Manual finishing process has been used throughout history to shine artifacts, weapons, and other metallic objects. Its modern equivalent, mass finishing, also known as mechanical surface finishing, has been around since the 1950s. The process aims to clean, descale, deburr, polish, burnish, de-rust, and brighten various metal complements via milling contact between surfaces.
As the process involves grinding contact, it is usually suitable for tougher parts. The constant rubbing, even though in liquid or solid media, can damage delicate components or the ones with intricate geometries. That’s why polishing delicate parts without any damage or alteration is a challenge.
So, how should you approach this?
Let’s start at the heart of this problem.
1. Defining the Characteristics of Delicate Parts
Delicate is a subjective term. When it comes to mass finishing, you have to consider size, thinness, protrusions, and your finishing requirements. Usually, small and thin parts lead to finishing issues. Flat metal parts, in particular, tend to stick together, particularly if you are using wet media.
Most die-cast metal parts also have thin walls and soft material. So, they are unable to withstand the abrasive force of vibratory or tumbler finishing process. Metal components with delicate protruding parts such as arms, slots or openings can also get damaged. Apart from these challenges, sometimes, customers may have special finishing requirements that might require you to take a non-conventional approach.
2. Which Finishing System Is the Best Fit?
Tumblers and vibratory systems appear to be gentle finishing machines, but may not always be the best for delicate parts. As you throw the metal pieces and media together in these systems, the chances of small and thin parts sticking together are higher.
Unfortunately, these machines often fail to break the capillary action that makes parts and media stick together. Flat parts also tend to hang on vibratory parts that discharge ramps and chutes, which in turn, reduces the quality of the finishing process.
You can use high-energy finishing machinery such as centrifugal disc and centrifugal barrel systems for finishing delicate parts. They can easily break the capillary action. You can also provide an additional buffer to the delicate pieces by using an extra quantity of media. The only limitation, however, is the excessive heat generated during the process. These processes usually have longer running cycles, resulting in more heat generation that causes damage.
While centrifugal disc systems can overcome all these problems and provide better finishing for delicate parts, they also lead to a unique problem over time. The gap between the stationary processing chamber and the rotating disc (spinner) widens over time. The delicate parts, especially small ones, get caught in this gap, getting damaged and also causing damage to the machine.
3. You Need to Consider the Right Media
Media is one of the most crucial elements of the finishing process, especially for the delicate parts. It smoothens surfaces, keeps the parts separate during the process, and scrubs the particle surface to clean them thoroughly. Different cuts, shapes, and weights made from aluminum, ceramic, quartz, aluminum oxide, silicon carbide, steel, and synthetic material usually used as media.
However, not all media is made equal. Steel media, owing to its substantial weight (approximately 300 pounds per cubic foot) is often considered ineligible for finishing delicate parts. Large-sized ceramic media can also cause similar problems. But, you can use a combination of small porcelain pieces and fine abrasive powders such as silicon carbide or aluminum oxide to facilitate the finishing process of delicate parts.
Water is added to this media to create the powdered slurry, which reduces the chances of damage significantly. However, as you can’t use a continuous flow of water during the process cycles, a substantial amount of heat is generated, especially in high-energy systems. It can affect the finishing quality as well as damage delicate parts.
As you can see, developing the right chemistry is probably the only way, going forward. You have to find the perfect balance between the finishing system, media, media, and parts ratio, and the cycle time. In recent years, a few new finishing processes have been developed globally with the help of advanced technology. Drag finishing and surf finishing are quite suitable for polishing delicate parts.
4. Other important systems for delicate parts processing
4.1 Drag Finishing
Last few years saw the rapid rise of drag finishing as an alternative for surface finishing, particularly for delicate and high-value metal components. The process comprises dragging the delicate pieces through the media just like driving a plow through the soil. The process is particularly valuable because of its high speed and high pressure.
Dragging the parts through the media at high-speed generates high pressure, which in turn, results in high-quality finishing. But most importantly, as you fix the pieces individually to the workstations on a carousel, there is no direct contact between two parts. As a result, they don’t cling to each other. You can add anywhere between four to twelve workstations on a carousel depending on the size of your machine.
Though it is not a low-cost alternative, drag finishing is one of the affordable solutions for polishing delicate parts such as medical implants. You can automate the process to get a consistent finding quality every day, it is not labor intensive unlike manual finishing, and the results are often worth the cost.
4.2 Surf Finishing
Surf finishing is another popular alternative that involves both, dry and wet processing methods. The most common benefits include higher process stability, easy automation, repeatability, and extremely short cycle times, making it suitable for smoothing and polishing of delicate parts.
You can use one or multiple six-axis robotic arms to lower the parts into the polishing media placed in a rotating processing bowl. With this process, you can polish complete or only the desired surface of the pieces. Owing to its high-process stability, many industries such as aerospace, automotive, hydraulic, and energy use it for finishing delicate components.
When it comes to polishing delicate and high-value parts with intricate geometries, you have to get creative as most of the conventional systems lack the necessary fineness. For the time being, understanding your polishing requirement, parts’ geometries, and using drag or surf finishing seem like the right options. However, going forward, developing new processes, trying new media and parts ratios, and looking for new systems and media alternatives is the best possible solution in this regard. Good luck!