01
Steel milling
The machinability of steel varies with alloying elements, heat treatment, and manufacturing processes (forging, casting, etc.).When processing soft mild steel, the main problem is that it will produce debris and burr on the workpiece.When machining hard steel, the position of the milling cutter relative to the workpiece will become more important in order to avoid edge collapse.
Advice:
When milling steel, optimize the position of the milling cutter to avoid the return of large thickness of the chip, must be considered in the case of cutting fluid without the use of dry cutting, especially in the process of rough machining.
02
Stainless steel milling
Stainless steels can be classified as ferritic/martensitic, austenitic, and duplex (austenitic/ferrite) stainless steels, each with its own milling recommendations.
1) ferritic/martensitic stainless steel milling
Material classification: p5.x
The machinability of ferritic stainless steel is similar to that of low alloy steel.
Martensitic stainless steel has higher working hardenability and requires very high cutting force when cutting in.Using the correct tool path and circular cutting method to obtain the best results, using higher cutting speed Vc to overcome the hardening effect.Higher cutting speed and higher toughness materials and enhanced cutting edges ensure higher safety.
2) austenite and duplex stainless steel milling
Material classification: m1.x, m2.x and m3.x
The main wear criteria for austenitic and dual phase stainless steel milling are cutting edge breakage due to thermal cracking, groove wear and chip/bond.For parts, burr formation and surface quality problems are the main problems.
Suggestions for rough machining:
Use high cutting speed (Vc=150-250m/min) to avoid debris accumulation
Dry cutting without cutting fluid to minimize the problem of heat cracking.
Suggestions for finishing:
1) in order to improve the surface quality, sometimes it is necessary to use cutting fluid or preferably oil mist/trace lubrication.There are fewer hot crack problems during finishing because less heat is generated in the cutting area
2) when cermet material is used, good surface quality can be obtained without cutting fluid
3) too low feed fz may lead to more severe wear of the blade due to the cutting edge cutting in the deformation and hardening area
03
Cast iron milling
1) grey cast iron
Material classification: k2. x
The main wear criteria for grey cast iron milling are abrasive/back face wear and thermal cracking.For parts, the main problems are edge breakage and surface quality.
Suggestions for rough machining:
1) it is best to dry cut without using cutting fluid to minimize the problem of heat cracking.Use thick coated carbide blades.
2) in case of workpiece edge collapse:
After inspection, the tool face is worn
Reduce feed fz to reduce chip thickness
Use a groove with a larger front Angle
Preferably use a 65°/60°/45° milling cutter
3) if the cutting fluid must be used to avoid dust, choose wet milling material.
4) coated cemented carbide is always preferred, but ceramic materials can also be used.Note that the cutting speed Vc should be very high at 800-1000m/min.Burrs on the workpiece limit the cutting speed.Do not use cutting fluid.
Suggestions for finishing:
1) use thin coated carbide blades or, alternatively, use uncoated carbide blades.
2) CBN material can be used for high speed finishing.Do not use cutting fluid.
2) ductile iron
Material classification: k3.x
1) the machinability of ferrite nodular cast iron and ferrite/pearlite nodular cast iron is very similar to that of low alloy steel.Therefore, milling Suggestions for steel materials should be used when selecting cutter, blade groove and material.
2) the pearlite ductile iron has higher abrasion, so it is recommended to use cast iron.
3) using PVD coating material and wet cutting can ensure the best machining capacity.
3) vermicular cast iron (CGI)
Material classification: k4.x
Pearlite content is below 90%.CGI of this type, which is most commonly used for milling, typically has about 80% pearlite structure.Typical components are the engine block, the cylinder head, and the exhaust manifold.
The recommendations for milling cutters are the same as for processing gray cast iron;However, a groove with a sharper cutting edge and a larger front Angle should be selected to minimize burrs on parts.Circular milling may be a good alternative to the traditional CGI cylinder boring method.
4) isothermal quenched ductile iron (ADI)
Material classification: k5.x
Rough machining is usually performed in a non-hardened state and can be compared to high alloy steel milling.However, the object of the finishing process is the hardened material with very high abrasiveness.This is comparable to ISO H hardened steel milling.The material with higher wear resistance is the first choice.Compared with NCI, the tool life is shortened to about 40% and the cutting force is increased by about 40%.
04
Milling nonferrous materials
Nonferrous materials include not only aluminum alloys, but also magnesium, copper, and zinc-based alloys.Machinability is mainly different with the silicon content.Subeutectic al-si alloys are the most common type, with a silicon content of less than 13%.
1) aluminum alloy with less than 13% silicon content
Material classification: n1.1-3
The main wear standard is the presence of a chip burr/bond on the cutting edge, resulting in burr formation and surface quality problems.In order to avoid scratches on the surface of parts, good chip forming and chip removal is very important.
Advice:
1) use PCD insert with sharp polishing cutting edge to ensure good chip breaking ability and prevent chip accumulation.
2) select the groove of the front corner blade with a sharp cutting edge.
3) unlike most other milling applications, aluminum alloys should always be processed with cutting fluid to avoid material bonding to the cutting edge of the blade and to improve surface quality.
Silicon < 8% : use a cutting fluid with a concentration of 5%
Silicon < 8-12% : use a cutting fluid with a concentration of 10%
> silicon 12% : use a cutting fluid with a concentration of 15%
4) higher cutting speeds generally improve performance without negatively impacting tool life.
5) the recommended hex value is 0.10-0.20mm (0.0039-0.0079in).Too small a value can lead to burr formation
6) due to the high table feed, should use the machine with the function of "pre-reading" to avoid size error.
7) tool life is always limited by the parts of the burr formation or surface quality.Blade wear is difficult to use as a tool life standard.
05
Superalloys and titanium alloys
Milling superalloys and titanium usually requires machine tools with high rigidity, high power and high torque to operate at low speeds.Groove wear and cutting edge breakage are the most common types of wear.The high heat produced limits the cutting speed.
Advice:
Use milling cutter with round blade as far as possible to increase chip thinning effect.
The use of circular blade milling cutters minimizes groove wear
When the cutting depth is less than 5mm, the main deflection Angle should be less than 45°.In practice, it is recommended to use a round front blade.
The radial and axial precision of the milling cutter is a necessary condition to maintain a constant load per tooth and smooth operation and to prevent the premature damage of a single blade.
The cutting edge shall always be of a straight front groove and be rounded with an optimized cutting edge to prevent chips from adhering to the cutting edge when the cutting edge is returned.
The actual number of cutting teeth involved in cutting during milling should be as large as possible.Under stable operating conditions, this will achieve ideal productivity.Use super - dense gear milling cutter.
Cutting fluid/coolantUnlike most other materials used in milling, coolant is always recommended to assist chip removal to control the heat at the cutting edge and to prevent chip secondary cutting.The preferred option is always internally cooled high pressure coolant (70 bar) applied through the spindle/tool rather than externally cooled and low pressure coolant.
Exception: when milling with ceramic blades, cutting fluid should not be used due to thermal shock.
When using carbide blades, internal cooling can be beneficial
Blade/tool wear
The most common causes of tool breakage and poor surface quality are groove wear, excessive wear on the back surface and edge line breakage.
The best solution is to rotate the cutting edge frequently to ensure reliable processing.The surface wear behind the cutting edge should not exceed 0.2mm(for milling cutters with 90° main deflection) or a maximum of 0.3mm(for round blades).
Ceramic cutter for rough machining of high temperature alloy
Ceramic milling is typically 20-30 times faster than carbide milling, although the feed rate is lower (about 0.1mm/z), which leads to a significant increase in productivity.Because of the use of intermittent cutting, the temperature of the milling process is much lower than that of turning.Therefore, the cutting speed of 700-1000m/min is used in milling, compared with 200-300m/min in turning.
Advice:
1) circular blades are mainly used to ensure small main deflection Angle and prevent groove wear.
2) do not use cutting fluid/coolant.
3) do not use ceramic blades when processing titanium alloys.
Ceramics can have a negative impact on surface integrity and other indicators, so do not use ceramic blades when you are about to process the shape of finished parts.
5) the maximum wear of the rear cutting surface is 0.6mm when the ceramic blade is used to process the superalloy.
06
Milling of hardened steel
The group contains tempered steels with a hardness greater than 45-65HRC.The typical parts of milling are stamping die, plastic die, forging die, die casting die, etc.The main problems are abrasive wear on the blade/back surface and edge breakage of the workpiece.
Advice:
1) use the groove type of the front corner blade with a sharp cutting edge.This will reduce the cutting force and produce a smoother cutting effect.
2) dry cutting, avoid using cutting fluid.
3) cycloid milling is an appropriate method, which can simultaneously achieve high table feed and low cutting force, so that the cutting edge and workpiece keep low temperature, which is beneficial for productivity, tool life and part tolerance.
4) in face milling, the processing strategy of light cutting should also be adopted, that is, keeping small cutting depth ae and ap at the same time.Use of super-dense gear milling cutters and relatively high cutting speeds.