CFRP machining optimised

The aerospace industry is reluctant to change functioning processes that have already been audited due to the large effort involved. However, growing cost pressures are also forcing this sector to make its production as efficient as possible. Aircraft manufacturers have so far identified the clamping technology as an obstacle on the path to higher performance. Large carbon-fibre parts are usually fixed using vacuum clamping technology. The limited holding forces of the suction cups require relatively low cutting speeds in order to prevent rising vibration. This can lead to a loss of quality and deviations in shape and position tolerances.

New clamping technologies now enable manufacturers to increase the cutting values. But with this came a new problem: under the changed process conditions, there was an increased risk of breakage due to the increased load on milling cutters that had previously worked perfectly. “Even very large manufacturers were affected by tool breakages after using the tools to their limits”, explains Tim Rohmer, Product Manager for solid carbide milling tools at MAPAL. The tool manufacturer saw a need to act and developed the OptiMill-Composite-Speed-Plus as a response to market demands.

The requirements for the groove profile also differ from the machining of metal, where feed, infeed depth and cutting width influence the chip thickness. Since the rake angle for CFRP is only slightly engaged due to a low feed per tooth, MAPAL has designed the cutting wedge for maximum stability.

The new OptiMill-Composite-Speed-Plus also has an optimised envelope contour to reduce leverage forces and thus for increased fracture resistance. It works well in practice, as Rohmer explains: “Typical parts for aviation consist of stacks, i.e. composite panels, with five to 15 mm usually being machined. Shorter tools are perfectly adequate for this.” While the predecessor tools were still longer than specified in DIN6527, the new tool series largely complies with the standard. MAPAL provides the tools with diameters of 4 to 20 mm.

The OptiMill-Composite-Speed-Plus also ensures high tool lives for machining abrasive carbon fibres with an innovative diamond coating. The uniform layer thickness distribution and the high repeatability with which MAPAL applies the diamond in the CVD process are exceptional. Conventional coating technologies often produce irregular layers that are thicker at the tip than further down on the cutting edge. This process ensures different edge rounding and thus fluctuating cutting pressure and wear and tear.

The homogeneous layer thickness over the cutting edge length contributes to process reliability. This enables consistent performance regardless of which part of the cutting edge is involved. This means that the tools can also be used for circumferential machining of a stack, regardless of height: users sometimes use the milling cutter until the end of wear and tear, then readjust it and continue working with a fresh part of the cutting edge. The shoulder milling cutter is suitable for a wide range of applications. In addition to circumferential machining, it is also used to produce slots, edges and pockets.

CFRP加工の一つの側面は、ワークピースによって加工品質が異なることです。ユーザーは、既存の複合材料に応じて、部品にどのような加工品質が要求されるかを判断し、理想的な工具を選択する必要があります。特にきれいなエッジが要求されるのは、接続点であることが多いです。MAPALは2種類のフライスカッターを提供しています。右側のスパイラルモデルは、引っ張り効果により軸方向に引張力を発生させ、左側のスパイラルモデルは、押し効果により軸方向に圧縮力を発生させます。ファイバーキャッチャーは、それぞれのスパイラル加工によって生じる力を打ち消します。

以前のモデルには、第3のニュートラル・バリアントがありました。しかし開発を重ね、新しいツールは軸力を最大40％削減することが可能になり、このバリアントはもはや必要なくなりました。新製品の2つのバージョンは、これまでニュートラル・バリアントが使用されていたすべての作業に対応します。工具寿命、静粛性、生産性、切削品質において、新型工具は従来品より最大30パーセント向上しました。

航空産業がコロナウィルスの不振から立ち直りつつある一方で、CFRPの利用は他の分野でも急速に拡大しています。自動車工学やレースに加え、一般消費者部門にも注目が集まっています。自転車、スキー、スノーボード、釣り竿などのスポーツ用品のメーカーが、この最新素材を採用するケースが増えてきています。

OptiMill-Composite-Speed-Plusは、鋭い切れ刃により熱可塑性プラスチックや熱硬化性プラスチックの加工にも使用できます。これらのプラスチックは研磨性がないため、コーティングは不要で鋭い切れ刃が使用されます。非コーティングのフライス工具は特に切削品質の点ではるかに優れているため、従来のルーター工具に取って代わります。MAPALは、ファイバーグラス材の加工にも非コーティング工具を推奨しています。