Department of Industrial and Engineering Technology

College of Science and Technology

Morehead State University IET 317

Group 5 Project

Group Members: James Forrest, Lowell Outland, Evan Scott,

Donald Snyder, Matt Wells

Steel Wheel Assembly Work Cell

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

WheelRim

Rack

Wheel Centers

Rack

Punch Press(Valve Stem

Hole)

Date Produced Stamped on Rim

Wheel Welder 1

Wheel Welder 2

Finish Grinder/Polisher

Inspection Gage

Manual Load/1 Person

ManualLoad/1 person

Manual offload/1 person

Note: Four Person Work Cell

Manual Load/1Person

Time Study AnalysisStep Time (in seconds)

Acquiring materials 6

Loading Punch Press 3

Small Punch Press (valve stem hole punch) 2Stamp Station Load 2Date Stamp (for quality assurance) 2Loading Weld Jig 20

Activate Hydraulic Clamp 2 (per operator)Welding Process** Approx. 30 (per operator)

Remove wheels 8Grind 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

Rotate conveyor belt 180 degrees•Will help make the process more linear(Refer to layout)

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

Consider adding a third welder(identified choke point)

•Move worker from first station to third

welder•Helps to alleviate choke

point

Move closer to paint booth •Reduces travel time to

paint

Condense entire wheel making operation

•Help speed up production cost prohibitive

Group Recommendations:

Recommend changing electric motors to pneumatic motors for more reliabilityRecommend moving work cell closer to paint booth to reduce part travel time after assembly Recommend adding a third welding machine to eliminate bottleneck in productionRecommend 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

WheelRim

Rack

Wheel Centers

Rack

Punch Press(Valve Stem

Hole)

Date Produced Stamped on Rim

Wheel Welder 1

Wheel Welder 2

Finish Grinder/Polisher

Inspection Gage

Manual Load1st

Person

ManualLoad/1 person

Manual offload/1 person

Note: Four Person Work Cell

Manual Load2nd

Person

ConclusionUsing 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