Keeping assembly simple
Roller conveyor provides a work platform that gently handles PCs while pacing work-in-process flow.
By Tom Feare -- Modern Materials Handling, 1/1/2000
Three words sum up the philosophy behind producing high-quality PCs using materials handling technologies at Howard Computers, Laurel, Miss. "Keep it simple," says Dan Lewis, vice president, manufacturing.Handling simplicity helps Howard cope with the basic complexity inherent in its manufacturing process, and thus focus its efforts on dealing with production matters.
Production at this plant is no cookie-cutter operation. Howard's process leans toward customized PC production. It builds six base PC models. But each model can be made in about a thousand different combinations of components, adding to manufacturing complexity.
With a shop floor team of a dozen associates or technicians, Howard has the capacity to turn out 200 high-quality PCs daily. That's a throughput of about 1 PC completed every two minutes during the team's single-shift operation. And each PC may be very different from the one behind or in front of it on the line.
A simple, semi-automated materials handling system gives Howard all the functionality it needs without creating further complexity. The system's simplicity limits the variability it might introduce into manufacturing.
A key feature of the system is a single, powered roller conveyor line laid out in a straight line. "Because the line's a straight shot, we have the visibility to see if we have any flow problems developing," says Lewis.
This conveyor is integrated with ball-bearing tables for ease in transferring work-in-process (WIP) off the line and into workstations. Team members also use portable bar code scanners to track and verify that the components installed are the correct ones. Scanning bar coded serial numbers also supports future service and warranty needs.
The conveyor system chosen (Shuttleworth, Huntington, Ind.; 219-356-8500 ) serves several key functions. It provides a means to move somewhat fragile PC units along the line very gently using low line-pressure accumulation. It also functions as the work platform for technicians as WIP moves through six progressive assembly work stations. And the conveyor, through its design which includes air-actuated controls to stop line movement, aids in WIP queuing and line balancing.
"We wanted this roller conveyor system to operate much like a power-and-free conveyor does," says Lewis. In other words, "it gives us capabilities for production line balancing and pacing of work flow, instead of continually indexing product forward," he adds.
The ability to stop and temporarily hold sections of the line is important, he stresses. Part of each technician's job is to perform a quality assessment of work done upstream. A temporary halt to continued WIP flow gives technicians the time to make their individual quality checks, then complete their other, assigned assembly tasks.
Varied mix of PCs produced
Howard Computers is a division of Howard Industries, a manufacturer of electrical distribution transformers and lighting ballasts. Production of PCs has evolved into a business of making desktop, mini-, and mid-tower PCs. Howard sells the computers to schools, banks, and other business users, as well as to customers needing a home PC.
Thus, the model mix coming down the production line at any one time can be very varied, as Tony Thornton, vice president, engineering, points out.
"We build six base models. But each base model can be made in about a thousand different combinations of hardware components that can change," Thornton says. Adding one of two operating systems-Windows NT or Windows 98-and then loading all the specific software applications a customer wants, further increases the variety in the mix of finished PCs.
With this variety to deal with, Howard starts production by pre-kitting the components needed for each PC to be built. Kitting reduces the number of line changeovers needed, explains Lewis.
Simplicity again prevails at the kitting stage: Components are pulled from shelving and put into kits. Currently, Howard uses manual carts to bring kits to the head of the conveyor line. Expansion plans, however, call for conveyor spurs to be added so they can route kits from kitting to assembly on multiple lines.
After kitting, the assembly line process begins: Two trays, or mini slave pallets, will be sent to the first progressive assembly station: One tray holds a kit of parts, one tray transports the PC chassis into which the kitted components will be installed.
Individual PCs move through the six progressive assembly workstations at the head of the line. Operators at each of these stations are cross-trained so they can perform any and all of the assembly steps required at the six stations.
Crosstraining helps in adjusting work flow, Lewis says. "By having all six stations manned or by having as few as two manned, or using any combination in between, we can further balance the line," he adds.
Each workstation operator will scan bar-coded part numbers so that Howard's database can verify that the parts correctly match those called for in the bill of materials for the specific PC under assembly, Lewis notes. Serial numbers of components also are scanned. This step supports any future customer service needs. The PC's own serial number is scanned too.
From progressive assembly, a PC travels by conveyor to the burn-in/software loading area. Parallel conveyor lines within this area help expedite the flow of WIP.
Once there, the PC is transferred into the nearest available work area. An air-actuated, pop-up, ball-bearing transfer units helps move the PC chassis off the conveyor and onto a ball table.
"We can push the PC to either side of the conveyor for burn-in/software loading," Lewis notes. "We thus have a temporary storage area for PCs with minimal transport necessary for the final assembly steps."
Next, burn-in for 8 hours will take place, followed by software loading of specific applications.
After successful software loading, the PCs will move to the end of the burn-in/software loading area. Exiting this area, PCs move along a single conveyor line to a quality control point where a customer audit technician examines each unit. Having passed inspection, the PCs proceed to a packout station where an operator will load each unit into its packaging with an ergonomic assist from a ball table/scissors lift.
Progressive workstations
A straightforward approach to making PCs
The road to each finished PC starts with a kit of components and a PC chassis entering the progressive workstation area. Using the conveyor as a work platform, technicans next install components. Then the PC moves to the burn-in/software loading area. After this two-step process is completed, the PC will undergo a quality control check by a customer audit technician. Finally, the PC is conveyed to a packout area where it will be loaded into its carton for shipment.
Manufacturer Profile
Howard Computers, Laurel, Miss.
VP, MANUFACTURING: Dan Lewis
VP, ENGINEERING: Tony Thornton
PC PRODUCT LINES: 6 basic models, up to 1,000 variations of each model, depending upon specific hardware components installed
ASSEMBLY CAPACITY, SINGLE SHIFT OPERATION: 200 PCs daily
LINEAR FEET OF CONVEYOR: 138 ft.
EMPLOYEES PER SHIFT: up to 12 operators or technicians
SYSTEM INTEGRATOR, CONVEYOR
SUPPLIER:
Shuttleworth 219-356-8500
BALL TRANSFER TABLES, ESD
DEVICES:
Z-mar Technology 704-841-8845
BAR CODE SCANNERS:
Intermec 425-348-2600
Measures to minimize electrostatic discharge
Minimizing ESD, or electrostatic discharge, is important to ensure high quality in finished PCs.
Among the steps Howard Computers takes to limit ESD are:
- Grounding the entire conveyor line
- Using conductive rollers and conductive foam parts in the conveyor system
- Ensuring operators work on grounded floor mats
- Having operators wear wrist straps for grounding
- Using AC-powered, brushless motors in screw drivers
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