Production engineering  jig and tool design

Production Engineering Jig and Tool Design Ε J Η JONES M.B.E., M.I.P.E Revised by H C TOWN C.Eng., F.I.Mech.E., F.I.Prod.E., F.R.S.A LONDON NEWNES-BUTTERWORTHS Tai ngay!!! Ban co the xoa dong chu nay!!! THE BUTTERWORTH GROUP ENGLAND Butterworth & Co (Publishers) Ltd London: 88 Kingsway, WC2B 6AB AUSTRALIA Butterworth & Co (Australia) Ltd Sydney: 586 Pacific Highway Chatswood, NSW 2067 Melbourne: 343 Little Collins Street, 3000 Brisbane: 240 Queen Street, 4000 CANADA Butterworth & Co (Canada) Ltd Toronto: 14 Curity Avenue, 374 NEW ZEALAND Butterworth & Co (New Zealand) Ltd Wellington: 26-28 Waring Taylor Street, SOUTH AFRICA Butterworth & Co (South Africa) (Pty) Ltd Durban: 152-154 Gale Street First published in 1940 by George Newnes Ltd Second edition 1941 Third edition 1941 Fourth edition 1945 Fifth edition 1948 Second impression 1954 Sixth edition 1956 Seventh edition 1963 Second impression 1964 Eighth edition published in 1972 by Newnes-Butterworths, an imprint of the Butterworth Group © Butterworth & Co (Publishers) Ltd, 1972 ISBN 408 00078 Standard 408 00079 Limp Filmset by V Siviter Smith ά Co Ltd, Printed in England by Hazell, Aylesbury, Bucks Birmingham Watson & Viney Ltd, Foreword When this book was first published in 1940 it was recommended by the institution of Production Engineers as being of outstanding merit The author, Mr E J H Jones was recognised as being an eminent authority on the subject of engineering manufacture, this being based and dependent upon a knowledge of cutting tools, jigs and fixtures The reception of the book by the engineering industry and technical colleges was such that, from the first publication to the present day, seven editions were produced and some new chapters were added Nevertheless, it was realised that, valuable as most of the material still is, for basic principles change but little, engineering development has proceeded so rapidly that both designer and manufacturer are faced with problems u n k n o w n a few years ago These problems relate to the introduction of new manufacturing processes, the use of high grade materials for machine construction, and the developments in cutting tool materials Of outstanding importance is the possibility of machine or tool control by compressed air or hydraulic operation to obtain an increase in productivity with reduced complication Thus it was considered that the time had arrived for a major revision of the book to be undertaken, and I was privileged to be asked to undertake the work More than half the book has been replaced to bring the work up to date, and it is hoped that in the future the book in its new form will prove as valuable to the engineering industry and educational establishments as it did at its inception by Mr Jones H C T O W N Preface This work is intended not only for the experienced jig and tool designer but also for the student of production engineering and the technical college lecturer Those readers already skilled in the science of jig and tool design will, it is hoped, find much of real value in many of the chapters The examples given have been tried out and used successfully on production programmes and can be relied upon as sound practice in relation to their respective problems There is in every jig, fixture, or tool layout certain essential elements upon which success or failure depends, and the designer competent to be trusted with important work is one who understands what the purpose is, and has a thorough knowledge of the functions they must perform The designer today has the advantage of several alternative power systems, so to mechanical operations descriptions have been added of the modern applications of pneumatic, hydraulic, and electrical actuation The subject of cutting tool materials has been well covered and prominence given to the science of surface technology and the effects on the economics of tooling, comparisons being made with multi-tooling operations and tracer controlled copying systems T o this has been added a section on the economics of jig and fixture practice Recent research on surface texture has focused attention on fine finishing operations, so a comprehensive chapter on diamond tools has been introduced to give the necessary information on boring and turning operations Much new information has been added to the chapter on inspection and gauging indicating the use of comparators and measuring machines, for the increased accuracy now required on many components shows the need for high precision which is not attainable by the traditional types of limit gauges This feature applies on the machine tool itself, and examples are given of the new features of preset tooling The chapter on air or oil operated fixtures contains new examples from actual practice, some of the pneumatic examples being applicable to holding small units where the machining time is in seconds, and the rapid insertion and removal of work is essential At the other extreme, material on hydraulic operation shows the advantages of oil clamping on large components, and what is rarely appreciated, the use of accumulators to simplify the system Methods of truing grinding wheels has been extended to include surface grinding, and means for generating spherical surfaces have also been described M u c h new information is given on boring operations and diamond compared with carbide tools Examples are given to show the means to eliminate vibration by corrective design Also included for the first time is the operation of honing with information on the new process of diamond honing As a contrast to the economic advantages of large scale production, the problem of small batch manufacture is discussed in a new section on G r o u p Technology and the cell system of workshop layout of machines in the plant H C T O W N Function and Organisation of the Jig and Tool Department It is not intended to explain all the functions of the departments relative to engineering organisation except in so far as the jig and tool department operates in collaboration Such reference is, however, briefly necessary in order that the position occupied by the department responsible for jigs and tools is appreciated The extent of the organisation necessary will vary in proportion to the size of the works in which it is installed In a very small undertaking it is possible to visualise one m a n performing all the duties of the tool department The following, however, is a brief survey of the organisation generally adopted When the management of a concern decides which type of mechanism or assembly is to be manufactured, the decision, if not made in conjunction with the chief engineer, is conveyed to him It then becomes his responsibility to provide the designs and carry out what experimental work may be necessary His arrangement drawings are then handed over to the chief draughtsman, who distributes certain units a m o n g his staff, whose duty it is to make detailed drawings of each individual piece, on which should be all the information required by the factory to produce the piece, including the whole of the dimensions, particulars of material and heat treatment, also including the limits to which certain parts are to be made and the finish required Surface technology It is difficult in practice to divorce surface finish from geometrical accuracy, for most problems involving consideration of fine surfaces are also concerned with problems of wear, i.e with one surface moving on another In such cases the surface finish and geometrical accuracy are inseparable, for example, it would be useless to make a cylinder bore perfectly smooth, if the errors in roundness and parallelism made it impossible for the piston rings to seal the bore In general, it can be stated that the more accurate a tool does its work, the better the surface finish FUNCTION A N D ORGANISATION OF THE JIG A N D TOOL DEPARTMENT Numerical assessment Most surfaces are irregular, and since it is undesirable to rate the surface on the basis of the highest peaks and lowest valleys, some method of averaging becomes necessary The British standard of using the micro-inch as the unit of measurement is now replaced by the micrometre, the centre line average height (CLA) method being used for the assessment of surface texture Thus a figure of 100 micro-inches now becomes 2-5 micrometres, and the table gives Figure 1.1 Chart showing surface finish values SPLINES X Y < ^t i e d * Figure 1.2 Milling machine spindle with surface finish assessment FUNCTION AND ORGANISATION OF THE JIG A N D TOOL DEPARTMENT a representative selection of degrees of surface finish obtainable by commercial equipment (see Figure 1.1) There are new surface roughness symbols for use on drawings, and Figure 1.2 shows a milling machine spindle with the type of symbols to be used, the symbol including a number indicating the number of micrometres The number indicates the C L A required, and for normal machining, say drilling or turning to be followed by grinding, the symbol itself is sufficient to indicate this, the number being restricted to diameters or faces where special accuracy is required Operation layout The work of deciding upon the type and sequence of the operations on a given component is the responsibility of the planning department whose members must have an intimate knowledge of the machines and tools available Thus, given a drawing such as Figure 1.2, but fully dimensioned with limits indicated in addition to the surface finish symbols shown, an operation sheet can be prepared on the lines indicated in Table 1.1 Table 1.1 M I L L I N G M A C H I N E S P I N D L E 0-4% C E N 80 mm dia χ 400 mm long Operation 10 11 12 13 14 15 16 17 sequence Saw to length Face ends and centre Copy turn full length, using 'Kosta' driver Grind spline section X to size Rough grind bearing diameters Y Grind flange Hob involute splines Drill full length of spindle, deep hole drill Copy bore front taper hole Bore hole in end for draw bolt, and chamfer Mill slot in end of flange Drill and tap holes in flange Induction harden taper bore and front face Finish grind taper bore Using taper plug, finish grind bearing diameters Y Grind end face and flange diameter Thread roll diameters Ζ Set-up time ( ) Time allowed ( ) Standard time ( ) 30 45 30 30 30 15 120 60 30 45 90 45 60 30 60 15 30 4-3 7-5 140 7-8 90 3-3 220 24-0 60 7-0 8-5 260 14-4 25-0 12-8 40 8-0 2-2 3-7 70 40 4-5 1-6 110 120 30 3-5 4-3 160 7-2 12-5 6-4 20 40 The sheet may also indicate which machines must be used for each operation, and also what fixtures, tools, or gauges are required, so that work can be scheduled and any particular machine's committment can be determined for a given period of time The production engineer can thus ascertain whether plant will be available In the heat treatment of components it is advantageous to use induction hardening as against carburising and the necessity of protecting parts to be drilled In the component shown the induction hardening process causes no FUNCTION A N D ORGANISATION OF THE JIG A N D TOOL DEPARTMEN1 difficulties with the drilled holes, while the operations of tracer-controlled copying and thread rolling are effective in reducing the operation time The economics of tooling The amount of money spent on tool equipment depends on the number of parts required, or the possibilities of repeat orders Considering the p u m p plunger shown in Figure 1.3a, this shows the tool layout to produce the plunger in small quantities on a standard lathe Eleven operations are required for completion, necessitating the use of three tools in the compound rest and four in the tailstock spindle The various parts of the plunger requiring machining are numbered with the same figures as the tools performing the operations, these being in the following sequence, (a) Turn diameter full length, (b) Turn diameter (c) Square out 5, 6, and face end (d) Cut shoulders 1, 2, (e) Centre and recess end of bore from tailstock (f) Drill main bore 10 (g) Drill small bore 11 using extension socket, (h) R e a m main bore, (j) Cut off to length using tool Using the same tools, but now on a capstan lathe, the set-up is that shown in diagram (b), use being made of the square and hexagon turrets The main feature is the saving in time by every tool being in a permanent position as against the re-setting required in case (a) In addition, stops are set to limit the tool traverses, so that depth measurement is not required If the plunger is required in large quantities, a more elaborate set-up is used as shown in diagram (c) The main difference from (b) is that tool is taken from the square turret and used in conjunction with the drill 10, so that turning and drilling proceed together A comparison of the three methods shows : Case (a) Machining time, including trial cuts, moving tools and tailstock, 60 per piece or 600 for 10 components Case (b) Changing tools 15 min, adjusting tools to size 17 min, setting stops 13 Total 45 Machining time 25-J- χ 10 pieces = 255 Full total time 300 Case (c) This set-up is for a total of 40 pieces, the machining time being 19 χ 40 = 760 Adding 180 for setting-up gives (760 + 180) ^ 40 = 23^ each Thus the respective times per piece are 60, 30, and 23^ It is obvious there is much to be gained by special tooling for large batches, but for a small number of parts, savings may be reduced by the setting-up time A simple formula for checking is one in which χ is the number of pieces on which production times of centre and turret lathes are equal T h u s : Time for centre lathe χ χ = turret set-up time + machining time χ χ (Case b) 60x = 45 + 30.x, χ = 1-5 (Casec) 60x = 180 + 19x, χ = 4-4 Automatic lathes The question as to when to introduce automatics instead of turret lathes is only partly affected by the number of parts required The time per piece will be less over a large batch, say 000, on an automatic than if produced on a FUNCTION A N D ORGANISATION OF THE JIG A N D TOOL DEPARTMENT i \ 11,10,4,5,6^ , I (a) 1,2,3 4,7 (b) 1,2,3 ] Ό = d (c) Figure 1.3 Diagrams showing the economics of tooling capstan or turret, but the cost of machine setters must be taken into consideration and the number of machines one setter can keep in operation may influence the final cost The initial cost of an automatic is greater than centre and turret lathes, and in the matter of production of multi-diameter shafts a multi-tool lathe with a front and back slide may provide the most economical proposition TRANSFER MACHINING A N D GROUP TECHNOLOGY RETURN CONVEYOR POWER DRIVEN N93 PLATEN RETURN 275 CONVEYOR \ \ SECTION flPRESSHS linjVIEw| WAY V TAPPING MACHINE SECTION N LIFT-UP FIXTURE SECTION CONTROL CONTROL DESK DESK cast-iron cylinder heads for a 6-cylinder commercial TURNOVER TURNOVER CRADLE FIXTURE engine cylinder head Each incorporates a multi-spindle attachment enabling as many holes as centre distances will allow to be drilled, reamed, or tapped simultaneously By means of pick-off gears the speeds a n d feeds can be adjusted to suit any changes that m a y be necessary in the future F o r setting purposes, each head can be operated independently a n d has its own cycle which may include quick approach, trip t o cutting feed, dwell, and quick withdrawal All heads in the same battery are interconnected so that the cycle is initiated in unison It will be appreciated that the time cycle of the various heads differs according to the depth a n d diameter of hole, a n d the type of operation being performed—i.e drilling, reaming, or tapping F o r this reason, each head operates on its own particular time cycle, which ends with the head in the raised position T h e overall time cycle for the entire battery is that of the head requiring the longest time cycle—i.e three minutes Thus, heads employing a shorter time cycle 'idle' in the raised position until the last machine has finished its cycle of operations a n d returned to the raised position When this occurs, the transfer b a r mechanism is set into motion to move each platen to the next head As soon as this movement ceases, all the heads simultaneously feed downwards a n d commence the next 3-minute cycle The cycle is initiated by pressure on a switch which holds automatically until it is overridden by another switch Master guide bars T o permit easy movement of the platens, a certain a m o u n t of 'play' between the table slides a n d the guides on the underside of the platen is unavoidable Thus provision must be m a d e to ensure accurate location of the platen under each head F o r this reason, a large-diameter circular-section master guide bar is provided on the sides of the heads, each guide bar incorporating a spring-loaded stripper (Figure 22.3) As the head descends, the rounded end of the guide bars enter two steel-bushed holes in the platen and then two bushed holes in the table, thus accurately locating it in position Continued downward movement brings the end of the spring-loaded stripper into contact with the platen, holding the latter firmly against the table slides while the head descends still farther to allow the tools to perform their work When the head retracts upwards, the tools clear the work first: as the guide 276 TRANSFER MACHINING AND GROUP TECHNOLOGY Figure 22.3 This close-up view of a machine head clearly shows the master guide bars for locating and clamping the platen ( Below the end of the platen is seen part of another bush which will be used when larger components are machined at some future date) bars rise, the strippers continue to maintain pressure on the platen until just before the ends of the bars leave the holes, when they themselves rise with them Speeds and feeds It was mentioned earlier that the longest 'machine cycle' is three minutes This rate ensures the best tool i i f e \ However, should it be necessary to to increase the rate of output, this can be achieved without any difficulty by raising the speeds and feeds, where necessary, throughout the line In effect, this means increasing the speeds and feeds of those operations which take the longest time cycle, and by introducing tungsten carbide tooling to reduce the longest operations to a lower time cycle Because of the efficiency of the transfer line, and in order to maintain balanced production with other departments, it has been necessary to use TRANSFER MACHINING A N D GROUP TECHNOLOGY 277 speeds and feeds that are lower than those normally employed As a result of this, tool life has increased amazingly, effecting considerable economies in both tool costs and resetting times As will be seen later, the need for using spanners has been avoided by the provision of quick-action clamping devices Transfer mechanism On the first and last sections of the line the platens are moved manually by the operator In the cases of the three groups of drills, however, they are moved from machine to machine automatically by transfer bars, one being provided for each battery These consist of long bars provided with a number of spring-loaded pawls (Figure 22.1) so designed that they are pressed back into recesses in the bar as they pass under the platen, and then spring upwards when they are clear By means of a small m o t o r and chain drive slider the bar is given a reciprocating movement with a stroke long enough to transfer the platens to the next machine The machines of each group are spaced the same distance apart Swarf removal A considerable a m o u n t of swarf is soon produced, and thus it is essential to provide some means of automatically disposing of it T o this, the sides of the interior of the conveyor track slope inwards to direct the falling swarf into a long narrow trough running the length of each battery of machines (Figure 22.1) This trough is, in fact, a vibrating conveyor which is so designed that each vibration causes the contents to 'jump' a short distance along the trough In actual fact, the vibrations are so rapid that the swarf flows forward in a continuous stream An important feature of this type of conveyor is that it can be set to cause the swarf to flow 'up-hill' F o u r such conveyors serve the line—i.e one for each battery of drilling machines— and these all deliver into an inclined conveyor discharging into a large storage bin which is emptied at intervals Operation sequence F r o m the following detailed description of the operations performed along the entire line, it will be seen that all the important requirements mentioned at the beginning of this chapter—particularly those referring to the elimination of operator fatigue—are fully met In addition, many of the items provide an extremely useful study of modern production practice The first operations The castings are brought to the beginning of the line by a fork-lift truck and the load deposited on an hydraulically operated adjustable table 278 TRANSFER MACHINING A N D GROUP TECHNOLOGY situated close to the first machine By movement of a single handle the height of the table is adjusted to bring the top layer of castings level with the machine table so that they can be transferred to it without any need for lifting—i.e by sliding them As the operator works his way through the castings, the table is raised to maintain the correct level of the top layer The first operation is concerned with continuous milling of the top and b o t t o m joint faces—i.e the top and bottom faces of the castings Cast on one face are three small location pads, and by locating all machining operations from these it is possible to guarantee that the complicated internal water passages, as well as the external surfaces and holes, are in correct relationship with each other The milling machine has two horizontally arranged face mills, one for roughing and the other for finishing Below them is a rotating circular table carrying four quick-loading fixtures Two of these are designed to hold the casting when rough- and finish-machining one joint face, and the others for machining the second face Locating from the three pads, the casting is secured in its fixture and is carried under the first (roughing) cutter, and then on to the second spindle (set to cut slightly lower than the first) which finish-mills the face It is then reversed and transferred to an empty fixture in front of it, in which it is located from the previously machined face, and is carried once more under the two cutters to rough- and finish-machine the second side: this fixture is identical with the first, except that it raises the casting slightly higher Figure 22.4 The first turnover cradle, which brings the cylinder head into its correct for moving along the line, i.e with the platen underneath (Below the cradle is seen the end of No platen return conveyor) position TRANSFER MACHINING A N D GROUP TECHNOLOGY 279 The fixture left empty when transferring the casting for machining of the second side is then loaded with an unmachined casting taken from the hydraulic table By this means, continuous milling is achieved with very little effort by the operator Turnover cradle As removed, the casting is slid on to a static roller track or 'table' arranged at the same height as the machine table, and pushed by hand to an adjacent radial a r m drill, where two service holes are jig-drilled and tapped The bolts for these are accurately machined to suit two bushed holes in the platen, thus ensuring very close location of the platen on the castings The platens are obtained from the platen return conveyor seen on the right of the drill (Figure 22.4) : this conveyor is described in detail later At this stage the platen is on the top of the casting, and it is now necessary to reverse the assembly so as to bring the platen to the b o t t o m — i.e to rest on the table The combined weight of the platen and casting is fairly considerable and in order to enable the operation to be performed without undue fatigue a turnover cradle is incorporated in the table (Figure 22.4) The assembly is merely pushed into the cradle and the latter rotated with very little effort to bring the assembly into its correct position It is then pushed along the rollers to the next station Turntable This is concerned with milling the two long sides—i.e the manifold cover face and the back cover face When in the loading position, the machine table practically touches the roller track, and thus the need for manual lifting is avoided In order to present the two sides to the cutters it is necessary to turn the casting through 90°, and to allow this to be done with minimum effort a turntable (Figure 22.5) is incorporated in the section immediately facing the milling machine T o load the machine, the table section is rotated through 90° and the casting pushed into the empty fixture The design of this fixture is interesting because it typifies the precautions taken throughout the entire line T o prevent any chance of mistakes, the clamping and location arrangements are interlocked so that it is impossible to secure the clamp unless the locating pins are correctly in position In the base of the fixture are two retractable large-diameter pins which locate the casting by entering two of the bushed holes in the base of the platen The design is such that until these pins are fully entered, the tip of the clamp cannot enter its mating recess In order to provide the necessary strength, the clamp is of fairly substantial proportions and, consequently, is rather heavy T o minimise fatigue when loading and unloading, it is accurately counterbalanced so that little more than finger pressure is required to raise and lower it The clamp is locked by rotation of a star-wheel, thus avoiding the effort of using a spanner The machining cycle is fully automatic, and when the operation is completed the table comes to rest close to the track, so that the casting can be slid 280 TRANSFER MACHINING AND GROUP TECHNOLOGY back on to the turntable The latter is then rotated through a further 90 to bring the platen in line with the track, and the casting pushed on to the next machine to mill the two short ends Figure 22.5 The turntable for directing the cylinder head into the fixture of the duplex milling machine for operations on the side faces As before, when in the loading position the machine table practically touches the roller track, and the casting can be slid into the fixture with very little effort This time it is not necessary to turn the casting, because it already lies in the correct position The operator locates the casting by moving a small lever to raise two pins which enter the holes in the platen Movement of another lever then operates a cam clamping device to secure the casting As on the previous machine, the two movements are interlocked to prevent clamping unless the casting is correctly located The transfer line The next part of the line consists of two rectangular-section rails which dip at a steep angle to bring the casting down to the level of the battery of six machines forming the first section of the transfer line proper The platen slides rapidly down the rails, gaining sufficient m o m e n t u m to carry it into contact with the first pawl of the transfer bar F r o m here onwards, the castings are moved from machine to machine automatically until they have passed under all the heads in the first battery The drilling, reaming, and tapping operations are performed automatically, the castings moving on to the next head at the end of each cycle TRANSFER MACHINING A N D GROUP TECHNOLOGY 281 After the casting leaves the last machine of the first group of machines it is necessary to reverse it in order to machine the face at present at the bottom This involves fitting another ( N o 2) platen, reversing the casting, and removing N o platen These operations are performed with the aid of equipment built in the next section of the table As the casting leaves the last machine it also leaves the transfer bar The operator now picks up a N o platen from the end of N o platen return conveyor and places it on top of the casting, where it is located by two dowels just drilled and reamed by the preceding machines This platen (see Figure 22.6) incorporates two clamps which enter cored holes in the casting to secure the latter to the platen The casting (and two platens) is now pushed to an adjacent turnover cradle built into the table, where it is reversed to bring N o platen uppermost: the two securing bolts are then removed This particular fixture can Figure 22.6 The counterbalanced lifting device which facilitates removal of No platen and subsequent fitting of the angular No platen seen on the right be swivelled as well as turned over, and it is now swivelled through 90° This permits N o platen to be pushed on to the end of N o platen return roller conveyor, which returns it to the head of the table for re-use The first section of the return conveyor slopes downward, allowing the platen to gain sufficient m o m e n t u m to carry it to the foot of a rising power-driven section This raises it to the top of another gravity roller section, down which it rolls to feed the first turnover cradle (Figure 22.4) After removal of N o platen, the lid of the cradle fixture is closed and the unit swivelled through 90° to bring the casting in line with the table The 282 TRANSFER MACHINING A N D GROUP TECHNOLOGY casting is now in the correct position for the next group of operations— i.e N o platen is at the bottom All the above work is done by the operator in charge of the first battery of machines Figure 22.7 The second transfer section, comprising five vertical and one horizontal duplex hydraulic drilling machines and one three-way multi-spindle tapping machine By pushing the casting for a short distance along the table slides it reaches a position where it is picked u p by the transfer bar serving the second group of machines (Figure 22.7) As before, the casting is then automatically transferred from machine to machine This second group comprises five vertical drills, one horizontal opposed-head drill, and one three-way tapping machine, all fitted with multi-spindle attachments Machining the angular holes The third group of machines is concerned with drilling, reaming, and tapping certain holes which lie at an angle of 20° to the joint face This could be done by using heads set over at an angle of 20° This scheme, however, possesses the disadvantage that any future modifications in the design of the casting would involve expensive and lengthy alteration of the machines In addition, the machines would have to be of special design instead of conforming to the standard design employed throughout the other groups F o r this reason it was decided that it would be more economical to employ machines of standard vertical-spindle design and to tilt the work by using platens having an angular top face (see Figure 22.6) Thus in the event of TRANSFER MACHINING A N D GROUP TECHNOLOGY 283 any future modifications, or the introduction of cylinder heads of different design, the only major alteration necessary would be to provide new platens Thus, when the casting leaves the transfer bar after the last machine of the second group it is necessary to replace N o platen by an angular-face N o platen T o this the casting is pushed under a 'lift-up' fixture astride the conveyor track (Figure 22.6) The two clamps are loosened and the casting raised, leaving N o platen on the track, from where it is transferred by hand to the adjacent N o platen return conveyor to be returned to the beginning of the second group of machines for reuse ; the design of this conveyor is similar to that of the N o platen return conveyor described earlier With the casting still suspended, a N o platen is removed from the end of the adjacent N o platen return conveyor and placed on the track, under the casting By means of a foot-operated control the operator is able slowly to lower the casting on to the platen, guiding it with his hands, both of which are free The casting is then secured by clamps forming part of the platen, as in the case of N o platen This change-over of platens is effected during the cycle by the operator in charge of the second batch of machines, who then pushes the casting along the table until the platen is engaged by the transfer bar serving the third group of machines Final stages The last machine in this group is a multi-spindle tapping machine, and when the casting leaves it, N o platen is removed with the aid of a lift-up device similar to that just described (Figure 22.6) It is then placed on N o piston return conveyor and returned to the end of the second group of machines This is done by the operator in charge of the third group of machines The table now changes to the form of a roller track, on to which the component is lowered and then moved along to a turnover cradle, where it is rolled over in order to remove the swarf from the internal passages and the holes Whilst in this cradle, an internal wire-brushing operation is performed with flexible drive equipment The next operation is concerned with drilling and reaming three holes in each end of the casting and then inserting plugs in them T o this, a turnover cradle is provided in the table to allow the casting to be turned to present first one end, and then the other, to the drill This fixture is actually attached to the side of the drill table, at the same level as the rollers After completion of the second end, the cradle is rotated through 90° to permit the casting to be pushed along the rollers to a washing machine During its passage through this it is washed by high-pressure jets of hot alkaline solution The use of hot liquid has two advantages, (1) it improves the efficiency of the solution, and (2) the heat gained by the casting helps it to dry very quickly, so that it is dry enough to handle by the time it reaches the next station After leaving the washing machine, the casting is pushed along the rollers to a foot-operated hydraulic press, where three copper injector sheaths are pressed into position This is done without removing the casting from the track 284 TRANSFER MACHINING A N D GROUP TECHNOLOGY F r o m here the cylinder head is moved to an adjacent station equipped for testing the porosity of the casting All water passage faces are sealed by quick-action rubber-faced clamps which, at two points, incorporate provision for the entry of compressed air F o r the test, the casting is immersed in a vat of hot water which, to prevent rusting, incorporates an inhibitor After removal, the casting passes for viewing at the last station on the line GROUP TECHNOLOGY The previous comments in this chapter have indicated the economic advantages when large quantities of a given component are required, but the problem still remains when production requirements are for small batches only T o attempt to achieve similar economic results in this latter case, group technology has been introduced In the layout of many machine shops, similar types of machine tools are grouped together, forming, for example, a turning department which comprises all types and sizes of lathes, with similar layouts for milling, boring, and the like The drawback then is the a m o u n t of time spent in work transference, and in group technology a complete departure from the above system is envisaged The approach is to analyse the product of a company and to select components related in size and shape and requiring similar production techniques Functional descriptions are of no significance, it is their shape envelope that is of importance, and the solution to the problem is to use a classification and coding system which identifies the shape and manufacturing requirements of the components by the allocation of a specific digit to each feature Having identified families of components, the next stage is to settle the quantities of each component required over a given period, the allowed machining and setting up times, and the sequence of operations Thus by a calculation of these factors an assessment of machine group load content of a component family can be established, each with a large batch of components with a high level of similarity If, for example, a firm is manufacturing lathes, the fast headstock and feed gear boxes would provide a large number of gear blanks, clutch units, and oil seals, as in Figure 22.8(a), requiring mainly machines and tooling for chuck work, while diagram (b) shows similar grouping of shafts, each requiring some milling and threading operations The actual group of machines provided includes a shaft ending and centring machine, small copy-turning lathes, milling machines, and a thread rolling machine F o r the production of headstock, tailstock, feed gear box, and apron castings, the group comprises milling machines, three unit double-head boring machines, and drilling and tapping machines All components enter the group as raw material and leave as finished parts Machine setting times are reduced for the machines are adjustable around a basic setting, rather than being completely re-tooled for each new component Waiting time associated with interoperational machine loading is eliminated and reduces the a m o u n t of work in progress Gear tooth production is established as a separate group, the machines comprising gear tooth hobbers, spline hobbers, tooth point thinner, de-burrer, gear shavers, induction hardening equipment, and gear tooth grinding machines GROUP TECHNOLOGY 285 (b) Figure 22.8 Components classified for group technology The relationship between component shape and manufacturing requirements used to establish the machine groups can be used to define the type and size of machines to produce them With this information, any future machine tool installation programme can be based upon the requirements needed to produce given components Analysis of present workshop machine capacity invariably reveals great unbalance between the size of workpieces and the machine tools producing them Investigations carried out in twenty large manufacturing firms on the work sizes and capacities of lathes, revealed the following information (1) % of all components had a diameter less than 200 mm Thus a 125 m m centre lathe would cover f of components (2) 70 % of all components had a length of less than 200 mm, but most of the lathes installed had length capacities from to m long F r o m these figures it can be deduced that investment is being mis-directed, and that 50 % of capital expenditure could have been saved and put to better use by the purchase of suitable machines In fact with group technology, because the size variation is limited, there is no need of wide speed and feed ranges, so that simple machines with pick-off gears instead of elaborate gear boxes can be used Economy is also obtained by the reduction in the sizes and types of cutting tools In the conventional workshop stocks are kept to cover a wide range of operations because it is never certain what tools will be required With group technology, tools are ordered and supplied to each machine to cover a limited range of specific operations, and there are no surplus or unwanted tools, either on the machines or wasting in the storeroom Similarly, considerable savings are feasible with the reduction in gauging and measuring equipment At the Gleason works, U S A in one year 4000 man-hours were saved by streamlining inspection processes and reducing the time spent by operators 286 TRANSFER MACHINING A N D GROUP TECHNOLOGY in going to the tool stores for gauges and instruments Again, with group technology, gauges and measuring instruments are assigned to certain machines, and not leave except for calibration The effect of applying group technology in a company can be significant Total component manufacturing times are generally reduced by a factor of or 5, while machine setting times are reduced on an average by about 70 % The design office can often assist by having records of components in production, and in considering new designs see if existing components will suit the purpose This feature will assist in formulating a programme of standardisation and to cite an actual case, a company manufacturing lathes and milling machines, were able to use a c o m m o n change gear drive for both types of machines Cell system This follows on the lines of group technology, but each 'cell' consists of machine tools disposed along a conveyor, so that as described, work supplied at one end is discharged completed at the other On valve components, a typical cell contains twelve machine tools, this number being required for the most complex component, whereas only five are required for the simplest part Five operators use all twelve machines as required, so that by this arrangement only a proportion of the machines in the cells are in use at any one time These are, however, simple low rated machines, and it is argued that this is a better proposition than to have work in progress to a value of three times the cost of the machines stacked on the shop floor waiting to be machined A very substantial reduction in movement of work can be achieved, and ir the cell arrangement, valve parts only move through 30 m, whereas formed) they were transported 205 m when machined in units on conventional layouts Moreover production rates increased from to 14 parts per hour Cel technology can utilise existing equipment, and the major physical change ii largely one of re-arrangement This is what must generally take place in ar existing plant, but in a new factory unit construction machine tools can b( installed, and if these are supported by a policy of standardisation anc variety reduction for the manufactured components, still greater économie: can be effected without detriment to the customer (Figures 1-7 in this chapter are reproduced by courtesy of A E C Ltd.) Index Abwood Machine Tools Ltd., 195 A.E.C Ltd., 266 Accumulator systems, 253 Adjustable limit gauges, 21 Adjustable reamer, 51, 219 Advantages, transfer machining, 268 Air operated jigs, 151, 245 Allowances on gauges, 17 Alloys, cutting tools, 34 Angular measurement, 29 Archimedean spiral, 116 Assessment, numerical, Automatic drill, 101 Automatic lathe, Automatic work clamping, 253, 267 Automatics, form tools, 107 Cemented carbide tools, 32 Ceramic cutting tools, 35 Chart, pull on broach, 166 Chart showing production, Chucks pitch line, 193 vacuum, 195 Clamping, air and oil, 248 Clamps cam, 128, 252 equalising, 131, 143 toggle, 77 Comparators optical, 25 air, electric, 26 Components, group technology, 285 Contour grinding, 209 Core drills, 46 Crushing grinding wheels, 212 Cutter heads, boring, 239 Cutters, milling, 57, 67, 258 Cutting tool materials, 31 Beeswax fixtures, 84, 194 Blocks and rollers, 24 Boring bar, dampers, 222 Boring, deep hole, 236, 243 Boring and facing bars, 230, 234 Boring fixtures, 217 Boring tools, 218, 220 Box jigs, 142 British standards gauges, 19 jig bushes, 124 Broaches types, 162 calculations, 171 pullers, 185 retaining catch, 169 Broaching fixtures, 177 outrigger support, 183 push, 184 surface, 174, 176 'D' boring bits, 45 Deep hole boring, 236 Design cam clamps, 129 faults, limit gauges, 19 milling cutters, 260 multi drill heads, 155 Development of form tools, 103 Devices for wheel truing, 199 Dial indicator, 25 Diamond tools, 38, 220 honing, 225 Dimensioning tool drawing, 103 Down-cut milling, 66 Dressing blocks, 215 Drill jigs, 133, 250 Carbon tool steels, 31 Cell system, 286 287 288 INDEX Drill jigs (contd.) grinding, 44 rifle and core, 45 Drilling multiple, 93, 153 spade, 48 High speed steel, 32 Hole basis, limits and fits, 19 Honing operations, 224 Hydraulic jigs and fixtures, 245 hand clamping, 256 Hydrostatics 85, 194 Economics of jigs and fixtures, 10 Economics of tooling, Ejector devices, 125 Electrical comparators, 27 Electro-limit head, 28 End mills, 61 Equalising clamps, 131 Indexing fixtures broaching, 181 drilling, 149 milling, 88 Indexing plungers, 132 Inspection examples, 30 Inspection gauging 15 Internal grinding fixtures, 190 Face milling cutters, 64 Factory inspection, 15 Fit diagrams, 18 Fixtures boring, 217 broaching, 177 grinding, 187 indexing, 88, 149, 181 milling, 72 Floating reamer, 51, 219 Flow production, 267 Fluid clamping, 84, 194 Foolproofing, 122 Form tools lathe, 103 relieved cutter, 63 tool holder, 215 Formulae broaches, 169 cam clamps, 128, 252 checking gauges, 30 copy turning, form tools, 103 jigs and fixtures, 13 negative rake, 260 spherical grinding, 208 Function, jig and tool dept., 16 Gang milling, 69, 85, 251 Gauges limit, 16, 21, 28 spline grinding, 201 Generating spheres, 208 Grinding fixtures, 187 wheel crushing, 212 wheel truing, 198 surface, 206 Group technology 266 Guide bushes, 124 Harrison, T S., Ltd., 3, 69, 206 High-rake milling cutters, 65 Jacks and supports, 130 Jig and fixture air and oil, 245 boring, 225 broaching, 177 details, 124 drilling, 133 economics, 10 grinding, 187 milling, 72 Jig locating bushes, 124 Keyway broach, 170 Latch jig, 140 Lathe form tools, 103 Lathe tools, negative rake, 265 Layout of transfer line, 274 Limits and fits, 17 Line inspection, 15 Locating drill bushes, 124 Logarithmic spiral, 116 Machine design, 269 Machining milling spindle, Mandrels, grinding, 188 Marking-off template, 134 Measurement angular, 29 by optics, 26 by rollers, 30 Measuring machines, 28 Method of setting diamonds, 42 Milling cutters, 57 down-cut, 66 pendulum, 68 negative rake, 258 Milling machine fixtures, 72 Multi-drill spindles, 146 Multi-drill spindle heads, 153 Multiple tooling, 93, 154 INDEX Numerical assessment, Oil operated fixtures, 245 Operation layout, 3, 96 Optical lever, 25 Pendulum milling, 68, 254 Pierce boring tools, 243 Pitch line fixtures, 191 Planing tools, 98 Pneumatic comparator, 26 Pneumatic fixtures, 245 Pot type jig, 139 Pre-set tooling, 98 Principles jig design, 117 minimum constraint, 23 precision measurement, 21 work location, 127 Quick-locking spindle, 101 Quick-change planer tools, 98 Reamer adjustable, 51 standard, 50 stepped, 49 Rifle drills, 45 Roller mill, 58 Rotary milling fixture, 82 Rotary tool setting, 99 Surface technology, Swarf removal, 277 Tables broach teeth, 167 carbon steels, 31 cut per tooth, 165 data, negative rake, 260 milling spindle, pitch, broach teeth, 163 speeds, ceramics, 37 Tapping chuck, 54 Taps, 52 Taylor's principle, 20 Templates, marking-off, 133 Terms, limits and fits, 18 Thread grinding milling, 55 rolling, 56 Toggle clamping, 77 Tool calculations, 103 Tool holders, 40, 220 Tooling, consecutive, 93 Tools diamond, 38, 220 grinding, 37 Torque arm for drill, 160 Transfer machining, 266 Truing devices, grinding, 198 Trunnion jig, 148 Tungsten-carbide tools, 32 Types of diamonds, 38 Universal tool holder, 215 Safety features, 246 Setting gauge, grinding, 201 Service milling, 74 Sine bar, 29 Shaft basis, limits, 19 Slideway grinding, 207 Slip gauges, 24 Small tools, 41 Solex comparator, 27 Spar milling fixture, 254 Speeds and feeds, 36, 276 Spherical grinding, 208 Spigot for broaches, 178 Spindle, milling machine, Stellite, 35 String milling fixtures, 80 Supporting jacks, 130 Vacuum fixtures, 195 Varying pressure system, 255 Vee location, 138 Vertical broaching, 180 Vibration problems, 67, 222 Wear allowance, gauges, 20 Welded jig, 135 Wheel dressing blocks, 215 Wheel truing devices, 198 Work ejectors, 125, 251 Work holding mandrels, 190 varying pressure, 255 vacuum chuck, 196 Work support trepan boring, 237 289