Splitting Large Parts using 3D Sprint and Joining with Adhesives

Splitting Large Parts using 3D Sprint and Joining with Adhesives

Best Practice

p/n 33-D275 Rev A

 

All 3D printers have a maximum build size based on technology and cost/weight/performance trade-offs. The build size of the 3D Systems ProJet 2500 is 11.6” x 8.3” x 5.6” (294mm x 211mm x 144mm) which is big enough for most application needs. However, there are times when larger parts need to be printed that would benefit from the MultiJet technology and materials, like for RTV molding applications, jigs and fixtures for example. The 3D Sprint software that comes with the printer was designed to easily split a large part and automatically add joining male and female features making reassembling the split part very easy. For example, the following is a rigid mold that is needed to make a large silicone gasket, but is too large to fit on the ProJet 2500:

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Large mold that will be used to make an RTV Silicone part

 

No special steps or preprocessing of the part is needed. Within 3D Sprint simply choose the “Split” feature tool from the toolbar”

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Split tool button in 3D Sprint

 

The first page of the wizard allows the user to choose to select a plane or line:

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Split tool wizard snaps to each plane, but can also be rotated to a specific angle

 

The plane first snaps to each axis but can also be rotated:

Split Large Parts _pic 4.jpgThe cut plane can also be scaled to allow a feature to be split in a part while avoiding another feature of the same part:

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Scaled cut plate allows one feature of a part to be split without affecting the entire part

 

Click “next” and the user can now see options for connectors:

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Numerous connector features can be added automatically with different sizes and layouts based on customer need

 

The “Plane” feature cuts along a user-defined plane and automatically generates a pattern of connectors. The user is able to make simple modifications to the pattern in the “Type” section including dimension, clearance, number, and spacing. The joining features can also be flipped in direction. The “Layout” section is helpful if a certain pattern is desired such as boundary or grid:

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Top: Layout “Boundary” selection
Bottom: Layout “Grid” selection

 

The connector type feature allows the user to choose between round and square pegs. The square can be especially helpful when you need large strong connector but only have room for one. Rather than increase the number and decrease the size and strength of the connectors, the square shape can prevent rotation:

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One large square feature can be optimal for certain connections

 

Connector settings are highly configurable. A very nice fit will be created by simply leaving the setting to their default value. For other needs, the specific settings chosen will depend on the pattern geometry and may require some iteration by the user. The following are some definitions and recommendations.

  • Connector Clearance: Additional length added to pins to separate the two split pieces. If you have a need for a larger seam set this value to a nonzero number. Typically, this is set to zero.
  • Type: Cylinder or square type connector.
  • Connector Width: Width of connector pin. (Recommended: At least 0.12 inch (3 mm) where applicable).
  • Connector Length: Length of connector pin. (Recommended: No more than 1/2 of connector width)
  • Clearance Width: Clearance for pin and hole width. This will enlarge the hole AND shrink the pin. Typically, this is set to zero.
  • Clearance Length: Clearance for pin and hole length. This will deepen the hole AND shorten the pin. Typically, this is set to zero.
  • # Of Connectors: Number of pins and holes.
  • Inset: Distance from the nearest edge. (Recommended: 0.1 inch (2.5 mm) from closest edge)
  • Spacing: Distance between each pin (Recommended: At least 0.12 inch (3 mm))

The “Line” feature allows the user to draw their own line (or series of lines) and then split a projection of the lines they drew. The user starts by first aligning to the view they desire to cut. Also, holding shift while drawing the line snaps it to an axis. Once a line is drawn, “teeth” options become available to apply to the line. Different patterns of teeth are available including straight and stepped. The number of teeth can also be varied. These features will be helpful in the alignment and reassembly of the two parts after printing.

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Top: Split “Line” hand drawn by user for split location
Bottom: “Teeth” option automatically adds a cut pattern

 

The connector or line cuts are automatically added by the software. The user is left with two individual parts that can be stacked in the z-axis and printed in one job, or saved as two different jobs and printed individually.

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Large atomically split by 3D Sprint software

 

Joining with Adhesives/Glue

Depending on the user applications and needs, after splitting, the two patterns can be used as-is, or can be glued together. The accuracy of MJP technology allows for fits that can be very tight by simply using the default values. For the right design and application, a simple press fit can be quite robust. However, the two parts will likely be glued back together with some type of adhesive. Many traditional adhesives designed for plastics can be used to join the two parts including two-part epoxy, super glue, specialty plastic glues, and multi-purpose glues. For certain geometries, some multi-purpose elastomeric adhesives and RTV rubber can create a robust joint that can also be disassembled in the future. Things that specifically do not work well include Elmer’s school glue and rubber cement. Additionally, many solvent-type adhesives for plastics that function by melting the parts as part of the joining process may not work well for MJP parts and should be tested by the user (like Weld-on and Testor’s model Cement). It is always best practice for users to test their application themselves with spare parts that are within their area or by printing parts for testing. There is an abundance of information related to adhesives available on line and at local businesses. General best practices and information published by vendors for adhesives will remain true when gluing MJP acrylate parts.

  • Make sure the part is properly post processed and the surfaces are clean and rinsed well of solvents, oils and support wax.
  • Additionally, cleaning the mating surfaces with IPA can help insure the surface is clean.
  • Make sure that both surfaces are clean and dry before you begin the gluing process.
  • Rough surfaces are easier to glue than smooth ones. You can use some sandpaper to roughen the surface of each piece that you will glued together.
  • Make sure and read the directions for the specific adhesive, as there are guidelines for each type that will improved success.
  • When adhering MJP parts to other materials (wood, metal, plastic…), some adhesives will work better than others. Refer to the vendor documentation and testing by the user is always recommended.
  • Be sure to read the set time on the package. The set time and cure time are different. When the glue is set, it means that it is bonded, but the glue is still soft and has not achieved its maximum strength. Set time (or handling time) and cure times should be listed on the package.
  • Make sure you read directions about the washing and care of the item once it is dry.
  • Always work in a well-ventilated area. It is best to work outdoors, or in a room with plenty of ventilation. The fumes from the glues can cause nausea, dizziness, lightheadedness, skin irritation, eye irritation, and headaches.
  • Some glues suggest the use of gloves to protect your skin. Be certain to get gloves made from the right type of plastic, or you could easily glue them together, or to your fingers.
  • Be sure to read all of the instructions and warnings on the glue label.

Published information from adhesive vendors and well as internal 3D Systems testing suggest that many different adhesives will work to bond MJP parts. Many applications will work with the use of most 2-part epoxy or multipurpose adhesives. Super glue can be used successfully for some applications where the fit between parts is tight and is held together with clamps. However, there are many other factors to consider when selecting an adhesive for your specific application. The following information is offered to the user to assist in the selection of their application needs.

  1. Strength: A measure of the maximum force that a glue can withstand. If the strength is sufficiently strong, the MJP part may fail before the adhesive bond.
  2. Flexibility: A measure of the ability of the adhesive to stretch and deform under a load.
  3. Gap Fillable: Some adhesives are very thin and unable to fill a gap and are best used for two tightly mating surfaces
  4. Color: Do you require a white, black or translucent color material?
  5. Cure Type: Knowing the curing type can help improve success. For example, is air or water/humidity needed for complete cure and/or will the material outgas a solvent during cure that requires extra ventilation. Also, 2-part epoxy adhesives are chemically cured and often cure fast and work well even in joints that are sealed from humidity.
  6. Set Time: The time it takes before the adhesive is sufficiently strong such that the two pieces are lightly held together without external forces being applied. Longer set time allows for more time to make adjustments.
  7. Cure Time: The time it takes before the adhesive reaches full strength.
  8. Removable: Can the adhesive be removed from the parts allowing their disassembly and/or reuse.
  9. UV Resistance: The adhesive ability to retain properties (strength, flexibility, color) when exposed to the sun.
  10. Flammability: The adhesive ability to resist burning when heated.
  11. Waterproof: The adhesive ability to resist water and hold a water tight seal after bonding.

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Example 1: RTV Silicone Molding

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Large RTV Silicone mold. Each side split with 3D Sprint and rejoined with adhesives

 

Example 2: Alignment Fixture

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Engineering development manufacturing alignment fixture. Multiple pieces split and rejoined using 3D Sprint and adhesives