As product development and manufacturing gets outsourced to overseas manufacturing facilities, it has become increasingly difficult to find products that are still made in the USA. In the race for the lowest possible pricing, quality is often compromised while chasing the least common denominator. At Stark Performance, quality is of paramount importance and if that means we have to do things the old fashioned way, by hand, in order to provide quality with reasonable pricing, then so be it. Doing things manually, however, comes at a price. Since a person’s time has value, the more skilled a person is, the more valuable their time. As such, labor intensive manufacturing methods by skilled artisans are by default, more expensive than parts made by machine, or by manual labor in countries that only pay $5/week. The parts we manufacture are made with attention to detail and fueled by passion. The following is a little insight into the past 18 months of development and refinement of our paddle shifter extension production process.
The first step was hand sculpted prototypes made from light cure acrylic putty; finished and painted to seal the surface as well as distinguish this master pattern from production castings. These prototypes represent over 160 hours of skillful sculpting, shaping, sanding, polishing, painting and prepping.
As a proof of concept, the hand sculpted prototypes were good, but had their flaws. They were then 3D scanned and manipulated in CAD to refine and even out the edges and contours.
Once the CAD work was completed, the new master patterns were 3D printed using Fused Deposition Modeling (FDM). While FDM is a good process for prototyping and proof of concept, it is not accurate enough for the tolerances required and the finish left much to be desired. As such, 3D printing is not a good manufacturing process for a part that will be handled on a regular basis. Another limiting factor for production was the 8 hours required to print each 3D master pattern. In addition, there were several misprints before achieving final, acceptable patterns. Once the master prints were complete, the ridges left over from printing were hand sanded smooth and the contact patches were further refined for a perfect fit. Creating a smooth surface that mated to the contoured surface of the factory paddles was not an easy feat and required multiple techniques to achieve.
Using these master patterns, silicone molds were made to cast parts. Each mold requires 4 days to make and is able to produce 15 – 25 parts before the silicone breaks down and fails to produce quality parts. There were multiple iterations using different mold designs, different durometer silicones and even different silicone chemistries before the molds produced parts with consistent fitment. This was due in part to the stiffness of the mold and its coefficient of thermal expansion that would cause distortion during the exothermic polymerization reaction that occurs in both the initial mold production as well as the casting process itself.
Through research and development several key pieces of specialized equipment were constructed to produce bubble free castings. Since polyurethane resin absorbs water from the atmosphere and the isocyanate in the resin reacts with water to form carbon dioxide gas during the polymerization process, bubbles will form very easily. In addition, the reaction is temperature sensitive and the liquid mixture solidifies faster when over 70 degrees Fahrenheit. If not poured within 30 seconds of mixing, the viscosity will increase to the point of failing to fill the mold and result in a miscast. The casting area therefore requires dehumidification and temperature control to mitigate bubble formation and ensure sufficient mold filling.
Each cast requires thorough degassing of the resin using a vacuum chamber to remove all the moisture and any entrapped air. A secondary vacuum resin trap is used to draw the resin into the mold cavities and once the mold is filled, it is placed into a pressure pot to compress any remaining bubbles before the resin has polymerized. The resin is allowed to fully polymerize in the pressure pot prior to de-molding.
Once the resin is polymerized, the parts are de-molded and the vents and sprues from casting are manually removed. The parts are left to finish curing overnight so they reach full hardness (Shore 80D). The result is a part that is as hard and stiff as ABS plastic (used to make most automotive interior parts) and has a temperature of deflection of 200 degrees Fahrenheit.
One of the advantages of having plastic parts that are touched regularly is that plastic has a relatively low coefficient of thermal conductivity. The human body is incapable of detecting temperature, but can detect heat transfer. When something feels hot, it is simply warmer than the part of the body that is in contact with it. The temperature differential results in heat transfer through conduction. Metals feel hotter or colder to the touch than plastic because metals transfer heat at a faster rate than most other materials. This is one of the reasons why modern automobiles use non-metallic parts for surfaces that are touched frequently and why these extensions are plastic as well.
Before any additional finishing work is done, the parts are checked for fitment using a water soluble paste. If the fitment is only slightly off, the part will be adjusted until it has good contact or discarded altogether.
Since a mold release is used to slightly prolong the short service life of the silicone mold, the parts are put into a vibratory tumbler to remove the mold release, ensuring good paint adhesion later on.
While the part finish is fair, there is still a parting line and the remainder of the vents and sprues are manually removed for a clean finish.
The parting line, vents and sprues are ground flush and every edge is smoothed to remove any irregularities felt while handling the parts.
The grinding marks are sanded smooth with a two stage wet sanding before they are ready for primer.
The parts are then masked off and mounted on a fixture for priming. This ensures that the fitment area does not get distorted by paint since the tolerance on that area is +/- 0.002”. Once primed, the surface is wet sanded, cleaned, and carefully inspected prior to the application of an automotive interior grade satin black paint followed by an automotive interior grade satin clear.
Once the finish is deemed satisfactory, the parts are then removed from the fixture and the die cut adhesive is applied.
The adhesive is a 3M VHB that has a long term temperature tolerance of 300 degrees and a short term temperature tolerance of 500 degrees. As such, the adhesive maintains an excellent bond at the elevated temperatures the interior of a car can reach when parked in the sun on a hot summer’s day. Several other adhesives were tested and found to perform poorly in comparison despite being rated for the expected conditions.
The end result is a part that is aesthetically pleasing and integrates seamlessly with the rest of the interior. It also provides excellent ergonomics while improving the overall driving experience.