Extrusion Blow Molded Pitchfork to Reduce Cost of Wooden and Metal Pitchforks
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PLET 323 EXTRUSION BLOW MOLDED PITCHFORK TO REDUCE COST OF WOODEN AND METAL PITCHFORKS BOBBI DOUBET AND JOSHUA STANFORD Penn State Erie, The Behrend College December 18, 2019 Introduction The product that will be created is a five-tined pitchfork. This fork will not be made into multiple pieces. This fork will be molded as a single piece. The fork will compose of a long, thin handle so that the user can easily grab the handle while using it. Instead of the plastic part ending at the bottom of the fork where the metal tines would start, the fork will morph into the fork portion. All five tines of the pitchfork will be made from plastic as well. As in any other extrusion blow molded part, this part will be hollow. For this part to be hollow, a small hole will be located on the top of the handle, so that the pressurized air will be allowed to blow the plastic so that it will conform to the mold surface. For the entire part to be hollow and to have a constant wall thickness throughout the part, the tines of the fork may have a thicker diameter so it will not be a solid little rod of plastic going all the way down the length of the tine. Even though the tines will be a larger relative diameter, the tips of the tines will still be sharp enough so that the fork can stab into the hay or into the dirt. A different design will be used when creating the tines. Old designs of forks show the tines being small in diameter and the tines very far apart. Stuff can fall through those gaps. In this design, the tines will be morphed together in a web-like structure to add more surface area to the part. This surface area will decrease the chance of substance falling off the fork. There will still be tines at the bottom of the fork part, but the top of the fork will look like a shovel. This will then morph into the thinner tines. This design will allow the fork to hold more material without it falling through the gaps, but also allows it to be used as a shovel, while still being able to scrape off manure behind a farm animal or being able to dig it into a pile of hay. Plus, having the webbing at the top of the fork part will also help in the design aspect as well, by creating a way for the part to be hollow and to create a passageway for the pressurized air to go down the tines of the fork. Figure 1 shows the modern pitchfork with a wooden handle and five metal tines and Figure 2 shows the preliminary design sketches of the hollow pitchfork [1]. Figure 1: Modern Pitchfork Figure 2: Detailed Designs of Pitchfork Pitchforks were first conceived around the time of the Middle Ages. These forks were used to aid the farmers in haying their animals and bedding their animals with hay and straw. These pitchforks were only made from wood, which lacked the metal tines of later pitchforks [2]. In the European Middle Ages, these pitchforks were sometimes used as improvised weapons by people who were poor enough to not afford higher end weapons, such as swords or guns [2]. When a man had to fight in the army, sometimes the pitchfork was the only weapon he had to defend himself. The pitchfork also became the weapon of choice for gangs of peasants and farmer and angry mobs [2]. There are multiple variations of forks. The number of tines a fork can have as few as two tines and can reach up to ten tines [3]. Eventually, metal was used to forge the tines of the fork. As a molten material, the tines would be shaped and cooled. Then the connector of the tines was forged to hook onto the wooden handle. These would eventually be screwed in by washers and bolts for easy changing of handles when the wooden handles eventually broke. In 1907, a patent was created by a man by the name of John C. Frees that allowed the pitchfork to be used in loading manure [4]. He designed the handle to be sturdier at the bottom of the fork so the load of manure or dirt could be applied. The tines also became curved to act like a shovel to pick up manure from the straw [4]. In the same year, another man named Arthur Holmes Knox patented an invention of the fork that allowed the material to slide off the tines of the fork without having clinging material left over [5]. Figure 1: Patent of Pitchfork by Frees [4] Figure 2: Patent of Pitchfork by Knox [5] Pitchforks today are still made with wood, such as pine, birch or ash, and made with metals and alloys such as steel and iron. Plastic is being used to make either the handles or the tines of forks. The following image is variation of the pitchfork that acts as a scooper [6]. The scooper is made of plastic, but the handle is made of metal. These products can also have over molded parts. Forks currently made with wooden handles and metal tines use these materials because they are made to be used for heavy-duty use. They are built to last a long time until the handle breaks off. Handles can be replaced. Plastic is being incorporated into the making of pitchforks to make them more lightweight but strong and to decrease the cost of a pitchfork. Figure 3: Scooper Pitchfork [6] Currently, extrusion blow molding is not used to create the whole pitchfork. Pitchforks with plastic still have either wooden or metal handles that are either machined or forged. The plastic parts are either made by injection molding and connecting the tines and the handle through secondary operations or are over molded onto the handles. One example that was found of a fork made entirely out of plastic was still being assembled through secondary operations after the pieces were created. The fork being designed in this project will be one hollow continuous piece. Application Extrusion blow molding will work very well with this new design of a pitchfork, because it is hollow. One of the main design features of this pitchfork is that it will be hollow. A hollow part will reduce the overall weight of the part. Plastic weighs a lot less than wood or metal, but the right material will still give it the strength it needs to perform its tasks. Producing the whole part out of plastic will reduce any costs associated with secondary operations, over molding, and assembling multiple parts together. The cost of molding multiple parts to be assembled into one working product will be the material cost used in both parts, the tooling cost of the two molds to make the plastic handle and the plastic tines, and the cost it takes to assemble the whole part, in other words, the entire time cost. Within the time cost parameter, there will be added time to assemble the two parts together with nuts, bolts and washers, adding an extra cost to the time cost. With extrusion blow molding, the secondary operation costs with two parts molded to be put together will not exist because the whole part will be created in one process. The only secondary operation that will occur on this part is to trim any excess plastic off from the fork. Extrusion blow molding will also reduce the cost of the wood and metal being used. When you buy a wooden handled fork with metal tines, the price of the fork ranges from as low as $20 to around $60, depending on what the fork is made out of, the length of the handle, and where the fork is being sold at. Sometimes it might be around $20 just for the wooden handle. The plastic-based scoopers cost considerably less, ranging from around $14 to $35. Just substituting plastic for wood and metal reduces the price, making it more affordable to the consumers and farmers. Extrusion blow molding, however, will reduce costs even further than that. For reducing the over molding costs associated with over molding a set of tines to a metal handle, extrusion blow molding will eliminate the tooling cost of the mold used in over molding the part. Any material costs used to make the over molded part will be eliminated as well. The time and assembly cost to make the over molded component and to assemble the two parts together will not exist in blow molding because the whole part is created in one shot. Plus, extrusion blow molding will reduce the amount of internal stresses the polymer and part will witness if the fork was being over molded. When over molding a component overtop of an existing part, the existing part will undergo another injection molding process, which can create internal stresses that can affect how the product will perform in its lifetime of use. Extrusion blow molding is also used to create large parts with ease. The fork is not very large when it comes to the width and depth of the part, but the fork will be a long part, possibly over five feet long in total length. Compared to injection molding, both the injection mold and the extrusion blow mold will be approximately the same size. However, with the injection mold, a runner system must be created and added to the part, so the polymer can fill the part evenly.