Patent ID: 12246382

DESCRIPTION OF EMBODIMENTS

An additive manufacturing apparatus according to embodiments of the present invention will be described in detail below with reference to the drawings. Note that these embodiments are not necessarily intended to limit this invention.

First Embodiment

FIG.1is a perspective view illustrating a construction of an additive manufacturing apparatus100according to a first embodiment. Note that in this embodiment and the subsequent embodiment as well, description is based on the assumption that the additive manufacturing apparatus100is a metal deposition apparatus using a metal substance as the fabrication material, but the additive manufacturing apparatus100may be a type that uses another fabrication material such as a resin. In addition, a product formed by the additive manufacturing apparatus100may also be referred to as a layered product. Moreover, the following description assumes that the additive manufacturing apparatus100melts the fabrication material using a laser for machining to perform lamination processing, but other processing method such as arc discharge may also be used for the alternative for the apparatus100. The additive manufacturing apparatus100of the present embodiment includes a machining laser1, a machining head2, a fixture5, a driven stage6, a line lighting device8, a computing unit9, and a control unit10.

The machining laser1is a light source that emits machining light30for use in forming processing of forming a product4on a workpiece3. As the machining laser1, a fiber laser using a semiconductor laser, or a CO2laser is used. The machining light30emitted by the machining laser1has a wavelength of, for example, 1070 nm. The machining head2includes a machining optical system and a light receiving optical system. The machining optical system focuses the machining light30emitted from the machining laser1onto a working position on the workpiece3. The light receiving optical system is configured to measure the height of the product4formed on the workpiece3. The light receiving optical system is also referred to as a measurement optical system or height sensor. In general, since the machining light30is focused onto the working position in shape of a dot, a working position is referred to hereinafter as a working point. The machining laser1and the machining optical system constitute a machining unit. Note that in this embodiment and the subsequent embodiment as well, description is given in the context of a line section method using an optical system used as a height measurement method, but another measurement method, for example, an optical method may also be used thereas. Examples of the optical method include a spot-type triangulation method and a confocal method. A height measurement method other than an optical method may also be used. In addition, in the present embodiment, the light receiving optical system is placed in the machining head2to integrate the height sensor with the machining head2. The additive manufacturing apparatus100may use another integration method as long as the height sensor is integrated with the work head2. For the purpose of size reduction of the additive manufacturing apparatus100, the machining head2desirably incorporates the light receiving optical system configured to make height measurement to integrate together the machining optical system and the light receiving optical system.

The workpiece3is placed on the driven stage6, and is fixed on the driven stage6by means of the fixture5. The workpiece3is a base for forming the product4. The workpiece3is herein assumed to be a base plate, but may also be an object having a three-dimensional shape. Driving the driven stage6causes a change in the position of the workpiece3relative to the machining head2, thereby causing the working point to move on the workpiece3. That is, possible working points are scanned over the workpiece3. The phrase “working points are scanned” means that a working point moves along a determined path, that is, to draw a determined trajectory. The additive manufacturing apparatus100performs an additive manufacturing process by depositing a molten fabrication material7at the working point that is a working position, while moving the working point on the workpiece3. In other words, the additive manufacturing apparatus100deposits the molten fabrication material7at the working point moving on the workpiece3thereby to perform the additive manufacturing process. More specifically, the additive manufacturing apparatus100drives the driven stage6to move candidate points for the working positions on the workpiece3. At least one of the candidate points on the travel path becomes a working point at which the fabrication material7is deposited.

The additive manufacturing apparatus100melts, at the working point, the fabrication material7supplied for performing the additive manufacture, by means of the machining light30. The additive manufacturing apparatus100repeats scanning of the working points to stack a bead produced by solidification of the molten fabrication material7, and so as to form the product4on the workpiece3. That is, the additive manufacturing apparatus100repeats an additive manufacturing process to produce the product4. In the initial additive manufacturing process, the additive manufacturing apparatus100deposits the molten fabrication material7on the workpiece3. After repetitions of the additive manufacturing process, the additive manufacturing apparatus100deposits the molten fabrication material7on the product4having already been formed at a start time of the manufacturing process. The driven stage6can be subjected to scanning in three axes of X, Y, and Z. That is, the driven stage6can be translated in a direction along any one of the X, Y, and Z axes. For the driven stage6, there is often caused a 5-axis stage that is rotatable also in the X-Y plane and in the Y-Z plane. In this situation, the driven stage6is assumed to be scanned along five axes, but the machining head2may be used for the scanning.

The line lighting device8applies a line beam40that is linear illumination light for measurement, to a measurement position on the workpiece3in order to measure the height of the product4having already been formed until the time of measurement. The measurement position is a position different from the working point. The line beam40reflects at the measurement position. The light receiving optical system is set in the machining head2to enable the light reflected at the measurement position to be received thereat. Further, the light receiving optical system is situated to have an optical axis being tilted with respect to the optical axis of the line beam40. Because a peak wavelength of thermal radiation light generated during manufacture is in an infrared range, it is desirable to use, for a light source of the line lighting device8, a green laser of a wavelength of about 550 nm or a blue laser of a wavelength of about 420 nm which is distanced from the peak wavelength of the thermal radiation light. Note that the illumination light for use in measurement of the height of the product4does not necessarily need to be the line beam40, but may also be a spot beam that is illumination light condensed in a dot shape. Use of a spot beam enables the height of a portion at the illuminated point on the workpiece3. Meanwhile, use of the line beam40enables a height distribution over the illuminated range on the workpiece3to be measured. The present embodiment assumes that the line beam40is used for measurement of the height of the product4.

The computing unit9computes the height of the product4at the point irradiated with the line beam40based on a position in which the light receiving optical system receives the reflected light of the line beam40on the principle of triangulation. The height of the product4corresponds to a position of the top surface of the product4in the Z-direction. In addition, the control unit10controls machining conditions for the additive manufacturing process using the height computed by the computing unit9. More specifically, the control unit10optimizes, using the height computed by the computing unit9, machining conditions such as a condition for driving the machining laser1, a condition for driving the driven stage6, and a condition for driving a wire supply unit that supplies a metal wire to be used as the fabrication material7. The condition for driving the wire supply unit includes the height at which the metal wire is to be supplied. The line lighting device8serves as a lighting device for measurement. In addition, the line lighting device8and the light receiving optical system constitute a height sensor. Moreover, the height sensor and the computing unit9constitute a height measurement unit. That is, the height measurement unit measures the height of the product4having been fabricated on the workpiece at a measurement position3.

The computing unit9and the control unit10according to the embodiment are implemented in a processing circuitry that is an electronic circuit that performs different processes.

This processing circuitry may be dedicated hardware, or a control circuit including a memory and a central processing unit (CPU) that executes a program stored in the memory. In this regard, the memory corresponds, for example, to: a non-volatile or volatile semiconductor memory such as a random access memory (RAM), a read-only memory (ROM), or a flash memory; a magnetic disk; an optical disk; or the like.FIG.2is a diagram illustrating a control circuit according to the first embodiment. In a case in which the processing circuitry is a control circuit including a CPU, this control circuit is, for example, a control circuit200configured as illustrated inFIG.2.

As illustrated inFIG.2, the control circuit200includes a processor200a, which is the CPU, and a memory200b. In the case of implementation based on the control circuit200illustrated inFIG.2, a functionality is implemented by the processor200areading and executing a program corresponding to different processes, stored in the memory200b. The memory200bis also used as a temporary memory in the processes performed by the processor200a.

FIG.3is a diagram illustrating a cross section in the X-Z plane of the additive manufacturing apparatus100according to the first embodiment. The machining head2includes a floodlight lens11, a beam splitter12, an objective lens13, a band-pass filter14, a condenser lens15, and a light receiving unit16. The machining light30emitted from the machining laser1passes through the floodlight lens11, and is reflected by the beam splitter12toward the workpiece3and condensed by the objective lens13onto the working point on the workpiece3. The floodlight lens11, the beam splitter12, and the objective lens13constitute the machining optical system included in the machining head2. For example, the floodlight lens11has a focal length of 200 mm, and the objective lens13has a focal length of 460 mm. The surface of the beam splitter12is coated with a coating that increases the reflectance at the wavelength of the machining light30applied from the machining laser1, and allows transmission of light having wavelengths shorter than the wavelength of the machining light30. In addition, the additive manufacturing apparatus100supplies a metal wire or a metal powder to the working point as the fabrication material7while driving the driven stage6to realize scanning of the workpiece3in the positive X-direction. This causes the fabrication material7to be melted at the working point by the machining light30each time the working point is scanned, and the melted material to solidify, thereby generating a bead such that the bead extends in the negative X-direction. In this regard, the positive X-direction is, for example, the direction in which the X-axis illustrated inFIG.1extends along its arrow. This generated bead forms a part of the product4. A new part of the product4is formed by deposition of a new bead on a part of the workpiece3serving as a base of the product4having already been formed, each time the working point is scanned. Repetition of this operation causes the fabrication material7to be deposited, thereby the product4that is the final product being formed.

The present embodiment will be described on the assumption that a metal wire is used as the fabrication material7. In addition, the present embodiment will be described in the context of the condition of a machining direction for forming in which the workpiece3is scanned in the positive X-direction and the bead extends in the negative X-direction, that is, in the direction opposite to the direction of supply of the fabrication material7. However, manufacture may be performed to cause the bead to extend in the positive X-direction, that is, the same direction as the direction of supply of the fabrication material7while scanning the workpiece3in the negative X-direction by driving the driven stage6. Note that in this embodiment and the subsequent embodiment as well, description is given in the context of the bead being formed to extend linearly, but another bead formation method may also be used, in which beads formed in shape of a dot are joined together to form a single bead.

The line lighting device8for use in height measurement is attached on a side face of the work head2, and emits the line beam40toward a measurement position on the workpiece3or on the product4having already been formed. The measurement position is determined in consideration of the direction of supply of the fabrication material7and the like. For example, use of a measurement position on the side opposite to the direction of supply of the fabrication material7with respect to the working point facilitates illumination of the measurement position without being blocked by the fabrication material7. The line beam40is formed using a cylindrical lens or the like to form a beam perpendicular to the bead-formed direction and spreading along a direction (the Y-direction) parallel with the top surface of the driven stage6. Thus, the line beam40is applied in form of a line to the product4having already been formed. The line beam40applied to the measurement position is reflected at the measurement position, enters the objective lens13, is transmitted through the beam splitter12and the band-pass filter14, and is focused onto the light receiving unit16by the condenser lens15.

The objective lens13and the condenser lens15are collectively referred to as a light receiving optical system. The light receiving optical system is constituted by, for example, two lenses, i.e., the objective lens13and the condenser lens15. The light receiving optical system, however, may also be constituted by three or more lenses in which, for example, the part for the condenser lens15has a two-lens configuration of a convex lens and a concave lens, as long as the light receiving optical system has a functionality of focusing the light onto the light receiving unit16. What is used for the light receiving unit16is an area camera or the like, the area camera being equipped with a light receiving element such as a complementary metal-oxide semiconductor (CMOS) image sensor, but the configuration of the unit16is sufficient to include a light receiving element having a two-dimensional arrangement of pixels. Note that the band-pass filter14that allows only light of irradiation wavelength of the line beam40to be transmitted therethrough is desirably put in an optical system ranging from the beam splitter12to the light receiving unit16. Providing the band-pass filter14enables removal of light of unwanted wavelengths, of machining light, thermal radiation light, ambient light, and the like.

The additive manufacturing apparatus100performs additive manufacture processes of supplying a metal wire as the fabrication material7to the working point, and applying the machining light30to the working point, thereby depositing a new layer on the product4having already been formed to produce a renewed product4.FIG.4is a diagram illustrating the height of the supply port for the metal wire relative to the product4according to the first embodiment. In this regard, the height of the supply port for the metal wire refers to the height of the supply port for the metal wire with respect to the top surface of the workpiece3. The height of the supply port for the metal wire may be hereinafter referred to simply as the height of the supply port. Note that setting of the amount of extrusion of the metal wire from the supply port to a known value enables the height of the leading end of the metal wire to be computed based on the height of the supply port. The amount of extrusion of the metal wire from the supply port represents a length from the supply port to the leading end of the metal wire. Control of the height of the supply port enables the height of the leading end of the metal wire to be controlled. It is assumed here that the amount of extrusion of the metal wire from the supply port is controlled to be maintained at a constant value, and that the height of the supply port and the height of the leading end of the metal wire are in a one-to-one correspondence. In addition, a suitable height range of the height of the supply port depends on the height of the product4already formed. As illustrated inFIG.4, failure in supplying the metal wire with a suitable height dependent on the product4having already been formed causes an unfavorable machined result. For example, assume that ha±α denotes the suitable height range of the supply port dependent on the product4having already been formed illustrated inFIG.4. In (a) ofFIG.4, the height of the supply port is at the center of the range of ha±α. In other words, in (a) ofFIG.4, the height of the supply port is ha. In (a) ofFIG.4, ha+α is represented as an upper limit value21. In (a) ofFIG.4, ha−α is represented as a lower limit value20. In (a) ofFIG.4, the height of the supply port is ha, i.e., within the range of ha±α, thereby not resulting in an unfavorable machined result. Meanwhile, in (b) ofFIG.4, the height hb of the supply port has a relationship of hb>ha+α, that is, hb is out of the range of ha±α. In this case, the metal wire melted by irradiation with the machining light30does not sufficiently adhere to the product4that has already been formed, thereby causing a molten droplet71to be generated, and surface irregularities to be formed on the product4after the machining. Furthermore, in (c) ofFIG.4, the height hc of the supply port has a relationship of hc<ha−α, that is, hc is out of the range of ha±α. In this case, the metal wire is excessively pressed toward the product4having already been formed, and thereby the metal wire is not entirely molten even upon irradiation with the machining light30, so that an unmelted portion72of the metal wire is caused. As a result, the product4after the machining adversely includes such an unmelted portion of the metal wire. In this situation, it is essential for high-precision machining to continue maintaining the height of the supply port dependent on the product4having already been formed, at a suitable value during machining.

For the first layer at the beginning of forming of the product4on the workpiece3, the forming process is appropriately performed with maintaining the height of the supply port at a constant value as long as the height of the workpiece3is constant. However, the second and subsequent layers need to be formed on the product4having already been formed until the previous forming process (previous layer). In this regard, the height of the product4having been formed until the previous time may be unequal to the design value. In this case, even if the supply port is elevated by the height equivalent to one design layer with respect to the height of the supply port at the previous deposition, the height of the supply port may in fact be out of a suitable range for the supply port corresponding to the current deposition portion, for a part in which the height of the product4until the previous deposition differs from the design value. In addition, there is contemplated a case where the height of the product4is not constant depending on the position. Even if the height in the second layer process falls within the suitable height range (ha±α), in other words, within a tolerance range, performing of multiple machining processes may cause the height in the n-th layer (n≥2) process to exceed the tolerance range (ha±α) due to accumulation of n times of a deposition error. In this situation, the height of the product4after a forming process needs to be measured, and this measurement result needs to be used at the next forming process to provide optimum control. In addition, the height of the product4is desirably measured after the temperature of the product4lowers.

Next, description is given for a method for maintaining the metal wire at a suitable height with respect to the product4having already been formed, using the measured height of the product4having already been formed. After a forming process of the product4, it is possible to scan the same path again for the measurement not for the machining, so as to measure the height of the product4having already been formed. However, in this case, it takes a lot of time since the machining path has to be subjected to scanning twice for additive manufacture per layer. In this regard, by measuring the height of the product4having already been formed during the machining, the number of times of scanning of the machining path for one layer of additive forming process can be just once, and both of the additive forming process and measurement of the height of the product4having already been formed can be performed.

FIG.5is a diagram illustrating an X-Z cross section at the working point during a machining process according to the first embodiment.FIG.5illustrates the case of performing machining such that the bead extends in the positive X-direction (the same direction as the wire). InFIG.5, the height of the product4having already been formed is measured at a position that has moved in the negative X-direction with respect to the working point. As used herein, the region where the machining light30is applied to the working point during the additive forming process and the metal wire is in a molten state on the workpiece3is referred to as melt pool31.

For example, when the driven stage6having the workpiece3placed thereon is subjected to scanning in the negative X-direction as illustrated inFIG.5, the working point moves on the workpiece3in the positive X-direction, thereby enabling the product4having a linear shape to be formed to extend in the positive X-direction. A portion at the working point near the melt pool31has a high temperature. Then, moving the driven stage6in the negative X-direction causes the melt pool31to be naturally cooled, but causes a region where the metal has a high temperature, i.e., a high temperature portion32, to appear behind (in the negative X-direction of) the melt pool31after a forming process. This high temperature portion then solidifies into a certain shape as a metal bead after a lapse of sufficient time. Accumulation of layers of this bead results in the product4. The high temperature portion32appears in the negative X-direction that is an opposite direction to the direction in which the working point moves on the workpiece3with respect to the working point. In this regard, the direction in which the working point moves on the workpiece3means the direction along the travel path of the working point.

Assume here that an end of the melt pool31is situated away from the center of the working point (optical axis of the machining light30) by a distance W, and the bead has high temperature, and that the high temperature portion32not yet sufficiently solidified is situated away from an end of the melt pool31by a distance U. The fabrication material7is melted in the melt pool31, and so it is difficult to correctly measure the height of the product4having already been formed. In addition, due to the melt pool31having a high temperature enough to melt the fabrication material7such as a metal, a thermal radiation light having a very high brightness is caused, and this thermal radiation light interferes with the measurement. Therefore, the measurement position at which the height is measured is situated desirably away from the center of the working point by at least the distance W. That is, it is desirable that the measurement position does not overlap the melt pool31.

In addition, the high temperature portion32is situated in a range of a distance of W+U from the center of the working point in the negative X-direction with respect to the working point. The bead has not yet completely solidified in the high temperature portion32, and so an accurate measurement of the height is difficult. Therefore, when the height is to be measured at a position that has moved in the negative X-direction with respect to the working point, it is more desirable that an irradiation position L of the line beam40is a position away from the center of the working point by a distance of W+U or longer. That is, the measurement position in which the height is to be measured is more desirably set to a position out of the range in which the fabrication material7is in a molten state at the time of machining.

FIG.6is another diagram illustrating an X-Z cross section at the working point during a machining process according to the first embodiment.FIG.6illustrates the case of machining such that the bead extends in the negative X-direction (the opposite direction to the wire). Also inFIG.6, the height of the product4having already been formed is measured at a position that has moved in the negative X-direction with respect to the working point. By the driven stage6having the workpiece3placed thereon being subjected to the scanning in the positive X-direction as illustrated inFIG.6, the working point moves on the workpiece3in the negative X-direction, thereby enabling the product4having a linear shape to be formed to extend in the negative X-direction. Also in this case, the high temperature portion32on the outer side of the melt pool31appears in a direction opposite to the direction in which the working point moves on the workpiece3with respect to the working point. In the case ofFIG.6, the working point moves on the workpiece3in the negative X-direction, and so the high temperature portion32on the outer side of the melt pool31appears in the positive X-direction with respect to the working point. On the contrary, the height of the product4having already been formed is measured at a position in the negative X-direction that is the same direction as the direction in which the working point moves on the workpiece3with respect to the working point. Because the high temperature portion32does not appear in the negative X-direction with respect to the working point, the measurement position just needs to circumvent only the melt pool31. Thus, it is sufficient that an irradiation position L of the line beam40is a position distanced from the center of the working point by the distance W or longer.

As described above, by setting the measurement position of the height in the same direction as the direction in which the working point moves on the workpiece3with respect to the working point, that is, in the travel direction along the machining or forming path, the height can be measured at a position closer to the working point. In other words, when a position on a path in which the working point moves, in which the working point moves as time advances, the height can be measured at a position closer to the working point. Accordingly, it is more desirable to set the measurement position of the height in the direction in which the working point moves on the workpiece3when viewed from the working point, that is, in the travel direction along the machining path. As illustrated inFIG.6, by setting the measurement position in a direction opposite to the direction in which the high temperature portion32appears with respect to the working point, the measurement can be performed without suffering from the effect of the bead becoming at a high temperature and in a molten state without solidification, and moreover, at a position closer to the working point. In the additive manufacturing apparatus100of the present embodiment, the line beam40is applied in the travel direction of the machining path with respect to the working point as illustrated inFIG.6.

Even in a case of setting the measurement position in the same direction as the direction in which the high temperature portion32appears with respect to the working point as illustrated inFIG.5, if an irradiation position of the line beam40is sufficiently far from the working point, the bead can solidify to a sufficient degree. Nevertheless, when the irradiation angle of the line beam40is fixed, installation positions of the line lighting device8and the light receiving optical system are both required to be situated away from the machining head2, thereby leading to increase in size of the apparatus. Besides, it is necessary to determine the magnification of the light receiving optical system to make a visual field larger so that the line beam40comes within an imaging area of the light receiving unit16, thereby leading to a problem in that resolution per pixel of the light receiving unit16lowers. Moreover, as a possibility, an integrated configuration of the machining head2and the line lighting device8may fail in performing the measurement. In a configuration as illustrated inFIG.5in which the driven stage6is subjected to scanning in the negative X-direction and the wire is supplied from a side in the positive X-direction, measurement along the travel direction (positive X-direction) of the machining path suffers interference from a wire supply part. However, in a case of no interference from the wire supply part using a method other than the method using the line beam40, a configuration as illustrated inFIG.5may be used in which the driven stage6is subjected to scanning in the negative X-direction.

A procedure of wire height control will next be described.FIG.7is a flowchart illustrating a procedure of wire height control according to the first embodiment. The term “wire height” refers to the height of a leading end of the fabrication material7irradiated with the machining light30, with respect to the top surface of the workpiece3. Note that the wire height is the height of the leading end of the fabrication material7when the fabrication material7is in an unmelted state. First, an additive manufacturing process of the first layer is started (step S1). The flat base plate has no bead formed thereon at the measurement position at the time of the additive manufacturing process of the first layer, and thus height measurement is not needed. Meanwhile, in a case of deposition on the product4, a case of use of a deformative base plate, or other cases like that, height measurement of the first layer is effective in order to perform accurate additive manufacture. At this point, measurement of the height of the product4is started along with the additive forming process of the first layer (step S2), and a measurement result of the height of the product4at the measurement position is stored (step S3). Then, in a case in which a next forming process is to be performed at the measured position of the product4, forming control is performed using the measurement result stored at step S3(step S4). In this operation, the interval of the height of the product4that is measurable is determined based on a frame rate of the image sensor used in the light receiving unit16as a light receiving element, and on a scanning speed of a machining axis (scanning speed of the working point). For example, assuming that the frame rate is F [fps] and the moving speed of the driven stage6is v [mm/s], the measurement interval Λ [mm] of the height of the product4in a scanning direction of the working point is Λ=v/F. Therefore, when “L” denotes a distance from the working point to the measurement point, a result of the measurement in the cycle before L/Λ times is a measurement result corresponding to the current working position. In fact, since the position of the stage at the working point is linked with the measurement position, the measurement result at the current working position can be looked up. That is, the height of a layered object on the (n−1)th layer at a certain measurement position is measured for forming of an n-th layer, and after L/Λ cycles from this measurement, use is made of the measurement result obtained by measurement performed for manufacture of the foregoing measurement position that is a working position, to perform optimum forming control. That is, the control unit10controls the forming or machining condition for newly depositing a layer at the measurement position in accordance with the measurement result.

FIG.8is a diagram illustrating the wire height when the additive manufacturing apparatus100according to the first embodiment forms a second layer. A method of forming control will now be described with reference toFIG.8. Assume that the product4having been formed for the first layer has a height of T1(=T0) as designed in a region I, where T0is a target deposition height. In this example, the term “target deposition height” refers to a preset height of a layered object which is a newly deposited on the product4. Also assume that the product4having been formed up to the first layer can have a height T2(>T0) that is greater than the design value in a region II, and can have a height T3(<T0) that is less than the design value in a region III. In this example, assuming that a wire height relative to the height of the product4having already been formed, such that the product4is formed with the target deposition height, is T0that is equal to the target deposition height, the wire height just needs to be 2×T0in order that the deposition height is 2×T0in forming the second layer. For simplicity's sake, the following description is given based on the assumption that the wire height for forming the product4to have a target height is T0that is equal to the target height of the product4, but the former may differ from the latter in practice.

In forming of the second layer in the region I, no particular change needs to be made in the forming condition because the measurement result T1on the second layer is the same as the target deposition height T0. Meanwhile, in forming of the region II, considering that the measured deposition height T2is greater than the target deposition height T0, the amount of deposition for the second layer needs to be 2×T0−T2to obtain the deposition height of 2×T0of the second layer. Although examples of a machining parameter (machining condition) for changing the amount of deposition may include various parameters such as the machining laser output, the wire feed speed, and the stage feed speed, a case of controlling the wire feed speed will herein be described. In the case of forming the region II, an amount of deposition needs to be less than the design value, and therefore, control is performed to reduce the wire feed speed thereby to reduce the supply amount of the metal material so that the total amount of deposition of both the first layer and the second layer is 2×T0. Similarly, in the case of forming the region III, considering that the measured deposition height T3measured is less than the target deposition height T0, the amount of deposition for the second layer needs to be T0−T32×T0−T3. Accordingly, control is provided to increase the wire feed speed thereby to increase the supply amount of the metal material so that the total amount of deposition of both the first layer and the second layer is 2×T0. That is, the machining condition is controlled by the control unit10depending on the difference between a preset height of a layered or deposited object newly deposited on the product4and the measurement result.

As described above, use of the result of measurement of the deposition height for the (n−1)th layer measured immediately before an n-th layer is formed, to optimally control the machining condition enables the deposition height with respect to the target wire to be constantly maintained within a range of ha±α as illustrated inFIG.4. Thus, the forming process can be continued without occurrence of forming failure. The above example has been described in the context of changing the wire feed speed to perform forming control, but another parameter or multiple parameters may be changed to perform forming control. For example, in order to use a smaller amount of deposition, there is contemplated a manner such that the laser output is lowered and/or the stage speed is increased. In addition, in a case in which the average height of the (n−2)th layer before forming the n-th layer significantly differs from the target deposition height T0, there is contemplate a manner such that the amount of change in the height of the wire to be raised for forming the n-th layer after completion of forming the n−1)th layer is determined to be the average of the height measured for the (n−2)th layer for T0that is the design value, and the measurement result for the (n−1)th layer is used during formation of the n-th layer so as to perform optimum forming control. In addition, in a case in which the measurement results of the height of the product4differ from one other between the regions among the region I of the n-th layer, the region II of the n-th layer, and the region III of the n-th layer as illustrated inFIG.8, the amount of change in the height of the wire to be raised may be changed for each region.

A height measurement operation using a light section method for measurement of the bead height after a forming process will next be described.FIG.9is a diagram illustrating an enlarged X-Z cross section of the product4irradiated by the line lighting device8according to the first embodiment. When ΔZ denotes the height of the product4relative to the top surface of the workpiece3, and θ denotes the irradiation angle of the line beam40, a difference ΔX between the position irradiated with the line beam40on the top surface of the workpiece3and the position irradiated with the line beam40on the product4is expressed as ΔX=ΔZ/tan θ.FIG.10is a diagram illustrating an image of the line beam40imaged on the light receiving element when the line beam40is applied onto the product4according to the first embodiment. Due to the difference between the height of the product4and the height of the workpiece3, the irradiation position of the line beam40is projected with being deviated by ΔX′. Use of a magnification M of the light receiving optical system yields a relationship of ΔX′=M×ΔX. When “P” denotes the size of one pixel of the image sensor, the amount ΔZ′ of change in the height per pixel is expressed as ΔZ′=P×tan θ/M. For example, a value set of P=5.5 μm, M=½, and θ=72 degrees results in ΔZ′=33.8 μm. As described above, the distance from the sensor to the target object can be computed from the projected position of the line beam40on the image sensor image based on the principle of triangulation. In addition, the height of the product4can be computed from the difference between the positions irradiated with the line beam40on the top surface of the workpiece3and on the top surface of the product4. Even when the height of the product4becomes higher than the top surface of the workpiece3, and the reflected light of the line beam40from the top surface of the workpiece3cannot be received, the distance from the sensor can be computed using the position irradiated with the line beam40reflected at the top surface of the product4within the visual field on the light receiving element.

The position irradiated with the line beam40is generally computed from the center-of-gravity position in the X-direction on the projection pattern of the line beam40. The X-directional output is computed for each Y-directional pixel, and the center-of-gravity position is then computed from the cross-sectional intensity distribution of the line beam40. Note that the position irradiated with the line beam40may also be appropriately selected and computed from the peak position of light intensity or the like, not only from the center-of-gravity position. The line beam40needs to have an irradiation width sufficiently large for computation of the irradiated position. For example, in the case of center-of-gravity computation, an excessively small irradiation width results in a failure in center-of-gravity computation, whereas an excessively large irradiation width easily causes an error due to an effect of variation in the beam intensity pattern. For this reason, about 5 to 10 pixels are desirable. In addition, the line length of the line beam40(irradiation width of the line beam40) only needs to be sufficiently longer than the width of the product4. As described above, the center-of-gravity position of brightness in the X-direction is computed for each pixel in the Y-direction of the image, and the result thereof is then converted into the height, thereby making it possible to measure the cross-sectional distribution in the height of the product4along the widthwise direction of the product4. In a case of use of a spot beam as the illumination light for use in measurement of the height of the product4, the cross-sectional distribution in the height of the product4cannot be measured, but a suitable selection of the spot size enables less erroneous measurement to be performed.

The foregoing description has been presented in the context of the method of computing the height of the product4based on the line beam40in the state of no forming process but when measurement is made in the process of forming, the working point becomes a highly bright light emitting point, and an image of the melt pool31appears in the image center. In this situation, installing the band-pass filter14within the light receiving optical system and increasing the output of the line lighting device8to a sufficient level enables the height to be measured based on the line beam40without suffering from an effect of light emission in the melt pool31.

FIG.11is a schematic diagram illustrating a result of imaging by the image sensor that is a light receiving element in the process of forming according to the first embodiment. As described above, because the position irradiated with the line beam40is made apart from the melt pool31, a thermal radiation light outputted from a working point50and the reflected light of the line beam40can be separated from each other. If the measurement position is set in the high temperature portion32, the bead is not yet completely solidified but is still in a liquid state, thereby possibly leading to failure in measurement of the illuminance distribution on the bead for the reason of insufficient reflection of the line beam40. Even if the measurement can be successfully made, different melting states are caused depending on the measurement positions, thereby resulting in a measurement error in the height of the bead with respect to the measurement position. Moreover, an error would also occur due to thermal shrinkage of metal in the solidified state relative to metal in the molten state. In contrast, the additive manufacturing apparatus100of the present embodiment makes measurement regarding the moving direction of the working point50for the working point50, and therefore can make measurement of the height of the deposition object with high accuracy by making the measurement position apart from an end of the melt pool so as to avoid suffering from an effect of melting of the bead in the high temperature portion32.

When “D” denotes a height range of heights to be measured, the amount S of movement of the line beam40with respect to the distance D can be expressed as S=D×M/tan θ. Therefore, the light receiving optical system is desirably designed to have, as a minimum requirement, a visual field of W+S, where W is the distance from the image center to the end of the melt pool. In this way, the additive manufacturing apparatus100of the present embodiment can maintain a target height of the layered object by measuring the bead height at a point in the travel direction of the additive forming process in the process of manufacture, and performing control to make a machining condition suitable in the next machining process. In addition, the additive manufacturing apparatus100of the present embodiment can maintain the height between the wire supply port and the layered object at a constant value, thereby achieving high-accuracy additive manufacture. Thus, the additive manufacturing apparatus100can prevent a reduction in accuracy in forming the product4. Moreover, the additive manufacturing apparatus100of the present embodiment can measure the height of the bead at a position close to the working point50, thereby enabling the height sensor to be integrated with the machining head2, and in turn enabling size reduction of the apparatus.

The above example has been described in the context of the configuration that provides size reduction of the apparatus by integration of the height sensor with the machining head2. However, the height sensor does not necessarily need to be integrated with the machining head2in a strict sense. It is needless to say that an arrangement in which the height sensor is disposed separately from the machining head2, and measures the height of the layered object at a point near the working point50can also exert a similar advantageous effect. In this regard, since the height sensor according to the present invention uses the line beam40to perform height measurement, the condenser lens15not for use in the combination of forming and height measurement is preferably of an optical system that allows only the line beam40to be focused onto the light receiving unit16.

FIG.12is another view illustrating a cross section in the X-Z plane ofFIG.1. For example, as illustrated inFIG.12, the center axis of the objective lens13and the center axis of the condenser lens15may be arranged out of alignment in a direction perpendicular to the center axis of the objective lens13. In this example, the objective lens13is a lens that focuses the machining light30onto the working position. Therefore, in the configuration ofFIG.12, the position of the center axis of the optical system for focusing the reflected light transmitted through the objective lens13onto the light receiving unit16does not coincide with the position of the center axis of the objective lens13for focusing the machining light30onto the working position. Use of such a configuration enables the reflected light of the line beam40, which is illumination light for the measurement, to be focused onto the light receiving element with a minimum effect of aberration of the lens, and can thus increase accuracy of height measurement.

A similar advantageous effect can be obtained, instead of configuring the positions of the center axes in an out-of-alignment arrangement as described above, with a configuration in which the center axis of a third focusing optical system that focuses the reflected light having passed through the objective lens13onto the light receiving unit16is tilted with respect to the center axis of the objective lens13that condenses the machining light30onto the working position. In addition, the lens surface of the condenser lens15may be changed in shape. Moreover, what is required for the visual field of the light receiving unit16is just to be broader than a range of movement of the line beam40within the range of height measurement, and use of a focusing system for enlarging only the range of movement of the line beam40enables the resolution of the line beam40to be increased, and can thus improve accuracy of height measurement.

Second Embodiment

The additive manufacturing apparatus100according to a second embodiment is configured similarly to that in the first embodiment, but the line beam for use in the height measurement has a different shape. The additive manufacturing apparatus100according to the second embodiment provides the line beam40having an irradiation shape that is not linear, but is a circular shape about the working point50. By such use of a circular irradiation shape for the line beam40, even if a formed shape is not linear and a scanning direction of the working point varies in the process of forming, the line lighting device8can apply light to the product4at a right angle to the product4(in the widthwise direction of the product4) crosswise. This can eliminate any rotation mechanism for a scanning stage, and can thus reduce the size of the apparatus. For example, rotation of the driven stage6in the X-Y plane enables the measurement position to be situated on the front side of the working point50even when the scanning is to be performed obliquely relative to the X-axis and to the Y-axis. Meanwhile, use of a circular irradiation shape for the line beam40enables at least some of the measurement positions to be situated on the front side of the working point50without rotating the driven stage6.

FIG.13is a first view illustrating an X-Y cross section in a case of performing machining while changing the direction of forming of the product4according to the second embodiment. Note that a dotted area each inFIG.13and the subsequent figures represents an area where deposition is to be made by the additive manufacturing apparatus100. As illustrated in (a) ofFIG.13, in a case of performing machining with the direction of forming of the product4being changed using a rotation stage, the workpiece3can be rotated by an angle of θ for forming the workpiece3as illustrated in (b) ofFIG.13using a rotation stage for the X-Y plane on the driven stage6. Therefore, the machining direction is always constant. In this case, even if the line beam40having a linear shape is used, it is possible to constantly apply the line beam40perpendicularly to the direction of machining of the product4.

FIG.14is a second view illustrating an X-Y cross section in a case of performing machining while changing the direction of forming of the product4according to the second embodiment. As illustrated in (a) ofFIG.14, in a case of performing machining while changing the direction of forming of the product4without using a rotation stage, the machining direction can be changed by controlling the moving speed in the X-axis direction and the moving speed in the Y-axis direction at a suitable ratio therebetween, but the machining needs to be performed obliquely to the X-Y plane. In this regard, if the line beam40having a linear shape is used, measurement cannot be made along a cross section perpendicular to the direction in which deposition is made such that the product4extends, in a case of performing machining in the oblique direction as illustrated in (b) ofFIG.14.

FIG.15is a third view illustrating an X-Y cross section in a case of performing machining while changing the direction of forming of the product4according to the second embodiment. As illustrated in (a) ofFIG.15, the line lighting device8uses a line beam40ahaving a circular shape. In this case, as illustrated in (b) ofFIG.15, even if the product4is to be formed in the oblique direction, the line beam40ais applied with a circular shape about the working point50, and thereby the height of the product4can be measured always at a constant distance from the working point50irrespective of the machining direction. The additive manufacturing apparatus100of the present embodiment measures the height using an irradiation region of the front side of the moving direction of the working point50on the workpiece in the movement direction3with respect to the working point50, of the irradiation area irradiated with the line beam40ain a circular shape.

The reflected light is focused onto the light receiving unit16from the entire circumference of the irradiation area having a circular shape. The additive manufacturing apparatus100of the present embodiment measures the height using the image of the reflected light from an arc portion on the front side of the working point50in the moving direction of the working point50, of the entire circumference. In a case of feeding the wire from a side in the positive X-direction, machining is often performed, in general, in a 180-degree range from the positive Y-direction through the negative X-direction toward the negative Y-direction. For this reason, although the line beam40ahaving a circular shape has been described herein, a strictly circular shape is not necessarily required therefor, and so the beam may have an ellipse-like shape, and a partially removed shape such as a semicircle may also be acceptable. As long as the amount of change in the direction of extension of the line of a line beam of 90 degrees or more, measurement of the height of the product4having already been formed can be realized, no matter in which direction the working point50is subject to scanning. For example, in a case of use of the line beam40ahaving an arc shape, the acceptable central angle is 90 degrees or higher. In a case of use of a line beam having a 90-degree arc shape ranging from the negative X-direction to the positive Y-direction, measurement is made immediately after a machining process when the bead is formed to extend in the positive X-direction and the negative Y-direction, whereas measurement is made immediately before a forming process when the bead is formed to extend in the negative X-direction and the positive Y-direction. In addition, in a case of use of a line beam having a curved shape, the amount of change in the tangential direction just needs to be 90 degrees or more. Moreover, when machining is performed only in two directions perpendicular to each other, a quadrangular shape such as a square may be used.

The configurations described in the foregoing embodiments are merely examples of contents of the present invention, can each be combined with other publicly known techniques and partially omitted and/or modified without departing from the scope of the present invention.

REFERENCE SIGNS LIST

1machining laser;2machining head;3workpiece;4product;5fixture;6driven stage;7fabrication material;8line lighting device;9computing unit;10control unit;11floodlight lens;12beam splitter;13objective lens;14band-pass filter;15condenser lens;16light receiving unit;20lower limit value;21upper limit value;30machining light;31melt pool;32high temperature portion;40,40aline beam;50working point;71molten droplet;72unmelted portion;100additive manufacturing apparatus;200control circuit;200aprocessor;200bmemory.