Bend tools

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Bend tools

  1. 1. BEND TOOLING INC.: Rotary-Draw Tube-Bending Tools ~ Die Sets ~ Mandrels ~ Wipers ~ Mandrel- Bending ToolsL-N Home | Technical Information | Intro A-B | C-D | E-K | L-N | O-Q | R-S | T-Zlaminated tubing — See double-wall tubing.length -- The horizontal dimension of a rotary-draw bending clamp die or pressure die parallel to thecavity of the die block; the dimension of such a block from its leading face to its trailing face; thedimension of a such a block lying in the plane of bend and perpendicular to blocks reach correspondingto the Y-axis of the tube-bending machine. Usually the cavity length of clamp die or a pressure die isthe same as the block length, but they can differ in the case of a notched die with a block length greaterthan the cavity length. For example, most models of rotary-draw tube-bender have a minimum blocklength for mounting purpose, but the cavity length must be shorter than that minimum length toaccommodate the restrictions of the part to be bent (typically a multi-bend part with a short mid-tangent). So attention must be paid to specifying the length of clamp dies and pressure dies in thesesituations. See height and reach.line of tangency —The line thatseparates the bentfrom the unbentportion of the tube;more properlyunderstood as aplane perpendicularto the plane of bendwhich divides thearc from the backtangent of thetube. The line oftangency isdistinguished fromthe point of bend inthat the point ofbend is region ofmaterial on bothsides of the line oftangency thatbecomesplasticized underthe force of thebending process. The line of tangency is geometrical entity, whereas the point of bend is a physicalregion of the tube. See geometry.In rotary-draw tube-bending the line of tangency is fixed in space; the tubing material passes through it
  2. 2. as it is bent. In compression bending, the line of tangency sweeps along the radius of the bend die asthe pressure die presses the tubing material into the cavity of the bend die. In press bending, two linesof tangency sweep away from a central starting point as the ram die pushes the tubing material througha pair of wing dies.Therefore, the key to the superiority of the rotary-draw method of tube-bending is that a fixed line oftangency allows for the fixturing of tools both inside and outside and all around the point of bend tocontrol the flow of material. [CLICK HERE FOR THE ROLE OF THE LINE OF TANGENCY IN THE 4-STEP SET-UP PROCEDURE]link — A joint-like component of a mandrel assembly which attaches balls to each other and to thenose of the mandrel shank. The link originates from a segmented tool patented in the 1890s to formthe spouts of tea kettles and underwent considerable refinement until the late 1950s with theintroduction of the universally flexing H-style link. The H-style link remains the predominant style todaywith the only major improvement being the development of the single-piece poppet variety in the late1980s.An alternative to link construction of a mandrel assembly is cable construction. The mandrel (or insert)link, center link, and end link are replaced by a cable which strings a series of balls together. One endof the cable is anchored inside the mandrel shank and the other is capped with a small ball or plug. Aspring mounted over the anchor usually provides the tension that prevents the cable from droopingunder the weight of the balls. Although cable construction overcomes the inherent weaknesses of theH-style link design at the extreme ends of its range of performance, cables lack the durability, easyreplacement of components, and reliability in high production of links. See mandrel link, center link,and end link. [CLICK HERE FOR A TECHNICAL ARTICLE ON THE ADVANTAGES OF POPPET LINKS] [CLICK HERE FOR LINK PRODUCT INFORMATION]lip — The extension of the bend die cavity past the vertical centerline of the tube which is the definingfeature of the captive-lip cavity design. The typical length of this lip is 6% of the tube diameter. The no-lip cavity design is actually a negative lip; the mating face of the cavity is relieved from the verticalcenterline of the tube usually by1% of the tube diameter. Seecavity.mandrel — 1. Short for mandrelassembly, this tool is a part of therotary-draw tube-bendingprocess. It controls the flow ofplasticizing material at the point ofbend in order to maintain theshape of tube as it sets into the arcof the bend. If the tube wall isthick enough relative to the overallsize of the tube or if thespecifications are not too severe(e.g., shallow depth of bend or alarge "D" bend radius), then amandrel may not be necessary,because the force of the bend isnot sufficient to buckle or collapse the tube wall at the point of bend. However, if the wall factor of atube exceeds 20, a mandrel is needed in most instances.The key to effective use of the mandrel is to set its nose so that it supports as much of the point of bendas possible. This ensures that the vertical cross-section of the arc of the tube bend, while it is in aplastic state, will take the shape of the nose as the tubing material is drawn over it. This plastic region
  3. 3. of the tube bend extends both behind and ahead of the line of the tangency, therefore, the mandrelnose must be set forward of the line of tangency into the arc of the tube bend in almost all cases. (Seeentry under "line of tangency" for further information on how a mandrel performs in the rotary-drawprocess.)The limiting factor of this forward placement is the point where the outboard line of the mandrelintersects with the tube wall of the outside radius; in other words, the point where the mandrel nosewould literally stick out past the bend. The location of this point can be determined by formuladeveloped from the Pythagorean thereom. Generally it is advisable to locate the nose (excluding thenose radius) about the two-thirds of the distance between this point and the line of tangency. This willallow for slight flattening of the tubes cross-section at the outside radius, which unavoidably occursbecause of the tension of the draw, without intersecting the mandrel nose.2. The mandrel body or shank, particularly in reference to a non-inserted mandrel assembly.3. A plug, i.e., a mandrel that does not require a ball assembly. [CLICK HERE FOR MANDREL SET-UP INFORMATION] [CLICK HERE FOR MANDREL PRODUCT INFORMATION]mandrel assembly — Often referred to loosely as the mandrel, which see, a complete mandrelassembly consists of: [1] a mandrel body, [2] a mandrel nose insert, [3] a mandrel link or insert link, [4]a mandrel screw, and, if necessary, [5] a ball sub-assembly. A non-inserted mandrel assembly,sometimes called an "aircraft type" or "aircraft quality" mandrel assembly, does not include the secondcomponent, the nose insert.mandrel ball, mandrel (ball) segment — A component of a mandrel assembly. See ball.mandrel body — The section of the mandrel assembly which connects the mandrel sub-assembly tothe mandrel rod of a tube-bending machine. In an inserted mandrel assembly, the mandrel body doesnot include a nose, which is a separate detachable component held to the body by means of the insertlink and the mandrel screw. Therefore, the mandrel body in this case is a relatively long-lived
  4. 4. component that needs to be replaced only after extreme wear.The mandrel body of a non-inserted mandrel assembly has an integrated nose to control the flow ofmaterial at the point of bend. Thus, such a mandrel body wears out when the nose does and isrelatively short-lived compared to that of an inserted assembly. Because a mandrel body cannot bereconditioned for re-use in the same tube-bending application (it is occasionally possible to re-machineit for another application), it must be discarded after its nose wears out. This is its primarydisadvantage. However, a non-inserted mandrel body remains the tool of choice for those applicationswith a high rigidity factor (for example, non-round tubing or compression-resistant materials like Inconel)because its strength is a more important consideration than tool life.Technically a mandrel body is not a plug. A plug is a complete, fully-functioning mandrel assembly,whereas, a mandrel body is a component of a mandrel assembly (although in the case of a non-inserted plug, the mandrel body is the only component of that assembly).mandrel flats — The wrench flats milled onto a mandrel body which facilitate screwing the mandrelassembly onto the mandrel rod of the tube-bending machine. These flats are typically on the end of themandrel body opposite of the nose, although they occasionally appear in the middle of the body. Thespecification for wrench flats usually varies with the threading of the mandrel body to ensure that thecross-section between a flat and the major diameter of the thread is as thick as possible.mandrel insert — Same as mandrel nose insert, which see.mandrel link — 1. The link connecting a ball sub-assembly to a non-inserted mandrel body. Becausethere is no mandrel nose insert, a mandrel link lacks the shoulder that is characteristic of the insertlink. Sometimes called a "shank link".2. An insert link.mandrel nose — Either the nose insert of an inserted mandrel body or the nose portion of a non-inserted mandrel body, both function in the same manner as the "working" end of the mandrel body. Itis positioned at the point of bend to control the flow of material and so takes the brunt of the wear in amandrel assembly.mandrel nose insert — The replaceable nose section of aninserted mandrel body. It is designed as a relatively inexpensivecomponent of a mandrel assembly to be detached from the mandrelbody when it is worn out and disposed of. Another feature is that amandrel nose insert of one material can be swapped with one ofanother material so that the same mandrel body can be used fordifferent tubing materials. [CLICK HERE FOR MANDREL NOSE INSERT PRODUCT INFORMATION]mandrel overall length — The overall length of the shank of a mandrel assembly — i.e., the length ofa non-inserted mandrel body or the combined length of a mandrel nose insert and mandrel body. Thisspecification does not include the ball assembly and typically varies according to set standards relativeto tube diameter. However, overall length may be increased and decreased from the standard toaccommodate special considerations involving the reach of the mandrel rod or the collet of a tube-bending machine.mandrel shank — Similar to the term "mandrel body", whichsee. Refers to both a non-inserted mandrel body or the combinationof a mandrel nose insert and mandrel body.mandrel sub-assembly — A ball sub-assembly, which see, plus amandrel nose insert. A one-ball mandrel sub-assembly includes thefollowing components: [1] mandrel nose insert, [2] insert link, [3]mandrel ball, and [4] end link. Multiple-ball mandrel sub-assembliesinclude a mandrel and a center link for each additional ball of the
  5. 5. assembly.mandrel thread — All mandrel bodies have internal threads at the end opposite of the nose in order toattach the mandrel assembly to the mandrel rod. The mandrel thread specification typically varies withtube diameter. Although there is no official standard, some common relationships have developed overtime for non-metric tube-bending machines. For tube diameters around 1", 1/2"-13 UNC threads aretypical, from about 1.25" to 1.375" 5/8-11 UNC, and from about 1.5" to 3" 1"-8 UNC.mechanical tubing — Tubing specified for structural or mechanical purposes as opposed to thecontainment of liquids and gasses. Most commonly mechanical tubing is steel. Compare pressuretubing.mid-tangent — A tangent located between two bends made on the same section of tubing. Compareend tangent; also see tangent. The mid-tangent becomes an important consideration in tool design andmachine process if its length is shorter than the recommended clamp length for the tube-bendingapplication. In those instances when a short mid-tangent compromises the optimal clamp design, aconflict arises between ease-of-bending and bend quality that often is not resolved unless compoundclamps are used. See the entries under clamp die and compound clamp for a full treatment of thisissue.mild steel — Low carbon unalloyed steel used for tubing that is relatively easy to form compared toalloy steels, high-carbon steels, and stainless steels. Aluminum-bronze mandrel and wiper tooling isusually recommended for working with mild steel tubing. Hard-chromed mandrel and untreated steelwiper tooling is sometimes preferred because of longer tool-life; however, extended tool-life with thesematerials is dependent upon continuous and heavy lubrication of the tubing material and toolingsurfaces. See steel.minimum wall thickness — A post-bend specification controlling wall thinning which sets the minimumwall thickness allowed for the finished part. In rotary-draw tube-bending wall thinning is unavoidable inthe extrados, which see, but it can be mitigated by proper placement of the mandrel nose relative to theline of tangency, using the least direct pressure the application requires, and using assist pressure tofeed material from the trailing tangent into the extrados. See wall thinning.mounting bracket — Same as hanger bracket, which see.mounting pattern — The specification of the number of screw holes, center-to-center location of thoseholes, location of the overall pattern, and threading of the mounting holes of a wiper die. Certainpatterns are quite common, such as two 3/8"-16 mounting holes on 1.5" centers for smaller wiper dies(under 3" tube diameter) and two 1/2"-13 mounting holes on 2" centers for larger wiper dies (over 3"tube diameter).mounting pin — The pin attached to the clamp slide of a tube-bending machine upon which a clampdie hanger bracket is located. This pin-type of clamp die mounting is standard on older models of Pinesbending machines. The T-key type of mounting is most common today.neutral axis — The line separating the regions of compression (intrados) and elongation (extrados) ofthe tube wall during the bending process. Because the intrados and extrados extend into the leadingand trailing tangents of a bend, so does the neutral axis which widens into an inactive zone at theseextremes. Contrary to common misconception, the neutral axis is not the centerline radius, which is ageometric entity. The neutral axis lies inboard of the centerline radius. See geometry for illustration.nitriding — A type of case-hardening for alloy and tool steels in which a surface is hardened by aninfusion of nitrogen. One advantage nitriding had over carburizing, which adds carbon to a steelsurface, is that quenching is not need to complete the hardening process, thus eliminating one sourcefor dimensional distortion. However, the nitriding process is an excellent treatment for alloy steelswhich have good shock-resistant qualities.no-lip — A common type of cavity design for tube-bending dies which is true to the size and shape ofthe tube to be bent (with minor allowances) and a bend die lip extending over the centerline of the
  6. 6. tube. Compare to "captive lip" under the entry for cavity.nominal diameter — The "name" for a pipe size. In various specification systems for pipe (e.g., IPS,EMT, K-type copper tubing) a pipe is identified by a nominal diameter that is significantly different fromits true diameter. For instance, an 1.5" IPS black pipe has a true diameter of 1.900 inches. Anotheraspect of nominal diameter specifications is that if the centerline radius is called out in terms of "D" ofbend, that "D" is a multiple of the nominal diameter and not the true diameter. For instance, the truecenterline radius of a 2-"D" bend for that 1.5" IPS black pipe is 3.000 inches (2 x 1.5" nominal), not3.800 inches (2 x 1.900" true). Because of the potential for confusion (especially with copper tubing) allbend specifications for a pipe application should be called out in both nominal and true terms.non-mandrel bending — A method of rotary-draw tube-bending that obviates the need for a mandrelassembly by the use of bending dies with heart-shaped cavities. By its nature, non-mandrel bendingdoes not replace bending with conventional bending dies for applications with sufficiently heavy tubewalls or large centerline radiuses to eliminate the need for mandrel tooling in the first place. Non-mandrel bending strictly replaces a conventional set-up for that narrow range of applications thatnormally require a mandrel but are amenable to control at the point of bend under the "pinch" of heart-shaped cavities. In practice this means applications within the range of 1.75- to 3-"D" centerline radiusand 12 to 35 in wall factor.Non-mandrel bending compromises bend quality for the benefit of eliminating mandrel and wiper toolingcosts. Quality suffers most in terms of the critical attributes of bend reduction and wrinkling, whichaccounts for the significant decline in the use of non-mandrel bending over the past several years. Theproblem of wrinkling can sometimes be solved with a wrinkle-control bend die, which see, butcustomers for bent tubing are increasingly resistant to any wrinkling, controlled or not. [CLICK HERE FOR DIE SET PRODUCT INFORMATION]nose radius — The radius of the mandrel nose. The greater thewall factor (i.e., the ratio of tube diameter to wall thickness) thesmaller this radius should be. Sharp radiuses are disfavoredbecause they tend to break down quickly; however, largerradiuses increase the gap in tube wall support between the crownof the first mandrel ball and the full diameter of the mandrelnose. Therefore, the radius must be sized to provide the greatestamount of support without wearing out too rapidly. Generally anose radius of between five to ten percent of the nose diameterwill optimize these competing requirements. Generally, a largeradius is preferred for low-pressure mandrel bending and a sharpradius for high-pressure. See the photograph to the right for anexample of each type of nose radius. MAIL TO: BEND TOOLING INC. ~ 1009 OTTAWA AVENUE, N.W. ~ GRAND RAPIDS, MICHIGAN 49503, U.S.A. TOLL-FREE (U.S.A. & CANADA): 1-800-BTI-TUBE (1-800-284-8823) ~ WORLDWIDE: 616-454-9965 FAX: 616-454-9958 ~ E-MAIL: INFO@BENDTOOLING.COM INQUIRIES | REQUESTS FOR QUOTATION | ORDER PLACEMENT | CUSTOMER SERVICE © Bend Tooling Inc., 2008

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