Preliminary Requirements

Safety Requirements

WARNING

IT IS THE RESPONSIBILITY OF THE OPERATOR TO OBTAIN AND OBSERVE THE MANUFACTURERS MATERIAL SAFETY DATA SHEETS FOR CONSUMABLE MATERIALS INFORMATION SUCH AS, HAZARDOUS INGREDIENTS, PHYSICAL/CHEMICAL CHARACTERISTICS, FIRE, EXPLOSION, RECATIVITY, HEALTH HAZARD DATA, PRECAUTIONS FOR SAFE HANDLING, USE AND CONTROL MEASURERS AND ALSO TO TAKE LOCAL REGULATIONS INTO CONSIDERATION.

Procedure

1. SUBTASK 70-31-03-310-001 The Theory of Electron Beam Welding

   1. This is a type of fusion welding done in a vacuum. Heat is made because a high speed electron beam is focused on the material work surface. The beams kinetic energy changes into thermal energy when it hits this surface. Fusion occurs in the direction of and around the beam. This area solidifies and the weld joint is made.

      1. The vacuum helps the free movement of the electrons, they can not hit gas or air particles (in a vacuum). Thus, deterioration (of the flow of electrons) does not occur in the device (gun) which gives off the electrons. Also, weld contamination is prevented.

2. SUBTASK 70-31-03-310-002 The Types of Machine

   1. The usual welding machines are of two types. These can operate on different anode/cathode voltages.

   2. The low voltage machines operate at 10 to 60 kilovolts (approximately).

   3. The high voltage machines operate up to 150 kilovolts (approximately).

      1. Special low or high voltage machines are made to get a fast operation, when many components are welded at one time. The machine chamber is operated at 'soft' vacuum conditions (a vacuum pressure of 0.01 mm/Hg) or 'hard' vacuum conditions (a vacuum pressure of 0.0001 mm/Hg or lower). The unit used to measure vacuum pressure is 'torr'.

      2. The welds made with the different machines are very similar. The TASKS given in the applicable Engine Manual will not specify a particular type of machine to use. Each machine must operate to get the correct geometry and metallurgy. The applicable TASK gives the necessary data to help you to set the particular machine in use.

      3. If a special procedure is necessary the TASK will tell you the type of machine to use to get the best results.

3. SUBTASK 70-31-03-310-003 The Control of the Machine Functions

   1. To control the weld geometry and quality you can make an adjustment to:

      1. The beam power, this is beam current and accelerating voltage.

      2. The heat supply through the complete weld.

      3. The dimension of the beam focus spot on the material work surface.

      4. The material work surface 'traverse' speed.

      5. If a special material is to be welded (and could be difficult to weld) the applicable TASK will tell you if more controls are necessary.

   2. To control the beam power you can make an adjustment to:

      1. The speed of the electrons in the beam. This is related to the voltage between the anode and the cathode. This is the 'accelerating voltage'. It is measured in kilovolts (kV).

      2. The number of electrons in the beam. This is related to the voltage applied to the cathode cup. This is the beam current. It is measured in milliamperes (mA).

   3. The supply of heat through the complete weld can be changed with the induction of low amplitude movement of variable high frequency in the beam. This is done with a programmed magnetic coil system. You can make the different movements with the beam; such as circular, elliptical or linear. Thus the heat supply is changed and this can cause a change in the solidification rate of the weld metal. This also gives a method to make the weld wider and more parallel.

   4. The dimension of the beam focus point on the material work surface is related to and controlled with:

      1. The beam point focus (the selection of a particular distance from the work surface of the focus point).

      2. The accuracy of focus (the change to the current in the focusing coils).

   5. The distance between the material work surface and the electron beam gun heatshield is calculated when you first set the machine. The accuracy of this distance must be repeated for each component.

   6. An adjustment of the material work surface 'traverse' speed can change the weld shape and the solidification rate (of the weld metal).

4. SUBTASK 70-31-03-310-004 The Types of Joint

   1. Before you make a decision on the type of joint to use for a particular repair, think about these things:

      1. If there is something special about the particular configuration which could limit the choice of joint. For example, if there is a limit to the available joint position. If there is access for the electron beam. If it is possible to machine the 'backing piece' (if used).

      2. Before you start the particular TASK, make a decision about the correct type of joint to use.

      3. If special weld geometry is necessary, such as the 'hourglass' shape, this will limit the joint alternatives.

      4. The properties of the material of the component can change the best joint design you could use, as follows:

         1. It can be difficult to get satisfactory underbead conditions on full penetration welds. Slotted, spattered and undercuts can be caused because material is pushed out too quickly.

         2. It is difficult to keep the weld geometry, when you weld slowly, because of the type of material. Metal can 'drop' during the time the metal becomes solid.

         3. Heavy porosity and cavitation in high vapor pressure materials is caused if the gas becomes caught. This gas is contaminated material and chemicals (these are both as ionized vapors) given off from the fusion zone. If a large quantity is made (because of the material) and it stays too near the weld, it becomes caught during solidification.

      5. If possible make an inspection of both sides of a repair weld before you complete the work (this is done during the last step).

      6. Make a decision about the correct type of joint in which the least heat quantity is necessary (if there could be a high level of distortion). Heavy penetration into a backed joint can badly change the heat put in and the shrinkage distortion in the component.

   2. The configuration of the different joints.

      1. Some different joint configurations can be used in repair. Refer to Figure, to see the given weld geometry. Joints can be put into groups, as follows:

      2. There are full penetration joints, where the weld goes through the total joint thickness.

      3. Partial penetration joints, where the weld goes through the joint, but the weld root goes into the 'backing' material.

      4. Full penetration joints.

         1. Refer to Figure (joints A, B, D, F, G and H are full penetration joints). When you weld these joints you must set the equipment correctly to get the specified geometry. This is important in the condition and the shape of the crown and underbead. Some materials can only be welded at low speeds, then it is very important to keep the correct equipment adjustment. This can be difficult. The difference between penetration which does not go through the joint and penetration which does, can be as small as 0.5 mA of beam current.

         2. When you weld materials at medium and fast speeds the equipment adjustment is not as important. When the equipment is used correctly, you can get good results with these joints.

         3. When you weld high vapor pressure materials and use the full penetration joint it can:

            1. Make it easier for the vapors to come from both ends of the fusion zone.

            2. This will reduce the caught gas which can occur if the partial penetration joint is used.

         4. Joints A and B are open butt joints, they do not have internal or external location points. The use of joint A is made necessary with the type of repair (if the component has had no joint preparation done to it or if the finish has been completed before).

         5. If the finish has not been completed on the component, joint B is used. A top step Y is made to add more filler material to the weld crown.

         6. Joint G has a small location spigot which becomes a top filler. The spigot is of low mass, because it must melt fully during welding. This will make the weld crown.

         7. In joint G you can not see the joint. To help you during welding use the spigot end face to accurately keep the 'tracking' correct (and the component is moved the necessary distance) this is the dimension X. This is done so that the beam will align with the joint line. Alternatively, machine a mark on the top surface of the spigot; in line with the joint face.

         8. A different type of joint G is also shown. It is important that the top vee of the spigot is correctly machined in relation to the joint face. The top of the vee is used to help you find the joint line.

         9. The other joints, D and F have thin backing plates. These are used for location. These are also used if it is necessary to machine off an underbead which is not satisfactory. The joints are full penetration joints, to help the vapor come out of the fusion zone.

         10. Shrinkage cracks can occur in the fusion zone of the thin backing of these joints D and F. These cracks can go into the primary weld.

         11. Distortion can occur in the thin backing plate used in joint D. The plate can come away from the joint. This occurs if high beam power levels are used. You must use test pieces to find the correct equipment adjustment.

         12. The last joint of the full penetration type is joint H. This is used if there is a limit in the selection of joint position. Also, if the machined shape will include some of the fusion zone. Refer to Figure and Figure. The depth of penetration is not in proportion to the thickness of the joint sides (where they come against each other). This depth of penetration can cause distortion. The necessary tools/fixtures must be used to let the heat go out of the material and to limit movement.

         13. Step Z is machined to give a line which helps you to know the joint position.

      5. Partial penetration joints.

         1. Refer to Figure. Joints C and E give good results if there is no problem of distortion, or if the vapor can go out of the fusion zone (also if these unsatisfactory properties can be prevented). It must be possible to machine off the backing part of welded joints. This is to make an inspection of the weld. The primary properties of these joints are as follows:

         2. The joint will easily engage because of its shape and type and is satisfactory to use on larger diameter components (because of the thickness of the backing).

         3. As the weld does not penetrate the joint fully, the weld crown does not fall. It is usual to get a full weld crown.

         4. It is not necessary to make the small adjustments to the beam power (compared with the full penetration joints). This is because small differences in the penetration depth are not so important.

         5. Weld root problems are prevented because the backing is subsequently machined off.

         6. The usual defect with this type of weld is heavy porosity at the root. It is important when you make these joints to make sure the root defects stay in the backing (through the use of the correct type of joint and beam power levels).

         7. All joints which use backing pieces (this includes the full penetration joints D and F) must be prepared correctly. All air must come from a small space at the bottom of joint (if it is there) during machine pump down. The space is made because of chamfers or radii. To let the air come out, make a groove 0.010in. (0.25 mm) deep axially across the mating diameter of the backing piece. Use a small rotary tool in a hand grinder or a hand scraper (prepared to make the groove) and a straight edge.

         8. There is no specified number or distance between grooves. In a joint of 12 inches diameter (30.5 cm), eight grooves which have an equal space between them would be correct.

      6. Planetary joints, refer to Figure.

         1. When you make a planetary weld joint (one where the joint interface is aligned with the vertical axis) you must decide which is the correct interference fit to use. The applicable interference must agree with the properties necessary for the type of work to be done.

         2. If a solid disk is installed into a material work piece (and the disk does not become smaller when its temperature is increased) you must use the highest interference you can correctly use. The high interface pressure will make allowance for some of the weld shrinkage. It will decrease the joint 'gapping'.

         3. If an internal or external ring is to be welded into or over a component it can be difficult to calculate the necessary interference. if a light internal ring of 15 inches (381.00 mm) is installed, and there is a high interference fit, distortion will occur (and 'gap' away from the component). This is caused because of the expansion stresses during welding. Also, with an external thin ring, a slow and continuous movement from the component could occur (if the "interference" used was too low). The control of the expansion defects are as follows:

            1. Procedure 1: Make the tooling hold the rings correctly and soak up the conductive heat.

            2. Procedure 2: Make the rings large and heavy so the heat goes out and makes them rigid, to stop the distortion.

         4. For the correct type of tooling and ring, use this example to calculate the interference necessary. This is 0.0005in. to 0.001in. (0.013 to 0.025 mm) for each inch (each 25.4 mm) of joint diameter. Use the larger interference for small diameters and the smaller interference for large diameters.

5. SUBTASK 70-31-03-310-005 Weld Geometry and Metallurgy

   1. The geometry of an electron beam weld is unusually special because of its larger depth to width ratio; also because of the small width of the heat affected zone. Refer to Figure, this gives an example of the geometry.

      1. Use care when you set the machine, this can help to keep the correct weld geometry and metallurgy. But the adjustment should be kept and good quality control used, to do this.

      2. When you do a weld, it is usual to make the weld of sufficient width for complete joint fusion. The joint can be aligned (in its tolerance limit) but can have small errors in it. Some distortion could have occurred during its use in the engine. An allowance could have to be made for small errors of the 'joint tracking', or when you 'spot center' the machine.

      3. Try to keep the width of weld between 0.030 to 0.040in. (0.76 to 1.02 mm) (measure this at its smallest width). You must make sure that the width of the weld root is correct. If this is not done the weld root will not be in line with the joint. If you can, use the 'hourglass' shape weld; refer to Figure.

   2. The effects of the control functions on weld geometry and quality.

      1. The properties of the weld material have the largest effect on the weld geometry and quality. All the Repair TASKS give the geometry and quality which is necessary. The effects of the differences in the adjustment of the controls on the weld shape are as follows:

         1. The relation between accelerating voltage and beam current.

         2. The welding speed.

         3. The dimension of the 'focus spot' on the material to be welded.

         4. NOTE

            Wide welds will result if you use the beam gun at its maximum limit (from the material to be welded) because the electrons will not hit together. These conditions make it difficult to carefully control the necessary weld geometry.

            The use of 'beam deflection' procedures.

      2. The effects of the beam power controls.

         1. The beam power is the effect of accelerating voltage and beam current. For a given beam power, the selection of a kV adjustment together with a mA adjustment is satisfactory.

         2. A small number of electrons at a high speed (high kV, low mA) can result in a weld that is not wide. If there is a large number of electrons at a low speed (low kV, high mA), it will result in a wide weld.

         3. Because of this, a low voltage machine (10 to 60 kV) will usually make a wider weld than a high voltage machine (if all the conditions are the same). Also there is an increase in the heat affected zone.

         4. When you weld at a low speed, the beam power levels must be kept at the specified value to get the necessary geometry. At higher speeds it is possible to increase the beam power more than the specified value. This will also give good results. This is because the molten metal has no time to 'drop' before it becomes solid behind the beam.

         5. With this procedure it is possible to weld a joint of different thickness (for example, between 0.075 to 0.750in. (1.91 to 19.05 mm)) at a constant power and speed. This will also give good geometry during welding. One more example is when you weld a double layer joint, such as a hollow airfoil, with one 'pass'.

         6. Undercuts at the edge of a weld can occur in some materials (more than others). You can decrease this defect with an adjustment to the accelerating voltage (without affecting the beam power) for the specified penetration.

      3. Welding speed.

         1. The most important thing to make a good weld is to get a constant satisfactory welding speed. It is important to weld in the correct speed range in relation to the material. This will give the geometry and metallurgy necessary.

         2. The primary effects of welding speed are:

            1. Weld width - a higher speed will make a weld which is not as wide (as usual).

            2. Weld solidification properties - the higher the speed, the faster the molten metal will become solid behind the beam.

            3. Distortion - the higher the speed, the less the heat distortion. Also the shrinkage distortion is less. This is because of the decreased volume of metal of the fusion zone.

         3. An important thing to think about is the effect of the welding speed on the metallurgy of the weld (the effect on the weld solidification properties). Low volume welds that become solid quickly can have 'grain boundary separation' and cracks in them. This can usually occur in 'air-hardening steels' and coarse grain structure materials. Refer also to step (8)(f).

         4. If these types of defect are in the weld, it is usually because the welding speed is too high. But if it is not possible to decrease the welding speed (because of distortion or other things) try the procedures given in steps (4) and (5).

         5. The shape and surface condition of the weld crown and underbead is also related to the welding speed, the effects change with different materials. For example, weld spatter (which is a quantity of small 'globules' of weld metal) immediately in the weld area. This is usually because a higher welding speed is used; while it is less usual to get undercuts (at the side of the weld) with an increase in speed.

         6. In electron beam welding it is better to use the highest possible 'traverse' speeds, to get the correct geometry and metallurgy.

      4. The size of the focus spot.

         1. There are different devices (which are not available at this time) to focus the electron beam at a point you can calculate. In the machines used at this time, it is usual to focus the beam visually. This is done with a tungsten or copper target adjusted at the focus height. The beam is adjusted for the smallest apparent 'spot size'; or for the color intensity in the 'target melt pool' (when the equipment is used at high powers).

         2. Both these procedures (used in step (a)) are not very accurate. It is also difficult to set the same adjustment again and again. Some new types of beam welding machines will be available subsequently. These will have an automatic device which will focus the beam and will be used for all regular work.

         3. The dimension of the focus spot on the material to be welded, will directly effect the weld geometry. If you focus the beam above or below the top joint surface, the weld is made wider (and is the same distance apart at all points). In some materials one more 'nail head' is made at the bottom of a full penetration weld. This gives an 'hourglass' geometry and a good shaped underbead. The shape and surface condition of the weld crown and underbead are usually made better with this procedure.

         4. The procedure used in step (c) will also slow the weld thermal cycle and prevent cracks. It also helps the vapor to come out of the weld. The use of this procedure must agree with the material thickness and component shape (for each time it is used).

         5. Use test pieces to find the necessary quantity the focus spot will be out of focus. Also to find the position of the focus point (if it is to be above or below) in relation to the joint top surface.

            1. The applicable Repair TASK gives the adjustments and type of machine which you can use as an aid (as used by IAE during the preparation of the applicable TASK).

         6. Do not use the dimension of the focus spot (on the material to be welded) to find the focus point. The correct procedure is to accurately focus on a tungsten or copper target block. This is set in the chamber at the calculated focus height.

      5. Beam deflection procedures.

         1. Beam deflection procedures can be used to set the weld geometry and the thermal conditions (it is almost the same procedure as in step (4)). Although it is not as satisfactory to make better surface conditions or to make the 'hourglass' shape of weld. On some materials you can make the surface conditions worse, for example porosity can occur. But, the procedure has the value of control of the heat given across the weld. This is because of the different 'tracking patterns' and cycle frequencies that can be put into the machine to control the beam. For some welding problems the beam deflection procedures can be the only solution.

         2. Beam deflection is usually not used unless it is necessary. This is because of problems when you try to get the same adjustments each time. At this time there is no sure procedure to measure and keep the amplitude of a deflection pattern constant, again and again (to find the solution to this problem, is the cause of some research).

         3. The procedure at this time is to set the amplitude visually with a scale graticule. It is not easy to find 'the spot boundary' accurately. You can not always get an adjustment, calculated with a theory, each time this is necessary (this usually occurs if the machine is used by different persons). This can also occur during the spot focus procedure, although you can get more accuracy with the visual spot focus procedure (if you try to find a minimum spot dimension than when you try to measure a spot shape made by a deflection amplitude).

         4. The problems given in step (c) do not occur if you use linear deflection (the deflection is at the same distance apart at each point to the joint, with no effect on the width of the weld). You can use this to adjust the weld solidification properties without a decrease in the welding speed. This does give better geometry than you will get with only a decrease in speed. The accuracy of the amplitude when you do this is less important. Also, the visual adjustment when done carefully is satisfactory.

      6. Beam slope-out.

         1. For continuous welds the welding machine lets the beam power be automatically decreased to zero when the weld 'start' is 'overlapped'. This time is known as the 'slope-out' time. It is usual for the beam current to decrease at a controlled mA/sec rate. Although it can sometimes help if you 'slope-out' with a decrease of the accelerating voltage.

      7. Geometric defects.

         1. For the geometric defects, refer to Figure and as follows:

            1. The most important defect of this type (and difficult to find) is the 'missed joint' condition. Refer to joints A and B. The primary causes of 'missed joint' conditions are:

            2. An unsatisfactory view of the joint during the welding procedure.

            3. The beam spot not adjusted correctly to find the specified position it has to go to, with the machine scale graticule.

            4. The movement of the beam spot with a change in beam power.

            5. The beam comes on the joint at an angle to the joint surface (beam 'impingement').

            6. The beam moves away from the joint because of expansion of the component.

         2. One of the most usual defects is seen in joint A. It can be found with careful preparation and examination of the bottom of the joint. It also can occur as not sufficient fusion, immediately at the edge of the weld, through much of the joint thickness.

         3. The condition in joint B is possible if an 'hourglass' weld is used. Also, if the weld is made at a small angle (from the vertical) to the joint line. It is difficult to find.

         4. If you use incorrect beam power related to the speed, where the welding speed is low. This causes the 'dropped' weld conditions in joints C and D.

         5. Undercuts at the edge of the crown or underbead can be seen in joints E and F. This defect can have a bad effect on the components stress conditions (because of the bad 'notch' conditions made).

         6. The underbead conditions of joint G are caused because the weld root metal has come away from the joint (this is 'jettisoning') and a slot is made. Usually this occurs when you try to weld an open joint in some 'difficult' materials. Use a 'backed' joint (as given in Figure, joint C or E) if the defect can not be corrected with the weld adjustments set differently. The root defects are machined away with the backing.

         7. If the underbead conditions of step (f) are found in the test pieces do as follows. Take a longitudinal piece and measure the vertical quantity of the 'jettisoning'. The result of this procedure is then used to make the 'backing' (this is the dimension of the fault, with a specified allowance added to it).

         8. If the weld has penetrated, as in joint H (because of a decrease in the volume of the weld root metal during solidification) a 'notch ' effect is seen. This defect is not so deep. It can be made sufficiently smooth and regular to be satisfactory to the approved limits.

      8. The metallurgical defects.

         1. The metallurgical defects are given in Figure and as follows.

         2. Porosity is shown in joint A. This is a quantity of small bubbles which are caught in the weld. It is usually found in materials which have a high quantity of unwanted chemicals in them.

         3. Internal cavitation is shown in joint B. This is a much more important defect. It is caused because of high vapor pressure in the weld before it becomes a solid (the vapors can not come out of the weld, at a sufficiently fast rate). In very bad examples this cavitation makes long 'tunnels' along the weld.

         4. Weld root porosity shown in joint C, is very usual in partial penetration welds. The weld penetration must be sufficient to make sure that the defect is kept in the joint backing. This type of porosity decreases during the slope-out time because of the controlled decrease of the weld energy.

         5. The most satisfactory beam weld is a vacuum-melted cast structure; made of equiaxed crystals, close together, with no linear structures. You can not always get this type of structure. Although the weld must not have some specified defects, other structures are satisfactory.

         6. A structure which can be usually made in the air-hardening steels is joint D. As the weld becomes solid behind the beam the columnar crystal structure is made in the material. This structure goes inwards from the edges of the fusion zone. When it comes against the opposite crystals, a plane of weaker structure is made down the center line of the weld. If in this center plane, a good structure of equiaxed crystals is made, then the weld has the satisfactory metallurgical qualities necessary. The usual defect found (with this structure) is that shrinkage stresses make this center plane weaker. Also grain boundary separation and cracks occur (as in joint E).

         7. Shrinkage stresses cause the defect in joint F. The structure of the fusion zone can be much better than the coarser grain of the initial material. Although there is failure in the edges of the grain structure in the weld heat changed zone. The structure becomes weak. This is 'inter-granular breakdown' or 'separation'. It can have a very bad effect and can change into cracks which can go in to the weld fusion zone.

         8. More shrinkage effects are:

            1. In some joints the 'traverse' weld shrinkage can be stopped because of the type of joint (for example in planetary welding of a solid disk piece). Separation and cracks occur usually along the edge of the weld.

            2. With low volume welds, which become solid quickly. This can make cracks, these go across in the weld surfaces. These are usually seen as a number of very small cracks. These can usually be machined away.

            3. Most separation and crack defects in welds can be prevented if there is a decrease in the weld thermal cycle. Although, in some materials it can be made better with an increase in welding speed. The applicable Repair TASK will give the necessary procedure to weld the materials where these defects can occur.

      9. The data necessary in the Repair TASK.

         1. All electron beam welding Repair TASKS come from procedures which are tried and approved. These TASKS give the correct geometric and metallurgical standards necessary.

         2. The Repair TASK will give the type of machine and adjustments to use, to help you complete the TASK satisfactorily. If an equivalent machine is to be used, use test pieces for the initial welds (before you repair the component). This gives you the correct adjustments to use and makes sure the machine is correct for the TASK.

         3. If a different machine is to be used, you must make the correct weld on test pieces. These must agree with the instructions given in the applicable TASK.

         4. The applicable Repair TASK will give the necessary figures to show the weld geometry and the tolerance of the dimensions (at the applicable reference points). Refer to Figure. If necessary, photomicrographs of the metallurgical structure will be given.

         5. The weld adjustments given in the Repair TASK will not be the same if you use a different machine. But, these can be used to find:

            1. Welding speed.

            2. Beam power levels.

            3. The procedure to find the dimension of the focus spot ('de-focusing').

            4. The deflection procedures.

            5. Special overlap or slope-out procedures.

6. SUBTASK 70-31-03-310-006 Test Pieces

   1. To get the correct geometrical and metallurgical repair weld, test pieces must be used. Pieces of the test piece are cut, from across the weld. These are polished, etched and examined. This is done as the procedure continues.

      1. The test pieces given in the Repair TASK will be materials usually kept in the welding facility (as 'stock items'). If low value components are to be used, the Repair TASK will give the necessary instructions.

      2. The initial work is done on flat test pieces to find the basic conditions for the geometry and metallurgical qualities. Usually this will let you continue the Repair TASK. This is not always possible if, for example, more important components are to be welded (primary components of the engine which turn or large components). More work is to be done on test pieces, which are equivalent to the applicable component.

      3. This is necessary because the temperature of the components with long weld 'runs' will increase continuously, as the low welding speeds are used. If you get distortion, which is difficult to stop, a component 'simulator' must also be welded. This is to measure the levels of distortion.

      4. There are two types of test pieces, flat test pieces and component 'simulator' test pieces.

   2. Flat test pieces, refer to Figure.

      Much of the work done on test pieces will be 'melt run' welding. This is fusion of the metal, where a mechanical joint is not necessary. This type of procedure is usually used if 'simulators' are to be welded at a subsequent time. There are three types of test pieces, as follows:

      1. Plain flats machined to the thickness of the thicker joint piece on open butt joints; also to the total thickness of both the joints together on backed joints and those with external spigots. Refer to joint A. These test pieces are applicable to get the basic procedures, such as:

         1. The welding speed.

         2. The focus point.

         3. The approximate power levels.

         4. The correct geometry and metallurgy.

      2. These pieces are satisfactory in use because of the many 'melt run' welds that can be made on each one. Although the piece must cool between each one.

      3. Shaped flats machined to the correct joint configuration, on which 'melt run' welds are made, refer to joint B.

      4. Shaped flats machined to the correct mechanical joint condition, refer to joint C. These are necessary when you make an analysis of the metallurgical qualities, if different metals are joined. Also these are necessary if backed or external spigot joints are used. Refer to Step, for the metallurgical defects with these joints.

      5. It is recommended to let the test piece become cool between each weld (while you find the adjustments). You can, subsequently in the procedure, make the equivalent length of component weld with continuous welds next to each other. This is done to make an analysis, about the effect of the increase of the components temperature on the weld geometry (and other related things). You can not directly compare this with the conditions in the component. It can give you an indication of the weld conditions.

      6. When there are quantities of low value components to be repaired, it could be better to use some as test pieces. These can be used to make the final weld adjustments before the 'batch' repair continues.

      7. If the procedure is to be prepared for a continuous weld, the necessary overlap and slope-out (of the weld) must be made on a flat test piece. Do this unless you make an analysis on this part of the weld on a component 'simulator', subsequently in the procedure.

   3. Component 'simulator' test pieces.

      1. This type of test piece is made to give the equivalent conditions found in component repair conditions. This is to help you make and analysis on the effects of an interference fit, expansion, shrinkage (and other related things).

      2. The mass and shape of the component and replacement part can effect the thermal conditions and geometry of the weld. These conditions are difficult to make again (with precision) on flat test pieces. If there are Repair TASKS where such conditions are important, the use of 'simulator' test pieces will be of value. They will help you find the best final weld adjustments to use. Also they help when you make an analysis related to the distortion levels.

      3. For large components the 'simulators' are usually made smaller in size (that is, 'scaled down') but this does not include the joint configuration.

      4. You can use the 'simulators' to prepare most of the necessary procedures for welding (after the basic procedures are completed on 'plain flats'). This is done with short weld 'runs' on a 'simulator' joint. This is then followed with a full weld on a different 'simulator'.

   4. The preparation and welding of the test pieces.

      1. Obey the same necessary instructions when you prepare and weld the test pieces, as when you weld the component.

      2. The test pieces must be in the correct heat treatment condition for welding. For a metallurgical examination they must be given the post-weld heat treatment (given in the applicable Repair TASK). You can make an immediate analysis of the weld geometry after welding, because the heat treatment does not effect it.

      3. On materials where weld embrittlement can occur, make a hardness inspection across the weld heat-affected and fusion zones. This is done after the post-weld heat treatment, as given in the applicable Repair TASK.

      4. When you prepare for welding hold the flat test pieces away from the backing plate. The joint surface is to be at the same height, in the chamber, as the component joint will be (set) for the repair. The backing plate material must agree with the material to be welded. This is to prevent weld contamination with vapors pushed out from the backing plate, refer to paragraph A.(4). Also, prepare and clean the test pieces correctly, as given in Step to Step.

7. SUBTASK 70-31-03-220-001 Examine the Welded Test Piece Surfaces

   1. Visually examine the weld crown and the underbead for shape and surface defects. Examine the specified areas with a magnification of 7X in a good light, with a binocular microscope of intrascope.

8. SUBTASK 70-31-03-310-007 Prepare and Etch the Welded Test Piece

   1. Cut a piece off, from across the weld of the test piece.

   2. Polish the surfaces of the piece to give a good finish, with no scratches on it.

   3. NOTE

      It is satisfactory to use alternative procedures if these are available.

      Etch the surfaces as follows:

      1. During this procedure keep the piece clean. It is important that there is no solution contamination. This will give good results.

      2. Continue to etch the piece with the CoMat materials given in step (3), until you can see the fusion and heat affected zones of the weld clearly. Also, the metallurgical structure must be clearly seen with the binocular microscope.

      3. 
         CAUTION
         DO NOT USE GLASS CONTAINERS WHEN YOU ETCH WITH HYDROFLUORIC ACID. PLASTIC CONTAINERS MUST BE USED.

         Use these specified CoMat materials and procedures to etch the piece as follows:

         1. Use 10 percent CoMat 03-012 OXALIC ACID (COOH)2 (Electrolytic) to etch nickel-based alloys, stainless steel (S/CNT, 18/8), 12 percent chrome steel (S/SJ2, S/ST) and Inco 901.

         2. Use the electrolytic procedure with a 4 volts DC supply. Attach the piece to be etched to the anode. The cathode must be made of platinum.

         3. As an alternative to the electrolytic procedure, etch the 12 percent chrome steel with a solution made-up of one gram of CoMat 03-014 PICRIC ACID (NO2)3C6H2OH with five milliliters of CoMat 01-099 HYDROCHLORIC ACID and 100 milliliters of CoMat 03-015 ALCOHOL.

         4. Clean the nickel-base alloys to remove the oxalic acid (this is seen as a brown stain), lightly apply water to the specified surface with a quantity of cotton wool. Dry the piece with CoMat 03-013 METHYLATED SPIRIT and hot air.

         5. For other materials use the CoMat materials as follows:

         6. Magnesium S/MOB: 2 percent Nital (2 percent CoMat 01-025 NITRIC ACID HNO3, TECHNICAL GRADE in CoMat 03-015 ALCOHOL).

         7. Aluminum: 2 percent CoMat 01-027 HYDROFLUORIC ACID (2 percent HF in water).

         8. Titanium: 2 percent CoMat 01-027 HYDROFLUORIC ACID HF-10 percent CoMat 01-025 NITRIC ACID HNO3, TECHNICAL GRADE.

      4. Clean the etched piece fully in water to remove the etchant. Dry the piece with CoMat 03-013 METHYLATED SPIRIT and hot air.

9. SUBTASK 70-31-03-220-002 Examine the Etched Test Piece Surfaces

   1. Examine the etched piece for the correct geometry.

   2. If the geometry is satisfactory, examine the piece for metallurgical defects. Use a binocular magnification of 30X.

   3. Do the procedure in Step, if the geometry and metallurgy is satisfactory.

10. SUBTASK 70-31-03-310-008 Make a New Test Piece

    1. If the geometry and metallurgy is satisfactory from the initial test piece, weld a new test piece.

    2. Use the same overlap and slope-out (where applicable) as found with the initial test piece.

    3. Heat treat the new test piece. Refer to the applicable Repair TASK.

    4. If necessary, machine the weld surfaces as given in the applicable Repair TASK (to machine the component).

    5. Do a crack test on the new piece. Use an approved dye penetrant procedure. Examine the possible unsatisfactory areas with a binocular microscope.

    6. Do an X-ray examination on the welds.

    7. Use the test piece to find the correct procedure for the ultrasonic inspection, if this is given in the applicable Repair TASK.

    8. Cut across the welds of the test piece to make more pieces. Include in the pieces, those with overlap and slope-out.

    9. Prepare and etch the welded test pieces for metallurgical inspection. Refer to Step. Make sure the etchant shows the grain structure of the material.

11. SUBTASK 70-31-03-220-003 Examine the Pieces from the New Welded Test Piece

    1. Examine the new welded test pieces with a binocular microscope at a magnification of 60X. Look for intergranular separation or cracks in the fusion and heat affected zones and the adjacent metal.

    2. If it is difficult to prevent distortion during the repair of the component, use component 'simulators' (before you weld the component). Make sure there is no distortion in the 'simulators' before you weld them, after you weld them and after the heat treatment.

12. SUBTASK 70-31-03-310-009 Tooling

    1. The tools and fixtures used in electron beam welding are almost the same as those used in other welding procedures (as an example, as those tools used in argonarc welding). The tools and fixtures hold the mating components in the necessary relation to each other. They give the necessary force to hold the component and are used to take the heat away from the component. There is usually less of a distortion problem in electron beam welding. The tooling can then be of lighter construction, it is not necessary to make it to hold the argon gas (for the gas shield).

       1. There must be no closed spaces made when the component is assembled in the fixture. This is because the welding is done in a vacuum. These spaces could fail to become empty during the time the chamber is emptied ('chamber pump-down'). Holes or slots must be made in the tooling.

       2. This must be done to let the spaces become empty, if they are near the weld or not.

       3. The gas which comes out during the welding cycle will cause chamber contamination. Possibly this could cause the current to come out of the beam gun or 'flash over'. Make sure the holes go completely through the tooling and the gas can come out easily. The gas could become caught behind a setscrew and only come out slowly, around the threads.

       4. When full penetration joints are welded the beam-energy is not completely used up in the weld. The beam will come out from the bottom of the joint. In relation to the power level used and joint thickness, this remaining beam could have sufficient energy to cause damage. The beam could go on the component or tooling in the beams direction. It is necessary to give the tooling 'impingement shields' to catch the remaining beam. You can have shields which are not part of the tooling; an item you can replace, or part of the tooling.

       5. When the remaining beam goes on the shield, ionized gas material is given off. This will move up the beam to the negative source. This can cause contamination in the weld (if the gas material does not agree with the weld conditions).

       6. Many alloys used in the components in the V2500 engine can be open to contamination with unwanted vapors during welding. It is most important that the materials used to make the shield agree with the materials to be welded. They must be of the same material group. This is very important on components which turn in the engine and work in hot, highly stressed conditions.

       7. Position the shield as far as possible below the joint surface. This is to decrease 'spatter' (these are the small round particles of metal which are pushed from the shield and can go on different surfaces). This 'spatter' must be removed after welding. Alternatively, use CoMat 04-001 BERKATEKT, apply this compound on the bottom face, with a brush. This prevents the bond of the 'spatter' on the surface. After welding you must fully clean the component to remove this compound.

       8. Use a good quality stainless steel shield when you weld all steels. The use of copper is possible, but it must be plated with chromium. This is to prevent copper contamination of the weld.

       9. When you make the tooling you must think about the access of the beam to the joint. Also you must clearly see the joint line in the machine view system. If it is necessary for the tooling to be installed near to the joint line it must not be nearer than 0.125in. (3.18 mm). If the tooling must be near to the joint (and the part of the fixture which prevents movement is of a thick dimension) you must have an open angle of view. The tooling will have a chamfer, as given in Figure.

       10. All joints must have some interface pressure, to prevent the part of the joint not welded 'gapping' as you weld. This does not include closed 'interference fit' joints. This pressure is applied with the tooling, the name of this is 'end load'.

       11. Usually to keep a quantity of 'end load' springs are used, refer to Figure. The 'end load' is not applied with only the springs. The tool surfaces touch along their length. The spring effect occurs after the weld cycle and subsequent shrinkage has started.

       12. Alternatively, a hydraulic load can be used.

       13. In Figure, if the springs are not there (and a sufficient torque load is put on the nut) the arbor will give the 'spring' effect. This is caused because of the compression loads on the flexible vertical end of the arbor. If the springs are necessary or not, will be related to the particular type of the repair.

       14. When you weld large diameter components for which an 'end load' is necessary do as follows, where possible. Apply the 'end load' with divided segments, refer to Figure.

       15. One end plate is cut in segments with sawcuts, this is done to let isolated loads be applied. These loads are applied to parts of the joint through the bolts. This lets the end plate be flexible, as the weld shrinkage occurs around the joint.

    2. Tool materials.

       1. Before you make the selection of the materials (to make the tooling from) think about these things:

       2. The type of 'impingement shield', it could be part of the tooling or could not be part.

       3. The removal of the remaining magnetism.

       4. Chamber contamination.

       5. The total weight of the component/tooling.

       6. For the types of 'impingement shield', refer to the data given before, in this SUBTASK.

       7. The removal of the remaining magnetism.

          1. Use materials which are not magnetic or can be easily de-magnetized, with the usual procedures. As an example, do not use high tensile steel bolts. It is very difficult to remove the remaining magnetism from these materials. It is better to use stainless or mild steel bolts. Use brass nuts in the tooling/fixture, this will make it easier when the time comes to disassemble it.

          2. For the larger tools necessary, there is a limit in the selection of materials that are not magnetic, which you can use (because of the high monetary value). It is usually satisfactory to use 'commercial' quality mild steel, for example, for tooling/fixtures which are symmetrical. If the tooling/fixture is not symmetrical (for example, if there is a large, isolated part of it near a weld joint) you could have to make this part from a material which is not magnetic. Alternatively, a 'shield tube' could be used, refer to Step.

             Do not use cadmium plating to give the corrosion protection on parts of the tools/fixture.

       8. Chamber contamination.

          1. Do not use low quality cast materials. It is possible this could cause a slow and continuous 'out gassing' from porosity after 'chamber pump-down'.

       9. The total weight of the component/tooling.

          1. When you make the selection of the materials for a large tool/fixture, you must think about the weight. This is important if it is to be turned about a horizontal axis in relation to the light weight gearbox of the welding machine. Use holes or slots in the material to make the tooling lighter. The careful use of light materials, for example aluminum, will result in the easier use of the tooling.

          2. When a large heavy assembly is operated at low speed on a horizontal axis (one half rpm is not unusual) a low friction bearing will give better operation. This could be a ball bearing assembly installed on a 'vee block'. Although this is not necessary if the machine tailstock has a satisfactory 'center' on which it turns.

          3. 'Tack welds' can be used in electron beam welding (as in argonarc welding) this results in easier to use tooling. These could be argonarc 'tack welds' (if the material agrees with this type of welding). Alternatively, they could be electron beam 'tack welds', used before the full power weld. The argonarc 'tack welds' could decrease 'set-up' time on quantities of small components. This lets you use easier to use tooling ('lash-up' tooling). Electron beam 'tack welds' includes the use of full 'sealing runs' with little depth welded at low power, to prevent joint 'gapping'. If this procedure is not used, much more tooling will have to be used.

          4. These procedures must only be used if given in the applicable Repair TASK or, if these are fully tested on test pieces.

          5. The tooling used when you weld a high interference fit joint must help prevent assembly damage to the joint interface. In many of the procedures it is possible to put the necessary qualities in to the tooling.

13. SUBTASK 70-31-03-120-001 The Procedure to Clean for Welding

    1. It is most important to correctly clean and prepare the component parts for electron beam welding. This is to get the necessary good quality welds.

       1. If electron beam welding is necessary during the components overhaul, clean them to remove the oil and carbon deposits (with the specified procedures).

       2. If specified in the Repair TASK, both sides of the joint to be welded must be abrasive cleaned; or 'scurf mopped'. Remove all the unwanted abrasive material with a specified detergent cleaner. It is most important no abrasive material becomes caught in the component. The abrasive blasted joint area will not be shiny compared with the shiny surface of the replacement part. This can help you to see the joint more easily in the welding machine.

       3. The primary components which turn in the engine (for example rotor and turbine disks and shafts) must only be abrasive cleaned if the applicable Repair TASK tells you to.

14. SUBTASK 70-31-03-220-004 Make an Inspection to Prepare for Welding

    1. Before you assemble the components parts, make an inspection of the surface finish. Make sure also, no damage has occurred because of the movement of the parts from one procedure to a different procedure. A surface finish of 32 microinches (0.8 micrometers) is satisfactory for electron beam welding. Although a surface finish of 80 microinches (2.0 micrometers) has given good results.

    2. Carefully remove all the raised metal (refer to step A.). When you remove the burrs, keep the corners sharp at the top of full penetration joints. This is done to give the maximum material, to hold the weld crown structure.

    3. Make an assembly measurement to make sure the clearance between the joint faces is not more than 0.0015in. (0.038 mm). This is not necessary for those components which have a diametral interference fit with replacement parts. An assembly measurement is very important when the backing is part of the joint. This is done to make sure there is no 'binding' in the corner radius at the bottom of the joint.

    4. Measure the quantity of "interference" on interference fit joints. Make sure it is correct. This is very important to get the necessary standard of weld.

15. SUBTASK 70-31-03-160-001 Clean the Surfaces of the Components Before Final Assembly

    
    CAUTION
    YOU MUST USE CLEAN LINEN GLOVES BEFORE YOU TOUCH THE CLEANED PARTS/COMPONENTS. DO NOT TOUCH THE JOINT FACES WITHOUT THE PROTECTION OF GLOVES ON THE HANDS, BETWEEN THE PROCEDURE TO CLEAN AND THE ASSEMBLY PROCEDURE.

    1. Clean the components surfaces.

       1. Before you final assemble the component do as follows. Clean the joint faces with a cloth, that has not lint, made moist with CoMat 01-124 ISOPROPYL ALCOHOL or CoMat 01-031 ACETONE (CH3)2CO.

       2. Alternatively do the special procedures, as necessary, to clean the components; as given in the applicable Repair TASK.

16. SUBTASK 70-31-03-310-010 The General Procedure to Assemble the Components

    1. It can be difficult to assemble interference fits. No oil or grease must be used to help you. You must use the thermal expansion differential between each part to help you during assembly. If possible make the tooling/fixture control the assembly of the components.

    2. Assemble the components as given in the applicable Repair TASK.

    3. Alternatively, use the procedure which follows:

       1. Heat the external component in an oven to a maximum temperature of 392 deg F (200 deg C). It is important to use an oven. Do not use heat from an isolated source, for example gas flames.

       2. Freeze the internal component in liquid air or CoMat 03-026 LIQUID NITROGEN. Put the component fully in to the liquid until the bubbles stop. Immediately before assembly clean the joint face with a cloth made moist with alcohol, refer to Step. Do not let the face 're-frost'.

       3. If before the full assembly is completed the parts 'bind' and become tight, do not use force to assemble the parts. Damage to the joint interface will result. You must disassemble the parts and examine them. Always correct the damage to the joint faces.

       4. When the damage is corrected you must clean the component and start the assembly procedure again.

17. SUBTASK 70-31-03-310-011 The General Procedures to Demagnetize the Component

    1. The electron beam is a flow of negatively charged particles. These operate with the control of the electromagnetic fields. These are made with the focusing and deflection coil systems in the electron beam gun assembly.

       1. Unless the welding machine includes special components to correct the beam, the remaining magnetism will control and deflect it. These special components could be of a high monetary value and difficult to make. The remaining magnetism could be in the parts (to be welded) or the tooling. Subsequently, this could give decreased tracking precision.

       2. It is necessary then, to demagnetize the parts to a specified level (until the remaining magnetism does not cause the beam to be out of control). This level is usually one gauss or less. A gaussmeter must be used to measure this.

    2. Demagnetize the parts to be welded in a strong alternating magnetic field. Then you must let the field close, slowly, at the specified constant rate as follows:

       1. Put the part through the fixed frame coil. The axis of the coil is put in an east to west direction.

       2. Move the part along the coil axis for a minimum distance of six feet (182.88 cm). Set the switch to the off position. A satisfactory result is related to the type of material; the shape of the part and the position of it when it is put through the coil.

       3. If necessary do the procedure again (from step (2)) two or three more times. Each time, change the position of the part when you move it through the coil. This is done to get the necessary level of demagnetization.

       4. As an example, when you demagnetize a circular part do as follows:

          1. Move the turbine disk or shaft through the coil along its own axis.

          2. Then change the axis of the part so it is at 90 degrees to that of the coil. Turn the part slowly as it goes through the coil.

          3. Each time you move the part, it must be a minimum distance of six feet (182.88 cm) away from the coil sides. Set the switch to the off position.

          4. Do not demagnetize the part and the tooling when they are assembled together. They must be disconnected before you demagnetize them.

          5. You must always measure the level of the remaining magnetism with a gaussmeter, when the part is assembled to the tooling.

       5. The procedure given in step (4) can be difficult, because of the large parts included. Alternatively do as follows:

          1. Wind a heavy duty flexible coil the correct number of turns on a non-magnetic frame. The supply of current is from a welding transformer.

          2. Lift the frame from the part to the necessary height before the current is set to the off position.

       6. If it is not possible to demagnetize the part/tooling to the specified level, seal the beam from the magnetism.

          1. Hang a mild steel tube, with a bore diameter of one inch (25.4 mm) from the gun heat shield (this is where the beam is given off). Put the bottom end of the tube as close as possible to the joint.

          2. The tube will give the necessary protection to the beam from magnetization. Although it will not give the protection from magnetization (if it is there) very close to the joint.

          3. You can make the tube telescopic. This will let you use it on more than one type of component or part.

       7. Refer to the applicable Repair TASK for the given procedure to use.

    3. A gaussmeter has a limit in its use to show the magnetic effects on the beam. More procedures are available to calculate the remaining magnetism of the assembly. These also show the effect on the beam.

       1. The cathode-ray tube (CRT).

          Make the inspection which follows outside the machine chamber. Do this with the component and tooling assembly set for welding.

          1. Make a basic electrical circuit to operate a small CRT. Make a mark on the center of the screen face, to give a small black dot.

          2. NOTE

             On a screen which is completely neutral the black dot will not let you set the spot. The earth's magnetic field will give a small change in the position of the spot. An allowance is made for this 'offset', when you measure the deflection.

             Set and operate the CRT at maximum sensitivity. Focus the spot carefully and make sure it is correctly focused.

          3. Hang the CRT above the joint line at the equivalent position of the beam, with the same operational distance. Move the component to be welded. Use the same procedure as during welding.

          4. Lower the CRT gradually in two or three steps to the joint. Look at the quantity of spot 'offset' after each step. Do this until the CRT screen face is one inch (25.4 mm) away from the joint surface. If you use a mirror to see the CRT screen face, make sure it has no magnetism.

          5. With this procedure you will see the effects and location of the remaining magnetism. To calculate the quantity of deflection, use this formula as follows:

             Deflection = the sum of each of the spot 'offsets' measured in (d) multiplied by:

             .

             	EHT voltage of the CRT
             	EHT voltage of the electron beam

       2. Beam tracking.

          To examine the effects of magnetism in the component and tooling, the beam can be used as follows:

          1. Low power tracking.

             1. Set the part in the machine and 'pump down' the chamber, as for welding. Adjust the beam current to a sufficiently low level (so you can use it focused on the parts surface with no 'impingement' damage). Move the part, as for welding, look for magnetic effects through the view system of the machine.

             2. An effect which can cause you problems (although the assembly could be demagnetized to the specified level) is from the electron beam. The beam could cause magnetism in an assembly. This is possible if the assembly is not symmetrical. Use the tube (refer to paragraph A.(6)) to seal the beam, to prevent the effect.

          2. Beam pulsing.

             1. Some machines have a beam pulsing system installed in them. With these, the beam can be used at full welding power to examine for 'drift'. This can be done without component damage.

             2. Set the pulse so that the 'beam on' time is very short in relation to the 'beam off' time, and the joint 'welded'.

             3. The beam will make a mark on the parts surface with a number of 'melt spots'. These 'spots' will not have a large depth (because of the short 'beam on' time). You can then see if the beam has moved from the joint line.

             4. The conditions for this procedure must be done with test pieces, before it is done on the component.

18. SUBTASK 70-31-03-310-012 The Welding Procedure

    1. The procedure to use before you weld the component.

       1. Set the component and tooling assembly (installed on the machine manipulator) in the machine chamber, or on the applicable trolley prepared for installation in the chamber.

       2. Examine the component for its remaining magnetism. Refer to Step.

       3. Make sure the components surfaces are in the correct position in relation to the beam axis.

       4. Set a focusing target block at the correct height in relation to the joint surface.

       5. Install the component assembly into the machine chamber (if necessary). Make sure the distance from the joint surface to the gun heatshield and the traverse speed are correct. These are to be the same as found with the test pieces.

       6. Make sure the joint is correctly aligned in the view system scale graticule. It must be no more than 0.003 in. (0.076 mm) on each side of the zero line (that is a total error of not more than 0.006 in. (0.15 mm). Do this procedure unless the Repair TASK gives a different procedure.

       7. Remove the air from the machine chamber.

       8. With the target block make the beam spot center to the graticule. Focus the beam. If a low power 'tracking run' is to be done on the joint, to make sure of the accuracy, do as follows:

          1. Set the beam current so no 'impingement' damage can occur.

          2. Do the 'tracking run'.

          3. Make sure the beam spot is center to the graticule before each weld.

    2. Welding the component.

       1. Set the beam power controls to the same values as those found with the test pieces.

       2. Continuous welds must be 'overlapped' on the full power 'run' before the 'slope out' starts. On joints up to six inches (152.4 mm) diameter, the 'overlap' must be between five and ten percent of the joint circumference. On larger diameter joints the 'overlap' must be between one and one half inches (38.10 mm) and two and one half inches (63.50 mm). The 'slope out' must be made with the beam current set at the rate of six mA/second. This rate must be used unless the Repair TASK gives a different rate.

       3. When you weld large diameter joints 'beam steering' could be necessary. This is used to keep the joint travel in the specified limits. It is also used during welding, when the joint moves away from the beam (because of heat expansion).

          NOTE

          To get the correct results with this procedure it is related to the traverse speed of the joint. This procedure can be used if the differences in the joint position are not too large, in relation to the beam. You must do this procedure satisfactorily on test pieces and be approved in its use.

          There are different joint 'tracking' devices you can use. When the accurately made stylus 'tracks' near the joint position it gives a signal to a servo mechanism. This corrects the differences in the joint position, in relation to the beam.

       4. Look through the machine view system as you weld. Use the machine manual traverse controls to correct the joint position, in relation to the beam.

       5. When welding, do not use 'tack' weld procedures unless it is given in the Repair TASK; or make an analysis with component simulators, refer to Step. During welding, if defects occur (for example, if the beam does not go on to the joint or the joint clearance has become larger) do not continue to weld. Remove the component from the machine and find the correct procedure to complete the weld.

       6. When the weld is completed, remove the component and tooling from the machine. If it is possible that distortion could occur let the assembly cool in the local air temperature. Do this before you disassemble the component from the tooling.

    3. The welding procedure to correct the defects.

       1. If a weld is not satisfactory (because of not sufficient penetration, or low quality surface conditions) it is possible to correct the defects, with more welding procedures. This can be one more full power 'run' or a low power 'dressing run'. Although, it is necessary to make sure there is no remaining magnetism in the component. This could have occurred because of the welding procedure.

       2. It is necessary to find the line of the joint again. To find this, make a line on the weld with a scriber tool. Use an applicable part of the component as a datum.

       3. If the defect is not sufficient penetration, use the bottom of the joint (the part with no penetration) to find the joint line. Use the position of this line to scribe the joint line on the weld crown.

       4. If the defect is weld crown 'notching', it is possible to correct this defect. Use a low power 'dressing run', to make the weld crown shape correct.

       5. If the replacement part has a large allowance, to machine it to the final dimensions (for example, a top 'step', refer to Figure, joint B), you can get better crown conditions as follows:

          1. Make the 'dressing' beam go on to the top step, to melt more metal on the crown. This is the 'offset'. Do not use a larger 'offset' than 0.010 in. (0.25 mm). If it is necessary to use a larger 'offset' than this, make sure you get the specified geometry with test pieces. Do not use a beam power level for these 'dressing runs' of more than 30 percent of the initial welding power.

          2. If low power 'dressing runs' are used on air-hardening steels, a large quantity of embrittlement could occur in the weld. You must use the low power adjustment and a test piece, before you weld the component.

          3. After the test piece is welded, do a heat treatment procedure on it to remove the embrittlement.

          4. Cut the test piece across the weld. Examine the heat affected and fusion zones and measure the hardness values across these zones.

          5. If the heat treatment has not removed the embrittlement, do as follows:

             Make more 'dressing runs' on a test piece. Use different weld adjustments to make the condition of the weld better. It is possible you could have to make a decrease in the welding speed, with an adjustment of the beam power (so it agrees with it).

       6. Full power welds to correct the defect of decreased penetration are permitted. Before you do this procedure, to correct 'missed joint' conditions (refer to Figure, joints A and B), make an analysis with test pieces. Make sure the conditions you get (with the test pieces) have satisfactory geometric and metallurgical properties.

       7. The 'missed joint' conditions in primary components which turn (for example, rotor and turbine disks and shafts) must not be corrected with the procedure given in step (6). Do not use 'dressing runs' to make the weld surface conditions better with these types of components.

       8. You can repair some defects with argonarc welding. Examples of these are: surface cavitation, surface cracks and undercuts. The material must agree with the use of argonarc welding. Also, to use this type of welding, the distortion levels must not be so important. Refer to the SPM TASK 70-31-02-310-501-001 to SPM TASK 70-31-02-310-501-017; or the applicable Repair TASK could give the necessary instructions for the procedure to use. Do not repair primary components which turn (refer to step (7)) with argonarc welding, unless given in the applicable Repair TASK.

19. SUBTASK 70-31-03-280-001 Quality Control

    1. Each overhaul facility, which does electron beam welding for component repair, must use the necessary quality control procedures. An authority will control the preparation, the welding and the inspection of the electron beam welds, during repair.

       1. The authority must make sure the procedures and equipment used are satisfactory. Examples of these procedures follow:

       2. When you find the weld procedures for new welds.

       3. When you examine and make sure the usual welds are satisfactory.

       4. That all the necessary procedures are done before welding (this includes demagnetization).

       5. After the weld adjustments are found with the test pieces (the authority must give its approval of these).

       6. A record must be kept of the weld adjustments used for the test pieces and components. Refer to Figure, for a data sheet you can use for this procedure.

       7. It is not permitted to change or use different adjustments from those approved by the authority. All the welding done to make a correction to the defects, must be approved by the authority.

       8. Record all the limits and conditions used, during the welding, to make the corrections.

       9. The quality control function makes it necessary to make 'proving runs' on flat test pieces. This is done before welding a primary component.

       10. A visual analysis must be made on the test pieces, to make sure the weld can be done again and again (and to keep the necessary weld conditions).

       11. On primary components which turn or for components of a high monetary value a 'proving run' must also be made, as follows:

       12. After a filament is replaced.

       13. After a current discharge or 'flashover'.

       14. After a different person continues the welding procedure.

       15. After machine servicing, or if a failure of the machine occurs.

       16. Make a record of all the hours the filament is in use. Make sure there is sufficient filament life available before you start a weld on a primary component. If you are not sure of the remaining life of a filament, replace it with a new filament.

       17. The authority must make sure the necessary machine servicing procedures and the routine maintenance work is done (to the maker's instructions).

Figure: The types of joint

The types of joint



Figure: The machined shape of joint H and an example of a planetary joint

The machined shape of joint H and an example of a planetary joint



Figure: Electron beam weld geometry

Electron beam weld geometry



Figure: Geometric defects

Geometric defects



Figure: Metallurgical defects

Metallurgical defects



Figure: Weld dimension reference points

Weld dimension reference points



Figure: Flat test pieces

Flat test pieces



Figure: Examples of tooling as welding aids

Examples of tooling as welding aids



Figure: Examples of tooling as welding aids

Examples of tooling as welding aids



Figure: The electron beam welding data sheet

The electron beam welding data sheet