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Hybrid Process Improved by Using Referencing to Orient Preform with AM Build

Friday, July 24, 2020
 


This schematic of a hybrid approach using referencing shows 1. a preform with pre-machined holes on the build plate; 2. laser scanning of the preform and holes with light-reflection detection; 3. automatic x, y and θ orientation correction; and 4. the optimized building of the geometry.
Parts with features demanding large quantities of material, as well as parts necessitating excessive additive manufacturing (AM) build supports, are good candidates for hybrid manufacturing. Manufacturers can efficiently and economically produce such parts by pre-machining a preform and then using AM in areas where the technology proves most beneficial. In addition, printing directly on a section of the final part geometry eliminates the costly cutting operation to remove the part from the build plate.

Consider injection molds, which include high volumes of material. Fully building these parts layer by layer in an AM machine take dozens of hours and requires redesigning, cooling channels and feed systems that would be difficult to remove in subtractive operations. 

This type of hybrid process must start with the preform fixed on the build platform before it is referenced, to align the preform and the intended printed section. Referencing can be especially challenging because, unlike in CNC machining, no physical link exists in AM between the optics and the preform. Instead, manufacturers generally must rely on visual alignment or external coordinate measuring machines to confirm positioning accuracy. Both techniques are time-consuming and, in the case of simple visual alignment, prone to operator error. With variance in excess of 100 µm, these techniques also cannot provide the accuracy required for most final applications. 


A machined tool holder (left), and with the metal-AM cutting head attached (right), shows how a hybrid process using referencing software can produce components.
To solve the referencing challenge, GF Machining Solutions and 3D Systems have developed a software solution that leverages the melt-pool monitoring hardware available on GF Machining Solutions' and 3D Systems’ DMP series of metal-AM machines. In machines such as the DMP Flex 350, DMP Monitoring in-process monitoring software acquires melt-pool data during the printing process in order to detect potential defects such as pores, or lack of fusion.

The DMP Calibration Tool function leverages light-sensing melt-pool monitoring hardware for another purpose: scanning preforms to identify pre-machined locating holes in the part’s surface. Naturally, a part surface and hole offer much greater contrast than the reflectivity differences used to optimize highly precise metal-AM processes, allowing for an extremely reliable method for establishing the part’s precise location, according to GF Machining Solutions officials. 

With user-defined threshold values, this referencing process reportedly offers exceptional repeatability and accuracy without risk of human error. Furthermore, the use of the laser can reference multiple parts on the same build plate in a single operation, further accelerating high-volume applications. And, the level of precision results in higher final-part quality.

This method of subtractive-first hybrid manufacturing employing the referencing software has many obvious benefits for producing mold-and-die inserts and machined tool holders with AM tool heads, for example, but also proves useful for part production in such industries as medical and aerospace. Shops can cut preforms prior to building complex part features via 3D metal printing. Applications include aerospace components and medical devices that feature complex internal structures, as well as the creation of functional surfaces for products such as implants, which benefit from geometric precision inherent in AM for building metal forms that promote improved integration with existing skeletal and vascular structures.

Most beneficial for this process: a turnkey system in which every piece of the equipment and software package has been calibrated for seamless hybrid workflows, according to officials from both companies. One example in the GF Machining Solutions Additive Manufacturing ecosystem: the 3DXpert all-in-one software for AM part design, optimized for DMP-series machines and compatible with GF Machining Solutions’ Mikron Mill machines used to simplify post-processing operations.

 

See also: GF Machining Solutions, 3D Systems


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