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Table 1: Contrasts between multilayer drilling and conventional single layer drilling Fiber Reinforced Polymer (FRP) composite materials are of increasing importance in multilayer stackups, especially in the aerospace industry. The primary challenge in FRP modeling is that FRP materials are heterogeneous and exhibit strong anisotropy. Clear distinctions have to be made between the strong, reinforcing fiber and the soft polymer matrix. Hence, for accurate modeling, information on the constitution of the composite has to be explicitly known, which may either be deterministic or stochastic.

Table 1 Contrasts between multilayer drilling and conventional single layer drilling Fiber Reinforced Polymer (FRP) composite materials are of increasing importance in multilayer stackups, especially in the aerospace industry. The primary challenge in FRP modeling is that FRP materials are heterogeneous and exhibit strong anisotropy. Clear distinctions have to be made between the strong, reinforcing fiber and the soft polymer matrix. Hence, for accurate modeling, information on the constitution of the composite has to be explicitly known, which may either be deterministic or stochastic.

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the formation of burrs, significant productivity gains as well as improved part quality can be achieved. In order to accomplish this goal, several approaches to the modeling of burr formation have been formulated. Finite Element Modeling (FEM) has been the primary approach to gaining valuable information for drilling in flat surfaces, curved surfaces, and stacked materials. This modeling has been supplemented by experimental results and the compilation of an online burr expert database (available at http://www.burrexpert.com) to predict burr formation based on drilling parameters. Furthermore, tool path planning has been optimized with respect to burr formation in face milling by controlling the exit angle. These topics on burr formation — with a focus on the work done at the Laboratory for Manufacturing Automation (LMA) at the University of California-Berkeley — are reviewed in this paper, emphasizing their impact in the aerospace industry.
the formation of burrs, significant productivity gains as well as improved part quality can be achieved. In order to accomplish this goal, several approaches to the modeling of burr formation have been formulated. Finite Element Modeling (FEM) has been the primary approach to gaining valuable information for drilling in flat surfaces, curved surfaces, and stacked materials. This modeling has been supplemented by experimental results and the compilation of an online burr expert database (available at http://www.burrexpert.com) to predict burr formation based on drilling parameters. Furthermore, tool path planning has been optimized with respect to burr formation in face milling by controlling the exit angle. These topics on burr formation — with a focus on the work done at the Laboratory for Manufacturing Automation (LMA) at the University of California-Berkeley — are reviewed in this paper, emphasizing their impact in the aerospace industry.
n conventional drilling, the morphologies and the sizes of the exit burrs are determined primarily by the feed rate and the speed of the drilling operation. Three main ypes of burr morphologies have been identified: uniform burrs, crown burrs, and transient burrs [4]. At low eed rates and speeds, a uniform burr is generally formed while at higher feeds and speeds, a crown burr is usually ormed. A transient burr is a combination of both a uniform and crown burr. A photograph of these three ypes of burrs can be seen in Figure 2.
n conventional drilling, the morphologies and the sizes of the exit burrs are determined primarily by the feed rate and the speed of the drilling operation. Three main ypes of burr morphologies have been identified: uniform burrs, crown burrs, and transient burrs [4]. At low eed rates and speeds, a uniform burr is generally formed while at higher feeds and speeds, a crown burr is usually ormed. A transient burr is a combination of both a uniform and crown burr. A photograph of these three ypes of burrs can be seen in Figure 2.
Figure 3: Formation of a uniform burr using a finite element simulation with a relatively low feed rate [5] formation and crown burr formation can be seen in figures 3 and 4, respectively.
Figure 3: Formation of a uniform burr using a finite element simulation with a relatively low feed rate [5] formation and crown burr formation can be seen in figures 3 and 4, respectively.
Figure 4: Formation of a crown burr using a finite element simulation with a relatively high feed rate [5]
Figure 4: Formation of a crown burr using a finite element simulation with a relatively high feed rate [5]
Burrs in curved surfaces are rather unpredictable and end to occur only on certain parts of the exit hole rather han uniformly around the exit. This is a function of the geometry of the exit surface as well as the geometry of he drill. On certain parts of the exit surface, the drill is pushing into the workpiece whereas on other parts it is pushing out of the workpiece. This can be modeled hough the definition of an “interaction angle”, @ [7]. A positive interaction angle will produce a burr by pushing out the workpiece while a negative interaction angle will not produce a burr by pushing into the workpiece. This is modeled in Figure 5. These interaction angles have been studied based on their relation to drill geometries and process parameters. Simulations have been run to calculate the interaction angle to predict where the burrs will form. A sample of the simulation output and the user interface is shown in Figure 6.
Burrs in curved surfaces are rather unpredictable and end to occur only on certain parts of the exit hole rather han uniformly around the exit. This is a function of the geometry of the exit surface as well as the geometry of he drill. On certain parts of the exit surface, the drill is pushing into the workpiece whereas on other parts it is pushing out of the workpiece. This can be modeled hough the definition of an “interaction angle”, @ [7]. A positive interaction angle will produce a burr by pushing out the workpiece while a negative interaction angle will not produce a burr by pushing into the workpiece. This is modeled in Figure 5. These interaction angles have been studied based on their relation to drill geometries and process parameters. Simulations have been run to calculate the interaction angle to predict where the burrs will form. A sample of the simulation output and the user interface is shown in Figure 6.
Figure 6: Simulation used to model the interaction angle and burr formation in the exit of a curved surface. Green and red lines indicate negative interaction angle (no burr) and positive interaction angle (burr), respectively [7] to identify the best drill for a given surface. One of the key problems in achieving this is obtaining a good model for the drill. The complex geometries of the web, point angle, chisel edge angle, lip relief, etc., make this a formidable task.
Figure 6: Simulation used to model the interaction angle and burr formation in the exit of a curved surface. Green and red lines indicate negative interaction angle (no burr) and positive interaction angle (burr), respectively [7] to identify the best drill for a given surface. One of the key problems in achieving this is obtaining a good model for the drill. The complex geometries of the web, point angle, chisel edge angle, lip relief, etc., make this a formidable task.
Progress has been made to achieve more reliable models and simulations that show accurate burr formation in drilling. In addition to DEFORM, Third Wave AdvantEdge is also another FEM package that may be employed to study burr formation in drilling.
Progress has been made to achieve more reliable models and simulations that show accurate burr formation in drilling. In addition to DEFORM, Third Wave AdvantEdge is also another FEM package that may be employed to study burr formation in drilling.
Figure 8: Section of a horizontal stabilizer of a commercial aircraft made of a metal (Ti) — composite (CFRP — Carbon Fiber Reinforced Polymer) — metal (Ti — unseen) stackup [2] increasingly being used as constituents of these stackups in the aerospace industry, as seen in Figure 8.
Figure 8: Section of a horizontal stabilizer of a commercial aircraft made of a metal (Ti) — composite (CFRP — Carbon Fiber Reinforced Polymer) — metal (Ti — unseen) stackup [2] increasingly being used as constituents of these stackups in the aerospace industry, as seen in Figure 8.
assist in the achievement of these goals and help improve aerospace manufacturing techniques for drilling. Figure 9: Entrance burr and gap formation in stacked SS304L drilling [8]
assist in the achievement of these goals and help improve aerospace manufacturing techniques for drilling. Figure 9: Entrance burr and gap formation in stacked SS304L drilling [8]
Currently, the burr control charts are material specific. Although a chart for every individual material is unreasonable, this problem can be solved by adding a third dimension to the chart that accounts for material properties. The influence of material properties has been acknowledged by a great many researchers, but Link was the first to quantify this effect with a parameter called the “burr tendency”, G [13]. This burr tendency value is higher when burrs are more likely to form in a material. To understand how a three dimensional control chart might appear, Link’s G-value is used as the third axis in Figure 11. The more ductile stainless steel forms burrs more easily than low allow steel (Type Il burrs appear closer to the origin) according to the burr tendency G-value.
Currently, the burr control charts are material specific. Although a chart for every individual material is unreasonable, this problem can be solved by adding a third dimension to the chart that accounts for material properties. The influence of material properties has been acknowledged by a great many researchers, but Link was the first to quantify this effect with a parameter called the “burr tendency”, G [13]. This burr tendency value is higher when burrs are more likely to form in a material. To understand how a three dimensional control chart might appear, Link’s G-value is used as the third axis in Figure 11. The more ductile stainless steel forms burrs more easily than low allow steel (Type Il burrs appear closer to the origin) according to the burr tendency G-value.
The first stage of the Burr Expert website will include modules and case studies from UC Berkeley’s short course on burr minimization. It will also provide a forum for members to exchange ideas and technology, thus providing users a fast and effective source of data and insights from researchers in the area.
The first stage of the Burr Expert website will include modules and case studies from UC Berkeley’s short course on burr minimization. It will also provide a forum for members to exchange ideas and technology, thus providing users a fast and effective source of data and insights from researchers in the area.
Figure 13: Definition of exit angle in face milling
Figure 13: Definition of exit angle in face milling
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EngineeringMechanical EngineeringBurr formation
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