Transcript Department of Industrial and Engineering Technology

Department of Industrial and
Engineering Technology
College of Science and Technology
Morehead State University
IET 317
Group 5 Project
Steel Wheel Assembly Work Cell
Group Members:
James Forrest, Lowell Outland, Evan Scott,
Donald Snyder, Matt Wells
Central Motor Wheel of America
(CMWA)
CMWA was established in 1987.
Location: Paris, Kentucky
Employs approximately 500 people.
CMWA Products
OEM supplier of Steel and Aluminum Wheels.
Steel Wheel Customers:
Toyota, Honda, and Hyundai
Aluminum Wheel Customers:
Toyota and Lexus.
Rationale for selecting the
Steel Wheel Assembly Station
 The rationale for our chosen process is simple
 A work cell is a collection of equipment required to
make a single complex part
 The part being produced is the steel wheel
 The Steel Wheel Assembly Station itself has many
parts. (Including: the operators, robotic loaders,
punch press, date stamp device, welders, grinders
and inspection)
 Multiple factors can lead to the occurrence of waste
Rationale cont.
 If diligent lean techniques aren’t practiced in this
work environment, the efficiency of the work cell
could easily deteriorate, wasting valuable
company time and money
 In our efforts to make improvements we analyzed
the processes of the Steel Wheel Assembly
Station
 Identified areas that can be improved
 Made suggestions on how to improve them to
make it a more lean and efficient process
Description of Steel Wheel Assembly Station
The cell is used to assemble two main components of a steel wheel. The two components are the center disk
(wheel center) and the Rim (outer part of the wheel). These parts are placed near an operator at the beginning of the
assembly line. At the beginning of the wheel assembly machine there is one operator. This individual is responsible for
loading the center disk onto the conveyor belt and loading the rim into a small punch press. This punch press is
responsible for punching out the valve stem hole.
The punch press side of the line will be discussed first. The operator grabs a rim (6sec.) and places it onto the
punch press (3sec.), he then activates the press which locks the rim into place and almost simultaneously punches the
hole for the valve stem (2 sec.). Once this operation is finished a mechanical arm pulls the rim onto a conveyor belt
directly in front of the punch press (Note: as the mechanical arm is pulling the rim on to the conveyor the operator is
loading a center disk onto the other line). The rim continues down the conveyor to the stamp station which
automatically positions and clamps the rim (2sec.). This station stamps a date (2sec.) onto the rim so that when the
two parts are welded together the company has a record for quality assurance purposes. On the wheel center side of
the line, the operator has to just load the part so that it travels down and stops near the two weld fixtures. Please note
that the operator is responsible for keeping both conveyor lines full.
At this point two additional operators are simultaneously grabbing a rim or a center disk and loading it into a
weld jig. They then retrieve the opposing part and place it into the jig (20 sec per operator). The operators then
activate the hydraulic clamps (2sec. per operator) to hold the parts together during welding. The welding process
automatically starts as soon as the parts are clamped together. The welding robot is equipped with four MIG (Metal
Inert Gas) guns that feed the wire continuously to create a seamless weld. The pallet that the parts are clamped to
only has to rotate approximately 92 degrees to create the finished weld. The welding process takes about (30sec per
assembly.). Once the parts have been full welded the newly formed wheels are removed by mechanical arms and
placed (8sec.) onto another conveyor belt. The wheels then travel to an automated grinder that grinds/polishes the
welded seam (15sec per wheel).
The wheels then travel on to an inspection station where they are checked for visual and mechanical defects
by a fourth individual. This takes approximately 15-25sec per wheel. There are time variances due to anomalies in the
weld or grind finish that occurs from time to time and also indicated run out noticed on the inspection gage.
The total amount of allowed run out is 0.3mm. This is the end of the journey for the newly minted wheel. The
wheels next stop will be the powder coat/paint booth which is another work cell. Please note that the work cell is full
of parts at all times so conveyor length is not a factor. As it was explained to our group the work cell is not timed
linearly due to the fact that mechanical breakdowns are anticipated especially where the welders and grinders are
concerned. Also, the nozzles must be cleaned and guides replaced after X-amount of wheels are welded.
Work Cell Layout
Steel Wheel Assembly Machine
Wheel
Rim
Rack
Manual
Load/1
person
Punch Press
(Valve Stem
Hole)
Date
Produced
Stamped
on Rim
Finish
Grinder/
Polisher
Wheel
Welder 1
Wheel
Welder 2
Wheel
Centers
Rack
Note: Four Person Work Cell
Manual
Load/1
Person
Manual
Load/1
Person
Inspection
Gage
Manual
offload/
1 person
Time Study Analysis
Step
Time (in seconds)
Acquiring materials
6
Loading Punch Press
3
Small Punch Press (valve stem hole punch)
Stamp Station Load
2
2
Date Stamp (for quality assurance)
Loading Weld Jig
2
20
Activate Hydraulic Clamp
Welding Process**
2 (per operator)
Approx. 30 (per operator)
Remove wheels
8
Grind weld seam
15
Visual inspection*
15-25
Total cycle time
110-120 per assembly
* Time
anomalies due to defects found on assembly during inspection.
**Times inaccurate due to required maintenance
i.e. cleaning nozzle and replacing guards
Suggested Improvements
 Improve /Eliminate Finish Grinder
•Electric motors breaks down
frequently
•Change to more reliable air
motors
 Consider adding a third
welder(identified choke point)
•Move worker from first
station to third welder
•Helps to alleviate choke point
 Rotate conveyor belt 180 degrees
•Will help make the process
more linear(Refer to layout)
 Move closer to paint booth
•Reduces travel time to paint
 Move wok cell closer to punch press
•Use conveyor between punch
press and work cell
•Help speed up production
 Add robot to place parts onto
conveyor at beginning of work cell
•Eliminates need for
manpower at this position
•Helps speed up production
 Condense entire wheel making
operation
•Help speed up production
cost prohibitive
Group Recommendations:
 Recommend changing electric motors
to pneumatic motors for more
reliability
 Recommend moving work cell closer
to paint booth to reduce part travel
time after assembly
 Recommend adding a third welding
machine to eliminate bottleneck in
production
 Recommend rotating welding
machines 180 degrees to create a more
linier product flow as shown by
recommended layout
Recommended /Revised Work Cell Layout
Wheel Assembly Machine
Wheel
Rim
Rack
Manual
Load/1
person
Punch Press
(Valve Stem
Hole)
Date
Produced
Stamped
on Rim
Wheel
Centers
Rack
Note: Four Person Work Cell
Finish
Grinder/
Polisher
Manual
Load
1st
Person
Wheel
Welder 1
Manual
Load
2nd
Person
Wheel
Welder 2
Inspection
Gage
Manual
offload/
1 person
Conclusion
Using Time and Motion Studies are very useful
The assembly cell can be improved
The entire wheel production operation should
be reexamined
Room for cycle time improvements