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VERICUT ensures production can change up a gear

Recent developments in CNC control technology, tooling and CNC simulation software VERICUT have enabled multi-tasking mill-turn machine tools to run complex gear hobbing operations. This method of producing gears on standard CNC mill-turn machines provides precision engineering companies with increased operational flexibility.

Prior to these developments the production of high quality precision gears was the preserve of dedicated hobbing machines. However, it is difficult to justify the purchase of these machines if production quantities are too low. Hobbing machines are also limited on the size of gear that can be produced, so multiple hobbers may be required to accommodate various demands. Fortunately, CNC multi-tasking lathes can be used for much more than turning.

As well as negating the need for a dedicated gear shaping machine, there are a number of advantages when hobbing on a mill-turn lathe. A CNC lathe is a more economical investment and it has the potential to machine the part to completion in one setup. Machining of complex gears is possible and the hob function is straightforward to set-up.

With the machine tool platform available compact hobs with indexable inserts have been developed by tooling specialists such as Ingersoll Cutting Tools (part of the IMC Group) and Sandvik. The hobs are engineered to work in the restricted envelope of a mill-turn machine.

As well as supporting the application of gear hobbing on mill-turning centres, VERICUT NC simulation software has been used in the IMC Group for a number of years. The software achieves interactive simulation of multi axis milling, drilling, turning and rotary milling; focusing on both precision production as well as the dynamics of the product development process. A fact that Ingersoll itself appreciates in the manufacture of standard and special tools. At nearly 20 IMC locations around the globe VERICUT has been in use, for decades in some instances.

At its facility in Haiger, Germany, Ingersoll designs, develops and produces a wide range of special tools such as single and multiple gear hobs of different designs and sizes for the gear cutting industry. Batches are typically high complexity and high variety, with batches of one to five bodies being the norm, because almost every hob is a new development tailored to suit the application and machine’s spindle coupling. This is one of many core competencies that is being applied to bridge from CAM to production.

Ingersoll’s range of hobs with full profile inserts offer a number of improvements over solid steel hobs: higher cutting speeds, a significantly longer service life and predictable cutter life. Consisting of a base body with milled spirals, the tool can be equipped with a relatively high number of efficient single-edged inserts. If a single cutting edge needs replacing, substitution is quick and easy as only the insert is changed, not the complete hob. This means significantly better flexibility for its customers.

The stated aim when IMC Group originally introduced VERICUT in 1996 was a ‘safe cutting process and simulation of machine tool movements’, where in addition to the machine simulation of complex machining programs the collision checking of the 5-axis machining centres was, and remains, at the forefront.

Virtually all manufacturing programs at Ingersoll run through the VERICUT simulation of material removal, with verification and analysis. From the outset, the checking of NC programs for multi shift production with the VERICUT module Auto-Diff proved particularly effective. Here, the system checks the accuracy of the part to be machined in synchronisation with the CAD model generated. If the tool comes into contact with the CAD model, taking into account the user-defined tolerance, the collision is documented and displayed graphically. Any volumes of raw material that were not machined are also recorded graphically, so that any missed machining operations are detected. Productivity increases in the double-digit percentage range are generated not least by the VERICUT module OptiPath at Ingersoll. Depending on the actual geometry, OptiPath automatically optimises feed and speed and takes into account both the exit and entrance cutting conditions.

Customers get it ‘done-in-one’

Until now specialist gear cutting companies have often invested in a minimum set of three solid steel hobs: one in production; another in preparation, and a third being reground. An additional benefit of using an indexable hob is that a change of raw material only requires a new set of inserts of the required grade.

Another measureable benefit for customers of the new hob cutters is the ‘done in one’ workflow philosophy. Gear machining on a conventional 5-axis or multi-axis mill-turn machine tool means that precision contract manufacturers do not have to invest in a new machine or outsource gear cutting to a specialist, which up to now has mostly been the case: the cost of procuring a special gear cutting machines not being a realistic option in the face of limited volumes.

Even complex parts such as planetary gears can now be machined on CNC machining centres, particularly as turning and milling can be done first, followed by the gear teeth being cut on the same machine. Using multi-task machines and machining centres in this way significantly reduces processing time, work-in-progress and also negates any accumulated errors moving components between different machines.

Simulation by VERICUT in version 7.4 is the indispensable ‘back-up’ for any new processing options. The market leading CNC simulation software from CGTech is the industry standard in 55 countries. It ensures reliability and increased efficiency of machining by checking the corresponding NC program for errors offline, such as collisions between the machine tool, fixture and workpiece, before the real machine run. NC simulation becomes essential as industry trends towards smaller batch sizes and rising order numbers. In the specialist area of gear production experience has shown that programming involves a considerable amount of time and effort. Safe machining with no defects and avoiding machine crashes with incalculable consequential costs are key challenges to production.

“We always make every effort,” says CGTech Managing Director, John Reed, “to align our simulation solution to the cutting edge of industry. To promptly reflect new developments in the machines and tooling areas, such as these recent gear hob cutter innovations. While an Ingersoll hob with inserts costs significantly less than a dedicated hobbing machine it is still several thousand Euros, VERICUT removes the risk of damaging it and the machine tool.”