When examining a new car in detail, it has become a normal, quick quality check by anyone from a specialist engineer to a member of the buying public to give the dashboard a sharp tap. Is it hard plastic? Or is it something altogether softer and more hapitically pleasing, such as slush molding?
Slush-molded technology is now used on a wide span of models, from down market to premium, to enhance the tactility and surfacing quality of interiors. Johnson Controls Inc. has just announced two-color slush skins that can be produced in a one-step manufacturing operation, adding design variety without adding any significant cost.
Hans Hendriks, the company’s Vice President Global Product Development, said slush skins already achieved the highest quality demands for color characteristics while meeting requirements for complex geometries such as high precision large undercuts and small radii. “Now we are able to produce two-color slush skins in a single production step. Until now, this was only possible in a single color, which restricted the way the process could be used,” he said.
It is the application of subtle masking technology that has made two-color slush skins a cost-effective and practical product option.
Slush-skin technology shapes a plastic from a galvanically produced original mold. Its production for an instrument panel/dashboard application sees a bath of slush powder connected to a galvanic mold and heated to 230°C (446°F). The bath is then rotated with the galvanic mold, the resultant coagulating PVC powder distributed over a grained tool surface, the quantity of powder sticking to the mold being adjusted via temperature, rotation, and time selections, explained Hendriks.
Once the powder has settled on the heated surface of the mold’s inside wall, the powder bath is separated from the mold and the melted PVC powder coagulates in the tool, so forming a homogeneous slush skin. Once cooled to about 50°C (122°F), the skin can be removed from the mold.
“When the substrate is coated, for example in an instrument panel blank, it results in an extremely precise fit, and the even material thickness ensures a pleasant touch, including such critical areas as undercuts and tight radii,” said Hendriks.
Different shine levels and haptic effects can be achieved including imitation stitching.
The reason slush skins have traditionally been unicolored is only specific PVC powder is used over the entire mold. To achieve the two-color option, Johnson Controls uses masking technology. The tool is partially covered by a mask, and a robot sprays a 0.6-mm (0.023-in) powder layer on the uncovered areas of the mold. Next, the mask is removed and the established process is then started.
Hendriks explained that two-color slush skins could therefore be produced without a specific additional production step. The spray and slush-skin process is said to work with identical materials of different colors to achieve required high consistency of appearance and tactility. Visible color divisions can also be produced.
Johnson Controls uses oil-heated galvanic tools, which it regards as superior to those heated by air, the oil providing precise temperature distribution throughout for consistent wall thickness and the avoidance of hot spots.