Patent Application
20220048434
The present invention relates to a method of manufacturing a hitch step apparatus that may be installed in a hitch receiver of a vehicle. The inventive method includes a multi-step pressurization process which results in a hitch step having high strength, low warpage and reduced air pockets when compared to parts manufactured by prior art manufacturing processes.
The present invention is particularly intended for use on commercial vehicles, which may include a step for the vehicle operator to step up into the vehicle cab or to step up onto the side of the vehicle to secure a load or check the engine, for example. Prior art steps are large devices having intricate framing to support the weight of a vehicle operator without deforming. Accordingly, there is a need for a method of manufacturing a streamlined device that supports the weight of a vehicle operator.
The present invention provides a hitch step that may be secured to a vehicle in a hitch receiver, and a method of manufacturing the same, that overcomes the disadvantages of the prior art. The present invention provides a multi-step pressurization method that produces a strong, compact hitch step that is cost effect to manufacture.
The hitch step of the present invention, in one preferred embodiment, is a solid one piece Aluminum die cast step sized to be secured in a two inch receiver that is installed on many types of today's vehicles. The inventive hitch step is designed to be easily and releasably plugged into the receiver socket of the hitch receiver on a vehicle. The hitch step can be extended or retracted in different positions with respect to the hitch receiver. The tread pattern is designed so as to be easy to clean up and to provide a gripping texture. The hitch step is reinforced to handle a two-to-one weight safety factor. The hitch step is designed with smooth corners. The hitch step can be manufactured as cast or may be finished in a variety of different finishes. The hitch step can be made from several different Alloy combinations of Aluminum or other durable materials as may be desired. The inventive hitch step and the die casting process is described below.
One preferred embodiment of the present invention includes a die casting process which may include an aluminum melting phase, a die cast injection phase, a solidification phase and a part removal phase. In particular, a cold chamber die cast injection phase includes a casting shot profile that is comprised of multiple phases. When metal is transferred from the crucible to the machine, it is delivered by a ladling system and poured into a cylindrical shot sleeve. In the typical die casting process, that sleeve is only partially filled with metal, in our case aluminum. In order to get the material from the sleeve into the cavity, it is pushed by a plunger 62. The plunger's position relative to time and the pressure it applies on the metal are what defines its shot profile. The first phase of the shot profile is the slow shot. The purpose of this phase is to begin moving the molten metal toward the die cavity at a slow enough velocity so as to not spit molten metal out of the pour hole that it was delivered into. The next phase of the profile is the intermediate shot. The purpose of this phase is to force the entrapped air in the shot sleeve out by filling it with the molten aluminum. This phase takes place at a set velocity so as to develop a wave front that does not entrap any excessive air in the metal. The next phase is the fast shot. During this phase, the metal is accelerated to a much higher velocity and delivered into the cavity. The high velocity is used to fill the cavity quickly before the metal solidifies. Once the fast shot phase is complete, the plunger comes to a near stop and the intensification phase begins. During this phase, the cavity is full so high pressure is applied to the metal instead of the force of the piston moving at a high velocity. This high metal pressure serves to compensate for shrinkage porosity that inherently develops as the casting is solidified. These settings are controlled with a human machine interface (HMI) on the die cast machine panel box and are generally left alone once the machine is in steady state and making quality parts. The present invention may also integrate extra features into the shot profile such as a deceleration phase. The die casting method should be designed around what machines are available and their features. Since every die casting job is different, there are no specific quantities that apply across the board. Pressures, velocities, etc. may vary for different types of parts and materials used, and there may be a range of acceptable values depending on customer demands and many other variables. The process will now be described in more detail. However, Applicant has found that including four phases within the injection phase will result in manufactured parts having properties superior to parts manufactured by prior art methods.
The die casting method of the present invention involves heating a material, such as aluminum, well into its liquid phase for injection. The melting point of aluminum is specifically dependent on its alloy, but generally the full liquid phase is met at above 1,100 degrees Fahrenheit. In the present invention, the aluminum temperature is generally taken several hundred degrees higher than this to assure that alloy chemistry is maintained. The aluminum is melted in furnaces using ingots purchased from qualified suppliers and may also include re-melt excess material from the casting process. Once melted and taken up to the desired temperature, the aluminum is ready to be injected into the mold.
When a die cast machine is ready for its next cycle, i.e., when the die halves 50 and 52 are closed, secured together, and ready for shot, an automated ladle 60 removes a prescribed volume of molten material 64, such as molten aluminum 64, from a holding furnace 66 and pours it into the shot sleeve or chamber 58. Once pouring is complete, the injection phase begins.
The first injection phase is the slow shot phase where the shot plunger or ram 62 moves forward in a direction 70 at a low speed to begin pushing air out of the sleeve 68 and to move past the pour hole 72 in the sleeve. After a prescribed distance 74, such as past pour hole 72 in shot sleeve 68, depending on process set up, the plunger 62 enters an intermediate speed phase where the speed is increased to fill the runner system 76 with aluminum. Once this is complete, the machine enters a fast shot phase where velocity is greatly increased to fill the part cavity 78 with aluminum. After the part cavity 78 is filled and the plunger 62 has stopped moving, the hydraulic cylinder 80 pushing the plunger 62 is pressurized to a higher pressure. This intensification or squeeze phase takes the aluminum pressure within the die 42 to over 10,000 psi to ensure proper fill and to minimize aluminum shrinkage problems.
The die cast machine 34 continues to hold the die halves 50 and 52 together at its rated tonnage during the solidification phase. The die cast dies are water or oil cooled to remove heat from the molten material, such as aluminum, during solidification. After a prescribed amount of time, where the resulting casting, i.e., the solidified material in the die, has sufficiently solidified and cooled, the die opens the ejector or moving half 50 of the die 42.
Once the machine is fully open, the die cast ejection is triggered. Die cast dies 42 have ejector pins 54 that extend through the part cavity 78. These pins 54 are mounted in an ejector plate 82 on the back of the die cast tool. Once ejection has moved fully forward, the casting 84 is removed by an operator or an automated machine or robot 86. The casting 84 is cooled to a temperature suitable for subsequent operations. This cooling can be achieved with a cooling device 88 such as a fan driven air cooling device or the unfinished cast part 84 can be water quenched. Quenching reduces casting temperature more rapidly, but the process must be controlled to prevent part distortion.
In one preferred method the total length the piston will travel in direction 70 is in a range of 10 to 20 inches, and in a preferred method is approximately 16 ¾ inches. The timing of the entire piston movement phase is in a range of 10 to 60 seconds, and in a preferred method is approximately 15 seconds. The shot pressure, which is how much pressure the molten material is subjected to during the intensification phase, is in a range of 1000 PSI to 1500 PSI, and in a preferred method, is 1200 PSI. The temperature of the molten aluminum is in a range of 1100 to 1500 degrees Fahrenheit, and in a preferred method is approximately 1275 degrees Fahrenheit. The cooling process may be in a range of 3 to 10 minutes, and in a preferred method is approximately 5 minutes after the part is pulled from the mold.
In a preferred embodiment utilizing aluminum to cast a part, during the first, or slow, shot phase the piston 62 will move in direction 70 at a speed in a range of 0.1 to 3 inches per second, and in one embodiment, will move at approximately 1 inch per second. During the second, or fast, shot phase the piston 62 will move in direction 70 at a speed in a range of 5 to 20 inches per second, and in one embodiment, will move at approximately 11 inches per second. During the third, or start of impact, phase the piston 62 will move in direction 70 at a speed in a range of 15 to 25 inches per second, and in one embodiment, will move at approximately 18 inches per second. During the fourth, or intensification, phase the piston 62 will move at a speed in a range of 10 to 20 inches per second, and in one embodiment, will move at approximately 16 inches per second.
As may be understood from the above description and drawings, the present invention has many advantages over prior art hitch steps and manufacturing processes. In the above description numerous details have been set forth in order to provide a more through understanding of the present invention. It will be obvious, however, to one skilled in the art that the present invention may be practiced using other equivalent designs and method steps.
