N U T A S S E M B L I E S

Transcription

1 NUT ASSEMBLIES

2 Emhart Teknologies Nut-Assemblies What is an Emhart Teknologies Nut Assembly? An Emhart Teknologies nut assembly is defined as a pre-positioned fastener assembled to one or more components. Emhart Teknologies has three types of fastener assemblies under the Gripco brand. The three assemblies are staking, clinching and welding. In some cases, after a fastener is positioned onto a component it is then assembled onto another component. A good example of this type of nut assembly is the Gripco cage-nut assemblies. A clinch nut-plate sub-assembly is placed in a stamped cage so that once the cage is welded into position, the nut plate will float to provide for manufacturing tolerances. What is an appropriate application for a Nut-Assembly? When the main purpose of the assembly is for fastening, it makes sense for Emhart Teknologies to supply the assembly. Emhart Teknologies will ensure that the critical details of the component, such as thread quality and prevailing torque, meet the specifications of a given application. In addition, any assembly problems can be detected and corrected with tremendous efficiency since all the activity is within the same manufacturing facility. Emhart Teknologies can provide fasteners designed for different platings. How do I know what type of nut to use in my Nut-Assembly? Emhart Teknologies uses three methods of pre-positioned fasteners: Gripco staking flange nuts, Gripco clinching clinch nuts and Gripco welding weld nuts. It is very important to choose a method that is suitable for the application. As always, an Emhart Teknologies representative is available to offer assistance in matching the fastener with the application. Why is a Nut-Assembly used? Nut-Assemblies are used as an aid to manufacturing. Today s manufacturing methods require reduced labor requirements along with quality improvements. With the use of a pre-positioned fastener, labor required to tighten the fastener and bolt is reduced because the operator only needs a torque gun to complete the task. Conventional tightening methods require the operator to use both a torque gun and a wrench. Pre-positioned fasteners reduce ergonomic concerns because the operator is using only one tool. Using one tool allows lower labor costs due to the fact that only one tool needs to be aligned with the fastener rather than two tools. Safety concerns are reduced because the chance of wrench slippage is reduced. What is the difference between staking, clinching and welding? Staking a Flange Nut. The flange nut is mated with a plate that has a hex hole slightly larger than the hex of the flange nut. The nut is inserted into the hex hole and the corners of the hex of the nut are shaved down to stake the plate between the flange and the shaved corners. Advantages: A) Typically uses a standard IFI recognized nut. B) The nut can be made from a wide variety of materials including high strength (medium carbon). Flange nuts are available in class 8, 9 and 10. C) The mating material can also be made from a variety of materials and does not necessarily have to match the nut material. (Note: Special care is taken to avoid galvanic corrosion.) D) Gripco prevailing torque feature is available on flange nuts. E) The nut can either be staked tightly or loosely (depending upon the application).

3 Clinching a Clinch Nut. A clinch nut is a specially designed nut featuring a hex shaped body on a hex shaped pilot. To pre-position the clinch nut in the mating plate, the pilot is inserted into a hex shaped hole and a punch strikes the nut from the opposite side clinching it into the plate. Advantages: A) The nut can be made from a wide variety of materials including high strength (medium carbon steel). These fasteners are available in class 8, 9 and 10. B) The mating material can also be made from a wide variety of materials and do not necessarily have to match the nut material. (Note: Special care can be taken to avoid galvanic reaction.) C) Gripco prevailing torque feature is available on clinch nuts. D) A coining operation can be done in the mating plate to provide a near flush condition. E) Special large flange clinch nuts can be used for base materials with relatively low tensile strength. Welding a Nut. Although weld nuts are not standard fasteners as described by IFI, many companies have their own standards for weld nuts. Projection weld nuts are typically resistance welded. Weld nuts using this process have a number of projections (3,4 or 6). Electric current is directed through these projections to generate enough heat to melt the projection and a portion of the base material. By using the correct combination of pressure, current, and time, a reliable weld can be achieved. Advantages: A) The hole size for weld nuts only need to be slightly larger than the bolt. B) Gripco prevailing torque feature is available on weld nuts. C) Weld nuts can have a flush bottom surface. What are the types of Nut-Assemblies available from Emhart Teknologies? 1. Gripco weld nut assemblies. 2. Gripco handle nut assemblies. 3. Gripco flag nut assemblies. 4. Gripco clip nut assemblies. 5. Gripco clinch nut assemblies. 6. Gripco cagenut assemblies. 7. Gripco T-nut assemblies. What is the difference in the Nut-Assemblies? 1. Weld nut assemblies. Used to provide additional bearing surface for structural integrity. 2. Handle nut assemblies. Used in applications where restricted space eliminates the ability to position a wrench 3. Flag nut assemblies. Flag nut assemblies are used in anti-rotation applications. In addition, flag nuts can be used to manually position a nut in a hard to reach area. 4. Clipnut assemblies. Clipnut assemblies are snapped into position 5. Clinch nut assemblies. Used for high strength applications such as engine cradle attachments. 6. Cagenut assemblies. Cagenut assemblies provide a clinch nut assembly inside of a retaining cage. 7. T-nut assemblies. T-nut assemblies provide a T-nut fastener inside of a retaining cage. 8. Multiple nut assemblies. Multiple nut assemblies can be provided for any of the above listed assemblies.

4 When are the Nut-Assemblies used? 1. Weld nut assemblies. Weld nut assemblies are used when additional bearing surface is needed. By increasing the bearing surface, rupture or pull-through in parent material is reduced. Weld assemblies are produced using SAE 1008 or SAE 1010 material. 2. Handle nut assemblies. Handle nut assemblies are used in tight or restricted areas such as narrow channels, tubing and hydroformed parts. Handle nut assemblies can be produced from SAE 1010 material or SAE 1050 material. Most common used material is SAE 1050 heat treated to RC Flag nut assemblies. Flag nut assemblies are used in areas where the fastener needs to be positioned in hard to reach areas. Gripco flag nut assemblies are offered in four different configurations: straight, single bend, offset bend and double bend. Emhart Teknologies engineering team can assist in specialty designs for almost any application. Flag nut assemblies are produced using SAE 1010 or SAE 1050 material. SAE 1050 material heat-treated to RC Clipnut assemblies. Clipnut assemblies are used when the fastener position is near the edge of the parent material. A flange nut is staked into the clipnut assembly. The flange nut can be either tight or loosely staked depending upon the application. The clipnut is formed with retaining tabs that allow the assembly to be snapped into correct position. 5. Clinch nut assemblies. Gripco clinch nut assemblies are available in low and medium carbon steels. Low carbon steel clinch nut assemblies can be welded (either by mig or resistance) into position. Medium carbon clinch nut assemblies are used in applications requiring larger bearing surface with high strength. 6. Cagenut assemblies. The cage retains the clinch nut plate but allows the clinch nut plate to float. This float allows the clinch nut plate +/- 3.5mm of movement (float can be reduced or increased depending upon the application and upon the size of fastener used) in both X and Y-axis. The cagenut assembly was designed for applications where manufacturing variations require a high strength fastener with float along with the ability to either resistance or mig weld the retaining cage. The floating feature of the clinch-nut plate provides perfect alignment every time. The nut-plate is manufactured from medium carbon steels while the retaining cage is manufactured from low carbon steels. Cagenut assemblies are designed to resist primer build-up sticking. 7. T-nut assemblies. A cage retains the T-nut but allows the T-nut to float. T-nut assemblies are physically smaller than cagenut assemblies allowing use in restricted areas. The bearing surface of the T-nut assembly is also smaller than cagenut assemblies. Float of the T-nut assembly is +/- 3mm. T-nut assemblies also provide resistance to primer build-up 8. Multiple nut assemblies. Gripco nut assemblies are available for multiple applications. Nut- Assemblies have been provided with four clinch nuts in one assembly plate for transmission mounting. Four staked nut assemblies have been used in heavy-duty suspension applications. Cagenut assemblies have been manufactured with a single floating plate with two nuts. Cagenut assemblies have also been manufactured with two individual floating plates inside of one cage assembly. Emhart Teknologies can provide engineering design assistance for many assembly applications.

5 How to identify assembly applications. Assemblies are used for different reasons. Applications where operators can be injured from wrenches slipping are good applications for assemblies. Applications where the operator installs a bolt, adds a washer, starts the nut, applies a wrench to the nut, then aligns the torque gun to the bolt are excellent candidates for assemblies. This also reduces part numbers by eliminating the washer. An area where the operator has trouble removing the wrench after tightening a nut is an area where assemblies should be used. Areas where large holes have been cut out to provide access for wrenches should also use assemblies. Nut stripping or bolt failures are areas where cagenut assemblies can be used. Watching the production line and observing where operators take extra time to tighten bolts will identify areas to investigate. Other areas to look for assembly possibilities are in the repair or reject area of the plant. High repairs are normally caused by misalignment of the bolt and nut. (High torque, plating issues or mismatch of nut and bolt grade can also cause repairs. Be sure to identify the true root cause.

6 Clinch Nut Plate Advantages Gripco Clinch Nut Plate Extruded Nut Plate 1. Medium Carbon Steel Nut Low Carbon Steel 2. Heat Treated Rc Not Heat Treatable 3. Single Diameter Thread Engagement Length Requirement 3. 2 to 2 1/2 Diameter Thread Engagement Length Requirement 4. Cut Tapped Threads After Heat Treat 4. Roll Formed Tapped 5. Hexagon Shape Adds Wrenchability 5. Round Barrel Deters Wrenching 6. Nut Threads Do Not Plastically Deform During Loading 6. Nut Threads Deform Plastically During Loading 7. Broken Bolts Free Spin Out of Nut 7. Broken Bolts Clamped Tightly By Deformed Threads 8. Heat Treated Medium Carbon Steel Plate 8. Non-Heat Treatable Low Carbon Steel Plate 9. Lower Weight 9. Higher Weight 10. Permits Use of Shorter Bolt 10. Requires Longer Bolt 11. Narrow Torque Tension Scatter 11. Less Narrow Torque Tension Scatter 12. Thread Form Controlled To Allow For Uni-Prime Build Up 12. May Require Teflon Due To Poor Thread Capability 13. Medium Carbon Plate Carries Load Without Deflection 13. Nut Base Deflects Losing Bearing Area And Clamp Load

7 Flange Weld Nut Plate Advantages Gripco Flange Weld Nut Plate Extruded Nut Plate 1. Hoop Strength at Flange Allow for Class 10 Strength With Single 1. 2 to 2 1/2 Diameter Thread Engagement Length Requirement Diameter Thread Engagement 2. Hexagon Shape Adds Wrenchability 2. Round Barrel Deters Wrenching 3. Nut Threads Do Not Plastically Deform During Loading 3. Nut Threads Deform Plastically During Loading 4. Plate Thickness is Independent of the Thread Size 4. Plate Thickness Depends on Size of Extrusion 5. Lower Weight 5. Higher Weight 6. Permits Use of Shorter Bolt 6. Requires Longer Bolt 7. Thread Form Controlled To Allow For Uni-Prime Build Up 7. May Require Teflon Due To Poor Thread Form Capability

8 Clinch Nut Plate Advantages Gripco Clinch Nut Plate Standard Weld Nut 1. Medium Carbon Steel Nut Low Carbon Steel Nut 2. Nut Is Heat Treated RC Nut Can Not Be Heat Treated Without Damaging Weldability 3. Nut Has Cut Tapped Threads After Heat Treat 3. Nut Can Not Be Heat Treated Without Damaging Weldability 4. Nut Threads Do Not Plastically Deform During Loading 4. Nut Threads May Deform Plastically During Loading 5. Broken Bolts Free Spin Out of Nut 5. Broken Bolts Clamped Tightly By Deformed Threads 6. Narrow Torque Tension Scatter 6. Wider Torque Tension Scatter 7. Thread Form Can Be Controlled To Allow For Uni-Prime Build Up 7. May Require Teflon Due To Poor Thread Capability 8. Weldable Steel Plate Provides A Larger Bearing Surface 8. Standard Weld Nut Has A Small Bearing Surface

9 General Question To Help Decide On The Appropriate Prepositioning Method Question Welding Clinching Staking Are these assemblies available in: No- the materials required for Yes Yes IFI Metric Class 10 these specifications are not IFI Inch Grade C & G weldable. However, in some SAE Inch Grade 8 cases the proofloads for these specifications can be achieved by designing special geometries. What is the risk of damaging the Although Gripco takes special care Because the clinching process is Because the staking process is threads in the assembly process? to ensure the quality of in-house mechanical there is essentially no mechanical there is essentially no welded assemblies, the welding chance of thread damage in the chance of thread damage in the process presents the greatest clinching process. staking process. potential for thread damage. Causes of thread damage could include weld splatter on the threads and/or thread distortion due to the heat and pressure. What are the material requirements for The mating plate must be of The mating plate may be of any The mating plate may be of any the mating plate? weldable material similar to that material strong enough to survive material strong enough to survive of the weld nut. (low carbon steel) the clinching process. the staking process. How flush is the bottom bearing surface Absolutely Flush The clinching process can be The bearing surface using the of the mating plate? designed to provide a near flush staking method is limited to the bearing surface. One way is by bearing surface of the flange coining the mating plate so that the nut used. The bottom of the mating clinched pilot rests above the plane plate would not normally be a of the mating surface. Another bearing surface. method is to design the pilot and the hole so that the pilot is flush with the plane of the mating surface. The drawback to the latter method is that the pushout strength of the fastener is greatly reduced.

10 General Question To Help Decide On The Appropriate Prepositioning Method Question Welding Clinching Staking What prevailing torque features are The toplock prevailing torque Because of the need for a flat top Because the staking method available? feature is most common lock for in the clinching process, the attaches from the top down on a weld nuts. It provides a good toplock prevailing torque feature standard flange nut, any locking locking feature without significantly is used to provide a good lock for method can be used that would reducing the surface area on top these types of assemblies. normally be used on a flange nut. of the nut for the electrode. The crownlock prevailing torque feature would be recommended since it is the best all-metal locking feature available. Can the nut be attached with some No, welding does not allow for float. Yes, there is a process of Yes, it is possible to allow a small float to allow for misalignment? clinching that will allow a small amount of float. amount of float. This process is very similar to the staking method. Can a "standard" nut be used? Any type of weld nut may be The process of clinching uses a The staking process can be done used. Although weld nuts are not specialized nut. However, Gripco with a standard flange nut as designated as standard parts by produces clinch nuts as a regular defined by IFI. The process may the Industrial Fastener Institute part of their product line. also use a special flange nut. (IFI), many large nut users define their own standards for weld nuts. What type of hole id required in the Round hole Hex hole Hex hole mating plate?

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17 Glossary of Common Fastener Terms ASTM- Americal Society for Testing & Materials. Bolt- An externally threaded fastener, designed to hold components together in assembled parts and normally tightened or released by torquing a nut. Brinell Hardness Test- Also known as the Brinell Hardness Number (BHN). A method similar to the Rockwell test, the hardness of a metal is determined by applying a standard load to a standard size steel ball placed upon a prepared surface of the metal, then measuring the diameter of the impression produced. This test, as with the Rockwell test, is only valid for materials thick enough to prevent the indentation from making an impression on the backside of the material. Carbon Steel- Any steel made by combining carbon with iron. The amount of carbon, expressed in %, determines whether the steel is low, medium or high carbon. Case Harden- Hardening a ferrous alloy so that the outer portion is made substantially harder than the inner portion. Clamping Force- Or preload, expressed in pounds, denotes the amount of tension force created that holds two or more pieces together when a fastener is tightened. In an ideal assembly, to prevent failure due to loosening, overloading, or fatigue, the clamping force produced must be greater than the external forces wanting to separate the connection. When multiple fasteners are used on one assembly, the clamping force of each fastener (determined by its grade, diameter and thread pitch) is combined. Their sums must be greater than the external loads applied to that assembly. Class- Used to identify strength of metric fasteners. Class 5 is made from low carbon steel and is not heat treated. Class 9 is made from low to medium carbon steel and or may not be heat treated. Class 10 is made from medium carbon steel and is heat treated. Class of Thread- Classes of threads are distinguishable by the amount of tolerance or tolerance and allowance specified. 1A, 2A and 3A are external class threads. 1B, 2B and 3B are internal class threads. Class 2 is used when the threads are to be plated, causing a dimensional increase and class 3 threads are for a non-plated, very close tolerance thread fit. Corrosion- Gradual chemical or electrochemical attack on a metal by atmosphere, moisture or other agents, such as salts and acids. Cut Threads- Made by using a thread cutting die or lathe cutting. The thread is formed by removing the metal from the full shank diameter to produce the grooves. Diamond Pyramid Hardness Test- Another hardness test that can be made on relatively thin materials. Samples are mounted in a metallographic specimen that is viewed under a microscope. A square-based diamond pyramid is pressed into the surface under a standard load whereby the diagonal of the indentation is optically measured, then calculated to produce the hardness expressed as D.P.N. (Diamond pyramid number) or V.P.N. (Vickers pyramid number). Ductility- A term used to express the degree of flexibility of materials. The property that enables solid substances, particularly metals, to undergo cold, visible, plastic deformation, (drawing) usually as a result of tension. The metal may thus become permanently extended (elongated), with a corresponding reduction in cross-sectional area without actual fracture or separation. Elastic Limit- The maximum stress that can be applied to a body that will allow it to regain its original dimensions after removal. It is the maximum stress that can be applied with no significant measurable after-effects. Once this value has been exceeded for a particular body, the body becomes permanently elongated and will not return to its original dimensions.

18 Elongation- The change in length of a piece of material that has been stretched beyond its elastic limit or to its breaking point, expressed as per cent. Elongation and reduction of area are means of determining the ductility of steel. Grade- Used for classification of inch series fasteners. Grade A is made from low carbon steel and can not be heat treated. Grade B & F is made from low to medium carbon steel and may or may not be heat treated. Grade C & G are made from medium carbon steels and is heat treated. Heat Treating- An operation involving the heating and cooling of a metal in certain time cycles to obtain specific desireable conditions or properties. IFI- Industrial Fastener Institute. Knoop Hardness Test- A diamond indentation hardness test used for determining the hardness of the individual microconstituents of alloys. The test is used for thinner materials but is similar to that devised by Brinell. The indenter is rhombic in shape. Result is optically measured as in DPH. Major Diameter- The distance across the crest or top of the threads on a bolt. This would be the same as the inside diameter of a tube that would slip snugly over the threads. Largest diameter of a screw thread. Minor Diameter- The distance across the base or root of the threads of a bolt. If the threads were carefully removed on a lathe, the re- maining diameter would be the minor diameter. Smallest diameter of a screw thread. Non-Ferrous- An element or material not containing iron; e.g., brass, aluminum, copper. Pitch- The number of threads in one inch of the threaded length of a cap screw, expressed as threads per inch (TPI). The pitch of one thread is the distance that a nut would advance on a bolt when turned one full turn. In Metrics, the pitch is determined by measuring the distance between the crest of one thread to the adjacent thread. This value is expressed in millimeters (mm). Fatigue- A cause of failure which takes place under conditions of repeated flexure or fluctuating stress below the ultimate stress of the material: Fatigue failure generally occurs at loads which applied statically would produce little perceptible effect. The fracture is usually progressive, and in most cases, you can see how it occurred. In the loading of a metal part, the maximum stress occurs at the surface, so performance in service under repeated stress directly depends on the surface stress range and surface properties. Failure often starts at a small, even microscopic, crack or discontinuity and spreads with each repetition of the stress. The faces of the crack rub together, producing a sort of burnished appearance. When the service conditions are such that the stress varies, being from low to high, the rate of growth of the crack will vary. This gives rise to rub mark zones which are visually distinguished by "beach marks" or an "oyster-shell" appearance. Local stress concentration produced by nicks, notches, or scratches, caused by using the "wrong" side of a flat washer against the fillet of a bolt head, are nuclei (staring points) for progressive fatigue failure. Other stress breaks start because of tool marks, rough surfaces, quenching and grinding cracks, poor fillets, as well as inclusions in the metal, corrosion, etc. Ferrous- A Latin and chemical term meaning iron or some substance containing iron; i.e., ferrous alloy. Float- The amount of float the the fastener can move in the X, Y or Z axis. Galvanize- To treat steel with a bath of molten or electrodeposited zinc to prevent rusting through establishment of a sacrificial anode. The zinc rusts first, therefore, protecting the substrate metal. Hot dip coatings are very thick. The 1A thread pitch is used for bolts that are hot dip galvanized.

19 Pitch Diameter- The diameter halfway between the major and minor diameters. Point- The chamfer on the threaded end of a bolt that permits easier starting of a nut. Prevailing Torque- The torque required to rotate the nut on or off the mating bolt. Prevailing On Torque- The torque measured when the nut is advanced toward its seated position. Prevailing Off Torque- The torque measured when the nut is being removed. Proof Load- A specified test load which a fastener must withstand without any indication of siginificant deformation or failure. Quenching- The rapid cooling of a heated metal by contact with liquids, solids or gases. Torque- The amount of twisting force, or twisting moment (expressed in inch-pounds or foot-pounds), applied to the nut, when a nut is used, or applied to the head of a bolt when it is being used as a cap screw (threaded into a tapped hole). Twelve inch-pounds or one foot- pound of torque would be created by exerting a one pound pull on a point of a wrench handle exactly 12" from the center of a bolt. Rockwell Hardness Test- A method of determining hardness by measuring the comparative depth of two carefully controlled indentations, one superimposed on the other. Root- The deepest point of the V-notch that forms the groove of a thread. A well designed fastener should incorporate a radiused or rounded root. SAE- Society of Automotive Engineers, along with IFI and ASTM, is responsible for the preparation of fastener standards and specifications. Shear- Force exerted 90 degrees to the center line or length of the bolt that tends to cut the bolt into two or more pieces. Shear Strength- The amount of force usually expressed in psi, required to shear the bolt into two pieces. This is referred to as single shear and usually has a value of about 67% of the tensile strength. Double shear, where shearing forces are applied at two points along the shank of the body, would cut the bolt into three pieces. Double shear strength is usually about 175% of the tensile strength. Tempering- A secondary heat-treatment process used on already hardened alloy steels in order to produce changes in physical properties and grain structure. Completely hardened steel is often too hard or too brittle for many applications. Tempering induces modifications in the physical properties. By reheating to a suitable temperature below the transformation range, depending upon the alloy, then allowing to cool in a suitable manner, one may reduce the hardness and brittleness and increase the toughness. In general, as the hardness is reduced, so is the tensile strength, but the ductility is raised. Tensile Strength- (Also called Ultimate Tensile Strength) The load, usually expressed in pounds per square inch (psi), required to cause failure in tension (stretch). The tensile strength, in pounds, of a given size bolt is obtained by multiplying the psi tensile strength by the stressed area. In Metrics, the value is expressed in Mega Pascals (MPa). Tension- Load that is applied in line with the center line of a bolt that stretches it. Torsion- Radial force that is applied to the head or the threads of a bolt, when a nut is being tightened, that applies a twisting force to the bolt due to the fractional forces encountered by the mating of the threads as the bolt stretches. UNC- Unified National Coarse thread series previosly known as USS. UNRC- Same as above but specifying rolled threads with mandatory radiused thread roots. UNF- Unified National Fine thread series previously known as SAE. Washer Face- A circular boss on the underside of the bolt head or on the surface of a nut which acts as a bearing surface to evenly distribute the loads on the surface of the clamped materials. Also prevents the sharp, hex edges from digging into the work surface causing an increase in friction. Wrench Pad- The flat surfaces on a fastener head designed to permit an externally applied wrench to grip the sides of the head.

20 EMHART FASTENING TEKNOLOGIES P.O. Box 868 Mt. Clemens, MI Tel. (586) Fax (586)