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The gap between improvement and perfection

Updated: Nov 20, 2018

What’s happening here? A plant for a global rubber molding business that produces seals or diaphragms made from rubber and fabric wants to reduce customer complaints, improve on-time delivery, and reduce internal scrap. The business together with A. Stout & Associates has already identified the major opportunity (or culprit), and indeed streamlining the production of that family of parts has resulted in 25% greater output and a dramatic drop in scrap.  Should the business continue to focus on this family of parts for yet-greater improvement, or should it look elsewhere for additional barriers to efficient production?  And by how much more can output be increased, anyway?

The Situation as observed on the shop floor:

The work being done in each molding press consumes only 16 minutes of each hour; thus this equipment is used only 27% of the time.  The decision to continue improving this “troubled family” of parts is to take advantage of that unused time.  The process has four steps: cut the fabric to size and treat it; pre-form the fabric at 525 degrees for 75 seconds with low pressure; mold the fabric and rubber together at 350 degrees for 4 minutes at 2,000 pounds of pressure; and trim the part. The operator manually cuts and weighs the slugs of rubber while she waits for the press to cycle. When the press opens, she removes the parts, cleans and treats the mold, places the next pieces of fabric and rubber into the cavities, and closes the press.  The molded parts are trimmed two at a time and inserted into a plastic tray that is placed in a box. A quality operator inspects each box of parts prior to shipment. Three operators work full time on this product on both shifts. The average production is 62 parts each hour.

The Findings

Each operator works independently at each operation, completing the entire order just for that operation. The fabric that was pre-formed loses its shape under the weight of multiple pre-forms, because they have all been stacked atop each other before final molding. Also, any loose pieces of thread stick and contaminate more pre-forms. Thus, the operator must sort and remove defective pieces frequently throughout the process. At four different times in the process the operator counts the number of pieces needed for each operation to complete a shipment and anticipates how many extra parts are needed to replace defective ones. The spray-on mold release that is applied while the mold is hot evaporates before bonding to the mold, requiring more frequent treatment of the mold and more cured rubber stuck to the mold contaminating the next parts molded.

The Solution

The problem/opportunity is to utilize the equipment to its fullest in an ordered sequence with the operator by bringing all the work together. This will maximize what one operator can produce.  Merging the operations to include pre-forming the fabric, molding the rubber, trimming, and packaging the part maximizes the opportunity to complete the most work.  Art Stout revamped this process to sequence all of the operations and synchronize them with each other. A state-of-cure test showed that increasing the temperature 25 degrees from 350F to 375F shortened the time to cure the rubber 25% from 4 minutes to 3 minutes. An existing but idle extrusion press was put into use to portion out the right amount of rubber. One pre-form press, molding press, extrusion press, and trim press were moved into a circle allowing one operator to work all four presses. Step-by-step instructions were developed and posted. Everything was placed in sight of the operator.  The tools were located on one side of the presses and the shipping materials on the other.

The Results

The number of pieces made per hour increased from 62 to 130 pieces with the molding press being utilized 80% of the time.  The output per day increased from 931 pieces to 1,950 pieces. The floor space needed went from 1,020 SQ-FT to 318 SQ-FT. Customer complaints dropped 67% over the next 12 months.


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