Automated Flat Finishing Improves Quality and Increases ProductivityA two-step flat finishing process can enhance the benefits of fineblanking by meeting the demand for high-volume, burr-free parts. During the past 30 years, significant driving forces behind the growth of fineblanking have resulted from pressures to improve quality and boost pressroom productivity. Now, in their quest for even higher quality, fineblankers are electing to integrate abrasive flat finishing systems into their manufacturing process to produce a burr-free radiused edge component. Originally, fineblanked parts primarily were used in watches, office equipment, cash registers and clocks. More recently, parts for medical instruments, appliances, sporting apparatus and recreational equipment were added to the list of fineblanked components. Automotive ApplicationsToday, a large number of fineblanked parts are supplied to the automotive industry. In addition to internal parts, such as gears and transmission components, automotive suppliers are fineblanking an increasing number of net-shaped exposed parts. 
| | Fig 1. - Micro-photo of unfinished fineblanked part. |
The near-zero clearance and exacting tolerances for fineblanking dies can produce a high quality, net-shape, part—when the dies are relatively new. However, over time the dies wear. This often results in metal pull-down, creating an extruded edge on features of the part. It is the malleable metal that creates the undesirable burr (Fig 1). Edges that contain burrs are very sharp and can pose a hazard to persons in material handling, assembly and inspection operations, as well as during end use of the product. If the part is installed in a moving assembly, the burr can work loose. This can cause mechanical wear problems and premature failure. Furthermore, exposed burrs do not project the image of high quality that consumers and manufacturers demand. Removing BurrsThere are two ways to remove burrs from fineblanked metal parts. One is by hand using a file or other abrasive tool. The other is to use an automated or semi-automated process. Manual methods add labor costs, and there is a lack of finish consistency from part to part. Automating the process can reduce production cycle times significantly and improve finish quality.  | Fig 2. - Micro-photo of part finished with abrasive belt (160). |
Burr removal can be accomplished with a two- or three-head flat finisher. In a two-stage unit, the first stage is an overhead abrasive-belt grinder, which is used to remove stock. The second stage is a planetary-face brush that radiuses all edges. Stock removal, scale or oxide removal, and fine multi-directional deburring are benefits of this system (Fig 2). Flat Finishing MachinesA flat finishing machine consists of a continuous moving-belt conveyor that transports parts under one or more finishing heads. Workpieces may be loaded onto the conveyor using a batch (bowl) feeder or directly from the fineblanking press (Fig3).  | | Fig 3 - Typical flat finishing machine |
Production rates with a flat finish machine usually are limited only by the deburring requirements of the workpiece. It is not uncommon for a system of this type to finish as many as 3000 parts per hour. An operator can quickly and easily adjust the speed of the conveyor drive depending on the part being finished. The feed conveyor material is either an evenly callipered abrasive belt, or a rubber and fabric ply belt (which can be fixtured if necessary). The final finish of the part is affected by at least three factors. First is the grit and type of abrasive material used on the belt. Conveyor speed and hence the amount of time the parts spends under the abrasive belt is the second factor. The third variable is the amount of pressure exerted by the abrasive belt head against the workpiece. How These Machines WorkParts are loaded onto the conveyor belt, which transports them over platens used to support the conveyor belt and workpiece under each finishing head. Plain platens are used for nonmagnetic work, while variable density electro-magnetic platens are used for ferrous parts. These magnets hold the part in position as it passes under the head at a controlled speed, which prevents slippage during the grind. A variable speed control is important when changing from one size workpiece to another (Fig 4).  | | Fig. 4 - Abrasive head used in flat finishing machine |
Spring-loaded hold-down rolls also help to prevent part slippage by holding the work against the conveyor belt under each head. Sometimes formed-in cleats on the conveyor belt can be used for backing parts that are shorter than the distance between the hold-down rolls. Flat finisher heads and conveyors, are available in 6 inch and 12 inch widths. All units are designed for wet operation. Heads are equipped with pneumatic belt-tensioning devices and automatic tracking which keeps the belt in its proper orientation (± .25 inches) during operation. Two Heads Are Better Than OneDepending upon finishing requirements (and how much stock is to be removed), two grinding heads may be better than just one. With two heads, one grit of belt can perform the initial cut while a second belt can further remove stock to achieve the required finish. Additional, independently controlled heads can be designed into an automatic flat finishing system. Flat finishing machines are production surfacing machines. They should not be confused with precision machines such as surface grinders. Stock removal on flat finishing machines can range from a high of from 0.010 inch to 0.020 inch per pass. However, they are not as accurate as surface grinders. Parallelism and size control are in the range of ±0.001 inch or ±0.002 inch, depending on a number of factors. Edge RadiusingAfter abrasive belt grinding of the extruded burr, the surface is a plane, but the edges are still very sharp. Edge radiusing is the next step. This is accomplished with a planetary head featuring abrasive impregnated nylon filament face brushes (Fig 5). Generally, three face brushes are arranged on a planetary head that has a slow, relative rotation. Each face brush is rotated individually at high speed. One of the brushes counter-rotates with respect to the others. The rotational pattern of the brushes generates vigorous edge deburring on all part features. For instance, holes are uniformly deburred through a full 360 degrees. This degree of uniformity is not possible with straight-line or simple arcs generated by other types of brushing methods. Effective edge deburring occurs only when the bristle up-cuts from below the part plane. On a complex part,  | | Fig. 5 - Planetary head used to power abrasive impregnated nylon filament face brushes in flat finishing machine |
this means that the bristles must arrive at all angles to the part during the cycle. The planetary head with nylon brushes will generate a 0.002 inch to 0.004 inch radius (in steel) on all features including the full part circumference (Fig 5).On certain parts, a finely grooved finish is desirable and can be obtained with a stiff-bristle brush. Examples of such parts are those that rub against other parts and a lubricant is used. The microscopic grooves act as riverbeds for the lubricant between components, thus extending their service lives. Some workpieces require finishing on both top and bottom. Such applications may employ a flat finishing machine that can be configured with heads located above and below the workpiece. Also, machines may be engineered with an automatic part rollover station (Figs. 6, 7 and 8).  | Fig. 6 - Unfinished fineblanked part |  | Fig. 7 - Fineblanked part (same as shown in Fig.6) after passing through the abrasive belt station |  | Fig. 8 - Finblanked part (same as shown in Fig. 6 and 7) after passing through the planetary head |
Because flat finishing machines usually use coolants in the stock removal process, coolant filters are recommended. Automatic advancing paper-type filters require no extra floor space and include a sludge tank to receive used paper and grinding swarf. Other machine options, which include part wasters, demagnetizers and conveyor brushes, help to make an automated abrasive flat finishing system complete. BenefitsFineblankers that integrate automated flat finishing systems into their pressrooms receive multiple benefits. First, and perhaps most important, deburring production rates improve significantly. Quality, as well as surface uniformity, of the finished part likewise is greatly improved. Not to be overlooked by the stamper is the ability to extend the useful life if expensive fineblanking dies. Taken together, automated flat finishing of fineblanked parts can give stampers an economic advantage in an increasingly competitive and quality conscious marketplace.
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