2018 ARP Catalog rev4
10 800-826-3045 THE COMPANY THE “AEROSPACE QUALITY” MYTH In areas from hose ends to engine fasteners the terms “Aerospace material and Aerospace Quality” have become buzz words imply- ing the very best in design, materials and quality control. “It isn’t necessarily so”, says Gary Holzapfel, founder and CEO of Santa Paula, California based ARP, Inc. ARP (Automotive Racing Products) supplies extremely high strength and fatigue resistant threaded engine fasteners to NASCAR, IndyCar, NHRA, IMSA TUDOR and Formula 1 engine builders and manufactur- ers. Holzapfel explained his reasons in an interview with Carroll Smith. Smith: “Gary, do you believe that the term “aerospace qual- ity” is over rated in the specialty fastener industry?” “Yes I do. First of all, the term is meaningless. Any AMS (Aerospace Material Specification) material must be matched to the specific application. As an example, some airframe bolts (AN3-20) are legitimate “aerospace parts” and are very well suit- ed for the low stress applications for which they were designed. But with a minimum ultimate tensile strength of 125,000 psi, and a relatively low temperature limit, they would be completely unsuitable for use in a racing engine. We started out in the aerospace fastener business and we understand it. That’s why we’re not in it any longer. What is not generally understood about aerospace fasteners is that the fastener manufacturers do not design the product. The nuts, bolts and studs are spec’d by the airframe or engine designers and put out for bid. As long as the supplier certifies that the product meets the minimum requirement of the specification and it passes the customer’s inspection procedures, low bid wins.” Smith: “Are you implying that the aerospace fastener man- ufacturers cut corners in order to win contracts?” “No, it’s a matter of manufacturing goals and simple econom- ics. The aerospace market is price dominated. In order to get the contract, the fastener manufacturer’s goal is to meet the specifica- tion at the least cost, not to produce the best possible part. This means that they are going to use the least expensive steel and manufacturing processes that will meet the specification. There is nothing wrong with this approach. It certainly does not mean that certified aerospace fasteners are unsafe in any aspect. They will do the job for which they were designed. There is another factor. Airframe and aircraft engine manu- facturers design their components to a very high margin of safety. Further, aerospace structures are designed to be “fail safe.” There is a back up or second line of defense for virtually every structural component so that an isolated failure will not lead to disaster. They are also subjected to frequent and rigorous inspections.” Smith: “What’s different about motor racing?” “Quite a lot, really. While the demands for strength, fatigue resistance and quality control can be similar, and the assembly and inspection procedures in racing can be as rigorous as aero- space, in professional racing very few parts are over designed and there are no fail safe features. There are no back up provisions for component failure. A failed (or even loosened) nut or bolt in a racing engine means disaster – instant catastrophic failure. An expensive engine is destroyed and a race is lost. That is why random failures are unacceptable in motor racing, and why aerospace standards should be only a starting point. This means that a specialist in the production of high performance engine fasteners must design and manufacture the very best fas- teners that can be produced.” Smith: “So where does the production for a new racing fastener begin?” “The design process begins with the customer’s requirements the operating conditions and loads to be expected, the packaging con- straints and the weight and cost targets. This allows us to select the optimum material for the part, and to do the initial mechanical design. There is more to material selec- tion than simply choosing the best alloy. It means using only the cleanest and purest steel available, which, in turn, means researching to identify the best and most modern steel mills. It means work- ing closely with the mills both to insure consistent quality and to develop new and better alloys. There are not only a myriad of alloys to choose from; but for each alloy there are several grades of “aircraft specification” steel wire from which fasteners can be made. We believe that only the top (and most expensive) grade – shaved-seamless, guaranteed defect-free – is suitable for racing engine applications. We also believe that samples from each batch should be sub- jected to complete metallurgical inspection.” Smith: “How many alloys do you work with?” “We are currently producing fasteners from at least 10 differ- ent steel alloys from 8740 chrome moly to the very high strength chromium-cobalt-nickel alloys such as Custom Age 625+. We also use stainless steel and titanium. With UTSs (Ultimate Tensile Strength) from 180,000 to 270,000 psi, we can suit the material to the job and the customer’s cost restraints. We are continually researching and experimenting with new alloys and manufactur- ing processes – some with all around better strength and fatigue properties.” Smith: “Once the design work is done and material has been selected, what’s next?” “Next comes the actual process of manufacturing. It goes without saying that all high strength bolts must have rolled rather than cut threads, and that the threads must be rolled after heat-treatment. But there is more to it. The old saying to the effect of, “If you are doing something in a particular way because that’s the way it has always been done, the chances are that you are doing it wrong,” holds true in fastener technology. Technology advances, and we have to advance with it. All of the manufacturing processes should be subject to continuous experimentation and development. As an example, with some alloys, cold heading produces a better product than hot heading, and vice versa. The number and force of the blows of the cold heading machine can make a significant difference in the quality of the end product. Excessive numbers of blows can lead to voids in the bolt head. ARP, in fact, holds significant patents on cold heading procedures for the higher nickel and cobalt based alloys. In a typical aerospace manufacturing process, these alloys are hot headed from bars, reduced in diameter from 48 to 50% by cold drawing, resulting in a hardness of about Rockwell C46 which is too hard for cold heading. So, the blanks are locally induction heated in a very narrow temperature envelope and hot headed. If care is not taken the process can reduce the hardness of the bolt head and the area immediately under it as much as 3 to 5 This spring was wound from un-shaved material. It failed on the seam line.
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