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©2019 by Diabase Engineering.

Case Study:

Automated Gripper

Background:

An industrial partner utilized a printed Nylon component as an end effector to slide a tube off a mandrel in one of their production machines. The end effector was designed with thin, elongated fingers that provided compliance against the mandrel. The part was to be printed from Nylon, specifically in an SLS process, so it was limited to a single material. The SLS printed samples worked well for a short number of cycles, but quickly cracked and failed, causing machine down-time.

Prior attempts to print the replacement part on-site were unsuccessful due to the limitations of typical FDM machines: minimal part strength and difficulties generating overhanging features.

As-designed (PA SLS) and trial replacement (typical FDM) parts. Replacement part was not functional due to limitations in standard FDM capabilities.

Solution:

Two unique features of the H-Series machine enabled the successful development of a replacement part for this automated process: 

  1. Multi-material 3D printing (3 materials, in this case)​

  2. Low-durometer TPU 3D printing

Other functions of the H-Series were also useful during the development of the gripper part. To begin, rather than printing the entire component from scratch, we set up the existing parts for rework using H-Series fixturing blocks.  

We located the parts in machine coordinates using the touch probe, then milled off the existing fingers and milled dovetail pockets into the surface to act as anchor points.  After this, we printed new TPU fingers onto the original parts.  The adhesion to the SLS Nylon was poor, but adhesion to the FDM printed ABS part was excellent. This allowed us to get initial feedback on the new shape and rigidity of the TPU fingers.  

Existing printed parts reworked by milling off existing fingers and printing replacements from TPU

The flexible fingers were not the only challenging feature of this part. Given the underside geometry required to interface with the actuator mechanism, a typical FDM process could not produce a high-quality part with sufficiently accurate downward-facing features.

Complex geometries on both top and bottom make this part impossible to print for a typical FDM machine

 In order to create the finished parts, a 3-material print was required. The materials chosen were:​

  1. High-durometer TPU (75 Shore D) for the main part body - extremely durable and comparable stiffness to unreinforced Nylon (pink below)

  2. Low-durometer TPU (85 ShoreA) for the gripping fingers and support infill (orange)

  3. Dow Evolv3D dissolvable support material for the interface to the finished part (purple)

As-sliced 3-material 3D print with full-interface support material

 The print finished cleanly in approximately 3.5hrs. In order to remove the support material, the part was soaked overnight in a heated and stirred water bath. 

Completed 3-material 3D printed gripper

This application is a good example of the usefulness of mixed material parts in solving real world problems. The systems on the H-Series are what directly enable the architecture of this part. The compliant, unbreakable gripper fingers are enabled by the accurate dispensing of TPU via Flexion Extruders. The small overhanging features critical to the end use are enabled by the clean and accurate tool changing between part materials and dissolvable support. This process combined with the large selection of materials available in filament form offer a broad range of possibilities to the design engineer.  In the world of machine-building and automation, it is often the finishing components: the end effectors, grommets, strain reliefs, gaskets, and covers that cause headaches.  They often require the most customization and are the most difficult to source in low quantities. This is one example of where the H-Series can provide real value to the industrial user.