuracy of both speed and position. The turret spindle motor and the table (C axis) torque motor are direct-drive units that are also controlled by a NUMDrive X servo drive; these motors eliminate the need for mechanical power transmission components, such as worm and helical bevel gears, and provide precise backlash-free movement. The turret spindle offers speeds up to 1,200rev/min, while the table can rotate at up to 280rev/min; this allows use of the latest high-speed cutting tools.
The NUMgear suite of gear production software supplied with Betek’s machines includes dedicated hobbing functions and a precision ‘electronic gearbox’ that allows all master axes and the turret spindle to be fully synchronised. This electronic gearbox minimises synchronisation time by predicting the acceleration rate as well as the speed of the axes. Operator interaction with the machine is via a NUM FS152i panel with a custom HMI. The panel features a 15in LCD screen with 22 large function keys and an industrial PC. The HMI makes extensive use of graphics and has been designed to allow users to operate the machine after just a few hours of training. Gear manufacturing data can either be input using a simple ‘fill in the blanks’ method or derived from previously processed parts. Database management capabilities are also provided. The custom HMI software was developed specifically for Betek’s machine by Changzhou Mactool Precision Machine Tools Co Ltd, which specialises in the design of gear cutting machines and user interface software.
The six-axis YK3132Z gear hobber accommodates gear blanks up to 320mm in diameter; and with the CNC system’s ability to undertake five-axis interpolation, complex gear tooth profiles can be created smoothly and efficiently. The entire gear is cut as part of a single process, without interim removal/re-insertion of the gear blank or manual tool changeover. Moreover, virtually any type of gear can be cut, including unusual types such as parallel shaft, herringbone, taper and non-circular gears.
The company that is now Muffett Gears was established in 1920 and went through various stages of development before specialising in the manufacture of precision gears. Since 1950, gear design and production has been the core competency of the Tunbridge Wells-based company, which is now in its third generation as a family-owned business.
Muffett Gears (
www.muffettgears.co.uk), which is ISO 9001 and aerospace BS EN 9100 compliant and accredited,
designs and manufactures gears and gearboxes. The company also produces prototypes and undertakes first-batch production for customers — plus it offers a range of standard products, including spur, helical, bevel, racks, worm and worm-wheels, internal gears and moulded gears. Batch quantities for these range from single items to 1,000 off.
With a customer base that covers aerospace, medical, mining, defence and construction, Muffett Gears is called upon to manufacture gears of all shapes and sizes, from minute gears that are used in artificial hands through to large gear shafts for industrial pump systems. Other projects have included manufacturing components for medical scanners and camera mounts, as well as supplying gearboxes for the latest commercial aircraft. To achieve the 5µm accuracies that some of its work requires, Muffett Gears has an extensive range of gear-cutting machines, allowing it to produce any gear form. It also has a range of ‘more conventional’ machine tools, one of the more recent being a Perfect PFG-D4080AH surface grinder from Erith-based
RK International Machine Tools Ltd (
www.rk-int.com). This numerically controlled (NC) grinder was bought to replace an ageing manual grinder, with one specific component in mind — spur gear filler plates used in an oncology radio-therapy machine. The old machine was becoming inconsistent and required constant manual intervention to maintain size, which was adversely affecting productivity.
Muffett Gears’ works engineer Alan Kennard said that, having researched the market, the Perfect PFG-D4080AH stood out for its simplicity of operation and value for money. “Many of the surface grinders that we looked at were over-specified for what we wanted, which in turn meant that they were more expensive. Our requirement was pretty straightforward: we needed a grinder that would be consistent and accurate, without all the bells and whistles, but would give us some level of automation, while at the same time allowing manual operation
for when we needed to use it as a tool-room grinder.”
Another benefit offered by this Perfect grinder is its table size, which at 400 x 800mm allows three components to be ground in a single set-up, as opposed to two on the old machine. This gives a 40-50% improvement in productivity, with around a 90% reduction in input from the operator.
Shift supervisor Rob Hudson adds: “We had no previous experience of NC surface grinding, but setting the Perfect machine couldn’t be simpler. We simply touch down on the work, dial in the amount of material to be removed and set the number of passes. We tend to use 50µm roughing passes with a 25µm finishing pass. After that, it is a case of pushing the button and waiting for the cycle to finish. The machine grinds to size every time, and we have never had a scrap part from it. Compared to the old machine, we have total control of sizing. If we want to remove another 5µm, we simply dial it in, and the machine will remove exactly 5µm.”
The consistency and accuracy of the Perfect PFG-D4080AH are attributable to its construction: the column and base are manufactured from high-quality castings, the slideways are coated with Turcite B to ensure smooth movement and long-term accuracy, and the cartridge-type spindle is assembled using class P4 precision angular contact bearings (these give a run-out accuracy of less than 2µm). The grinder also has a distance of 550mm between the wheel and table surface (650mm is available as an option). The wheel itself is 405 x 50 x 127mm.