R&D Update: Dieless NC forming
Dieless NC forming or incremental sheet forming is a numerically controlled incremental process that can produce complex shapes from various materials. The process is based on localized plastic deformation in the sheet metal blank. It was developed as an alternative manufacturing method to prototype sheet metal stampings and produce panels in small lot sizes.
The principles of dieless forming are demonstrated on a three-axis CNC machine.
Source Amino Corp.
Editor's Note: This column was prepared by the staff of the Engineering Research Center for Net Shape Manufacturing (ERC/ NSM), The Ohio State University, Professor Taylan Altan, director.
Dieless NC forming, or incremental sheet forming, is a process that can produce complex shapes from various materials. This process is based on localized plastic deformation in a sheet metal blank.
It was developed as an alternative manufacturing method for prototyping sheet metal stampings and producing panels in small lot sizes (1 to 500 pieces per month).1
Complex sheet components are produced by the CNC movement of a spherically tipped forming tool in combination with a stationary die geometry. The process is slow and well-suited for small-lot production, rapid prototyping, and production of service parts and may reduce time to market.
Principles of the dieless NC forming process are illustrated in Figure 1. Three-dimensional CAD data for a part is converted to NC data and downloaded to the machine controller's three-axis servo system. A sheet metal blank is clamped securely over a stationary die, which is fixed on the X-Y table.
Sheet clamping does not allow draw-in from the blank holder. The blank holder is free to move along in the vertical direction on guideposts. The X-Y table and a spherically tipped Z-axis forming tool are actuated simultaneously. The Z-axis tool movement begins at the highest point of the component and follows a predetermined 2-D contour of the part at a constant vertical position.
The blank holder incrementally descends over the stationary die while the spherically tipped forming tool presses against the sheet metal blank, causing localized plastic deformation. The dieless NC forming process forms the sheet metal blank incrementally from top to bottom according to the CAD data.
The stationary die, which is mounted on the X-Y table, can be manufactured from low-cost materials such as plastics or hardwood.2It is necessary for the die to represent only the general outline of the part.
Process Advantages and Limitations
Dieless NC forming has the following advantages:3,4
- Simplified dies result in lowered tooling costs.
- Prototyping can be faster and inexpensive.
- Digital CAD data allows for easy part modification.
- The process can be done on a three-axis CNC mill.
- The process is quiet and safe and requires minimal floor space.
- It can form intricate shapes.
In contrast to deep drawing sheet metal, the plastic deformation zone in dieless NC formed parts is small and limited to the contact area between the Z-axis forming tool and the sheet metal blank. Workpiece thinning is the dominant failure mode and is related to a component's surface angles. This imposes a limitation on formable surface angles. For example, large angles will produce excessive thinning in the sheet metal blank.5
Process limitations include:
- Suitable only for small production lots
- Slow forming speed
- Limited accuracy
Dieless NC forming research is being conducted by several universities.6In many cases researchers have equipped a CNC milling machine with a spherical end tool and a deep-drawing die ring to deep-draw the sheet incrementally into the cavity. Research issues investigated include:
- Comparing the economics of dieless forming for prototype stamping with other prototyping techniques such as hydroforming.
- Improving accuracy and reducing springback.
- Using thick sheet or plate for shipbuilding applications.
- Using rollers or spherical balls at the moving tool tip to eliminate friction.
- Using preforms or hydraulic counterpressure against the deforming tool to increase formability.
This prototyping technology may find a niche in industrial applications because it reduces prototyping time as well as part modification.
Taylan Altan is a professor and director of the Engineering Research Center for Net Shape Manufacturing, 339 Baker Systems, 1971 Neil Ave., Columbus, OH 43210-1271, 614-292-9267, fax 614-292-7219, www.ercnsm.org. The ERC/NSM conducts research and development; educates students; and organizes workshops, tutorials, and conferences for the industry in stamping, tube hydroforming, forging, and machining.
1. H. Amino, K. Makita, and T. Maki, "Sheet Fluid Forming and Sheet Dieless NC Forming," New Developments in Sheet Metal Forming (Stuttgart, Germany: Institute for Metal Forming Technology of the University of Stuttgart, 2000), pp. 39-66.
2. A. Kochan, "Dieless Forming," Assembly Automation, Vol. 21 (2001), pp. 321-322.
3. Amino et al, "Sheet Fluid Forming and Sheet Dieless NC Forming."
4. J. Jeswiet, "Incremental Single Point Forming," Transactions of the North American Manufacturing Research Institution of SME, Vol. 29 (2001), pp. 75-79.
5. G. Hirt, S. Junk, and N. Witulski, "Incremental Sheet Forming: Quality Evaluation and Process Simulation," in proceedings from the 7th ICTP, Vol. 1 (2002), pp. 925-930.
6. University of Saarbrucken, Germany (Prof. G. Hirt, firstname.lastname@example.org), University of Dortmund, Germany (Prof. M. Kleiner, email@example.com), University of Bath, U.K. (Prof. A. Bramley, A.N.Bramley@bath.ac.uk), University of Calabria, Italy (Prof. F. Micari, >micari @unical.it), Queen's University, Canada (Prof. J. Jeswiet, firstname.lastname@example.org).
STAMPING Journal is the only industrial publication dedicated solely to serving the needs of the metal stamping market. In 1987 the American Metal Stamping Association broadened its horizons and renamed itself and its publication, known then as Metal Stamping.