METHOD FOR ADDITIVE MANUFACTURING USING ELECTRON BEAM MELTING WITH STAINLESS STEEL 316L

Abstract

Before performing additive manufacturing of an article to be formed, a first scale plate is scanned in a first scanning speed so that a trace of the electron beam is depicted. An electric current value through a focusing coil with which the trace of the electron beam becomes narrowest is found and set as a melting electric current value. Then, a second scale plate is scanned similarly in the first scanning speed so that a trace of the electron beam is depicted. An electric current value through the focusing coil with which the trace of the electron beam cannot be seen is found and set as a preheating focusing electric current value. Dispersed metal powder is scanned with electron beam of the preheating electric current value as set before in a second scanning speed 20 to 30 times of the first scanning speed. Thereafter, the additive manufacturing is performed.

Claims

1. A method for additive manufacturing using electron beam melting with SUS316L executed by use of an additive manufacturing apparatus using electron beam melting, in which electron beam is used as an energy source and which is equipped with an electron optical system comprising a astigmatism correcting coil, a focusing coil and deflecting coil that makes scanning with and converges the electron beam in two-dimensions according to additive manufacturing data prepared by laying out three-dimensional CAD data of at least one article to be formed through additive manufacturing, and a start plate having a temperature sensor held on a back face thereof and the start plate is disposed on an upper face of a raising and lowering mechanism, that is also a face on which the electron beam is converged, said method being executed, after dispersing metal powder on the start plate heated preliminarily and smoothing the metal powder with a rake to be flat, through scanning with the electron beam in two dimensions to melt the metal powder and forming a layer for each step and performing additive manufacturing of the article to be formed by laminating layers in successive steps by lowering the raising and lowering mechanism, wherein said method further comprises: using stainless steel SUS316L as the metal powder, before performing the additive manufacturing of the article to be formed, placing a first scale plate on the start plate, scanning the first scale plate with the electron beam in a first scanning speed set to be 500 mm/sec to 650 mm/sec while varying the converged point by varying electric current value through the focusing coil so that a trace of the electron beam is depicted on the first scale plate, taking out the first scale plate, and setting a melting electric current value for melting the metal powder from an electric current value through the focusing coil found to be one with which the trace of the electron beam becomes narrowest, placing a second scale plate on the start plate, scanning the second scale plate with the electron beam in the first scanning speed while varying the converged point by varying electric current value through the focusing coil around the melting electric current value so that a trace of the electron beam is depicted on the second scale plate, taking out the second scale plate, and setting a preheating focusing electric current value for preheating the metal powder from an electric current value through the focusing coil found to be one with which the trace of the electron beam cannot be seen, and performing additive manufacturing after preheating the metal powder of stainless steel SUS316L dispersed on the start plate and smoothed with a rake to be flat by scanning the metal powder with the electron beam having the set preheating focusing electric current value in a second scanning speed of 20 to 30 times of the first scanning speed.

2. The method for additive manufacturing using electron beam melting with SUS316L according to claim 1, wherein a material of the first scale plate and the second scale plate is stainless steel SUS316L.

3. The method for additive manufacturing using electron beam melting with SUS316L according to claim 1, wherein the additive manufacturing is performed when the temperature detected with the temperature sensor is 875 C. to 925 C.

4. The method for additive manufacturing using electron beam melting with SUS316L according to claim 2, wherein the additive manufacturing is performed when the temperature detected with the temperature sensor is 875 C. to 925 C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0041] FIG.1 is a schematic view showing a composition inside of a vacuum chamber in a method for additive manufacturing using EBM.

[0042] FIG.2 is a graph showing a strength distribution of electron beam.

[0043] FIG.3 is an explanatory view of disposing a scale plate used in the method for additive manufacturing using EBM according to the present disclosure.

[0044] FIG. 4 is a view showing an example of a scale plate used in the present disclosure.

DESCRIPTION OF THE EMBODIMENTS

[0045] The present disclosure provides a method for three-dimensional additive manufacturing using electron beam melting with SUS316L executed by use of an additive manufacturing apparatus using electron beam melting, in which electron beam is used as an energy source and which is equipped with an electron optical system comprising an astigmatism correcting coil, a focusing coil and deflecting coil that makes scanning with and converges the electron beam in two dimensions according to additive manufacturing data prepared by laying out three-dimensional CAD data of at least one article to be formed through additive manufacturing, and a start plate having a temperature sensor held on a back face thereof, wherein the start plate is disposed on an upper face of an elevator that is also a face on which the electron beam is converged,

[0046] said method being executed, after dispersing metal powder on the start plate heated preliminarily and smoothing the metal powder with a rake to be flat, through scanning with electron beam in two dimensions to perform heating and preliminary sintering of the metal powder, thereafter irradiating electron beam on and melting the metal powder in necessary sites thereof according to data to form a layer for each step and successively performing additive manufacturing of the article to be formed by repeating each step of forming a layer while lowering the elevator and dispersing metal powder on the layer formed in the previous step,

wherein said method further comprises:

[0047] before performing the additive manufacturing of the article to be formed, placing a scale plate on the start plate, scanning the scale plate with electron beam in a scanning speed set to be 500 mm/sec to 650 mm/sec while varying the converged point by varying electric current value through the focusing coil so that a trace of the electron beam is depicted on the scale plate, taking out the scale plate, and setting a converging electric current value for melting the metal powder from an electric current value through the focusing coil found to be one with which the trace of the electron beam becomes narrowest,

[0048] raising output of electron beam to set preheating focusing electric current value, varying electric current value through the focusing coil around the melting-converging electric current value so that a trace of the electron beam is depicted in the aforementioned scanning speed, taking out the depicted trace to be observed and setting an electric current value through the focusing coil found to be one with which the trace of the electron beam cannot be observed as electric current through focusing coil at the time of preheating,

[0049] preheating dispersed metal powder in a scanning speed set to be 20 to 30 times of the aforementioned scanning speed, and

[0050] performing additive manufacturing with stainless steel SUS316L.

[0051] Embodiments of the present disclosure will be explained in detail, referring to figures. FIG. 3 is an explanatory view showing a composition inside of a vacuum chamber in which a scale plate is disposed in a method for additive manufacturing using EBM. When electric current is fed from an electric circuit (not shown) to heat a filament 1, electrons are generated.

[0052] The electrons are accelerated via a grid cup 2 and an anode 3, to which a high voltage is applied from a high voltage power source (not shown), and emitted through an opening of the anode to be electron beam 7. At this time, the electrons are accelerated to have about a half of velocity of light.

[0053] The electron beam is converged for scanning with a magnetic lens consisting of an astigmatism correcting coil 4, a focusing coil 5 and a deflecting coil 6 and is converged onto a scale plate 15 placed on a start plate 12 disposed on an elevator 9. The scale plate has a purpose of measuring a diameter of electron beam and optimizing it. For this sake, a suitable plate size is selected by taking it into consideration to remove effect of warping due to heat and besides to measure change in diameter due to focusing variation explained below, etc.

[0054] In an example, a plate size of 240 mm (vertical)240 mm (horizontal)5 mm (thickness) is selected.

[0055] In such a condition, a trace by scanning is depicted with current value through the filament, current value through the deflecting coil determining scanning velocity and current value through the focusing coil controlling a convergent point as parameters. At this time, scanning is performed with an initial setting for measuring the diameter of electron beam such that scanning speed is 500 mm/sec to 650 mm/sec and electric current value through the filament is 10 mA to 25 mA.

[0056] FIG. 4 is a photograph showing an example of a scale plate in which scales are marked on a stainless steel plate. In FIG. 4, setting is made in such a manner that electric current at the time of melting is 10 mA, electric current at the time of preheating is 20 mA, offset of electric current through the focusing coil at the time of melting is +10 mA and offset of electric current through the focusing coil at the time of preheating is +100 mA. With the offset value being large, electron beam becomes defocused. Best focusing is selected at the time of melting to make adequate melting and defocusing is selected at the time of preheating to cause powder not to be in a too solidified state. It is recommended to make measurement using a tool microscope for observation of electron beam traces in the scale plate shown in FIG. 4.

[0057] Here, it is preferable that material of the scale plate is the aforementioned SUS316L. The reason for this is that, by use of SUS316L for the scale plate, action effect of electron beam on the scale plate becomes approximated to that of metal powder because material of the scale plate is identical with that of metal powder, hence range of current to be set through the focusing coil for preheating can be narrowed.

[0058] Further, it is preferable that additive manufacturing is performed when temperature detected with the temperature sensor is 875 C. to 925 C. It was recognized from experiments that sintering is insufficient at 850 C. and residual strain remains at 950 C., thus temperature of 875 C. to 925 C. is suitable.

[0059] Additionally, a trademark HTLebmMTL according to a trademark application 2017-14021 is intended to be used for the metal powder of the stainless steel SUS316L employed in the present disclosure.

[0060] The stainless steel SUS316L for example, comprises carbon (C): 0.03 mass %; silicon (Si); 1.00 mass %; manganese (Mn); 2.00 mass %; phosphorous (P): 0.045 mass %; sulfur (S): 0.030 mass %; chromium (Cr); 16.00-18.00 mass %; molybdenum (Mo): 2.00-3.00 mass %; nickel (Ni); 12.00-15.00 mass %, and the balance being iron.