Inside Manufacturing: Tooling Method Replicates Intricate Woodgrain in Fiberglass Doors
Fiberglass entry doors have been growing in popularity with homeowners and contractors since they were introduced in the 1980s. Although metal and wood doors still dominate the world’s residential entry door market, with the majority in metal, fiberglass — primarily compression molded sheet molding compound (SMC) — has steadily gained market share in recent years and now accounts for about 30 percent of the U.S. market. While Canadian and U.K. usage is lower than that figure and there is currently little penetration in the rest of the world, some experts predict fiberglass doors soon will account for 50 percent of U.S. entry door installations, and they believe the product has good potential for growth around the globe.
One of the key drivers of fiberglass door popularity is design versatility. SMC is capable of picking up fine-grain detail and can be painted or stained to resemble wood. Since the 1980s, door manufacturers have worked to improve the accuracy with which SMC mimics the “warmth” of wood — in other words, how precisely it replicates the unique lines and grain patterns of specific tree species. Most efforts have focused on development of better artwork with which to acid-etch steel tooling. While these efforts have improved grain detail significantly, Ken Kussen, Home & Building business manager for toolmaker Weber Manufacturing (Midland, Ontario, Canada), notes that the two-dimensional nature of the artwork limits the toolmaker’s ability to replicate the three-dimensional texture of real woodgrain. “Also, it tends to have a more ‘mechanical’ — overly regular — look, failing to capture the variation natural to real wood,” he says.
Opening the closed door
More than a decade ago, Weber developed a hard tooling technology based on its patented nickel vapor deposition (NVD) toolmaking process that the company says more accurately replicates authentic 3-D wood grain directly in composite parts like fiberglass door skins. The result was a door that successfully combined the engineering advantages of composites with the beauty of wood. For more than 10 years, a licensing agreement kept this tooling technology exclusive to a single door manufacturer.
In the intervening years, however, the doors that Weber’s customer made were widely recognized for their superior quality. Weber’s vice-president Rob Sheppard, P.E., notes that other door manufacturers repeatedly requested that Weber make its technology available to them — despite the fact that NVD tooling is priced about 30 percent higher than acid-etched steel. Kussen adds, “We knew that many entry door manufacturers, tired of losing customers and market share to fiberglass, were actually buying and rebranding composite doors from other manufacturers.”
Recently, a downturn in the always cyclical automotive tooling market prompted Weber to expand its services to the home building market. “Renegotiating our agreement to make nickel tooling available to any door manufacturer was the logical first step,” Kussen explains, but notes that a second factor introduced an unanticipated twist: Several of Weber’s potential door OEM customers had no experience molding composites and were understandably reluctant to make the investment in tooling, compression molding equipment, training and process development. Based on its decade of experience with Weber’s initial customer, Kussen says, “We decided to offer not only tooling, but also to mold fine-grain door skins for any door manufacturer.”
Starting with real wood
One reason for the greater accuracy and depth of image in Weber’s fiberglass door panel skins is that the company’s toolmaking process does not rely on 2-D artwork and acid etching. Rather, it begins with a master model — an actual wooden door — made from solid hardwood, such as oak, cherry, walnut or mahogany, that is selected for its exceptional aesthetics and grain characteristics.
Negative and positive intermediates are cast directly from the wood master. Weber’s patented vapor deposition process then is used to build a nickel shell production tool directly on the positive silicone cast. The resulting tools can withstand high-speed compression molding and, according to Kussen, are “the most accurate means to date for recreating the rich dimensionality of natural wood. Our customers want the authentic grain replication nickel can provide. This gives the final product a higher perceived value.”
“Nickel shells are an excellent fit for tooling that needs to replicate the natural textured products used in the construction industry,” Kussen points out. “The process offers unsurpassed texture reproduction, whether replicating wood, leather, slate or other natural materials.”
Developing the tool
Unlike the wood entry doors they mimic, fiberglass and metal doors are sandwich constructions. Decorative facing panels are adhesively bonded to a rectangular frame (made up of a lock-side stile and a hinge-side stile on the long sides, which permit drilling for attachment of latches, deadbolts and hinges, and top and bottom rails) inside of which is an insulating foam core.
The process of making the fiberglass facing panels begins with development of a master mold. Here, Weber’s model shop sources and selects hardwood and actually builds a door that displays beautiful grain. The master model is checked and approved by the door customer for aesthetics and checked for dimensional accuracy, using a coordinate measuring machine supplied by Canadian Measurement-Metrology Inc. (Mississauga, Ontario, Canada).
Next, Weber’s patented replication process is used to prepare a mandrel for nickel vapor deposition. This is done by casting a silicone moldmaking compound between the support and the master model. The silicone rubber not only accurately duplicates dimensions but also can pick up the finest grain details, resulting in an exact cast of the master model’s woodgrain texture in negative. The silicone negative is then used to make a hand-layed fiberglass cast, which is identical to the wooden master model. This fiberglass cast is then stained and sent to the customer for approval.
Simultaneously, a steel mandrel is CNC-machined on a 5-axis Deckel Maho machining center (Gildemeister AG, Bielefeld, Germany) from CAD data obtained from the wooden door model. However, these data are negatively offset by 1.5 mm/0.060 inch to allow for the space that will be occupied by the silicone skin. The silicone negative is affixed to a support frame, face-side up. The newly completed steel mandrel is placed against the face side, leaving a small gap between the silicone negative skin and the mandrel. Then a second, 1.5-mm/0.060-inch thick silicone skin is cast between the mandrel and the silicone negative, forming a matched positive cast of the door. The positive skin sticks to the steel mandrel and the negative skin is peeled off and saved for use with other castings.
The mandrel with positive skin is then placed in Weber’s NVD chamber, heated to 180°C/356°F, and pure nickel is deposited — a molecule at a time — directly on the positive silicone cast at a rate of 0.25 mm/0.01 inch per hour. The deposition process combines ground nickel powder with carbon dioxide gas in a reactor. The resulting vapor is condensed into a liquid and pumped into the deposition chamber, were it is reheated and vaporized. The vapor adheres to any surface preheated above 180°C/356°F, in this case, the mandrel surface. When the nickel layer reaches a thickness of 10 mm/0.4 inch, the mandrel is removed from the chamber and the nickel shell is carefully stripped off the silicone skin, which usually is damaged during the stripping process. Therefore, if additional nickel shells for multiple molds are desired, a new positive silicone skin must be cast from the silicone negative.
At this point, the nickel shell is carefully stripped from the mandrel, and the latter, which can be reused multiple times to make additional tools, is either cleaned and prepared for a new deposition cycle or stored.
The nickel shell is sent to mold build where it is mounted on a steel backing plate. During this step, undercuts in the woodgrain are removed and any other unwanted imperfections that have transferred from the wood master are corrected. The tool then is trialed on Weber’s compression molding press. SMC parts are molded; some are painted to check for flatness and others are stained to check for appearance. When Weber’s quality team is satisfied with the results, test parts are sent to the customer for approval. When the tool is declared defect-free, it is sent out for chrome plating. Because Weber not only builds but also tests all its nickel tooling, each mold is certified production ready before it leaves Weber’s facility. The nickel-shell tooling is then used to produce the fiberglass facing panels for entry doors.
For door customers that already stamp fiberglass with standard etched-steel tools, Weber claims that a move to nickel tools is a simple drop-in exchange because the nickel molds process the same way and require no special connections or press modifications. For metal door manufacturers that want to expand into fine-grained fiberglass faux wood doors, the process of mating the SMC door skins to the OEM’s frame and foam core is essentially the same as that used for metal skins. The door OEM has the option to purchase its skins directly from Weber, contract with a third party molder for skin production or set up its own production line.
At the door manufacturer’s assembly plant, the SMC skins, together with rails and stiles (made either from solid wood or wood laminate, depending on the price point of the door), are brought together in an assembly jig. The skins and the stile-and-rail wood frame are bonded to each other with structural adhesive. In most cases, a port is left open in the bottom of the door, through which pour-in-place polyurethane foam is injected. The foam forms the door’s insulating core and adheres to skins, rails and stiles, tying the entire structure together as an integral unit. The assembled door “slab” then is drilled and machined to accept hinges, door latches, deadbolts and, if part of the design, glass inserts. Depending on the features to be added, the bottom rail may be machined to attach a weather seal. The door may be factory stained or shipped as-is for staining at the building site. Further, the door slab may be sold to fit an existing opening, or it can be mounted and sold as a prehung door.
Beyond aesthetics, Weber’s door skins offer a host of benefits in common with other composite door constructions. Unlike traditional wood, the composite does not warp, rot, shrink, swell, split or crack. Unlike steel or aluminum, it won’t corrode or dent. Moreover, SMC’s low expansion/contraction characteristics keep doors from sticking in hot or humid weather. Fiberglass door durability and insulative qualities make storm doors — a must with natural wood entry doors — an option rather than a necessity. While they are not maintenance-free, fiberglass doors require less attention over their life spans. Paint and stain adhere far longer to the matrix resin than to wood or metal, because the finish and resin chemistries tend to have greater compatibility.
Depending on its features (graining, stain or paint, raised panels, window inserts) and other items included in a finished entry door system (e.g., transoms and/or sidelites) the retail price of fiberglass doors can range from $300 to more than $5,000 (USD).
Opening some new doors
Weber now is exploring similar applications for its tooling process. Weber already supplies NVD tooling for polymer skins to Mercedes, Nissan, Mazda, GM and Ford programs. “During the 11 years our exclusivity agreement was in force in the door arena,” Sheppard explains, “we concentrated our efforts on the automotive interiors market, another industry where fine-grain replication is important and valued.” Weber contends that NVD tooling can accurately reproduce virtually any texture, and therefore sees opportunities for woodgrain interior trim. Potential applications also include an obvious but as yet untapped piece of the residential home building market: there are currently no composite window frames or siding products that are molded and stained to approximate the natural beauty of wood — making it an area of interest at the company. Further, test tools for fine fiberglass furniture, such as home or boardroom tables, have been produced at Weber, and the company’s sales team is checking customer feedback in that arena as well.