Cracking - Bulk

11min

Bulk Cracking
Cracks/fissures form during the thermal curing process at high stress points.
 
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How to Identify
Bulk cracking can be diagnosed as follows:
Cracks appear as thin, dark lines in the part, occurring at stress points such as a corner
Lines appear after baking. Parts look fine off of the printer and after washing.
Bulk cracking is differentiated by other types of cracking by where it occurs on the part. This is a geometry-based form of cracking that occurs solely at stress points.
Reference Cracking - Medial Axis﻿ and Cracking - Excessive Solvent﻿ for other types of cracking.
Cause - Inconclusive
Cause - Inconclusive
Troubleshooting
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Process, Material, and Hardware Checks
If any of these conditions apply to your print, take the corrective action and reprint to see if the problem is resolved.
Follow solvent exposure times closely in the resin post-processing protocol.
﻿Do not exceed maximum solvent exposure times and reduce exposure time when possible if parts are fully clean.
Use swabs in corners, or other stress points that trap solvent.
After washing, dry parts on a blue towel or raised mesh (with air flow around the whole part) until all solvent is evaporated prior to baking.
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Check that the correct bake schedule was used per resin protocols.
Resins most susceptible to cracking use a bake schedule that ramps up temperature gradually.
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Print Preparation or Part Design Adjustments
The following solutions will address print or part-related causes of the defects. Choose among the suggested actions below and select the best approach for your application. Usually only one type of adjustment is needed.
Add fillets or chamfers to corners, or similar stress points, to mitigate bulk cracking.
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If problems persist, please reach out to Carbon Support.
Explanation & Causes
Explanation
Bulk cracking occurs when stresses build up during the print and are then released in the bake. The most susceptible conditions of bulk cracking are: 
Sharp inside corners
Excessive solvent exposure
Brittle resins: EPX
Causes
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Root Issue
Problem
Why Defect Presents
Washing
Solvent exposure
Too much solvent exposure weakens the material, making stress points weaker.
Baking
Wrong bake schedule
The most common resins for bulk cracking are the brittle resins (EPX) that use a ramping program to raise the temperature slowly and prevent thermal shock.
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Root Issue
Problem
Why Defect Presents
Design
Sharp inside corners
Stress points such as sharp inside corners are weaker under thermal shock.
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Root Issue	Problem	Why Defect Presents
Washing	Solvent exposure	Too much solvent exposure weakens the material, making stress points weaker.
Baking	Wrong bake schedule	The most common resins for bulk cracking are the brittle resins (EPX) that use a ramping program to raise the temperature slowly and prevent thermal shock.

Root Issue	Problem	Why Defect Presents
Design	Sharp inside corners	Stress points such as sharp inside corners are weaker under thermal shock.

Cracking

Cracking - Medial Axis