The lack of knowledge about FSW parameters and their interaction
is the motivation behind this study. The objective of this work
is to establish a steady-state model that describes relationships
between FSW process inputs (feed rate, spindle speed, tool depth)
and various measurable outputs for 7075 aluminum.
Despite the in-depth research over the past decade,
the fundamentals of the FSW process are not well understood.
There is a lack of understanding regarding essential parameters,
how parameters affect one another, and how they might
be utilized to best control the FSW process. Most openly
published literature on weld parameter interaction come
from observations made during experiments. Most have neglected
the most fundamental aspects of the process, and lack
the breadth to instill any confidence in the trends observed.
Interactions between weld parameters have not been studied.
In-depth studies which focus on how FSW parameters affect
the process, resulting weld qualities and properties are
required. This is illustrated in Figure 1. This information
is crucial in order to better understand the process fundamental,
influence tool design, and guide better process control
Figure 1. Schematic illustrating the parameters to be investigated.
This thesis work will investigate the relationships
between different FSW parameters in 7075-T7351 aluminum.
The goal is to develop a steady state model that establishes
relationships between multiple input and multiple outputs.
As part of this work, the author will investigate change
in tool temperature, loads and torques as a function of
input parameters and explore interactions.
7075 aluminum (3/8” thick) will be used with a standard
tool with 0.25-inch pin length. The tool is instrumented
with 3 thermocouples. All processing will be performed
on a custom built, instrumented friction stir welding
machine which records many process variables. A 3-factor,
4-level Design of Experiments will be used and data analysis
will be sufficient so the conclusions will be statistically
sound. Feed rate, spindle speed, and tool depth will be
varied throughout the experiments since these are the
variables that are controlled directly. The welds will
be allowed to reach steady state for a given set of input
conditions, and the multiple outputs will be recorded
Status of Program
Figure 2. Practice weld and machine set up
will begin shortly for this study. However, new insight
has already been discovered about FSW while the experimental
setup (shown in Figure 2) has been developed and tested.
For example, thermal couple imbedded in the tool revealed
that the center tip of the pin is the hottest part of
the tool. This is contrary to many papers and conference
discussions which believe the outer diameter of the tool
to be the hottest location. Many new discoveries are anticipated
based on the instrumentation, scope of work and analysis
to be performed.
This study aids in understanding how parameter inputs
affect the process performance and reliability. Methodology
developed in this thesis will be used to investigate FSW
parameters for high temperature materials and other tools.
Furthermore, the relevance of this project comes into
play for those who would want to automate FSW in a production
facility. FSW parameter studies also help provide a general
understanding of the FSW process which can help with the
development and use of new materials, new tool designs,
and new applications.