Method To Calculate The Tool Life And A Method Which Can Uplift The Production Online Tutoring

ABSTRACT

In a company that is manufacturing in batches which cross digits where the majority of parameters like large scale procurement of raw products and job order and the time consumed in production is much looked into, there was not a devised to calculate the life of the tool. It is  the case for many companies, but we provide a much more reliable and precise method to calculate the tool life.  We proposed a method where a small factor which can make an ultimate uplift to production. A tool is a material which is subjected to wear and friction simultaneously, but a protective layer which can act as a binding layer on the tool surface takes up much of the aftermaths friction and wear. There was a substantial increase in production. And when the batches are in a wide range it can prove its effectiveness.

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Terms and symbols used:

Torr – A unit of pressure, being the pressure necessary to support a column of mercury one millimeter high at 0° C and standard gravity, equal to 1333.2 microbars.  We use this to measure the level of vacuum in our PVD  coating vessels.

LIN       –          Linear Meters (in meters)

N –   Number of Gear Teeth

OD         –          Outer Diameter

NPPC     –          Number of Parts per Cycle (parts in stack)

FW         –          Face-Width (in meters)

Cos (HA) –        Cosine Function Of Gear Helix Angle

USEN –        Usable Length of Hob Teeth (within hob shift limits)

USELEN –         Usable Length of Hob (along hob axis between hob shift limits)

NCP        –       Normal Circular Pitch of the Hob

FLUTES -Number of Flutes

PARTS    –         Parts between Re-Sharpening

CHAPTER 1

INTRODUCTION                 

1. ABOUT THE COMPANY

Bonfiglioli Riduttori was established on 16 April 1956 to put into practice the business ideas of Clementino Bonfiglioli, who brought to his new company years of experience in the design and manufacture of gearboxes for agricultural machinery and motorcycles (including legendary names like Ducati, Gilera and MotoMorini).

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The new company was baptized “Costruzioni Meccaniche Bonfiglioli” and for the first few years of its existence concentrated on the production of gearboxes for the agricultural and motorcycle industries, both highly significant on the local industrial landscape in Bologna at that time.

Towards the mid-1960s, however, a profound transformation began to sweep through the local area: the automation industry rapidly assumed major proportions and a large number of packaging machine manufacturers established themselves in and around Bologna.

The area soon became the centre of the world’s packaging industry and earned itself the nickname of “Packaging Valley”. Bonfiglioli was quick to see the great opportunity that this dramatic change presented and began to design and manufacture a range of power transmission gearboxes that rapidly set new standards for the automation industry.

In particular, Bonfiglioli designed and patented a new two-stage planetary gearbox which proved so successful that no improvements were required for the next fifteen years.

Growth accelerated even further when Bonfiglioli intelligently extended its product range by strategically acquiring other companies.
The acquisition in 1975 of Trasmital, a specialist manufacturer of planetary gearboxes for earth moving machinery based in Forlì, allowed Bonfiglioli to become a leader in that sector. The close attention with which Bonfiglioli monitored the market and its continually changing needs then led to the creation of Bonfiglioli Components, a company dedicated exclusively to the design and production of power transmission components.

With the benefit of hindsight, this policy of specialization and full process manufacturing of all components proved to be such a winner that Bonfiglioli soon found itself occupying the position of leader on all its reference markets.

2. PRODUCT RANGE:

• Combined gearbox
• Planetary drive for mobile application
• Planetary gear motor
• Planetary gears for marine application
• Planetary steering gears for marine applications
• Transit mixer drives
• Wheel drive
• Electric wheel drive
• Solutions for electric airport equipment’s
• Electric power train
• Front wheel drive for grades
• Idle steering systems
• Gear shift final drive
• Pneumatic tyred rollers wheel drive
• Wind turbine yaw control gearmotor
• Filtration module casting
• Fork gear shift

3. CUSTOMERS:

The Bonfiglioli Group, with a turnover of over one billion dollars, is the largest manufacturer of transmission components in world.   CARS/HEAVY VEHICLES: §  CUMMINS §  General Motors §  FORD §  DELPHI TVS §  TATA Motors §  VOLVO §  HYUNDAI §  RENAULT TRUCKS §  HONDA §  MERCEDEZ BENZ §  DAIMLER INDIA §  VISTEON §  TURBO TECHNOLOGIES

CHAPTER 2

MACHINING

Machining is a process in which a piece of raw material is cut into a desired final shape and size by a controlled material-removal process. The processes that have this common theme, controlled material removal, are today collectively known as subtractivemanufacturing, in distinction from processes of controlled material addition, which are known as additive manufacturingexactly what the “controlled” part of the definition implies can vary, but it almost always implies the use of machine tools.

Machining is a part of the manufacture of many metal products, but it can also be used on materials such as wood, plastic, ceramic, and composites. A person who specializes in machining is called a machinist. A room, building, or company where machining is done is called a machine shop. Machining can be a business, a hobby, or both. Much of modern day machining is carried out by computer numerical control (CNC), in which computers are used to control the movement and operation of the mills, lathes, and other cutting machines.

2.1. MACHINING OPERATIONS

The three principal machining processes are classified as turning; drilling and milling. Other operations falling into miscellaneous categories include shaping planning, boring, broaching and sawing.

• Turning operations are operations that rotate the work-piece as the primary method of moving metal against the cutting tool. Lathes are the principal machine tool used in turning
• Milling operations are operations in which the cutting tool rotates to bring cutting edges to bear against the work piece. Milling machines are the principal machine tool used in milling.
• Drilling operations are operations in which holes are produced or refined by bringing a rotating cutter with cutting edges at the lower extremity into contact with the work-piece. Drilling operations are done primarily in drill presses but sometimes on lathes or mills.
• Miscellaneous operations are operations that strictly speaking may not be machining operations in that they may not be swarf producing operations but these operations are performed at a typical machine tool.

2.2. CLASSIFICATION OF MACHINING

Machining can be classified as conventional and unconventional machining.

2.2.1. CONVENTIONAL MACHINING VS NON-CONVENTIONAL MACHINING

Conventional machining usually involves changing the shape of a work-piece using an implement made of a harder material. Using conventional methods to machine hard metals and alloys means increased demand of time and energy and therefore increases in costs; in some cases conventional machining may not be feasible. Conventional machining also costs in terms of tool wear and in loss of quality in the product owing to induced residual stresses during manufacture. With ever increasing demand for manufactured goods of hard alloys and metals, such as Inconel 718 or titanium, more interest has gravitated to non-conventional machining methods.

Conventional machining can be defined as a process using mechanical (motion) energy. Non-conventional machining utilises other forms of energy.

The three main forms of energy used in non-conventional machining processes are as follows:

• Thermal energy
• Chemical energy
• Electrical energy

One example of machining using thermal energy is laser. Thermal methods have many advantages over conventional machining, but there are a few of disadvantages.

1. Inconel 718, titanium and other hard metals and alloys have a very high melting point. Using thermal methods will require high energy input for these materials.
2. Concentrating heat onto any material greatly affects its microstructure and will normally cause cracking, which may not be desirable. Safety requirements for thermal methods, especially laser, are demanding in terms of time and cost.
3. Machining large areas or many surfaces at the same time using thermal methods is not normally possible.

The methods using electrical energy are electro-discharge machining (EDM) and anodic machining (AM), which are similar in practice. EDM, often referred to as spark erosion, uses pulsed voltage to remove material from a work-piece and a non-conductive medium to clear the debris. Because the medium is electrically inert the tool is a direct reverse of the work-piece and no complicated tool design criteria are required. But the shock of spark erosion can affect the microstructure on the surface of the work-piece. Also, EDM has a lower material removal rate than AM.

The chemicals used in AM are non-toxic and the energy required is less than other nonconventional machining processes. It has no effect on the microstructure of the work-piece. The electrolyte can even be common sea water, enabling AM to be used in a sub-sea capacity. The hardness and thermal resistivity of the work-piece material do not matter therefore hard metals and alloys can be machined using tools made from softer materials. The only disadvantage is that tool design is a little more complex than that of EDM, but software is being developed to make this easier. The controllability, environmental versatility, speed, safety and absence of change in work-piece microstructure make AM a competitive manufacturing process.

2.3. CUTTING TOOL

A cutting tool has one or more sharp cutting edges and is made of a material that is harder than the work material. The cutting edge serves to separate chip from the parent work material. Connected to the cutting edge are the two surfaces of the tool:

1. The rake face
2. The flank.

The rake face which directs the flow of newly formed chip, is oriented at a certain angle is called the rake angle “α”. It is measured relative to the plane perpendicular to the work surface. The rake angle can be positive or negative. The flank of the tool provides a clearance between the tool and the newly formed work surface, thus protecting the surface from abrasion, which would degrade the finish. This angle between the work surface and the flank surface is called the relief angle.

There are two basic types of cutting tools:

1. Single point tool; and
2. Multiple-cutting-edge tool

A single point tool has one cutting edge and is used for turning, boring and planning. During machining, the point of the tool penetrates below the original work surface of the work part. The point is sometimes rounded to a certain radius, called the nose radius.

Multiple-cutting-edge tools have more than one cutting edge and usually achieve their motion relative to the work part by rotating. Drilling and milling uses rotating multiple-cutting-edge tools. Although the shapes of these tools are different from a single-point tool, many elements of tool geometry are similar.

2.4. TYPES OF CUTTING TOOLS

2.4.1. Cutting tools with inserts

Cutting tools are often designed with inserts or replaceable tips. In these, the cutting edge consists of a separate piece of material, either brazed, welded or clamped on to the tool body. Common materials for tips include cemented carbide, polycrystalline diamond, and cubic boron nitride. Tools using inserts include milling cutter, tool bits, and saw blades.

2.4.2. Solid cutting tools

The typical tool for milling and drilling has no changeable insert. The cutting edge and the shank is one unit and built of the same material. Small tools cannot be designed with exchangeable inserts.

2.4.3. Holder

To use a cutting tool within a CNC machine there is a basic holder required to mount it on the machine’s spindle or turret. For CNC milling machines, there are two types of holder. There are shank taper (SK) and hollow shank taper (HSK).

2.4.4. Leather Cutting Tools

Leather cutting tools are essential tools in the industry today, playing a huge role in the manufacture of leather products. As leather is an expensive material, it is important that the tools used to cut leather do not damage it and perform accurate clean cuts. Some examples of leather cutting tools include swivel and utility knives, rotary cutters and shears. Utility knives often have disposable blades which are able to perform deep cuts making them very convenient; even though swivel knives are an ideal choice for carving out the initial outline of a design in leather. This process is important as it would affect the processes following after and therefore should be performed with the care and the right cutting tools. These kind of decorative cuts are referred to as dress cuts and require practice to master. Rotary cutters are used for cutting soft leathers and leather shears are heavy-duty cutting tools used cut lightweight and medium weight leather.

2.4.5. Metal Cutting Tools

As metal is a very hard material, cutting tools required to cut metal have to be very strong. These tools tend to require frequent replacements and sharpening due to wear and tear during the cutting processes. In industrial processes, metal cutting tools such as drills, reamers which create holes with accurate sizes are used, as well as inserts that have two or more cutting edges. In domestic uses, metal cutting tools are smaller and not meant for heavy-duty cutting. Two examples of such tools can be snips and hacksaws. The size of snips ranges between 5 to 14 inches and they do not remove metal during the cutting process, but instead are able to cause small fractures along the edge of the cut. Hacksaws are ideal for cutting metal that saws cannot cut. Some examples include metal pipes and bars.

2.4.6. Glass Cutters

Glass cutters are glass cutting tools that are designed to score glass, thus making it easier to be able to snap a piece of glass in any desired shape and size. Cutting glass can be a very difficult process as glass is very brittle and it is very easy to break the glass, casing potentially dangerous shreds to spread across the work area. Today, there are several different types of glass cutters available in the market to match the requirements of the domestic and industrial users. When cutting glass, the user uses a glass cutter to create a score in the glass. This creates a line of weak in the glass which can be easily snapped off, causing the glass to break. This process makes the job of glass cutting easier and safer, allowing more control of the shape that is formed after the cutting process.

2.5.5. FACTORS AFFECTING TOOL LIFE

The life of tool is affected by the following factors:

1. Cutting speed.
2. Feed and depth of cut.
3. Tool geometry.
4. Tool material.
5. Work material.
6. Nature of cutting.
7. Rigidity of machine tool and work.
8. Use of cutting fluids

2.6. CUTTING PARAMETERS

The cutting speed is calculated from rotating speed for any turning operation as the following:

v_c=pDN/1000

Where,

N: spindle speed (r.p.m)

VC: cutting Speed (m/min)

D: work diameter (mm),

π: 3.14

2.7. TOOL WEAR

It has been recognized widely that tool life can be divided into three phases characterized by three different flank wear processes.

(i) Break-in.

(ii) Normal wear.

(iii) Abnormal or catastrophic wear.

The sudden rise in wear rate observed during the abnormal tool wear phase is of interest here as an indication of the need for tool replacement. Because many factors affect tool wear, the wear curve usually fluctuates and is not smooth.

2.8. TOOL LIFE

In this case of manufacturing where large amount of products are being machined. The tool life is calculated as the number of components machined between two successive re-grindings. But the cnc used cannot alter its rpm and it is a totally preset machine, with all cutting parameters auto controlled. The work station labor is only capable of restricting the speed in case of any changes in tool length that is used and if the blank material is of poor quality. In this case tool life is calculated by Tool Life Factor (LF) which is also a parameter of measuring the tool life. Another factor known as Life in Meters (LIN)

LIFE FACTOR – ()

LIFE IN METERS – N (NPPC) ()

USEN – (FLUTES) ()

LIN -Linear Meters (in meters)

N -Number of Gear Teeth

OD -Outer Diameter

NPPC – Number of Parts per Cycle (parts in stack)

FW – Face-Width (in meters)

Cos (HA) – Cosine Function Of Gear Helix Angle

USEN -Usable Length of Hob Teeth (within hob shift limits)

USELEN – Usable Length of Hob (along hob axis between hob shift limits)

NCP–Normal Circular Pitch ofthe Hob

FLUTES -Number of Flutes

PARTS    –           Parts between Re-Sharpening

CHAPTER 3

WAYS TO IMPROVE TOOL LIFE

3.1. COATING

Machining efficiency is improved by reducing the machining time with high speed machining. When cutting ferrous and hard to machine materials such as steels, cast iron and super alloys, softening temperature and the chemical stability of the tool material limits the cutting speed. Therefore, it is necessary for tool materials to possess good high-temperature mechanical properties and sufficient inertness. The machining of hard and chemically reactive materials at higher speeds is improved by depositing single and multi-layer coatings on conventional tool materials to combine the beneficial properties of ceramics and traditional tool materials.

Schintlmeister et al had summarized the effect of coatings in the following statements:

1. Reduction in friction, in generation heat, and in cutting forces
2. Reduction in the diffusion between the chip and the surface of the tool, especially at higher speeds (the coating acts as a diffusion barrier)
3. Prevention of galling, especially at lower cutting speeds.

3.2. COATING MATERIALS

The majority of inserts presently used in various metal cutting operations are cemented carbide tools coated with a material consisting of nitrides (TiN, CrN, etc.), carbides (TiC, CrC, W2C, WC/C, etc.), oxides (e.g. alumina) or combinations of these. Coating cemented carbide with TiC, TiN and Al2O3 dramatically reduces the rate of flank wear. A primary contributor to the wear resistance of the coating materials is that they are all much less soluble in steel than WC at metal cutting temperatures. High hardness is beneficial in resisting the abrasive wear. Retention of hardness even at higher temperatures is very important since the tool bit experiences a temperature in the range of 300-1000°C depending on the machining parameters and the materials to be machine.

They all exhibit a decrease with an increase of temperature, and the decrease of hardness was much more pronounced in the case of TiC. Interestingly, the micro hardness of Al2O3 was significantly lower than TiC at room temperature but retained almost 40 % of its room temperature hardness at 1000 °C Coating with three layers of TiC-Al2O3-TiN as seen from the substrate are widely used for machining of many types of steels. This type of coating improves the wear resistance of the tool by combining the properties of the three materials. The ranking of the solubility products and limits of TiC, TiN and Al2O3 in iron, compared to the carbide substrate, is in the order TiC > TiN > Al2O3.

Therefore there is less driving force for significant dissolution-diffusion wear of Al2O3 to take place. Thus, having a coating layer of Al2O3 over an under layer of TiC help decrease the dissolution/diffusion wear at the TiC coating layer. This enhances the performance of the cutting tool, by including the TiC layer with a low wear rate and protecting it with a layer of Al2O3 to decrease the effect of diffusion/dissolution wear. The softer TiN outer layer helps in reducing the propagation of cracks into the inner coating layers, in addition to decreasing the welding of the chips to the cutting tool. Another reason for having the TiN as an outer layer, as opposed to inner layer, is that at higher temperatures of oxidation, the growth of TiO2 (rutile) under layer may affect the performance of the protective alumina over layer of the oxide.

3.3. SURFACE FINISH

Surface roughness and tolerance are among the most critical quality measures in many mechanical products. As competition grows closer, customers now have increasingly high demands on quality, making surface roughness become one of the most competitive dimensions in today’s manufacturing industry. There are several measurements that describe the roughness of a machined surface. One of the most common is the arithmetic average (AA) value usually known as Ra. The AA value is obtained by measuring the height and depth of the valleys on a surface with respect to an average centerline. The higher the AA value is, the rougher the machined surface.

3.4. WORK-PIECE MATERIAL

The cutting performance tests were performed on AISI 1018 cold rolled steel. Based on the AISI-SAE standard carbon steel table, it is a non-re-sulphurized grade steel and its composition is 0.15-0.2% C, 0.6-0.9% Mn, maximum of 0.04% P and maximum of 0.05% S. The work piece material used was 1.5 inch in diameter and 20 feet long. However, in order to meet the requirement of the ISO 3685 that the length/diameter ratio of the work piece material to be used should be less than 10 during testing, the bar was cut into 20 pieces (12 inch length) using the metal cutter shown in Figure 2-5 which is located in the machine shop of the Industrial Engineering department.

3.5. WEAR OF TIN COATED VS. UNCOATED TOOL

To compare the performance of the TiN coating, the flank wear of the TiN coated tool was compared with the flank wear of the uncoated tool. The SAS output for the regression of flank-wear on the number of cuts for both TiN coated and the uncoated tools. A null hypothesis (Ho) that the TiN coating has no effect on the flank wear and an alternative hypothesis (Ha) that the TiN coating has an effect on flank-wear were used. Again using a a-value of 0.05, the null hypothesis is rejected in favor of the alternative hypothesis since the P value for this regression is<0.0001.And so it can be concluded that the TiN coating has asignificanteffect on tool flank wear for the TiN coated tool.

 CHAPTER 4

TOOL COATING

4.1. TYPES OF TOOL COATINGS:

4.1.1. TIN COATING:

Titanium nitride (TiN) (sometimes known as “Tinite” or “TiNite” or “TiN”) is an extremely hard ceramic material, often used as a coating on titanium alloys, steel, carbide, and aluminium components to improve the substrate’s surface properties.

Applied as a thin coating, TiN is used to harden and protect cutting and sliding surfaces, for decorative purposes (due to its gold appearance), and as a non-toxic exterior for medical implants. In most applications a coating of less than 5 micrometres (0.00020 in) is applied.

4.1.2. CERAMIC COATING:

There are a wide range of ceramic coatings that can be applied to metal components in order to enhance their functional properties. Most ceramic coatings are electrically nonconductive (making them excellent insulators), have a significantly higher level of abrasion resistance than most metals, and are capable of maintaining their integrity under severely elevated temperatures, sometimes up to 4,500 degrees Fahrenheit. Wear-resistant ceramics, such as titanium nitride and chromium carbide, can be applied to work steels and air-hardening tool steels via chemical vapor deposition (CVD), which is one of the more common application methods currently in use.

Plasma Spraying: In plasma spraying, ceramic powder is passed through an ionized gas at extremely high temperatures, sometimes approaching 30,000 degrees (F). The pressurized gas speeds molten ceramic particles toward the substrate where they bond onto its surface. The result is a strongly-adhering and high-density coating, but the process can be very expensive.

4.1.3. ALCHRONA:

Alchrona pro is the type of coating which we preferred for the given tool. The term alchrono pro is abbreviated has aluminium chromium coating which is coated at an amount of 0.2 t 0.8 microns. These type of coatings are suited for best coatings on tool and gives maximum productivity.

4.2. PROCESS

In its simplest incarnation, CVD involves flowing a precursor gas or gases into a chamber containing one or more heated objects to be coated. Chemical reactions occur on and near the hot surfaces, resulting in the deposition of a thin film on the surface. This is accompanied by the production of chemical by-products that are exhausted out of the chamber along with un-reacted precursor gases. As would be expected with the large variety of materials deposited and the wide range of applications, there are many variants of CVD. It is done in hot-wall reactors and cold-wall reactors, at sub-torr total pressures to above-atmospheric pressures, with and without carrier gases, and at temperatures typically ranging from 200-1600°C. There are also a variety of enhanced CVD processes, which involve the use of plasmas, ions, photons, lasers, hot filaments, or combustion reactions to increase deposition rates and/or lower deposition temperatures. There are also many derivatives of the CVD terminology, such as metal-organic chemical vapour deposition (MOCVD) or, less commonly, organo-metallic chemical vapour deposition (OMCVD), which are sometimes used to note the class of molecules used in the deposition process. Some practitioners chose to differentiate epitaxial film deposition from polycrystalline or amorphous film deposition, so they introduced a variety of terms that include “epitaxy” in the acronym. Two of the more common variants are Organometallic Vapour Phase Epitaxy (OMVPE) and Metalorganic Vapour Phase Epitaxy (MOVPE) which are often used in the compound semiconductor epitaxy literature.

CVD encompasses a wide range of reactor and process types. The choice of process/reactor is determined by the application via the requirements for substrate material, coating material and morphology, film thickness and uniformity, availability of precursors, and cost.

Here, we discuss the general types of reactors used for CVD, and refer the reader to the other chapters in this and other books for detailed information on specific systems. Hot wall reactors represent one of the major categories of CVD reactors. In such systems, the chamber containing the parts is surrounded by a furnace that heats the system. The parts are loaded into the system, it is heated to the desired temperature, and then the reactive gases are introduced. The reactor may be equipped with shelves for coating many parts at once, or be sized for specific large parts. These systems are often run at very high temperatures, limited only by the materials used in constructing the furnace, and at reduced pressures, on the order of Torr totens of Torr. Low- Pressure CVD (LPCVD) batch processing in the microelectronics industry.

In this case, a specialized support holds a large number (over a hundred) of closely-spaced silicon wafers for simultaneous processing. In general, hot wall reactors have the advantages of being able to process large batches of substrates, and having relatively uniform substrate temperatures and thus coating thicknesses. The primary disadvantages are that the walls get heavily coated, requiring frequent cleaning and causing particle problems, and that it involves higher thermal loads and energy usage.  Cold wall reactors are the other major category of CVD reactors. In such systems, the substrates are heated but the walls are cooled .This system has water-cooled quartz walls, with a rotating holder for (silicon or compound semiconductor) wafers that is resistively heated from below. Other commercial cold-wall reactors include lamp heated single-wafer reactors that are widely used in microelectronics fabrication, and inductively heated horizontal flow reactors.

Cold-wall reactors are often run at relatively high pressures, several hundred torr to atmospheric total pressure, and usually have the reactive precursors diluted in a carrier gas. Most compound semiconductor CVD processes use reactors of this type. Cold wall reactors have the advantages of reduced deposition of material on the walls, which means less cleaning, lower thermal loads on the substrates because of faster heat-up and cool-down times, lower energy consumption, and the avoidance of vacuum equipment. The primary disadvantages are larger temperature non-uniformities on the substrate, which may lead to film thickness non-uniformities, the smaller batch sizes, and possible thermal stresses on the substrates if the heating/cooling is too rapid. In this system, the surface to be coated moves underneath a set of gas injectors and is heated from below. In some cases, the substrates (wafers) are placed on a belt moving over a set of rollers. In other cases, such as the large-scale application of optical coatings (i.e.  low-E coatings) to glass, the moving belt could be the float-glass sheet itself. These systems are essentially open to atmosphere–the reactive gases are contained by “curtains” of inert gas on either side of the deposition zone. Such systems have the advantage that they can do very large scale production, and avoid vacuum equipment. The disadvantages are a relatively high rate of gas consumption, potential non-uniformities in film thickness, relatively low operating temperatures because of the high volumes of gas involved, and relatively low efficiency for precursor use.

4.3. ADVANTAGES:

1. PVD coatings are sometimes harder and more corrosion resistant than applied by the electroplating process. Most coatings have high temperature and good impact strength, excellent abrasion resistance and are so durable that protective topcoats are almost never necessary.
2. Ability to utilize virtually any type of inorganic and some organic coating materials on an equally diverse group of substrates and surfaces using a wide variety of finishes.

• More environmentally friendly than traditional coating processes such as electroplating and painting.

1. More than one technique can be used to deposit a given film.

4.4. DISADVANTAGES:

1. Specific technologies can impose constraints; for example, line-of-sight transfer is typical of most PVD coating techniques, however there are methods that allow full coverage of complex geometries.
2. Some PVD technologies typically operate at very high temperatures and vacuums, requiring special attention by operating personnel.

• Requires a cooling water system to dissipate large heat loads.

CHAPTER 5

HOB TOOL

Hobbing is a machining process for gear cutting, cutting splines, and cutting sprockets on a hobbing machine, which is a special type of milling machine. The teeth or splines are progressively cut into the work-piece by a series of cuts made by a cutting tool called a hob. Compared to other gear forming processes it is relatively inexpensive but still quite accurate, thus it is used for a broad range of parts and quantities.

5.1. CLASSIFICATION

1. Roller chain sprocket hobs
2. Worm wheel hobs
3. Spline hobs
4. Chamfer hobs
5. Spur and helical gear hobs
6. Straight side spline hobs
7. Involute spline hobs
8. Serration hobs
9. Semi topping gear hobs

 

5.2. TERMINOLOGY:

5.3. COST:

The cost of the gear hob tool is rated about 5,000-6,000 RS without coating over the tool. And once the tool is coated it will be recycled for five to seven times.

5.4. HOB LIFE (NOMINAL LIFE):

The gear life of the hob depends upon on the required number of components it runs on. Basically the hob’s nominal life is about 3 to 4 months and this time period is calculated by adding the re-sharpening time period.

CHAPTER 6

EFFECTS OF COATING TOWARDS PRODUCTIVITY

The effect of coating towards productivity is been a great aspect in production line of the company. Due to coated tool the number of components in the plant has reached its outraged level.

6.1. NUMBER OF JOBS DONE AFTER COATING:

Component name: planetary gear worm.

Number of components: 900

Cycle time: 14.00 minutes

As the components is machined after the coating the number has been increased to excess of 40 numbers in every single cycle time.

6.2. RELIABILITY

At the same time, expectations for gear reliability are high. Additionally, there is a diversity of planetary gears for different applications.

Photo elasticity is used to estimate the stresses in a loaded element. Polarised light is transmitted through the transparent model of a slice of the element. The model deforms under load, causing the transmitted beam to interfere with a reference beam. Photoelastic model of gears the resulting interference pattern consists of a series of bands, each representing an area of constant prototype stress whose value can be predicted by calibration and by counting bands from unloaded areas. Qualitatively, the closer these bands are bunched up in the model, the higher are the prototypical stresses.

Apart from one-off overloads, there are three common modes of tooth failurebending fatigue leading to root cracking,surface contact fatigue leading to flank pitting, andlubrication breakdown leading to scuffing.

6.3. TOOL SAFETY

Tool safety is defined has reducing the wear of the tool or avoiding it by checking the tool in regular intervals. So the tool should be changed or removed once the tool has reached its required number of components. So by routine checks and correct movement of tool to re-sharpening will increase the tool life above the estimated level.

6.4. RESHARPENING PERIOD

The current time period for re-sharpening period is about 3 days which involves 5 stages. The first main stage is cleaning of the hob which is cleaned under 8 steps and once after cleaning hob is not touched in bare hands. Then hob is taken for re-sharpening where a minute amount of hob cutting phase about 0.6 t0 0.8 microns are removed under the process before the coating process.

The current process is the major part of the Hob which is the deposition of coating on the Hob by physical vapour deposition which coated over the tool about 0.8 microns. This process will take place around to 12 – 16 hours to finish to coating process. Then it is taken to a mathematical check-up and finally a physical inspection is done before the dispatch.

CHAPTER 7

MACHINE UNDER WATCH

The machine which we took under for watch is GP300 a product of GLEASON company which is gear hobbing machine for production of components.

7.1. GLEASON:

Founded in 1865, Gleason Corporation is a global leader in the technology of gearing. Products and services include machinery for the production, finishing and testing of gears as well as a worldwide support system which provides cutting tools, workholding, replacement parts, field service, application development services, gear design and inspection software, training programs, engineering support and machine rebuild and upgrade services. The Company is also a leader in the theory of gear design and in the application, testing and analysis of prototype and production gears. Customers include leading companies in the automotive, aerospace and aircraft, energy, truck, recreational vehicle and power equipment industries.

7.1.1. GP300:

The GP300 Gear Hobbing Machine is designed for dry and wet machining parts up to 300 mm OD and module 6 mm. Manual or automatic loading options provide versatility to cover different customer requirements. Optional integrated chamfer and deburring unit available.

It can be equipped with Gleason’s backlash-free, direct-drive mechanical shaping head (“S” model) and, for maximum flexibility and the production of helical gears, an electronic helical guide (“ES” model). The ES model’s electronic helical guide uses powerful Siemens 840D CNC and proprietary software to superimpose the additional rotational motion on the cutter spindle necessary to generate any required helix angle. As a result, the high procurement costs, and delivery and changeover time, associated with mechanical helical guides generally used by conventional shaping machines is eliminatedGleason GP300.

The GP family of Gear hobbing machines has been designed by combining the best features of the Gleason and Pfauter machines along with new innovations. The basic concepts incorporate many modular parts and assemblies. This reduces the number of parts which increases the reliability of the parts and the assembly process. The result are operator and maintenance friendly machines.

7.1.2. SPECIFICATIONS

Nominal work-piece diameter: 300mm

Nominal module: 6 mm

Maximum axial slide travel: 250 (440) mm

7.1.3. RELATED CUTTING TOOLS:

1. High Speed Steel Hobs
2. Worm Gear Milling Cutters

• Opti-Gash® Hobs

1. Solid Carbide Hobs

7.2. REPORTS ON PROCESSING IN GP300:

These are the current reports which are taken on the machine GP300. A complete time study is done on the machine and the product worm gear is checked for one complete cycle. Here in this GP300 the cycle times will be varying for different components.

The component which can be machined in this machine is upto to 300 MM and 6 module working parameter is given to the machine.

 CHAPTER 8

COATINGS

The cutting tool industries are constantly facing the very common industrial challenge of reducing cost of machined parts and at the same time improving the quality of the machined surface. These issues are generally addressed by improving cutting tool materials, applying advanced coating, improving the geometry and surface characteristics of the cutting tools, optimizing machining parameters. The need for the use of newer cutting tool materials to combat hardness, wear situation has resulted in the emergence surface coatings, which contributes in reducing cost per machined parts through increasing productivity and extending tool life. The benefits of advanced coatings are of higher hardness, low friction at the chip tool contact, higher wear resistance, high hot hardness and high thermal and chemical stability. The machined surface quality with the coated cutter can also be improved by avoiding any built-up edge due to the reduced friction between the tool and work piece. Based on the abundant advantages of surface coatings and the requirement of industrial development and requirement, it is necessary to develop TiN, TIC, coatings on Tungsten carbide cutting tool. Based on these driving force, it is necessary to do surface coating of TiN, TIC, on Tungsten Carbide cutting tool to give good mechanical and tribological properties.

Fig8.1 Coatings

During machining operations,small scratches and grooves are invariably introduced into the work-piece surface by cutting tool action. These surface markings can limit the fatigue life. It has been observed that improving the surface finish by polishing will enhance fatigue life significantly. One of the most effective methods of increasing fatigue performance is by imposing residual compressive stresses within a thin outer surface layer. Thus, a surface tensile stress of external origin will be partially nullified and reduced in magnitude by the residual compressive stress. The net effect is that the likelihood of crack formation and therefore of fatigue failure is reduced.

TYPE OF COATINGS:

1.CVD (Chemical Vapor Deposition)

2. PVD(Physical Vapor Deposition)

a. Using Plasma

b. Using Electron Beam

8.1. CVD (CHEMICAL VAPOR DEPOSITION)

CVD (Chemical Vapour Deposition)-processes use chemical reactions in the vapour phase which proceed at pressures between 0,01 and 1 bar and at temperatures from 200°C to 2000°C under the presence of thermal and/or radiation energy. To form a CVD coating the respective process has to form a solid product along with a volatile by product. The gaseous precursor components are introduced into the reaction chamber together with an inert carrier gas (mostly Ar). In the chamber the solid is formed either by a heterogeneous reaction as a coating and or as a powder if a homogenous reaction is involved.

Chemical vapour deposition (CVD) is a widely used materials-processing technology. The majority of its applications involve applying solid thin-film coatings to surfaces, but it is also used to produce high-purity bulk materials and powders, as well as fabricating composite materials via infiltration techniques. It has been used to deposit a very wide range materials. As indicated by the boxes the majority of the elements in the periodic table have been deposited by CVD techniques, some in the form of the pure element, but more often combined to form compounds.

Four basic types of reaction can be distinguished

1. Chemosynthesis (Reactions with gases)

[z.B.: TiCl4 (g) + 1/2N2 (g) + 2H2 (g) 600-1000°C10-900mbar> TiN(s) + 4HCl (g)]

2. Pyrolysis (Thermal decomposition)

[z.B.: SiH4 (g) C650°<↔Si(s) + 2H2 (g)]

3. Disproportionation

[z.B.: 2GeJ2 (g) <====> Ge(s) + GeJ4 (g)]

8.1.1. HOTOPOLYMERIZATION

CVD processes are used for manufacturing coatings of refractory and other metals, of semiconductors, of borides, carbides and nitrides as well as of oxides. The advantage that many materials can be deposited close to their theoretical density with high purity, good adhesion and high thickness uniformity is counteracted by the fact that no chemical reaction may be existent for selected materials, that the substrate has to withstand (mostly) high reaction temperatures and that it has to be chemically stable against the presence of the reaction partners.

8.2. ELECTROCHEMICAL AND CHE MICAL DEPOSITION

8.2.1. INTRODUCTION

Electrochemical and chemical processes used for the deposition of coatings can be divided into galvanics, anodic oxidation and chemically-reductive (electro-less) deposition:

8.2.2. GALVANICS

Galvanics comprises the deposition of metals and alloys on a metallic substrate in a suitable electrolyte by current flow. The substrate serves as the cathode. Exposed points and edges of the substrate experience higher deposition rates than holes (see Fig. 2.37a.) due to the tip effect (higher current density due to a larger electric field). A uniform coating thickness can be achieved by a suitable arrangement of anodes and shields.

8.2.3. ANODIC OXIDATION

The electrochemical formation of coatings by current flow in a suitable electrolyte with the substrate serving as anode is termed anodic oxidation (“anodization”). The coating uniformity is better than in galvanically deposited coatings but still edges and holes experience lower deposition rates.

8.2.4. CHEMICALLY REDUCTIVE DEPOSITION

In this case the deposition happens without an exterior current source (“electro-less”). The electrons necessary for the deposition of the metal from the electrolyte are provided by suitable reducing agents. Because of the absence of an exterior current source, which would lead to un-uniform current densities, the coating thickness even on edges and in holes is very uniform. Therefore it is possible to coat parts with complex geometries very uniformly.

8.3. THERMAL SPRAYING

Thermal spraying methods allow the coating of components with metals, ceramics, cermets and other special materials. The coating material is supplied as powder or wire and is molten within a heat source of high power density. Fine droplets of the completely or partially molten material are accelerated towards the substrate by suitable means. The substrate is kept at temperatures below 200°C and is roughened by sand or glass blasting to increase adhesion.

Upon impact on the surface the droplets are flattened and cooled by heat transfer to the substrate. Usually no metallurgical interconnection (intermixing by diffusion) is observed even if the combination coating/substrate has the inclination do inter-diffuse or to weld. The coating adheres locally by mechanical interlocking and chemical or Vander Waals bonding. The excellent adhesion is caused by the shrinking of the cooling droplets onto the roughness peaks of the surface.

The advantages of thermal spraying are:  

1. Compared to PVD and CVD methods the deposition rates are higher by two orders of magnitude. Coating Thicknesses of some mm can readily be achieved.
2. The process is suitable for mass production, but also for coating single components. Apart from vacuum plasma spraying parts can be coated in the lab as well as in the field (e. g. dredger buckets).

• Since the substrates are not highly thermally loaded also Al, Sn or Zn based alloys as well as some polymers can be coated without shape change, oxidation or changes in microstructure.

1. The deposition of coatings consisting of metals, ceramics cermets, hard materials as well as of selected polymers is possible.

Disadvantages which are present especially for flame, arc and plasma spraying are:  

1. The coatings are very porous and can only be densified by certain post treatments e. g. (re-melting or sealing).
2. The strength of the coatings is lower than the strength of the bulk material.

• Sometimes there may be low adhesion strength.

These disadvantages are not relevant for detonation spraying and vacuum plasma spraying.

8.4. APPLICATIONS

8.4.1. CHROMIUM COATINGS

Important applications of Cr coatings are related to the fields of: combustion engines (piston rings, pistons, and cylinder linings), mechanical engineering, aerospace industry, printing and paper industry (rolls in paper mills). The so called hard chrome plating is used for decorative coatings with thicknesses of 0.2 – 2 µm and for engineering purposes with thicknesses from 20 – 500 µm. The formation of thick coatings is limited by residual stresses.

8.4.2. COPPER COATINGS

Cu coatings are used for electrically conductive coatings with thicknesses from 10 – 100 µm.

8.4.3. NICKEL-COATINGS

Ni coatings are used for decorative purposes with thicknesses from 10 – 50 µm. Coatings with a thickness from 0.2 – 2 mm are used on parts which are subjected to severe corrosion.

8.4.4. ZINC- AND CADMIUM-COATINGS

They are used in corrosion protection. Approximately 40% of the world production of Zn is used for the corrosion protection of steel.

8.4.5. TIN- AND TIN-LEAD-COATINGS

They are deposited on steel, Cu and Cu alloys. Steel sheets coated with 0.5 – 1.5 µm Sn are used for manufacturing tin cans. Steel sheets with a 5 – 20 µm Sn coating deposited on a Cu interlayer which serves as diffusion barrier exhibit a surface which can be soldered and are also used for manufacturing corrosion resistant food containers. Lead bronze coatings (the binary system Sn10-Pb90 or the ternary system Sn15-Pb65-Cu20) are used as plain bearing coatings due to their resistance against wear and fatigue.

8.4.6. LEAD-COATINGS

Lead coatings can be deposited with thicknesses from 10 – 500 µm. They are used in chemical engineering due to their resistance against certain chemicals and also for manufacturing accumulators.

Noble Metal and Noble Metal Alloy Coatings

The metals Au, Pt, Pd and Rh serve as protective materials against high temperature corrosion in aerospace devices and as electronic contact materials. Au, Ag and Pt also find applications in the jewelry industry as materials for noble metal coatings.

8.5. PHYSICAL VAPOR DEPOSITIONEVAPORATIONPROCESS

8.5.1. INTRODUCTION

For the evaporation process the substance to be evaporated is heated in a dedicated container (ceramic crucible, Ta boat, W spiral wire etc.) by the introduction of energy (electrical current, electron beam, laser, arc discharger etc.) to a suitable temperature. The thermally released atoms or molecules leave the surface of the evaporated material and form a coating on the substrate or on the surrounding walls. As the process is usually conducted under High Vacuum (HV, p<10-5mbar = 10-3Pa) the coating particles basically move from the source to the substrates on straight trajectories, i.e. without collisions with residual gas atoms To guarantee well defined film properties the substrate temperature often has to be as high as some 100°C. This can be achieved by using heating rods or quartz lamps. Employing glow electrodes allows for a cleaning of the substrate by ion or electron bombardment which is extremely important for a good coating adhesion. A suitable vacuum system equipped with gas inlets and different mechanical devices (screening arrangements, shutter, and motor powered substrate movement) has to be available to perform an evaporation process

8.5.2. FUNDAMENTALS OF COATING

Residual gas pressure:

For evaporation under hv the pressure p of the residual gas has to fulfil two conditions:

1. The film forming particles have to move on straight lines to allow the production of Straight edges by evaporating through a mask.
2. The ratio between residual gas particles and evaporated particles has to be reasonably small at the substrate to allow for the deposition of a clean coating.

8.6. PRINCIPLE:

8.6.1. MAGNETRON SPUTTERING

The scope of applications especially in the field of high technology significantly could be widened by the introduction of the so-called magnetron sources. Magnetron systems allow for the achievement of high deposition rates at low working gas pressure (even below 0.1 Pa) and at low substrate heating. In principle a magnetron works as follows: Above the cathode (target) a so-called “electron trap” is generated by a magnetic field B which is transversal to the electric field E. Within this region a closed annular current is formed by the trapped electrons due to the ExB-drift.

The magnetic field Bhas a strength of some 10 mT (= 100 G) and therefore does not influence the heavy ions but only the electrons with their low mass. In their general appearance magnetron discharges are similar to a common glow discharge. Cathode dark space, plasma and anode fall are observable.

An electron emitted from the target by an ion collision has an initial energy of some eV. After leaving the target it will describe a cycloidic arc and will only stay free if, within the first cycloidic arc, it suffers a collision with an energy loss which is larger than the initial energy. Each time the electron loses energy by a collision a new cycloidic trajectory is started and electron proceeds radially towards the anode. Therefore, within the ExB-direction a current with the density J is generated.

8.6.2. FILM THICKNESS UNIFORMITY AND SUBSTRATE HOLDER

As it has been shown in the last section the film thickness on a specific substrate depends on its location on the substrate holder. To guarantee a high thickness uniformity on one or more substrates often rotating substrate holders are employed. The rotation periodically moves substrates from positions near the source to locations far away from the source. In addition one can use small adjustable carriers which may be tuned in respect to the evaporation characteristic.

8.6.3. EVAPORATION SOURCES

Evaporation sources can be categorized by the method of energy supply. One has also to consider that not each material can be evaporated from each source. Chemical reactions between crucible and evaporation material are possible which can lead to impurities in the film and/or to the destruction of the evaporation source. In addition the power density in different source types may vary strongly.

8.6.4. DIRECT RESISTIVE HEATING

Some (electrically conductive) elements which exhibit a vapour pressure >10-2 mbar (1Pa) below their melting point can be evaporated by sublimation. The evaporation material has the shape of wires or rods and is directly heated by a high electrical current. This method is not frequently employed since it is limited to only few materials (e. g. C, Cr, Fe, Mo, Ni, Pd, Rh, Ti, Al).

8.6.5. INDIRECT RESISTIVE HEATING

The principle of this frequently employed method is to put the evaporation material on or into a container (called “boat”), spiral wire, ribbon or crucible made from W (or Mo, Ta, C, Pt, BN, TiB2) which is heated by a high electrical current and to evaporate it from there

8.6.6. HARD PVD CERAMIC THIN FILM COATINGS

Hard materials suitable for thin films are usually carbides, nitrides, borides and silicides of the IVth, Vth and VIth groups of the periodic table. The materials are formed by depositing metals in a nitrogen, hydrocarbon, or silicide atmosphere. It is thought that the ceramic compound is formed at the surface of the substrate. An example of such a hard ceramic is titanium aluminium carbo-nitride, TiAlCN.

Hard PVD ceramic coatings are used extensively in cutting tool applications because of their outstanding wear resistant properties. They have continually developed over the years but can be divided into four coating generations.

8.6.7. HARD PVD CERAMIC COATINGS – Single metal nitride PVD coatings e.g. TiN, CrN, ZrN

The first generation of hard PVD ceramic coatings were simple metal nitrides such as TiN, CrN and ZrN. These coatings have been deposited commercially since the middle of the 1980’s because of their higher hardness compared to uncoated high speed steel or cemented carbide. They have also an attractive appearance and therefore are also used in decorative applications. TiN has a yellow-gold colour, CrN looks like chrome and ZrN has a green-gold colour. TiN, ZrN and predominantly ZrCN are used to simulate gold in decorative applications such as watch cases or to provide a hard wearing under layer for gold plating.

These PVD coatings are still used extensively however their oxidation resistance is insufficient for applications such as high speed machining. TiN for example oxidises and breaks down at 450 °C. Therefore scientists and production engineers worked on improving the operating temperature range for applications such as high speed machining and general high temperature wear protection.

8.6.8. HARD PVD CERAMIC COATINGS – Alloyed elements improve oxidation Resistance, e.g. TiAlN

The improvement in oxidation resistance was achieved by depositing other elements such as Cr, Al or Y at the same time as TiN. The addition of Al caused a stable aluminium oxide to form on the surface preventing further oxidation. Small levels of chromium increased the density of the oxide and yttrium tended to migrate to grain boundaries and prevented the substrate elements from diffusing up through the coating as the temperature rose.

8.6.9. HARD PVD CERAMIC COATINGS – The development of super lattices

Further developments increased the hardness and oxidation resistance of PVD coatings resulting in multilayers and super lattices. These are thin films formed by alternately depositing two different components resulting in a multi-layered structure. Multilayers are defined as super-lattices when the period of the different layers is less than 100Å.

Super-lattice coatings of materials with similar crystal structures tend to form columnar crystals which extend through the whole coating, provided that the thickness of the individual lamellae is sufficiently thin, typically 5–25 nm. One of the first examples of super-lattice coatings was obtained by combining TiN/VN and TiN/NbN. This type of multilayered coating structure can improve the hardness, corrosion resistance, oxidation resistance as well as the toughness, compared to single layers of the same materials.

8.6.10. HARD PVD CERAMIC COATINGS – THE RECENT DEVELOPMENT OF NANOCOMPOSITE COATINGS

A nano-composite coating consists of at least two distinct phases: a nano- crystalline phase and an amorphous phase, or two nano-crystalline phases. The basic idea for developing nano-composites is based on thermodynamically driven segregation in binary (ternary, quaternary) systems. This segregation results in self-organization of a stable nano-scale structure. The use of this generic concept led to the development of nano-composite PVD coatings. These PVD coatings have nano-meter sized grains and exhibit enhanced yield strength,hardness and toughness properties as a result of the well-known Hall-Petch effect.

8.6.11. LOW FRICTION COATINGS

Hard, wear resistant, low friction coatings such as Graphit-iC™, MoST™ and Dymon-iC™ have been developed with the automotive industry again the driving force.

CHAPTER 9

COATING PROCESS

The coating process is basically a set of processes which involves a sequence of processes which are followed one after the other. They involve a basic cleansing and the second stage of a chemical cleansing and drying. Later it is stripped and racked. The racked tools are sent to re-sharpening. The next step involves blasting. The final step involves the coating of the material on the substrate i.e., the respective tool. The coating is a brief process invisible to the naked eye. The process takes place in a closed PVD plasma coating machine. The time taken for the coating varies to a maximum of 12-18 hours.

The Following Steps Are Involved In The Coating Process.

1. Pre-cleaning
2. Stripping
3. Re-sharpening
4. Blasting
5. Fixture and Loading
6. Coating

Step1: Pre-Cleaning

The initial step of coating process as observed is pre-cleaning. The tool which is delivered by the vendor, it is procured by the transportation department and then taken to this initial section. This step involves the cleaning of the tool by blowing air from a compressor through a tube manually by a labor on the tool to remove the lubricating oil from the surface of the tool for the later processes of re-sharpening and coating. The tool should be free of lube oil and any other obstructions that may hamper the entire process of coating. This process also removes any burrs and chips which still lie on the surface of the tool.

Step2: Stripping

This is a brief step involves sequence of processes, the tools are dipped and treated in number of tanks filled with alkali and de-mineralized water, in alternate tanks. So that the alkali is not mixed with the other alkali mixtures in other tanks.

The 1^st tank has jets of water which removes the remaining lube oil on the surface of the tool. The 3^rd, 5^th,7^+TTh,9^th tanks have alkalis and the 2^nd,4^th,6^{th, 8th, 10th, 11th} tanks are filled with de-mineralized water

The tanks are fitted with ultrasonic vibrators vibrating at a frequency of 20-40 hertz, these vibrations enable the remaining lubricant sticking on to the tool to be washed off. The alkali wash gives an un-harmful effect to the tool surface. Acids prove as a worthy remover but the cutting face which is the at most preference here, the alkali wash is opted. The tool is initially attached in fixtures. This set is completely taken through the process. The fixture is important as the vibrations at times might eventually pop out the tool from the attachments.

Step3: Re-Sharpening

Re-Sharpening process is normally done on every cutting tool that goes through the re-coating process. Re-grinding stations are present for each type of cutting tool. There are grinding stations for drill bit, hob and broaches which are performed both manually and part manual machines which are operated by well trained personnel. The hob re-grinding is done on a Gleason

The seven axes hob grinding machine which gives a wet cut to the hob. It acts as like a threading tool moving along the curved axis of the teeth along the hob axis. Precision and accuracy is imparted in the grinding. Only the cutting face of the hob is grinded. In case of flank wear separate measures are taken in removing off the flank abrasions.  The allowance for the grinding of the faceis 0.3 to 0.5mm and at Gleason 0.3mm is achieved every time owing to the efficient workmanship and precise machining.

The tool used for re-sharpening as seen is a grinding wheel CBN.

Step4: Blasting

Blasting is a wide variety of processes normally blasting is sand blasting which is carried on for varied purposes, think of blasting as sanding the surface by using a sandpaper. One of the main advantages of media blasting is it gives the surface to be powder coated a profile or tooth

The sand blasting is performed by using coarse sand as abrasive and air as the carrying medium. The grit or sand blasting is carried out by throwing the metallic particles by centrifugal force from a rapidly rotating wheel.

Blasting process is doneblasting is done on the hob to make it easier for the coating. The blasting allows the powder coat to get to all the low points in the metal. Sanding marks straight lines on the surface of the metal.  But blasting gives a uniform porous surface called as profile. Without a surface profile the powder coat peels off from the surface

In this case the blasting operation is performed by using aluminium powder. The aluminium is coated onto the surface

Step 5: Fixture and Loading

Fixtures are structures which are set up to support the tools which are to be coated. Effective fixtures and correct loading of components are basic requirements for an economic coating process and best coating.

Loading process involves fixing the tool on the fixture to various slots and stands provided in the structure and racks on the entire fixture. Prior to loading the tool is handled with care and sterilized so that there is not even a small dust or grain of chip from the re-grinding process. So that the coating done does not peel off.

There are many details which are to be taken, all with an optimistic influence on quality and reproducibility of the coatings

1. Process and chamber compatible loading
2. Faultless operation of mechanical parts and magnets
3. Axis rotation
4. Process temperatures up to 500^o c
5. Vacuum maintained in the chamber
6. Accessibility to the surfaces on which the coating is to be done
7. Minimal mass to shorten heating and cooling times

Step6:Coating

This is the final and important step in coating process. The base metal to be coated is made as a plate of nearly 700-900gms where in the metal to be coated is used up for 500gms and the remaining is left for the next cycle where the base metal is again deposited on the plate.

The tools to be coated are racked up in the fixture and loaded into the machine. It is a Plasma Assisted Physical Vapor Deposition (PAPVD).The chamber is emptied first by sucking the air out of it by a vacuum pump. It is supplied with inert gases such as argon or helium as the coating has to take place in an inert atmosphere. a twisted coil is placed on many places inside the chamber which is covered by the plates which has the base metal to be coated in this place it is Aluminium-Chromium alloy in nitrogen atmosphere and it is scattered by the magnetic field at higher temperatures between 250^o – 400^o C and with the help of plasma the atoms are evenly distributed over the surface of the tool. It takes from 4 hours to 12 hours of time depending on the surface area of the area to be coated.

CHAPTER 10

TOOL LIFE CALCULATION

10.1. GEAR HOB DATA

Number of flutes: 15

Number of threads: 1RH

Lead : 11.0085

Lead angle: 2º46″30

Normal module            : 3.5

Normal pressure angle: 27^o

Helix angle                   : 0^o (SPUR)

No of teeth                    : 22

Length of the hob          : 170mm

Machining allowance on 0.035/flank (normal)

Hob Diameter                : 87.20 (±0.2)

Root Diameter               : 72.912

Circular pitch                  : 15.18mm

Usable length                  : 130mm

10.2. COMPONENT DATA

The job that is being manufactured is a spur gear. It is completely manufactured in a CNC machine. It is GLEASON GP300 which is a vertical milling machine. The machining is done by the machine automatically by the CNC. Loading and unloading is done manually.

Number of teeth                  : 27

Number of parts per cycle   : 300

Face-width                           : 50mm

Outer diameter                     : 104.2mm

S.NO	Part No 6642011120	SAP Cycle Time for        machining component (6642011120) in minutes	Total Production Qty (in nos)	Total time taken for the Qty produced(in minutes) (Total Qty x Cycle Time)
BEFORE COATING
1.		4	600	2400
AFTER COATING
1.		4	900	3600

Table 10.1Total batch production

10.3. HOB LIFE

Hob life in many industries are calculated as the number of components between successive re-grinding of the hob. But it is not an efficient method to calculate the tool life of a hob. Here we calculate the life in LIFE IN METERS (LIN) and life factor. In this case the rpm is not changeable in a CNC. The rpm is fixed in a CNC based on the tool material state and component material and metallurgy.

LIFE FACTOR       –   ()

LIFE IN METERS    –    N (NPPC) ()

USEN                     –    (FLUTES) ()

LIM       –          Linear Meters (in meters)

N –   Number of Gear Teeth

OD         –          Outer Diameter

NPPC     –          Number of Parts per Cycle (parts in stack)

FW         –          Face-Width (in meters)

Cos (HA) –        Cosine Function Of Gear Helix Angle

USEN –        Usable Length of Hob Teeth (within hob shift limits)

USELEN –         Usable Length of Hob (along hob axis between hob shift limits)

NCP        –       Normal Circular Pitch ofthe Hob

FLUTES -Number of Flutes

PARTS    –         Parts between Re-Sharpening

Number of Teeth (N):

It denotes the number of teeth on the gear component of outer diameter of 104.2mm. It is measured by using a vernier scale.

N- 27 teeth

Number of Parts per Cycle (N):

It denotes the number of parts produced in a cycle. It is also the number of parts that is stacked.

NPPC – 300 parts

Face Width (FW):

It is the length of the gear tooth’s land measured across the gear’s axis.

FW – 50mm (0.05m)

Usable Number of Teeth (USEN):

It is the usable number of teeth between the shift limits of the gear hob. It is calculated from the formulae given above. The total number of teeth is manually counted as follows

USEN – 180 {(15rows) *(12teeth per row)}

OUTER DIAMETER:

The Outer Diameter of the Hob Is Given As 104.2mm

OR- 104.2mm

USABLE LENGTH OF THE HOB (USELEN):

It is the usable length of the hob between the shift limits of the hob. Here in this hob it is noted as 130mm.

USELEN – 130mm

LIFE IN METERS (LIN):

Life of the hob that it has to cut through the total material for the entire batch.

NORMAL CIRCULAR PITCH (NCP):

Fig 10.3 Pitch

It is the distance between two successive similar points on the mid points of the teeth of a hob.

NCP – 15.18mm

10.4. CALCULATION

10.4.1. LIFE IN METERS

LIFE IN METERS – N (NPPC) ()

BEFORE COATING

LIFE IN METERS (LIN) – 27 (245) ()

LIM – 330.75m

AFTER COATING

LIFE IN METERS (LIN) – 27 (300) ()

LIM – 405 m

10.4.3. USEN

USEN – (FLUTES) ()

USEN – (15) ()

USEN – 128

10.4.4. LIFE FACTOR

LIFE FACTOR – (LIM) ()

BEFORE COATING

LIFE FACTOR – ()

LIM – 7.74

AFTER COATING

LIFE FACTOR – ()

LF – 9.49

OBSERVATIONS FROM THR EXPERIMENT 

It was observed that the tool life of the hob showed a prominent improvement after being coated by ALCRONA which had significant improvements in avoiding the wear and acting as a protective layer for the hob and thereby increasing the overall life of the hob between two successive re-sharpening periods.

REFRENCES

1. Harvey tools
2. pvd-coatings.co.uk
3. Physik und Technologies Dünner Schichten
4. ASM International, Materials Park ,Ohio, USA
5. Oerlikon Balzers Coating Guide
6. Hand Book of Manufacturing Process by James G Bralla.