Design for Additive Manufacturing: What Does That Really Mean?

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On August 23, 2017, Posted by , In Aerospace,Marine, With No Comments

Figure 1 UUV Housing As-Printed (EBM Ti6Al4V)

The story of designing for additive manufacturing (AM) is always told through eccentric geometries and topology optimization, but does it really have to be that complex?  What is often misunderstood is that AM is primarily a tool to solve problems. Just because the technology allows for the design of extremely complex shapes does not mean it has be done.  As with designing for any method of manufacturing, engineers must analyze their application and determine the most efficient solution.  This blog will address the key design factors to consider when designing for AM by looking at an example part.

Addaero developed a rear housing for an Unmanned Underwater Vehicle (UUV) as a demonstration for the US Navy.  The part was fabricated in the Arcam Q20+ EBM system using Ti6Al4V alloy and is approximately 13 inches tall by 10 inches across.  It is a great example of both additive manufacturing for defense applications and additive manufacturing for marine environments. There are three key elements of design for AM in this example that are highlighted below.

  1. Minimized Supports: One of the first areas of consideration is design for manufacturing.  In this situation, the goal was to minimize the supported areas. In the EBM process, overhanging surfaces of 60° or less from the build plate require support material. By orienting the shape as shown in Figure 2, the supports on the outside surface are minimized.  On the inside, all of the flanges used for holds use hanging supports.  This is one of the key benefits of EBM as the supports do not have to extend down to the part or plate below to perform their function.  As a design solution, minimizing supports makes the AM process more efficient, leading to improvements in part reliability, time, and cost.

    Figure 2 UUV Housing CAD Model with Supports (in blue)

 

  1. Design for Machining: For parts that require finish machining, AM allows the user to design in features that will simplify or improve the reliability of post-machining operations. In the rear end of the housing there are locations for actuation fins for maneuvering (Figure 3).  With the UUV going to depth one of the critical items is to ensure the pressure ring is concentric.  By designing the actuation pockets with a flat feature on the outside and a concentric feature on the inside the printed part will require minimal machining while achieving structural integrity.  Another way to design for machining is to add sacrificial structures.  That could be implemented on the UUV by adding flat features on the nose and tail of the UUV.  The features would serve as built-in tooling that a machinist could use to fixture the part and quickly endmill the outer contour and actuation pockets.

    Figure 3 UUV Housing Actuator Pockets. Left = Sectioned View. Right = Inside Concentric Feature

 

  1. Part Consolidation: The final area that is one of the most critical is the ability to use additive to consolidate multiple parts together.  As shown in Figure 4, this part has integrated motor mounts (highlighted in blue), battery holders (highlighted in red), and actuation pressure ring (highlighted in green).  Typically, these parts would all require multiple part numbers, higher administrative costs (purchasing, inventory, configuration management, etc.) and most importantly multiple engineers designing each part.  AM allows one engineer to design one part and save time and money in the design and lifecycle management process.

Figure 4 UUV Housing Internal Assembly (Color-coded)

Complex, organic, or topology optimized designs are not the only way to utilize AM.  While these highly engineered designs do improve on the benefits of AM as a resource, the UUV housing highlights three quick and effective design methods that fully employ the strengths of AM.  In the coming months, we’ll go deeper into this topic, discussing further ways to improve AM design.  We’ll be focusing on what the economic impacts are of taking advantage of these tools and how it can improve your bottom line.

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