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The smallest metal parts can often be among the most critical components in larger products, and how they are specified, designed and manufactured can play a vital role in overall product reliability and cost. While small and seemingly insignificant, electrical grounding contacts keep sophisticated electronic or electrical equipment operational by conducting stray electricity safely to the ground. For this reason, even the lowly electrical contact requires the proper design and manufacturing considerations when designing the larger system.
When it comes to electrical contacts, variability in requirements from part dimensions and materials to contact area, location, and spring quality can make ordering from a parts catalog difficult. Complicating matters, the design engineer doesn’t necessarily know what features are going to be a manufacturing problem or add significant expense. Choosing a competent manufacturing partner and using the best manufacturing technology for the job can have big payoffs in design reliability and cost.
Brent Brown is an engineering consultant for Yesco, a Salt Lake City-based designer and fabricator of custom signs, electronic displays, and outdoor media. Brown will take on some challenging jobs, e.g. a 135-ft. tall, double-faced, 100-ft. by 50-ft. LED sign for the Wynn Las Vegas casino hotel. The hotel called for 10,000 printed circuit board sub-assemblies controlling computer sequenced LED lights for a “message center” with a moving eraser that glides silently up and down over the LED board, appearing to change the graphics as it goes.
Brown quickly realized he would need some custom parts to design and manufacture the right group of grounding clips for the sub-assemblies. “At first, you look for an off-the-shelf part that’s manufactured in higher quantities but unless it’s a very common application you typically end up having to design it yourself,” said Brown. “An off-the-shelf part seldom works as well as if you designed it for the purpose and in this case it had to be custom.
“Since the displays are typically in service for 10 to 15 years outdoors, quality, corrosion, cost per part, spring tension, and spring-back were among the issues considered for these contacts.”
After Brown defined the first part, a surface mounted grounding contact to be soldered onto PCBs on tiny pads, he talked to a variety of companies and e-mailed them concept drawings to find out who had the expertise to help with its design and manufacture. “We had a number of companies quote the part and tooling, including those using hard, dedicated tooling such as power press progressive dies. But the tooling and parts were too expensive.”
The Process Makes the Penny
He eventually found a partner in a Bristol, Conn.-based parts supplier called Fourslide, which specialized in the integrated stamping and forming parts operation. The supplier, said Brown, was chosen as the least expensive for both the tooling and the parts, that price point made possible by a special tooling process.
The process begins with the raw material in flat strip form off a coil, which is stamped or blanked in the progressive die section of the machine, which is a fully functional but lighter version of the progressive die found in most power presses. Its trick is a process that typically starts with material the width of the finished part, generating less scrap.
The Right Material
Each time Brown emailed the parts supplier a concept drawing or sketch of the part he wanted, he received an e-mail back with suggestions and minor tweaks to help with part manufacturability and cost. To provide a good combination of spring properties and electrical conductivity for the grounding clip at reasonable cost, the supplier suggested using phosphor bronze as a material over beryllium copper since the spring properties and electrical conductivity of the four-times-as-expensive copper wasn’t necessary for the application. Going with bronze eliminated the cost of a secondary heat treating operation along with the risk of material deformation.
Through testing, Brown determined that half hard phosphor bronze was sufficient for the application, noting that bronze’s anti-corrosive properties would helps with the application’s outdoor weather requirements.
Satisfied with the first surface mounted grounding contact produced, Brown designed an additional two types of surface-mounted grounding contacts, plus two types of pin-mounted grounding contacts whose pins go through holes in PCBs perpendicular to its pads. “Depending on which configuration of grounding contact it is, the tab that sticks up from the circuit board is the spring and conductor at the same time,” said Brown.
From the time Brown placed orders to the time the first article parts were shipped for his approval took about eight weeks for all five types of parts. Two months may seem like a long time but the parts manufacturer informed Brown that many progressive dies can take 12 weeks or longer since power press progressive die work requires more complex tooling changes, and is typically done overseas with substantially longer lead times.
In testing, Brown mounted the prototype grounding contacts on circuit boards and put them into the sub-assemblies. He checked for compression to see whether the parts yielded or not, whether they were hard enough to maintain contact strength, and if they met additional requirements.
“The prototypes and products worked the first time, and we haven’t had any trouble with them,” said Brown. “Because the grounding clips resist corrosion and don’t lose spring, they should be good for many years. If we do another sub-assembly that requires a different grounding contact, it would be relatively easy.”
An animated demonstration of the manufacturing process is available at www.fourslide.com/fourslide-reference.htm.
A custom integrated fabrication process is often necessary for producing smaller metal products of complex configurations or in lesser volumes. Improvements in stamping processes are making this less expensive. The above were created using a process of four sliding stamps against a center tool.