Flexible production capacity

Hoffmann Group
Hoffmann Group

In this article, Michael Knauer, director of milling at the Hoffmann Group discusses how production methods such as Parabolic Performance Cutting (PPC) can help toolmakers to maintain production capacity and effectively scale up their operations again post Covid-19.

With the right tools and state-of-the-art CAM software, toolmakers and mould makers can keep their production capacity flexible, and will be able to ramp it up by up to 85% once the economy picks up again.

Toolmakers and mould makers are amongst the companies keeping a firm handle on the impact of the coronavirus pandemic. Many businesses are asking themselves how they can weather the storm unscathed as far as possible and adapt their capacity quickly once the market improves.

This has placed the spotlight on production methods such as ‘circle-segment milling’, also known as Parabolic Performance Cutting (PPC) or barrel milling. PPC tools enable the finishing work for a tool mould to be completed up to nine times faster or, alternatively, the surface quality to be improved up to 80-fold.

For example, Koller Formenbau GmbH from Dietfurt in the Altmühl valley has used PPC milling cutters supplied by the Hoffmann Group to reduce the finish machining time for geometrically defined surfaces from 100 hours to 15 hours. The PPC method is also ideally suited to finish machining work on 3D-printed parts.

Reasonable expense


On PPC tools, the main cutting edge on the milling cutters is curved. Compared against a classic ball-nosed slot drill where the effective radius is half the tool diameter, PPC tools have a much larger effective radius – up to 1,000mm – thus permitting a significantly larger engagement length on the workpiece. However, their more complex geometry means they place higher demands on the CAM software.

The software not only needs to offer the circle-segment milling strategy, it must also have a tooling database which holds the exact geometries of the PPC tools. What’s more, since the tools are aligned obliquely to the workpiece, the method can only be employed in conjunction with a 5-axis milling machine.

Not all five axes need to be in use here. Often, once the tool has been set-up, the draft angles can also be finished with one to two axes clamped. It may also be possible for flat faces and freely accessible surfaces with no interfering contours to be machined on a 3-axis machine.

In the past there were only a few software programs that offered the circle-segment milling functionality, however, that is no longer the case. Koller Formenbau for instance, already used a 5-axis machine and HyperMILL software from Open Mind, so they only needed the right tool. The company was able to boost productivity by up to 85 percent cost-effectively, thereby increasing its capacity without having to procure a new machine.

Tool diversity increases productivity


Parabolic Performance Cutting (PPC) is particularly effective when the tool profile fits the workpiece contour precisely. To maximise the productivity gains, different types of main cutting edge are required such as straight, tangential, conical and stub conical, as each of these shapes are specifically designed to machine certain surfaces.

Another factor to consider is the tool’s approach angle to the workpiece. A steeper approach angle, for example, makes it easier to avoid interfering contours. Moreover, some manufacturers like the Hoffmann Group also offer precision copy milling cutters with PPC indexable inserts.

In certain cases, they may be a viable alternative to solid carbide milling cutters. As a result, when selecting PPC tools it is important to consider whether the supplier is able to offer the corresponding range of products. You also need to factor in all the different materials that need to be machined.

By making a moderate investment in software and tooling, companies can use CAM-controlled circle-segment milling to increase flexibility when scaling up their production capacity and respond to changing market conditions.

Hoffmann UK www.hoffmann-group.com/GB/en/houk/

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