AIA: Two-step Heat-staking Boosts Throughput
Among its many sensor, switching, automotive and motion-control products, Saia-Burgess Group (Murten, Switzerland) produces the MagShift solenoid, an electric park lock that prevents a driver from shifting out of park without first stepping on the brake.
Part of the production process involves heat staking a plastic post to hold the assembly together. In the past, Saia-Burgess performed this operation using a manually operated benchtop heat-staking machine. However, the company wanted to both increase throughput and increase the strength of the assembly, so it implemented an automated, indexed Sonitek heat-staking cell from Sonic & Thermal Technologies Inc. (Milford, CT).
One of the unique things about the heat-staking system is that it performs two separate heat-staking operations to create each assembly. In the first step, an MP572/2lb heat-staking machine partially stakes the plastic post on the part. Afterward, the part is indexed to a second machine where the post is staked to its final position.
This approach not only shortens cycle times, it also drastically improves the strength of the heat-staked head: from a 10-pound holding force in its initial configuration to 100 pounds of holding force in its final configuration. (The heat staking tip was also changed to create a rosette-style head to help increase strength.) Because the pre-staked plastic post was both long and narrow in diameter, it had been prone to bending or breaking when staking was performed in a single step. However, this problem was eliminated using the "two-stage progressive" approach.
During the second step, air is blown on the hot tip while it is holding down the formed head. This destroys any memory in the remolded plastic, so it won't lift up from the metal surface-thereby achieving extremely tight stakes. This "post cooling" technology also prevents sticking, stringing and adhesion of plastic resin in the tip cavity. In essence the heat-staking machine is emulating the injection molding process by forming the plastic into a hot cavity and then cooling it prior to release.
To further decrease defective parts, each staking machine incorporates an "out of temperature alarm," which stops production if the heated tooling is not within the proper application parameters. It also monitors stroke and final staking positions, and incorporates pick-and-place removal of defective assemblies into eject chutes. Sensors in the chutes ensure that each defective part has been removed from the system.
Currently the system is producing nine product versions at a rate of 1.3 million parts per year. By this spring, it will be producing 2.3 million parts annually. Previously, Saia-Burgess Group could only produce 1.2 million parts per year.
For more on heat staking, call 203-878-9321, visit www.sonitek.com or eInquiry 2.
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