Skip preheat—doesn’t mean every insert cracks. But big temperature swings? Sloppy heat-up, sloppy cool-down? Now you’re asking for it. What’s next: what’s actually going on, how to check a crack you think is thermal, and what to look at when you’re buying inserts or picking a manufacturer.
How Pre-Heating Helps Protect PDC Inserts During Brazing
A PDC insert is usually a diamond layer bonded to a tungsten carbide substrate. Diamond does the cutting—hard, wear-resistant. Carbide backs it up and carries the load into the bit.
But the two don’t react to heat the same way. Different expansion. Different heat transfer. Different mechanical properties. So when one spot heats or cools faster than another, stress builds up inside. Get past what the material can handle, and it cracks.
Three things to watch:
- ● Heating rate: Blast it with a torch and you’ll get a hot spot right next to a cold one. That uneven expansion puts stress right around the insert, the substrate, or the joint.
- ● Peak temperature and dwell time: Too hot, or too long, and you can damage the composite or change its properties. What’s acceptable depends on the insert and what the manufacturer says.
- ● Cooling rate: Cool it too fast or unevenly, and you add residual stress. Follow the cooling procedure for the insert, bit body, and brazing system.
The brazing alloy matters too. Its working range, joint clearance, wetting, and compatibility with the base materials all affect joint quality. Preheat can’t fix a bad alloy, poor joint prep, or too much heat.
Why cracks show up after brazing
A crack can start in the diamond table, the carbide substrate, or near the interface. It can also show up in the bit body or the brazed joint. Don’t confuse those with damage inside the insert.
You can see obvious defects with your eyes. But finding where the crack started may need magnification or more. And don’t assume every crack is from skipped preheat. Material defects, handling damage, wrong brazing parameters, poor fit, residual stress—they can all look similar.
Field Applications: Recognizing Brazing-Related Cracks Before Drilling
Thermal damage during assembly is hard to tell apart from handling damage or damage that shows up under drilling loads. This matters for compact inserts in mining, hard-rock drilling, and other jobs where cutting elements take repeated hits.
A practical overseas manufacturing case
During final inspection, technicians spot hairline cracks on several newly installed composite inserts. The tools haven’t been used yet. So downhole abrasion isn’t the cause.
Expected result: The revised process is meant to reduce avoidable thermal damage and make assembly more consistent.
What inspectors should look for
Choosing Reliable Inserts and Controlling Supplier Quality
Recommended pre-assembly quality checklist
FAQ
Does skipping pre-heating always cause PDC inserts to crack?
No. Cracking depends on materials, geometry, and heating rate. Skipping it raises risk, but it’s not the only cause.
What quality documents should buyers request?
Ask for product drawings, dimensional tolerances, inspection records, batch traceability, and product-specific brazing guidance.
Contact Ninestones Superabrasives
Discuss product specs, OEM requirements, and application-based technical support.
About the Author: Michael Carter is a drilling technology writer focused on PDC cutting technology, superabrasive materials, and drilling tool manufacturing.
- Aramco Journal of Technology — Advanced Coating to Mitigate PDC Cutter Thermal Degradation.
- Machine Tool & Hydraulics — Thermal Stress Analysis of PDC Drill Bit Body Cracking.
- International Journal of Refractory Metals and Hard Materials — The Brazing of Diamond.
- Welding International — Influence of Solder and Flux Composition on Thermal Stability.
Post time: Oct-10-2026
