Chip-Formation

I used to think chip breaking was entirely about feed rate. If the chips were too long, I increased the feed until they broke. That works up to a point, but the drill’s chip breaker geometry sets the baseline for what feed rate will work. Understanding chip breaker geometry helps you choose the right drill for the material and know whether a regrind is maintaining the correct geometry. What a Chip Breaker Does A chip breaker is a groove or step ground into the rake face of the gun drill tip, just behind the cutting edge. As the chip slides across the rake face, it hits the chip breaker and curls. The curl creates bending stress in the chip, and when that stress exceeds the material’s fracture limit, the chip breaks. ...

The Five-Step Troubleshooting Sequence When something goes wrong during a deep hole drilling job, I teach operators a five-step sequence. This sequence solves about 80% of all problems without needing engineering support. I post this sequence on every machine in the shop. The sequence follows the most likely cause first. Starting with the most common problem saves time. Do not skip steps and do not jump to conclusions. Step 1: Check Coolant Pressure Low coolant pressure is the root cause of more problems than anything else in deep hole drilling. It causes chip packing, tool breakage, poor surface finish, and oversized bores. ...

Chip formation simulation uses finite element analysis to predict how chips form under different cutting parameters. I have seen it used mostly by cutting tool manufacturers and large aerospace shops. For deep hole drilling, where a broken drill means scrapping the part, simulation pays for itself fast. How Simulation Works for Gun Drilling The simulation models material behavior at the cutting zone using Johnson-Cook constitutive models. These models account for strain hardening, strain-rate sensitivity, and thermal softening. The software divides the tool and workpiece into a mesh of elements, usually 10,000 to 100,000 nodes, and calculates the stresses at each node as the tool advances. ...

I read chip shape to tell whether my parameters are correct. I have caught three imminent drill failures this year alone by spotting a change in chip color before the tool broke. Chip shape is the best indicator of process health in deep hole drilling. Good chips mean good parameters. Bad chips mean trouble. There is no sensor on the machine that tells you what chip shape tells you. I check chips at every tool change on production runs — it takes about five seconds and tells me more about process health than any gauge on the machine. ...