16-05-2014, 02:18 PM
A SEMINAR REPORT ON HARD COATING ON TOOLS
HARD COATING .doc (Size: 91 KB / Downloads: 122)
ABSTRACT
Present seminar report covers new features of TiN TiA1N, etc. special coating on cutting tools. The initial articles deal with necessity and types of tool coating. The industrial tool coating procedures PVD and CVD have been explained in detail. Preparation of tool surface for coating process is equally important for good adhesion and long life. The performance of coated tools is critically examined in various applications under several parameters. These results are graphically represented for better understanding. Different types of coatings having different properties are discussed. The relative performances of various coatings are graphically represented for milling cutters and drills.
INTRODUCTION
Wearing of machine tools is a major problem in machining industry. Since more and more processes are automated and interlinked wearing of individual parts hinder the process. The increasing time raises the cost of the products. Hence wear protection is essential from the economic viewpoint. Multilayer coating of mechanical resistant materials (hard coating) have proved successful in increasing the life of machine tools.
It is proved for a long time that nitrates and carbides of certain compounds are
very hard. These materials exhibit good sliding behaviour and extremely high resistance to wear. Though these materials are brittle and fracture susceptible in bulk solid state they exhibit totally different properties when coated in thin film form.
Thin coating of nitrates and carbides on steel and other tools confirm to the toughness of the base material. Due to these coatings extremely hard, abrasion resistant surfaces are produced. The coating increases the toughness of the surface (wear resistance) secondly, certain coatings like titanium nitrate (TIN) gives attractive golden appearance to the surface. This property is used in increasing the appearance of the finished product.
With this data at hand an extensive study of the hard coating processes is under taken in the present seminar. The coating processes (CVD, PVD) are studies in details. The relative merits and demerits of these processes are compared. The increase in tool life as a result of coating is compared from standard data. Attempt is also made to explain the physical significance of increase in strengths. Essential diagrams and industrial data from standard source supplement the present study.
NECESSITY OF COATING
The industrialists had to increase their production, due to pressure to ever increasing human needs. This lead to improve and innovations in the existing technology, which in turn helped to increase the productivity and efficiency then existing units.
Industrial production is largely dependent on the state of technology and its advancements. Machinery and tools play a vital role in production process. In fact it is the key factor for improving productivity. This motivated the scientists and technicians to think of modifying and improving tools.
In the year 1984, the process of coating tools was first introduced. This was important landmark in the history of industrially advanced countries. Even though the tool existed in the olden days, they were far inferior and suffered from many drawbacks, some of them are-
i) Firstly, tools were short lived; they were used to become useless after one use.
ii) This lead to enormous wastage of material and labour, the cost of which could not imagine.
iii) Need for changing and resetting the new tools every now and then was the main hurdle in the productivity as there was lot of wastage of time for changing and resetting the tools.
These all drawbacks lead to the invention of coating tools which has helped to increase the productivity nearly 2.5 times than the original. Thus, coating process is boon for the modern industry.
Surface Preparation
Coating improves only top quality tools. Tools with coarse and rough surfaces may not perform as designed after coating, since the coating material may wear unevenly over the high spots finely ground surfaces free from burrs grinding burns, grinding resides glazing and cracking provide optimum coating adhesion. The coating centre may reject tools showing any of these problems.
Polishing, burnishing, and buffing should be carried out to avoid incorporating abrasive compounds into the substrate trapped compounds can cause coating adhesion problems.
Over polishing and EDMing both leave residual stress in the tool. Subjecting the tool to PVD temperatures will relieve those stresses, which can cause the warping or dimensional changes. Residual stress should be relieved before the tools is shipped for coating by heat treating it to 500F less than the ideal tempering temperature.
Once the tools have safely arrived at the coating centre, they undergo a final inspection and cleaning immediately prior to coating.
Titanium Nitride Coating
Titanium ‘Nitride(Tin) is one of the best of the new ultra-hard coatings for gear cutting tools. Press tools and other engineering tools and parts. The performance of HSS cutting tools can be enhanced by TiN coating which give greater chip removal rates as well as INCREASED TOOL LIFE. TiN coating virtually eliminates the formation of built-up edge, and also protects the base material from abrasive wear. TiN can applied to finished precision tools by physical vapour deposition (PVD) and chemical vapour deposition (CVD) which are widely employed the world over.
IONVAC uses the physical vapour deposition (PVD) method, which offers considerable technical and economical advantages over the chemical vapour deposition method.
Physical vapour deposition (PVD Arc) is a new process switch is accepted to provide increased life and productivity for cutting and ornamental applications and of wear and corrosion. This process can be applied to finished products without affecting prior metallurgy dimension clearance surface finish, edge sharpness or degree of distortion.
Tin is a very hard wear resistant applied coating which has been shown to greatly increase the life and performance of cutting tools particularly high speed steel cutting tools and other steel components subjected to several operations. TiN coating has been applied to carbide inserts since the 1960.
Application
IONVAC technique of TiN coating is widely used for metal cutting application. The following tools are currently being coated in this field of application resulting in substantial increases in the lifetime.
Hob Cutter, Shaper Cutter, Broaches, Coniflex Cutter, Shaving Cutter, Pinion type Cutter, and Milling Cutter are some of the applications. Another wide field of application is for metal forming tools. Coating of the metal forming tools not only leads to considerable increased lifetime, but frequently improves the quality of the machined workpieces, with a much better surface finish. The following tools are currently being coated in this field. Form Tools, Piercing Punches, Trimming dies, Cold heading dies, Thread Chasers, Thread Rollers and Die plates. In addition to this the following tools are also currently being coated with IONVA – TiN coating to enhance the life time. Drills, Taps, End Mills, Reamers and Carbide Inserts.
Titanium Aluminium Nitrate Coating (TiAIN)
TiAIN is the newest PVD hard coating for carbide / H.S.S. tools with the substitution of aluminium for some of the titanium in the coating. TiAIN develops an amorphous AI2O3 layer on the surface of the coating at very high temperatures. This allows TiAIN to retain its hardness at higher temperatures than any coating. Thus TiAIN out performs those coatings in application such as high-speed continuous turning operations. Most tool coaters prefer powder-metal (PM) TiAI source for TiAN coating because they are easier and cheaper to machine for the coatings properties depend greatly on aluminium percentage in the coating. TiAIN has hardness of 300 – 3300 (HK 0.05 on hard metal) with higher roughness of Ra 0.67 to 0.75 in micro mm. It has a higher oxidation stability (upto 800 °C) than any other coatings. It also gives good ductility and adhesion to besaid coating TiAIN coating can be used for wear protection in applications like interrupted cut, difficult machining materials like Titanium and it’s alloys/ nickel alloys stainless steel and cast materials.