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Heating test without vacuum chamber:


The oven is built around an 2.5kW induction heater module from Aliexpress


2020-12-02 First sintering test

  • 1210 °C target temperature
  • low vacuum at 5-10mbar, no process gas
  • PolyMIM 17-4PH feedstock, unmodified granules (not debindered)
  • Heating cycle
    • T+0min: Start: 15°C, 5mbar, cooling water temp 15 °C 
    • T+10min: Heating finished, 1210°C, 10mbar, cooling water temp 19 °C 
    • T+23min: Switched heating off, 1210°C, 8mbar, cooling water temp 25 °C 
    • T+33min: switched vacuum pump off, pressure stays at 4mbar
    • ca T+53min: opening chamber, ca 250°C

Results:

red: unsintered granule, soft, can be scratched easily
green: sintered granule, hard, scratching just removes dark skin, shiny metal is revealed

  • Granules are not completely sintered, only a skin of ca 0.5-1.0 mm
  • Yet they are quite strong, they can not easily be cut using a wire cutter

Thermal imaging revealed several hot spots that need to be addressed:

Top of chamber reaches almost 200°C. Not a big issue, but putting a cap on the crucible probably would reduce the heat significantly

SSR get too hot. Needs heat spreader

Output side of power supply too hot. Needs further investigation. Bad cable connection?

Cable connecting induction module with copper pipe gets hot (right cable only). Bad connection, need something better


2021-09-08 Repairs and replacements done

SSR was not sized appropriately for the device current and had a strong tendency to release magic smoke, so it was replaced by a MOSFET and accompanying driver (IRFP064N and MC34151P).
The MOSFET sits on a heat sink, which is at drain potential! Do not ground the heat sink, or electrically connect it to anything else.

To avoid issues with the burden voltage across the power meter shunt the electronics were rewired. Now the power meter is connected directly with the power supply, and everything else in the circuit (voltage regulators, PID controller and of course the induction heater itself) is connected to the power meter.

2021-09-09 Successful sintering

  • 1350 °C target temperature
  • low vacuum at 4*10⁻² mbar, no process gas
  • PolyMIM 17-4PH feedstock, 3D Print (Bottle opener), debindered as per datasheet
  • Part covered in sand-blasting media
  • Heating cycle
    • T+0 min: Start: 25°C, heated up to 600 °C and held, 4*10⁻² mbar
    • T+60 min:  heated up to 1350 °C, vacuum unchanged
    • T+120 min: Switched heating off
    • T+150 min: Switched vacuum pump off and opened chamber at ~200 °C

Results:

Part covered in sand blasting media, small but visible cracks (part not dried well, or heated too quickly?).

Wirewheeling revealed solid metal part with high detail conservation.


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