Sometimes even the simplest of everyday items can have a rather extensive materials and manufacturing history. For example, consider the standard wire paper clip. By the 13th century, paper had become the standard material for written documents, and there was a need for attaching pieces together when the assembly did not merit permanent binding in the form of a book. The earliest method of fastening paper was to thread a string, strip of cloth, or ribbon through two parallel slits that had been made in the upper left-hand corner of the papers by a sharp knife. The ends could be sealed with wax to ensure that no substitutions had been made. Pins, made of metal or bone were also used as paper fasteners. Bent-wire paper clips did not become common until the late 1800s. Various designs were introduced, all based on creating two metal surfaces that are pressed together by the elasticity of the metal wire. Various designs were proposed and were marketed with some of the following claims: Does not catch, mutilate, or tear papers Does not get tangled with other clips in the box Holds a thick set of papers Holds papers securely Is thinner and takes less space in files Is easily inserted; Is light in weight and requires less postage Is cheap, because it uses less wire The familiar double-oval ‘‘Gem’’ paper clip was developed around 1900 and has proven to be a satisfactory product for more than a century. For this case study, assume you have been challenged to take the concept and design of the now-standard paper clip and transition it to manufactured reality. The following questions relate to materials selection, process selection, and surface treatments.
1. Material Selection:
a. What are the necessary mechanical properties?
b. What are the necessary physical properties?
c. What would be appropriate families or classes of candidate materials?
d. What specific metal, alloy, or other material would you recommend?
2. Process Selection:
a. Because the design is essentially a bent wire product, describe the features you would specify in purchasing your starting material. Would you want to purchase it in the annealed (weakest with greatest ductility) condition? By positioning the last anneal in the wire-making sequence, the final wire can be produced with a specified amount of residual cold work. This wire would be stronger but less ductile than an annealed product. Would some amount of cold work in your starting wire be a desirable asset? Do you have any concerns about surface finish at this stage of manufacture?
b. In converting the wire to the double-oval paper clip shape, cold work is imparted in the bend regions. The properties will no longer be uniform in the product. Is this acceptable in your final product?
c. In separating the starting wire or finished clip from the long length, sheared ends will be created. Are there any concerns about these ends?
d. Is any form of final heat treatment needed to impart the desired final properties?
3. Surface Treatment (Depending on the material selected in Part 1, it may be necessary to apply some form of coating or surface treatment to suppress corrosion and possible rust marks on the paper.)
a. In addition to corrosion resistance, are there any other surface requirements?
b. What types of surface treatments would you consider to be possibilities?
c. Which of the preceding possibilities would you recommend?
d. At what stage of manufacture do you want to perform the surface treatment and by what method? Give consideration to the following observations:
If applied to the starting wire, the coating will have to have sufficient ductility to endure the shaping operation.
If applied to the starting wire, the sheared ends will not be coated.
If applied to the finished product, the gap between the parallel wires may be bridged or may not be coated.
If the coating is applied at elevated temperature, the coating process may anneal the underlying wire. Some coating operations may affect the ductility of the underlying material, such as hydrogen embrittlement.
Some processes, such as hot dip immersion in molten metal, apply a thicker-than-desired coating. If this is applied earlier in the wire-making process, will the subsequent wire drawing operations maintain the integrity of the coating, or simply wipe off the deposited surface?
e. Would stainless steel be a desirable material for paper clip manufacture? Which type or variety would you recommend (ferritic, austenitic, or martensitic)? Would there be any advantage to having a nonmagnetic austenitic paper clip?
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