Elevate the capacity of the constraint
You've Exploited the constraint fully and let the non-constraint resources subordinate to the constraint to get the most throughput out of the bottleneck. Both of these measures are essentially "free", you're getting the most out of resources you've already paid for. But you can't squeeze any more throughput out of the system. What now?
It's time to start investing a bit.
Look at ways to elevate the capacity of the constraint resource to generate throughput:
- Buy better tools, so people can work faster and more accurately
- Train or coach people; send them to conferences or lectures; let them read books; give them time to experiment and learn... so that they become more skilled
- Hire more people. Do take the learning curve into account...