Performance boost in aluminum forming: enabling cost-effective trimming of aluminum with Tetrabond™ (ta-C)
High-quality parts need calibrated machining processes
Shearing is one of the most frequently used processes in sheet metal manufacturing and forming operations. This process of stamping parts from sheet metal includes blanking, trimming and piercing, and is widely applied in different industries such as primary metal, automotive or household appliances. The overall quality of the stamped part is defined by the height of the burrs on the sheared surface, the dimensional accuracy of the part and the absence of splitting. To meet quality standards and customer expectations, stamped parts frequently need a manual metal-finish operation for deburring. This is time consuming and adds costs to the stamped part.
These days, aluminum alloys are popular because they help reduce the weight of automotive body panels. That means the quality of shearing operations has increasingly come into the spotlight. Aluminum alloys are replacing low carbon steel because they can improve fuel economy while maintaining strength for passenger safety purposes. However, many manufacturing processes were originally designed for low carbon steel, and now need to be adapted for use with aluminum alloys. This is especially true of trimming, as both materials demonstrate different forming behavior due to differences in mechanical and chemical properties and mass density.
Tetrabond deposited on trimming dies for sheet aluminum forming
Confocal 3D surface image of Tetrabond™ for forming and molding tools (largest scale 1.75 µm)
Slivers and burrs – the challenges that arise from trimming
A common defect arising from the trimming process is sliver formation. This is one of the main obstacles preventing the high-volume production of aluminum alloys for automotive body panels. Slivers are highly undesirable as they adhere to the blank surface and get distributed to the dies following the trimming process. The accumulation of slivers on both the die and blank surface can result in an unacceptable surface finish, as the slivers on either side can be pressed into the blank surface during pressing. A second common defect to arise directly from the trimming process is the production of burrs. Burrs can cause a decrease in quality and accuracy of stamped parts and are considered the source of potential splits in following forming operations.
From defect removal to defect prevention
Many technical solutions have been developed to remove these defects after the trimming process. However, removing slivers from the dies and blanks can be time-consuming and expensive, in particular when cleaning the die requires an interruption of the automated stamping process. Therefore, it is also important to identify technical solutions to prevent defects from occurring during the trimming process.
One approach to minimizing the occurrence of burrs and maintaining acceptable surface quality, for example, is an accurate alignment of the upper and lower shearing edges during the trimming process. A more promising approach to eliminate the root cause of sliver and burr generation is the use of hard, wear-resistant coatings deposited by physical vapor deposition (PVD).
Ionbond Tetrabond™ drastically reduces the scrap rate
Ionbond has developed the Tetrabond™ coating as part of our forming and molding tool coating portfolio. It is an economical solution that ensures excellent product quality of stamped parts and increases the productivity of highly automated stamping processes by drastically reducing the scrap rate. Tetrabond™ is a non-hydrogenated tetrahedral amorphous carbon (ta-C) coating that belongs to the class of diamond-like carbon coatings. It was tailored to the specific need of forming tools with a sp3 ratio (sp3/(sp3+sp2+)) between 60 % and 70 % and a hardness above 3,000 HV0.02.
- Is a thin and extremely hard coating designed to maintain maximum forming tolerance and edge sharpness
- Has an abrasion resistance comparable to nanocrystalline diamond coatings deposited by chemical vapor deposition (CVD)
- Has an extremely smooth surface
- Has a minimum adhesion tendency (anti-sticking) towards non-ferrous metals
- And has a very low coefficient of friction.
That makes it the perfect match for trimming aluminum alloys.
Compared to conventional hydrogenated DLC coatings (a-C:H), Tetrabond™ has an enhanced temperature stability up to 500 °C, which extends the range of forming applications and choice of workpiece materials. Tetrabond™ can be deposited on complex tool geometries and on a broad range of tooling materials, including cold-work, hot-work and high-speed steels, stainless steels and cast iron. A proprietary decoating process allows refurbishment of production tools after regrinding, making the best use of expensive forming tools.
Comparison of abrasive wear resistance of TiN and Tetrabond™