Incremental sheet forming (or ISF, also known as Single Point Forming) is a sheet metal forming technique where a sheet is formed into the final workpiece by a series of small incremental deformations. However, studies have shown that it can be applied to polymer and composite sheets too. Generally, the sheet is formed by a round tipped tool, typically 5 to 20mm in diameter. The tool, which can be attached to a CNC machine, a robot arm or similar, indents into the sheet by about 1 mm and follows a contour for the desired part. It then indents further and draws the next contour for the part into the sheet and continues to do this until the full part is formed. ISF can be divided into variants depending on the number of contact points between tool, sheet and die (in case there is any). The term Single Point Incremental Forming (SPIF) is used when the opposite side of the sheet is supported by a faceplate and Two Point Incremental Forming (TPIF) when a full or partial die supports the sheet.
Types
Single-point incremental forming (SPIF) and double-sided incremental forming (DSIF) are the two variants of the IF process. In the DSIF process, two tools are used to form the sheet on either side, while the SPIF process only uses a tool on one side of the sheet. Thus, a component having features on either side of the sheet, e.g., an inverted cone can be effectively formed by the DSIF process. [1]
Advantages over conventional sheet metal forming
Because the process can be controlled entirely by CNC processes no die is required as is in traditional sheet metal forming. The elimination of the die in the manufacturing process reduces the cost per piece and decreases turnaround time for low production runs because the need to manufacture a die is eliminated. However, for high production runs the time and cost to produce a die is absorbed by the higher per piece speed and lower per piece cost.
Several authors recognize that the formability of metal materials under the localized deformation imposed by incremental forming is better than in conventional deep drawing.[2] In contrast, there is a loss of accuracy with the ISF process.[3]
Implementation
The ISF process is generally implemented by clamping a sheet in the XY plane, which is free to move along the Z axis. The tool moves in the XY plane and is coordinated with movements in the Z axis to create the desired part. It is often convenient to retrofit a CNC milling machine to accommodate the process. Spherical, flat-bottomed, and parabolic tool profiles can be used to achieve differing surface finishes and forming limits.[4]
The machine employs a combination of stretch forming by drawing the sheet incrementally down over a die, with the CNC tool approach described above. This is said to produce a more even distribution of thickness of the material. The process is well suited to one-off manufacture though difficulties in simulating the process mean that toolpaths are complex and time-consuming to determine.
Ford Motor Company has recently released Ford Freeform Fabrication Technology, a two-point incremental sheet-forming technique being implemented in the rapid prototyping of automotive parts. Complex shapes such as the human face[5] and cranial implants[6] have been manufactured successfully using this manufacturing process. Advances in the technology are expected to increase adoption in the near future by other sheet metal-reliant manufacturers.
Applications
Incremental forming (IF) is a recent manufacturing process having a wide range of applications in the following areas.[7]
Biomedical Implant
Automobile
Aerospace
Nuclear Reactors
Defense
List of process parameters
The mechanics of the process is influenced by many parameters, including:
Research is underway at several universities.[14][15] The most common implementation is to outfit a traditional milling machine with the spherical tool used in the ISF process. Key research areas include
Developing rolling tools to decrease friction.
Reduce thinning of sheets after forming
Increase accuracy by eliminating springback[16][17]
Develop novel uses, especially extending the process to new materials (e.g. composites) and to apply heating [18]
^Nagargoje, Aniket; Kankar, Pavan; Jain, Prashant; Tandon, Puneet (9 February 2021). "Performance Evaluation of the Data Clustering Techniques and Cluster Validity Indices for Efficient Toolpath Development for Incremental Sheet Forming". Journal of Computing and Information Science in Engineering. 21 (3): 031001. doi:10.1115/1.4048914. S2CID228968844.
^Strano, Matteo (31 December 2004). "Technological Representation of Forming Limits for Negative Incremental Forming of Thin Aluminum Sheets". Journal of Manufacturing Processes. 7 (2): 122–129. doi:10.1016/S1526-6125(05)70089-X.
^Examining Tool Shapes in Single Point Incremental Forming (Cawley et al, 2013)
^Behera, Amar Kumar; Lauwers, Bert; Duflou, Joost R. (2014-05-01). "Tool path generation framework for accurate manufacture of complex 3D sheet metal parts using single point incremental forming". Computers in Industry. 65 (4): 563–584. doi:10.1016/j.compind.2014.01.002.
^Duflou, Joost R.; Behera, Amar Kumar; Vanhove, Hans; Bertol, Liciane S. (2013-01-01). "Manufacture of Accurate Titanium Cranio-Facial Implants with High Forming Angle Using Single Point Incremental Forming". Key Engineering Materials. 549: 223–230. doi:10.4028/www.scientific.net/kem.549.223. ISSN1662-9795. S2CID136559821.
^Nagargoje, Aniket; Kankar, Pavan; Jain, Prashant; Tandon, Puneet (9 February 2021). "Performance Evaluation of the Data Clustering Techniques and Cluster Validity Indices for Efficient Toolpath Development for Incremental Sheet Forming". Journal of Computing and Information Science in Engineering. 21 (3): 031001. doi:10.1115/1.4048914. S2CID228968844.
^Hamilton, K.; Jeswiet, J. (2010). "Single point incremental forming at high feed rates and rotational speeds: Surface and structural consequences". Cirp Annals. 59: 311–314. doi:10.1016/j.cirp.2010.03.016.
^Golabi, Sa’id; Khazaali, Hossain (August 2014). "Determining frustum depth of 304 stainless steel plates with various diameters and thicknesses by incremental forming". Journal of Mechanical Science and Technology. 28 (8): 3273–3278. doi:10.1007/s12206-014-0738-6. ISSN1738-494X. S2CID110179841.
^Davarpanah, Mohammad Ali; Mirkouei, Amin; Yu, Xiaoyan; Malhotra, Rajiv; Pilla, Srikanth (August 2015). "Effects of incremental depth and tool rotation on failure modes and microstructural properties in Single Point Incremental Forming of polymers". Journal of Materials Processing Technology. 222: 287–300. doi:10.1016/j.jmatprotec.2015.03.014.
^Carrino, L.; Giuliano, G.; Strano, M. (2006), "The Effect of the Punch Radius in Dieless Incremental Forming", Intelligent Production Machines and Systems, Elsevier, pp. 204–209, doi:10.1016/b978-008045157-2/50040-7, ISBN9780080451572
^Fan, Guoqiang; Gao, L.; Hussain, G.; Wu, Zhaoli (December 2008). "Electric hot incremental forming: A novel technique". International Journal of Machine Tools and Manufacture. 48 (15): 1688–1692. doi:10.1016/j.ijmachtools.2008.07.010.
^Walczyk, Daniel F.; Hosford, Jean F.; Papazian, John M. (2003). "Using Reconfigurable Tooling and Surface Heating for Incremental Forming of Composite Aircraft Parts". Journal of Manufacturing Science and Engineering. 125 (2): 333. doi:10.1115/1.1561456.