Hobs..

Hey!
Hello again. Today, we will talk about hobs. :)

What's milling?
Milling is a process which made by removing the sawdust from the workpiece. It provides that made by linear motion with a multi-tip tool rotating around its axis. In today's milling process, the tool can move to the workpiece in almost every direction. The cutting tool has many cutting edges and each edge has a certain amount of chip removal capacity.The advantages of the milling machine are high machining efficiency, good surface quality, precision and flexibility in shaping.Milling is a process usually used for machining plane surfaces, upright corner and channels.

Process the material
If you want to process a material, you should choose a cutter that is suitable for your material. So, you should use a harder cutting tool from your material. Okay? Therefore, the cutting tool material is very important in terms of machinability. Cutting tools developed with technology is favorable for our work in many applications. But the main feature expected from cutting tool material is the higher movement rate at higher cutting speeds. The cutting tool must have high abrasion resistance, high toughness and high red hardness in order to be able to do this. Despite the diversity of cutting tool materials, the most commonly used tool materials are HSS (high speed steels) and carbides.* But ... High-speed steels are not as hard as carbide, although they are much toughness than carbides.  In addition, it prolongs process time. Alright! How should  material of cutting?


Required features at a cutting tip

• High hardness. (Low hardness causes the tool profile to deteriorate.The tool tip will be deformed.The tool material must be harder than the hardest component of the workpiece)
• High durability
• High wear resistance 
• High fatigue resistance 
• It must be compatible with the sawdust (ie, must not occur a reaction between the sawdust and the cutting tip during process.)
• Low Expansion Amount
• High elastic module (If elastic modulus increases, stiffness increases. So, the higher the elastic modulus, the less deformed it becomes. I do not wanna change the tweening of cutting tip during the process. Otherwise, How can i handle to the workpiece?)
• High thermal shock resistance (Rapid heating and cooling occurs during process. Cutter tip must be resistance this.)
• High toughness (Cutter tip must not to be affected by mechanical shocks which occurs during the process)

As you can see, there are many features and it is still difficult and expensive to find them together in today's technology. For example diamond, the queen of cutting tools, has narrow application area cause of is expensive despite carrying a majority of these features. We needed to find an alternative to this and we produced high speed steels. But I said up there. It will spend your time. We need to find something more optimal.

Here it is,

We had to find a cheap cutting tip to replace the diamond. And these are carbides. Imagine abrasion resistance of carbides which is thought to replace diamonds. Moreover, the life of carbides is longer than HSS. So our hero are carbides.  :) 95% of the cutting tools produced from carbides are tungsten carbide-based.

What is Tungsten Carbide? (WC)

The general composition of the Co-Cr-W alloy, referred to as Tungsten's most widely used Stellite; 38-46% Co, 25-35% Cr, 4-25% W and 1-3% C. The hardness of the alloy ranges from 40-60 HRC depending on the ratio of tungsten and carbon. No heat treatment is required. This alloy has features such as high hardness, high wear, oxidation and corrosion resistance and excellent red hardness. The combination of these properties makes this alloy using suitable as cutting tip at the milling machine.

Metallurgical references belong to me:) Alright. We are now passing this issue. Let's come to my drawings. I designed cutter tips which has several different geometries at Solidworks.

VOILAA!!

I have uploaded  my studies this link. You can download and look at it. ^^

C ya.

*Barkın B., 2005, Cnc Freze Tezgahlarında Kullanılan Karbür Parmak Freze Takımı Geometrisinin İşlenebilirliğe Etkilerinin İncelenmesi, Marmara Üniversitesi, Fen Bilimleri Enstitüsü, Makine Eğitimi Anabilim Dalı, Yüksek Lisans Tezi, s.6-12