Development of Automated Manufacturing Line for After Market White Goods Controllers

The objective of the project given to this expert was to develop a lean manufacturing line for a customer to build 21 different products consisting of three families, for After Market White Goods. This project was a personal award winning project from the vendor. The volume of this production line was considered to be of moderate volume of 200 to 500 boards per day for each product. Consideration was given for the occasional repair product required immediately, thus requiring a line that could provide lot size 1. These changeovers from one product to the next would be automated to the extent possible. It was important to minimize the amount of set up performed, thus removing the potential for error. The amount and type of automation was given careful consideration, providing ease of troubleshooting. It is easy sometimes to automate for the sake of technology.

The beginning of the production line started with a conveyor called a de-stacker. There were two de-stacker units on each conveyor containing up to 200 (2-up) printed circuit boards. The 2-up panel was established to have a common size or form factor to minimize line and machine setup. Each panel contained a carrier strip on the top and bottom to provide the difference in width between each product type and a location on the bottom strip for a bar code label.

When a new stack of printed circuit boards were loaded into one of the de-stack units, it was sensed that a new stack was just loaded. The operator would verify the silk screen part number on the printed circuit board matched the paper work. The part number was then scanned from the bar code on the paper work into SQL Database. When the first panel would be unloaded on to the next step in the assembly process to attaché a printed circuit board label to the bottom carrier strip, at the same location every time. The first board would stop at a buffer before the label applicator would apply the label. A light tower would be lit to inform the operator that was the first board loaded and to verify the product loaded in the de-stacker was the same product id on the label,( in code 128 ), to be applied. When this was accomplished, then the line would run automatically from this point forward until the stack of printed circuit boards was depleted. After the label was applied, the printed circuit board moved into a verification station to make sure that the label was readable. If the label failed, a light tower would light and an operator would remove the printed circuit board panel from the line.

In front of the screen printer was a buffer area containing a bar code reader connected to the PLC in the conveyor. When a new product was ready to enter into the screen printer, the printed circuit board would stop and a light tower turned on. Operator would then change out the stencil on the screen printer. Auto paste dispense on the screen printer minimized the amount of time spent placing solder paste on the stencil. Auto inspection of the solder paste was accomplished using an Optical Inspection in-line unit after the screen printer for first article. When the proper deposition of solder paste was accomplished the operator would then let the rest of the batch of boards enter into the screen printer. One of the driving factors for the reliability of the line was to control the amount of solder paste. If the process was stable and the amount of solder paste consistent on the printed circuit board, then the manufacturing process would remain stable. The surface mount components packages were larger then electrically required to avoid any miss pick or misplacement issues.

The next step in the process was the placement of surface mount components and a few odd form connectors. Eliminating setup was the main driving factor in this expert's task and this was accomplished by using two single head high speed chip shooter surface mount placement machines and one pick and place surface mount placement machine for connectors and a few large active devices. The driving factor for the number of machines was the number of components to be placed for the 21 different products. The common component feeder setup was optimized on the machine, based on the total production requirements and allowing for 20% empty feeder space. Expert consideration was given to create a pull system for each machine as best possible and still maintain machine utilization. When a new printed circuit board would stage in front of the first surface mount machine, the bar code would determine the product ID, automatically change the machine program and when the program was changed, SMEMA signals would allow the board to enter into the machine for population. This was accomplished for each of the three surface mount machines.

Reflow oven process was the next step in the manufacturing process and was able to accomplish a common reflow oven profile for each of the 21 different products. Thus, no secondary automation or setup was required in this step of the manufacturing process.

Printed circuit boards proceed then to the testing area consisting of three perpendicular lines off from the main assembly line and downstream from surface mount placement. Testing was based on performing an ICT (In-Circuit-Test) for each family of product, thus the three process lines for test. Each tester was configured with a common test fixture to handle all of the products within each family. Printed circuit boards were directed to the appropriate test line via their bar labels. A turn unit conveyor's PLC controller was connected to the bar code readers. Each product name within the respective family was located within a table and as each product came down the line it was checked against the table at each turn unit. This provided the lot size one capability, although the line was generally run with 200 to 500 boards of the same product. Defective printed circuit boards were automatically removed from the test line and good product returned to the main manufacturing line via a common return conveyor.

Final assembly for this product was fairly simple, consisting of a few standalone work stations, semiautomatic equipment for blister packaging, adding some hard ware, some primary pack and secondary pack. Three final assembly line conveyor stubs were setup via the family of product being completed. There were directed via a bar code reader connected to a turn conveyor unit to direct the product to the correct line.

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