Deburring: simple Operation but Complex Decision
Automated deburring can be an uneventful process when integrated properly.
Often the only setup required is changing the bed opening (for different part thicknesses), and this can be done in a matter of seconds. Sometimes the setup requires changing an abrasive belt for a different finish, and this usually can be accomplished in less than three minutes. Occasionally an operator may need to change out a barrel brush, but this typically takes less than an 15 minutes.
In most cases, however, cut parts simply undergo deburring and then flow consistently to downstream processes. With the right type of machine and abrasives, automated deburring may seem almost invisible. It just works, with little fuss.
Some upfront work required to determine the proper configuration includes weighing all the factors—wet versus dry; number of heads; abrasive media type; part feed and abrasive rotation speed; the parts themselves, including size, material grade, and thickness; and the grain finish desired. At best, automated deburring makes a relatively inconsistent manual process much more predictable and reliable. Often this initially requires trials using several different options. Once that configuration is defined, however, operating an automated grinding machine is simple and cost-effective. For a fabricator’s primary cutting operation, this can be a very good thing.
Deburring Basics
Abrasive media depends on job and machine.
It might seem like flat deburring is as simple as putting a part into a single-head machine and watching it emerge burr-free, but there often is more to it than just that. Consider edge burrs sticking up on leading and trailing plate edges. On a single-head machine, the wide-belt abrasive cuts the burr off but sometimes leaves a portion of that burr lying flat on the leading edge; this is what’s known as a secondary burr, which extends horizontally off the part. That may or may not be acceptable for the job. Regardless, that sharp secondary burr can cut into the hands of material handlers, press brake operators, and others.
In this situation, a multihead machine may work better. After the initial abrasive belt (rotating with the material feed) cuts the burrs off, a barrel brush rotating in the opposite direction softens the leading-edge burr. This produces a burr-free part that’s safe to handle.
A flat-part deburring machine can have one or more heads that hold various abrasive tools. The most common are a wide-belt abrasive that rotates around a drum; a cylindrical barrel brush positioned horizontally across the machine width; and discs that rotate over the material surface. Each belt and brush combination can be configured for the application and can include several custom abrasive media.
The drum that holds the wide-belt abrasive has a specific hardness rating, as do barrel brushes and other finishing media. Application requirements—including material type, thickness, and desired finish—dictate the hardness of the wide-belt-abrasive drum as well as the brushes. Some of the softest contact drums are 30 durometer (a little harder than a bicycle gel seat). Generally, the softer the durometer rating of the heads, the more of a radius is put on a part edge.
A machine may require multiple heads to eliminate all burrs. In this case, a wide-belt abrasive cuts the burrs but also leaves a secondary, lateral burr. To eliminate this, a barrel brush removes the secondary burr and softens the plate’s leading edge.
Abrasive media, feed speed, motor horsepower, and drum hardness determine the amount of stock that can be removed in one pass. A hard, wide-belt-abrasive drum with an aggressive abrasive and high horsepower may remove 0.02 mm of material or more, while a rotary brush may not remove a significant amount, except at that radius on the part edges.
Grit size also plays a role, especially in achieving a specific grain finish. Generally, coarse grains remove more material. On a four-head machine, the first belt might be 60 grit; the second would be 100 grit; the third would be 150 grit; and the finishing belt would be 180 grit. That 150-grit belt may be able to put a No. 3 finish on the part, while that 180-grit belt may put a No. 4 finish. (Unfortunately, when it comes to finishes, no manufacturing-wide standard exists. A No. 3 finish for one automotive customer may be different from a No. 3 finish in the appliance industry.)
Used in combination, multiple heads and brushes—running with and against the material feed—can eliminate most if not all edge burrs on flat part profiles. If laser-cut parts have tiny edge burrs in slots only 1,5mm wide, chances are some combination of abrasive media will eliminate burrs wwith slots. If a part has burrs on the top and bottom edges, passing it through the machine twice should eliminate them (though some specialized, high-volume machines do have abrasive media above and below the workpiece, effectively eliminating all burrs in one pass).
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Type of Abrasive
Choosing the right abrasive is central to getting the best performance out of your machine.
Make sure you pay attention to attributes like the:
- Type (coated, non-woven, etc.)
- Grade (very fine, 120 grit, etc.)
- Mineral (ceramic, aluminum oxide, etc.).
Additionally, you need to consider the pros and cons of belt-, disc-, and brush-style abrasives:
- Belts: These run on drums that loop on a continuous basis. By feeding workpieces onto the belt at slight angles, operators can ensure that the sides as well as leading and trailing edges are effectively deburred. The chief downside of belts is that, while they excel at removing vertical burrs, they do tend to roll excess material over the edges of a workpiece to create lateral burrs. These are relatively easy to remove, but they do require additional processing.
- Discs: Discs are best suited for handling small and sensitive parts, including cladded or galvanized materials. The direction in which the pads rotate creates a swirl-like pattern on the workpiece. This helps to prevent the piece from fracturing when bent, making disc deburring ideal if you need to do subsequent work with a machine like a press brake.
- Brushes: Like discs, brushes work effectively with parts as small as playing cards and delicate parts since they are able to remove burrs without affecting surface coatings like cladding, zinc, or laser film. Brushes also excel at edge rounding—something discs have more trouble with—and are able to complete more complicated 360-degree deburring and finishing tasks.
What’s right for you will ultimately depend on your needs. If you simply need to deburr the sides of your parts, a straightforward belt sander could be ideal. If your needs are more complex or varied, you will need a machine ready to keep pace with those demands.
Workholding Considerations at automatic deburring Machines
How the machine holds the workpieces in place factors into the equation when choosing which abrasive belts and brushes to use. For instance, if small parts are conveyed on a conventional conveyor belt, abrasive heads may cause parts to slip, resulting in inadequate deburring or finishing action. The abrasive head may even pick up or throw the slipped part, potentially damaging the machine.
In many situations, the part length must be at least equal to the distance between the pinch rolls, so there is always at least one pinch roll holding the part against the conveyor belt. Part thickness plays a role here too. A part’s length or width should be large enough in relation to its thickness to prevent the part from tipping during the grinding process.
For parts shorter than the distance between the pinch rolls, there are some options. For deburring extremely small parts, processing a group tabbed into place in a skeleton can work well. Of course, breaking the tabs to remove the parts may leave small burrs or marks, which may require further manual grinding if they are severe enough. In some cases, fixtures can hold parts in place during deburring, though such fixtures must be designed for each part or part family.
A vacuum bed is another option. This is a conveyor belt with small holes and a blower. The blower draws air through the holes and the machine bed, creating enough vacuum pressure to keep small parts stationary during grinding. If a small part can be held with a magnet, some machines also may be fitted with a magnetic chuck. As another workholding alternative, a deburring system with a sticky conveyor belt may be able to hold small parts in place throughout the process. As always, the workholding method depends on the application.
Should you use a wet or dry deburring machine?
Each system has its advantages and disadvantages.
Wet deburring machines flood coolant into the work area. Gravity returns the coolant with dirt and grinding particles to a filter that catches the particles and recycles the coolant to the main tank. Some machines have a filtering system as a stand-alone unit, while others have a filtration unit under the machine to save space. Wet systems eliminate the need for a dust collector, offer long belt life, and minimize hazards when working with different metals.
Wet systems do require a strict maintenance regimen. Certain coolant mixtures work best with certain materials, and excessive corrosion occurs if proper water and lubricant mixtures are not maintained. A number of factors affect the water chemistry in a machine. For example, regular tap water has sodium, calcium, magnesium, and sulfur dissolved in it, and as water evaporates from the tank it leaves these harmful minerals behind.
Daily cleaning and monitoring the chemical makeup of the coolant are vital for optimal machine performance. Some wet machines have stainless steel in critical areas to prevent corrosion. A few machines are made entirely of stainless steel to suit even the most rigorous applications.
Bearing life is the most troublesome problem with wet machines. On some newer systems, pressurized bearings prevent moisture from entering, but this is a relatively new, somewhat untested technology. As always, proper maintenance is the most effective solution.
Dry machines can require less maintenance, provide a longer machine life, and can be less expensive to purchase and operate. However, it is very important to be aware of potential problems. Aluminum dust can accumulate in ducting, and all it takes is one spark to start a fire. Again, maintenance is critical, and cleaning the machine after changing from one material to another is essential.
Dry machines also can leave dust particles and grit on the part surface. If those flat parts are not cleaned, they can prematurely wear press brake tooling, which can be expensive, especially if you’re using hardened, precision-ground punches and dies.
Dry systems also require either dry or wet dust extractors. Dry extractors are adequate for collecting dust from various processes. They must be changed regularly and disposed of properly. However, they do pose some serious hazards if they aren’t maintained properly. Dry filters consist of cloth, paper, synthetic, and other materials. Various metals, abrasive grits, brush fibers, and oil residue can get into the filters, and a hot spark could cause a fire. Check with your fire department for local laws on dust collection.
This is why wet dust extractors have become some more popular. They eliminate the cost of regular filter changes and disposal. But more important, the filter medium—usually just tap water—saturates the particles and quenches any hot sparks. The dust is pulled into a water wash or scrubbing system, and particles settle to the bottom where they can be removed easily. Most wet filters are stainless steel, so rusting isn’t a problem.
Most heavy-duty grinding applications are done dry. When running both aluminum and steel in the same machine, a wet dust collector must be used to prevent fires caused by ignition of the dust. Regardless of what collector you use, though, it is imperative that you check and clean ductwork daily to eliminate any fire hazard.
Ultimately, the type of machine and options you choose will depend on the type of burr removal and finish you require. The decision between a wet or dry machine, and the options needed, should be made after samples have been run by the machine builder.
WET vs. DRY
A basic decision that must be considered is whether the material should be processed in a wet or a dry machine. Wet and dry machines both process the material in the same way; wet machines simply add coolant that is sprayed on the part as it is processed.
Dry Machines are often the first choice because they are generally less expensive to purchase and often have a longer life. However, there are numerous advantages to processing materials on a wet machine.
Wet Machines include a filter unit that also pumps the coolant on the part, and usually include a drying unit that removes the coolant from the part as it leaves the machine.
Several advantages of a Wet Machine are:
• A significant factor when choosing wet versus dry is the possibility of fires when a variety of metals will be processed on the same machine. Some metal dust (such as aluminum) is very flammable, and in a dry machine this dust can be ignited by the spark created when running steel. Timesavers recommends the use of a wet machine when a single machine will be used to process different metals.
• When processing dry, heat buildup due to friction of the abrasive belt on the work piece can cause unwanted warping, particularly on thin materials. A wet machine virtually eliminates this possibility.
• Wet processing improves abrasive belt life due to reduced friction, heat and loading that occurs when grinding dry.
• Wet processing usually provides a finer finish (a lower the RMA) when same grit belts are used to process wet versus dry.
• Parts processed on a wet machine exit clean and dry where-as a dry machine sometimes leaves residual dust on parts.
• A dry machine requires dust collection which means the dry system will have two foot-prints (one for the grinder, one for the dust collector), while a wet machine usually has one footprint.
• Should you choose to process dry, Timesavers recommends the use of a Wet Dust Collector attached to the dust hood/s of the sander. Wet dust collectors capture metal grinding dust in a reservoir that must be cleaned regularly.
• Wet machines do cost more and require more maintenance to achieve these advantages however in most cases the positives outweigh the negatives.
Tailor-made deburring - for enhanced quality in sheet metal.
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Whether thick or thin parts, heavy or light burrs: We offer a suitable deburring machine for punched, laser or plasma, flame-cut parts. In order to offer you the optimal machine solution, we specifically focus on your parts and your edge processing requirements. Ultimately, we strive to provide you with the best and most consistent parts quality, while achieving low unit costs.