Rear Corner Post Project

Defect Analysis & Correction

Problem Definition

In 2008, the average weekly repacks of product due to broken corner posts & film issues ran about 80 per week until week 23.

Cost to repack a unit due to these problems at normal levels is $800/week.

In weeks 23 & 24, this number of repacks spiked to 400 & 1000 respectively. This created a cost of $4000 to $10000 per week.

Project Phases

Phase 1 – Data Collection & Analysis Collect sufficient data to identify all possible root causes of the

problem. Define causes to be addressed & make any short term corrections

to improve part robustness. Phase 2 – Develop part testing

Develop a procedure to test the current & future parts to determine any improvement from changes that are made.

Test should be able to be done on-site and in a relatively short period of time. This will allow for multiple improvement iterations within a day.

Phase 3 – Process Corrections & Testing Develop corrections to improve part robustness. Prioritize which corrections would have the greatest effect &

complete first or in a parallel manner. Retest production parts after each change is made and document

the initial improvement. Correlate the change with data received from warehouse regarding recrates.

Phase 1

Data Collection & Analysis

Data Collection

Analysis of warehouse data showed the following: 93% of the total repacks were due to the rear corner

posts. 79% of the total repacks were due specifically to the

left rear corner post. 77% of the total repacks were on products built on

Lines 1 & 3. This total broke down as follows: 41% for Line 1 36.3% for Line 3

Data Analysis

Since 93% of the repacks were for the rear corner posts, a process variable such as material and/or a design related issue is suspect.

Since 79% of the repacks were specifically for the left corner post, something that is happening to the left side of the product and not the right needs to be investigated.

Since 77% of the repacks were on Lines 1 & 3 products, a variable common to these two lines and not to Line 2 is suspect.

Process Analysis & Changes

Visual inspection of parts showed several areas where the part did not fully form. Air pockets were indicated. This pointed to insufficient venting.

Design Analysis & Changes

A review of the design showed that the interior corner of the part is formed to a sharp right angle of 90 degrees.

Since this interior corner receives the bulk of the stress, a sharp corner increases the likelihood of fracture at this point.

A more robust design would be either a beveled or rounded interior corner allowing more material to flow into it, increasing the strength.

Worked with the tooling engineer to have those changes implemented. Plan was developed to modify tools that are held in

reserve first, then begin switching them out with production tools.

Left Corner Post Analysis & Changes

Followed product after crating to the shipping department.

Discovered a point in the stream where the product hits a backstop before being transferred to another conveyor heading perpendicular its original heading.

Product was not square to the direction of travel. This caused the left rear corner post to strike before the left front corner post, thereby forcing the rear corner post to absorb most of the impact force.

Worked with maintenance to add more padding to the backstop & to install bar stock to the conveyor section prior to the backstop to square the product to the direction of travel.

Lines 1 & 3 Analysis

The cabinets from these two lines are common to the 27-station foamer, while Line 2 is from the 12-station foamer.

Since the corner post is formed at a 90 degree angle, a check of the cabinet corner these posts rest upon should be made.

Lines 1 & 3 Cabinet Data Collection

A simple angle measurement tool was constructed from a protractor & a piece of gauge stock. (See next slide)

Cabinets were measured as follows: 3 cabinets were measured from all fixtures in

service. Measurements were taken from 4 locations on

both the right & left rear corners on each cabinet.

Highest and lowest angles from each corner were recorded.

Cabinet Measurement Tool

Cabinet Data – Left Side12-Station All

SamplesAverage 96.8 98.8 96.5 97.9 96.8 98.4 97.54Min 94 96 93 96 95 96 95.67Max 101 102 101 103 99 101 101.17Median 96 98 96 97 96 98 97.00Mode 96 97 96 97 96 97 96.33

1 2 3Sample #

27-Station AllSamples

Average 98.9 102.3 98.0 102.3 98.1 102.6 100.35Min 96 99 94 100 96 98 98.33Max 102 106 101 104 101 106 102.67Median 99 102 98 102.5 97 103 100.33Mode 98 102 98 104 97 101 99.67

Sample #1 2 3

Cabinet Data – Right Side12-Station All

SamplesAverage 96.2 98.7 96.9 98.9 96.0 98.5 97.53Min 94 98 95 97 93 96 96.00Max 99 101 98 100 99 101 99.17Median 96 98 97 99 97 98 97.67Mode 97 98 98 99 97 98 #N/A

Sample #1 2 3

27-Station AllSamples

Average 99.1 102.0 98.6 102.4 98.5 102.0 100.48Min 97 99 96 99 95 99 98.00Max 103 107 101 107 101 106 103.83Median 99 101 99 103 98 101.5 100.33Mode 98 101 100 103 98 101 99.67

Sample #1 2 3

Cabinet Data Analysis & Changes

Data shows that no fixture in either foamer produces a rear corner that is 90 degrees.

Data further shows that cabinets from the 27-station foamer have a rear corner angle that is consistantly 3 degress greater (in both mean and median) than cabinets from the 12-station foamer.

This higher angle adds to the stress placed upon the interior corner of the corner post.

Working with the process engineer, experiments were conducted using foam fixture shims to reduce the cabinet angle.

Several experiments yielded no consistent improvement. While this is considered to be a variable in the failure mode, no

further analysis will be conducted due to the following: Significant capital investment would be required for equipment to make

changes required. It is very likely that the cabinets have always exhibited this condition, and

since it has not changed, is unlikely to be a contributor in this particular event.

Phase 2

Develop Part Testing Method

Equipment

A Tinius-Olsen 2000 machine was selected as our test machine. Capable of various speeds in both

extension & contraction modes Calibrated both internally & externally Capable of custom fixtures Readings in both standard & metric

Test Fixture

Open air fixture was selected as the most useful type. Supports the ends of the part profile, but not

the middle. Allows for part to spread as force is applied. “V” form effector simulates external force

placed upon the outer corner.

Designed fixture based upon the part profile & submitted to skilled trades for construction.

Test Procedure

Based upon the data collection, force placed upon the corner post is sudden. Test procedure will be done with the

machine set at its highest speed. Test will flex the part no more than ½”

Readings will be taken in Standard units (ft/lbs).

Test System

Baseline Testing

Initial testing began with samples from current production that exhibited a high failure rate.

Samples were tested both “green” and “cured” (2 days later) to check for differences. No significant difference was noted.

Sample Date Kurtz # CavitySample

## Compression

"Green"Cured Test

Date# Compression

"Cured"Crack Fill Setting

1 3 1 40.5 381 3 2 43 41.51 4 1 43 441 4 2 40 391 5 1 38 36.51 5 2 41.5 481 7 1 45 44.51 7 2 38 39.5

6/16/2008 6/18/2008 0

Phase 3

Process Corrections & Testing

Increase Crackfill Setting

Initial parts showed poor adhesion of bead and parts where insufficient bead caused voids.

Working with the process engineer, adjusted the “crack fill” setting from 0 to 3 and then 3.5 to allow for additional venting & a fully formed part.

Testing Results of Increased Crackfill

Parts with higher crackfill setting resulted in a 5 to 10 ft/lb improvement in testing across all part “buckets”.

Crackfill was left at 3.51 3 1 45 48.51 3 2 52.5 50.51 4 1 46.5 461 4 2 54 50.51 5 1 59 491 5 2 44.5 471 7 1 44.5 44.51 7 2 51.5 46.5

6/17/2008 6/19/2008 3.5

Autoclave Setting

Research into low density EPS processes settings indicated that adjustment to the Autoclave setting could produce a stronger part.

Autoclave is a timing cycle which uses steam to bake the outer skin of the part and harden it.

Differs from Cross Steam which forces the inner beads to “pop” to a specific size.

Standard production setting for Autoclave was 1.1 Samples were ran at settings of 1.2 & 1.3 A setting of 1.4 caused the part to stick to its

“bucket” which halted production.

Testing Results of Increased Autoclave

Parts with Autoclave at 1.2 did not show significant improvement initial setting.

Parts with Autoclave at 1.3 produced parts that required 30 ft/lbs more than original production & 20 ft/lbs more than Crackfill improved parts to break.

Additionally, the testing fixture had to travel farther to create a crack in the part. This indicated a part that was more flexible than the original. This allows for small impacts to have no effect on the part robustness.

1 3 1 68.5 65.51 3 2 61.5 651 4 1 65 61.51 4 2 58 651 5 1 76 67.51 5 2 63 70.51 7 1 65.5 601 7 2 58 71.5

6/20/2008 6/23/2008 3.5

Mold Maintenance

Investigation into the standard preventative maintenance scheduled showed that routine cleaning of the buckets with high pressure water had not been done.

Established a schedule to perform an initial cleaning of the buckets as soon as possible, then periodically thereafter.

Correlation with Warehouse Repacks

Production of improved parts were allowed to run for 1 month.

Repacks by production week were correlated to weeks where process improvements were made.

Correlation Results

Units Repackaged at FDC for Damage

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Production Week

Crackfill set to 3.5

Autoclave to 1.3

Continuous Monitoring

Based upon data collected, an inspection plan was set up to monitor ongoing production.

Samples from each bucket are collected three times per week and tested.

Control limits were set a “yellow” zone to alert when corrections need to be made to process conditions, and a “red” zone to indicate production should stop and immediate action should be taken.

Results from testing & actions taken are tracked in an Excel spreadsheet that automatically color codes reading taken.

Corner Post Testing Tracking SheetTest Date

Production Date

Production Shift

Cavity Sample Reading AverageTarget Mean

LCL Comments

1 1572 1291 1052 1411 1152 1171 842 1421 1132 137

125 116 87Sent message to supervisor and quality engineer.

113 116 87Contacted supervisor by radio.

116 116 87

123 116 87

143 116 87

3-Mar-10 3-Mar-10 1

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Corner Post Testing - GraphEPS Rear Corner Post Fracture Test 2009

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Project Conclusions

Prior to the project, it took an average of 45 ft/lbs of force to break a corner post. After all corrections to the process, it now takes an average of 120 ft/lbs of force to break one. An improvement of over 200%.

As a result of the project, a process that was costing an average of $800/week ($40k annually) during normal conditions, and had risen to $4k/week ($200k annually) has been stabilized.

After the corrections that were made, recrates now only cost $120/week on average. This results in an 84% cost reduction and an annual savings of $35k/year ongoing.

Project Conclusions (con’t)

An inspection process that did not exist for this part now is in place. This inspection acts as an early warning system to identify when the process is no longer in control so that corrections can be made before recrates increase.

Since the inspection process checks all 5 cavities of the parts, it is useful in determining the source of the problem and what corrective action is taken: If only 1 bucket is showing weakness, that bucket is

pulled and maintenance is performed. If all 5 buckets are showing weakness, checks are made

regarding steam pressure & temperature, reading of “popped” bead, water quality & injection heads.

This prevents “going down the wrong road” in the problem solving.

Project Conclusions (con’t)

Since testing showed that there is no difference between “green” and “cured” parts, changes made to processes & materials can be tested immediately to determine if parts have returned to nominal.