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Garage Door Opener Production Line
Consultant
DIG is a Senior System Engineer, Electronics Engineer, Printed Circuit Board (PCB) Assembly Expert with world-class expertise in manufacturing systems for the production of electronic products and components, providing management leadership including sales, marketing, proposal development, project presentation, project planning, specification development, engineering, build, implementation, completion, and installation and follow through, as well as development of manufacturing processes and design of corresponding hardware/software systems to automate operations.
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The objective of this new manufacturing project was to provide one totally automated manufacturing line for the production of key fob transmitters and one manufacturing line for receivers. The customer wanted to be the first in the industry to replace the large sun visor transmitter with the innovative key fob. The manufacturing project was divided into two phases. The first phase was in development and installation of the manufacturing lines for the production of the surface mounted printed circuit boards, for both the receiver and the transmitter. The second phase was in development of the mechanical assembly of the key fob and placing it in a plastic bag. No primary or secondary packaging was required as the end product was packaged into totes for shipment to a final assembly plant. Since this line was a relative high volume production line, the quality of each component and its associated packaging was evaluated for automated placement reliability. Maintaining Lean design principles, each component was evaluated. These types of continuous improvements making a difference in reliable manufacturing process lines. The objective was to have as few operators on the line as possible, minimize the system stoppages and downtime.
The printed circuit board design was in a panel format, divided into circuits of 4 X 6 for the key fob product. The panel layout was 4 circuits in "y" machine plane and 6 circuits in the "x" machine plane. The overall panel size was 5.1" in the "y" machine plane and 6.6" in the "x" machine plane. Each circuit was partially routed at the printed circuit board manufacture. It was important not to over route each circuit, causing sag on the conveyor belts during transport from one process to the next. These partially routed circuits were totally routed from the panel after ICT testing was completed.
The receiver panel was a two up panel, with overall dimensions of 6.3" wide in the placement "y" machine plane and 8.4" long in the "x" machine plane. The receiver would eventually end up in the garage door opener itself. The receiver circuitry was more complex then the transmitter and used more odd form type components like coils, relays, connectors and through-hole electrolytic capacitors. The receiver printed circuit board manufacturing line was similar to the transmitter production line.
This consultant wanted to review a couple of items that most production engineers take for granted, but can really make a difference to the reliability of the production line. Connectors and some other odd form parts were sourced and purchased in China. The placement of these parts was terrible. The pocket within the tape was too small for the connector part, so with normal tolerance, some parts would stick in the pocket of the reel tape and cause a miss-pick. We went back to the Chinese supplier and specified the pocket dimensions, appropriate for the part. Clearance specified was .008" - .010" between the connector side walls and the side walls of the reel tape. The EIA specifications for pocket clearance are larger and can allow parts to shift in the pocket, causing miss picks. Some surface mount connectors came with pick tabs for vacuum pickup and some connectors required custom grippers. Grippers were used on some connectors that would not sit in a tape pocket or have a vacuum pickup location. Custom grippers were developed for the surface mount equipment. This required a special pocket with a shelf in the reel tape for the connector to rest on and keep the connector oriented in the proper position for machine pickup. The clearance for the grippers was .020" on either side of the connector side wall of the tape pocket.
Panels on the transmitter line were selected one at a time from a bare board de-stacker conveyor and moved on an edge belt conveyor to the screen printer, for the application of solder paste. The transmitter key fob was a simple product using 0603 component chips and small SOIC's with normal lead separation of .031", it was determined that solder vision inspection was not needed. Solder paste balls were consistent in mesh size and the isotropic properties of the paste over older formulations, displayed stable properties. It was determined that the process was stable after first article inspection and only required sampling on an AQL level. Screen printers of provide good pressure repeatability and repeatable squeegee materials. The stainless steel stencils that were etched with lasers were accurate and repeatable.
There were three variations of products in the key fob product line, requiring only slight changes in a few component values and placement location; this provided an easy means for a common feeder set up and programs for all products to be resident on the machines. When new products were introduced to the transmitter line, the only set-up change was out the stencil in the screen printer and to change the pattern program in the surface mount placement machines. Changing the machine pattern programs was 10 seconds. The transmitter line contained two single beam high speed chip machines, having the capability of placing components as large as 6mm in height and 30mm X 30mm in width and as small as a 0201 chip. This provided the full spectrum of components on the transmitter, so a pick and place machine was not required. The throughput of the transmitter line for the surface mount area was 36k components per hr (cph). Maintaining Lean Manufacturing principles, the second high speed machine in line was programmed to provide a faster processing time. If there were any interruptions down stream, the system had time to correct itself, after the interruption was cleared. One day supply of component reels were kept on the manufacturing floor, next to the placement machines. Actual consumption of components were kept and sent up-line to a SQL data base for shop floor monitoring. The SQL data base was connected directly to the machines. Each placement was kept track of via part number automatically reported to the SQL database. A SAP portal from the automated ordering module, within the MRP system, would use the consumption data to trigger the new order for components.
Vision inspection, after component placement, on the transmitter process line was determined unnecessary. Component chips were 0603's, moving to 0402's, it was determined the accuracy of the machine and component pad design were adequate to reliably place the components. A manual visual AQL inspection of the printed circuit board could be done, at this step in the process. If there were to be any problems in the process, it was determined it would occur after the reflow process, because of inadequate paste distribution or too much paste on the surface mount pads. Vision inspection was introduced into the system after reflow, providing the best solution to any quality issues for placement errors. Although, this position in the assembly process was the most expensive to repair, the amount of defects would be extremely small, it was cheaper to remove them from the system and through them away. Defective circuits within the panel were marked with a white ink dot. This allowed them to be sorted and removed further down the process after de-paneling.
The reflow process for the transmitter product was very stable, because the panel and circuit boards did not change. The mass of the product going through the reflow oven was consistent, thus no adjustments were required for conveyor speed, air flow or temperature settings.
Printed circuit panels moved from the reflow process into a programmable buffer. This buffer acted as inline control of the production line. The buffer was programmed to store a preset amount of printed circuit boards and then shut down the input to the reflow oven by shutting off the SMEMA signals. Using Lean or pull manufacturing techniques, the downstream final assembly was faster then the surface mount portion of the assembly line. When stoppages occurred, they would clear themselves after the problem had been addressed. The FIFO buffer allowed the printed circuit boards coming in from the oven to accumulate in the buffer for a predetermined amount of time to cool. This provided a consistent temperature for the printed circuit boards entering the vision inspection system, but more important the ICT (In Circuit Tester) that followed. Having consistent low temperature readings, the chip and wire bonds were more stable in test. Both ICT and Vision Inspection allowed for a faster process time then full functional testing, especially when the down stream process steps needed to be slightly faster providing for a pull system.
The next step after test was to de-panel the circuits. With the panel being partially routed, the final routing process removed the short tie stub holding the circuit to the panel. Special grippers would hold four circuits at a time in the "y" machine plane and after cutting the tabs, would hold all four circuits, until the last circuit was cut. Then all four were dropped on to a flat belt conveyor, where each circuit was clamped and held by custom tooling for a Cartesian Robot to pick up all four circuits at one time. A pallet holding plastic bases of the key fob were moved into position for the robot to place each circuit into the base, using a four headed vacuum pickup end effectors. Plastic bases contained 4 locking latches so when the circuit was pushed into the base, it was latched into place. Plastic bases contained a chamfer of .100" at 45 degrees around the outside perimeter, were previously loaded into the pallets in a Cartesian robot operation. This allowed the circuits to be reliably inserted into the base without vision to guide the robot. The positioning accuracy of the robot was .003". Pallet fabrication was done using a machine able plastic. The plastic pallet was routed to the maximum plastic key fob base tolerance, plus .002", with a .003" nominal tolerance. Key fob pockets on the pallet contained lead in edges of .100"
Pallets containing 24 circuits moved from inserting individual circuits into the bases, to the next position in the final assembly process. The final assembly process was an oval architectural configuration using roller chain, with position stops for each assembly step in the process. The final assembly oval conveyor with robotic stations along the conveyor ran perpendicular to the back end of the surface mount line. The pallet was located using pneumatic locators at each step in the process. The locators used a cone style pin inserted into a .250" round hole. The second locator also used a .250" hole, but was elongated in the machine x plane. This assured the location of the pallet in reference to the robotic placement points. The next step in the process was to insert the circular watch battery into a spring clip. The packagings of components were as important to the assembly process, as the robot assembly itself. The batteries were loaded at the supplier into tubes that could be fed into a multi tube stick feeder. The batteries would slide down a custom machined slide for robotic pickup. The feeder could handle a stack of 15 sticks and each stick could handle 80 batteries. With this inventory of batteries on the assembly line, little operator intervention was required. Process time at this stage of the assembly was getting progressively faster to maintain the integrity of Lean and JCIT manufacturing. Multiple feeders were placed at each cell to minimize part handling and to assure placement reliability.
A Cartesian Robot with special end effectors would spread a spring loaded clamp located on the printed circuit board and then insert the battery using vacuum pickup nozzles. With the nozzles holding the battery in place, the custom end effectors' holding clamp was released. When this was completed for each of the circuits in the pallet, the pallet would move into the next step of the process, placing the membrane switch over the printed circuit contact points.
Placing the membrane switch was one of the more complex steps of the final assembly. Although the membrane was relatively small, it was hard to handle for automated placement. Packaging of the membrane was placement into precision matrix trays. Minimizing the amount of time for replacement of membranes by a Cartesian Robot, two stackable matrix tray feeders containing 10 trays each were used. Each matrix tray contained 50 membranes. Placement of the membranes became a challenge, picking from matrix trays, keeping them flat for placement and not sagging or hanging off the end effectors. Vacuum end effectors were used with multiple ports to keep the membrane flat. When the membrane was placed on the printed circuit board, a small amount air was blown through the ports to make sure the membrane did not stick on the end effectors. Vision had to be used to merge the alignment of the membrane to the contact points on the printed circuit board. There were four small circular tabs that protruded .200" from the bottom of the membrane and .200" diameter circle. These were place into a circular hole of .250". The objective of these tabs was to keep the membrane from moving on the circuit board within the pallet, during the time the pallet was moved from process step to process step on the roller chain conveyors..
The original design of the top plastic cover required it to be secured using screws. This was a good place within the process to use design for assembly techniques and design for automation. Designing a top cover to be self aligning with snap fit features, eliminated a complete process step, automatically driving screws. Driving screws would not the most reliable process, so by eliminating it, the system reliability was improved. The cover contained an edge chamfer of 45 degrees, .100" wide. There was enough tolerance with this chamfer to eliminate the placement tolerance, pallet tolerance and base molding tolerance. Covers were picked from matrix trays populated at the vendors and placed ten high, two wide on automatic matrix tray feeders mounted on a Cartesian Robot.
This next step in the process was the most expensive and the slowest, thus requiring multiple stations. The key fob needed to be tested for operation and to verify the frequency was within the spectrum tolerance range. Older units would require manual tuning using a plastic probe in an adjustable coil. The new design used precision surface mount coils and capacitors to assure the frequency was accurate. If for some reason the frequency was out of spectrum or the transmitter was not working, the key fob would be thrown out. A dedicated pneumatic picker finger would remove the key fob from the pallet and place into a special rf fixture drawer that would open. When the key fob was in place, the rf drawer would close and energize the unit for testing. Good units were then placed on a continuously running flat belt conveyor. The defective units were discarded on a parallel continuously running flat belt conveyor and dumped into a hopper.
The last step within this manufacturing facility was to place a paper label on the back of the key fob and place into a plastic bag for shipping to the secondary facility to integrate the electronics into the mechanical portion of the garage door opener. The key fobs were separated on the moving flat belt and captivated using dedicated automation. They were flipped over for a preprinted paper label to be applied on the back side of the unit. Automatic bagger then placed the unit into a plastic bag and they were placed into a tote for shipping to the secondary manufacturing facility.
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