PRACTICALLY EVERY METAL FINISHING TECHNIQUE: Your Guide to Project Success Metal Finishing | 2 www.mchoneind.com ● P3 -- Intro to Finishing ● P5 -- Material Choice ● P6 -- Naturally Occurring Finishes ○ P6 -- Anodizing ○ P7 -- Passivation ● P8 -- Smoothing Finishes ○ P9 -- Polishing ○ P9 -- Buffing ○ P9 -- Brushing ○ P10 -- Blasting ○ P12 -- Metal Grinding ○ P13 -- Barrel Tumbling ○ P14 -- Vibratory Finishing ○ P15 -- Others CLICK TO NAVIGATE ● P16 -- Protective Finishes ○ P16 -- Plating ○ P18 -- Hot Blackening ● P19 -- Nonmetallic Coatings ○ P19 -- Paint ○ P19 -- Powder Coating ● P20 -- Which Finish Should You Choose? ● P21 -- Where Else Do You Need Help? Metal Finishing | 3 www.mchoneind.com Intro to Finishing “Finish” means to bring a task to an end or complete it. Likewise, in metal manufacturing, a quality product often isn’t complete until it receives the appropriate finish. In this case, “finish” means to give a part the surface texture you desire. For example, many parts need deburring for smooth edges or powder coating for a bright look. Some of these processes fall under the term mass finishing. (Definition: Abrasive processes during which metal parts get processed in bulk and gain a certain surface effect.) Did you know? ● The finishing cycle can serve as a check on the quality of fabricated parts. ● Poor-quality parts will require more time on the finishing line. ● You should NOT rely on finishing processes to fix errors made in earlier stages of the manufacturing process. You can save time and money if you consider your finishing needs during the design, production, and quality control stages. An all-in-one manufacturer can help you keep track of these needs. Metal Finishing | 4 www.mchoneind.com NOW, ON TO YOUR GUIDE ----> Metal Finishing | 5 www.mchoneind.com Material Choice Many common metals are unsuitable for a variety of applications in the form in which metal makers initially produce them. Raw steel, aluminum, and other metals are quite vulnerable to corrosion and need their surfaces altered to make them more useful for applications in which retaining strength and aesthetics is key. Knowledge of the exact alloy you want (again, your manufacturer knows the differences) is critical to successful finishing. It’s equally important, especially for anodizing, to keep different alloys separated. Mixing alloys in a group or a weld will always result in a less uniform finish, and can even result in the destruction of your parts. Each metal requires a somewhat different pretreatment. Aluminum, for example, cannot be cleaned in solutions formulated for cleaning steel. Metal Finishing | 6 www.mchoneind.com Naturally Occurring Finishes Anodizing Only aluminum is invited to this party. Anodization happens when the naturally occurring oxide coating on the outer surface of aluminum changes to a tightly adhering layer. This coating is much more resistant to corrosion and abrasion than what’s hidden inside. You can then use the aluminum in more strenuous applications. Note that anodizing coats very uniformly and will therefore not fill or smooth out a rough or damaged surface Anodizing is recommended for virtually all aluminum alloys. It is critical, however, that alloys not be mixed in a weldment, or within a single order. Alloys such as 2024, if mixed or welded to 6061, may be destroyed during the process. Metal Finishing | 7 www.mchoneind.com Passivation This one is specific to stainless steel. It’s a removal and oxide growth process. The metal forms an inert, protective oxide film when exposed to oxygen in atmosphere. While stainless steels are naturally corrosion-resistant, they are not entirely impervious to corrosion. Your manufacturer must remove contaminants down to the surface grain so they don’t inhibit the formation of the oxide film that protects stainless steel. Metal Finishing | 8 www.mchoneind.com Smoothing Finishes Deburring is the breaking up of sharp edges The design of a metal product affects finish quality and can influence deburring and finishing costs. Have someone knowledgeable in burring review your part’s design. That helping hand may recommend you relocate webs, change hole sizes, and more. Don’t get nervous -- an expert vendor can do all this while keeping the same part function and reducing finishing costs! Cost is one factor that may decide the choice in some cases. Vibratory systems, due to their massive construction, are much more expensive pieces of equipment. Barrel tumbling systems wear out tumbling media at half the pace of vibratory systems, but have to run longer to do the same job. Applications: ● Finishing: Add matte or satin finish, frost, decorate, remove glare, blend tooling marks and imperfections, hone and burnish ● Cleaning and removal: Rust, paint, burrs, etc. ● Surface preparation: Helps with etching and cleaning parts before welding or coating. ● Surface treatment: Strengthen, increase wear properties, reduce corrosion susceptibility, etc. Metal Finishing | 9 www.mchoneind.com Polishing Polishing refers to surface enhancement by means of metal removal. It’s used for decorative products that benefit from luster and smoothness. A coarse line pattern remains afterward. FYI: Polishing does not + buffing. Processes that use abrasive belts are referred to as polishing, and processes that involve cloth wheels with a compound applied are called buffing. Buffing One use of buffing is to remove considerable amounts of material. The other, more familiar use, is to smooth out a surface. We advise against using these processes (both polishing and buffing) for applications with complex, fragile, or recessed specifications. Brushing Unlike plating, this is is an great method for removing surface flaws. An abrasive belt or wire brush creates a uniform, parallel grain surface to smooth out a product’s exterior. Furthermore, the belt or brush can make slightly rounded edges perpendicular to the grain. Metal Finishing | 10 www.mchoneind.com Blasting Bead Blasting (Tumble Blasting Machine) Most machines use glass beads and steel shot in the blasting process. Glass beads are gentler, leave no residue, and are more environmentally friendly than sandblasting. Glass bead blasting is also more affordable than many other abrasive methods. The beads themselves are relatively cheap to produce. Glass is the most common blasting ammo. Often used as all-purpose media for general cleaning and finishing, including contaminant, coating, or burr removal; honing, blending, and peening. Or, you could use the toughness of steel beads to remove surface debris without damaging or removing the underlying metal. Steel shot lowers surface preparation time by up to 75% compared to some other methods, resulting in some nice labor cost savings. Steel beads are also commonly used. Solid, round particle that causes peening and produces dimpled surface. This shot has a relatively high mass, which gives it greater impact and a hammering action. Metal Finishing | 11 www.mchoneind.com Sand Blasting In this process, parts are tumbled slowly to provide random exposure to a sandblasting gun using an abrasive. The sand removes light burrs or texturizes your parts, resulting in an attractive finish. It penetrates the smallest crevices and goes through holes to get cross drill burrs. Sand blasting performs best with parts around 2” or less. Large, heavy parts can be dented. On the plus side, sand blasting comes with a low labor factor. On the downside, it’s not environmentally friendly like bead blasting. Metal Finishing | 12 www.mchoneind.com Metal Grinding Grinding machines use friction, attrition and/or compression to smooth out your part’s surface. Different machines deliver different levels of smoothness. For example, a ball-grinding mill is an excellent fine grinder for cement products, but may not work for more extensive smoothing projects. Rod mills are used to make metal rods, while semi-autogenous grinding (SAG) mills and autogenous grinding mills smooth luxury metals like: ● Copper ● Gold ● Platinum ● Silver Metal Finishing | 13 www.mchoneind.com Barrel Tumblers (aka Rotary Tumblers) Barrel tumblers are reminiscent of a rock skidding down a hill. The tumbler's corners lift the load as the barrel rotates until the load slides down the side. Each part is smoothed as it bumps against the machine and the other parts. Barrel finishing produces a more uneven surface and generally rounds off corners before deburring much material from your surface. Depending on your design, this can be good … or not so much. For brute-force stock removal, the barrel tumbler is a winner. Foundry castings and parts with heavy radii are usually run in a barrel tumbler. Specify the barrel tumbler's peening action to work tougher parts and stress-relief machined parts. You can use hardened and polished steel shot in a barrel tumbler for producing a quick luster on parts. You can also use this media in a vibratory machine, but the barrel tumbler yields a denser and more lustrous surface. It’s admittedly a long process cycle, but your vendor’s operating cost is low. Other benefits: ● Components to be cleaned may be loaded manually, mechanically, or automatically ● Gentle tumbling of parts for consistent, overall blast pattern exposure ● Individual cycle times based on cleaning requirements. So if cleaning isn’t important to you, your project can get through the line more quickly. Metal Finishing | 14 www.mchoneind.com Vibratory Finishing Need a quick method of finishing? Vibratory finishing is a type of mass finishing manufacturing process used to … ● Deburr ● Burnish ● Radius ● Clean ● Descale ● and brighten … a large number of relatively small workpieces. In this batch-type operation, your vendor tosses specially shaped pellets of media and your workpieces into the tub of a vibratory tumbler. Vibratory finishing systems tend to produce a very smooth flat finish because it really laps the parts. The vibratory tumbler will also cut inside a tube- or cup-shaped piece, deburring any spot the stone can reach. Metal Finishing | 15 www.mchoneind.com Other Centrifugal Barrel Finishing This is a high-energy finishing process in which energy created within mass in a container is greater than that obtained with standard vibratory or other methods This machine can process parts that are: ● Frail ● High-precision ● Small Centrifugal Disc Finishing The machine for this process is an open-top cylinder or bowl with stationary side walls. The machine drives the disc to rotate at a high speed. ● Part size limitation exists ● Process cycle is short Spindle Finishing Your vendor accomplishes this by mounting parts on spindles and immersing them in mass of relatively fine media contained in an open-top tub or bowl. Media flows against and over your component’s edges and surfaces to deburr and refine them. ● Low media cost ● High labor cost Metal Finishing | 16 www.mchoneind.com Protective Finishes Plating Electroplating (aka Electrodeposition) The electroplating method involves depositing a thin layer of metal onto the surface of a component (called the “substrate” during this process). The manufacturer uses an electrical current to force the desired reaction. For many projects, the main goal of plating is to improve resistance to corrosion and wear. It’s also a cosmetic choice. (Ex.: A layer of gold is electrodeposited onto metal jewelry to improve its color and luster.) Other uses for electroplating include: ● Building the thickness of a metal surface ● Improving electrical conductivity — Ex.: Plating a copper layer onto an electrical component ● Preparing surfaces for enhanced adhesion prior to painting or e-coating ● Reducing friction ● Protecting against surface abrasions ● Improving surface uniformity Metals commonly used in electroplating include zinc, copper and tin, as well as precious metals such as gold, silver and palladium Metal Finishing | 17 www.mchoneind.com Electroless (Autocatalytic) Plating In this process, a chemical reaction prompts metal atom reduction. It uses nonconductive substrates, so no electricity necessary here. Note that it’s hard to control the plating parameters, and the plating bath has a limited lifetime. The most used electroless plating method is electroless nickel plating, but you can use this method to also apply: ● Copper ● Silver ● Gold Immersion Plating (Displacement Reaction) This time, the metal ion is reduced from solution by way of an exchange with a metal atom from the substrate. The deposited metal must have more electromotive force than the dissolved metal. Metal Finishing | 18 www.mchoneind.com Hot Blackening Hot blackening involves machines spreading a thin layer of oxide onto your part’s surface to create a matte black finish. The end result? Your parts have high abrasion resistance. Hot blackening is most commonly used in the production of: ● ● ● Firearms Auto parts Tools Metal Finishing | 19 www.mchoneind.com Nonmetallic Coatings Paint Paint is used to increase surface protection at a low cost. Mostly, it adds color for cosmetic projects. Unfortunately, the process is fraught with waste and is less environmentally friendly than other options like powder coating. Powder Coating This process allows for greater productivity and higher repeatability -- and therefore savings for you. Powder coating’s color and texture variety can equal or surpass paint. It can even increase your part’s durability and impact resistance. Need more? Powder coating is environmentally and wallet-friendly. Whatever falls off your part goes through a filtration system and back into our gun, saving you material expenses. Powder coating is easier to automate, ensuring spray and run efficiency. Metal Finishing | 21 www.mchoneind.com Which One Do You Choose? There are a few considerations that can help you narrow your choices in selecting a technique that fits your project’s needs. Keep in mind these factors: ● Cost efficiency: Certain services can seem expensive, but they may compensate by offering faster cycle rates. Seek the advice of a full-service manufacturer who’s familiar with the finishing process. ● Production speed: How quickly does the technique apply finish to the product? ● Metal toughness: Harder metals typically need more convincing to do what you want. That may mean a tougher abrasive or a more severe finishing option. Metal Finishing | 21 (716) 945-3380 | www.mchoneind.com If you’ve made it this far, you’ve covered a lot. If your head is spinning, we can step in for you. Feel free to drop us a line with your questions, or schedule a free, no-pressure, 30-minute engineering consultation. We also provide assembly, design assistance, bending, fabrication, and other services, so a consultation might do more than improve your component’s finish -- it might change your supply chain forever! If you found this e-book helpful, please share it with your peers! McHone Industries has excelled at metalworking for over 4o years. We strive to provide value, creative engineering solutions, and high-quality all-in-one manufacturing every day.
