The blade, called a mixing knife, in the TM5™ and TM6™ is engineered with a safety breakpoint outside the bowl, so the pressure required to break the knife will break the shaft before the blade. This is a safety feature so the blades in the TM5™ and TM6™ do not have any pieces that could break free. The blades have undergone rigorous testing in many scenarios to ensure they are safe to use.
If the motor is moving but the blades are not, a new mixing knife is needed. You can order a new mixing knife on shop.thermomix.com. If you have any questions or concerns please call Customer Service at 888-867-9375 for next steps.