Round insert milling cutters are suitable for milling titanium, because their main declination angle can be changed appropriately. As long as these milling cutters are equipped with special inserts and the correct cutting parameters are applied, stability and overall performance can generally be improved. It is very important to set the minimum feed per tooth.
Titanium alloy milling requires suitable conditions
Compared with the machining of most other metal materials, titanium machining is not only more demanding, but also more restrictive. This is because the metallurgical properties and material properties of titanium alloys may have a serious impact on the cutting action and the material itself. However, if you choose the right tool and use it correctly, and optimize the machine tool and configuration according to the requirements of titanium machining, then you can fully meet these requirements and obtain satisfactory high performance and perfect results. Many problems encountered in the machining of traditional titanium metal are not inevitable. As long as the influence of titanium properties on the machining process is overcome, success can be achieved.
Various properties of titanium make it a very attractive part material, but many of these properties also affect its machinability. Titanium has an excellent strength-to-weight ratio, and its density is usually only 60% of steel. Titanium has a lower modulus of elasticity than steel, so it has a harder texture and better deflection. Titanium is also more resistant to corrosion than stainless steel and has low thermal conductivity. These attributes mean that titanium metal will produce a higher and more concentrated cutting force during machining. It is easy to produce vibration and cause tremor during cutting; moreover, it also easily reacts with the cutting tool material during cutting, thereby aggravating the wear of crescent craters. In addition, its thermal conductivity is poor, because the heat is mainly concentrated in the cutting area, so the tool for machining titanium must have high thermal hardness.
Stability is the key to success
Some machining workshops find that titanium metal is difficult to process effectively, but this view does not represent the development trend of modern machining methods and cutting tools. Part of the difficulty is that titanium metal machining is an emerging process and lacks experience to learn from. In addition, the difficulty is usually related to the expected value and the operator’s experience, especially some people have become accustomed to the machining of materials such as cast iron or low alloy steel, and the machining requirements of these materials are generally very low. In contrast, machining titanium metal seems to be more difficult, because the same tool and the same speed cannot be used for machining, and the life of the tool is also different. Even compared to certain stainless steels, the difficulty of machining titanium is still higher. We can of course say that different cutting speeds and feeds must be taken and certain preventive measures must be taken when machining titanium. In fact, compared with most materials, titanium metal is also a material that can be directly processed. As long as the titanium workpiece is stable, the clamping is firm, the machine tool is selected correctly, the power is appropriate, the working conditions are good, and the ISO50 spindle with a short tool overhang is installed, all problems will be solved-provided the cutting tool is correct.
But in actual milling, the conditions required for titanium machining are not easy to meet, because the ideal stability conditions are not always available. In addition, many titanium parts have complex shapes and may contain many dense or deep cavities, thin walls, bevels, and thin brackets. To successfully process such parts, you need to use a tool with a large overhang and a small diameter, which will affect the stability of the tool. When machining titanium, it is often more prone to potential stability problems.
Must consider vibration and heat
The non-ideal environment also contains other factors, one of which is that most machine tools are currently equipped with IS040 spindles. If you use the machine tool intensively, you will not be able to maintain the new tool for a long time. In addition, if the part structure is more complicated, it is usually not easy to clamp effectively. Of course, the challenge does not stop there. Sometimes the cutting process must be used for full slot milling, side milling or contour milling, all of which may (but not necessarily) generate vibration and create poor cutting conditions. Importantly, when setting up the machine, care must always be taken to improve stability to avoid vibration trends. Vibration can cause blade breakage, blade damage and produce unpredictable and inconsistent results. One improvement is to use multi-level clamping to bring parts closer to the spindle to help offset vibration.
Because titanium metal can still maintain its hardness and strength at high temperatures, the cutting edge will encounter high forces and stresses, and the high heat generated in the cutting zone means that work hardening is likely to occur, which can cause certain problems Produced, especially not conducive to the subsequent cutting process. Therefore, choosing the best indexable insert grade and geometry is the key to successful machining. Past history has proven that fine-grain uncoated blade grades are very suitable for titanium metal machining; today, blade grades with PVD titanium coating can greatly improve performance.
Accuracy, conditions and correct cutting parameters
Tool runout accuracy in the axial and radial directions is also important. For example, if the insert is not properly installed in the milling cutter, the cutting edge around the milling cutter can be quickly damaged. When cutting titanium, other factors, such as poor tool manufacturing tolerances, wear and tool damage, defective or poor tool holders, machine tool spindle wear, etc., will greatly affect the tool life. Observations indicate that 80% of all cases of poor machining performance are caused by these factors. Although most people prefer to use positive rake angle cutters, in fact, slightly negative rake angle cutters can remove material with a higher feed, and the feed per tooth can reach 0.5mm. But this also means that the best stable state must be maintained, that is, the machine tool should be very strong and the clamping should be extremely stable.
In addition to plunge milling (preferably using round inserts), the use of a 90 degree declination should be avoided as much as possible. This usually helps to improve stability and obtain overall performance, especially when used at shallow depth of cut When performing deep cavity milling, a recommended practice is to use a tool with a variable length through the tool shank instead of using a long tool with a single length in the entire process.
Adjusting cutting parameters to overcome the vibration caused by reducing the feed per tooth is the traditional solution, but this method is not appropriate because it will have a catastrophic effect on tool life and cutting performance. Indexable inserts require a certain amount of cutting edge rounding to increase cutting edge strength and obtain better coating adhesion.
When milling titanium, the tool is required to work with at least the minimum feed-usually 0.1mm per tooth. If there is a tendency to vibrate, the problem of blade damage or shortened tool life will be inevitable. Possible solutions include accurately calculating the feed per tooth and ensuring that it is at least 0.1mm.
Also can reduce the spindle speed to achieve the initial feed rate. If the minimum feed per tooth is used, but the spindle speed is incorrect, the impact on tool life can be as high as 95%. Reducing the spindle speed usually increases the tool life.
Once the stable operating conditions are established, the spindle speed and feed can be increased accordingly to obtain the best performance. Another approach is to remove some inserts from the milling cutter or choose a cutter with fewer inserts.