seminar on case study of investment casting by manish pujara

Prepared byPujara Manish7th Mechanical

Guided by Proff. P.H. DarajiMechanical Dept.

C.U SHAH COLLEG OF ENGG. & TECHWADHWAN CITY-363 030

of 38

WADHWAN CITYDIST: SURENDRANAGAR

CERTIFICATE

This is to certify that MR PUJARA MANISH is studying in Sem. – VII of B.E. MECHANICAL having Roll No-65 has completed his seminar on the following topic successfully.

Topic Name: A SEMINAR ON CASE STUDY OF INVESTMENT

CASTING

Staff – In charge Head of Dept.

Date: ___________

of 38

ACKNOWLEDGMENT

I am grateful to p.h.daraji professor of mechanical engineering, for all help &guidance given for this study. I should also like to thank manager of I&PCL for permitting visit

of 38

ABSTRACT

This seminar is based on my orientation visit to investment & precision casting limited at Bhavnagar.

investment casting process is powerful casting process. Investment casting process is used where high tolerance is required .in this process wax pattern is used.

Today in this era new casting technology is developing so everyone look for good quality production to satisfy all this need, investment casting is the better casting process.

INDEX

of 38

Page no

AcknowledgmentAbstract1. Introduction 5 2. Classification of casting 63. process of investment casting 7

3.1. engineering section 73.2. die making section 73.3. waxing section 10 3.4. selling section 14 3.5. melting section 153.6. surface finishing section 193.7. heat treatment process section 293.8. testing section and inspection section 33

4. application of investment casting 345. merit & demerit of investment casting 376. conclusion 38Reference

1. INTRODUCTION

of 38

Investment casting is also known as the lost wax process. This

process is one of the oldest manufacturing processes. The Egyptians used it in the time of the Pharaohs to make gold jewelry (hence the name Investment) some 5,000 years ago. Intricate shapes can be made with high accuracy. In addition, metals that are hard to machine or fabricate are good candidates for this process. It can be used to make parts that cannot be produced by normal manufacturing techniques, such as turbine blades that have complex shapes, or airplane parts that have to withstand high temperatures.

The mold is made by making a pattern using wax or some other material that can be melted away. This wax pattern is dipped in refractory slurry, which coats the wax pattern and forms a skin. This is dried and the process of dipping in the slurry and drying is repeated until a robust thickness is achieved. After this, the entire pattern is placed in an oven and the wax is melted away. This leads to a mold that can be filled with the molten metal. Because the mold is formed around a one-piece pattern, (which does not have to be pulled out from the mold as in a traditional sand casting process), very intricate parts and undercuts can be made. The wax pattern itself is made by duplicating using a stereo lithography or similar model-which has been fabricated using a computer solid model master.

The materials used for the slurry are a mixture of plaster of Paris, a binder and powdered silica, a refractory, for low temperature melts. For higher temperature melts, sillimanite an alumina-silicate is used as a refractory, and silica is used as a binder. Depending on the fineness of the finish desired additional coatings of sillimanite and ethyl silicate may be applied. The mold thus produced can be used directly for light castings, or be reinforced by placing it in a larger container and reinforcing it more slurry.

Just before the pour, the mold is pre-heated to about 1000 ºC (1832 ºF) to remove any residues of wax, harden the binder. The pour in the pre-heated mold also ensures that the mold will fill completely. Pouring can be done using gravity, pressure or vacuum conditions. Attention must be paid to mold permeability when using pressure, to allow the air to escape as the pour is done.

Tolerances of 0.5 % of length are routinely possible, and as low as 0.15 % is possible for small dimensions. Castings can weigh from a few grams to 35 kg (0.1 oz to 80 lb), although the normal size ranges from 200 g to about 8 kg (7 oz to 15 lb). Normal minimum wall thicknesses are about 1 mm to about 0.5 mm (0.040-0.020 in) for alloys that can be cast easily.

The types of materials that can be cast are Aluminum alloys, Bronzes, tool steels, stainless steels, Stellite, Hastelloys, and precious metals. Parts made with investment castings often do not require any further machining, because of the close tolerances that can be achieved.

of 38

2. CLASSIFICATION OF CASTING PROCESS

a) casting in expendable mouldThese are only once and must be broken up to free solidified casting

b) casting in percent mould These last up several casting

CLASSIFICATION BASED ON THE PURPOSE OF CASTINGa) ingote,slab,and billet casting

Metal is wrought alloy, in preparation for rolling, extrusion or forging, it is cast into a simple shape suitable for furthered working.

b) shape casting The metal is cast into the final shape, which need only cleaning and /or machining to produce finished part.

OTHER CASTING PROCESS

a) sand castingSilica sand is used more universally for making casting than any other mould material and it is called sand casting

b) die castingThis process employs a metal mould into which molten metal can be transferred with or without the use externally applied presser .in this casting process, presser is used to inject molten metal into the die cavity. Die casting have excellent surface finish and dimension accuracy

c) shell castingThis is modification of sand casting in which a relatively thin shell forms the mould cavity into which metal is poured .this molding involves the use of resinous material the phonon formaldehyde or urea formaldehyde type as binder agent for silica sand.

d) investment castingIn this process wax pattern is used.

e) centrifugal castingThis casting is used for rotational symmetry, such as long cylinder .in this process metal is poured into mould and this mould is rotated about its axisSymmetry

f) plaster castingIf sand citing is changed so that plaster of perish is replaced for sand as the molding material

g) slush casting

of 38

Hollow casting such as statues, can be made by pouring a low melting point alloy into a bronze or a plaster mould

h) continues casting Generally, this is used for production part such as road, pipes, sheet metal and other partial known as semifinals products in uninterrupted process

In this process, molten metal is poured into tower nearly 300 m high.

3. PROCESS FOR INVESTMENT CASTING

3.1 ENGINEERING SECTIONIn this section, auto cad & pro-e type software is used for

drawing to pattern, runner, riser and pouring cup .

Advantages1. accuracy in dimension.2. speedy work.3. not require old instrument of drawing.

Disadvantages1. require skillful person.

3.2 DIE MAKING SECTION

Make a mold. A mold is the negative shape of your pattern. The mold is created from a mixture consisting of casting plaster, sand, and water. The dry mixture of 1 part 30-minute casting plaster and 2parts 30-grit sand is known as 30-30 mix. When it is mixed with water, it forms viscous slurry. After about 30 minutes (sometimes less), the mixture “sets up” or becomes solid. You will need the following things for this step: Cardboard, duct tape, 30-minute casting plaster, 30-grit sand, 2 5 gallon buckets, and A bucket with quart graduations for measuring.

of 38

A. Place some brown paper on the floor in the area where you are going to work. (From the roll in the machine shop, near the band saw.) Working with plaster is exceedingly messy and hard to clean up; layout a lot of paper (at least a 12’ x 12’ area, probably in the foundry or outside) and you will thank to yourself come cleanup time.

B. Prepare the pattern. Draw the parting line or lines on the pattern with a pencil or a score lightly with a blade. Parting lines should be drawn so that there will be no undercuts. That is, if you immerse the pattern into the plaster up to the parting line, you will be able to remove it when the plaster has hardened. This is important: if you have undercuts in your clay pattern you will not be able to remove your wax pattern later on without destroying it. You should also coat the Pattern with Vaseline which will make it easier to remove from the plaster.

C. Make a 5-sided (open topped) cardboard box that is about 2 inches wider, longer, and thicker than your pattern. Tape the sides together with duct tape. You will be pouring the liquid 30-30mixture into this box.

D. Make up some 30-30 dry mixes: Three things are very important in this step. The first is crucial to your health: wear a dust mask to protect your lungs. Dry plaster consists of very fine particles which become airborne, and are quite bad for you. Dust masks are available from a TA. The second and third things are

of 38

crucial to the success of your project: When you mix the sand and plaster together, do not assume that 8 qts of sand and 4 qts of plaster make 12 qts of mix. The Plaster particles are much finer than the sand and will fill in the gap between the sand particles, creating a smaller volume than the sum of the two individual volumes. Also, make sure that the buckets you use are spotlessly clean and completely dry. If there is a little bit of water in the dry mix bucket, it will form hardened bits of plaster which will catalyze the reaction when you mixWater with 30-30 mix causing it to set up too quickly. Mix 2 parts 30-mesh sand and 1 part 30-minute casting plaster in a spotlessly clean and completely dry bucket. 8 qts of sand and 4 qts of plaster is about the most you can easily mix in a 5 gallon bucket.

E. Compute the amount of water and 30-30 mix required. To do this, measure the volume in cubic inches of the cylinder you are using, and convert to quarts. 1 quart = 58 cubic inches. Multiply the number of quarts by 0.65 to get the volume of water you’ll need. The ratio of 30-30mix to water is 2.4:1 by volume; compute the amount of dry 30-30 mix required. If the volume of water required is less than 2.5 gallons, you will be able to mix the plaster in one bucket with the help of just one other person. If it is larger, you will need two people and two 5-gallon bucketsPer 2.5 gallons of water. If this is the case, you will need to have each set of two people mix the plaster and water simultaneously so that it is ready to pour at exactly the same time.

F. Measure out the water into a 5-gallon bucket. Again, make sure that the bucket is spotlessly clean. Any little bit of plaster left over from the last time someone investment will make thePlaster set up before you have a chance to pour it around your pattern. In addition, the ratio of water to plaster is important, so take considerable care in measuring the amount of water

G. Measure out the 30-30 mixture into a clean and dry 5-gallon bucket. Remember you must measure out the mixture now - do not assume that the 8 it's of sand and 4 it's of plaster you mixed before have made 12 quarts of mix! Many investments have been ruined by this error.

H. Prepare to pour the mold. Place your cardboard box and the two 5 gallon buckets (one with water, the other with 30-30 mix) on the floor, and make sure your clay pattern is nearby. You will need to recruit one other person to help you at this point.

I. Make sure that your hands and the hands of your helper are clean and dry, and then sift the 30-30mix into the water with your hands. You should do this quickly so that the plaster does not start To set up to early. Try to do the sifting in about 3 or 4 minutes. Try sifting the mix from just above the water, to not agitate it. Also, try to sift evenly over the water so that the dry

of 38

midgets well distributed and does not end up in one gigantic mountain in the center of the bucket.

J. Wait for 2 or 3 minutes so that the water has a chance to soak up the plaster.

K. Mix with your hands gently to combine the 30-30 mix and the water. Work out any lumps of plaster.

L. Pour the plaster into the box until it is half-full. You should do this as soon is the plaster is mixed, since you only have a limited time until it sets up. Place the clay pattern into the plaster up to the parting line. Hold it there until the plaster has set up (probably less than 10 minutes; if it hasn’t set up in 20 minutes you probably used to much water and it will never set up, in which Case you should pull your pattern out and go back to .

M. After the plaster has set up, carve three hemispheres about the diameter of a pea into the plaster with a wax-working tool or knife. This will insure that the two halves of the mold line up. Leave the pattern in place and cover the first half of the mold with Vaseline.

N. If you have only one parting line, then mix the plaster as before and pour it into the other half of the box. If you have more than one parting line, see the variations section...

O. When the plaster has set up take the mold apart and remove the pattern. You may need to pry the plaster apart with a flat head screwdriver by working it around the outside of the parting line.

P. Carve a channel into one plaster section of the pattern so that it is possible to pour wax into the void.

3.3 WAXING SECTIONIn this waxing section, four process done which is given below

following manufacturing of runner ,riser ,gate of wax manufacturing of wax pattern inspection of pattern and runner ,riser, gate assembly of wax pattern and runner ,riser ,gate

I. manufacturing of runner ,riser ,gate First of all runner, riser, gate are designed according to given

below

Design of gate

a good gating design ensures that the distribution of the metal in the mould cavity at a proper rate without excessive loss ,turbulences loss ,and entrapped gases and slage .after

of 38

melting the metal is poured or infected into the mould cavity , if the liquid metal the is poured very slowly ,then the time taken to fill up the mould is rather long and the solidification starts before the mould has been completely filled up .this problem can be avoided by using too much superheat ,but then gaze solubility may cause a problem . Now on the other hand if the liquid metal impinges on the mould cavity with high velocity, the mould surface may be eroded. The design of gating system depend on both the metal and mould composition .the getting design can be classified into three categories

I. vertical getting:-the liquid metal is poured vertically to fill the mould with atmospheric pressure at the base

II. bottom getting :-the liquid metal is filled in the mould from bottom to top, thus avoiding splashing and oxidation associated with vertical gating

III. horizontal getting:-additional horizontal portion are introduced for better distribution of the liquid metal with minimum turbulence

Time taken to fill up a mould The integrated energy balance equation on the basis of per unit mass flow, more commonly known as Bernoulli's equation will be used to calculate filling time. in case of simple vertical as shown in fig, it is assumed that pressure at point 1 and 3 is equal i.e.p1=p2 and liquid metal level at point 1 is maintained constant. Thus the velocity at point 1 is equal to zero (v1=0). Moreover, the friction losses are neglected. Then, the energy balance equation between 1 and 3.

(P1/qg)+ (v1

2/2g) +Hf= (p3/qg) + (v32/2g) +0

Since p1=p2 and v1=0 v3= (2ghft) 1/2

Where v3 is the velocity of the liquid metal at the gate or may be denoted as vg

Vg=v3= (2ght) 1/2

So, the time taken to fill up the mould is Tf=V/Ag *v3

Where Ag=the area of cross section of gate and V= volume of mould

For bottom gating as shown in fig, the time to fill up the mould can be calculated by applying Bernoulli's equation between points 1 and 3

So, we can get equation for time taken to fill up the riser is calculated by below equation

Tf=Ar/Ag*(2g) 1/2* 2((hf) 1/2) =Ar/Ag (2/g) 1/2 *(hf) 1/2

Where Ar=riser cross section area Ag=gate cross section area

of 38

Why is gating system used?

1. To prevent continuous, uniform feed of molten metal, with as little turbulence as possible to the mould cavity. excessive turbulence result in the aspiration of air and the formation of dross

2. to supply the casting with liquid metal at best location to achieve proper directional solidification and optimum feeding of shrinkage cavities

3. to fill the mould cavity with molten metal in the shortest possible tome to avoid temperature gradient

4. To provide with a minimum of excess metal in the gates

and riser, inadequate rate of metal entry, on the other hand, will result many defect in the casting.

5. To prevent erosion of the mould walls.

6. to prevent slag ,sand and other foreign partial from entering the molding

What is pouring basin?

This reduces the eroding force of the liquid metal stream coming directly from the Furness .a constant poring head can also be maintained by using pouring basinWhat is runner?in large casting ,molten metal is carried from the sprue base to several gates around the cavity thoroughly a passageway called runner .the runner is generally proffered in the drag ,but it may sometime be lo9cated in the cope , depending on the shape of the casting .it should be streamlined to avoid aspiration and turbulence.

What is riser?

A riser is a hole cut or molded in the cope to permit the molten metal to rise above the highest point in the casting. The riser a several number of useful purposes .it enables the pourer to see the metal is as it falls into the mould cavity. If the metal does not appear in the riser .it significant that either the metal is insufficient to fill the mould cavity or there is some obstruction to the metal flow between spur and riser and riser remove gas and steam from the mould cavity.

Manufacturing of wax pattern:

of 38

Wax pattern is made by using of wax injection molding machine and in this process die is used as master pattern .wax at 150 to 170 of is injected into die halves at a presser 7 to 70 kg /cm2

Below wax is used for investment casting:1. RC10 and RC11(paraffin wax)

Temperature and humidity is maintained in this section. Temperature is between 26 to 30 degree Celsius and humidity is nearer 56

Inspection of pattern and runner, riser, gate, poring cup:

Dimension of pattern and its auxiliary is checked by inspector. If any defect is founded, it is removed by worker.Instrument used for this purpose is like knife.

Attach the gates to the spree, the sprue to the pouring cup, the gates to the pattern and the vents between the pattern and pouring cup. This step is tricky; “welding” the wax pieces together requires some practice. Weak welds are very common among beginning casters. Set aside some time to practice in order to get your technique down... You do not want your pattern to fall apart before it is invested in plaster. Heat the flat (spatula-like) end of a wax-working tool with a candle lantern; slide it in between the two pieces of wax to be welded. Slide out the tool, and then hold the wax pieces together for a minute. You need to hold the two parts together very steadily in order to avoid weakening the weld. With practice you can get a strong weld this way. If you think the weld may be weak, you can improve the strength of the weld byAugmenting it with thin (~1/16”) slivers of wax which are warmed by holding in the palm of your hand, then placed so that they overlap the weld line. You can then use a heated wax tool to blend these slivers in. As an alternative to a heated wax tool, you can use an electric soldering iron to heat the wax.

Insert core pins if your pattern is hollow. Core pins are used to keep the core (or hollow center) of your pattern in place after the wax melts out. Failure to use core pins, or improper use of them, results in core shift (which means the plaster core moves), and can ruin the casting. You should use silicon bronze boating nails which have hatch marks in them. The hatch marks help keep the pins in the plaster. They are available at West Marine in Mountain View.

3.4 CLEANING AND COATING SECTION:

In this section, below processes are performed:1. Cleaning of wax assembly

of 38

2. Coating of wax assembly

Cleaning of wax assembly:

First of all assembly is dipped into the tank of nirma powered and after this assembly dipped into water. After this process, assembly is dried for sometime.

Coating of wax assembly:

Assembly is coated by three materials which is refractory material coating slurry material coating (fist time) slurry material coating (second time)

Refractory material coating:

Refractory material is used for protect to investment mould from high temperature of molten metal. Material used as refractory such like silica and alumina and sometime this coating is known as free coating.

Slurry material coating:

Slurry material coating is a coating over the refractory material coating for produce investment mould .specially ceramic slurry is poured around the wax assembly and is allowed to harden wax pattern assembly. Investment harden after 8 hrs of air –drying

3. 5 MELTING SECTION:

Melting section consists below following process: burn –out(auto claw) melting of metal preheating of investment mould maintain to material composition

Burn-out:

After the investment has sat for 24 hours, it is ready for the kiln. You will need to pour the metal immediately after removing from the kiln.

A. Remove the wood base from the flask.

B. Load the investments into the kiln. Be gentle with them. You should arrange each investment on top of firebricks so that the

of 38

pouring cup is on the bottom but is not directly on top of a firebrick. This allows the wax to drip out of your pattern. It is a good idea to put the largest investments near the front of the oven, since they will be the last to burn-out and it will be easiest to check and see if they are burnt-out. It is also hard to pull a large investment out of the back of the oven.

C. Decide on an appropriate burn out schedule. Burn-out schedules can be found in the appendix. Ask a knowledgeable TA or Dave Beach (also knowledgeable) if you need help picking a schedule.

D. Set up a temperature measurement system. The shop owns a fluke voltmeter with a temperature probe which is an excellent choice.

E. Turn on fume hoods. Turn the one on which is over the oven/kiln area, and also the one which is near the muller/royer area. Open all the windows except for the ones near the muller/royer area (otherwise this fume hood just sucks in air from outside.) The fumes created by melting wax are not good for you!

F. Ignite the Kiln. First, make sure that the kiln door is closed. Round up a couple of paper towels and a lighter (or propane torch). Observe that at the back of the oven there are two gas petcocks, located at about knee level, one on the right, and one on the left. These regulate the amount of gas which flows into the oven. In the middle at about waist height there is an air flume. As you are looking at the back of the oven, off to your right and behind you a bit is a gas valve located on a pipe which goes to the kiln. This is the main valve. You will want to do the following steps fairly rapidly, so make sure you understand all the steps before you start. (A TA should definitely be present for this part.) Put on a long sleeve shirt and some fireproof gloves. Make sure that the two gas regulators are completely closed. Gas valves are closed when handle Perpendicular to the axial direction of the pipe. Open the flue to the 2.8 marking. Open the main valve all the way (so that the handle is in-line with the pipe). Roll up a paper towel into a wand shape. Light the end of it, and stick it into the hole below one of the petcocks. Open this petcock part way so that it makes a 45 degree angle with the pipe. At this point, the gas should ignite and you should see a flame burning if you look into the hole. If this doesn’t happen, turn off the regulator immediately, and try to figure out what happened. It is very dangerous to have the oven fill up with gas, since when it is ignited, it can explode and blow the shop to Kingdom Come. If everything went well with lighting the first petcock, light the other one

of 38

G. Watch the oven. You should do this in shifts since it is not only boring but also unsafe to have one person sit by the oven for too long. Oven sitting has two major responsibilities. Most importantly, you should make sure that the kiln stays lit (check to see that there is a fire coming out of both regulators). Otherwise, the kiln and room are filling up with explosive gas. You should also make sure that the oven is following the burnout schedule. You can moderate the temperature by adjusting the 2 regulators at the back of the oven. Remember, in line is completely open, perpendicular is completely closed. A few hours after the burn-out has begun, you will hear the sizzle of molten wax, and smell the associated noxious vapors. Position yourself away from the oven at this point, and only walk over there every 10 minutes or so to check on the temperature and flame. These vapors aren’t exactly good for you.

H. After the investments have soaked at the maximum temperature for the full length of time suggested by the burn-out schedule, check to see that they have all burnt-out. A TA should do this. Suit up in the full silver space suit gear, including the hood. Turn off the main gas line and close the flue. Closing the flue is important because if you don’t do it, cold air will rush

in the open door, out the flue, and perhaps cause enough thermal shock to the investments that they crack. Open the oven door. Note that the inside of the oven is quite hot! If any flames are coming out of the pouring cups or vents, the investments are not burnt out, and you should close the door and relight the kiln. (Explained below) Tilt the investment up so that you (or someone else also wearing a silver suit) can look up into the pouring cup. The casting is burnt out fully if and only if the pouring cup is white with no black streaks. Black streaks indicate that a carbon residue still remains in the investment, and that more burn time is needed. Pouring metal into completely burnt-out casting is catastrophic-the metal can explode back out of the investment which is dangerous. If the largest casting is completely burnt-out, then it is likely all the others are too. In this case, you can leave the oven off with the door closed, and let the investments cool bit to the pouring temperature. If the castings are not entirely burnt-out, close the door, open the flue, and open the gas line. You will probably not have to relight the kiln, it is probably hot enough that the incoming gas will ignite itself. But check to make sure that you can see a flame through the hole underneath both regulators

Burn-Out Schedules

of 38

Pick a burn-out schedule according to the size of your casting. 7 hours is almost always sufficient for ring-sized castings. 12 hours is good for stuff smaller about the size of a hot-dog, while 16 for something the size of the machinery’s handbook (provided it is hollow), and 24 is good for stuff the size of a hollow loaf of bread. Remember, you should always check to make sure that your casting is completely burnt-out before you pour. You may find that you have underestimated the burn-out time, in which case you will simply need to let it keep on coo kin’, and check periodically to see if it is done. Too long of a burn is not nearly so disastrous, but it will diminish the surface quality of the casting. It is best to plan on a burn ending in the middle of the day sometime, so if you go overtime you are not pouring metal at four in the morning. Also, if the parts are going to be hand poured, whoever is in charge of the burn (a TA) should get a decent night’s sleep so she can be well rested for the pour. Burn out schedules consists of a ramp (casting brought up to temperature), a soak at some maximum, and a ramp down to the casting temperature. It is important not to bring the investment up to temperature too quickly so as to avoid thermal shock (and cracking) of the investment. Larger investments need to be brought up more slowly because of their greater thermal mass. The maximum temperature is chosen to be above the temperature at which all of the carbon residue left behind by molten wax will completely vaporize, but below the temperature at which the investment begins to break down. Unfortunately, this is a very small temperature range and the kiln temperature must be carefully monitored. The casting temperature is generally chosen to be below the maximum burnout temperature, since a lower temperature means lower energy, and better surface finish. The temperature should not be too low however, since a warm flask allows for better flow of metal in thin sections of the casting, and will avoid the risk of thermal shock (and cracking) to the investment.

You should always check the castings to insure they are completely burnt-out before pouring them. Remember, that if the casting is not completely burnt-out it can explode quite violently.

7-Hour burn 12 –Hour burn

time from start temp time from start (hrs) temp( c) petcock 0 room 0 room 0.2 1 200 1 150 0.2 2 325 2 260 0.5 3 450 3 371 1.8 4 575 4 482 2.1 5 700 5 593 3 6 700 6 700 3.3 7 500 7 700 3.5 8 700 3 9 700 2.5 10 700 2.3 11 700 off 12 500 off

of 38

Preheating of investment mould:

If material is filled into investment mould without preheating, cracks produce investment mould and mould break up so that investment mould is preheated before use about 900 to 1000 Celsius degree.

Maintain material composition:

Some material is added for maintain the property of part such like aluminum

Melting of metal

a. Pour the metal. You can pour just like you would for sand castings. As usual, try to pour quickly so that the metal does not have a chance to cool

b. Allow the castings to cool. Wait at least 6 hours before breaking the castings open. This is more than enough time, but it is much better to wait too long than not long enough.

Break open your casting.

Lay down brown paper in the usual fashion, and use a chisel to knock out the dried plaster. Be sure to dispose of the dried plaster in the dumpster, and not down the sump.

3.6 FINISH YOUR CASTING.

Finishing is a time-consuming and difficult process, but it is also extremely crucial if you want your casting to look good. This section is admittedly sparse. Much could be written about finishing. Here are the basic steps

A. Remove the sprues and gates. This can be done on the band saw. You will probably need to do some fancy fixturing if your casting isn’t rectilinear. You can probably construct a stable structure using wood clamps and scraps of wood. Get a TA to help you with the setup - this is tricky and dangerous.

B. Sand or grind off what is left of the gates. Depending on the geometry of the gates you can use a belt sander, die grinder, or dremel tool. Ask a TA if you need help.

C. Remove the core pins. Sometimes they can be pulled out, but usually they will need to be drilled out. D. Fill in the core pin holes or any sinks that may have occurred. Make sure that you fill them in with the same material that you

of 38

used for the casting. PRL has a variety of welding rods including aluminum and silicon bronze. Probably the best way to get this done is to be nice to someone who knows how to TIG weld and get her to fill in the holes.

E. Regrind the TIG welds.

F. Finish. The best way to finish your casting is to polish it. Patina’s speed up the natural oxidation and corrosion processes. This gives the castings a beautiful and venerable look. There are hundred of recipes for patinas, and they create all sorts of different color finishes. An excellent reference on this topic is “Metal Techniques for Craftsmen” by Oppi Untracht. Dave Beach has a copy. The PRL has had the most success with the black (it’s really more of a dark brown) Liver of Sulphur patina, so this one is recommended.

Process for finishing:

Fire scale Removal:

Many shops begin the finishing procedure before the castings are even cut off the tree. Investment removers will go a long way toward deoxidizing your castings. Pickling in Safe-T-Pickle, Sparex or other pickling agent is quite common (virtually all dry pickling agents like Sparex are simply expensive trade names for a very inexpensive chemical compound, sodium bisulfate). Another common procedure many shops employ is to deoxidize and brighten their castings by bombing. A few shops sand blast their castings.

Investment removers and pickling agents will not take off any metal from the castings. Bombing will dissolve some of the metal into the bombing solution. Sandblasting with glass beads will not remove any metal, but sandblasting with any other media will remove metal. Sandblasting with glass beads will brighten clean castings but is not very aggressive in removing fire scale. For more detail on bombing and sandblasting procedures and gold recovery from them, refer to separate Shor instructions on these procedures.

We recommend pickling for fire scale removal. Pickling will do a fine job of removing the fire scale yet it will not remove any It is a very fast and easy procedure which requires little or no equipment. In addition, the entire tree can be pickled at the same time.

of 38

Sprue, Parting Line and Other Flaw Removal:

When a casting is cut from its tree, there remains a bit of the sprue left (no matter how close you cut to the ring). This remnant of the sprue must be removed, and with it, any parting line (if it exists) and other blemishes (like little pimples, bumps etc). Most large shops grind these flaws off. Most small shops use a variety of tools including hand files and flexible shaft machines and other tools.

Even for the smallest shops (even for I man shops), we strongly recommend the use of MX grinding wheels to remove sprues, parting lines and other blemishes on the outside of the ring. MX wheels do a much faster and much better job than files and flex shaft machines. They have the following advantages:

Fine grit MX wheels leave only very fine, easily removed grinding lines (lines that are actually finer than many sanding lines.

MX wheels do not clog nearly as quickly as other wheels.

The edge of the MX wheel should be prepared, after purchase, by cutting it with a diamond dresser to conform to the curvature of your rings (see Shor MX wheel instructions for this procedure). When this has been done, the sprue and parting lines can be removed in just a few seconds and the curves of the ring will be much more perfect than if the grinding had been done with files or a flex shaft machine.

MX wheels are run on a polishing motor. That leaves both hands free for better control. The high torque of the motor results in very fast removal of the flaws. And last, but certainly not least, removal of the metal on a polishing motor makes it much easier to control metal losses.

If the castings are rings, you may want to grind the inside of the shank. We recommend the use of a rotary file for this purpose. However, there are other options: emery paper mandrels, wood emery paper mandrels, shoulder and standard mandrels, emery ring shells and cartridge rolls. While these other options are fine, rotary files are better because: they give a consistent finish, cut quickly (even the fine) and last for a very long time. We

of 38

recommend the use of fine grade rotary files because they leave only fine grinding lines which are easier to remove.

Sanding should not be necessary if using a fine grade of MX wheel and rotary file. If there is a need to sand, then the best way to sand large areas quickly and consistently is with a cone-lok drum sander, this is a rubberized steel wheel that accepts strips of emery cloth and fits on your polishing motor.

We recommend that MX wheels and all grinding, rotary filing and sanding be done on a motor, hood and dust collector devoted only to this purpose. If it is not practical to devote a dust collector for this purpose, then don't use a dust collector for grinding. The grindings are heavy enough to obviate the need for a dust collector. If it is not practical to devote a motor to grinding, then devote just a hood to grinding. Before grinding, sanding or filing, remove your polishing hood and replace it with a grinding box (a closed hood with no exhaust vent). We recommend the use of the Shor locked grinding box. This is a box with a screen at its base and a locked drawer underneath the screen. While there is no way to insure that gold grindings walk out of your shop with your workers, the locked grinding box goes a long way toward this assurance. If you are doing the grinding yourself or do not want to invest in a prefabricated grinding box, any plastic box of the right size and with a light in it will do.

Ultrasonic and Ionic Cleaning:

It is a good general policy to clean the pieces between each finishing procedure. This could be done by hand, but a much faster way is to use an ultrasonic. Ultrasonic have come way down in price since Shore first introduced them to the jewelry industry back in the early fifties. Now virtually every shop can afford one. An inexpensive and very effective alternative to the ultrasonic is the ionic cleaner. Ionic cleaners, in general, are just as effective as ultrasonic and they appear to have a better longevity track record.

Brightening Crevices and Hard to Reach Areas

Both how and when to brightening crevices will vary from shop to shop. Brightening of crevices can be done at any time up and including the time of the final finish. There are 3 basic ways of brightening the crevices:

1. Bombing or stripping

of 38

2. Tumbling with steel pins 3. Polishing with brushes

Each technique has its advantages and disadvantages, which will be outlined as follows. Please refer to the appropriate Shor instructions for "how to" details.

Bombing and Stripping-

These techniques both use baths that are primarily cyanide and water to brighten jewelry (non-cyanide stripping solutions are available but they do not work as well and the primary ingredient, thiourea, is a suspected carcinogen). Each has its advantages and disadvantages.

Both bombing and stripping have the advantage that they allow a shop to do many pieces at one time very quickly and with a minimum of labor. Both have the disadvantage that they work with cyanide solutions (cyanide solutions can be safely used and disposed of only under tightly controlled conditions-see the appropriate Shor instructions for these conditions). Stripping has the advantage that its solution can be reused many times. Bombing solutions, only once.

The most important difference between the two techniques, however, is that bombing removes metal from and brightens the entire piece evenly but stripping tends to remove more metal from the high points (like prongs). This means that stripping, in general, will remove more metal than bombing from the castings (greater losses) and may actually damage the prongs on very

light weight pieces. For this reason, we recommend bombing over stripping. See the appropriate Shor instructions for how and when to bomb and strip how to recover gold from bombing and stripping solutions.

Rotary Tumbling with Steel Pins

The advantage to tumbling is that it brightens large numbers of pieces will little labor (mass finishing). Tumbling requires much more time than bombing or stripping but requires slightly less labor. Tumbling with steel shot removes no metal. In general, tumbling does not get into the crevices as well as bombing.

Tumbling brightens pieces by hammering the surface with steel "shot". Because this technique results in a fine "hammered"

of 38

effect on broad flat surfaces (an effect that must later be removed from these surfaces to get a quality finish), we recommend that all tumbling be done prior to Tripoli work. The Tripoli work will remove the hammered effect from the broad surfaces, but will not reach the crevices where the brightening will remain. Most steel shot has relatively few pins in it. Yet the pins are the component of the shot that brightens the crevices. For this reason we recommend adding pins to your shot mixture.

A good ratio of pins to standard ball shot is 50/50, however, trial and error will tell you what works best for you. For detailed "how to" instructions on tumbling, see the appropriate Shor instructions.

Magnetic Tumbling with Steel Pins

This is a relatively new technology and is excellent for burnishing the hard to reach areas as well as any surface which is not very flat. Flat surfaces tend to get a bit of a "haze" on them by this means of finishing. If using on flat pieces, a quick buff with a wheel easily removes the haze. The high G's produced in magnetic tumblers results in a burnishing action that is just not possible with standard tumblers or vibratory machines. With media as small as .010 in diameter and .250 in length, these stainless steel pins are able to work in areas such as undercuts, recesses, and slots etc. where no previous method has been found suitable. Finishes the most intricately detailed parts. Very quiet when compared with most other forms of finishing. Typical finishing time on gold and similar metals is only about 30 minutes. This is an excellent method of automatic finishing, producing rapid final finish results with an absolute minimum of labor.

Polishing with brushes-

This technique, without question, gives the greatest luster. It is, however, very labor intensive. When properly done, most retail customers cannot tell the difference between a bombed

of 38

piece and a brushed piece. For this reason, we do not recommend the use of brushes for most pieces. To find out how to choose the right brush for the right job, see the appropriate Shor instructions.

Sandblasting-

Sandblasting does a great job. If sandblasting, use first a coarse media (like carborundum grain or pumice or sand) to do the Tripoli work. Next, change the media to a glass bead to do the polishing. When finishing with a sandblast machine and with these media, it is generally not necessary to bomb or tumble and sandblasting can replace virtually all of the hand Tripoli work and almost all of the hand rouge work. Unlike mass finishing machines, sandblasting has the advantage of allowing the operator to use his intelligence when required to blast a little

More here or a little less there. Mass finishing machines do not provide for this option. Another advantage of sandblasting is that the media gets into every little nook and cranny. Mass finishing media generally doesn't do that. On the other hand, sandblasting is more labor intensive than tumbling or vibratory finishing. And, while sandblasting will remove much less metal than hand finishing, it is very difficult to recover the gold from the sandblast media.

Tumbling-

Generally speaking, tumbler cannot work well with any media except steel shot. Steel shot, because it is not abrasive, does not lend itself well to removing grinding or sanding scratches.

Hand polishing

of 38

Tripoli work done by a skilled polisher will yield excellent results especially in those circumstances where a little intelligence is necessary. And when lapping is necessary, there is no substitute for hand lapping. In addition, there is no faster way to do Tripoli work. On the other hand, hand polishing is very labor intensive and generally results in much greater gold losses than any other technique. This makes hand polishing a very expensive technique that should be reduced to a bare minimum.

Vibratory Finishing-

Vibratory finishers do the Tripoli work by using a light weight plastic media impregnated with a cutting compound (like carborundum, silicates or aluminum oxide). Vibratory finishing takes longer than other techniques but will accept hundred of pieces at the same time and requires almost no labor. The result is a very dull but smooth piece, ready for the rouge work. Very little metal is removed in this finishing process (approximately 1/10th of 1% per hour of running time with a fine grade media- average time 8 hours) and the metal is reasonably easy to recover. Vibratory finishers cut very evenly on all surfaces. That means that the vibratory finisher will preserve details. It also means that they will preserve flaws, so it's important to do a good job removing those flaws before the pieces reach the Tripoli stage. For more details on the process of vibratory finishing, please consult the Shor instructions on vibratory finishing.

Polishing (Intermediates Work)

This is the step between the Tripoli work and the final polish. This step is often skipped by many shops, and it is not absolutely necessary. Each shop must determine what works best for them.

There are several ways in which the intermediate polish can be accomplished. A common technique is to use a tumbler with steel shot as the media. It is our opinion that, at this stage, tumbling is unwise and should be avoided. The shot will impinge on the broad flat surfaces of the work and leave a beaten hammered effect (an effect that must later be removed in the final polish in order to achieve a quality finish). In addition, the shot also has the effect of bending or breaking prongs.

Hand polishing with intermediate compounds like gray star and white diamond is another possibility, but hand polishing at this stage has the same drawbacks as it did at the Tripoli stage.

We recommend that, for most pieces, you should either vibratory finish with a rouge impregnated walnut shell or corn cob- or you should skipped this intermediates step altogether.

of 38

Vibratory finishing will take the dull smooth jewelry and transform it with a luster just short of a final finish (for stampings and silver, this is often a final finish). Vibratory finishing at this stage will not remove any metal at all. It does, however, require a minimum of 24 hours processing time.

Final Polishing (Rouging)

This must be done by hand. Please refer to the appropriate Shor instructions to choose the appropriate polishing compounds, buffs, ring buffs, brushes, felt wheels, laps and cones to suit your particular needs (or call us at Shor International 914-667-1100).

Summary Chart

Process Strengths Weaknesses

Rotary Tumbling

Inexpensive to finishes curved surfaces and brighten settings.

Very short learning curve to gain the basics on how to use equipment.

With a lot of experience, almost all of the weaknesses can be overcome.

Burnishing removes no metal.

Tends to give flat surfaces a "beaten" appearance.

Tends to round off sharp edges, obscure fine details and bend thin prongs.

Uses steel shot, which tends to get stuck in settings.

Even though the basics of tumbling are learned in an afternoon. To obtain the best results requires a lot of experience.

Not very good for cut-down process (the Tripoli work)

Magnetic Tumbling

Very fast.

Short learning curve.

Excellent for getting into small crevices

Burnishing removes no metal.

Relatively expensive.

Relatively small capacity.

Gives slightly frosted look to large flat surfaces (light buffing removes this haze).

Vibratory Finishing

Excellent for cut-down (tripoli work)

Works with very light media and which is relatively slow.

of 38

Good for rouging work.

Very inexpensive.

High capacity

Short learning curve when using proper instructions.

Preserves details. Very little rounding of edges.

Rouging removes no metal.

Not good for crevices. Not good for inside settings.

Electro polishing

Lightning fast. Finishes in seconds.

Finishes crevices and settings better than any other equipment.

Preserves details better than any other equipment.

Excellent for flat surfaces as well.

Inexpensive to operate.

Gold is recovered as flakes of gold. Does not need to be extracted from an abrasive or polishing media. 100% recovery.

Parameters can be adjusted to polish more aggressively at high points or in crevices.

Uses cyanide based salts.

Expensive to purchase

Relatively long learning curve to determine the best parameter settings for your particular rings.

Stripping Inexpensive to purchase and to run.

Finishes in seconds or a few minutes.

Gold is recovered as flakes of gold. Does not

Uses cyanide based salts.

Does not work well with white gold.

Does not work well with low and high karat gold.

of 38

need to be extracted from an abrasive or polishing media. 100% recovery.

Is much more aggressive at the tips of prongs than inside the settings.

3.7 HEAT TREATMENT PROCESS

Objective of heat treatment presses:

Heat treatment is carried out to archive one or more of following objective: improvement in ductility Relive internal stresses set up during cold working, welding,

casting, and forging. refinement of grain size increase hardness and tensile strength improvement in toughness increase heat ,corrosion ,wear resistance

Types of heat treatment process:

Depend upon the method of heating, the furnace atmosphere, the heating temperature, the cooling media, and the property desired, varios heat treatment process follow 1. annealing2. normalizing3. hardening4. tempering5. case hardening6. surface hardening

1. Annealing:

Annealing may be defined as heating the casting material to a certain predetermined temperature, holding it at that temperature a sufficient time to allow the necessary changes to occur slowly at a predetermined temperature rate.

2. Normalizing:

Normalizing is defined as heating the steel to austenite phase and holding at that temperature for sufficient time followed by cooling it in air.

3. Hardening:

Hardening may be defined as rapid cooling (quenching) of steel from the austenite phase.

of 38

the rapid cooling is obtained by immersion of steel in water or oil bathe this rapid cooling of steel from the austenite phase gives faster cooling rate than critical cooling rate and martensite is obtained .martensite is harder than pearlite which accounts for the increased hardness of the rapidly cooled steel.Hardening followed by tempering is carried out to achieve one or more of the following purpose:

1. To increase hardness of steel for better wear resistance.2. To improve strength with sufficient ductility.

Quenching medium:

a quenching medium is one into which heated metal objects are plunged in order to withdraw heat from object rapidly .

The quenching medium must provide for a cooling rate above critical value to prevent austenite decomposition in the pearlite, etc.

In the martensite transformation temperature range, cooling should be slower to avoid high internal stresses, warping of the hardened part and cracking.

Types of quenching media:

Given below are some industrial quenching media, in order of decreasing quenching severity;1) 5 to 10 % caustic soda …….very drastic quenches.2) 5 to 20 % brine (Nacl).3) Cold water. 4) Warm water.5) Mineral oil.6) Animal oil.7) Air…..least drastic quench.

Quenching media Cooling rate relative to that of water at 18 Celsius degree720 to 550 0c 200 0c

1 10 % caustic soda 2.06 1.362 Water at 00c 1.60 1.023 Water at 18 1.00 1.004 Oil (rapeseed) 0.30 0.0555 Water at 100 0c 0.044 0.716 Air 0.028 0.007

Tempering:

when a piece of steel is taken out of the quenching medium , as already stated , it is hard ,brittle and will have severe unequally distributed internal stresses besides other unfavorable characteristic . In general, tempering restores ductility and

of 38

reduces hardness and result in some decrease in hardness. The primary objectives of tempering are, therefore, as follow.

1. To stabilize the structure of the metal.2. To reduce internal stresses produce during previous heating.3. To reduce the hardness and increase the ductility of the

metal.4. To give the metal right structure condition combined with

toughness and shock resistance.

The tempering treatment requires:

1. Holding it for a considering time.2. Slow cooling. It is desirable that the temperature of the steel

shall be maintained for not less than 4 to 5 minutes for each millimeter of the section.

Exact temperature at which tempering should be carried out depend upon the purpose for which the article or tool is to be used. According to the heating temperature, ranges of which are classified into 3 types. They are:

1. Low temperature tempering which is done in the temperature from 150 to 250 Celsius degree. The purpose of this produce is to increase the ductility without reducing the hardness.

2. Medium –temperature tempering which involve heating the work to 350 to 450 Celsius degree .the structure of steel is altered by procedure. Martensite is transformed into secondary troostite. The results are reduction in hardness and strength of metal and an increase in the elongation and ductility. Medium temperature tempering is mainly applied to article and parts which are subject to impact loads: hammers, spring, spring plates, etc.

3. High temperature tempering which is done in the range of 500 to 650 Celsius degree. At these temperature sorbite is formed in the steel and the internal stresses are almost completely eliminated .high temperature tempering imparts high ductility to parts, yet permit them to retain adequate hardness. this is applied to machine parts which are subject to high stresses and impact ,gear wheel , shaft ,connecting roads, etc

Tempering baths

Bath using tempering oils may be employed for temperatures up to approximately 230 Celsius degree. Tempering oils are usually mineral oils. For temperature above about 230 Celsius degree, liquid salt bath are preferred. These salt baths consist of nitrates. For higher temperature chloride and fluorides are employed .steel parts are often tempered in eclectically heated Furnaces within which the air is circulated to produce uniform temperature.

of 38

Case hardening:

It is known as chemical heat treatment of steel. Components like crankshaft, gear, camshaft, connecting road, dies etc. require different properties at surface and the core (center portion). Their surface (known as case) should be hard and wear résistance and core should be tough and soft to withstand shock and avoid propagation .these type different properties can not archive by normal heat treatment process.

These property are achieved in low carbon (<0, 3 percentage carbon) steel with require core properties by adding of carbon, nitrogen or both at the surface layer unto certain depth and hardening the surface layer. This process of increasing of hardness of case is known as case hardening or chemical heat treatment. The basic principal of this process is that the interstitial space occupied by carbon atoms in iron increase with increasing temperature. This result in increasing rate of diffusion and therefore higher the temperature more carbon atoms can be diffuse to the surface layer. Time is also an important factor and depth of diffusion layer varies with time as

Case depth =k *√tWhere k=2d is diffusion co efficient t=time of diffusion Depending upon whether carbon, nitrogen or both

carbon and nitrogen are added into the surface layer. The case hardening processes are as follows:

1. carburizing 2. nitriding 3. cyaniding

Carburizing:

This method of introducing carbon into low capon steel to produce hard case (surface). It is also known as cementation. It is carried out in the temperature range 900 -930 Celsius degree for several hours in contact with gaseous, liquid or solid carbon containing substance

Nitriding:

This is a process of enriching the surface of steel with nitrogen by holding in an atmosphere of ammonia at 500 Celsius degree for a prolonged period (40 to 100 hrs)

Cyaniding:

In this process carbon and nitrogen both are added to steel surface by subjecting low carbon steel to high temperature in molten cyanide. It is also called as liquid

of 38

carbonitriding. The cyanide bath s consists of sodium cyanide. Sodium carbonates and sodium chloride. The temperature of the bath is maintained at 800 to 850 Celsius degree. Atomic carbon and nitrogen from the bath diffuse into steel surface and give thin wear resistance surface layer. After cyaniding the components are quenched in water or oil followed by low temperature tempering.

3.8 TESTING AND INSPECTION SECTION:

Testing and inspection are required for increasing quality and reliability of product. so below processes are used for testing the final product of investment casting.

1. liquid penetration test2. magnetic particle test 3. pressure test

Liquid penetration test:These test revel discontinuities that are open to

surface and may use dyes or fluorescent materials. They are especially useful for non ferrous metals and nonmetallic substances. The simple test involves dipping the component into kerosene, wiping it dry, and then coating it thinly with whiting. Cracks will be revealed by a discolored "line" appearing in the whiting, this being produced when kerosene trapped in the cracks seeps out slowly. Dyes may be used instead of kerosene, but fluorescent materials are probably the most widely used.In the fluorescent test, the sample is immersed for some time in a hot bath of a strong fluorescent compound such as anthracic, used as a penetrating agent. The solution enters the cracks, if any, and remains there. The metal is then dried and examined under a quartz tube mercury vapor lamp. Any penetrated solution will be detected by the fluorescence caused by the ultraviolet radiation of the light.

Magnetic particle test:

Magnetic crack detection apparatus is designed to detect normally invisible crack on or extending near to the surface of the articles made of magnetic materialThe design of magnetic crack detector is based on the principle that, if a crack or flaw is present in a magnetic field is passing, the lines of force will be distorted near the fault owing to the total change of permeability associated with it .in the case of piece without any flaw, lines of force will be uniform and straight.

of 38

Cracks and flaws can also be detected by magnetizing a ferrous metallic part, then sprinkling very fine iron dust over it. The magnetic poles formed at the crack gather a line of dust and outline the crack the special equipment for this magnetic testing for crack is known as magna flux. The basic principle is shown in fig

Pressure testing:

this testing is used for finding defect in parts which is used in refrigeration and air –condition in which leakage caused dangerous problem

Procedure for testing:

In the process, high presser air fill in component and this component is dipped into water .now if any water bubbles produce in water; this is the mark of defect in parts.

Other testing :

1. Other instrument used for checking the dimension of parts such like digital micrometer.

2. And for testing the composition of part material, metallurgical microscope and radiographic test

4. APPLICATION:

1. Investment castings produced by this process have a good surface finish and are exact reproduction of the master pattern. This is used for casting turbine plats, parts of motor –car, sawing machines, type writers. And calculating machines, As well as for various instruments.

2. application of investment casting in the aerospace section

Exceptional accuracy, thin wall capability, complexity, and fine detail reproduction. From jewelry and medical implants to larger industrial components, this process has evolved due to both market demand as well as technology

I. Reducing costly joints, machining and weight of the final structure. What makes the investment casting

of 38

process so unique is the ability to cast thin walls using preheated mold and attainment of predictable mechanical properties by actively controlling the solidification speed of the alloy.

II. With the decline of the military hardware market in the late 1980’s, many investment casters looked for alternate market places for their built up capacity. Numerous companies diversified into commercial products such as high end automotive (F1 & NASCAR), industrial parts (printers, telecommunications, instruments), and recreational/medical products (cycles, artificial limbs, firearms). The commercial aero-engine market was one of the first to convert from sand and plaster mold to investment casting for lighter and higher accuracy parts. Air intake fan frame structures and gearboxes are now commonplace applications today (seen here).

The journey to develop larger structural airframe castings for both military and commercial programs has evolved significantly over the past decade. Once limited to aFew military and engine programs, structural investment castings are being increasingly considered as an alternative in mainstream airframe construction.

Large airplane applications such as the YC-14 bulkhead and F-16 vertical tail gained much attention but little acceptance from conservative airframes. Walls were too

of 38

heavy, draft angle a problem for fasteners, and mechanical properties “spotty” with variations in strength from gate to chill locations. The experience gained, however,Enabled advanced material properties, Military Design Handbooks (MIL-HDBK-V), and commercial aerospace (AMS 4241/4249) specifications to be developed. OtherApplications such as machined gearboxes, engine parts, and missile bodies gained greater commercial success.In order to capture a portion of the lucrative aluminum commercial airframe market, Howmet-Aluminum and others began development of a series of technologies in theEarly 1980s in order to combine the thin wall capability of investment casting with high strengths achieved through rapid solidification. Engineer developed several processes,All based upon casting aluminum alloy into a pre-heated ceramic shell mold, and subsequently extracting the metal superheat in a controlled and rapid manner. As superheat needed to be extracted through the relatively insulating ceramic shell mold, large thermal gradients were needed to move heat quickly enough from the solidifying casting. Some processes were extremely efficient in heat removal but placed restrictions on shell mold size or geometry. Other processes could handle larger structures but provided sufficiently rapid solidification in thinner wall sections only. Finally a process was developed which could handle large parts and efficiently solidify both thin and heavy walled sections. The “Sophia” process combined the best of investment casting features with rapidly solidified cast and dense microstructure. Since then other foundries have developed competitive technologies to achieve similar performance.

Pros and Cons:

The investment casting industry has literally designed and opened the doors in the aerospace industry because of the opportunities it had offered. The process has the ability to achieve precision tolerances, combine numerous previously used detail sub assemblies, achieve predictable levels of static and fatigue resistance, and is inherently corrosion resistant. The pressurized door sub-structure shown here is one of several, on commercial jets.

A disadvantage of using investment casting for aerospace is the number of iterations

Involved to make a sound casting, and establish a fixed process for manufacture. As design or quality needs may change quickly, re-qualification of the casting also ads time to the overall program milestone. Cost is a factor that can enrich or detract from investment casting. Some components are ideal for complex castings, reducing assembly and machining, which reduces cost. Others have a simple configuration and can be

of 38

made faster through another process, such as high speed machining.

5. ADVANTAGES OF INVESTMENT CASTING

Design Flexibility for the base of the parts. Versatile Fin Geometries & Configurations. High Efficiency, Lightweight parts Designs. Suitable for Short- & Medium-Run Production. Fine Surface Finish. High Dimensional Accuracy & Consistency. Minimal Need for Secondary Operation. Suitable for mass production of small sized casting. Sound and defect free casting may be obtained. Thin section, to the extent 0.75 mm. can be cast

successfully. machining can be reduce or eliminated since tolerance

close to ± 0.1 mm. and surface finish of around 1 -5 micron are possible.

of 38

6. LIMITATION

unsuitable for casting of more than about 5 kg weight (rarely 10 kg for making pump impeller)

Precise control is required in all stage of casting. Expensive in all aspect. Mould can not reuse. Lost of wax in every new production.

CONCLUSION:-

Two trends are currently having a major impact on the casting industries:-

The first is continuining mechanization & automation of casting process .

Second major trends is increase in demand for high quality casting with close dimensional tolerances & no defect. So investment casting is best than other castings.

REFERENCE

1. Material science – by prof. j. p. patel - By prof. g .h. Upadhyay

2. workshop technology – s. k. hajara choudhury3. Material science & metallurgy – by o. p. khanna4. www. Google .com 5. www.yahoo.com 6. Investment & precision casting limited at Bhavnagar near nari

road.

of 38

http://www.yahoo.com/

seminar on case study of investment casting by manish pujara

Documents