Springs come in a wide variety of sizes, shapes and materials.
Mechanical springs come in a wide variety of sizes, shapes and materials. Compression, extension, torsion, constant force and Belleville springs are commonly used by manufacturers. Each type of spring presents unique challenges to automated assembly systems.
Compression springs are widely used with automation. They consist of a helical spiral that compresses and becomes smaller when presented with a load. According to Rick Amendolea, president of Centricity Corp., compression springs are typically found in automotive valves and ballpoint pens. Challenges include tangling, size variation, stiffness and end conditions.
Extension springs stretch apart to create load. They are often used in screen doors. “Common process challenges include loop ends tangling, loop orientation and size variation,” says Amendolea.
Torsion springs rotate around an axis to create load and release their load in an arc around the axis. They are often the most difficult to automate. Torsion springs are typically found in clothes pins, mouse traps and garage doors. End condition and end orientation cause numerous automation problems for engineers.
“Torsion springs present a challenge for pre-load procedure, as they need to be twisted or compressed prior to being applied to the part,” says Kate Stiltner, technical writer at JR Automation Technologies LLC. “Torsion springs can drive the cost of production up, as the springs must be either operator-fed or robot-fed, which typically slows down cycle time.”
Constant force springs are made from a band of steel that’s wrapped around itself several times to create a spiral. The rotational force releases a constant amount of load. “Constant force springs are typically found in tape measures, clocks, hose reels, wind-up toys and counter balancers,” says Amendolea. “Automation challenges include end orientation and telescoping.”
Belleville springs consist of a coned disk that contains a hole in the center. They are typically used in applications that require high loads without much movement, such as ball valves in plumbing fixtures. Common challenges that engineers encounter when using automation include orientation, shingling and flipping over.
As a rule of thumb, any type of tapered or conical spring, in addition to open-ended springs, can be more difficult to use with automation. “Tapered springs can nest together and open-ended springs will interlock to the point a separator can’t untangle them,” says Carl Nelson, president of Performance Feeders Inc. “Thin-gaug,e open-ended springs will create a nest as they come out of their formed coil and cause havoc in a separator.”
In addition to shape, the type of material that a spring is made out of can affect automation. For instance, springs made from softer materials, such as copper or plastic, can act differently than harder materials, such a stainless steel.
“Material can make a difference,” says Nate Sornborger, engineering manager at Arthur G. Russell Co. “Steel springs can get magnetic, plastic springs can be excessively flexible and plated springs can flake.”
“The make up of the part can affect the feeding characteristics of the part,” adds Nelson. “Softer metals absorb vibration differently than denser ones do, just like lighter colors of injection-molded parts can feed differently than darker colors.”
The type of coating or finishing that’s used on springs can also make a difference. “Some coating can wear off, causing build up in the bowl,” Nelson explains. “This can happen at selectors, and that can affect rates and cause jams.”
According to Stiltner, material can greatly affect a bowl-fed spring’s performance. “Steel springs are harder to bowl-feed than stainless-steel springs, as the bowl-feeding motion can cause the steel springs to generate a greater magnetism, consequently increasing the likelihood the springs will cling together and become tangled,” she explains. “The spring material can also affect sensing devices.
“Stainless-steel springs often cannot be detected by a simple proximity switch, requiring specialized sensing devices to detect part presence,” Stiltner points out. “A photo eye is often helpful to detect part presence vs. a laser or straight beam. Because the spring can be so small, with flexibility that makes it hard to control, it is often difficult to place the spring in a position for a photo eye to sense the presence.”
JR Automation has tackled the material challenge by integrating flex-feed systems into automated assembly equipment. “Flex feeding works especially well for torsion springs by using a vibrating feeder or conveyor system and a vision-guided robot to pick parts,” says Stiltner. “The robot can then identify the spring by part type, orientation and position, and pick-and-place into the part as necessary. Flex feed systems also solve many of the issues with compression spring systems by using vibration instead of a linear motion, which causes the springs to become tangled less easily and reduces the amount of back pressure applied to the springs.”
Types of Springs
May 28, 2010