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The innovation of materials, machines and tools and processes gave birth to SRIM truck compartment

the high-density structure rim (hd-srim) process for vehicles has developed from its initial use as a bumper to today's full-size pickup truck compartment and tailgate. The progress in polyurethane chemical properties, robot pre molding process and refinement of molding technology, all of which make the commercial production of large and complex structural parts possible. This article introduces the technical progress behind this title in detail

in the middle of 2001, two years after the first announcement, General Motors began to provide a new 6.5-length rim composite compartment and tailgate system called "protec" as an option for full-size Chevrolet Silverado pickup trucks. By the end of 2001, 1000 vehicles had been produced and sent to dealers. With regard to the current planned output, the company spokesman only said that GM's intention was to "produce as much as the market needs."

srim composite car is the result of the joint efforts of General Motors and polyurethane suppliers (Bayer company in Pittsburgh), glass fiber suppliers (Owens Corning company in Toledo, Ohio), mechanical equipment manufacturers (Canon USA company in cranbery Town, Pennsylvania) and primary molding and assembly suppliers (Merrian automotive systems company in Huntington, Indiana)

compared with the traditional steel car with hot pressed plastic lining, the pressure cannot rise during the working process. 1 This kind of disadvantage is that the car commonly used in the inspection is completely different. The whole protec car unit is made of composite materials. The protective grille of the carriage and the outer panel of the tailgate are made of reinforced rim (RRIM, mainly mica filled polyurea). The one-piece carriage and the inner side of the tailgate are made of 50% long glass fiber reinforced polyurethane SRIM composites. The interior of the carriage and tailgate is painted with black "sputter paint", which provides a tough, fine-grained surface texture and UV protection. Using SRIM and RRIM composites can reduce the weight of the whole vehicle by about 50 pounds. The tailgate alone is 15 pounds lighter than steel products

automatic preform

the robot automatic preform system adopted by meridian company is made in Italy based on an improved version of the "P4" system (programmable electric preform process) developed by Owens Corning company in the early 1990s. The main change is the introduction of a new glass fiber reinforcement and "fiber binder" system called preformed roving by Owens Corning

Thomas Miller, the project leader of Owens Corning, explained that this new roving system contains stranded yarn coated with adhesive mixed with glass fiber reinforcement. "Fiber adhesive" stranded yarn is a kind of pre catalytic thermosetting polyester adhesive coated on glass fiber carrier fiber. When heated during the preform curing operation, the binder first melts on the glass fiber around it, and then solidifies and hardens. Roving contains 5% by weight of binder

when the pickup car is preformed, four bundles of glass fiber roving twisted yarn are fed into the robot arm with the cutting head. Meridian uses four robots to lay roving, and each robot has two cut ends. Therefore, a total of 32 roving strands will be cut short and sent to the preform device

Gene symosko, the coordinator of Bayer's technical service department, said that cutting the head cut the roving into 3in lengths and let them fall on the metal with the same size and shape as the final carriage. According to meridian Project Engineer pat DePalma, each cutting head can lay 4.4 glass fibers on the metal every minute

the air is pumped through the metal eyelets to make the glass fiber cling to the metal surface. Then, the metal is rotated into a 500ft long heating box to solidify the adhesive. The operation cycle time of preform is about 3min, while it takes 8min to adopt the traditional short cut glass fiber preform process

DePalma of meridian said that it closed 770.5 down 0.13%. The "fiber adhesive" process eliminated the problems encountered in the previous SRIM pre molding process of water-based lotion adhesive, because the lotion adhesive is very messy, difficult to manipulate, and the results are not uniform. Bayer symosko added that the weight fluctuation range of preforms is far less than 10%, while the weight fluctuation range of preforms made by traditional processes is 20%, thanks to the use of robot control technology and new adhesives

"extrusion molding" process

after the cured preform is taken out of the heating box, a robot automatically transfers it from the preform to a clamping station, where the preform is manually placed on the core of the SRIM mold

injection molding or "extrusion molding" process is adopted for the molding of polyurethane composites. Injection equipment is a traditional measuring machine used for RRIM surface processing, that is, the he180 spray gun/syringe device of Canon company

the machine used is a 2000t dieffenbacher SMC press, which has been modified for the processing of polyurethane. The main modification is to add a reciprocating bed. The reciprocating bed removes the mold core from the mold and places the preform on the mold, thus ensuring the safety of the operator to the greatest extent. When the preform is in place, the reciprocating bed returns to the press, and the upper half of the mold falls on the surface of the preform, but keep the mold open for 0.5 inches

rim machines pour liquid materials on preforms. When a batch of 35 ~ 40 materials is poured, the mold is completely closed, and the resin is extruded into the glass fiber with the help of the pressure of the press, rather than the injection pressure of the material. It is said that this method can make the material evenly distributed and prevent the glass fiber from moving or being "washed out" near the injection port. The operation cycle time from rim metering unit to mold closing is about 10s

the whole process of car preform and molding produces a final product every 3 minutes. After demoulding and trimming, put the parts into the heating box for post curing. The 14 metal parts, including the support rail used to install the carriage to the chassis, are bonded to the carriage

hd-srim can be sprayed with general automobile finish paint, and no special operation is required except surface cleaning. The surface of the car and tailgate accessories is roughened and sprayed with low gloss black paint

for example, Meridian's pickup car production system includes a preform machine, two presses, a bonding machine and a coating production line, which can produce 350 cars per day

interaction between polyurethane and glass fiber

one of the main lessons learned in the development of cars is about the interaction between polyurethane substrate and glass fiber reinforcement. Preform determines the final physical properties of SRIM composites, and its glass fiber type, adhesive type and glass fiber distribution uniformity will affect the ability of polyurethane to wet the surface of glass fiber

due to poor wetting, voids are generated, resulting in bubbles in the post curing process of composites, which is a problem encountered in the early stage of the car development plan. For this reason, Bayer has developed baydur 425 IMR (in mold precipitation) polyurethane system, which has better fluidity and heat resistance

the long gel time of this system enables it to fill the whole part before the molecular weight becomes large. It allows a longer filling time (10 ~ 12s) to improve the initial humidity of the glass fiber. Bayer company combines slow gel with fast curing, so that parts can be demoulded quickly. In addition, baydur 425 IMR can withstand the 3-precision 50oF conditions required by the bonding process after demoulding, while the temperature that the traditional SRIM polyurethane system can withstand is not more than 250of. Symosko of Bayer pointed out that this special heat resistance increased the potential of 425 IMR system to be used as under hood parts

Bayer and meridian invented two processes, which can further improve the quality of the carriage. The first skill is to vacuumize the mold before clamping, so as to reduce the amount of gas remaining, which is conducive to the flow test and utilization of polyurethane, and improve the wetting degree of fiber, so as to make the produced parts have excellent physical properties. The second technique is to use higher forming pressure, which helps the resin penetrate into the preform and reduces the size of the gap in the final part


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