Brandt J. Ruszkiewicz

Incrementally Formed Stiffeners Effect on the Reduction of Springback in 2024-T3 Aluminum After Single Point Incremental Forming

Single Point Incremental Forming (SPIF) is a relatively new process to form sheet metal. SPIF utilizes machines such as CNC’s and mills to form a part by making several spiraled passes, deforming the metal a certain distance, known as the step-size, with each pass. One major issue with this process is global springback. Once the metal is removed from its clamping fixture, the residual stresses that resulted from the forming process cause the material to springback. The purpose of this paper is to demonstrate how incrementally forming a stiffener on the outside of the desired geometry will manipulate the stress concentrations in the metal, and effectively reduce the amount of global springback that occurs after the specimen is unclamped from its fixture. For these tests, stiffeners were formed on the outside of a truncated pyramid; the material used for these test was 2024-T3 aluminum. After the work pieces were removed from their clamping fixtures, the amount of springback that they experienced was examined using Geomagic software to determine the ideal stiffener parameters for reducing global springback for a truncated pyramid in 2024-T3 aluminum.Copyright

Direct Electric Current Spot Treatment’s Effect on Springback of 90 Degree Bent 2024-T3 Aluminum

One of the largest issues for sheet metal forming techniques such as stamping and incremental forming is springback. Springback is the elastic recovery of a material after it has been formed resulting in distorted part geometries. Springback can be compensated for during the forming process, however, this often requires forming the metal further than the desired shape. Unfortunately, if a formed part is designed such that it is close to its forming limit, compensation could push the material too far and cause fracture. It has been shown that by pulsing electric current throughout an entire workpiece during forming, springback can be greatly reduced and sometimes eliminated.This paper examines the effect of pulsing direct electric current, through localized points of a workpiece after it has been deformed into a 90-degree bend, but prior to the reversal of the bending die (i.e., while the part is still constrained). It was found that, with a high current density for a short amount of time, springback could be greatly reduced without the need to run a larger current through the entire workpiece. The largest springback reduction was seen when the electric current was forced to flow across the bend in the specimen. This finding is advantageous for industry as it will allow springback reduction in large parts that would normally require much larger power sources to generate the correct current density, if current is run through the entire part. A potential barrier between industry and this technology is that machines would need to be either created or modified to apply electric current at known places at a specific current density and time. To modify an existing machine may be difficult because the machine would need to be insulated from the electric current.Copyright

Locally Applied Direct Electric Current’s Effect on Springback of 2024-T3 Aluminum After Single Point Incremental Forming

Incremental forming is a sheet metal forming technology that utilizes a spherical tipped tool and a CNC machine to form a part through a series of spiraling tool paths. Springback is one of the largest concerns for incremental forming since a part can be the exact shape desired after forming until the part is unclamped from its forming fixtures, at which point it will springback due to the residual stresses resident in a part due to the forming process. This paper demonstrates how locally applied electric current can be utilized to reduce the springback due to residual stresses. The tests conducted in this paper demonstrate this concept via incrementally formed truncated-pyramid shapes that were formed from 2024-T3 aluminum. The residual stress concentration locations of the pyramid were determined using FEA. Direct electric current was locally applied to the stress concentrations of the pyramid prior to unclamping. Various current densities, time intervals, and electrical pulse locations were examined to find the ideal conditions for reducing springback for a tested geometry of 2024-T3 aluminum.Copyright

Electrically Assisted Global Springback Elimination After Single Point Incremental Forming

There has been a push in the automotive and aerospace industries towards die-less forming processing that are able to reduce both part cost and part energy. Incremental forming is a die-less forming process that fabricates parts using hemispherical tools following a tool path (similar to that found with conventional milling operations), that slowly deforms the sheet metal into the final desired configuration. Global springback for incremental forming, as defined herein, occurs after the part is unclamped from the retaining fixture. This form of springback is currently a significant impediment to the process since, when the part is released, the residual stresses created during the forming process result in significant part distortion and thereby, undesirable part geometries. To reduce this issue, this paper examines the effect on direct electric current on residual stress and springback elimination when applied post forming, which previous work has shown the potential to reduce this issue. This work is an extension of previous work resented at MSEC 2015. The previous work examined applying electric current to areas of high residual stress through the material’s thickness. This work examines the effect of applying electric current along the length and width of a part (path testing). This work concludes that running multiple paths increases springback reduction and the order in which the path testing is conducted has very little appreciable effect on the springback reduction during path testing.© 2016 ASME

Electrically Assisted Compression of Tungsten Carbide and its Implications for Electrically Assisted Machining

It has been shown that electrically assisted machining has the ability to reduce cutting force, change chip type, and improve surface finish. However, the effect of electricity on tungsten carbide has not been examined, a material often used to create cutting tools used in electrically assisted machining. During machining processes, depending on the type of cut, a small amount of the tool may be in contact with the workpiece. This will lead to an increased current density at that point on the tool which could lead to undesired effects with respect to tool wear and life. This paper conducts electrically assisted compression tests on uncoated tungsten carbide rod to examine the effect of electricity on the material and determine if there are any current densities that cause large magnitude weakening of the tungsten carbide. It is concluded that there is a maximum current density that can be passed through tungsten carbide before thermal softening becomes a problem. At a current density lower than this threshold, electricity has little effect on the strength of the carbide. This work is related to past electrically assisted turning experimentation.Copyright

Effect of Toolpath on the Springback of 2024-T3 Aluminum During Single Point Incremental Forming

Incremental forming is a nontraditional forming method in which a spherical tool is used to asymmetrically deform sheet metal without the need for expensive allocated dies. Incremental forming employs a tool path similar to that used when CNC milling. Hence, when forming a part, the forming tool makes a series of passes circumferentially around the workpiece, gradually spirally stepping down in the z-axis on each sequential pass. This tool path deforms the sheet metal stock into the final, desired shape. These passes can start from the outer radius of the part and work in (Out to In, OI forming) or they can start from the center of the shape and work outward (In to Out, IO forming).As with many sheet metal operations, springback is a big concern during the incremental forming process. During the deformation process, residual stresses are created within the workpiece causing the final formed shape to springback when it is unclamped, sometimes very significantly. The more complex the geometry of the final part and the more total deformation that occurs when forming the geometry, the greater the residual stresses that are generated within the part. The residual stresses that have built up in the piece cause more significant distortion to the part when it is released from the retaining fixturing. This paper examines how the step size (in the z direction), OI vs. IO forming, and final part geometry affect the total springback in a finished piece. For all of these tests 0.5 mm thick sheets of 2024-T3 aluminum were used to form both the truncated pyramid and truncated cone shape. From this investigation it was found that smaller step sizes result in greater springback, IO is significantly less effective in forming the part (due to workpiece tearing), and final part geometry plays an important role due to the creation of residual stresses that exist in corners.Copyright

Feasibility of End Mill Cooling Using the Venturi Effect With Compressed Air

In many machining applications tool wear is a major problem. Cutting edges on tools wear out with repeated use leading to their inevitable failure. This tool failure causes a poor surface finish on the work piece being cut. Currently cutting fluid is applied during the cutting process to extend the life of a tool and is effective. Cutting fluid is considered a hazardous material which causes problems during disposal. Disposal of hazardous waste can be expensive causing a push to find alternate green cooling methods. This paper focuses on the feasibility of using the venturi effect on compressed air to replace water based cutting fluids. The two processes are to be compared on the grounds of cooling of the tool and work piece as well as chip removal. Cooling comparisons will be made through the examination of a straight channel cut, and chip removal will be gauged by how large of a mass the air streams can move. It was found that, in these areas, an accelerated stream of compressed air through the correct diameter nozzle outperforms the liquid cutting fluid in both aspects during end milling operations. These findings lead the authors to believe that in the future compressed air, or other pressurized gas, will be the most economical and effective green cooling technique.Copyright