Today, a group of metals stands out for which it is necessary to create special conditions before starting to work with them. Titanium processing belongs to this category of work. All the difficulties and features of the process are associated with the fact that this material is characterized by increased hardness.
Description
Titanium is characterized by the fact that it is very durable, has a silver color, and also has great resistance to the rusting process. Due to the fact that a TiO 2 film is formed on the metal surface, it has good resistance to all external influences. Only the effect of substances that contain alkali in their composition can negatively affect the properties of titanium. Upon contact with these chemicals, the raw material loses its strength characteristics.
Due to the fact that the product has increased strength, when turning titanium, you have to use a tool made of heavy-duty alloy, as well as create other special conditions when working on a CNC lathe.
What should be considered when processing?
If you need to work with titanium, the following properties must be taken into account:
- The first is sticking. When titanium is processed using a lathe, a high temperature is created, due to which the material begins to melt and adhere to the cutting tool.
- During processing, fine particulate dust also occurs. It can detonate, and therefore during operation it is very important to strictly observe all safety rules.
- In order to qualitatively carry out the cutting process of such a heavy-duty metal, a tool is needed that can provide a suitable mode.
- It is necessary to specially select a cutting tool also because titanium is characterized by low thermal conductivity.
After titanium treatment is completed, the finished part is usually heated, after which it is allowed to cool in the open air. Thus create a protective film on the surface of the material, which was described above.
Classification of processing methods
In order to cut such raw materials, you need a special tool, as well as a CNC lathe. The process itself is divided into several operations, each of which is carried out according to its own technology.
As for the operations themselves, they can be primary, intermediate or preliminary.
When machining titanium on machines, you need to remember that vibration occurs at this time. In order to partially solve this problem, it is possible to fix the workpiece in a multi-stage manner, and also do it as close as possible to the spindle. To reduce the influence of temperature on the processing process, it is recommended to use fine-grained carbide cutters without coating and plates with special PVD. It is worth paying attention to the fact that during the processing of titanium by cutting from 85 to 90% of all energy will be converted into heat, which will be absorbed by the chips processed by the workpiece, cutters and liquid, which is intended for cooling. Typically, the temperature in the work area reaches 1000-1100 degrees Celsius.
Adjustment of processing parameters
During processing of such a heavy-duty material, three main parameters must be taken into account:
- angle of fixation of the working tool;
- feed dimension;
- cutting speed.
If you adjust these parameters, then with their help you can change the processing temperature. At different processing modes, different parameters of these characteristics are observed.
For pre-processing with a cut of the top layer up to 10 mm, an allowance of 1 mm is allowed. To work in this mode, the following parameters are usually set. Firstly, the fixing angle is from 3 to 10 mm, and secondly, the feed dimension is from 0.3 to 0.8 mm, and the cutting speed is 25 m / min.
An intermediate version of titanium processing involves cutting the top layer from 0.5 to 4 mm, as well as the formation of an even 1 mm allowance layer. The fixing angle is 0.5-4 mm, the feed dimension is 0.2-0.5 mm, the feed speed is 40-80 m / min.
The main processing option is the removal of a layer of 0.2-0.5 mm, as well as the removal of allowances. The speed of operation is 80-120 m / min, the fixing angle is 0.25-0.5 mm, and the feed dimension is 0.1-0.4 mm.
It is also very important to note that the machining of titanium on such equipment is always carried out only in the presence of a special cooling emulsion. The substance is supplied under pressure to the working tool. This is necessary in order to create a normal temperature operation.
Processing tool
The requirements for a tool for processing material are quite high. Most often, titanium and alloys are processed using cutters that have removable heads, and they are installed on CNC machines. During operation, the working tool is subjected to abrasive, adhesive and diffuse wear. Particular attention should be paid to diffuse wear, since at this time the dissolution of both the cutting material and the titanium workpiece occurs. Most actively, these processes occur if the temperature is in the range from 900 to 1200 degrees Celsius.
Tool Requirements
The peculiarity of titanium processing lies in the fact that it is necessary to select a working tool depending on which operating mode is selected.
To work in preliminary mode, the most commonly used plates are round or square iC19. These plates are made of a special alloy, which is marked as H13A and has no coating.
In order to successfully process titanium in an intermediate way, it is necessary to use only round plates from the same H13A alloy or from GC1155 alloy with PDV coating.
For the most responsible, basic processing method, round nozzles with grinding cutting edges are used, which are made of alloys H13A, GC 1105, CD 10.
It is important to add that when processing on CNC lathes, the smallest deviation from the shape of the part that was specified in the technical specifications is allowed. Most often, elements made of such an alloy do not have deviations from the norm at all.
The main processing problem
The main problem encountered when processing this raw material is sticking and tearing on the tool. Because of this, the heat treatment of titanium is very difficult. In addition, the fact that the metal is characterized by very low thermal conductivity causes a lot of problems. Due to the fact that other metals resist heating much weaker, in contact with titanium they most often form an alloy. This is the main reason for rapid tool wear. In order to slightly reduce the sticking and sticking, as well as to remove part of the generated heat, experts recommend doing the following:
- firstly, it is necessary to use coolant;
- secondly, when sharpening workpieces, for example, tools from the same heavy-duty materials should be used;
- thirdly, when processing raw materials using cutters, the speed is significantly reduced in order to reduce heating.
Oxidation and nitriding of titanium
It is worth starting with nitriding of titanium, since this type of treatment is much more complicated than oxidation. The technological process is as follows. A titanium product is heated to 850-950 degrees Celsius, after which the part must be placed in a medium with pure gaseous nitrogen for several days. After that, a titanium nitride film is formed on the surface of the element due to chemical reactions that will occur during these days. If everything went well, then a golden hue film will appear on titanium, which will be distinguished by increased strength and abrasion resistance.
As for the oxidation of titanium, the method is very common and belongs, like the previous one, to the heat treatment of titanium. The beginning of the process is no different from nitriding, the part must be heated to a temperature of 850 degrees Celsius. But the cooling process does not occur gradually in a gas environment, but abruptly with the use of liquid. Thus, you can get a film on the surface of titanium, which will be firmly connected with it. The presence of this type of film on the surface leads to an increase in strength and abrasion resistance by 15-100 times.
Connection parts
In some cases, titanium products are part of a large structure. This suggests that there is a need to combine different materials.
In order to connect products from this raw material, four main methods are used. The main one is welding, soldering is also used, a mechanical method of joining, which involves the use of rivets and bolting. Today, the main processing method for joining products into one structure is welding in an inert gas or special oxygen-free fluxes.
As for soldering, this method is applied only if welding is not possible or is not practical. This process is complicated by some chemical reactions that arise as a result of soldering. To make a mechanical connection with bolts or rivets, you will also have to use a special material.