Riveting, Forming, Welding, Projection Conveyors, Systems
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4 PERMANENT PART ASSEMBLY 8 INSIGHTS 10 HOW TO: CONSIDERATIONS
ORBITAL RIVETING
TUNE UP YOUR ORBITAL RIVETER
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The Orbitform Press
Some products do not need to be taken apart for shipping, maintance, or repair. This article e x a m i n e s basic applications and considerations for common fastening and joining techniques used in permanent part assembly.
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FIG 1.1
PERMANENT JOINT APPLICATIONS
FIG 1.1
FIG 1.2
NON-PERMANENT JOINT APPLICATIONS
There are many reasons products should not be taken apart: • Personal Safety - the product is inherently unsafe to repair. • Operational Safety – high product liability if the product fails during operation. • Extreme operating forces – high shock, vibration, Push-Pull, and Shear. • Regulatory requirements - part must be new, not repaired, as mandated by law. • Warranty / Product integrity - part must be new and not repaired. • Modular assemblies – a product contains permanently assembled components. • Security / Tamper-proof / Vandalism – you don’t want anybody messin’ with it. Industries familiar with these concerns include: Automotive, Medical, Aerospace, Aviation, Electrical, Power Distribution, Safety, Military, and basically any products where lives are on the line and product liability is high, for example: Airbag Canisters, Mountain Climbing Gear, and Fire Extinguishers. If your product doesn’t need to be taken apart, and you’re using a nonpermanent fastening method such as retaining rings, threaded fasteners, posts and cotter pins, etc., you may want to consider permanent assembly for some of the following reasons: • Reduce the cost of fastening hardware: retaining rings, threaded fasteners, nuts, washers, and cotter pins • Reducing the costs of machining operations: machining grooves and threads, drilling and tapping holes • Reducing the costs of assembly operations and cycle time: forming a rivet or post vs. installing a retaining ring, cotter pin, or driving a screw / nut • Superior retention - compared to cotter pins, retaining rings, and Loctite® • Improved aesthetics - Formed head versus bolt head, nut, screw head, cotter pin, or retaining ring.
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We recognize every application is different, and there is no “one size fits all” solution for permanent part assembly. Figure 1.3 is a matrix of fasteners & fastener processes, along with a few common joint requirements and costing considerations. The matrix rates generic process effectiveness for each joint requirement. All fastening processes are non-manual, using minimally‑automated methods and typical application requirements. For the rating, we examined the lowest cost and least number of machining steps to achieve the requirement in the simplest way possible. For example, a low profile joint may be achieved with a counter sink or counter bore, at the cost of extra machining, just as aesthetics is greatly determined by the type of fastener, coating and/or finish, which greatly impacts the fastener’s cost. A retaining ring or cotter pin is a more expensive fastener, compared to a rivet, especially if that cost
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Riveting, Forming, Welding, Projection Conveyors, Systems JOINT CHARACTERISTIC
PERMANANT
OVERALL COST
ASSEMBLY LABOR COST
EQUIPMENT COST
MACHINING COST
FASTENER COST
AESTHETICS
HOLE FILL
SHOCK VIBRATION RESISTANT
LOW PROFILE
COMPRESSION (CLAMP LOAD)
ARTICULATING
FASTENER / PROCESS
COSTING
TENON ORBITAL/SPIRAL TENON HOT UPSET SOLID RIVET IMPACT SEMI-TUBULAR RIVET IMPACT RIVET ORBITAL/SPIRAL
RIVET HOT UPSET BOLT/NUT FORMED
NON-PERMANANT
BOLT/NUT STUD/NUT SCREW RETAINING RING COTTER PIN
KEY:
POOR
FAIR
GOOD
BEST
FIGURE 1.3: FASTENERS AND FASTENER PROCESSES ORGANIZED WITH COST CONSIDERATIONS
includes a mating pin with groove or through‑hole, resulting in lower machining costs because only a through-hole for the pin is needed. Overall cost considerations include: fastener, machining, equipment/ utilities, and assembly costs, based on the best overall value. All cost estimates are relative to each other across processes. For example, a tenon has no fastener, and therefore, no fastener cost relative to a rivet or bolt, but a machined tenon has a greater machining cost than a thru-hole for a rivet or bolt. A tenon formed as a casting would result in a different costing analysis.
the part, progressively forming the material with each rotation. This process (fig. 1.4) reduces the amount of forming force required by approximately 75% of a standard press. The orbital process can form
Orbital-Riveting & Forming Orbital riveting and forming is a cold forming process using a peen tool held at a fixed angle to create a sweeping line of pressure around
mild steel solid rivets from less than 1/16” up to 1-1/2” in diameter. The orbital forming process creates a low profile, aesthetically appealing finish, and allows for joint articulation as seen in multi-tool pliers, automotive door hinges, casters, etc. Spiral riveting and forming, also known as Radial, is similar to the Orbital process, but the material is displaced from the center outward in a rosette or rose curve pattern; this creates less side force than the orbital process, which can cause parts to wobble during forming. This is especially true when forming small diameter rivets, and/or long rivets that are not held rigid by the part or part fixture during assembly. The Spiral process is not recommended for semi-tubular and/or hollow rivets because the peen loses contact with the part being formed. As a rule of thumb, 90% of all Radial/Spiral riveting can be done with the Orbital process, with lower maintenance costs as compared to the Spiral/Radial process. The complexity of the Spiral tooling head’s planetary gear, thrust plate, and pressure cup significantly increases overall cost of ownership. However, for long, thin, and unsupported rivets, Spiral/Radial may be the better option. In general, Orbital has a longer reach, which can be further extended using a special 3 or 4 degree longreach orbital head, or an orbital head extension. To form around obstructions, options include: a c-frame orbital head with an antirotate device, an offset orbital head, and/or a modified peen with antirotate device. In addition, orbital heads can be configured to form multiple rivets simultaneously, using multi-spindle or multi-point tooling heads. Clamp loading will vary based on forming a tenon or rivet, the type of material, tooling, and fixturing used. For example, If the part is supported (fig. 1.5), allowing a gap between the manufactured rivet head and the part, the final joint will allow the rivet to float and will not provide
FIG 1.4
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FIG 1.5
any compressive loading. If the manufactured rivet head is supported (fig. 1.6), eliminating the gap between the part and the rivet, the joint will exhibit compressive loading. To improve clamp loading options include: a pressure pad to pre-clamp the part, increasing the advance rate of the Powerhead, and/or using an orbital head with a reduced attack angle to increase downward force. Both Orbital and Spiral processes are recommended for low profile joints requiring articulation, because they form the rivet head without completely collapsing the shank. Clamp load can be adjusted to maintain some rotational torque/ friction, as required in applications such as surgical scissors. Retaining rings and cotter pins allow articulation, but do not provide compressive loading characteristics, and therefore allow vibration between the fastener and the parts. If the joint requires superior clamp loading and torque control, one fastening option is to use a bolt and nut, and then orbitally form the bolt against the face of the nut, locking the nut in place. Another option is to orbitally ring-stake the nut into the bolt’s threads to permanently lock them together. This additional operation adds to the production cost and reduces throughput. As a permanent solution, this is only recommended when extreme clamp loading and precise torque control is needed.
HOT UPSET FORMING & RIVETING The Hot Upset forming and riveting process (fig 1.7) uses heat and pressure to form the fastener. Similar to electro-forging, the heated material
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FIG 1.6
becomes malleable and collapses under pressure applied by the Powerhead. With this process it is possible to form a round fastener into a square hole, creating a high-torque joint. Unlike welding, in most cases the base material does not bond with
FIG 1.7
the fastener, but depending upon the material bonding may occur. In addition, this process may change the microstructure of the material being formed, altering its metallic properties. Testing the rivet or formed material is recommended. As a rule of thumb, Hot Upset is best suited for hardened materials that cannot be formed by other methods. This unique process provides greater hole-fill, over 98% percent, increases push-out force, and creates an overall tighter joint due to molecular contraction during cooling. This process is not recommended for joints that require articulation; it may also affect surface coating aesthetics. Example applications include automotive striker-wires, ball studs, and joints with high torque and high shock or vibration requirements, such as military weaponry. Hot Upset typically has a 3-4 second cycle time, which is generally slower than orbital or impact riveting.
In addition, hot parts require special handling considerations. Direct current (DC) powered systems are more efficient and precise than their AC counterparts, but come at a higher initial cost. Cost of ownership includes power consumption and tooling electrodes. Hot Upset systems also require a chiller to maintain optimal tooling temperature.
IMPACT RIVETING - SOLID & SEMI TUBULAR RIVETS Impact Riveting is a cold forming assembly process using pneumatic, electro-mechanical, hydrapneumatic, or hydraulic force to install a rivet. Joint characteristics can vary greatly depending on the rivet type, material and geometry. Some common rivet types include solid, semi-tubular, and self-piercing. The forming sequence is unique to each type of rivet. The shank on a solid rivet must swell to fill the hole before the head collapses. On a semi-tubular rivet, the hollow tenon curls over on impact, drawing the parts together with minimal shank swell. Self-piercing rivets (fig. 1.8), used to join sheet metal and other thin materials, pierce the upper layers of material until the bottom layer is displaced into a pocket in the anvil, creating a button shape similar to clinching. This process eliminates the
FIG 1.8
cost of machining a hole, but with the absence of a hole, some applications may require external fixturing to align the parts. Standard Impact Riveting machines have a much quicker cycle time than
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Riveting, Forming, Welding, Projection Conveyors, Systems
FIGURE 1.9: THE IMPACT RIVETING PROCESS
standard Orbital, Spiral and Hot Upset machines, and provide higher production throughput, commonly used for high volume commodity products such as HVAC duct work, brake pads, and circuit breakers. In addition, impact machines include automatic rivet feeding systems, eliminating manual rivet handling, making the process ideal for installing multiple rivets in a single part assembly. In most cases the operator handles the part, so there is no cost for part fixturing. High capacity impact machines can install solid rivets up to 5/8” inches in diameter, providing a robust, low-profile, solution for permanent assembly. Typical perishable tooling includes: Jaws, Drivers, and Rollsets. For high volume assembly of brittle materials like clutch assemblies, circuit boards and plastics, riveting machines can be configured with load-deflecting components. To consolidate equipment and reduce the work area footprint, a single machine can be configured to install up to four rivets simultaneously; other options for multi-riveting include dual head and multi-head machines. Using an offset driver accessory, riveting heads can be positioned as close as 1/16” of an inch between rivet heads.
ROLLER FORMING - ASSEMBLING CYLINDRICAL PARTS
to apply a symmetrical force to the part. Roller forming is used for flaring, forming a lip, crimping, or forming a groove in cylindrical parts too large for other processes. Assembly applications include: water pumps, bearings, ball joints, air bag
FIG 1.10
canisters, electrical sensors, fuses, solenoids, and parts where a groove or lip is needed, such as sealing the end of a tube. As a general rule, 90% of all Roller Forming applications are between 3/8” and 6” inches in diameter. Wall thickness can vary from 1/32” to over 1/4” of an inch depending on the type of material. The Roller-head RPM and advance rate are controlled by a Powerhead configured with an integrated Load Cell and LVDT for process monitoring and control. For part clamping, a Thru-Spindle Pressure Pad option is available.
For static Roller-heads, typical cycle times range from 3-5 seconds depending on the application. Articulating Roller-heads are used for navigating around part obstructions and applying horizontal pressure needed for crimping or grooving applications. Pneumatically actuated Articulating Roller-heads can deliver a horizontal force up to 5,000 lbs. @ 100 psi. Typical cycle times for an Articulating Roller-head range from 4-10 seconds depending on the application. Roller Forming’s non-impact symmetrical loading and precision control allows this process to form a retaining lip over glass or other brittle materials. Roller Forming can also replace multi-point crimping with a full 360 degrees of contact retention. If a torque resistant interface is required, rough or knurled mating component surfaces are needed to grip against the formed lip or groove. This process can, in some cases, replace welding to provide a strong joint with an aesthetically appealing finish, reducing production time and assembly cost. Sealing characteristics depend on the part’s design and usually requires the addition of a gasket or O-ring; customer testing is highly recommended.
IN CONCLUSION... If your product doesn’t need to be taken apart for shipping, maintenance or repair, permanent part assembly can be a cost effective solution to other fastening methods, in addition to increasing production throughput, and reducing fastener, machining, and overall assembly costs; you also get the many inherent benefits of permanently assembling your product. S. Cumming & J. Price
Another permanent fastening method, specifically designed for assembling large diameter parts, is Roller Forming. Roller Forming is a non-impact process using a spinning Roller-head with two or more rollers
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What is Orbital Forming? Orbital Riveting and Forming is a quiet, non-impact cold forming process using an angular contact peen tool combined with pressure to form the material. The orbital process creates a low profile, aesthetically appealing head forming and finish, and can allow for joint articulation as seen in multi-tool pliers, automotive door hinges, and casters. In the Orbital process. a Peen tool is held at a fixed angle, creating a sweeping line of pressure around the part, progressively moving material with each rotation. This process reduces the amount of forming force required by approximately 75% of a standard press. The orbital process can form mild steel solid rivets from less than 1/16” up to 1-1/2” in diameter.
FIG 8.1
FIG 8.2
Fig 8.1 A peen forms a rivet with an automated system Fig 8.2 Example of a captured form rivet head
• Smooth, non-impact • Precision Control • Articulating Joints • Aesthetic Appeal • Single & Multi-point • 75% Less force than using a press
FIG 8.3
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Riveting, Forming, Welding, Projection Conveyors, Systems With Orbitform’s orbital powerheads the components can last for years.
The Industry Standard Orbitform Powerheads are available in a wide range of sizes for custom applications. They are efficient at any angle and can be easily integrated with other assembly equipment. All Powerheads are available in single, multispindle, or multi-point configurations and include a standard orbital head and peen. Most Orbitform
powerheads come complete with pre-wired, built-in, internal limit switches. Motors are pre-wired for convenience.
Lubed for Life Designed for rugged lowmaintenance use, Orbitform Powerheads come with hassle-free lifetime bearing and seal lubrication. Without preventive maintenance the life expectancy of a competitor’s Powerhead is often greatly reduced.
Orbitform’s main drive spindle incorporates a set of angular contact bearings as opposed to a single row of thrust bearings. With this arrangement the comparable thrust capacity is significantly greater, by as much as 40 percent. Laboremp oremquaspic temporem consedipist, eost qui re sustibus, quam que voluptur? Icitaest et acesciet inci rerchil lecerum quo cuptas et aut quam, ex esciis earchil iur? Sum alignat urehenihil il ium ipicillor res eumquis modis re lit labo. Volupienis ad mi, ut que sin pero dolupta turecum sincipi caborem quatur atiae. At re ne id estissum nobitiande voluptius. Imi, es dita diti doloratamet escidusam fugia nihit ape lis aliandu cipsum non nonet aut quatemq uiaestrum es quam assit occum volor aut in cus nulparum repudi dolupta speruptis eliam quam nia vera consed eatis incim dolecat minia id ma con et ipsus eaqui cum que diorum alitaectur accabore,
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Permanently assembling parts using an orbital process offers many advantages including: 80% less force required than a conventional press, a low profile aesthetically appealing head-form, low cost fasteners, a high strength joint, and the option to allow a joint to rotate. Proper machine setup and maintenance is critical in achieving a desirable head form and consistent results. With over 25-years of experience, Orbitform’s application engineers and service technicians have seen what can happen on the factory floor. Here are a few tune-up tips to keep your orbital assembly equipment running smoothly, and producing quality parts. To assure a quality head form it is critical that the center of the orbital head be aligned with the center of the rivet being formed. A misalignment can produce undesired results, 10
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inside the orbital head. The peen is held in place with a magnet or set screw and should be easy to remove. Apply an anti-seize lubricant to its shank at least once a week.
rejected parts and possible damage to bearings and the orbital head. Alignment issues can come from: the fixture, the part, and/or the machine setup. The easiest method to check the alignment is with Orbitform’s Orbital Alignment Kit. Typically on a 1/4” diameter rivet, the center of the orbital head should be within 0.004” Total Indicator Runout from the center of the rivet.
THE PEEN The peen is the perishable tooling that touches the rivet or part being formed. Make sure the peen-holder turns freely
Check the peen for excessive wear. Never sharpen or machine a worn peen. Changing the length of the peen changes its point of contact, which can affect the resulting head form, and possibly lead to bearing failure. Always replace worn tooling. Make sure new tooling meets the standards for hardness, polish, and coating set by the manufacture. Check if the peen is too hot to touch after forming. Excessive heat can lead to or indicate bearing failure. A hot peen may mean it’s hitting the part too hard or dwelling on the part too long and/or not rotating properly. The flow control on the Powerhead’s exhaust may need to be adjusted to increase or decrease the Powerhead’s advance rate.
LUBRICATION Orbitform’s Powerheads are lubed for life and require little preventative maintenance.
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Riveting, Forming, Welding, Projection Conveyors, Systems floor drops, the Powerhead’s force will be diminished; this can effect cycle-time, and the overall head-form. Verify the recommended air pressure is within the machine’s specification.
However, the orbital head should be inspected and greased after approximately 100 hours of forming time. Do not confuse this with 100 hours of machine operation. If a part takes 5 seconds to form, that would be one minute of forming-time for every 12 parts, one hour for 720 parts, or 72,000 parts for every 100 forming-hours. Be careful not to over grease the orbital head. Typically, a single shot from a hand pump is all that’s needed. Over greasing can create extra drag on the bearings and restrict the peen-holder from rotating freely.
Just as important as air pressure is air volume. The more air-driven equipment added to a production line the greater the overall volume of air needed to run them. Air pressure may be within limits, but the machines may be starved for air, which can affect cycle-time and forming results. This is especially true when forming multiple rivets with quick forming cycles. Make sure the lines can deliver the required volume of air; if not an accumulation tank may be needed. An orbital riveting or forming process can solve many challenging assembly requirements; a well-tuned machine is the key to consistent forming results and quality parts.
J. Price
IT ALL STARTS WITH THE CUSTOMER’S PART
RIVETING FORMING
CONVEYORS
SYSTEMS ASSEMBLY EQUIPMENT SOLUTIONS Orbitform designs and builds assembly equipment, including Riveting, Forming, Welding, Conveyors, and Custom Assembly Systems. Orbitform manufactures its own line of assembly components, made in the USA since 1984. Services include Assembly Analysis, Tooling Development, and low-volume production runs. MADE IN THE USA
TOOLING
AIR Orbitform’s Powerheads are rated to 100 psi of air pressure. We generally size our Powerheads based on air pressure available in the plant. If the pressure on the factory
PROJECTION WELDING
POWERHEADS & ASSEMBLY COMPONENTS www.orbitform.com 1600 Executive Dr, Jackson, MI (517) 787-9447
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