Most dogs bark when they are angry, afraid, or when they are overexcited. The big trick with managing barking is to determine why the dog barks so much. Once you figure that out, one of the best ways to deal with excessive barking is through training.
Of course, when it comes to grooming, no amount of training may stop your dog from barking completely if he's not a fan of the process. You may need to find ways to distract your noisy dog or tire him out so he no longer has the energy or the desire to make much of a ruckus when it's time for grooming.
Chances are good that your dog is barking during grooming time because he is not happy about the whole process, especially the brushes, clippers, shears, and so forth. The more time you spend working to get him used to being around the tools you plan to use, the less he will fuss and bark. Be sure to use lots of patience and treats to help him relax and learn to enjoy being groomed.
The biggest step you can take towards keeping your pooch from barking during grooming is to find ways to keep him tired and distracted. Exercise treats, and toys all work well. The more fun you can make it for both of you, the less he is likely to spend time voicing his opinion. Have fun and turn grooming time into bonding time.