FR2481964A2 - METHOD AND DEVICE FOR MANUFACTURING EXHAUST PIPES OF MOTOR VEHICLES - Google Patents

Abstract

METHOD AND DEVICE FOR MANUFACTURING MOTOR VEHICLE EXHAUST PIPES. A CONTINUOUS BAND OF METAL 2 IS FOLDED AND WELDED TO FORM AN ENDLESS LENGTH OF TUBE 11 WHICH IS CONTINUOUS AXIALLY DRAWN WITH A PREDETERMINED SPEED, THIS LENGTH OF TUBE IS DRESSED IN 13 THEN CUT OUT OF TUBE 19 TRONCONS. PREDETERMINED LENGTH AS IT CONTINUES TO BE DRIVEN AT THE SUCH PREDETERMINED SPEED, THEN THE 19 LENGTH TUBE STUFFS ARE TRANSFERED TO AT LEAST ONE BENDING DEVICE 28, 29 IN WHICH THEY ARE BENDED TO PRESENT 38 STEPS PREDETERMINED CURVES.

Description

24 1,964

  Method and device for making

  exhaust pipes of motor vehicles.

  The present invention relates to a method for

  manufacture exhaust pipes of self-propelled

  movable, according to which lengths of tube of predetermined length are fed to a folding device to be folded therein, and then preferably the dimensions of the free end of the folded pipe are checked to see if they correspond to the desired dimensions,

following the main patent.

  The invention also relates to a device for

the implementation of this method.

  So far, the manufacture of exhaust pipes

  This is done in a discontinuous manner. According to a known method, rectilinear pipe sections of predetermined length are cut from lengths of

  prefabricated tubes, and these tube sections are usually

  stored in the store for delivery time and transported to one or more folding devices where they are angled

  in their final form to form escape pipes.

  ment. The accuracy of the dimensions is then checked.

  exhaust pipes, following which they

are ready for delivery.

  One reason for this distinction in time and space between the cutting of tube lengths

  in sections of tubing and the folding operation required

  It resides in the fact that the exhaust pipes have different configurations according to the types of motor vehicles. Therefore,

  tube sections necessarily have different lengths

  ferent. This difficulty is further increased when

  two exhaust pipes bent differently must

  may be assembled by welding to form a

  specific exhaust system. It is therefore

248 1964

  normal that such irregular work cycle be linked

  dead time disadvantageous from the economic point of view

  due to the fact that the lengths of pipe

  are removed from the production line, stored

  mentally in store then transferred from the store to a new finishing station. However, not only

  idle time translates into manufacturing costs

  cation, but they are often also

  the cause of non-uniform quality of the exhaust pipes

finished.

  The purpose of the invention is therefore to provide

  a method and a device for manufacturing in accordance

  exhaust pipes for self-driving vehicles

  mobile devices, which make it possible to avoid downtime, transport and storage that are disadvantageous from the point of view

  economic and ensuring a uniform quality standard

  form finished exhaust pipes.

  In a process of the type mentioned above for the continuous manufacture of exhaust pipes for

  motor vehicles, this problem is solved

  the invention by virtue of the fact that a continuous metal strip is folded and welded to form an endless length of tube which is driven axially axially

  continuous with a predetermined speed, that this length

  The tube is erected and then cut

  set in lengths of tube of predetermined length

  while continuing to be trained in the said

  predetermined length, since the sections of tubing set to length are transferred into at least one folding device in which they are folded to form

  exhaust pipes with predetermined curvatures

  completed. Preferably, the method also comprises a size control operation of an end of the elbow tube section while the latter is still

  maintained in the folding device.

281 96 4

  Preferably, the sections of cut tube are alternately transferred in two folding devices arranged on either side of a path along

  which the sections of tube

  the two folding devices being differently adjusted so as to bend the tube sections

  which are respectively brought differently.

  The method according to the invention consequently allows

  a sequence in time and space of the various operating phases to produce

  exhaust pipes with predetermined curvatures

  terminated from a substantially flat metal strip. It is particularly advantageous that, as mentioned above, two folding devices are arranged on either side of the path along which the cut tube sections move, which allows

  to choose a relatively high welding speed.

  It is also advantageous to be able to fold

  two sections of tube of different length to form exhaust pipes of different curvature,

  who can then be united to form a

specific exhaust system.

  The process according to the invention ensures a smooth

  uniformly of the operating phases because the manufacture of the pipe sections is followed quickly by the folding operations. There is no longer economically disadvantageous dead time that can result for example from an interruption of the manufacturing process. In addition, the rapidly following operational phases also provide a standard for

  high uniform quality of the exhaust pipes

  naked. This is reinforced by the fact that the dimensions of the exhaust pipes are controlled while they

  are still tight in the folding device.

  It is only once that the dimensions are correct that a signal is transmitted to the bending device which releases the finished bent exhaust pipes. The device for implementing the method

  according to the invention is characterized in that

  mainly carries means for continuously driving an endless metal band with a predetermined speed along a predetermined path extending in the longitudinal direction of the web, forming and welding means located on the web

  along the mentioned route to get in shape and

  der the tape continuously while moving

  at said predetermined speed, depending on the speed

  maximum welding temperature which can be obtained

  to form a continuous length of tube, cutting means located downstream of the forming and welding means for cutting the length of tube into sections of predetermined length during the continuous feed of said length of tube, and means for folding

  having an elongate mandrel for bending the sections

  successive tubes in the form of exhaust pipes

  is lying. Preferably, the device further comprises control means coordinated with the folding means to control the dimensions at the end of the elbow tube section while it is still

maintained by the folding means.

  The device according to the invention is composed by

  four manufacturing aggregates that co-operate

  to form exhaust pipes that are

  a continuous process. In this way, there is no

  no downtime disadvantageous from the economic point of view

  nomic and simultaneously one is assured of a uniform high quality standard. Therefore, thanks to the combination of the four individual aggregates mentioned

  in a single device, it becomes possible to manufacture

  even exhaust pipes of different shapes in an uninterrupted sequence, with uniform quality. The cutting means may comprise means

  machining or cutting without chip removal.

  In a preferred embodiment, the cutting means may comprise a rotating saw blade

  mounted on the end of the output shaft of a

  drive, and the latter is mounted on

  first guide means extending along a di-

  rection normal to the mentioned path, while these first guide means are in turn mounted on second guide means extending in parallel

  to this journey. In this way, the drive motor

  for the saw blade can be moved parallel-

  to the tube length with a speed that

  respond exactly to the speed of advance of this

  Niere. Therefore, the length of the tube section cut from the tube length depends only on the feed rate of the tube length and the distance over which the drive motor and the saw blade are brought back. rear on the second guide means after cutting a pipe section

from the tube length.

  According to the invention, it is also advantageous to provide, between the cutting means and the folding means, a roller train, extending according to the

  axial direction of the tube length, for sections

  we put the tube to length. This roller train can be inclined about its longitudinal axis, and at least one side magazine is located on one side of the train

  tileable rollers so that they can be transferred

  the lengths of pipe laid to length when the roll train is inclined. This store is

  therefore a storage station that allows for

  to adjust the welding speed of the tube and the bending speed, including the time required

248 1964

  to control the dimensions of the finished bent exhaust pipe; this avoids dead time and an excess of lengths of tube set to length. The

  tilting roller train also makes it possible to

  the length of tube to the left and to the right of the roller train, if, for example, two folding means are provided, to increase the production or to manufacture two pipes simultaneously.

  different form of exhaust which must be

  subsequently joined by welding to form a

  exhaust system in one piece.

  The transfer of the pipe sections from a storage station to the associated folding means is preferably effected by means of gripping and transfer means located between the storage station and the folding means to bring the pipe sections himself

  located in the storage station by means of folding

  ge. The gripping and transfer means may be inclined at an angle of at least 1800 around a horizontal axis, the base of the gripping and transfer means being able to move, within certain limits, parallel to the direction of displacement the length of tube, to fit sections

of different length tube.

  According to another advantageous characteristic of the invention, the control means for controlling the dimensions of the finished bent pipe comprise a measuring head comprising several feelers, adjusted according to the desired dimensions at the end of the section of the pipe.

  bent tube, and means for supporting the head of

  sure to tilt about an axis extending transversely to the elbow tube section and able to move in a direction normal to the inclination axis, to align the measuring head with the free end of the section of elbow tube. In this way, at the end of the folding operation, it is sufficient to place the measuring head on the end of the finished exhaust pipe. It turned out that in most cases it is sufficient to control the end

  of the exhaust pipe bent as

  in the folding operation are always reflected at this end. However, in some cases, it may also be advantageous, according to the invention, to penetrate the exhaust pipe in a head

  measuring device rigidly arranged during the last pro-

bending cessation.

  According to another characteristic of the invention, the welding means, the cutting means and the folding means can be stopped individually or together when the control means indicate

  that the actual values recorded come out of tolerances

  these allowed for the desired values for the finished exhaust pipe. In this way, it is possible, when a defective product is found, to make the necessary correction immediately at the level of the aggregate concerned, after which it can be continued.

  process to ensure a sequence of operations

  made. The invention will be better understood using the

  following description of a preferred embodiment

  non-limiting example shown in the accompanying drawings in which: - Figure 1 is a schematic top view of the device according to the invention for the manufacture of exhaust pipes for motor vehicles; FIG. 2 is a vertical sectional view along line II-II of FIG.

  the different elements in a position of function-

differently;

  FIG. 3 is a schematic view, partially

  in section and on an enlarged scale, of the folding head of a folding device with a head of

248 1964

measured;

  FIG. 4 is a schematic view, partially

  in section, the mounting of the measuring head; and FIG. 5 is a diagram of operations and displacements illustrating the sequence of operations

  made by the different elements of the provi-

of the invention.

  Referring to the figures, and more particularly

  Figure 1 shows that the device for the in-

  to continuously manufacture escape pipes.

  for motor vehicles comprises a metal strip wound to form a coil 1

  which is driven by an electric motor 4 to de-

  rolling a substantially flat metal strip 2 to

  shot from the reel. The metal strip 2 passes longitudinally

  nally on several forming rollers 6a-6e, which

  are respectively driven by electric motors

  5, to put the metal strip 2 in the form

  of a split tube 7 whose edges are united by

  resistance circuit in a tube-welding device 9 which comprises two welding rolls 10 of

known construction.

  The length of tube 11 coming out of the welding device 9 is then raised by means of rollers

  13 who are driven by electric motors

  12. The tube length hi may be subjected to an ultrasonic test or be provided with a coating, eg aluminum, by means of

known not shown.

  The length of tube 11 is then brought to a

  cutting device 14. The cutting device 14 comprises

  carries a rotating saw blade 16 mounted on the

  of the output shaft of a drive motor which in turn is mounted on a guide 18 extending in a direction normal to the longitudinal axis of the length of tube 11 to move thereupon

  direction. Guide 18 is itself mounted on a

  cond guide extending parallel to the direction of displacement of the length of tube 17. The motor 15 with the rotating saw blade 16 can move along the guide 18 with the aid of known means not shown, and the guide 18 can himself move the

  along the guide 17 using conventional means not

  presented, with a predetermined speed set to

  the speed of advance of the tube length 11 of

  that, in the direction of advance of the tube length 11, the rotating saw blade moves with

  the same speed as the tube length 11.

  The tube sections 19, cut by the saw blade 16 from the length of the tube 11, slide

  on a train of rollers 20 extending along the

  longitudinal rection of the length of tube 11 (see also Figure 2). The roller train 20 may be inclined about an axis 22 extending in the direction of advance of the tube length, by means of

  a tilting system 21 controlled hydraulically.

  When the section of tube at length 19 meets a stop 23 located at the end of the roll train, it is inclined, either to the left or to the right according to the bending program, for

  transfer the pipe section to the storage booths

  respectively 24 or 25 on each side of the

  roll train 20 and serving as a buffer between the operation

  welding ration and the folding operation that will be

described in more detail below.

  The pipe sections 19 in the positions

  storage rooms 24 and 25 are transferred to the

  folds 28 and 29 which are adjacent thereto, by means of reclining grippers or

  prehension and transfer 26 and 27 which are respectively

  located between the corresponding storage station and the associated folding device. The means of

248 "1964

  26 and 27 are respectively mounted on the plates 30, 31 of the two

  folding 28 and 29. These means of gripping and transmitting

  26 and 27 can respectively move within certain limits on guides 32 and 33 extending parallel to the direction of advance of the tube length 11. Each of these gripping and transfer means 26 and 27 comprises two reclining arms 34 provided at their free end with gripping members

  35 in the form of tongs, which can move, to help

  of hydraulically controlled piston and cylinder systems

  liquor, not shown, of known constitution, between an open position, shown on the side

  left of FIG. 2, and a closed position

  felt on the right side of this figure.

  In FIG. 1, an inner mandrel 36 is

  produced in the pipe section 19 which has penetrated into the folding device 28. The inner mandrel 36 can move in the axial direction and can

  out of the folding device 28 towards the rear,

  indicated by the arrow on the mandrel. For this reason,

  a cylinder and piston system 37 is provided

  feature of the chuck hydraulically controlled and whose stroke is low; after folding the pipe section

  19 to form an exhaust pipe 38 (as shown in FIG.

  felt at the level of the folding device 29), this system

  first releases me the inner mandrel 36 which

  the front end is engaged in the elbow pipe.

  Then, the inner mandrel 36 thus released is

  ti quickly hose backwards through a system

  39 with cylinder and pneumatically controlled piston.

  The pipe sections 19 in the arrangement

  Folding device 28 and 29 are held at their rear end by means of clamps 40 of known constitution. The collets 40 are respectively mounted on a carriage 41, described

4 8 1964

  more in detail in GB 80 21331

  to allow axial displacement as well as rotational

of the tube section 19.

  Once the folding operation is completed, the exhaust pipe 38 (see also FIG. 3) is held in the last folding position in the folding head 42 of the corresponding folding device,

  for example the device 29. The folding head 42 pos-

  inherits a classic constitution and is also. describing

  in detail in the patent application referred to above.

  above. Then, a measuring head 43 of a control station 44, which comprises several measuring probes

  , is brought to the end 46 of the exhaust pipe

  38. Given that possible errors in

  ge are reflected in particular at the level of the

  46 exhaust pipe 38, just check.

  the end 46 of the pipe. If the measurements made at the end 46 indicate that the dimensions of this end are within the tolerances

  -admissible, the corresponding folding device re-

  a signal which opens, in known manner, the clamp 40 to release the finished exhaust pipe which

  is then transferred to a kidnapping station.

  Figure 4 shows the mounting of the measuring head 43 to bring it to the end 46 of a finished bent exhaust pipe. As shown on

  FIG. 4, the measuring head is mounted on two

  guides 51 which are mounted so as to

  place longitudinally in guide bushes 52 mounted in a member 52a. Guide rods

  51 can move axially, with the help of a system

  53 mounted in the member 52a between the sockets 52.

  The member 52a is mounted on a column 57, which can tilt about a horizontal axis 55 and Can be fixed in any inclined position by clamping means 54, shown schematically 248n964 on the column 57 to the FIG. 4, and engaging in a slot 54a formed in the member 52a concentric with the inclination axis 55. The column 57 has a cylindrical extension 57a extending downwards and rotatably mounted in a corresponding vertical drilling of a base 57b. The column 57 can be maintained in any position by means of blocking means of known constitution and which are shown only schematically on the

figure 4.

  Figure 5 shows a block diagram for the sequence of the last folding operation

  carried out on a section of pipe, the operation of

  sure that follows, and then the transport operation. In this diagram, the curve 59 in solid line represents the displacement of the folding head 42; the curve 60 in solid line represents the displacement of the piston and cylinder system 53 to move the head axially

  measuring 43; curve 61 in continuous line represents

  senses the measurement result provided by the feelers of the measuring head 43; the curve 62 in solid line represents the displacement of the arms 34 of the gripping and transfer means 26 or 27; the curve 63 in solid line represents the displacement of the gripping members 35 on the arms 34; and the curve 64 in solid lines represents the displacement of the clamping flush 40. The successive phases 1-9

  are indicated on the horizontal axis 58 and the posi-

  of the various bodies mentioned are indicated

  on the vertical axis of the diagram. Line 65 in point.

  tilts indicates the forward position or folding of the corresponding folding head 42; the dotted line 66 indicates the rest position of the folding head, the dotted line 67 indicates the position

* before the measuring head 43; line 68 in

  tillés indicates the retracted position of this head of

248 1964

  measured; the dashed line 69 indicates a tuning signal of the feelers 45 of the measuring head 43; the dotted line 70 indicates that the measuring head

  does not work, while line 71 is

  les indicates that the feelers 45 indicate that the dimensions controlled by the feelers 45 are outside the predetermined tolerances; line 72 in

  dotted line indicates the front position of the pre-arm

  34 and line 73 indicates the position of

  return; the dashed line 74 indicates the posi-

  closed grips 35 and the dotted line indicates the open position; the dotted line 76 indicates the closed position of the collet 44 and the line 77 indicates the

open position.

  In phase 1, the folding head is in its inactive or idle position, as shown in the folding device 28 in Fig. 1; the measuring head 43 is brought back, with respect to the position shown in FIG. 4, by the cylinder and piston system 53; the feelers 45 on the head of

  measurement are therefore inactive; the arms of pre-

  tension 34 are in the position shown for the gripping and transfer means 26 in Figure 1, that is to say that the gripping members 35 are located in the vicinity of the folding head and are in the open position, and the collet 40 is closed to maintain the rear end of the tube section inserted in the folding head. When the head

  corresponding fold 42 has come into its posi-

  As indicated in step 2, an electrical signal is produced in a known manner as indicated

  arrow, and is applied to a control valve

  by a solenoid, not shown, cooperating with

  the cylinder and piston system 53, which makes it

  place the latter in its advanced position, as

248 1964

  shown in Figure 4, and when the head of me-

  43 reaches its advanced position (phase 3) a

  electrical signal, indicated by the arrow b, is applied

  to the feelers 45 of the measuring head. When the

  fears indicate that the dimensions at the end 46 of the finished bent exhaust pipe 38 are

  within the permissible tolerances, an electrical signal

  indicated by the arrow c, is applied to the mechanism

  control unit, not shown, of the arms 34 of the gripping and transfer means which pass through

  consequently from the retracted position to the advancing position

  CEE. When the gripping arms 34 reach their advanced position in the vicinity of the storage station, as indicated in step 4, two electrical signals are formed, as indicated by the arrows f and a. The

  electric signal represented by the arrow f is applied

  the valve cooperating with the cylinder system 53

  dre and piston so that it moves from its advanced position, as shown in Figure 4, to

  a remote position, and the electrical signal

  felt by the arrow a is applied to the organs of pre-

  tension 35 on the arms 34 so that they pass from the open position to the closed position, gripping a tube in the storage station. When the grippers arrive in the closed position, as indicated in step 6, an electrical signal, indicated by the arrow h, is applied to the control mechanism of the collet 40, passing it from the closed position into the open position so

  ability to remove the finished bent pipe that has been measured.

  When the collet 40 arrives in the position

  as shown in step 7, an electrical signal, indicated by the arrow i, is applied to the

  controlling the gripping arms 34 to

  be the latter from the advanced position to the remote position. When the arms 34 reach their retracted position, as indicated in step 8, two electrical signals, indicated by the arrows j and k, are formed. The electric signal indicated by the arrow j is applied to the control mechanism of the folding head 42 to bring it back to the starting position,

  while the signal indicated by the arrow k is applied

  gripping members 35 to move them from the closed position to the open position to place a new tube in the folding head. In phase 9, all the elements are thus again in the positions of phase 1. Naturally, the

  mandrel 36 must be removed before the exhaust pipe

  finished equipment can be removed, and although the

  chuck is not shown on the dia-

  gram of Figure 5, its withdrawal can be controlled by the signal indicated by the arrow h. However, if in phase 4, the feelers 45 indicate that the dimensions of the end 46 of the exhaust pipe are not within the allowable tolerances, as indicated by the dashed portion

  of the measuring curve 61, an electrical signal, indi-

  the arrow e, is applied to the

  bending head 42 to block this

  Niere. The welding device 10 and the cutting device 14 can continue to function to fill the intermediate storage stations 24 and 25, and the devices 9 and 14 can be stopped manually if these storage stations are full. Phase 4

  may continue only after the application of an ex-

  interior, issued by the operator as indicated by the arrow d. The electrical signals can be generated by limit switches with which the respective elements or other

  detectors such as electric eyes or

similar

  It will be understood that each, or two or more,

248 1964

  elements described above, can also

  be usefully incorporated into other types of

  positive for the continuous manufacture of exhaust pipes of types different from the types described above. As it goes without saying, and as it follows from elsewhere

  already of the foregoing, the invention is not limited to

  those of its modes of implementation and applica-

  which have been more especially envisaged; she

  embraces, on the contrary, all variants.

248 1964

Claims (15)

  A method for the continuous manufacture of exhaust pipes for motor vehicles, characterized in that it consists in folding and welding a continuous metal strip to form an endless tube length while axially driving this length of tube with a predetermined speed; to erect the length of tube; to cut this length of tube clockwise to form tube sections of predetermined length during the advance   continuous tube length at said predetermined speed   determined; and then transferring the sections of tubing set to length in at least one folding device in which they are bent to form pipes   exhaust having predetermined curvatures.   2. Process according to claim 1, characterized   in that the continuous metal strip is in the form of a coil and is unrolled continuously from this coil before being folded and welded   to form an endless tube length.   3. Process according to claim 1, characterized   in that the sections of tube placed at length are transferred alternately in two folding devices respectively disposed on either side of the path along which the sections of tube set to length.   4. Process according to claim 3, characterized   in that the two folding devices are differently adjusted so as to bend differently   the tube sections which are respectively trans- férés.-   5. Process according to claim 1, characterized   in that it also consists in measuring one end   of the bent pipe section while this one is   still maintained by the folding device.   6. Device for the continuous manufacture of exhaust pipes for motor vehicles, characterized in that it comprises in combination: means for continuously driving an elongated metal strip with a predetermined speed along a predetermined path s extending in the longitudinal direction of the strip; forming and welding means located along said path for forming and welding said web continuously during its advance at said predetermined speed, function   the maximum possible welding speed, to   sea a continuous tube length; cutting means located downstream of said forming and welding means for cutting said length of tube into lengths of predetermined length during the continuous feed of   this length of tube; and folding means comprises   an elongated mandrel to join the sections of   successive tube shaped exhaust pipes.   7. Device according to claim 6, characterized   risé in that two folding means are arranged on either side of said path and in that it comprises transfer means for alternately transferring successive tube sections to the two means folding.   8. Device according to claim 6, characterized   characterized in that the cutting means comprises a rotating saw blade and means for guiding said rotary saw blade in the direction of said path   predetermined and normally to this direction.   9. Device according to claim 8, characterized   characterized in that it comprises a drive motor for rotating the saw blade, the drive motor having an output shaft supporting the saw blade at its free end, and the guide means having first means for guide extending normally with respect to said path and for moving the drive motor in one direction 248 1964   normal to said path, and second guide means extending parallel to said path and for moving the first guide means in a direction direction parallel to the path.   10. Device according to claim 6, characterized   in that it includes means of transport -   whose longitudinal axis extends in the direction of the said path and situated between the cutting means and the folding means, and at least one storage station for the sections of tube placed at length situated on the side of the said means of transport, these transport means being able to be inclined around the longitudinal axis and comprising means for tilting the means of   transporting said longitudinal axis in order to trans-   to make pipe sections lying on the means   transport in the storage station.   11. Device according to claim 10,   in that the said means of transport are   in the form of a train of rollers.   12. Device according to claim 10, characterized   characterized in that it comprises means for gripping and transferring between the storage station and the cutting means for transferring sections of pipe located in the storage station of the latter to the cutting means.   13. Apparatus according to claim 7, characterized   terized in that it comprises a train of rollers   tending in the longitudinal direction of the path,   downstream of the cutting means, for receiving the sections   The length of said roll train can be tilted on both sides about its longitudinal axis, and in that it comprises two storage stations for length-lengthed pipe sections respectively located on each side of the tube. other of the roller train, means for alternately tilting the roller train in opposite directions around   said axis to transfer alternately sections   tubing of the roller train in said stations   storage, and means of prehension and trans-   between each storage station and the respective folding means for transferring sections of pipe   a storage station with folding means corresponding to ing.   14. Apparatus according to claim 6, characterized   in that it includes means of control   bending means for measuring the dimensions at the free end of a finished bent tube section while the latter is still maintained in the bending means, said control means   comprising a measuring head provided with several palms   adjusted to the desired dimensions at the end of the elbow tube section and means supporting said measuring head so that it   can be inclined around an axis extending transversely   with respect to the bent tube section and   move in a direction normal to said axis of   clinching to align said measuring head with the ex-   free end of said elbow tube section.   Device according to claim 14, characterized   in that the said control means are associated with   welding means, the cutting means and the folding means so as to stop at least the folding means when the feelers detect that   the end of the bent tube section has dimensions   which differ from the desired dimensions.