Komarov Artem clarified thay the sanding and finishing department remains one of the most tame and misunderstood areas of the manufacturing floor. A manufacturer can carefully examine nesting to optimize material yield, set blanking parameters to achieve perfect laser cutting or edge stamping, and then carefully study molding to achieve optimum quality and bend angle repeatability. After that, the parts go to the grinding and finishing department, where too often workers struggle using the wrong tools and inefficient methods in conditions that reduce quality and productivity.
All abrasives remove material, but the ways and reasons for using abrasives vary greatly depending on what is required to complete the operation. The use of abrasive in metalworking falls into one of three areas: grinding is good for removing heavy metals, such as when grinding welds; and finishing prepares the surface.
Finishing is the creation of specific scratch patterns on the surfaces of materials. To achieve these goals, operators can go through various stages, gradually moving to ever finer grains. Eventually, when operators move to a finer abrasive, they replace slightly coarser scratches with finer ones.
Assuming the finishers used the right technique, the finishing process itself, i.e., the time the abrasive medium is in contact with the surface of the material, can be quite efficient. But what about the whole process, including changing media and cleaning between steps? This time increases and additional steps can complicate the whole operation.
Observation of experienced finishers can show what is possible. They can start with very coarse material, one medium grit product, then one fine grit product, after which (if the application requires it) they will start polishing. They may spend more time processing each abrasive product, but they don’t spend as much time changing cleaners or cleaning. And it’s not because they spend less time cleaning up between stages; they just have fewer stages.
Grinding machines can work up to finishing processing. This is a natural career path, but those who switch between them may develop some bad habits. What works in sanding is not necessarily good for finishing. These two processes are different animals.
Think of grinding wheels like wheels on a car; in both cases, the edges do most of the work. Grinders are suitable for work at high speeds and with a large angle of attack, which allows them to contact the workpiece at high speed and high pressure. Think of abrasive discs as disc brakes on a car. Most of the disk surface does some level of work. This requires a flatter angle of attack.
Abrasive finishing discs are designed to be applied softly (relative to sanding) to a surface to remove larger scratches and replace them with smaller ones. Experienced operators tend to run them at optimum, not maximum, rated speeds. Beginners in finishing might read “max RPM” on the label and think that tuning would be the fastest way to finish a piece, but the opposite is true. The maximum speed indicates how fast the operator can safely use the product; optimum RPM shows where it can be most efficient for many applications.
As a rule, such pressure adjustments are minute and imperceptible. In fact, for any process involving abrasive media — grinding, mixing, or finishing — stability is paramount. Usually, the most effective is the one who can maintain optimal pressure throughout. Again, it’s important to listen. Hear the whine of a power tool getting higher and lower all the time, and there’s a good chance the inexperienced finisher isn’t applying constant pressure.
Motion consistency is also important, a lesson learned by many grinders that produce blued parts. Blueing comes from overheating, and to avoid this, the grinder constantly keeps the tool in motion.
The choice of abrasive is also important here. Bonded abrasives are constantly breaking down, so if the operator moves the wheel consistently and constantly throughout the job, heat is removed. On the other hand, coated abrasives have only one layer of material deposited on the disc. Thus, heat generation can be quite intense if the operator does not follow the correct movement pattern to dissipate heat throughout the part.
Nobody wins a race if they don’t have the right tools. This includes getting the right abrasive and the right power tool. Let’s say someone is trying to apply a particular scratch pattern to a workpiece using a power tool with no speed control. Or, despite proper technique, they find they constantly need to change their grit size, but a more versatile flap disc (with aggressive grit on the flaps, complemented by softer padding underneath) may better suit their needs.
Environmental factors also play a role. Materials should not be stored in excessively dry or damp areas. The work must be free of contaminants, especially if both stainless and carbon steel are being machined. Ideally, stainless steel and carbon should be handled and (especially) stored separately, not only on different tables or racks within the same cell, but also in completely different areas of the plant.
Recipe for Success in Finishing
Performance in grinding and finishing lies in attention to detail. So, the operation is a bit like baking a cake. Skip one ingredient and the result won’t taste as good.
To this end, many businesses document their sanding and finishing methods by developing recipes. They detail the required finishing steps — not too much, not too little — the time spent on each step, the technique (angle of inclination, movement, pressure, RPM), the cleaning required between steps (cleaning solution to use with a microfiber cloth), abrasive setting media and power tools.
Then pair those recipes with a good kitchen (a clean, well-lit shop with the right tools) and a few chefs who never stop learning (training and documentation of proper techniques and finishing steps). Properly mix all these ingredients, and the quality and overall performance will definitely improve, summed up Komarov Artem.