초경인써트 제조 공정
CVD vs PVD 코팅
CVD (Chemical Vapor Deposition - 화학적 증착법)
In a CVD coating process, the coating is formed by a chemical reaction of different gases. The inserts are loaded into the coating chamber on special trays designed to fit each insert style. Temparature, time, gas flow, gas atmosphere … are carefully monitored to steer the deposition of the coating layers. Depending on what type of coating, the temperature in the reactor is from about 800 to 1100 degrees centigrade. The thicker the coating, the longer process time. The thinest CVD coating today is below 4 microns and the thickest is above 20 microns. (Note: the human hair is approx 75-80 microns).
The advantages with CVD are:
• The ability of making thick coatings
• Ability to make even coating thickness
• Very good adherence to the carbide substrate
• The very good wear resistance
• Possibility to make oxide coatings
PVD (Physical Vapor Deposition - 물리적 증착법)
TiN or Ti(C,N) or
TiAlN or TiAlCrN
In a PVD coating process, the coating is formed by metal vapour condensating on insert surfaces. The inserts are loaded into the coating chamber on special trays designed to fit each insert style. Several metal sources (so called targets) are placed on the reactor chamber walls. The most common metal source is Titanium (Ti). These targets are heated, by using electricity, to such a high temperature that the solid metal turns to metal iones. By using a gas a s carrier these iones can then be transported from the targets to the inserts. Since the iones will percieve the inserts as being cold, the iones will condensate on the inserts. PVD actually works pretty much the same way as when humid air condensates on cold roads and forms a icelayer on the road. That is PVD but in large scale. As in CVD it is eqully important in PVD to have careful control of temparature, time, gas flow, gas atmosphere …
•PVD is done at a much lower temperature than CVD. Normal PVD process temperatures are around 500 dergrees centigrade. It is therefore the only possible coating method for products with brased tips since the brasing will melt in the high CVD temperatures. The coating thickness is in the range of 2-6 microns depending on application area for the insert.
One limitation with PVD is that it is a “line of sight” coating deposition. This means that only the parts of the inserts that are facing towrds the metal targets will get coating. Therefore inserts are mounted on caroussels that rotate during the coating process. This way one can esure to get coating on all sides of the insert. However there will still be some difference in coating thickness between the clearance side and the rake face on an insert (with hole) since the rake face will not directly be facing the target. In this case, the insert will have thicker coating on the clearence side than on the rake face. This is also the reason why you do not see coating in the holes of PVD coated inserts. Inserts without holes are mounted on magnetic tubes and have the rake face facing towards the targets and there you will get thicker coating on the rake face then on the clearence side.
The advantages with PVD coatings are:
• PVD gives good edgeline toughness.
• PVD maintains sharp edges.
• PVD can be used on brased tips.
• PVD can be used on solid carbide tool and tips.