ENGINE VALVE PRODUCTION

SUMMER PRACTICE F.D.

© 2010

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INDEX

2. INTRODUCTION…………………………………………………………………

3. MAIN TEXT OF THE REPORT…………………………………………………

3.1. WHAT IS VALVE? …………………………………………………………3

3.2. WORKING CONDITIONS OF ENGINE VALVE……………………….4

3.2.1. OPERATING STRESSES………………………………………………4

3.2.2. TEMPERATURES………………………………………………………4

3.3. MATERIALS…………………………………………………………………4

3.4. THE PRODUCTION TECNIQUES………………………………………...5-10

3.4.1. CHIP REMOVAL PROCESSES…………………………………………5-6

3.4.1.1. DRILLING…………………………………………………………….5

3.4.1.2. TURNING……………………………………………………………..5

3.4.1.3. MILLING……………………………………………………………..6

3.4.1.4. BROACHING………………………………………………………...6

3.4.1.5. GRINDING……………………………………………………………6

3.4.2. HEAT TREATMENT…………………………………………………….6-8

3.4.2.1. ANNEALING…………………………………………………………6

3.4.2.2. NORMALIZING……………………………………………………..7

3.4.2.3. TEMPERING…………………………………………………………7

3.4.2.4. CASE HARDENING…………………………………………………7

3.4.2.5. WELDING……………………………………………………………7

3.4.2.6. FORGING…………………………………………………………….8

3.4.3. CASTING………………………………………………………………….8

3.5. PRODUCTION STEPS OF THE ENGINE VALVE……………………...10-16

3.5.1. CUTTING ……………………………………………………………….113.5.2. BURNISHING…………………………………………………………….113.5.3. UPSETTING………………………………………………………………11

3.5.4. FORGING…………………………………………………………………11

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3.5.5. HEAD AND BAR POLISHING…………………………………………12

3.5.6. FRICTION WELDING………………………………………………….12

3.5.7. TEMPERING…………………………………………………………….12

3.5.8. TIP ROUGH GRINDING………………………………………………13

3.5.9. SAND BLASTING………………………………………………………13

3.5.10. WELD BURNISHING…………………………………………………13

3.5.11. STRAITGHING OPERATION……………………………………….13

3.5.12. 1st STEM ROUGH GRINDING………………………………………13

3.5.13. VALVE HEAD BURNISHING……………………………………….13

3.5.14. STELLITE DEPOSITION……………………………………………13

3.5.15. SEATING FACE ANGLE GRINDING………………………………14

3.5.16. HEAD DIAMETER FACING………………………………………...14

3.5.17. TIP GRINDING………………………………………………………..14

3.5.18. SEAT, GROOVE TURNING…………………………………………14

3.5.19. TIP HARDENING………………………………………………….....14

3.5.20. CHAMFER, GROOVE AND HEAD FACE BURNISHING………15

3.5.21. NECK PROFILE TURNING………………………………………...15

3.5.22. 2nd STEM ROUGH GRINDING ……………………………………15

3.5.23. GROOVE & VALVE TIP GRINDING……………………………..15

3.5.24. SURFACE FINISHING………………………………………………15

3.5.25. MARKING……………………………………………………………16

3.5.26. QUALITY CONTROL……………………………………………..16

4. CONCLUSION………………………………………………………………….16

5. APPENDIX……………………………………………………………………...17-24

TABLES, FIGURES & TECHNICAL DRAWINGS…………………………17-24

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2. INTRODUCTION

This engineering practice ( ME299 ) includes these issues:

-Heat treatment , hot working of steel;

-Chip removing operations as turning , grinding

-Press works

-Special purpose machines

-Welding operations

during production of engine valve. And, also foundry works.

The aim of the summer practice program for the junior year students of Mechanical Engineering Department is to reinforce and improve the theoretical and practical knowledge on production techniques and engineering drawing acquired in the previously completed coursework.

Theoretical knowledge is very important at the engineering part of a product. The engineer must know the criteria for the proper design of the product. But theoretical knowledge alone is not sufficient to manufacture a product. Some perfect designs might be developed with only theoretical knowledge, but such designs might not be manufactured because of the impossibilities on the production stage. Thus, practical knowledge has a great importance in the education of an engineer.

The summer practice has reached its goal that I have chance to see both production techniques and also working conditions. It is also very important to see how the procedure is running in a factory and how it got to be the relationships between workers and engineers

And aim of this practice report:

To analyzing the material and manufacturing processes that was involve in manufacturing engine valve and engine valve seat insert.

To learn the flow of processes that involve for producing a product.

The project is prepared with respect to the ME 299 Summer Practice Journal provided by University of ----- Faculty of Engineering.

Firstly, i’ m going to explain; What is valve , its working conditions and its production steps in the main text of report. Then, in the conclusion section , there is my opinions and discussions about summer practice.

3. MAIN TEXT OF THE REPORT

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3.1. WHAT IS VALVE?

Valves (shown in an engine in Fig. 3.1) are used to control gas flow to and from cylinders in automotive internal combustion engines. The most common type of valve used is the poppet valve (shown in Fig. 3.2 with its immediate attachments). The valve itself consists of a disc-shaped head having a stem extending from its center at one side. The edge of the head on the side nearest the stem is accurately ground at an angle – usually 45 degrees, but sometimes 30 degrees, to form the seating face. When the valve is closed, the face is pressed in contact with a similarly ground seat.

The two main types of internal combustion engine are: spark ignition (SI) engines (petrol, gasoline, or gas engines), where the fuel ignition is caused by a spark; and compression ignition (CI) engines (diesel engines), where the rise in pressure and temperature is high enough to ignite the fuel. Valves are used in these engines to control the induction and exhaust processes.

Both types of engine can be designed to operate in either two strokes of the piston or four strokes of the piston. The four-stroke operating cycle can be explained by reference to Fig. 3.3. This details the position of the piston and valves during each of the four strokes.

1. The induction stroke: The inlet valve is open. The piston moves down the cylinder

drawing in a charge of air.

2. The compression stroke: Inlet and exhaust valves are closed. The piston moves up the cylinder. As the piston approaches the top of the cylinder (top dead centre – tdc) ignition occurs. In engines utilizing direct injection (DI) the fuel is injected towards the end of the stroke.

3. The expansion stroke: Combustion occurs causing a pressure and temperature rise

which pushes the piston down. At the end of the stroke the exhaust valve opens.

4. The exhaust stroke: The exhaust valve is still open. The piston moves up forcing

exhaust gases out of the cylinder

3.2. WORKING CONDITIONS OF ENGINE VALVE

3.2.1. OPERATING STRESSES

During each combustion event, high stresses are imposed on the combustion chamber side of the valve head. These generate cyclic stresses peaking above 200 MN/m2 on the port side of the valve head, as shown in Fig.3.4. The magnitude of the stresses is a function of peak combustion pressure. The stresses are much higher in a compression ignition engine than a spark ignition engine.

3.2.2. TEMPERATURES

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A typical inlet valve temperature distribution is shown in Fig. 3.5. It was not made clear whether these were experimental or theoretical values or whether the valve was from a diesel or gasoline engine. The asymmetric distribution may have been due to non-uniform cooling or deposit build-up affecting heat transfer from the valve head. As shown in Fig. 3.6. , exhaust valve temperatures are much higher. Although both inlet and exhaust valves receive heat from combustion, the inlet valve is cooled by incoming air, whereas the exhaust valve experiences a rapid rise in temperature in the valve head, seat insert, and underhead area from hot exhaust gases.

3.3. MATERIALS OF ENGINE VALVES

New valve materials and production techniques are constantly being developed, these advances have been outpaced by demands for increased engine performance. These demands include:

Higher horsepower-to-weight ratio; Lower specific fuel consumption; Environmental considerations such as emissions reduction; Extended durability (increased time between servicing).

Most inlet valves are manufactured from a hardened, martensitic, low-alloy steel. These provide good strength and wear and oxidation resistance at higher temperatures.

I can list down the criteria of engine valve material:

Resistance to high-temperature corrosion [ ~700°C ] Hot strength (endurance strength at high temperature ) [ ~500MPa ] Hot hardness [ strength at ~700°C ] Resistance to oxidation Resistance to seizing and adhesive wear Availability of material supplied Overall cost (material and manufacturing costs) These criterias are due to high temperatures, thermal stresses, and corrosive gases.

For these reasons , in ------ Valves Inc. , these materials have been used in valve manufacturing: For exhaust valves ; 14871 Austentic steel ,and for inlet valves ; 1871 Martensitic Steel ,which include some alloying elements (shown in Table 2).

3.4. THE PRODUCTION TECHNIQUES

The production techniques employed are chip removal process, heat treatment, welding and forging. There is some brief information about these techniques.

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3.4.1. CHIP REMOVAL PROCESSES

3.4.1.1. DRILLING

Drilling is the manufacturing process where a round hole is created within a work piece or enlarged by rotating an end cutting tool, a drill. There is a technique called reaming is a similar process where a hole is enlarged to a very specific or accurate size by introducing a rotating end. There are six type of drilling process; twist drills, deep-hole drills, trepanning cutter, center drill and countersink, combination drills and spade drills.

3.4.1.2. TURNING

Turning is the machining of an external surface by rotating the work piece and feeding the tool along the work piece. The work piece rotates and a longitudinally fed single point cutter does the cutting. Machines used for this process are called lathes. Today, lathes are automatic or replaced with CNC’s.

Chosing a suitable cutting for turning operation:

Facing tools are ground to provide clearance with a center.

Roughing tools have a small side relief angle to leave more material to support the cutting edge during deep cuts.

Finishing tools have a more rounded nose to provide a finer finish. Round nose tools are for lighter turning. They have no back or side rake to permit cutting in either didection.

Left hand cutting tools are designed to cut best when traveling from left to right.

3.4.1.3. MILLING

Milling is a machining process by which a flat surface is generated by the removal of chips with the use of a rotating cutter. Milling process is used in a variety of industrial applications and whenever the complex shaping, removing large amounts of material, and accuracy is required. There are three main category of milling machines; column and knee machines, bed type milling machines, special purpose machines.

3.4.1.4. BROACHING

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Broaching is a unique process in which chips are removed by a number of seccessive teeth increasing in size. Roughing, semifinishing, and finishing teeth, consequently the related processes are combined in a single tool.

3.4.1.5. GRINDING

Grinding is a process which moves relative a surface in a plane while a grinding wheel contacts the surface and removes material, such that a flat surface is created. Produce a very flat surface, very accurate thickness tolerance and cutting tool sharpening are some of the reasons for grinding. This process is used in a big part of engine valve production.

3.4.2. HEAT TREATMENT

Heat Treatment is the controlled heating and cooling of metals to alter their physical and mechanical properties without changing the product shape. Heat treatment is sometimes done inadvertently due to manufacturing processes that either heat or cool the metal such as welding or forming.

Heat Treatment is often associated with increasing the strength of material, but it can also be used to alter certain manufacturability objectives such as improve machining, improve formability, restore ductility after a cold working operation. Thus it is a very enabling manufacturing process that can not only help other manufacturing process, but can also improve product performance by increasing strength or other desirable characteristics.

3.4.2.1. ANNEALING

Annealing applies normally to softening by changing the microstructure. It is usually relatively slow cooling in carbon and alloy steels. The more important purposes for which steel is annealed are as follows: To remove stresses; to induce softness; to alter ductility, toughness, or electric, magnetic or other physical and mechanical properties; to change the crystalline structure; and to produce a definite microstructure.

3.4.2.2. NORMALIZING

Normalizing is the process of austenizing ferrous alloys above the upper critical temperature and then cooling in air. Heating steels to approximately 100 F above the critical temperature range followed by cooling to below that range in still air at ordinary temperatures. This heat treat operation is used to erase previous heat treating results in carbon steels to 40% carbon, low alloy steels, and to produce a uniform grain structure in forged and cold worked steel parts. The main difference between annealing and normalizing is that fully annealed parts are uniform in softness (and machinability) throughout the entire part; since the entire part is exposed to the controlled

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furnace cooling. In the case of the normalized part, depending on the part geometry, the cooling is non-uniform resulting in non-uniform material properties across the part.

3.4.2.3. TEMPERING

Tempering is also called drawing. Reheating hardened, usually quenched, steel to some temperature below the lower critical temperature followed by any desired rate of cooling after the steel has been thoroughly soaked at temperature. A quench refers to a rapid cooling and a structure is formed during quenching which is called martensite forms. This form, martensite, is very hard and so brittle. In fact, tempering is used for martensite materials to relieve any internal stresses.

3.4.2.4. CASE HARDENING

Case Hardening is a heat treatment or a combination of heat treatments of surface hardening involving a change in the composition of the outer layer of an iron-base alloy in which the surface is made substantially harder by inward diffusion of a gas or liquid followed by appropriate thermal treatment. Typical hardening processes are carburizing, cyaniding, carbo-nitriding and nitriding.

3.4.2.5. WELDING

Welding is a fabrication process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpieces and adding a filler material to form a pool of molten material (the weld puddle) that cools to become a strong joint, but sometimes pressure is used in conjunction with heat, or by itself, to produce the weld. This is in contrast with soldering and brazing, which involve melting a lower-melting-point material between the workpieces to form a bond between them, without melting the workpieces. There are basically five groups in welding process; oxyfuel gas welding, arc welding, resistance welding, solid state welding.

Also, another welding type “friction welding“ exist; in this type of welding; the materials are rotated at high speed and forced together generating enough heat to bond together. Many dissimilar metal combinations can be joined using this process.

3.4.2.6. FORGING

Forging is the process in which metal, cold or heated, is shaped into a component geometry through the use of multiple blows with a drop hammer or through the application of pressure with a hydraulic press. For most forging processes, a set of dies are required. Due to grain orientation, forgings are a desirable choice when high strength and excellent fatigue life is required for the component. Many materials can be forged including aluminum and steel. There are four major types of forgings used in industry; hand, blocker, conventional, and pressed.

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3.4.3. CASTING

A casting may be defined as a metal object obtained by allowing molten metal to solidify in a mold , the shape of the object being determined by the shape of the mold cavity.

Certain advantages are inherent in the metal casting process. These often form the basis for choosing casting over other shaping processes such as machining, forging, welding, stamping, rolling, extruding, etc. Some of the reasons for the success of the casting process are:

The most intricate of shapes, both external and internal, may be cast. As a result, many other operations, such as machining, forging, and welding, can be minimized or eliminated.

Because of their physical properties, some metals can only be cast to shape since they cannot be hot-worked into bars, rods, plates, or other shapes from ingot form as a preliminary to other processing.

Construction may be simplified. Objects may be cast in a single piece which would otherwise require assembly of several pieces if made by other methods.

Metal casting is a process highly adaptable to the requirements of mass production. Large numbers of a given casting may be produced very rapidly. For example, in the automotive industry hundreds of thousands of cast engine blocks and transmission cases are produced each year.

Extremely large, heavy metal objects may be cast when they would be difficult or economically impossible to produce otherwise. Large pump housing, valves, and hydroelectric plant parts weighing up to 200 tons illustrate this advantage of the casting process.

Some engineering properties are obtained more favorably in cast metals. Examples are: More uniform properties from a directional standpoint; i.e., cast metals exhibit the same

properties regardless of which direction is selected for the test piece relative to the original casting. This is not generally true for wrought metals.

Strength and lightness in certain light metal alloys, which can be produced only as castings. Good bearing qualities are obtained in casting metals. A decided economic advantage may exist as a result of any one or a combination of points

mentioned above. The price and sale factor is a dominant one which continually weighs the advantages and limitations of process used in a competitive of enterprise.

There are many more advantages to the metal-casting process; of course it is also true that conditions may exist where the casting process must give way to other methods of manufacture, when other processes may be more efficient. For example, machining procedures smooth surfaces and dimensional accuracy not obtainable in any other way; forging aids in developing the ultimate of fiber strength and toughness in steel; welding provides a convenient method of joining or fabricating wrought or cast products into more complex structures; and stamping produces lightweight sheet metal parts. Thus the engineer may select from a number of metal processing methods that one or combination, which is most suited to the needs of his work.

The various steps in the production of castings are briefly summarized for the benefit of those who may be unfamiliar with foundries and the casting process.

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In Orjinal Casting , before production, casting molds are prepared with sufficent tolerance (for aliminium this tolerance is about %0.6) according to technical drawings of the products.

Aluminium casting processes are classified as Ingot casting or Mould casting. During the first process, primary or secondary aluminium is cast into rolling ingot (slab), extrusion ingot (billet) and wire bar ingot which are subsequently transformed in semi- and finished products.

The second process is used in the foundries for producing cast products. This is the oldest and simplest (in theory but not in practice) means of manufacturing shaped components.

This section describes exclusively Mould casting which can be divided into two main groups:

·         Sand casting

·         Die casting

Other techniques such as "lost foam" or "wax pattern" processes are also used but their economical importance is considerably lower than both listed techniques.

Sand Casting

In sand casting, re-usable, permanent patterns are used to make the sand molds. The preparation and the bonding of this sand mould are the critical step and very often are the rate-controlling step of this process. Two main routes are used for bonding the sand molds:

         The "green sand" consists of mixtures of sand, clay and moisture.

         The "dry sand" consists of sand and synthetic binders cured thermally or chemically.

The sand cores used for forming the inside shape of hollow parts of the casting are made using dry sand components.

This versatile technique is generally used for high-volume production. Normally, such molds are filled by pouring the melted metal in the filling system.

Die Casting: In this technique, the mould is generally not destroyed at each cast but is permanent, being made of a metal such as cast iron or steel. There are types of die casting. High pressure die casting is the most widely used, representing about 50% of all light alloy casting production. Low pressure die casting currently accounts for about 20% of production and its use is increasing. Gravity die casting accounts for the rest, with the exception of a small but growing contribution from the recently introduced vacuum die casting and squeeze casting process.

Low Pressure Die Casting: The die is filled from a pressurised crucible below, and pressures of up to 0.7 bar are usual. Low-pressure die casting is especially suited to the production of components that are symmetric about an axis of rotation. Light automotive wheels are normally manufactured by this technique.

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3.5. PRODUCTION STEPS OF THE ENGINE VALVE

Process involved for engine valves basically need high dimensional accuracy. And there is many production steps during manufacturing (shown in figure.3.8.). I am going to try to explain some of these steps below:

Cutting Bar Burnishing Upsetting Forging Head and Bar Polishing Friction Welding Tempering Tip Rough Grinding Sand Blasting Weld Burnishing Rectification 1st Stem Rough Grinding Valve Head Burnishing Stellite Deposition Seating Face Angle Grinding Head Diameter Facing Tip Grinding Seat ,Groove Turning Tip Hardening Seat ,Groove, Valve Head Face Burnishing Neck Profile Turning 2nd Stem Rough Grinding Tip Finish Grinding Groove Grinding Surface Finishing Marking Quality Control Packing

3.5.1. CUTTINGFirstly, the metal bars that are used in manufacturing, are cut in precise dimensions for

upsetting process.

3.5.2. BURNISHINGAfter cutting operation, next step is burnishing step. A good surface finish has a positive and

lasting effect on the functioning of engine valves. Poor surface finish increase production time,

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production cost and of course invalid tolerances. In manufacturing of valve dimensional accuracy is quite important condition.

Burnishing is one of the no-chip finishing process. That is why, after cutting operation, this process is applied on metal bars.

3.5.3. UPSETTING Electrical Upsetting of steel rods ranging from 6mm diameter to 40 mm diameter in the length

of about 100 mm to 500 mm long on electrical controlled up setters. Electrical upsetting makes a smooth material flow and reduces fatigue occurred during forging process. A variety of horizontal and vertical electrical upsetters are available to meet mass production requirements.

Steps are:1. The steel is heated to 1050 °C by electrical resistance between two contacts.2. As the steel reaches this temperature more material if forced through the

contacts by a hydraulic ram until enough volume is "upset" to make the pre-form.3. Then, the pre-form is then passed immediately to the forge.

3.5.4. FORGING

After upsetting process the upsetted part will go through forging process immediately. Forging is the term for shaping metal by using localized compressive forces. The forging process of producing engine valves is hot forging where the press capacity is 75 tons.

Advantages : Disadvantages :

1. Flexibility of design process 1. The skill involved is not easily acquired

2. Versatility of the forging itself. 2. Tooling needed represents a considerable

The design is not limited to the basic amount of time and money invested.

dimensions of the bar

3.5.5. HEAD AND BAR POLISHING

In this step, head and bar polished for labour easiness.

3.5.6. FRICTION WELDING

Friction welding is a process of joining head part of the engine valve with the straight rod use lathe machine. Friction welding technology is a completely mechanical solid-phase process in which heat generated by friction is used to create high-integrity joint between similar or dissimilar metals, and even thermoplastics.

Advantages : Disadvantages :

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1. Quality control cost is minimal with 1. Costs in tooling and setup

a guarantee of high quality welds 2. Tight concentricity requirements

2. Weld cycle is extremely short so that

the productivity is attractive

In engine valve production, this process use in to join valve head to the valve stem. This process is especially applied on exhaust valve. The reason of this, the material that use in exhaust valve production, is not easy to hardening, so different material is used in valve stem.

3.5.7. TEMPERING

The next step after the engine valve had been forged is heat treatment (tempering). After forging step, steel is harder and is too brittle for next steps. Also, severe internal stresses are really high. To relieve internal stresses and reduce brittleness, you should temper the steel. Tempering consists of heating the steel to a specific temperature (below its hardening temperature), in ------ valves the temperature is 660 °C, holding it at that temperature for an hour and then cooling it in air. The resultant strength, hardness, and ductility depend on temperature to which the steel is heated during the tempering process.

The purpose of tempering is to reduce the brittleness and internal stresses .Besides reducing brittleness, tempering softens the steel. That is unavoidable, that s why, after this process, some parts of valves are hardened again.

3.5.8. TIP ROUGH GRINDING

Grinding is a finishing process used to improve surface finish, abrade hard materials, and tighten the tolerance on flat and cylindrical surfaces by removing a small amount of material. In engine valve production, the grinding processes apply on step by step to get accurate dimensions.

This step is first step of tip grinding process.

3.5.9. SAND BLASTING

Sand blasting is the process of using rotated steel ball (1-3 mm dia.) in the closed area to clean working part’ s surface after heat treatments. Especially in inlet valve production, if head face and seat angle turning is not applied, cleaning is made by using this process.

3.5.10. WELD BURNISHING

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After friction welding process, there is a little outgrowth on welded area. So, you need to apply burnishing process on these parts.

3.5.11. STRAITGHING OPERATION

Sometimes, steel rods may not be straight after forging; in this case these rods are straighten by using , if it could.

3.5.12. 1 st STEM ROUGH GRINDING

This step is the 1st step of the stem grinding processes. In this step, stem is grinding to nearly its dimensions and surface finish. Stem run-out must be 0,8 mm.

3.5.13. VALVE HEAD BURNISHING

After upsetting and forging, we need to apply burnishing process on valve head.

3.5.14. STELLITE DEPOSITION

The follow up process after the heat treatment is satellite welding process. Stellite is a special alloys that welded onto the seat (shown in Fig.3.7.). Purpose is to improve the corrosion and high temperature wear resistance, mainly in exhaust valves; a cord of special material is placed onto the valve seat.

Advantages :

1. High residual stresses are relieved

2. Hardness improved.

3. Overlaid with corrosion and wear resistant material (stellite) for long service life.

In stellite deposition process Gas Tungsten Arc Welding (GTAW) is used. GTAW is frequently referred to as TIG welding.  TIG welding is a commonly used high quality welding process.  TIG welding has become a popular choice of welding processes when high quality, precision welding is required. 

In TIG welding an arc is formed between a nonconsumable tungsten electrode and the metal being welded. Gas is fed through the torch to shield the electrode and molten weld pool.  If filler wire is used, it is added to the weld pool separately.

Advantages:

Superior quality welds Welds can be made with or without filler metal Precise control of welding variables (heat) Free of spatter Low distortion

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Of course after this process, welding defects control is made by quality control technicians.

3.5.15. SEATING FACE ANGLE GRINDING

The coming up process is seat grinding. The typical seat angle is 45°but 30°and 20°also may be used. In ------ valves, set angle is 45°. The grinding process need to meet the accuracy required since seat angle is critical surface to ensure complete sealing of the combustion chamber with valve seat insert.

3.5.16. HEAD DIAMETER FACING

The next process is head diameter facing by turning process. Purpose of this process is to precisely produce the required diameter for the head part of engine valve. This process is applied in ± 0,15 tolerance. And of course, during the process the diameter of valve head controlled by labourer who apply head diameter facing.

3.5.17. TIP GRINDING

This step is the last grinding step before tip hardening and this grinding process more smooth than first tip grinding.

3.5.18. SEAT, GROOVE TURNING

In this step, turning process is used to make grooves at the end of the stem and to make seat angle. After these steps, groove diameter, dimensions and seat angle are controlled by control fixtures.

3.5.19. TIP HARDENING

The next process is tip hardening process. Valve Stem-End Induction Hardening machine is used and can provide perfect quality of hardening. The purpose of this process is to increase the wear resistant of the tip since this part is continuously pounded by camshaft during the operation of engine valve.This process purpose is to increase hardness of the tip of valve to 52 HRC. Also the hardness length is about 18-20 mm and hardness depth is about 2-3 mm.

After tip hardening, tempering process apply on again. This time, valve is heated to 200 °C and held it for around 10 seconds. Obviously, after this process the hardness is decrease but this decreasing is about 2-3 HRC.And of course , the reason of this process is to decrease the tip brittleness.

3.5.20. CHAMFER, GROOVE AND HEAD FACE BURNISHING

After turning and grinding processes, burnishing process apply on again to getting dimensional accuracy. Burnishing process allow to measuring and working on parts easily.

3.5.21. NECK PROFILE TURNING

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Following process is neck profile turning. Once again the exhaust valve will go through CNC turning process but this time is to make a curve at the neck of the exhaust valve.The curve radius is R8 ± 0.5 .

Advantages : Disadvantages :

1 Economical precision in desired 1. Need to combine developing precision

dimension. engineering technique with a high

2 Capability for nonrotationally- performance but flexibility computer

symmetric control. software.

3.5.22. 2nd STEM ROUGH GRINDING

In 2nd stem rough grinding step, valve stem take its exact dimensions. After this step, valve is ready to finish grinding and quality control operations.

3.5.23. GROOVE & VALVE TIP GRINDING

In this step, valve grooves and valve tip also take their exact dimensions and angles. For example; in Hyundai Excel exhaust valves; groove has these dimensions and angles: groove radius R0,57 ±0,05, and distance between two grooves 2±0.025 mm. Valve tip final diameter 4,45 – 0,15 mm , tip hatch dimensions 0,5 x 45°.

3.5.24. SURFACE FINISHING

The final step of engine valve production is surface finishing. In this step, engine valve surface is processed to specific surface roughness. For Hyundai Excel automobile engine valve, the surface roughness is between 0.8 and 3 micron.

3.5.25. MARKING

In this step, valves take their names and ready for quality control and packing.

3.5.26. QUALITY CONTROL

Specialized technician is provided with highly accurate tools such as contour measuring instruments, form and positional measuring instruments, surface roughness tester, profile projectors, qualified metrology staff also works in this area in order to achieve the best quality.

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After all processes; quality control technician takes a sample, then works on the sample with highly accurate tools. If the sample is not in standards, then takes another sample ; if the sample is in same condition, the series of this sample is cancelled.

Also after friction welding process, technician takes a sample, then applies a tensile test and after tip hardening process, the hardness test is applied for gain desired conditions.

4.CONCLUSION

The most significant experience that is gained in this summer practice is learning how to apply the theoretical knowledge into practice. This is improved by observing and discussing the technical processes, mostly concerning the manufacturing methods, with the engineers and the workers. With this way, more practical and theoretical knowledge is obtained.

As a result, this summer practice gave me some theoretical knowledge, some experience, some skills that are directly applicable and useful in my career in the future. I had the opportunity to observe how the projects go on, the personnel relations among their superiors and each other. So I can say that this summer practice has been very useful in comparison with most of the lessons I have taken at school.

------ INC.

BOARD OF MANAGEMENT

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Marketing Supervisor PLANT MANAGER Staff Supervisor

Accountant

Quality Control Supervisor Maintenance Supervisor Manufacturing Supervisor

Inspector Immobile Quality Draftsman Gage Staff

Controller

Packing Staff

Relay Foreman

Operator Mold Foreman Plating Foreman

Table.1. ------ Engine Valves Company Organization

------symbol

CNSMO4 SOS3 VM21 VM22 XM114 VA64 X21RB PERX2

 DIN no: 1.6511 1.4718 1.4747 1.4748 1.4871 1.4785 1.4882 2.4952

 Analysis %

 C 0,32-0,40 0,40-0,50 0,75-0,85 0,80-0,90 0,48-0,58 0,57-0,65 0,48-0,58 £ 0,10

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 Si £ 0,40 2,70-3,30 1,75-2,75 £ 1,00 £ 0,25 £ 0,25 £ 0,25 £ 1,00

 Mn 0,50-0,80 £ 0,80 £ 1,00 £ 1,50 8-10 9,5-11,5 8-10 £ 1,00

 P £ 0,035 £ 0,040 £ 0,030 £ 0,040 £ 0,045 £ 0,050 £ 0,045 £ 0,020

 S £ 0,030 £ 0,030 £ 0,030 £ 0,030 £ 0,035 £ 0,025 £ 0,035 £ 0,010

 Cr 0,90-1,20 8-10 19-21 16,5-18,5 20-22 20-22 20-22 18-21

 Mo 0,15-0,30 2,00-2,50 0,75-1,25 4-5

 Ni 0,90-1,20 1,00-1,75 3,25-4,50 £ 1,50 3025-4,50 rest

 V 0,30-0,60 0,75-1,00

 Co 15-21

 N 0,40-0,55 0,40-0,55

 Nb 1,75-2,25

 Al 0,80-2,00

 Fe rest rest rest rest rest rest rest £ 5,00

 Ti 1,80-3,00

XM114-Exhaust Valve Material VA64-Inlet Valve Material

Table 2.Alloying Elements which used in Production (Source by ------ Valve Inc.)

Figure. 3.1 Overhead camshaft valve drive

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Figure. 3.2.Engine Valve and Seat

INDUCTION COMPRESSION EXPANSION EXHAUST

Figure. 3.3.Four Stroke Engine Cycle

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400 (MN/mm2)

200

Figure.3.4.Tensile Stresses on the Surface due to Combustion Loading

Figure.3.5. Inlet Valve Temperature Distribution

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Figure.3.6. Exhaust Valve Temperature Distribution

Figure.3.7.Stellite Deposition Applied Areas On Valve

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Cutted Bars Upsetting Process Friction Welding

Grinding Process Valve Head Facing Tempering

Tip Hardening Quality Control Engine Valves

Figure.3.8. A Few Steps Of Production

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(a) Valve’s Overall Body(b) Valve Head Before Upsetting(c) Valve Head After Upsetting(d) Valve After Forging And Friction Welding Processes(e) Valve After Stem And Seat Grinding(f) Valve Stem After Stem Rough Grinding(g) Valve After Tip Grinding(h) Valve After Full Body Grinding(i) Valve After Surface Finishing

Figure.3.9. Picture of Workpiece After Production Steps

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