Abstract:
This document describes a process and a device for applying fluids, specifically particle material, on an area to be coated, which is viewed in forward moving direction of the coater, that fluid is applied on the area to be coated and then a leveling element is run over the applied fluid, whereby the fluid is led from a metering system provided with an opening, which oscillates when applying the fluid. The opening shall be designed in such a way that when the metering system is at a standstill this is closed by forming an angle of repose of the fluid.

Description:
TECHNICAL FIELD 
     This invention refers to a process and a device for applying fluids, especially particle material, on an area to be coated in accordance with the preamble of claims  1  and  6 . Furthermore the invention also concerns the application of a device and a process like this. 
     BACKGROUND OF THE INVENTION 
     The PCT publication script WO 35/18715 states to use a coater for the particle material, designed in form of a downward opening funnel, in a process for manufacturing three-dimensional objects out of particle material, such as a rapid prototyping process. This funnel vibrates during the coating process at right angles to the coater&#39;s direction of movement and parallel to the coating level. With a coater, as described in this document, an unimpeded emission of the particle material during coating can be guaranteed and densification can be achieved. 
     But this type of coating has a disadvantage. The particle emission cannot be switched, which means that when the vibration mechanism is deactivated, powder escapes the coater, unless this is closed from below. 
     It is also known from DE 102 16 013 A1 that in the case of a process to manufacture three-dimensional objects from particle material for the application of particle material, one container opened from the base, connected with a vibrating leveling element is used. 
     SUMMARY OF THE INVENTION 
     A significant advantage of this device is that the powder emission is controlled. The width of the gap is set so that when the coater is inactive, the powder is prevented from emission due to the particle bridges formed over the gap and the particle material only leaves the gap when the coater oscillates. 
     For very fine or/and very free flowing (fluid) powder materials, for example fluids with a particle size &lt;150 μm or powder, which mostly consists of round particles, this coating proves itself to be very complex because the gap has to be chosen very fine in order to achieve a spread of the particle material when the coater is inactive, because such materials are less likely to form particle bridges. 
     This requires an accurate alignment of the gap width to achieve the effect of the named invention. Moreover a constant gap width is necessary over the entire width of a coater. This requires a very precise alignment. For production reasons this is either barely possible or very costly. 
     This invention is challenged with providing a process, a device as well as a use of the device with which a controlled metering and application of any and therefore also fine and/or free flowing powder is possible. 
     According to the invention this challenge is solved with a process to apply fluids, especially particle material, on an area to be coated, this being viewed in a forward moving direction of the coater, that fluid is applied on the area to be coated and then a leveling element is run over the applied fluid, whereby the fluid is led from a metering system provided with an opening, which at least performs an oscillation during application of the fluid. The opening is closed when the metering system is at a standstill by the fluid forming an angle of repose in the opening. 
     The metering system features an oscillating container provided with an opening, in which the opening is designed in such a way that no material flows out when the metering system is inactive as an angle of repose is formed in the opening and when the vibration mechanism is activated the angle of repose breaks downs and the particle material is emitted. 
     The leveling element can be designed as a blade, which is either run only fixed over the fluid or also oscillates, if necessary, with the metering system. 
     Under the forward motion of the blade the direction of the coater shall be recognized in the coating stage. If coating is possible in two or more directions of the coater, the forward motion can also be possible in several directions. 
     As a leveling element a roller with an axle parallel to the surface area to be coated and vertical to the coating direction is also suited. The roller can be fixed, or rotate around its own axle. The direction of rotation is set in the opposite direction to the forward motion direction of the coater, in order to emit the fluid from the gap between roller and powder bed surface. 
     The fluid is coated according to this invention from a metering system provided with an opening, whereby the opening, described in the illustration, is designed in a vertical direction to the area to be coated seen with an angle α. In colloquial speech it is a type of “side” opening. No vertical application is made on the area to be coated. 
     The opening is blocked from particle material when the container is inactive due to the formation of an angle of repose in the opening. It no longer flows uncontrolled, as in processes of prior art, when the coater is at a standstill. Instead it is retained by the design of the opening according to the invention when the coater is at a standstill. 
     The opening can have any width adapted to the process. If a component essentially spans across the entire width of the area to be coated, the coater and the opening also span over their entire width favorably. One and/or several smaller openings would also be possible. 
     The oscillation of the metering system can be horizontal or/and vertical according to this invention. Especially good results could be achieved if the oscillation contains vertical as well as horizontal components. In particular an oscillation proved itself to be beneficial according to the type of rotation. 
     Especially good coating results could be achieved with a process in line with the invention, if the leveling element also oscillates when the applied fluid runs over. In the case of an especially preferred the embodiment of this invention the leveling element resonates with the metering system. 
     In such an embodiment of this invention the densification of the fluid can be achieved by two effects. 
     By means of the oscillation or vibrations of the container and the fluid, the particles of the material to be coated are graded to a higher packing density. In addition if the leveling element oscillates horizontally and/or vertically, a densification of the fluid under the leveling element is also achieved through movement. 
     However, it must be observed that too strong a densification of the particle material achieved this way can lead to movement in the powder bed over the actual layer and thus lead to a deterioration of the structure printed. 
     According to this invention, the particle material is compacted by the oscillation prior to coating in the metering system, so before laying the coat, the densification can be carried out gently by the leveling element. Damage to the area to be coated is therefore avoided. 
     The densification of the powder bed is essentially homogenous over the area to be coated and not dependent on the direction of the coater, as this Is the case In the process of the prior art. It is possible therefore to achieve an adequately good coating result in one coat. This leads to a time saving compared to the process of prior art, with which an adequately homogenous coating result only can be achieved typically after a second coat. 
     If it requires further definition of the rapid prototyping equipment, the coater and as the case may be, the metering system can be led back over the powder bed into the starting position after running over the area to be coated once, at increased speed and without oscillation and therefore without particle emission. The coating result achieved previously is thus not affected. 
     According to a favored embodiment of this patent a metering quantity of fluid required for the coating should always be smaller than residual volume of the fluid present in the container. 
     By means of oscillation of the metering system, and the container if the case may be, the fluid can be metered on the area to be coated. When activating the oscillation mechanism of the container the fluid, and if the case may be the particle material, is fluidized in the container and flows out of the opening of the metering system in front of the leveling element. If the oscillation mechanism stops, when an angle or repose is formed in the opening the particle material remains in the container. 
     The rotary motion of the coater&#39;s oscillation, the metering system and/or the leveling element is preferably achieved over the eccentric for the process in line with the invention, which are attached torque proof to the drive motor shaft. 
     The transmission of power from the eccentric to the coater, the metering system or/and the leveling element can be for example, form-fit, therefore illustrated by directly applying a ball bearing on the eccentric. 
     This process in line with the invention can be carried out preferably with a device to apply fluids on an area to be coated, whereby a leveling element and a metering device viewed in forward direction of the leveling element is provided, via the fluid to be applied on the area to be coated. The blade can be run over the fluid applied, whereby the metering device is provided with an opening and an oscillation can be performed. The opening is designed in line with this device, in such a way that when the metering system is at a standstill it is closed by means of the fluid forming an angle of repose. 
     In accordance with the preferred embodiment the device is designed in such a way that the metering system, and the container respectively is connected to the leveling element. 
     With such a preferred embodiment of the invention it is possible to place the emission of particle material as close as possible on the leveling element. Furthermore it is also possible that the oscillation mechanism as well as the metering system also drives the leveling element. 
     In line with an especially preferred embodiment the container of the metering system is essentially designed as a funnel. 
     In activating the oscillation mechanism of the container, so the funnel here, the particle material fluidizes in the funnel and flows out of the side opening, which can be designed as a gap, in front of the leveling element. 
     In another case the particle material stays in the container, if the gap (length and height) is set accordingly, so that due to the formation of an angle of repose in the opening other material is prevented from emission. The funnel can therefore convey a significantly larger quantity of material than is necessary for the actual coat. 
     On the one hand the result is a significantly lower quantity of waste material. On the other hand the requirements of the feed system, which meters the particle material Into the funnel, are reduced. An equal distribution of quantity in the container over the coater width or the width of the opening has to be ensured. 
     A possible over-filling or if the supply is lowered too heavily into the funnel could be monitored preferably with a fill level sensor and if necessary, it would be possible to top up the funnel from the feed system. This is possible after one coat. 
     The coating unit shall be designed as rigid as possible In order to be able to transfer the oscillations exactly. 
     The container opening, preferably a gap, shall be dimensioned in height and length so that when the coater is inactive no particle material flows out of the container or funnel and when the vibration mechanism is activated just as much material is emitted as is necessary for coating. The emission quantity is preferably regulated via the gap height and oscillation amplitude of the metering system. 
     It has thus emerged that a longer gap has to be chosen higher, in order to achieve the same material emission as a shorter gap. In order to achieve an equal emission over the entire coating width, it is useful to choose a long and high gap. In this way the metering system is easier to set, more tolerant compared to variations in the gap dimension and more unsusceptible to blockage of the gap. 
     If the gap is set too large, particle material is accrued in front of the blade during operation of the coater. In order to obtain a good coating result the quantity in front of the leveling element should remain constant during the entire coating process. 
     In a preferred embodiment this is therefore achieved so that the gap is fixed as close as possible over the surface area to be coated directly with the leveling element. The gap can be dimensioned in a way that when the vibration mechanism is activated relatively a great deal of particle material is emitted. In the coating the particle material is accrued until it reaches the metering opening. Through the accrued particle material now further material is prevented from escaping the supply through the opening. In this way a constant quantity of powder can be achieved in front of the leveling element without adjustment works on the gap height. 
     A self-regulating system like this has a significant advantage compared to well-known coating process, as no exact alignment of the opening is necessary. This is very complex particularly with very wide openings. 
     The leveling element smoothes and condenses the applied material. A changeable blade is preferably chosen with a specific support length, via the incline of the support area to the coating surface area the densification of the layer can set well. 
     The blade has rounded edges in accordance with a preferred embodiment. This prevents damage to the applied coating surface area. The round forms preferably have a radius of 0.2 to 1 mm. 
     The coater, which at least consists of a metering system and the leveling element, is activated to oscillate. One advantage is that the oscillation occurs mainly in the coating direction. However it is also possible to let the system oscillate with an additional vertical component, in order to achieve a higher densification of the particle material. But is must be observed that too strong a densification of the particle material can lead to a movement in the powder bed over the actual layer and thus lead to a deterioration of the structure printed. 
     Via the frequency and amplitudes (horizontal and vertical) of the oscillator, on the one hand the densification and on the other hand the emission quantity of the metering system can be set. 
     As already discussed the coating equipment in line with the invention is especially suited for the use of very fine particle materials (particle sizes &lt;150 μm), as they are used in the current rapid prototyping processes, like 3D printing or selective laser sintering established for example from the EP 0 431 924. In these processes the grain size of the particle material determines the possible layer thickness and therefore the accuracy and resolution of the printed parts. 
     Unlike the processes of prior art particle materials with rounded grain sizes and therefore high flow capability as well as powder with square-edged particles and lower flow capability can be processed. By means of fluidization of the particle material in the metering system the outcome in both cases is a homogenous coating result. 
     With the process according to the invention plastic particle materials such as PMMA, PA or PS, the most diverse forms of metal powder as well as form sands such as silica sand, zircon sand, magnetite or chromerz sand can be processed. The selection of material grade depends solely on the selected layer build method and the properties of the target material grade. 
     The particle materials can be homogenous or as particle mix or coated powder. It is also possible that other substances in the form of fluids are added to the particle material before the coating process. 
     Other powder mixes contain for example fiber materials for later strengthening of the component. 
     Other beneficial embodiments of this invention result from the sub claims as well as the description. 
     For a more detailed illustrated the invention is described in more detail below based on favored design examples with reference to the diagram. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The diagram shows: 
         FIG. 1  the sequence of a process in line with the invention according to a preferred embodiment; and 
         FIG. 2  the device as per the invention in accordance with a preferred embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     For example, below the process and the device according to the invention for use in layer design of cast models from particle material and binding agent in rapid prototyping process are explained. 
     In particular it can be assumed from very fine and flow-capable particle materials that a rapid prototyping process is used. 
     Referring to  FIG. 1  the sequence of the coating is described below according to the preferred, embodiment of the process in line with the invention. 
     In a set up process of a component, such as for example a cast model, a construction platform  4  on which the model is to be built, is lowered around a layer strength of the particle material  5 . Then the particle material  5 , for example very fine plastic powder is applied to the construction platform  4 . This has a required layer strength from the container, here a funnel  3 . Then the selective application of binding agent Is attached to one hardened areas. This can be carried out using a drop-on-demand-drop generator, depending on the type of ink-jet printer. These application steps are repeated, until the finished component, embedded into the loose particle material  5 , is obtained. 
     At the start coater  1  is in the starting position, which is represented in  FIG. 1   a . It Is first filled via a filling device, if the fill level sensor has recognized a sub level In a container, which is designed here as a funnel  3 . 
     As illustrated in  FIG. 1   b , the construction platform  4  is lowered to more than one layer. 
     Then the coater  1 , as shown in  FIG. 1   c , without oscillation movement and thus without feed effect in the position compared to the filling device  2 , until it is over the edge of the construction platform  4 . 
     Now the build platform  4  is raised exactly to the layer height, as  FIG. 1   d  shows. This means that the build platform  4  is now accurately lowered to the layer height. 
     Now the coater  1  begins to oscillate and goes in a constant run over the build platform  4 . Thus it emits particle material  5  in exactly the right quantity and coats the build platform  4 . This is shown in  FIG. 1   e.    
     The running speed of the coating is between 10 and 200 mm/s. The selectable coating speed depends on the emitted particle quantity and the movement of the individual particle. If the run speed is selected too great compared to the particle emission, imperfections (surface detects) are formed in the powder bed, which can lead to delaminating of the component in the worst case. Generally for reasons of productivity higher coating speeds are beneficial. 
     An unfavorable conformation of run speed in oscillation movement of the leveling element leads to so-called chatter marks on the powder bed surface. These have a negative effect on the component quality. Generally, the higher the coating speed chosen, the higher the oscillation frequency on the moved leveling element. 
     The coater  1  runs after the coating run without oscillation movement, which means as quick as possible, back to the starting position and can be refilled as required via the filling device  2 . This is shown in  FIG. 1   f , which corresponds to  1   a.    
     In order to balance an unequal filling of the coater  1  via its length, after a specific time the funnel  3  can be emptied via the waster container  6  by means of oscillation of the funnel  3  and subsequently refilled. 
     The printing process, or illumination process to harden the particle material provided with binding agent  1  can take place during or after the coating. 
       FIG. 2  shows a device In line with the invention according to a favored embodiment. 
     In particular also for carrying out the process according to the invention a device is suitable according to the demonstrated favored embodiment. 
     In line with  FIG. 2  particle material  5  is applied to an area to be coated, whereby a rocker  7 , which contains a metering device  3 , viewed in a forward direction  16  of the blade  14  particle material  5  on the build platform  4 . Furthermore a blade  14  is provided as a leveling element, which condenses, smoothes the applied material, and ensures a constant layer thickness H s  of the applied particle material  5 . 
     The rocker  7  is applied to the coater main bracket  10  according to the preferred embodiment in such a way that it can perform an oscillation depending on the type of rotary motion indicated by arrow  8 . The coater main bracket  10  spans over the entire width of the build platform  4  in accordance with the preferred embodiment. The rotary axis  9  of the rocker  7  is vertical to the running movement represented by arrow  16  in accordance with the preferred embodiment and parallel to the longitudinal axis of the rocker  7 . 
     In this case the metering device  3  contains a container, a funnel-shaped particle device, which is formed via the rocker  7  and a corresponding sheet  17 , and features a metering gap, located in the container, which resembles the shape of a funnel, sideways, which means vertical to the coating direction viewed with an angle α and In running direction in front and above the stripper blade  14 . In accordance with the diagram this is about 90°. This shall only serve as an example. 
     The sheet  17  and the blade  14  are arranged in such a way that the gap height H and gap length L of the opening  11  designed as a gap is measured so that when the vibration mechanism is deactivated no particle material  5  leaves the supply and when the vibration mechanism is activated more particle material  5  is emitted than is necessary for dimension of the compressed layer. The height of the gap  11  can be set by means of the locking bolt  18 . 
     The surplus material is collected in front of the blade  14 . If the surplus particle material  5  reaches the opening  11  in front of the blade  14 , which is formed here as a gap, further particle material  5  is prevented from leaving the opening  11 . This way in the coating run along the blade  14  an equally large accumulation of particle material  5  is set in front of the blade. This leads to a uniform coating result over the entire width of the coater and over the entire length of the section  4 . 
     The rocker  7  with the firmly connected or contained metering unit and blade  14  oscillates according to arrow  8  around the rotary axis  9  . By means of another arrangement of the rotary axis  9  a movement can be realized with an additional vertical share, in order to achieve an additional compression effect of the applied layer through an extra vertical movement of the blade  14 . 
     The oscillation of the rocker  7  can be set by the size of the eccentric  12  and its juncture  19  with the rocker  7 , so that the amplitude of movement of the blade  14  lies between 0.05 and 1 mm. 
     The amplitude and frequency of the oscillation are adapted so that there is a sufficient compression of the particle layer and adequate particle material  5  is supplied by the metering system. The amplitude and the oscillation direction shall be chosen so that no damage to the area below the layer occurs. 
     The device is designed according to the embodiment in a way that a propulsion of the coater  4  is made over at least a fast running electro motor, which brings the wave  7  to oscillation via an eccentric. 
     The motor used for driving the eccentric  12  has for example a nominal rotation speed at 12V of 3000 U/min, the hub of the eccentric  12  amounts to 0.15 mm, which corresponds to an amplitude on the top of the blade  14  of 0.20 mm according to the example described. At 15 V a rotational speed of 4050 U/min was measured. This value corresponds to 67.5 Hz. Depending on the width of the blade  7  It can be necessary, to provide several pivotal points. 
     The blade  14  features rounded edges  13 . This prevents damage to the applied coating surface area. The round forms preferably have a radius of 0.2 to 1 mm.