Difference between cheap and expensive tools.

Customers of TIZ IMPLEMENTS often ask the question “Why one cutter is more expensive than another, when they look almost identical?”. The answer to this question is obvious but not everyone is aware of this. The following article will present some differences between high-end tools and economy class cutters.

1. GRADE DIFFERENCE

The first difference concerns the quality of carbide grade of the fully monolithic carbide tool.

What you need to know about the cemented carbide?

The cemented carbide is mainly composed of two components. The main component is tungsten carbide (WC), the second is a binder stood cobalt (Co). Extremely high hardness, cemented carbide owes tungsten carbide and high strength adhesive (Co), which combines the millstones of tungsten carbide (WC). Its high hardness, cemented carbide generally dominates the high-speed steel HSSIt is known that steel reaches its highest hardness after quenching and that this state can not be described as stable as it softens after annealing. And the formed cemented carbide is maintained in a stable state in which almost never changes due to temperature hardness. Its extremely high hardness and unique thermo-stability causes the cemented carbide tools have a much longer life than high speed steel tools (HSS).

Cemented carbide is produced from WC and Co powders, which are mixed and applied to a plastic mass from which rough bars are extruded and then subjected to sintering. Heat treatment produces resistance cemented carbide.

Quality of cemented carbide largely depends on the quality of the powder..

Basic characteristics of the of cemented carbide mainly depend on the grain size of WC and Co content percentage. By reducing the grain size, hardness and bending strength increases, but the fracture toughness (ductility – toughness) decreases. If the content of Co in the cemented carbide increases, the strength will increase, but the hardness will decrease. The most important thing for manufacturers of carbide is that they have consistent characteristics. It should be noted that when sintering the formed grain size growth tendency. Manufacturers are trying to prevent this.

Best of cemented carbide grades are characterized by a uniform, ultra-fine grain structure with grain size of 0.2-0.4 µm, the hardness of > 1900 [kg/mm²], the bending strength of > 4000 N/mm². TIZ IMPLEMENTS mainly used this species. Most companies use cheaper grades are characterized by granulation with a hardness of 0.7-0.8 µm < 1700 [kg/mm²], the bending strength at 3200 N/mm².

Differences between carbide grades:

For comparison, were presented three different grades of carbide. The first two grades are usually used in the milling cutter cheaper economy class. The last grade is used by TIZ IMPLEMENTS the milling cutter in a series of UFG. Comparing the four most important properties of carbide grades can easily draw conclusions about the high quality grade used in the milling cutter UFG.

Grade features	Grade used in carbide tools
	Economic Mills #2	Economic Mills #2	UFG Mills
Granulation (grain size) carbide [µm]	0,7	0,6	0,2 – 0,4
The percentage of Co [%]	8	10	9
Hardness of cemented carbide [kg/mm2]	1700	1600	1900
The bending strength [N/mm2]	3200	4000	>4000
Figure macroscopic for comparison granulation

As you can see the difference of carbide grade has a major influence on the properties of the finished tool. Depending on grade a tool may be more or less hard, more or less resistant to bending or toughness.

2. THE COATING DIFFERENCES 

The second difference, which affects the quality of the cutter made is to cover coating. The coating greatly affects on the life of the tool.

What is the Nano Crystal coating composite ?

Composite, nanocrystalline coating is composed of single crystals of size less than 10nm, which are embedded in the amorphous grid. The grid is connected to a compound intergranular thickness of about 1 nm. This is a thermodynamically stable material. Stability of this material is manifested also in the grain size. In this case, the grain size does not increase with increasing temperature. Boundaries are used as binder intergranular cracking preventing – in this way defines a high hardness of the material.

Nano-crystalline structures or superstructures are created by applying very thin layers with different properties. The thickness of the next layer depends on the its properties. The optimum thickness is in the range of 3 to 10 nm and depends on the type of layer. The result is a very hard coating with high resistance to cracking.

The main advantages of applying nano-crystalline coatings:

The increase in tool life

• Improving the qualityof the workpiece

•  Can be used greater parameters – higher speeds and higher feed rates – resulting in increased productivity

•  The ability to reduce or avoid the use of coolant

•  Reduce the cutting forces – less power machine consumption

• Reduction of vibrations occurring during machining

• Easier chips leaching

In order to increase the smoothness and lubricity of the coating layer of lubricant is added. Combining coating with a layer of lubricant is a unique, patented technology based on evaporation using a low-voltage arc. Both the method interconnectivity nano-structures as well as their total factor lubricant has some advantages :

• Smooth surface layer with a reduced amount of macrostructure is achieved by the rapid movement of the cathode which is made ​​possible by using a magnetic field and a significant rotation of the electrodes and the equal erosion coated material

• Preparation of Nano-crystal layer is possible due to the high ionization plasma using the intense two-phase magnetic field

• Programming stoichiometric layers makes possible the preparation of differentiation layers and the combination of the various layers during the process of bonding

• Thanks to the optimal use of diversification and proper synchronization is possible to create multi-layered and nano-structures in a single process.

The combination of the above-mentioned advantages of automating the process of coating and a special method of cleaning before coating causes the combination of nano-coating of lubricating element is extremely effective. The applied coating layer must pass inspection consisting of the following :

• Analysis of hardness

• Analysis of adhesion

• Analysis of coating thickness

• Visual quality assessment of the coating 

Coating methoda

There are two basic methods for coating. One is CVD (Chemical Vapor Deposition – method of chemical deposition from the vapor phase) and PVD (Physical Vapor Deposition – physical deposition method from the gaseous phase). The CVD method is used with chemically active gases (i.e. TiCl3, CH4, AlCl 3, etc. …) heated to a temperature of from 900 to 1000 ° C. PVD is based on physical deposition methods (evaporation, spraying, …) of the compounds included in the coating. Another coating method is SHM, based on evaporation using a low voltage electric arc. In a conventional PVD method, the coating electrode has a cylindrical shape with flat end. This results in a concentration of cargo and unevenness of the coating layer. To distribution a uniform should be designed electrode shape.

As apparent from the above description, the coating is extremely difficult, and depending on many factors process.

For comparison, we present the most important parameters used two coats of economic cheaper milling cutter in general use and the properties of the coating used in monolithic carbide tools UFG type :

It is easy to deduce from the above information about the superiority of the coating used in type of tools UFG compared to TiN coatings universal or TiAlN. It is noteworthy that the coefficient of friction so that it is possible to easily chip discharge from the area of machining. As a result, the chip does not get between the blade and the tool and does not cause vibration or chipping blades.

3. DIFFERENCES IN GRINDING QUALITY

The third property of monolithic carbide tools that help to identify economic cutters from high-class cutters is a quality of grinding. Grinding quality is seen primarily in the accuracy with which the tool is made​​.

The main factor influencing the quality of the grinding is the use of appropriate technology and the use of appropriate grinding machines. The use of modern 5-axis CNC grinders greatly simplified and increased the level of quality of the tools. The stiffness and speed of such machines also plays a big role. However, the machinery equipment high-class is expensive. Time working on 5 axis CNC grinding machine is much more expensive than the working hours for conventional grinder.

Another factor influencing the quality of manufactured tools is the time of their execution. Unfortunately, despite the use of modern CNC machines and automation of the production process of some steps cannot be avoided. It is known that to have the tool made ​​in high-grade tolerances must be sanded to precise and slow manner. It is also known that each additional hour of work entails costs. But the effects can be observed during the inspection.

The figure above shows the difference between the two sferical multifluted cutters. The tolerance limits are ± 5μm. At first glance, you can see already that the cutter is made ​​of high grade tolerance. Cutter UFG28 TIZ IMPLEMENTS is in the assumed tolerance limit. Average tolerance ratio not exceed ± 2μm. In the case of economical cutter, which is not within the tolerance of ± 5μm, you will see that it has been insufficiently grinded.

There is another reason which determines the need for precision grinding tools. While the tool is reasonably well grinded – applying a coating causes the cutter becomes less sharp – coating rounds cutter blade. But when the tool is properly sharp applying a coating slightly “blunt” blade.

SUMMARY

Summarize the factors that affect the quality of the tools and simultaneously increase the price in comparison to the advantages they have :

Now you might ask yourself the question: to what purpose are produced (cheaper) economical tool? Economic tools are used for different applications. Main applications will present in the following table :