New tools maximize new machine designs
The primary tooling concerns when machining aluminum are: minimizing the tendency of aluminum to stick to the tool cutting edges; ensuring there is good chip evacuation form the cutting edge; and ensuring the core strength of the tools is sufficient to withstand the cutting forces without breaking.
Technological developments such as the Makino MAG-Series machines have made tooling vendors rethink the any state-of-the-art machine technology. It is vital to apply the right tooling and programming concepts.
Materials coatings and geometry are the three elements in tool design that interrelate to minimize these concerns. If these three elements do not work together, successful high-speed milling is not possible. It is imperative to understand all three
of these elements in order to be successful in the high-speed machining of aluminum.
Minimize Built-Up Edge
When machining aluminum, one of the major failure modes of cutting tools the material being machined adheres to the tool cutting edge. This condition rapidly degrades the cutting ability of the tool. The built-u
p edge that is generated by the adhering aluminum dulls the tool so it can no longer cut through the material. Tool material selection and tool coating selection are the two primary techniques used by tool designers to reduce occurrence of the built-up edge.
The sub-micron grain carbide material requires a high cobalt concentration to achieve the fine grain structure and the material’s strength properties. Cobalt re acts with aluminum at elevated temperatures, which causes the aluminum to chemically bond to the exposed cobalt of the tool material. Once the aluminum starts to adhere to the tool, it quickly forms a built-up edge on the tool rendering it ineffective.
The secret is to find the right balance of cobalt to provide adequate material strength, while minimizing the exposed cobalt in the tools for aluminum adherence during the cutting process. This balance is achieved using coarse-grained carbide that provides a tool of sufficient hardness so as to not dull quickly when machining aluminum while minimizing adherence.
Tool coatings
The second tool design element that must be considered when trying to minimize the built-up edge is the tool coating. Tool coating choices include TiN, TiAIN, AITiN, chrome nitrides, zirconium nitrides, dia
react to中文
mond, and diamond-like coatings(DLC). With
so many choices, aerospace milling shops need to know which one works best in an aluminum high-speed machining application.
The Physical Vapor Deposition (PVD) coating application process on TiN, TiCN, TiAIN, and AITiN tools makes them unsuitable for an aluminum application. The PVD coating process creates two modes for aluminum to bond to the tools――the surface roughness and the chemical reactivity between the aluminum and the tool coating.
The PVD process results in surface that is rougher that the substrate material to which it is applied. The surface”peaks and valleys” created by this process causes aluminum to rapidly collect in the valleys on the tool. In addition, the PVD coating is chemically reactive to the aluminum due to its metallic crystal and ionic crystal features. A TiAIN coating actually contains aluminum, which easily bonds with a cutting surface of the same material. The surface roughness and chemical reactivity attributes will cause the tool and work piece to stick together, thus creating the built-up edge.
In testing performed by OSG Tap and Die, it was discovered that when machining aluminum at very high speeds, the performance of an uncoated
coarse-grained carbide tool was superior to that of one coated with TiN, Ticn, TiAIN, or ALTiN. This testing does not mean that all tool coatings will reduce the tool performance. The diamond and DLC coatings result in a very smooth chemically inert surface. These coatings have been found to significantly improve tool life when cutting aluminum materials.
The diamond coatings were found to be the best performing coatings, but there is a considerable cost related to this type of coating. The DLC coatings provide the best cost for performance value, adding about 20%-25%to the total tool cost. But, this coating extends the tool life significantly as compared to an uncoated coarse-grained carbide tool.
Geometry
The rule of thumb for high-speed aluminum machining tooling designs is to maximize space for chip evacuation. This is because aluminum is a very soft material, and the federate is usually increased which creates more and bigger chips.
The Makino MAG-Series aerospace milling machines, such as the MAG4, require an additional consideration for tool geometry-tool strength. The MAG-Series machines with their powerful 80-hp spindles will snap the tools if they are not designed with sufficient core strength.
In general, sharp cutting edges should always be used to avoid aluminum elongation. A sharp cutting edge will create high shearing and also high surface clearance, creating a better surface finish and finish and minimizing chatter or surface vibration. The issue is that it is possible to achieve a sharper cutting edge with the fine-grained carbide material than the coarse grained material. But due to aluminum adherence to the fine-grained material, it is not possible to maintain that edge for very long.
Coarse compromise
The coarse grained material appears to be the best compromise. It is a strong material that can have a reasonable cutting edge. Test results show it is able to achieve a very long tool life with good surface finish. The maintenance of the cutting edge is improved using an oil mist coolant through the tool. Misting gradually cools down the tools, eliminating thermal shock problems.
The helix angle is an additional tool geometry consideration. Traditionally when machining aluminum a fool with a high helix angle has been used. A high helix angle lifts the chip away from the part more quickly, but increases the friction and heat generated as result of the cutting action. A high helix angle is typically used on a tool with a higher number of flutes to quickly evacuate the chip from the part.
When machining aluminum at very high speeds the heat created by the increased friction may cause t
he chips to weld to the tool. In addition, a cutting surface with a high helix angle will chip more rapidly that a tool with a low helix angle. A tool design that utilizes only two flutes enables both a low helix angle and sufficient chip evacuation area. This is the approach that has proven to be the most successful in extensive testing performed by OSG when developing the new tooling line, the MAX AL.
翻译
新工具使新机器设计最优
当加工铝时，我们主要关心的是：铝粘住加工切削边缘的倾向；保证有好的碎片排屑形成切削边缘；和保证工具有足够的中心强度来承受切削力而不被破坏。
技术发展，比如：Makino MAG系列，已经使工具商重新考虑任何工艺水平的机器技术。用正确的加工和编程思路是很重要的。
材料，涂料和几何形状是与减小我们所关注问题相关系的工具设计的三个因素。如果这些因素不能一起很好的配合，成功的调整磨削是不可能的。为了成功进行高速铝加工，理解这三个因素是很必要的。
使组合边缘最小化
当加工铝时，一个失败的切削工具模式是，被加工的材料粘住工具切削边缘。这种情况会很快削弱工具的切削能力。由粘着的铝形成的组合边缘会导致工具变钝，以至不能切削材料。工具材料选择和工具涂料选择是被工具设计者用来减小组合边缘出现的主要工艺。
亚微米微粒碳化物材料要求很高的钴浓度来获得良好的微粒结构和材料强度属性。随着温度的升高，钴与铝发生反应，钴使铝与暴露的工具材料碳化物相粘合。一旦铝开始粘住工具，铝会在快速的在工具上形成组合边缘，使工具不可用。
在切削的进程中，减小铝粘合着的工具的暴露碳化物的秘诀就是到正确的碳化物的平衡来提供足够的材料强度。在加工铝时，为了减小粘附，使用能提供足够硬度的纹理粗糙的碳化物来获得平衡，来使变钝变慢。
工具涂料
当尝试减小组合边缘时，第二个应该考虑的工具设计因素是工具涂料。工具涂料的选择包括：TiN, TiAIN, AITiN，铬氮化物，锆氮化物，钻石和钻石般的涂料（DLC）。拥有这么多的选择，航空航天磨削商店需要知道在铝的高速加工应用中哪一种工作最有效。TiN, TiCN, TiAIN, 和 AITiN工具的PVD涂装应用进程使这些选项不合适铝的应用。PVD涂装进程建立了两个使铝粘住工具的模式---表面的粗糙程度和铝与工具涂料之间的化学反应。PVD进程形成了一个表面，这表面是比底层材料更粗糙的。由这个进程
形成的表面“凹凸”使工具中的铝在凹处快速集结。由于涂料有金属晶体和铁晶体特征，PVD涂料是可以和铝发生化学反应的。一种TiAIN涂料通常是包含铝的，这铝很容易和相同材料的切削表面
粘合。表面粗糙度和化学反应特性将会导致工具和工作片体粘在一起，以致形成组合表面。
OSG Tap and Die主导的试验中，人们发现在高速加工铝时，一个没有涂染过纹理粗糙的碳化物的工具的表面优于用TiN, Ticn, TiAIN, 或者ALTiN涂染过的工具。这个试验不意味着所有工具涂料将减小工具的表现。钻石和DLC涂料可生成一个非常光滑的化学惰性的表面。在切削铝材料时，这些涂料很认为是能非常有效的提高工具的寿命。
钻石涂料被认为是表现最佳的涂料，但这种涂料要一个很可观的成本。对于表现价值，DLC涂料提供最佳成本，增加大约20%-25%的总工具成本，而寿命相对于未涂染过纹理粗糙的碳化物的工具来是，是增长得很明显的。
几何形状
高速铝加工工具设计的拇指定律就是使微粒排屑空间最大化。这是因为铝是一种非常柔软的材料。Federate通常是可以增长的，它生成更多更大的微粒。
Makino MAG-Series航空航天磨削机器，比如MAG4，要求额外关注工具几何休和工具强度。拥有强大
的80-hp的心轴的 MAG-Series机器将折断工具如果他们不是用足够的中心强度设计的。
总的来说，锋利的切削边缘一直都可以用来避免铝的延伸。一个锋利的切削边缘将形成高剪切和高表面清洁，形成一个更好的表面和使表面振动最小化。结果是用优良的纹理碳化物材料比纹理粗糙的碳化物材料更有可能获得一个锋利的切削边缘。但由于铝能粘住纹理好的材料，长久保持这各边缘是不太可能的。
粗略的折衷方案
纹理粗糙的材料是最好的折衷。那是一种很强大的材料，它能拥有一个可观的切削边缘。试验结果表明；在获得长的工具寿命的同时拥有好的表面的可以的。通过工具来进行油雾冷却是可以改进切削边缘的保持的。雾化逐渐使工具冷却，消除温度急增的问题。
螺旋角度是一个额外的工具几何考虑因素。传统上来说，当加工铝时，带有高螺旋角度的工具已经被运用。高螺旋角度可以使微粒更快地从部分脱离，但却增加力和热，这是由切削运动导致的。一个高螺旋角被用在工具上，并且很大数量的凹槽可以使微粒排泄。
当以非常高的速度加工铝时，由增加的力形成的热量可能会引起微粒与工具焊接在一起。此外，一个有很高螺旋角的切削表面将比低角度的更快产生微粒。仅仅利用两个凹槽工具设计使低螺旋角和足够微粒
排泄区域成为可能。由OSG 主导的延伸性试验中，当发展新工具流水线时，这被证明是最成功的方法。

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