CVD can be coated with TiCN with excellent wear resistance and Al2O3 thick film with excellent heat resistance.
Therefore, it can show long service life in high-speed and high-efficiency machining that produces high temperature.
PVD is generally used at the same or higher cutting speed as uncoated cemented carbide and high-speed steel to prolong tool life.
It has less restriction on the substrate and less damage, so it is especially suitable for tools requiring wear resistance and edge collapse resistance, and also suitable for low feed machining and finishing or thread machining tools requiring sharp edges.
CVD coating is shown in Fig. 2-23.
Fig. 2-23 CVD coating
PVD coating is shown in Fig. 2-24.
Fig. 2-24 PVD coating
In the cooling process after coating, the difference of thermal shrinkage between the coating film and the substrate will lead to internal deformation in the coating film, resulting in residual stress.
The residual stress of CVD method is shown in Fig. 2-25, and that of PVD method is shown in Fig. 2-26.
Fig. 2-25 CVD residual stress
Fig. 2-26 PVD residual stress
The coating treatment of cutting tools is one of the important ways to improve the performance of cutting tools.
The appearance of coated tools has greatly improved the cutting performance of cutting tools, and the application field is expanding.
Coated tools have great potential in the field of NC machining, and will be the most important tool variety in the field of NC machining in the future.
At present, the coating proportion of cemented carbide indexable inserts abroad is more than 70%, and that of European gear cutters is as high as 90%.
The coating technology has been applied to end mills, reamers, compound hole machining tools, gear hobs, gear shaving cutters, forming Broaches and various machine clamps, which can be converted into blades to meet the needs of high-speed machining of various steel and cast iron, heat-resistant alloys, non-ferrous metals and other materials.
Table 2-23 shows the application scope of coated tools by CVD and PVD methods.
Table 2-23 respective application scope of CVD method and PVD method
| CVD method | PVD methods | |
| Suitable processing conditions | 1. Machining with high cutting temperature (high-speed machining, large feed machining);2. Mass processing;3. Processing with a certain amount of back cutting;4. Tool linear feed. | 1. Machining with small back cutting amount;2. Large feed processing;3. Machining with high requirements for machining surface;4. Processing of easily bonded workpiece materials;5. Processing of back cutting amount change;6. Tool curve, multi angle feed. |
| Main coating substances | TiC, TiCN, TiN, Al2O3 | TiC, TiCN, TiN.（Al, Ti） N, (Al, Ti, Si） N, CrN |
| Advantages | 1. It can be coated with Al2O3 with excellent thermal stability, which can be used for high-speed machining;2. The substrate and coating have good tightness, which can form a relatively thick coating with excellent wear resistance and long service life;3. By changing the feed gas, multiple substances can be continuously coated in the same unit. Easy to apply multiple layers of material. | 1. It can be coated at lower temperature (below 700 ℃), so it has less restriction on the substrate. It can be applied to high-speed steel, welding tools, cemented carbide, cermet and other materials;2. The strength (toughness) of the cutting edge decreases less.Applicable to cutting tools with sharp edges;3. Compressive residual stress is generated on the coating film, which has strong wear resistance and heat cracking resistance;4. The coating surface is smooth and suitable for finishing. |
| Disadvantages | 1. It needs to be treated at high temperature (900~1100 ℃), so it has restrictions on the base material and is not applicable to high-speed steel and welding tools. The matrix is limited to cemented carbide;2. It may cause the strength of the surface and cutting edge to decrease. It is not applicable to the cutting tools with sharp edges that are easy to be damaged;3. Tensile residual stress is generated on the coating film, which will reduce the damage resistance. Special cemented carbide matrix materials are required;4. the coating surface is easy to fuzz, and bonding may occur during finishing. | 1. It is difficult to coat various non-conductive oxides (insulators);2. The substrate is difficult to be close to the coating and is not suitable for thick film coating;3. The adhesion of coating is worse than that of CVD. |
|
Suitable processing conditions |
CVD method |
PVD method |
|
|
Adaptability to various cutting tools |
Blade for general turning |
suit |
More suitable |
|
Ordinary milling blade |
suit |
suit |
|
|
Drilling blade |
Suitable platform |
suit |
|
|
Precision machining blade |
More suitable |
suit |
|
|
Integral and welded end milling cutter |
Not suitable |
suit |
|
|
Integral and welded drill bit |
Not suitable |
suit |
|
The coating selection for steel processing is shown in table 2-24, and that for cast iron processing is shown in table 2-25.
Table 2-24 coated tools for machining steel
| Coating | Application | Remarks |
| I universal coating | ||
| Physical vapor deposition of TiN coating on particulate substrate | Cemented carbide coating | Especially suitable for high quality taps |
| Chemical vapor deposition TiC/TiCN/TiN coating | Usually used to process steel | Low and medium speed machining |
| Chemical vapor deposition TiCN/IiN/-TiC-TiCN/Al2O3/TiNcoating | Preferred tool for machining steel | High wear resistance and high strength |
| Chemical vapor deposition TiCN/Al2O3/TiN coating | It can cut and process steel in a wide range | It can also be used to process Cast Iron |
| TiC+TiCN/a-Al2O3 coating | Finish and semi rough machined carbon and alloy steels | The most wear-resistant tool material in common tools |
| Multilayer Al2O3 Ti (N, B) chemical vapor deposition coating | High speed turning of carbon steel and stainless steel | Resistance to oxidation and adhesive wear |
| Ⅱ coatings used in different processing methods | ||
| TiCN/TiC/Al2O3 coating | Machining stainless steel | It is not easy to form swarf |
| TiCN/Al2O3/TiN chemical vapor deposition composite coating on high strength substrate containing cobalt | Intermittent processing steel and stainless steel | Wear resistance and high strength |
| TiCN/Al2O3/TiN chemical vapor deposition composite coating on high hardness substrate containing cobalt | Dry cutting can be carried out in excess of 300m/min | Best high temperature resistance |
| TiN/Al2O3/TiCN/TiC/TiCN/IiN chemical vapor deposition composite coating on cobalt containing cemented carbide substrate | Heavy duty intermittent cutting | Highest strength |
| Physical vapor deposition of TiAIN coatings on particulate substrates | Finish milling die steel at the speed of 120~150m/min | Coating on integral square shoulder end milling cutter and spherical milling cutter |
| Physical vapor deposition TiAIN/TiN coating on Cermet substrate | Finish machining and semi finish plus intermittent cutting with cutting fluid | Good resistance to thermal vibration and cracking |
| Physical vapor deposition of TiN coating on welded CBN tip | High precision Turning Hardened Steel at high speed | The coating increases the strength and wear resistance of the tool tip |
| Physical vapor deposition of TiAIN coating on welded CBN tip | High speed continuous cutting or medium speed intermittent turning of hardened steel | Good wear resistance and long tool life |
Table 2-25 coated tools for machining cast iron
| Coating | Recommended application range | Remarks |
| TiCN/Al2O3/TiNchemical vapor deposition, in which TiCN and A12O3 are thick coatings | Turning gray cast iron rotary parts, coating the same material on the high-strength substrate can be used for heavy cutting | High wear resistance and high temperature performance |
| TiCN/2×A12O3/TiNchemical vapor coating | High speed turning cast iron | Al2O3 thick coating and high hardness tin layer, with strong wear resistance |
| Chemical vapor deposition of TiCN/Al2O3 coatings on hard substrates | High speed turning grey cast iron | Anti flank wear |
| Chemical vapor deposition of TiCN/Al2O3 coatings on special substrates | Cutting ductile iron at speeds up to 200m/min | It has good adhesion resistance, with ultra-fine a1,03 layers |
| Integral cubic boron nitride tool coated with TiN | High speed processing pearlitic gray cast iron; First choice for processing chilled cast iron | Good abrasion resistance |
| Coating TiN and Al2O3 on Si3N4 ceramic matrix | Common grades of high-speed intermittent machining cast iron | With or without cutting fluid |
Common CVD and PVD coating grades are shown in table 2-26.
|
Type |
Shop sign |
Picture |
|
CVD coating |
GC2015（M15，P25） GC2015 has a substrate dedicated to high-speed cutting. The gradient zone near the substrate surface has strong toughness, which can provide better edge safety. The multi-layer coating up to 5.5μm thick can provide good heat and wear resistance, reduce friction and avoid the formation of chip nodules. |
|
|
GC235 (M40, P45) GC235 has a very strong base, which can provide excellent cutting edge safety. It is coated with a 2.5μm cvdtic TiCN TiC coating to ensure stronger wear resistance and lower friction. GC235 meets the needs of rough machining applications, such as intermittent cutting and low-speed cutting. Excellent performance in low to medium cutting speed steel and stainless steel applications. |
|
|
|
PVD coating |
GC1005 (M15, S15) has 4μm PVD TiAlN TiN coating. The perfect combination of its strong and wear-resistant coating and hard fine grain matrix not only provides the characteristics required for sharp cutting edges, but also has safety and prevents chip impact. In the finishing of high-quality heat-resistant alloy and stainless steel, this brand can obtain very small tolerance and excellent surface quality. |
|
|
GC1020 has a layer of 1~2μm PVD TiN coating on the top of fine grain matrix, which is specially developed to obtain high-quality threads. Excellent performance in material groups P, M and K. |
 |
The correct choice of coating is the premise of rational use of coated tools and full play of coating functions.
Here are three bases for the selection of PVD coating.
First of all, the classification and hardness of workpiece materials should be considered.
Common tin and TiCN are generally used for processing steel and cast iron, and TiAlN can be used for high hardness;
Processing stainless steel coating with good thermal conductivity and anti adhesion;
When machining difficult to machine materials such as titanium alloy and nickel base alloy, with high cutting temperature, TiAlN, AlTiN and other coatings with good heat resistance and high oxidation temperature shall be selected;
CrN coating can be used for processing copper except for general tin;
Wear resistant coating such as TiCN shall be used to process high silicon aluminum alloy;
Diamond coating or tin, TiCN coating shall be selected for processing synthetic materials.
The selection of coating is shown in table 2-27.
Table 2-27 coating selection
| Steel and cast iron | Tin and TiCN coatings are generally selected, and TiAIN or AITiN is selected for high-speed cutting, hard cutting and dry cutting. |
| Stainless steel | Tin and TiCN coatings shall be selected, and TiAIN shall be selected for cemented carbide tools. |
| Titanium alloy nickel base alloy | Tin, TiCN and TiAIN coatings are selected, in which tin is used for low speed and TiAIN can be used for high speed;PCBN brand with good toughness +tiain or AITiN coating;TiCN is suitable for milling. |
| Copper alloy aluminum alloy | Select general TiN, TiCN coating or special ZrN, CrN or DLC coating;TiCN coating is used for machining high silicon aluminum alloy, and diamond coating is used for occasions with high cutting speed. |
| Synthetic materials | TN and TiCN coatings are generally used;Glass fiber and carbon fiber reinforced plastics shall be coated with diamond. |
Secondly, according to the process categories of turning, milling, drilling, tapping and gear hobbing.
For continuous cutting processes such as turning and drilling, the coating with good heat resistance should be selected, while for intermittent cutting processes such as milling and hobbing, the coating with good toughness should be selected, and the coating with small surface roughness value, difficult adhesion and favorable chip removal can be selected for drill bits and taps.
Finally, the cutting conditions are considered.
For low cutting speed, select the coating with wear resistance and adhesion resistance, for high cutting speed, select the coating with high heat resistance and oxidation temperature, and for processing with cooling lubricant, select the coating with good toughness.