LMT Tools

Radial cutters: With great commitment to success

| Author / Editor: Mark Flommer / Rosemarie Stahl

LMT offers different variants of radial cutters, including cutters with a lens profile.
LMT offers different variants of radial cutters, including cutters with a lens profile. (Source: LMT Tools)

The more a cutting edge is tangentially engaged during milling, the faster the machining. LMT Tools has found a solution for radial cutters that ensures significantly shorter throughput times and better surface quality. What exactly is behind the increase in performance and where are radial cutters used?

Tool, machine and CNC program: The interplay of these three basic factors determines how quickly and precisely a milling process takes place on a freeform surface. In industries such as die and mould-making or the aerospace industry, there are high requirements, because, on the one hand, only minimal machining tolerances are accepted on the complex components, and, on the other hand, cost pressure is increasing massively. Significantly faster and more effective milling processes are a permanent objective of production planners - and the basic requirements for this are better than ever. Even the most demanding machining strategies for a 5-axis machine can be created safely and quickly with modern CAD-CAM systems. These possibilities are taken advantage of by the radial milling system: The tools have a special cutting profile with large radii and drive over the component with precisely programmed movements tangentially to the freeform surface. The decisive factor is that the radial tool engagement on the component is very high. A much larger proportion of the cutting edge is used. And that means: Per run, the possible line spacings are much higher, and thus the number of tool paths required overall also decreases while the surface quality remains the same.

There are four basic tool forms. They are individually adapted to geometric challenges such as deep cavities, steep walls or vaults.
There are four basic tool forms. They are individually adapted to geometric challenges such as deep cavities, steep walls or vaults. (Source: LMT Tools)

How this approach makes such enormous performance increases possible only becomes apparent when comparing the milling process using conventional ball nose copy cutters. With these tools, many contours can be produced. However, there is a decisive disadvantage right from the start: Only a small part of the tool cutting edge is used. To be able to produce a smooth surface with appropriate quality, significantly more tool paths (each with smaller line spacing) are required, which of course leads to longer machining times. There are also higher axial forces, and thus more vibrations occur - for example, in the case of more unstable components, under which the surface quality of the surface to be machined suffers. Conversely, these vibrations are significantly reduced when using radial cutters. Even components with a small wall thickness, such as those found in aircraft turbine construction, can therefore be manufactured with high process reliability. In addition, the cutting edges are loaded very evenly during the process and lower forces are thus exerted on the tool. The tool life thus increases.

Incidentally, users benefit from the high machining quality of the radial cutters. The microscopic view of the finished surfaces makes it clear: As when milling with ball cutters, a wave-shaped workpiece surface is also produced during radial milling. The theoretical surface roughness (Rth) results from the respective line spacing (br). When using radial cutters, however, the line spacing is greater – the longer cutting edge in the "complete insert" makes it possible. Therefore, the resulting theoretical surface roughness is also lower. It creates smoother surfaces that are only polished briefly or not at all.

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With regard to precision and efficiency, it is also important that different tool variants are available for radial milling. These "basic forms" are individually adapted to the geometrical details of the component with their radii, angles and diameters as well as the cutting lengths:

  • The drip profile tool has a peripheral cutting edge with uniform radius and is suitable for the milling of lateral contours in deeper cavities or less accessible areas.
  • The barrel profile also has a uniform radius along the peripheral cutting edge and a neck clearance. When machining lateral contours and undercuts, this geometry plays out its strengths.
  • The conical form is available in two variants (Form A and B). Both have several radii merging into one another. Form A is used when milling steep walls with an attack angle of more than 45 degrees. Form B, in turn, is suitable for the finishing of pocket bottoms as well as flat surfaces.
  • In the case of lens profile tools, the milling process is performed with a convexly shaped axial surface – the peripheral cutting edge is thus, for once, not responsible for the milling process. The tool is suitable for the machining of curved flanks.

 A whole range of current applications shows the possibilities of these accurately fitting tools. A good example is the machining of a new type of turbine blade. The component made of the material TiAl6V4 is only 1.5 millimetres thin and fragile. Nevertheless, it has to undergo a total of three milling processes with maximum process reliability: roughing, semi-finishing and finishing.

Additional Information
 
Three arguments for radial milling:

During finishing, for example, the radial cutter requires only about 20 percent of the machining time of a ball nose copy cutter.
During finishing, for example, the radial cutter requires only about 20 percent of the machining time of a ball nose copy cutter. (Source: LMT Tools)

Originally, the user relied on a ball nose copy cutter for machining, including the aforementioned (excessively) strong vibrations. This had a negative effect on the surface quality, the cycle time and the tool life. Alternatively to this, LMT Tools developed three different radial cutters with a conical profile and different effective radii. The effective cutting lengths were 25, 50 and 75 millimeters – ultimately the basis for a significantly higher material removal. With the radial milling cutters, significantly less vibrations occur on a thin-walled and sensitive component.

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Radial milling cutters are used in aerospace, power engineering, die and mould-making and in general mechanical engineering. The establishment of the overall process takes place individually: LMT Tools designs and produces accurately fitting tools for the individual machining task. A new tool will be available in a few weeks. In addition, LMT Tools has a standard range of high-performance radial cutters that are available ex-stock. When programming the CAM system, LMT specialists also support the users and provide their process knowledge of components, geometric details and materials.

With radial cutters, the effective radius (reff) and the line spacing (br) are larger resulting in smoother surfaces (lower surface roughness, Rth).
With radial cutters, the effective radius (reff) and the line spacing (br) are larger resulting in smoother surfaces (lower surface roughness, Rth). (Source: LMT Tools)

All in all, radial milling fits in perfectly with LMT's guiding principle, “Exactly Yours”: The company focuses its expertise on selected technology niches and applications to give its customer a competitive advantage. Radial milling more than lives up to this claim. Currently, the importance of this process is growing, which makes full use of the possibilities offered by 5-axis machines. Its fast and stable processes, high surface quality and long tool life are an ideal basis for significantly reducing the cost of time-consuming freeform milling processes.

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