Hot Stamping for Three-Dimensional Parts
by Allan Quimby
KURZ Transfer Products, L.P.
The 3DHS machine employs a vacuum process to pull the foil over the part before a heated die ensures adhesion.
At K 2013, the triennial international trade fair for plastics and rubber, held in Dusseldorf, Germany, in October, the company Leonhard Kurz, represented in the US by KURZ Transfer Products, L.P., lauched its patented 3DHS finishing process. 3DHS is an abbreviation for three-dimensional (3D) hot stamping. Visitors to the KURZ booth were able to see a 3DHS machine in action as it was used to partially coat an automotive air vent panel with a chrome foil. The special characteristic of this specific decoration application was that the air vent had a pronounced 3D geometry that would not have been able to be coated in a conventional hot stamping process.
Optimal for decorating thin or moderately-sized parts, the 3DHS process utilizes three components that have been tailored to work together: a special hot stamping foil, a 3DHS die system and the 3DHS machine. The hot stamping foil is available as a true-chrome coating, as well as in a range of metallic tones, a variety of brushed designs and a large selection of pigmented colors.
Advantages to 3D hot stamping
In the past, plastic elements with a curved part geometry, such as the automotive air vent panel demonstrated at K 2013, typically have been decorated by means of galvanization, which requires two injection-molded parts: an undecorated base component and a ring galvanized with chrome that is mounted onto the air vent. The 3DHS process, however, allows a single-component panel to be partially coated with a metallic, patterned or pigmented foil. This finishing method eliminates the need for an injection mold, along with the associated molding operation and assembly step and, therefore, offers significant cost advantages.
The alternative decoration solutions used to achieve a metallic finish, such as galvanizing a single-piece component over the entire surface, also would be more expensive due to the larger coating area.
A further advantage of the 3DHS technology is that it is more environmentally friendly and versatile since design changeovers can be performed simply by exchanging the hot stamping foil. Color changes in chrome plating require a change and disposal of the plating bath, which typically consists of hazardous solutions – either a chromic acid solution or a less toxic solution based on trivalent chromium salts. The traditional metalizing process involves application guns and either combustible gasses or compressed air. The 3DHS is a dry and solvent-free process that makes a spraying tool and a spray procedure unnecessary, which again leads to cost savings.
The 3D hot stamping process
The 3DHS coating process requires three components that have been optimally tailored to one another: a special hot stamping foil, a 3DHS die system and the 3DHS machine. The hot stamping foil developed by KURZ has been specially formulated to meet the requirements of three-dimensional decoration. It has a high elasticity, which enables it to be thermally shaped to match the geometry of the plastic part in a work operation prior to the stamping process.
In a normal hot stamping process with heat and pressure, pressure is applied in a vertical motion to the foil and the substrate to make a transfer. In this application, a vacuum is pulled down over the foil and the foil is pre-heated to give it the elasticity it needs. Then the vacuum is pulled even tighter over the part, and a heated die is brought down to ensure adhesion and make the impression.
One of the main advantages of the process is the ability to avoid wrinkles. In the past, if a designer wanted to decorate the outer ring of a part, that normally only could be done if the part geometry was flat and consistent. In traditional hot stamping, wrinkles can become an issue if the part geometry has not been designed for a suitable hot stamp, but the vacuum and the flexibility of the foil in the 3DHS process eliminates that concern.
The cycle time for the 3DHS process is longer than traditional hot stamping because of the drawing of the vacuum, but the amount of extra time necessary is project- and size-dependent. Cycle time, however, as it relates to alternative decoration mediums, is very competitive. It often could be considered to be faster because of the modular design and ability to place the decoration inline in the manufacturing process.
Decorative options for 3D parts
This technology gives designers a little more freedom of design. They can think in three-dimensional shapes and still avoid some of the hazardous processes, such as chrome dipping and plating, by using a hot stamping solution. Studies from KURZ show that 3DHS could be a fraction of the cost of a traditional coating or plating process. This is, of course, part size- and volume-dependent. Applications could include automotive interior and exterior applications, household appliances, electronics, consumer goods, health and beauty aids and many others.
In addition, KURZ can support chrome foils that are 100-percent corrosion-resistant and are used on many outdoor and automotive applications. The wear resistance also is built into the construction of the foils, with robust topcoats to pass the most difficult wear and abrasion testing.
The key is that each stamping solution is specifically designed to the specific application requirements. An engineering study is performed to assist the customer in designing the part geometry, ensuring that it lends itself to this decorating process. The tooling and machine solution is then created to match the application and required results. The foils are specially designed to essentially stretch around the part, and the color or pattern is created to the customer specifications. With the 3DHS process, parts with a pronounced 3D geometry that would not have been able to be coated in a conventional hot stamping process now have a new decorating option.