Heat Treating 3D Additive Manufactured Parts

At present there are two main techniques used in the additive manufacturing of 3D metal parts. These take time but are outstanding for creating complex or ‘impossible’ parts which cannot be created using traditional casting or machining methodologies. This has already resulted in the creation of a multitude of prototype pieces as well as countless ‘impossible parts’ for the aerospace, automotive, tooling and medical sectors.

Electron Beam Manufacturing (EBM) in a vacuum chamber does not require heat treatment of the manufactured parts. Metal powders or wire (such as Titanium, Ti-6AI-4V, CoCr, Inconel 718 and Inconel 625) are welded together in successive layers using an electron beam as the heat source in a process that results in fully dense metal components. The process avoids oxidisation of the material as it takes place in a vacuum.

Direct Metal Laser Sintering (DMLS) uses a laser in a pure inert Argon atmosphere. The process is digitally driven, direct from 3D CAD data. For each slice of CAD data a thin even layer of fine sieved metal powder (titanium alloy Ti6Al4V, cobalt chromium, stainless steel, nickel alloys Inconel 625 and Inconel 718 and aluminium alloy AlSi10Mg) is deposited across the build plate before the selected areas of the powder are precisely melted by the laser. This process is repeated building up, layer by layer, until the build is complete.

DMLS can be used for very small parts and features and can reproduce geometries that might be impossible to machine such as enclosed spaces. Layers can be as thin as 20 microns and tolerances on small features can be as small as ±50 microns.

At present build rates for components using a DMLS process are slow. Costs are also high as raw metallic powders must be produced using a ball-mill/grinder and then sieved and tested prior to usage. Current DMLS machinery obviously requires a substantial investment at this time. However, if the required part has dimensions under 250mm x 250mm x 350mm the process could well be perfect for those who require rapid prototyping or small quantities of complex or ‘impossible’ parts that can subsequently be machine drilled, slotted, milled or reamed. They can also be powder coated, painted, polished or anodised.

The market for 3D Additive Manufacturing is growing rapidly. Journals, websites and tradeshows have blossomed as 3D manufacturing times have been reduced, maximum part sizes have increased, powder alloys have become more available and components manufactured for the aerospace, medical, tooling and automotive sectors in this way have gained standards approval in increasing quantities.

Heat Treating 3D Additive Manufactured Parts using a Carbolite Gero Furnace

The Direct Metal Laser Sintering process requires a heat-treatment solution with precise temperature uniformity. This ensures the manufactured parts adhere to the proper metallurgical properties of the selected metal alloy.

The heat treatment stage occurs in an inert (typically Argon) atmosphere to ensure the sintered part is not contaminated by oxygen molecules which can alter the chemical and physical properties (porosity) of the final component. This inert process must be repeatable with a well measured gas flow monitored to achieve an AMS 2750E Classification specified by the customer. In fact, in one specific example throughout the entire manufacturing process the atmosphere is maintained at <1000ppm (0.1%) oxygen which can be reduced to as low as 100ppm (0.01%) oxygen if a reactive metal such as titanium is employed.

The General Purpose Chamber furnaces from CARBOLITE GERO with Type B instrumentation meet the requirements of AMS 2750E Class 1 when used with an Inconel or Haynes 230 retort. Various sizes are available (Laboratory Furnace CWF 13/65 or Industrial Furnace GPC 13/131, 13/200, 13/300, 13/350 & 13/405) with capacities for between 1 and 4 build plates which are ideal for those involved in DMLS Additive Manufacturing.

A recent GPC 13/300 retort furnace with a working volume of 400mm x 400mm x 350mm, automatic on/off gas control using a Eurotherm 3508 controller and 6180 XIO data logger. Argon/Nitrogen gas flow and trace levels of oxygen in the retort’s modified atmosphere are constantly monitored. The CARBOLITE GERO GPC range has under hearth heating along with heating from the top and sides to improve temperature uniformity inside the retort where temperature thermocouples are located. The positioning of the Cascade Controls inside the retort enables faster heating times which can substantially reduce customer cycle times when used in conjunction with optional forced cooling.

To further shorten cycle times, the 13/300 furnace has a temperature interlocked swing-out door facilitating quick and easy access for loading / unloading with a water-cooled silicon rubber door seal which maintains a modified atmosphere inside the chamber throughout the entire heat treatment process.

GPCMA/174 Retort Furnace

In Conclusion

CARBOLITE GERO has intentionally designed their GPC range with retorts for 3D Additive Manufacturing to the highest specifications. They avoid the issues that are frequently experienced with furnaces from other manufacturers.

The most common issues reported by users with other furnaces are their inability to maintain an inert atmosphere, their requirement for large volumes of expensive inert gases or the need for extra equipment to remove the retort when loading / unloading parts. All of these detracting issues have been overcome by CARBOLITE GERO to ensure everyday operating costs for our customers are minimised; unwanted oxidisation is eliminated and temperature uniformity is “best in class”. Most importantly, production cycle times are significantly reduced thanks to heating on four sides, a forced cooling option and easy loading / unloading through our unique water-cooled silicon sealed swing out door.

To best demonstrate our capabilities, CARBOLITE GERO is now offering customer trials for any organisation wishing to validate a heat treatment process for their DMLS components. This paid-for testing is charged at just £800 per part and is fully refundable on placing an order for a CWF 13/65 or GPC 13/300 specified to a required AMS 2750E classification.

For further information or to discuss heat treatment for your specific DMLS parts, please call Richard Bilson or Paul Haigh at CARBOLITE GERO on +44 (0)1433 620011.

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