To date, a group of metals is distinguished, for which it is necessary to create special conditions before you start working with them. Machining titanium falls into this category of work. All the difficulties and features of the process are due to the fact that this material is characterized by increased hardness.
Description
Titanium is characterized by being very strong, having a silvery color and also being extremely resistant to the rusting process. Due to the fact that a TiO 2 film is formed on the surface of the metal, it has good resistance to all external influences. Only the influence 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 high strength of the product, when turning titanium, it is necessary to use an ultra-high-strength alloy tool, as well as create other special conditions when working on a CNC lathe.
What should be considered during processing?
When working with titanium, the following properties must be taken into account:
- The first is sticking. When machining titanium using a lathe, a high temperature is created, due to which the material begins to melt and stick to the cutting tool.
- During processing, fine dispersed dust also occurs. It can detonate, and therefore during operation it is very important to strictly observe all safety regulations.
- 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 also necessary to specially select a tool for cutting because titanium is characterized by low thermal conductivity.
After the processing of titanium is completed, the finished part is usually heated, after which it is allowed to cool in the open air. Thus, a protective film is created on the surface of the material, which was described above.
Classification of processing methods
In order to cut such raw materials, a special tool is required, as well as lathe with CNC. 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 basic, intermediate or preliminary.
When processing titanium on machines, it must be remembered that vibration occurs at this time. In order to partially solve this problem, you can clamp the workpiece in a multi-stage manner, and also do it as close to the spindle as possible. To reduce the influence of temperature on the machining process, it is recommended to use uncoated fine-grain carbide cutters and special PVD inserts. Here 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, the workpiece being processed, the cutters and the liquid that is intended for cooling. Usually the temperature in the work area reaches 1000-1100 degrees Celsius.
Adjusting Processing Parameters
During the processing of such a heavy-duty material, three main parameters must be considered:
- fixing angle of the working tool;
- feed dimension;
- cutting speed.
If you adjust these parameters, then with their help you can change the processing temperature. Under different processing modes, different parameters of these characteristics are also observed.
For pre-treatment with a cut of the upper 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 rate is from 0.3 to 0.8 mm, and it sets 25 m / min.
An intermediate version of titanium processing involves cutting off the upper layer from 0.5 to 4 mm, as well as the formation of an even layer of an allowance of 1 mm. Fixation angle 0.5-4 mm, feed rate 0.2-0.5 mm, feed speed 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 working speed is 80-120 m/min, the fixation angle is 0.25-0.5 mm, and the feed rate is 0.1-0.4 mm.
It is also very important to note here that titanium is always carried out on such equipment only if a special cooling emulsion is supplied. The substance is supplied under pressure to the working tool. This is necessary in order to create a normal temperature regime work.
Processing tool
The requirements for the material processing tool are quite high. Most often, the processing of titanium and alloys is carried out 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. Special attention it is worth paying attention to diffuse wear, since at this time the process of dissolution of both the cutting material and the titanium blank takes place. These processes are most active if the temperature is in the range from 900 to 1200 degrees Celsius.
Tool Requirements
The peculiarity of titanium processing also lies in the fact that it is necessary to select a working tool depending on which operating mode is selected.
For work in the preliminary mode, plates with a round or square shape of the brand iC19 are most often used. These plates are made from a special alloy, which is marked as H13A and has no coating.
In order to successfully process titanium in an intermediate way, it is already necessary to use only round inserts from the same H13A alloy or from GC1155 alloy with a PDV coating.
For the most responsible, basic processing method, round nozzles with grinding cutting edges are used, which are made of H13A, GC 1105, CD 10 alloys.
It is important to add that when machining on CNC lathes, the smallest deviation from the shape of the part that was specified in terms of reference. Most often, elements made from such an alloy do not have deviations from the norm at all.
The main problem in processing
The main problem encountered in the processing of this raw material is sticking and tearing on the tool. Because of this, the heat treatment of titanium is very difficult. In addition, a lot of problems are caused by the fact that the metal has a very low thermal conductivity. Due to the fact that other metals resist heat much weaker, when in contact with titanium, they most often form an alloy. This is the main reason for rapid tool wear. In order to somewhat reduce scuffing and sticking, as well as to divert some of the heat generated, experts recommend doing the following:
- firstly, it is imperative to use coolant;
- secondly, when sharpening workpieces, for example, tools made of the same heavy-duty materials should be used;
- thirdly, when processing raw materials with cutters, the speed is significantly reduced in order to reduce heating.
Oxidation and nitriding of titanium
It is worth starting with titanium nitriding, since this type of treatment is much more difficult than oxidation. Technological process as follows. The titanium product is heated to 850-950 degrees Celsius, after which the part must be placed in an environment with pure nitrogen gas for several days. After that, a film of titanium nitride is formed on the surface of the element, due to chemical reactions that will take place during these days. If everything went well, then a golden-colored 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 and in a gaseous environment, but abruptly and with the use of a liquid. Thus, it is possible to obtain a film on the surface of titanium, which will be firmly bonded to it. The presence of this type of film on the surface leads to an increase in strength and resistance to abrasion by 15-100 times.
Connection of parts
In some cases, titanium products are part of a large structure. This suggests that there is a need to connect different materials.
In order to connect products from this raw material, four main methods are used. The main one is welding, brazing is also used, a mechanical connection method that involves the use of rivets and bolted connection. Today, the main processing method for connecting products into one structure is welding in an inert gas environment or special oxygen-free fluxes.
As for soldering, this method is used only if welding is impossible or impractical. This process is complicated by some chemical reactions that occur as a result of soldering. To make a mechanical connection with bolts or rivets, you will also have to use a special material.
It is generally accepted that titanium can be machined like stainless steels. This means that titanium is 4-5 times more difficult to machine than regular steel, but it's still not an unsolvable problem.
The main problems in the processing of titanium are its high tendency to sticking and scuffing, low thermal conductivity, and the fact that almost all metals and refractory materials are dissolved in titanium, as a result of which it is an alloy of titanium and a hard material of the cutting tool. Such processing causes rapid wear of the cutter.
Coolants are used to reduce sticking and tearing and to remove a large amount of heat that is released during cutting. The turning of the workpiece is carried out using carbide cutters, and the processing speed is usually lower than when turning stainless steel.
If it is necessary to cut titanium sheets, then this operation is carried out on guillotine shears. Long products of large diameters are cut with mechanical saws, using hacksaw blades with a large tooth. Less thick bars are cut on lathes.
When milling, the titanium stays true to itself and sticks to the cutter teeth. Milling cutters are also made of hard alloys, and lubricants with high viscosity are used for cooling.
When drilling titanium, the main concern is to ensure that the chips do not accumulate in the discharge grooves, as this quickly damages the drill. High-speed steel is used as a material for drilling titanium.
When using titanium as a structural material, titanium parts are connected to each other and to parts made of other materials by various methods.
The main method is welding. The very first attempts to weld titanium were unsuccessful, which was explained by the interaction of the molten metal with oxygen, nitrogen and hydrogen in the air, grain growth during heating, changes in the microstructure and other factors leading to the fragility of the weld. However, all these problems, which previously seemed insoluble, were solved in the most short time titanium welding is a common industrial technology these days.
But although the problems have been solved, titanium welding has not become simple and easy. Its main difficulty and complexity lies in the need for constant and rigorous protection of the weld from contamination by impurities. Therefore, when welding titanium, not only an inert gas is used high purity and special oxygen-free fluxes, but also a variety of protective visors, gaskets that protect the cooling ones.
To minimize grain growth and reduce changes in the microstructure, welding is carried out with high speed. Almost all types of welding are carried out under normal conditions, using special measures to protect the heated metal from contact with air.
But world practice also knows welding in a controlled atmosphere. Such protection of the weld is usually necessary for high-critical work, when one hundred percent guarantee is required that weld will not be contaminated. If the parts to be welded are not large, welding is carried out in a special chamber filled with an inert gas. The welder clearly sees everything he needs through a special window.
When large parts and assemblies are welded, a controlled atmosphere is created in special capacious sealed rooms where welders work using individual life support systems. Of course, these works are carried out by welders of the highest qualification, but ordinary welding of titanium should only be carried out by people specially trained in this matter.
In cases where welding is not possible or simply not advisable, they resort to soldering. The soldering of titanium is complicated by the fact that it is chemically active at high temperatures and is very firmly bound to the oxide film covering its surface. The vast majority of metals are unsuitable for use as solders when soldering titanium, as brittle joints are obtained. Only pure silver and aluminum are suitable for this purpose.
It is also possible to connect titanium with titanium, as well as with other metals, mechanically - with riveting or with the help of bolts. When using titanium rivets, the riveting time is almost doubled compared to the use of high-strength aluminum parts, and nuts and bolts made of a new industrial metal are invariably covered with a layer of silver or Teflon synthetic material, otherwise, when screwing the nut, titanium will, as it invariably inherent, stick and bully and the threaded connection will not be able to withstand high stresses.
The tendency to sticking and scuffing, due to the high coefficient of friction, is a very serious disadvantage of titanium. This leads to the fact that titanium alloys wear out quickly and cannot be used for the manufacture of parts operating under conditions of sliding friction. When sliding on any metal, titanium sticks to its surface, and the part gets stuck, seized by the sticky layer of titanium.
However, to say that titanium alloys cannot be used in the manufacture of rubbing parts is wrong. There are many ways to harden the surface of titanium and eliminate the tendency to build up. One of them is nitriding.
The process consists in the fact that parts heated to 850-950 degrees are kept in pure nitrogen gas for more than a day. A golden-yellow film of titanium nitride of high microhardness is formed on the metal surface. The wear resistance of titanium parts increases many times over and is not inferior to products made of special surface-hardened steels.
Another common method for eliminating titanium's tendency to scratch is oxidation. In this case, as a result of heating, an oxide film forms on the surface of the parts. With low-temperature oxidation, free access of air to the metal is hindered, and the oxide film is dense, well-bonded with the main thickness of titanium.
High-temperature oxidation consists in the fact that for 5-6 hours the parts are kept in air heated to 850 degrees, and then they are rapidly cooled in water to remove loose scale from the surface. As a result of oxidation, wear resistance increases by 15-100 times.
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One of the main specializations of our company is the turning of titanium of all possible grades (basic vt1-0, vt3-1, ot4-1, pt3v, vt16) and types (bar, plate, sheet, pipe, forgings). We also carry out welding and aging of titanium and parts based on it. The photo below shows a very complex product made by our company from VT1-0 titanium with welding and aging!
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Turning titanium is accompanied by numerous difficulties, which distinguishes it from other metals. This is explained by the fact that titanium has:
– high strength and significant weight;
– low thermal conductivity and excellent corrosion resistance.
Due to these properties, titanium is very popular among manufacturers who are engaged in turning parts. At the same time, these characteristics make this metal very inconvenient for cutting and processing. So, for example, there is a vibration. The cutting element wears out quickly.
If these phenomena can be compensated, then the processing becomes extremely efficient. Use of the most advanced turning and milling machines, compressor units and other necessary equipment made the processing much easier.
For machining titanium on a lathe, the part is securely fixed on a powerful machine. Correctly selected cutting block. However, the creation of ideal conditions is sometimes impossible to implement, because the parts may have a complex shape and too thin walls.
With such complexities, the units on which the turning of titanium takes place quickly become unusable. Details that have a complex shape, sometimes, cannot be fixed properly.
Titan does not lose his specifications and during processing. At the same time, a lot of heat is released. Therefore, there is a high risk of defects on the surface of the part, which means that choosing the cutting element correctly and correctly is an extremely important stage. Practice shows: great option is the use of fine-grained metal alloys as a raw material for creating a cutter. Thus, cutting and drilling become efficient.
In addition, when machining titanium on a lathe, the chips rise up and stick to the cutting elements. This disadvantage is eliminated by oxidation: the titanium billet is heated to 900 degrees Celsius and exposed in this form to the open air. After that, the blank must be quickly cooled in water and the turning of titanium parts should be continued.
Properties of titanium: it is the viscosity and thermal conductivity that causes the cutter to become very hot. As a result, even extremely durable and high-quality turn-mill tools are quickly destroyed. Due to the significant vibration that occurs when working with titanium, powerful machines are required, the frame of which is securely fixed to the bed.
Manufacturing of titanium parts
In order for the manufacture of titanium parts on a CNC lathe to be easy, it is necessary that:
- machines with high power were used, where it is possible to adjust the speed of rotation of the workpieces;
– tools and blanks were fed with a small overhang;
– the moving parts were securely and perfectly matched.
In addition, cutting tools and fixing units must have high thermal resistance, because titanium, remaining cold, heats the metal of the cutter to the utmost, along with the surrounding cut site.
Much attention should be paid to the vibration of titanium parts, which occurs when titanium is processed on a CNC lathe. It occurs due to:
– small dimensions of parts;
- the use of a long cutting tool when turning parts made of titanium;
- the viscosity of the metal. Strong heat and high speeds cause the standard spindle taper to become unusable very quickly.
We will make a prompt calculation according to your drawings, send them by e-mail . You can call 8 3439 38 00 81, 8 3439 38 98 01, delivery throughout Russia.
You can solve this problem by:
– by reducing the distance that separates the part and the spindle;
- precisely adjusting the moving parts of the machine;
- by rigidly fixing both the frame of the unit on which titanium is turned, and its fixed units.
Accordingly, vibration compensation (elimination) is possible if:
- accurately and accurately adjust absolutely all blocks of the machine;
- carefully fit a small size heat-resistant cutting tool;
- bring the place of attachment of the cutter and the part itself as close as possible to each other.
Thanks to these measures, the machine will be able to work for a long time, if you do not increase the overall tolerances on the workpiece.
There are a number of additional methods that ensure the stability of the titanium turning process. It is advisable to reduce the number of revolutions, precisely adjust the position of the cutter, securely fastening it, because the beating of the tool destroys the cutting tool assembly completely.
Among non-specialists, there is an opinion that titanium has a clear resemblance to stainless steel. This means that it can be machined. At the same time, such a metal is still stronger than steel, so working with it is about five times more difficult. However, metalworking should not cause any special problems.
Difficulties in processing titanium products
In fact, everything is somewhat more complicated than it seems at first glance. This metal is characterized by reduced thermal conductivity, is able to bully and stick. In addition, the difficulty lies in the fact that titanium is extremely strong and is capable of soldering with a cutting tool during thermal work (after all, the cutter also consists of metal and almost always turns out to be softer than the workpiece). As a result, the tool wears out particularly quickly and requires constant replacement.
Speaking of metal processing, professionals mean several different types of work with titanium parts. They have their own secrets to neutralize the negative properties of this metal or minimize them. For example, special coolants can help reduce metal picking or sticking, as well as reduce the amount of heat generated when cutting titanium.
Titanium sheets are cut using guillotine shears. Rolled bar metal of large diameter is usually cut with special saws of a mechanical type. This tool is different in that the tooth of the blade is quite large. If the bar has a smaller diameter, a lathe can be used. By the way, the turning of this metal is carried out with cutters made of especially strong alloys. But even under this circumstance, the speed of work must be reduced and is usually inferior to the speed that is observed when machining stainless steel.
Milling titanium parts also causes difficulties: metal begins to stick to the milling teeth. To avoid this, it is necessary to use a cutter made of high hardness alloys. As coolants, liquids are used, the level of viscosity of which is increased.
Special attention should be paid to drilling titanium elements. Chips can accumulate in the grooves, as a result of which the drill begins to deform. Titanium can be drilled with steel high-speed tools.
Titanium can also be used as a material for the components of any structures. Parts made of this metal need to be joined, and several methods are used here. It is worth considering this issue in more detail.
Features of welding work on titanium
Welding is the most commonly used connection option for titanium parts. At first, any attempt at titanium welding ended in failure. The reasons for this were various. It was believed that changes occur in the microstructure of the metal, that titanium reacts with nitrogen, oxygen and hydrogen, which are contained in the air. Among other factors, an increase in graininess during heating of the metal was mentioned. In any case, the seams were extremely fragile. However, all these problems were quickly solved with the help of new technologies. Therefore, at present, welding of titanium elements does not cause any particular difficulties and is considered commonplace.
However, certain nuances in carrying out welding work are still observed. Most often, this is expressed in the fact that the weld must be constantly protected from impurities that pollute it. To avoid this, welders use fluxes that operate without oxygen, as well as pure inert gas. Specialized pads and visors are also used for protection - they allow you to cover the cooling seams and prevent contamination.
Such metalworking services involve increased welding speed. This makes it possible to reduce the increase in graininess and delay any deformation of the microstructure of the material. Welding is carried out under standard conditions. Separate preventive measures are used to protect the hot metal from reacting with air.
Welding can also be carried out in an atmosphere of complete control. It must be observed when it is required to avoid even the possibility of contamination of the seam. Such requirements are put forward for the most critical welding work with a guarantee of 100% purity.
If it is necessary to connect parts of small volume, the work is carried out in a special chamber, which is completely filled with an inert gas. In order for the welder to see the entire scope of work, the chamber is equipped with a special window.
If it is necessary to connect large structural elements, the work is carried out in a hermetically sealed room. Any welding should be carried out by trained people, and in this situation only more professional welders with impressive experience are allowed to work. For them, life support systems are provided in the room.
Other Ways to Connect Titanium Parts
Sometimes welding titanium looks impractical. In this case, soldering is often used. This kind of processing of titanium material is rather complicated. The reason is that when exposed to temperature, the oxide film on the surface of the part leads to a very weak connection, regardless of which metal titanium is soldered to. Therefore, of all the metals that ideally interact with titanium during soldering, only aluminum and high-purity silver are suitable.
Another way to connect titanium products to each other or to parts made of other metals is riveting. This method, like the use of bolts, is mechanical. If a titanium rivet is placed, the work is significantly lengthened. When using bolts, it is necessary to cover them with Teflon or silver, otherwise titanium sticking cannot be avoided, and the connection itself will be quite fragile.
Ways to neutralize the minuses of titanium
The disadvantage of this unique metal is scuffing, sticking, which occurs during friction. The result is accelerated wear of the titanium alloy. If metal milling is used, this circumstance cannot be ignored. Sliding on a metal surface, titanium reacts and begins to stick, gradually absorbing the entire part.
However, the top layer of titanium can be made more durable, resistant to abrasion and sticking. In particular, nitriding is used for this purpose. The method consists in keeping the part in nitrogen gas. The product must be heated to an average of 900 degrees, and the exposure time is more than a day. As a result of nitriding, the surface of the element is covered with a nitride film, which gives titanium a special hardness. As a result, the wear resistance of the titanium part is increased.
Another method to improve the properties of a metal is its oxidation. It helps eliminate sagging. The titanium part must be heated so that an oxide film forms on its surface. It tightly covers the top layer of metal, not letting air inside.
Oxidation can be low- and high-temperature. In the latter case, the product is kept for several hours in a heated state, and then lowered into cold water. This helps to eliminate scale. The part oxidized in this way becomes more resistant to wear by several orders of magnitude at once.
Milling titanium parts
Titanium is used in a wide variety of industries, including aircraft and astronautics. In these industries, parts made of titanium are most often used.
It should be borne in mind that metal milling is complex. Therefore, for such work, it is required to use sharp cutters with increased speed. It is also necessary to reduce the contact of the part with the cutter as much as possible. Milling starts in an arc, and at the end of the work, the chamfer must be removed at a certain angle.
The qualification of a miller plays a serious role not only in the performance of the work itself, but also in determining their cost. Much will also depend on how complex the geometry of the element created from titanium looks.
The machinability of steel depends on the composition of alloying elements, heat treatment methods and the method of obtaining the workpiece (casting, forging, etc.).
When machining mild steels, the main problem is the formation of build-up and burrs. When machining high hardness steels, the relative position of the workpiece and cutter is important to prevent chipping of the cutting edge.
When milling steel, always strictly adhere to our recommendations for positioning the cutter to avoid excessive chip thickness at the exit, and if possible, do not use coolant, especially when performing roughing.
Stainless steel milling
Stainless steel can be divided into ferritic/martensitic, austenitic and duplex (austenitic/ferritic). At the same time, for each type, its own recommendations for milling are offered.
Milling ferritic/martensitic stainless steel
Material classification: P5.x
Ferritic stainless steels have similar machinability to low-alloy steels and can therefore be machined using general guidelines for milling steel.
Martensitic stainless steels are more prone to work hardening during cutting and cause very high cutting forces when plunging into the workpiece. For best results, choose the correct tool path and arc cut entry method, and more high speed cutting v c to overcome the hardening effect. Higher cutting speeds and a tougher grade combined with a stronger cutting edge contribute to improved stability.
Milling of austenitic and duplex stainless steel
Material classification: M1.x, M2.x and M3.x
The main types of wear during milling of austenitic and duplex stainless steels are chipping of the cutting edges resulting from the occurrence of thermal cracks, the formation of notches and built-up edges, and material sticking. Typical part defects include burr formation and poor surface quality.
Thermal cracks
Cutting edge chipping
Burr formation and poor surface quality
- To avoid build-up on cutting edges, select a high cutting speed ( v c = 150 - 250 m/min).
- Run dry to minimize the risk of thermal cracking
- Sometimes it is necessary to apply a coolant, preferably in the form of an oil mist or a very thin film, to improve the surface quality. When finishing milling, the risk of thermal cracking is reduced, since less heat is generated in the cutting zone.
- Use cermet type alloys to ensure High Quality surfaces when working without coolant
- Feed value too low f z can cause excessive insert wear as the cutting edge will work in the case hardened zone.
Cast iron milling
There are five main types of cast iron:
- Gray cast iron (GCI)
- Nodular Cast Iron (NCI)
- Ductile iron (MCI)
- Tempered malleable iron (ADI)
Gray cast iron (GCI)
Material classification: K2.x
The main types of wear in the milling of gray cast iron are abrasive wear along rear surface and thermal cracks. Among the characteristic defects of parts are chipping in the area where the cutter exits from cutting and the poor quality of the machined surfaces.
Typical insert wear
Painting on parts
- Run dry to minimize the risk of thermal cracking carbide inserts thick coated.
- In case of chipping of the workpiece material:
- Check flank wear
- Reduce feed f z to reduce chip thickness.
- Choose sharper geometry
- Preferably use 65/60/45 degree cutters
- When it is necessary to use coolant for the deposition of dust particles, select the appropriate grades of alloys.
- The first choice should always be coated carbide. However, it is also possible to use ceramics. Please note that the cutting speed v c must be very high: 800 to 1000 m/min. The formation of burrs on the workpiece limits the cutting speed. Do not use coolant.
- Use thin or uncoated carbide inserts.
- For finishing at high cutting speeds, CBN-based grades can be used. Do not use coolant.
Nodular cast iron
Material classification: K3.x
The machinability of ferritic and ferritic-pearlitic nodular cast iron is very close to that of low alloy steels. In this regard, the choice of tools, grades and insert geometries can be guided by general recommendations for milling steels.
Pearlitic nodular cast iron is more abrasive and therefore recommended for use with cast iron grades.
For best results, use PVD coated grades with coolant.
Compact graphite cast iron (CGI)
Material classification: K4.x
This type of CGI iron often has an 80% pearlitic structure and is most commonly milled. Typical parts include engine blocks, cylinder heads and exhaust manifolds.
Circular milling can be a great alternative to traditional CGI cylinder boring.
Tempered malleable iron (ADI)
Material classification: K5.x
As a rule, roughing is carried out in a non-hardened state and can be compared to milling high-alloy steel.
On the contrary, finishing is carried out on hardened material, which is highly abrasive. This process can be compared to milling hardened steels of the ISO H group. Therefore, it is preferable to use grades with high abrasion resistance.
Compared to milling compacted graphite iron, tool life in tempered ductile iron is about 40% lower and cutting forces are about 40% higher.
Milling of non-ferrous metals
The group of non-ferrous metals includes not only aluminum alloys, but also alloys based on magnesium, copper and zinc. Machinability may vary, primarily depending on the silicon content. The most common type is hypoeutectic aluminum with a silicon content below 13%.
Aluminum with silicon content below 13%
Material classification: N1.1-3
The main types of wear are build-up and sticking of material on the cutting edges, which leads to the formation of burrs and deterioration of the quality of the machined surfaces. Good chip formation and evacuation is essential to prevent scratches on the surfaces of parts.
Cutting insert with PCD inserts
- Use inserts with PCD inserts and a sharp, polished cutting edge for good chip control and built-up prevention.
- Choose inserts with positive geometry and sharp cutting edges.
- Unlike milling other materials, aluminum alloys must always be machined with coolant. This prevents sticking of material on the cutting edges and improves the quality of machined surfaces.
- Silicon content< 8%: Используйте СОЖ с концентрацией 5%.
- Silicon content 8-12%: Use coolant with a concentration of 10%.
- Silicon content > 12%: Use coolant with a concentration of 15%.
- Higher cutting speeds generally improve results and do not adversely affect tool life.
- It is recommended to choose a value h ex in the range from 0.10 to 0.20 mm. Too low values can lead to burr formation.
Attention: do not exceed the maximum speed of the cutter.
- Due to the high minute feed, perform machining on machines with a path calculation function based on pre-reading and program code analysis to avoid dimensional violations.
- Tool life is often limited by burr formation and poor quality treated surfaces often. Insert wear cannot be a criterion for tool life.
Milling of high temperature alloys (HRSA)
Heat Resistant Alloys (HRSA) can be divided into three groups: nickel, iron and cobalt based alloys. Titanium can be commercially pure or be part of an alloy. Both high-temperature and titanium alloys are characterized by poor machinability, especially after aging, which places special demands on cutting tools.
Heat resistant alloys and titanium
Milling of high temperature alloys and titanium often requires machines with high rigidity, as well as high power and torque at low speeds. Notching and edge chipping are the most common types of wear. The release of a large amount of heat limits the cutting speed.
Use round inserts to minimize notching
- Always use round inserts whenever possible to enhance chip thinning effect
- With a depth of cut of less than 5 mm, the entering angle must be less than 45°. In practice, it is best to use round inserts with positive geometry.
- High cutter accuracy in both axial and radial direction is essential to maintain a constant tooth load and process stability and avoid damage to individual cutter inserts
- It is recommended to choose inserts with positive geometry and optimized cutting edge rounding to avoid chip buildup at the edge exit from the cut.
- The effective number of teeth involved in the cutting process should be as high as possible. This will provide good performance with proper stability. Use cutters with fine pitch
= tool life
= decrease in tool life with increasing cutting data
Changing cutting conditions affects tool life to varying degrees. Cutting speed has the biggest impact v c , then a e, etc.
coolant
Unlike the milling of most other materials, machining must always be carried out with coolant. This makes it easier to remove chips, limit heat generation in the cutting zone and prevent chip recutting. In this case, it is preferable to supply coolant through the spindle/tool at high pressure (70 bar) instead of external supply at low pressure.
Coolant through the tool
provides certain advantages in
using carbide inserts
Wear of cutting inserts/tools
Notching, excessive flank wear, and edge chipping are the most common causes of tool breakage and poor surface finishes.
The best way to avoid this is to change the cutting edges regularly to ensure a reliable and stable process. Flank wear should not exceed 0.2 mm for cutters with a 90 degree entering angle, and a maximum of 0.3 mm for round inserts.
Typical insert wear
Cutter with ceramic inserts for roughing high temperature alloys
Cutting speeds with ceramic inserts are typically 20 to 30 times faster than with carbide, at lower feed rates (~0.1 mm/t), resulting in higher productivity. Due to the interrupted nature of the cut, less heat is generated during this operation than when turning. As a result, cutting speeds can reach 700–1000 m/min in milling compared to 200–300 m/min in turning.
- Preferably use round inserts to maintain a small entering angle and prevent notching
- Do not use coolant.
- Do not use ceramics on titanium.
- Ceramic renders Negative influence on surface properties and therefore should not be used in finishing machining steps.
- The maximum flank wear when using ceramic inserts for machining high temperature alloys is 0.6 mm.
Milling hardened steels
This group includes hardened and tempered steels with a hardness > 45–65 HRC.
Typical parts for milling:
- Tool steel embossing dies
- Press forms
- Forging dies
- foundry dies
- fuel pumps
The main problems are abrasive wear on the back surface of the inserts and chipping of the workpiece material.
- Use inserts with positive geometry and sharp cutting edges. This will reduce cutting forces and provide a smoother cutting process.
- Work without coolant.
- A suitable method is trochoidal milling, which involves high minute feeds combined with low cutting forces, which helps to reduce the temperature at the cutting edge and workpiece and, as a result, positively affects productivity, tool life and dimensional accuracy of parts.
- In face milling, it is also recommended to use a machining strategy that can be described as "light and fast", i.e. with a small depth of cut. a e and a p . Use fine pitch cutters and choose a relatively high cutting speed.
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