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Spin Welding is the preferred technique for thermoplastic parts with a circular axis joint which have high bond strength/hermeticity requirements. During spin welding, one part is held stationary in a holding fixture while second part is rotated against it under pressure at speeds up to 16,000 rpm. This resulting friction causes the joining surfaces to melt and fuse together, producing strong hermetic welds. Forward has been designing and building Spin welding systems since 1993. We offer a multitude of models ranging in maximum speeds from 3,500 to 16,000 RPM and are available in both servo-electric (orientation based) and pneumatic (inertial based) models for a wide array of applications. Spin Welding Process Advantages
Spin Welding is a frictional welding technique capable of producing strong, air-tight welds in thermoplastic parts with a circular-axis joint. In this process, friction occurs by rotational motion controlled by either a servo electro-magnetic or pneumatic powered motor and motor control system which regulates the RPM (Revolutions Per Minute) and motion control of the system. Friction is achieved through motion between two parts, one is held stationary, the other rotating at a controlled RPM (typically 200-20,000 RPM) while clamped under pressure. Melt occurs only at the interface of the joint area of the plastic part halves. The part is cooled under pressure and permitted to solidify. |
About Orientation (Servo-Electric Drive) Spin Welding
About Inertial (Pneumatic Drive) Spin Welding
Orientation vs. Inertial Spin Welding
Designing for Spin Welding
Spin Weld Tooling
Spin Welding vs. Other Welding Methods
About Orientation (Servo-Electric Drive) Spin Welding
Orientation Spin Welding or Servo Drive Spin Welding has several additional benefits over Inertial Spin Welding. The main benefit is the ability to stop the part being welded at a specific point during its 360 degrees of rotation and index to a specific spot with respect to the mating part with an accuracy of ±1°. Also this indexing is available at both ends of the stroke. At the head up position, the driver can be rotated to any position for loading purposes or part pick up, making it ideal for automation applications.
Another benefit of Orientation Spin Welding is that there is no need to store energy or inertia in a spinning flywheel because of the torque generated by the servo drive motor. So it is possible to contact the part with the driver and to apply pressure to the part before rotation begins to either compress or align the two mating parts before welding. Therefore, the circumference speed calculations found in Inertial Spin Welding do not apply to Orientation (Servo) Spin Welding.
With orientation spin welding applications it is also important to have the appropriate conditions for spin welding success along with sturdy driving features to allow for proper orientation.
Orientation (Servo) Spin Welding Advantages
- Higher power
- Position-Based indexing possible
- Requires less velocity (better for engineering resins)
- Improved Process Control
- Easier to Automate (driver position remains constant for automatic loading)
Orientation (Servo) Weld Process Steps:
| Head Down: | Upper spin driver moves downward (typically without rotation) until the part halves make contact. |
| Spin: | Upon contact, a slight delay occurs to insure parts are seated properly and rotation is maintained at the user programmed RPM until the programmed number of revolutions and final axis of rotation (degrees) of the weld is achieved. If orientation is not required, user may program RPM and one of the following: a) Time, b) Collapse Distance, c) Absolute Distance during the weld. |
| Hold/Cooling: | Pressure is maintained on the part after rotational welding motion has ceased. Allows thermoplastic material to solidify, ensuring the optimum bond of the two part halves. |
| Home: | Servo motor rotates back to its indexing or home position automatically. |
Back to topAbout Inertial (Pneumatic Drive) Spin Welding
Inertial Spin Welding is an economic yet highly effective technique of assembling thermoplastic components with a circular joint.
With Inertial Welding, energy (inertia) is stored in a spinning driver (and flywheel) and then lowered with applied pressure to the mating part in the fixture. In this process one part is held stationary in a fixture as the driver is rotated into it with pressure. The driver must be loaded with the mating part or must engage the part while rotating. With this process it is not possible to contact the part with the driver and apply pressure to the part before rotation begins to either compress or align the two mating parts before welding.
With Inertial spin welding applications it is important to have the appropriate conditions for spin welding success along with sturdy driving features to allow for proper engagement of the driver.
Inertial (Pneumatic) Spin Welding Advantages
- Lower Cost
- Higher speed (good for softer materials)
- All inertia is transferred to part (part/part contact stops rotation)
Inertial (Pneumatic) Spin Weld Process Steps:
| Spin-up: | At cycle start, air motor and spin driver begin rotation and build up to the user programmed RPM (rotation speed). |
| Motor-off: | When target RPM is reached, the supply to the air motor is shut off and head begins to decend. Spin Driver remains in rotation due to stored inertial. |
| Head-down: | Upper tooling moves downward until the part halves make contact. Parts act as a brake and rotation stops. |
| Hold/Cooling: | Pressure is maintained on the part after rotational welding motion has ceased. Allows thermoplastic material to solidify, ensuring the optimum bond of the two part halves. |
Inertial Spin Welding Rotational Speed:
The key requirement for spin weld applications is part symmetry around a common axis. This allows the parts to rotate around the spin weld joint. For proper welding, it is necessary for the weld to be rotated at a predetermined speed.
For Inertial Spin Welding, the range of the weld speed is expressed in the circumference speed, which is usually in feet/second. The appropriate inertial rotation can be derived from the following formula, linking the rotational speed with the part diameter:
An air motor can then be selected to fit the part requirement: 4800RPM or 16,000 RPM, Flywheels are available in various diameters to accommodate a wide range of materials and part diameters.
An Electromagnetic Brake Option is often incorporated for parts less than 1" in diameter for melt control purposes.
Orientation vs. Inertial Spin Welding
Orientation (servo motor) Spin Welding | Inertial (pneumatic motor) Spin Welding |
| Higher weld power capability. System allows rotation to begin with part to part contact under the full force available from the actuator. | Lower weld power capability. System requires full RPM and inertia to be built up prior to part to part contact. Results in higher required RPM to create same weld as orientation (servo motor) based systems. |
| Higher cost. Servo motors and control systems increase equipment price significantly. | Lower cost. Simple pneumatic motors and simplified controls allow lower equipment pricing. |
| Position-based part to part indexing possible. Servo control allows indexing control of as little as 0.5°. | No control possible of part to part indexing. Rotation ceases when all stored inertia is released into the parts which can vary significantly enough from weld to weld to prevent any indexing control. |
| Lower operating speeds available may limit joint strength on some soft materials (application and material dependant). | Higher operating speeds often improve joint strength on lower durometer materials such as PE and PP. |
| Requires less velocity (RPM) which can significantly improve weld strength for semi-crystalline engineering resins such as PA, POM, PBT, PPO & PET. Rotation can be halted under tight control prior to material re-solidification. | Requires higher velocity (RPM) which can result in lower weld strength for semi-crystalline engineering resins such as PA, POM, PBT, PPO & PET. RPM required for these resins must be high enough to create heat but low enough to prevent weld fracture due to excessive rotations after molten material has begun to re-solidify. |
| Most process energy is transferred to the part, however some efficiency is lost in that the motor requires energy to build up to target RPM and to halt motor when target position/depth/time is reached. | All process energy (inertia) is transferred to joint area as part to part contact causes rotation to cease, similar to a brake. |
| Improved process control allows welding by Orientation, Collapse Distance, Absolute Distance or Time. Process limits (windows) available on any method not already controlled for welding. | Limited process control allows only absolute distance control if parts are under 1.0" diameter and optional electromechanical brake is purchased. No user control or process limits on weld Orientation, Collapse Distance or Time. Limits exist only for final part height (absolute distance plus hold/cooling distance only). |
| Low compressed air requirement due to minimal volume of air required to move actuator up/down only. | High compressed air requirement due to large volume of air required for pneumatic motor and movement of actuator up/down. |
| Higher power requirement as power is generated electrically (servo motor). | Low power requirement as power is generated pneumatically. |
| Easier to automate as the driver rotational position is re-indexed each cycle to insure repeatable starting/home position for automatic loading of spinning part half into the driver. | More difficult to automate as the starting driver rotational position is different each cycle. If spinning part half is designed with drive features, the part may be either difficult or impossible to load automatically into the driver prior to the start of each cycle. However, parts designed to interface with a 10˚ engagement driver (no drive features) and no orientation requirements can most often easily automatically loaded/welded. |
Our existing line of spin welders includes four unique models. Orientation and inertial versions are available. From manually loaded and unloaded machines to semi and fully automated in-line systems, each of our spin welders is designed to accommodate a specific range of application requirements.
Critical Spin (Orientation or Inertial) Welder Parameters:
- RPM
- Contact Force
- Weld Force
- Weld Collapse/Absolute Distance
- Weld Time
- Hold/Cool Time
- Hold/Cool Force
Designing for Spin Welding
Spin Weld Strength:
The spin welding process produces a welded joint which, in many cases, yields a weld strength that is consistently equal to or stronger than any other area of the part. As a result, the weld area can most often be exposed to the same strains and stresses as any other area of the part.
Common Spin Welded Materials:
- Acrylonitrile Butadiene Styrene (ABS-Cycolac)
- Acrylic-Styrene-Acrylonitrile (ASA-Geloy)
- PolyOxy-Methylene (POM-Acetal & Delrin)
- PolyAmide (PA-Nylon & Zytel)
- PolyButylene Terephthalate (PBT-Valox & Enduran)
- PolyCarbonate (PC-Lexan & Makrolon)
- PolyCarbonate / Acrylonitrile- Butadiene- Styrene (PC/ABS-Cycoloy & Bayblend)
- PolyCarbonate / PolyButylene Terphthalate (PC/PBT-Xenoy)
- PolyCarbonate / PolyEthylene Terephthalate (PC/PET-Xylex & Makroblend)
- PolyEthylene (PE)
- PolyEthylene Terephthalate (PET-Polyester)
- PolyMethyl MethAcrylate (PMMA-Acrylic & Lucite)
- PolyPhenylene Oxide (PPO-Noryl)
- PolyPhenylene Sulfide (PPS-Ryton)
- PolyPropylene (PP)
- PolyStyrene (PS)
- PolySulfone (PSO-Udel)
- PolyVinyl Chloride (PVC-Vinyl)
- PVDF (PolyVinylidene Fluoride (PVDF-Kynar)
- Thermo-Plastic Elastomers (TPE-Santoprene)
Spin Welding Joint Designs:
A good spin welding joint should have a weld area equal to or greater than a typical wall section of the part. Joints should also provide sufficient part-to-part alignment.
| Shear Joint | Flanged Shear Joint | Tounge & Groove Joint |
Other Spin Welding Design Considerations:
- Parts joint must be on a circular axis.
- Determine whether or not final orientation of parts is required.
- Joint design must take into account flash/particulate produced during the process.
- Preferably, upper part half will be designed for use with drive features (areas for driver to engage part).
- Ideal parting line will be parallel to the force applied by the driver.
- Joint design must allow for sufficient collapse distance, insufficient collapse may cause poor weld strength/quality.
- Material selection may have an impact on welder type (orientation or inertial).
- Part must be designed so that there is no contact (other than the joint area) between the spinning part half and the fixtured part half.
Spin Weld Tooling
Driver: Custom-made tool used to "spin" the part and generate the weld. Drivers commonly use raised or relieved surfaces to engage raised or relieved drive features on the spinning part half. Tapered silicone drivers can also be used on parts that do not have risen or relieved drive features.
Holding Fixture: The non-rotating part half must be held securely so that one part half does not rotate and remains in alignment with the spinning part half. Part details such as protrusions and lugs/ribs on the outside of the part aid greatly in preventing rotation.
Advantages of Forward Technology Spin Tooling:
- Over 95% of all tooling is designed and manufactured for your application by our in-house Tooling Design and Fabrication department in Cokato, MN.
- This in-house capability insures optimal quality and scheduling control as well as reducing time requirements in the event of product design changes.
- No charge/obligation complete application review and joint design assistance.
- Full prototyping capability.
- All tools are designed for ease of maintenance, adjustment, and maximum life.
- Tools provide support and location of joint area as well as accurate alignment throughout the welding process.
- Virtually every tool is thoroughly tested and debugged at our facility on equipment in our laboratory.
- Full start-up service/support at your facility is available.
Standard Spin Tooling:
- Steel, Aluminum, Titanium, Urethane, or Delrin tooling components.
- Lightweight Aluminum backing plate on base fixtures.
- Custom base fixture slides for support, part retention, part alignment and part detection
CNC Machined Spin Tooling:
- Precision CNC cut driver and fixture supports joint area of each part half.
Cast Silicone Spin Tooling:
- Used when drive features are not available/necessary on the upper and/or lower part half.
- Driver and/or holding fixture is often a ¼” to 3/8” or similar CNC-machined aluminum translation of the actual part based on CAD data.
- Typically a 10° taper engages either outside or inside diameter of part for gripping of the part during the spin process.
- 40-60 Durometer Silicone skin is applied to the contour of the driver.
- Silicone skin both acts as a gripping surface and protects the parts surface from marking.
Spin Tooling Options:
- Part Presence Sensors verify part presence/position prior to allowing machine to cycle.
- Part Eject eases removal of welded parts from tooling.
Spin Welding vs. Other Welding Methods
Spin Welding vs. Ultrasonic Welding
SPIN WELDING | ULTRASONIC WELDING |
| Typically higher cost. Spin motors and control systems are less common and mechanical actuators must be designed to withstand rotational torque, resulting in increased manufacturing costs. | Typically lower cost. Ultrasonic components are relatively common and the mechanical actuator may be designed without regard to withstanding rotational torque, permitting reduced manufacturing costs. |
| Typically higher joint strength with a given material due to ability to weld parts with much higher engagement area and material displacement during the weld. | Typically lower joint strength with a given material due to limits in part to part engagement area and material displacement. |
| Particulate and flash are commonly produced (amount is application and material dependant). The increased process friction and larger engagement areas and amount of material displaced during the weld create higher potential for excess material exiting the joint area. | Minimal to no particulate/flash (application and material dependant) due to limited degree of material displacement during the weld. |
| Ideal for welding soft materials such as PP and PE due to aggressive nature of the spin process. | Difficult to weld soft materials such as PP and PE due to the materials absorption of the gentle ultrasonic amplitude instead of adequate transfer to the joint area. |
Slower cycle times:
| Faster cycle times:
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| Can easily weld most semi-crystalline engineering resins including PA, POM, PBT, PPO & PET due to aggressive nature of spin process. | Difficult to weld some semi-crystalline engineering resins such as PA, POM, PBT, PPO & PET due to the gentle nature of the ultrasonic process. |
| Limited to welding parts with circular joint. | Allows welding of parts with many joint shapes/geometries. |
| Increased ability in joining dissimilar materials due to aggressive nature of the spin process. | Limited success in joining most dissimilar materials due to gentle nature of the ultrasonic process. |
| System components generally quite durable (servo motors/amplifiers). More difficult to damage componentry. Very few wear items and most are relatively inexpensive. | System components are fairly delicate (convertors, power supplies, horns, etc…) and tend to have a limited lifespan. |
| Only Orientation (Servo Motor) systems allow welding by Time, Collapse Distance and Absolute Distance. | Many systems allow welding by Time, Energy, Collapse Distance and Absolute Distance. |
| Occasionally more difficult to automate as the spinning part half must engage the driver. However, parts designed to interface with a 10˚ engagement driver (no drive features) and no orientation requirements can most often easily automatically loaded/welded. | Generally easier to automate as the vibrating part half does not necessarily need to engage the horn for adequate welding to occur. However applications without flat interface of horn/part will require more complex placement. |
| Process fairly immune to even moderate part size and geometry changes due to increased material displacement and ability to weld even when making high initial part to part contact. | Process very sensitive to even minute part size and geometry changes due to limits in material displacement and minimal initial part to part contact requirements. |
Forward Technology is a Crest Group Company