Sintering furnace

Patent metadata

Field	Value
Publication number	US-2019255612-A1
Application number	US-201916277100-A
Country	US
Kind code	A1
Filing date	Feb 15, 2019
Priority date	Feb 18, 2018
Publication date	Aug 22, 2019
Grant date	—

Abstract

According to one aspect, embodiments herein provide a furnace for debinding and sintering additively manufactured parts comprising a unitarily formed retort having at least one open side, a heater for heating a sintering volume within the retort to a debinding temperature and to a sintering temperature, an end cap sealing the at least one open side, a forming gas line penetrating the end cap for supplying forming gas at a flowrate, and a heat exchanger within the retort, outside the sintering volume, and adjacent a heated wall of the retort, the heat exchanger having an inlet connected to the forming gas line and an outlet to the sintering volume, wherein the heat exchanger includes a heat exchange tube length sufficient to heat the forming gas to within 20 degrees Celsius of the sintering temperature before the forming gas exits the outlet.

First claim

What is claimed is:

1 . A furnace for debinding and sintering additively manufactured parts, comprising:
a unitarily formed retort having at least one open side; a heater for heating a sintering volume within the retort to a debinding temperature and to a sintering temperature; an end cap sealing the at least one open side; a forming gas line penetrating the end cap for supplying forming gas at a flowrate; and a heat exchanger within the retort, outside the sintering volume, and adjacent a heated wall of the retort, the heat exchanger having an inlet connected to the forming gas line and an outlet to the sintering volume, wherein the heat exchanger includes a heat exchange tube length sufficient to heat the forming gas to within 20 degrees Celsius of the sintering temperature before the forming gas exits the outlet.

2 . The furnace according to claim 1 , further comprising:
a pressure control mechanism, including a vacuum pump, coupled to the retort and configured to control pressure in the retort.

3 . The furnace according to claim 2 , further comprising a control system configured to:
operate a flow control module to control the flowrate of the forming gas; operate the pressure control mechanism to control the pressure in the retort; and operate a heat control module to control a level of heat provided by the heater to the sintering volume.

4 . The furnace according to claim 3 , further comprising:
a moisture sensor configured to sense an amount of moisture in the sintering volume and to be in communication with the control system; and a Liquid Petroleum Gas (LPG) sensor configured to sense an amount of hydrocarbon gas in the sintering volume and to be in communication with the control system.

5 . The furnace according to claim 1 , further comprising:
a series of baffle shields adjacent the end cap and configured to reduce a temperature between the sintering volume and the end cap.

6 . The furnace according to claim 5 , further comprising:
a dip tube penetrating the series of baffle shields to the sintering volume and configured to remove debinding decomposition gas from the sintering volume.

7 . The furnace according to claim 6 , further comprising:
an inert purge gas supply penetrating the end cap and having an outlet at the end cap, the inert purge gas supply configured to introduce a purge gas between the series of baffle shields and the end cap that keeps the debinding decomposition gas away from walls of the retort adjacent the end cap.

8 . The furnace according to claim 1 , wherein the heat exchanger is formed as a stainless-steel tube having an exchange tube length greater than the length of the sintering volume.

9 . A method for controlling heating and gas supply in a furnace for debinding
and sintering additively manufactured parts, comprising:
heating a brown part in a sintering volume using a sintering temperature ramp to sinter metal powder in the brown part;
sensing an amount of moisture in the sintering volume; and
increasing a supply of forming gas to the furnace in response to a detection of the amount of moisture in the sintering volume being greater than a predetermined threshold amount.

10 . The method according to claim 9 , further comprising:
initiating the supply of forming gas at an initiation level substantially at the beginning of the temperature ramp; and limiting the increase in the supply of forming gas to a maximum level of ten times the supply of the initiation level.

11 . A method for controlling heating and gas supply in a furnace for debinding
and sintering additively manufactured parts, comprising:
heating a brown part in a sintering volume using a debinding temperature ramp to debind a polymer binder in the brown part;
sensing an amount of hydrocarbon gas in the sintering volume; and
terminating the debinding temperature ramp in response to a detection of the amount of hydrocarbon gas in the sintering volume being lower than a predetermined threshold amount.

12 . A method for controlling heating and gas supply in a furnace for debinding
and sintering additively manufactured parts, comprising:
heating a brown part in a sintering volume using a debinding temperature ramp to debind a polymer binder in the brown part;
sensing an amount of hydrocarbon gas in the sintering volume;
terminating the debinding temperature ramp in response to a detection of the amount of hydrocarbon gas in the sintering volume being lower than a predetermined threshold amount;
initiating sintering of the brown part in the sintering volume using a sintering temperature ramp to sinter a metal powder in the brown part;
sensing an amount of moisture in the sintering volume; and
increasing a supply of forming gas in response to a detection of the amount of moisture in the sintering volume being greater than a predetermined threshold amount.

13 . A supply panel for a sintering furnace, the supply panel comprising:
at least one input configured to be coupled to a gas supply; a first moisture sensor in fluid communication with the at least one input and configured to receive gas via the at least one input; a supply gas filter in fluid communication with the first moisture sensor and configured to receive gas from the first moisture sensor; a second moisture sensor in fluid communication with the supply gas filter and configured to receive gas from the supply gas filter; and an output configured to be coupled to the sintering furnace and to provide gas from the second moisture sensor to the sintering furnace.

14 . The supply panel of claim 13 , further comprising:
a control system configured to be in communication with the first moisture sensor and the second moisture sensor, and configured to analyze information provided by the first moisture sensor and the second moisture sensor.

15 . The supply panel of claim 14 , wherein the first moisture sensor is configured to:
directly measure moisture contamination in the gas from the at least one input; and provide a measurement of the moisture contamination in the gas from the at least one input to the control system.

16 . The supply panel of claim 15 , wherein the second moisture sensor is configured to:
directly measure moisture contamination in the gas from the supply gas filter; and provide a measurement of the moisture contamination in the gas from the supply gas filter to the control system.

17 . The supply panel of claim 16 , wherein the control system is further configured to:
compare the measurement of the moisture contamination in the gas from the at least one input provided by the first moisture sensor to the measurement of the moisture contamination in the gas from the supply gas filter provided by the second moisture sensor; and determine whether the measurement of the moisture contamination in the gas from the at least one input provided by the first moisture sensor is larger than or equal to the measurement of the moisture contamination in the gas from the supply gas filter provided by the second moisture sensor.

18 . The supply panel of claim 17 , wherein the control system is further configured to:
identify, in response to determining that the measurement of the moisture contamination in the gas from the at least one input provided by the first moisture sensor is larger than the measurement of the moisture contamination in the gas from the supply gas filter provided by the second moisture sensor, that there is a leak between the supply gas filter and the second moisture sensor.

Assignees

• Markforged Inc

Inventors

• Mark Gregory Thomas

Classifications

• B22F2003/1042

  with support for articles to be sintered · CPC title

• B22F3/10 Primary

  Sintering only · CPC title

• B22F10/18

  by mixing binder with metal in filament form, e.g. fused filament fabrication [FFF] · CPC title

• B22F10/73

  of powder · CPC title

• B22F10/12

  by photopolymerisation, e.g. stereolithography [SLA] or digital light processing [DLP] · CPC title