The overall goal of this procedure is to generate representative material of a larger scale industrial process for model validation and linking macrostructural evolution to processing inputs. This method can help answer key questions in the field of incremental forming with techniques such as how the combination of heat input and high levels of deformation effect in service performance. The main advantage of this technique is that it is cost effective and easily adaptable to different work piece geometries and materials.
The applications of this technique extend toward process model validation and generating small amounts of processed material for mechanical behavior assessment. Though this method can provide insight into metal spinning at elevated temperatures, it can also be applied to similar processes at ambient temperatures. Because of the bespoke nature of the equipment and manual processing involved, visual demonstration method is critical.
As the preparation steps are difficult to learn. To begin this procedure, acquire azcast work pieces machined to the mandrill size. Such that the inner diameter run out is 0.2 milometers.
While the outer diameter retains as much caste surface as possible. Preheat a coffin furnace able to receive the entire workpiece to 135 degrees Celsius. Clean the workpiece with de greaser.
And place it in the furnace for an hour to prepare for thermal barrier coating application. After one hour, rapidly remove the workpiece from the furnace and place it on a coating jig. Using an automotive type paint sprayer, apply a thin layer of thermal barrier dye coating to the inner diameter.
After preparing the experimental apparatus, loosen the jam nut assembly on the roller stand with a wrench. Set the approach or attack angle on the roller assembly using a tool maker's protractor, and tighten both internal and external nuts. Next, assemble the three clamp assebmlies by first engaging the M12 shoulder bolt to connect element two to the clamp bracket.
Inspect for any thermal distortion which will prevent element two from smoothly running against the clamp bracket. To ensure that element two moves freely, lightly sand the contact surfaces with dried 320 grit silicone carbide paper. Apply a thin layer of high temperature molybdenum based lubricant with a cloth as needed.
Move the roller tool stand completely away from the mandrel towards the spindle. Move the tail stock in centered to be clear of the mandrel. Then manually slide the workpiece onto the mandrle, ensuring even engagement.
Now assemble the clamps on to the mandrle by engaging the tapered dye pins and hand tightening the M16 bolts running though the mandrle into the clamp blocks. Ensure that there is even pressure being applied by rotating and manually tightening. Followed by a pneumatic impact wrench set to 50 newton meters.
Start the heating system and immediately start the mandrel rotating at 20 rpm. Extinguish the heating system and stop the rotation of the mandrel, such that the first clamp is accessible with an impact or manual wrench. Within 30 seconds, tighten all clamps with the impact or manual wrench, and record the surface temperature of the workpiece in three locations along the length of the forming region with a read type thermocouple probe.
Next move the roller axially and radially, into position for forming. With the heating system on, increase the rotation rate of the lathe to the intended forming speed and engage the roller to a preset depth into the workpiece. Then, activate the screw cutting feed to move the roller axially along the length of the workpiece.
After each forming pass, ensure that the temperature does not drop below the optimal forming temperature, by stopping the mandrel and checking the temperature with the read type thermocouple probe. Once the desired level of deformation has been obtained, stop the heating system, undo all the clamps, and disengage the tail stock to obtain clearance for workpiece removal. Gently tap the workpiece with a piece of brass to separate it from the mandrel.
If this proves to be ineffective, reengage the heating system and rotate the mandrel at 20 rpm with gentle tapping, until the blank separates. Finally, using an appropriate manipulation tool such as heavily insulated gloves, quench the workpiece in water at 60 degrees Celsius to prevent further aging. A representative transient thermal response of the aluminum A356 workpieces that underwent a preheating cycle, is shown here.
Cross sections and micro structure of the azcast blank and those obtained in multi pass sample are shown here. The azcast microstructures, refined by the process with dendritic features barely discernible. The inter dendritic eutectic is broken up by the deformation imposed, creating a more homogenous micro structure and improving the overall ductility as well as fatigue and fracture properties of the component.
Once mastered, this technique can done in 30 minutes with two hours of preparation, if it's performed properly. When attempting this procedure it's important to walk through each of the steps on a dry run, as thermal processes can not be stopped or paused. Following this procedure, further heat treatment, metallography, and mechanical testing can be performed in order to answer additional questions regarding micro structural evolution during a parts manufacturing process.
After its development, we envision this type of technique to pave the way for researchers in the field of materials processing, to explore simplified methods for larger scale industrial processes. After watching this video you should have a good understanding of how to obtain indicative processing conditions for warm spinning of caste aluminum, including the critical aspects of workpiece preparation, and performing operations. It's very important to remember that working with machine tools at elevated temperatures can be extremely hazardous and precaution such as using appropriate personal protection equipment should always be taken while performing this procedure.
