THE PRACTICE AND PRINCIPLES

OF TUBE MANIPULATION

A Thesis by T. H. WILKES, A.M.I.Prod.E.

THE principles and methods referred to in thisThesis are those which are being employed in the

production of bent pipes and assemblies in such in-dustries as aircraft, light engineering, and motor carproduction. It can also be applied to many otherindustries, having been used to great advantage in theproduction of preformed plumbing sets for prefabri-cated dwellings in the building industry.

An account of the methods used in the productionof solid drawn tube is given at the commencement asan introduction to the subject of tube manipulationwhich follows.

The headings of the sections dealing with this sub-ject are as follows :-

1. the production of seamless brass and coppertubes;

2. design and layout of bent pipe assemblies;3. functions of production;4. unfilled machine bending;5. mandrel bending;6. rilled bending;7. production planning;8. production control;9. costing.

1. The Production of Seamless Copper and BrassTubes

The first stage of production is the preparation ofthe basic materials, which are then melted down andcast in the form of cylindrical billets, about 6"- 12"

in diameter and about 4' - 6' long. This consists ofprocess scrap and virgin metal, the proportions ofwhich are specified by the laboratory, and carefullychecked during manufacture to ensure that the re-quirements of the specification are satisfied. Thetubes may be formed either by extrusion on a press,or by drawing through dies and over plugs on adrawbench. In the case of extrusion, the billets aresawn into lengths of approximately 8" -15" long,which are now called blooms. The blooms are heatedin a suitable furnace situated close to the extrusionpress, which may be something in the region of 1,500tons capacity. The bloom is placed in position onthe press by a mechanical conveyor and the actionperformed by the press is as follows :-

A hole is first pierced through the middle of thebloom by the end of the ram, which is specially re-duced in size for this purpose. This reduced portionis long enough to extend the full length of the bloombefore the main part of the ram (which is nearly equalto the bloom in diameter) comes in contact with thebloom by means of a pressure plate, and forces itthrough a die (Fig. 1). The die determines the out-side diameter and the punch of the ram and insidediameter of the tube so formed.

In the case of solid drawn tubes, the full lengthbillet is heated and a hole pierced through the middlein a rotary piercing machine (Fig. 2), in which thebillets are forced over a bullet nose plug by means oftwo barrel-shaped rolls set at a skew angle to eachother. The plug is held in position by a mandrel ofsmaller diameter than the plug, to allow clearance

BLOOM

BEFORE PIERCING OR EXTRUSION AFTER PIERCING

FIG.AFTER COMPLETE EXTRUSION

32

for the pierced billet as it is propelled from left toright by the rolls. The mandrel in turn is firmlysupported against a back stop.

The hollow shell so formed is now drawn throughdies by means of a dog fixed to a chain conveyorbuilt into the drawbench. The inside diameter of thetube is formed by a plug held in position by a rod.The shell or tube is first slightly reduced on the endso that it can be inserted through the die, after whichit is loaded on to the plug. The rod holding the plugis then secured in position, and, at the same time,correctly located in relation to the die. The portionof the tube which is already protruding through thedie is now attached to the " dog " on the drawbench.The grip is self-imposed by the load required to pullthe tube through the dies. This process is then re-peated the required number of times, using variousdies and plugs until the desired size is produced. Thecold drawing of the metal in this manner results in aconsiderable increase in the hardness, and it is there-3UTU3}IOS JO Suipguutf we }no Axreo 03 Axesssoau 9JOJoperation in. between each operation to restoreductility. This is followed by pickling in acid in orderto remove any scale so formed. Before despatchto the customer, the tube will be hydraulically pres-sure-tested to the required test pressure, and mayalso be heat treated to impart the necessary physicalproperties required.

2. Design and Layout of Bent Pipe Assemblies

The shape of a pipe may be determined either onthe drawing board, resulting in a fully dimensioneddrawing, or by the creation of a master pipe foundfrom a trial run on the job. Whichever the methodadopted, the shape of the pipe and size of bends soproduced, will, to a large extent, determine themethod of production to be adopted. The exercise ofthe greatest care at this stage will be more than wellrewarded by ease of production and economicalmanufacturing costs.

The guiding principles to be borne in mind are :-(a) the provision of bends of true curvature;(b) allowing ample straight portions of not less

than approximately 2" in between the bends;(c) specifying bending radii which may be pro-

duced with the minimum of trouble. Ingeneral, and with certain limitations, theseshould be as large as is practically possible.

The subject of bend radii for light gauge tubes isa complex one. The following formula devised by theAuthor for 20 swg. tubes can be used as a verysound guide for most practical purposes and withmost metals where bends are produced with accuratetools on suitable bending machines: RR = D2/3 G;the root (or inside) radius of bend being equal to theoutside diameter of the tube squared, divided by threetimes the wall thickness of the tube. Bends havingthese radii can be produced without resorting to fill-ing. While not being unduly large they will haveminimum distortion and be suitable for aircraft pur-poses. Where necessary, however, bends of a muchsmaller radii can be produced by filling the tubes.

FIG. 2

This may be done with one of several fillers, or bya special bending machine fitted with a mandrel forsupporting the tube during the bending operation.By using the mandrel method, machine bends canbe produced approximately five times smaller than inthe above method or RR = D2./. 15 G. With specialequipment, bends of even smaller radii than this canbe produced, but these, however, take considerablylonger. Similar results can be obtained by the useof fillers which solidify in the tube, although the com-parative time required for a method of this sort isvery much greater, and the tube may require dressingto remove wrinkles which may form.

3. Functions of Production

There is a choice of methods from which to selectthe particular one to suit individual requirements.The choice will depend on the consideration of thefollowing points :-

1. total quantity required with progressivedeliveries;

2. standard of dimensional accuracy required;3. design of pipe, whether simple, moderately

difficult, or complex.If the quantity is large, and the shape simple or

only moderately difficult, these may be producedeither in a press by means of suitable punch and diesor, as is more generally the case, on production bend-ing machines. The production of dies for this appli-cation is usually an expensive business, and these willonly be of value for any one particular item. On theother hand, a production bending machine, whileundoubtedly having a higher initial cost, is capable ofproducing an unlimited number of different itemsusing mainly standard equipment.

There are several different types of machines avail-able, and the choice will depend both on the quantitiesinvolved and the standard of dimensional accuracyrequired. These machines vary from simple handbenders, costing a few pounds, to precision semi-automatic machines running into thousands.

If the pipe is of a complex shape it may be advis-able to design and produce special tools or machinesspecifically for the purpose, or a standard machinemay be utilised by making adaptation and usingspecial bending tools. This of course would only bewarranted where large quantities are required.

33

for the pierced billet as it is propelled from left toright by the rolls. The mandrel in turn is firmlysupported against a back stop.

The hollow shell so formed is now drawn throughdies by means of a dog fixed to a chain conveyorbuilt into the drawbench. The inside diameter of thetube is formed by a plug held in position by a rod.The shell or tube is first slightly reduced on the endso that it can be inserted through the die, after whichit is loaded on to the plug. The rod holding the plugis then secured in position, and, at the same time,correctly located in relation to the die. The portionof the tube which is already protruding through thedie is now attached to the " dog " on the drawbench.The grip is self-imposed by the load required to pullthe tube through the dies. This process is then re-peated the required number of times, using variousdies and plugs until the desired size is produced. Thecold drawing of the metal in this manner results in aconsiderable increase in the hardness, and it is there-3UTU3}IOS JO Suipguutf we }no Axreo 03 Axesssoau 9JOJoperation in. between each operation to restoreductility. This is followed by pickling in acid in orderto remove any scale so formed. Before despatchto the customer, the tube will be hydraulically pres-sure-tested to the required test pressure, and mayalso be heat treated to impart the necessary physicalproperties required.

2. Design and Layout of Bent Pipe Assemblies

The shape of a pipe may be determined either onthe drawing board, resulting in a fully dimensioneddrawing, or by the creation of a master pipe foundfrom a trial run on the job. Whichever the methodadopted, the shape of the pipe and size of bends soproduced, will, to a large extent, determine themethod of production to be adopted. The exercise ofthe greatest care at this stage will be more than wellrewarded by ease of production and economicalmanufacturing costs.

The guiding principles to be borne in mind are :-(a) the provision of bends of true curvature;(b) allowing ample straight portions of not less

than approximately 2" in between the bends;(c) specifying bending radii which may be pro-

duced with the minimum of trouble. Ingeneral, and with certain limitations, theseshould be as large as is practically possible.

The subject of bend radii for light gauge tubes isa complex one. The following formula devised by theAuthor for 20 swg. tubes can be used as a verysound guide for most practical purposes and withmost metals where bends are produced with accuratetools on suitable bending machines: RR = D2/3 G;the root (or inside) radius of bend being equal to theoutside diameter of the tube squared, divided by threetimes the wall thickness of the tube. Bends havingthese radii can be produced without resorting to fill-ing. While not being unduly large they will haveminimum distortion and be suitable for aircraft pur-poses. Where necessary, however, bends of a muchsmaller radii can be produced by filling the tubes.

FIG. 2

This may be done with one of several fillers, or bya special bending machine fitted with a mandrel forsupporting the tube during the bending operation.By using the mandrel method, machine bends canbe produced approximately five times smaller than inthe above method or RR = D2./. 15 G. With specialequipment, bends of even smaller radii than this canbe produced, but these, however, take considerablylonger. Similar results can be obtained by the useof fillers which solidify in the tube, although the com-parative time required for a method of this sort isvery much greater, and the tube may require dressingto remove wrinkles which may form.

3. Functions of Production

There is a choice of methods from which to selectthe particular one to suit individual requirements.The choice will depend on the consideration of thefollowing points :-

1. total quantity required with progressivedeliveries;

2. standard of dimensional accuracy required;3. design of pipe, whether simple, moderately

difficult, or complex.If the quantity is large, and the shape simple or

only moderately difficult, these may be producedeither in a press by means of suitable punch and diesor, as is more generally the case, on production bend-ing machines. The production of dies for this appli-cation is usually an expensive business, and these willonly be of value for any one particular item. On theother hand, a production bending machine, whileundoubtedly having a higher initial cost, is capable ofproducing an unlimited number of different itemsusing mainly standard equipment.

There are several different types of machines avail-able, and the choice will depend both on the quantitiesinvolved and the standard of dimensional accuracyrequired. These machines vary from simple handbenders, costing a few pounds, to precision semi-automatic machines running into thousands.

If the pipe is of a complex shape it may be advis-able to design and produce special tools or machinesspecifically for the purpose, or a standard machinemay be utilised by making adaptation and usingspecial bending tools. This of course would only bewarranted where large quantities are required.

33

BEND GAUGE PLANE GAUGE

1i

FORMER

BENDING ARM

TUBE

FIG. 3

A case in point is the production of cycle handle-bars. Whilst a basically standard machine may beused, it would be so adapted and tooled that itvirtually became a special purpose machine suitablefor that particular job only.

In the case of small quantities, these may be dealtwith in a variety of ways, again, depending on thecomplexity of the pipe, and the standard of finishand dimensional accuracy required. A pipe of simpleshape, having bending radii of favourable ratio totube diameter and gauge, could be dealt with by theuse of standard bending machines and equipment byany one reasonably proficient in this type of work.On the other hand, with conditions contrasting in anopposite direction, a machine would be of little assist-ance, due mainly to the expense of providing specialtools and the time necessary for adjusting and settingup. Pipes of this nature could be produced by skilledcoppersmiths with no special tooling or formers,other than those usual to their particular type oftrade. The production methods adopted would varyaccording to the quantities involved and the rate ofdelivery at which they are required. Where thequantities involved constitute a production run ofsuitably designed pipes, production would commencewith the issue of either a drawing or a master pipe tothe shops, and from this a checking gauge is made.This would be made of a suitable combination

of hardwood and Jabroc, and so constructed as toform an accurate profile shape of the form required.The base of the jig would be constructed from goodquality ply, of ample thickness, and suitably rein-forced to prevent distortion taking place. If large

SLIPPER

FORMER

SPACING. GAUGE/

FIG. 4

quantities and a long production run are anticipated,with resulting heavy wear on the jig, it may be advis-able to construct this of metal.

If the shape of the pipe is not difficult and thestandard of accuracy required not too exacting, thedeveloped length of the pipe may be determined andall pieces cut to finished size before bending. Somevariation however, will occur, particularly in regardto the overall length. With aircraft pipes and suchlike, however, manufacturers now insist that a work-ing tolerance of ± .010" similar to that applied tomachined components is maintained. In this case,an allowance must be added to the overall length ofthe pipe to allow for a final trimming to lengthoperation after bending.

The length having been determined, the next stageis to determine on a bending machine the varioussetting positions for each bend, both in relation to oneanother, and to one end of the pipe. The exactmethod used will depend upon the type of machineused, whether for instance this is nothing more thana simple bending head, or one equipped with settingand indexing features for reproduction. Fig. 3 showsa sketch of a suitable machine, designed by theAuthor and manufactured specifically for dealingwith repetition bending for accurate reproduction ofbent pipes. In the former case the pipe will requireto be " reset up " each time, (with specially providedequipment); in the latter the data can be logged forfuture reference. There are, of course, machines withvarying degrees of facilities lying between these twoextremes with the further possibility, where very largequantities are concerned, of special purpose tools ormachine attachments of a permanent type.

Batches of work will now be issued to the shops, incut lengths. The setting position for the first bend willbe located, and this bend will be made in each pipe ofthe batch.' The machine will then be changed for thesecond bend, and this will be carried out again oneach pipe of the batch. This procedure will continueuntil all bends in the batch are completed. It maybe necessary to carry out further alterations to themachine between bends, due to bends of differentradii being present in the same pipe. It is obviously

34

advantageous to use bends of standard radii in thesame pipe wherever possible. If the pipe is beingproduced to aircraft and similar requirements, it will .be necessary to carry out some hand adjustments inbetween bends to overcome variations caused bydifferences of temper in the material and possiblevariations caused by machines or tools, again, de-pending on the grade used.

If the pipe has not been cut to finished length, ascarfing operation on one or both ends will now berequired in order to finish it to exact length. Thiswould be carried out either in a cutting-off machine,or by hand using hardened half-blocks as a guide,depending on quantities involved.

Where necessary, flaring operations would now becarried out for the pipes to accept AGS pipecouplings. Other pipes may require nipples, nuts, andbanjos to be attached to the pipes by either brazing,soldering or welding. Where banjos or flanged typefittings are required, however, it would be necessaryto provide a suitable jig in order to locate the facesand holes centre correctly during the process. Dueallowance must be made for expansion and contrac-tion of the assembly in the tool. It simplifies mattersconsiderably if either of these operations can becarried out on one end of the pipe before bending.

It is not usually necessary to carry out annealingon the tubing before bending, as the material is norm-ally supplied in a suitable condition. In specialcircumstances, however, heat treatment may be neces-sary in order either to anneal before bending, stressrelieve after bending, or to impart special propertiesto the material to bring it to specification. In allcases other than those of light alloys, this operationwould have to be followed by a descaling operation,where the presence of scale could not be tolerated.

The treatment is best carried out in a temperaturecontrolled furnace, due reference being made to themaker's instructions. Where the quantities are small,this may be done with the use of a blow lamp, inwhich case extreme care is necessary to see that thematerial is not made too hot.

Descaling after heat treatment may be carried outby either pickling in suitable acid, or by shot oraqua-blasting.

The pipes, or pipe assemblies as they may now be,would then proceed through the normal finishingoperations such as attaching of part number plate

by either soft solder or silver soldering, pressure testing, painting or other finishing process.

One of the final operations would be a cleaningoperation in the bore of the pipes, carried out by firstflowing pure warm trichlorethylene through the pipe,followed by a tight fitting pull-through, and finallyby blowing through the pipes with clean dry com-pressed air. The ends of the pipes would then besealed to avoid the ingress of foreign matter duringstorage or transit.

4. Unfilled Machine BendingThis is the quickest and easiest method of bending

and is adopted wherever possible. Fig. 4 shows atypical former and slipper such as is used for lightgauge tubes. It has an accurately machined grooveextending for an angle of 200° on a given radius,together with a straight portion, which may be usedfor clamping the tube. The diameter of the grooveshould be such that the tube will be a push fit in it.The depth of the groove should be about three-quarters of the tube diameter. This will ensure thatthe tube has the maximum support against distortionduring bending.

The pressure for bending is applied through themedium of the slipper, which is grooved to the tubediameter, and is a push fit inside the former. Thetube is inserted in the former (Fig. 3) with one endlocated in the spacing and plane gauge. The slipperis inserted between the tube and bending roller andthe roller adjusted by means of an adjusting screwto give the required bending pressure. For normalpurposes this will be achieved by allowing a clearanceof 1/16" between roller and slipper in the neutralposition. The bending arm rotates on the same axisas the spindle locating the former, through an angleof not less than 200°. By this means bends of 180°or return bends can be made. The bend is made byrotating the bending arm through the required angle,the amount of travel being accurately controlled bythe bending gauge. The former and tube are firmlysecured throughout the bending operation by meansof a quick-acting toggle clamp.

5. Mandrel BendingTubes which, by virtue of the small ratio of the

bending radius to tube diameter and wall thickness,require support during bending, to prevent either

• BENDING LEVERCLAMP

CLAMPBLOCK SLIPPER

viiiii/itii/iii/muimm

MANDREL TUBE MANDREL ROD

FORMER

FIG. 535

BALLS MANDREL

FLEXIBLE WIRE

FIG. 6

acute distortion, wrinkling of the inside, or completecollapse, may be loaded with a variety of fillers, or,in all but exceptional cases, supported mechanicallyby means of a mandrel bending attachment. Fig. 5shows a typical set-up with mandrel in position forthis operation. With the exception of the mandrel,the same tools are used as for unfilled bending. Theaction, however is reversed in this instance and is asfollows :-

The bending arm now remains stationary, or isreplaced by special adjustable support rollers, whichtake the bending reaction through the medium of theslipper. The tube is clamped to the former by suitablemeans and rotates about its axis to the predeterminedangle of bend. The mandrel is located inside the tubein such a way that the tangent of the radius on theleading edge is between approximately 0" to 1/8"further forward than the centre line of the former.This adjustment is very critical and varies withdifferent materials, gauges and diameter of tube. Onvery acute bends, or when using very thin gaugetubes in the region of 22 and 24 swg. the mandrelhas the addition of one or more trailing balls or seg-ments thereof attached by a flexible wire or chain(Fig. 6). Where these are used, however, a means ofextracting the mandrel must be provided, as when thebending action is finished the balls are firmly grippedin the bend of the tube. The extraction may becarried out hydraulically, mechanically, or manually,as circumstances dictate. The mandrel and ballsshould be made of alloy steel and should be given asmooth polished finish. The amount of clearanceallowed between the bore of the tube and the man-drel is important, and is in the region of .005" to.015". The mandrel should be suitably lubricatedduring the bending operation.

6. Filled Bending

For certain reasons, such as close proximity of bendsto one another, bends not having a true radius, andcompound bends formed in two planes, it may not bepossible, or is uneconomical due to the cost of tooling,to produce bends by either of the above methods. Inthis case a filler is used, and this is usually either alow-melting point alloy such as Cerrobend, or Hoytmetal containing bismuth, lead, tin and cadmium, andwhich melts at 160°F. (in hot water), or a mixture ofpitch and rosin, These are poured into the tubes inthe molten state and allowed to solidify, being meltedout again when bending is complete. Bending may

proceed by machine as described under Section 4. Ifthe bends are too complicated for machine bending,however, they are bent by skilled coppersmiths freehand, using whatever aids are possible. Either ofthese systems, howeve^ are very much more costlythan the other previously described.

7. Production PlanningThe Order Department, having received the

customer's order, produce the Works Order, copies ofwhich are distributed to the Planning Department,Production Control Office, and wherever elsenecessary.

Production does not commence until the PlanningOffice have dealt with all preliminaries. These in-clude requisitioning all materials and fittings on theBuying Department, and deciding what items shallbe bought out, or made in the works, depending onthe tools, machines and general capacity available.They determine the methods and machines to beused on production, and assess any special tools whichit may be necessary to produce, passing the broadprinciple to be adopted to the Drawing Office, to-gether with a requisition covering the supply of same.If necessary, they may be required to submit a de-tailed estimate of production, tooling and machinecosts either for quotation purposes before the orderis received, or as a basis for piece work rates and con-trol of production costs.

The operations are then planned in detail and en-tered on a planning card (Fig. 7) against tooling andmaterial requirements, together with times allowed

PLANNING CARD

PART No

DATE FIRM CARD No

NO OF CARDS

MATERIALS FITTINCS+-

OP No

123456789

OPERATION

• -

TOOLS/MACHINE

TOTALS

PREP TIME CRADE

FIG. 7

36

PART No NAME PERIOD

OR

DE

R

No

OR

DE

R

No

REOUIRE-MENTSPROGRESSIVETOTAL

DELIVERIES

PROGRESSIVETOTALADVICENOTE

DATE

INDICATOR

REQUIRE-MENTS -PROGRESSIVETOTAL

DELIVERIES

PROGRESSIVETOTALADVICENOTE

DATE

INDICATOR

JANUARY

MAY

FEBRUARY '

JUNE

__

FIG. 8

for the operations. These times may be obtainedeither from (a) standard times, (b) by estimate, inwhich case it is checked or proved in actual produc-tion before it is established, or (c) by a physical timecheck on a trial run, which, apart from establishedstandard times, is the best and fairest way of all.

8. Production Control

Copies of the planning card are distributed to theCost Office, Production Control Office, the WorksForeman's Office, and wherever else may be necessary.It is the responsibility of Production Control toorganise the flow of work through the factory insuch a manner that customer requirements aresatisfied, delivery dates met, and a balanced produc-tion maintained. Instructions or advice on this matterwill be forthcoming from the Sales Office and theWorks Order Office, and the Planning Office whopass on information concerning customer's require-ments, and production capacity.

This control is achieved through the use of deliveryschedules, progress charts, and the issuing of job cardswith instructions as to when they must be completed.

In many factories, the Progress Department iscombined with Production Control, the responsibilityof progress being to see that all requirements calledup by Production Control are fulfilled. This is doneby close co-operation with the foreman and produc-tion personnel, and by keeping a watchful eye onprogress charts from which it can be seen if produc-tion is proceeding normally or lagging behind.

The majority of orders placed by a customer callfor deliveries on a weekly or monthly basis at a givenrate, until the order is completed. The first task ofProduction Control, on receipt of a Works Order,will be to fill in this information on a delivery

schedule specially devised and printed for the pur-pose. Fig. 8 shows an abbreviated version of a typicalexample. The focal point in the schedule is thequantity required, shown weekly or monthly. Againstthese requirements are shown the actual deliveriesmade together with the progressive total. Using thisschedule as a guide the job cards are made out, thetotal quantity being divided into batches on a weeklyor monthly basis. The job cards (Fig. 9) are typed outin sets of four which include one white stiff copy forthe Time Office, one buff stiff copy for Production,one white paper copy retained by Production Con-trol, and one half-size paper copy to Cost Office.These cards and sheets have the various headingsprinted on them, which are filled in when they areissued. The top half of one side of all copies isidentical, and contains all the common basic informa-tion, together with the job numbers. The otherheadings vary according to the different functionwhich they have to fulfil. The information requiredis filled in under the various headings as productionproceeds, and when the job is complete, these cardsprovide a complete record and history of its passagethrough the works. Details of all job cards issued willbe entered on progress charts (Fig. 10) containing allbasic information, such as name of firm, job number,quantity in batch, delivery period for completion, andheadings for each operation. As operations are passedoff by the Inspection Department, tickets are issuedto that effect which are first handed in to Progress.This is entered on the progress chart and the ticketspassed on to the Time Office.

When the completed items are despatched to thecustomer, an Advice Note is made out giving ordernumber, part number, and quantity being delivered,etc. One copy is sent to the customer and copiesdistributed to various internal departments includingthe Cost Office.

37

FIRM

ORDER No

BATCH No

NAME OF PART

PART No

JOB No

DATE No ISSUED OTY ORDERED

MATERIAL

RELEASE No

FITTINCS

RELEASE No

DATES | D E L I V E R Y | ENDORSEMENTS | STAMP

REMARKS

OPERATION DATE TIME OTY. NAME B

FRONT OF JOB CARD (SHOP COPY) BACK OF JOB CARD (OFFICE COPY)

FIG. 9

9. CostingThe functions of this department are manifold and

include the assessment of manufacturing and actualcosts, determination of working overhead costs, pro-viding unit cost of production by analysis of all costs,providing advice to estimating department for dealingwith quotations, to planning department in connec-tion with the fixing of rates, and direct responsibilityfor all piecework or incentive schemes.

Copies of all paperwork dealing with outside pur-chases and stores requisitions, together with all thetime booked against the order, are sent to this officewhere they are recorded in convenient form.

When the order is completed, this information isanalysed, and the overhead costs added, giving theactual manufacturing cost per unit, and this is shownagainst the selling priGe quoted, or if no quotationhas been made, the selling price is now determined.

The job record, as it may be called, is commenced,when one of the sheets of the job card set issued byProduction Control is received in the Cost Office.This job sheet will give such preliminary informationas name of firm, job number, order number, drawingor part number, quantity issued in batch, full quantityon order, together with full details of material issuedby stores.

A copy of the planning card (Fig. 7) for this itemwill already have been received, and this will show the

amount of time required for production, together withthe grade of labour to be used, and details of toolsand material requirements. In many cases, items arepriced directly from the information on these planningcards before production commences. They will alsohave received copies of requisitions bearing the mainorder number for any material issued against tools,and copies of purchase orders, for outside purchasesin this connection.

These orders usually show the cost of the items,although in practice the cost is not entered on the jobrecord until the price has been ascertained from theinvoice.

Whilst the job is in production, each operationis booked on at the Time Office by the operator con-cerned. The operator hands in to the time clerk theshop copy of the job card (Fig. 9) stating the opera-tion being worked on, and whether starting or finish-ing. The time clerk records this information on hiscopy of the job card set, and also on a documentcalled a summary sheet.

It may be several weeks before all operations arefinished and the job completed. In order that costingmay proceed apace with production, the Cost Officeis furnished with details of all completed operationson a weekly basis. This is supplied by means of thesummary sheet, a copy of which is made out for eachoperator engaged on production. This serves the

38

additional advantage of supplying information in con-nection with production bonus, enabling any timegained against time allowed/ to be paid in the form ofbonus each week. All operations are examined by-inspectors as they are completed. In addition toentering in the quantity passed and placing theirstamp or the job card against the particular operation,the inspector fills in a small ticket showing jobnumber, " o p " number, operator, and quantitypassed. This is passed to Progress and ProductionControl, who enter information on their charts, andimmediately pass it on to the Time Office. This en-ables the Time Office to mark up completed opera-tions, and assess the time allowed for the quantitypassed, crediting time saved for payment of bonus.

Any scrap which may be incurred, necessitating theproduction of further items and the issue of morematerial, is shown by inspection who issue rejectionnotes, a copy of which is sent to the Cost Office. Anyfurther details which may be issued from the storesfor incorporation in production, are issued on receiptof a requisition bearing the order number, a copy ofwhich is sent to the Cost Office.

All this information, having been entered on thejob record, will cover the direct manufacturing costs.In addition to these, however, many other indirectcosts are involved, which have to be added to directcosts in order to find the actual costs. These includesuch items as salaries of all staff and non-productiveworkers, depreciation of plant, machinery, buildings,vehicles and consumable stores (where these are not

directly chargeable to jobs); cost of maintenance ofplant, buildings, vehicles, etc., cost of power, gas, alloffice requirements, consumable tools such as drills,dies, taps, cutting tools, saw blades, and all such ex-pendable items needed either for the running of thefactory or for use on production, but not directlychargeable.

A separate record is kept of these expenses, and atfixed intervals, such as three or six months, they areset against the direct manufacturing costs of wagesand material, and the ratio shown as a percentage.This figure, called the overheads, will then be used asa basis for costing and assessing prices. Practice re-veals that this figure varies tremendously betweendifferent firms, and may be anything between 100%to 600% of production costs. Usually, however, wherethe overhead costs are high, they are largely offset bythe production costs being low. Among the reasonsfor the great variation in overheads are the type ofproduction involved, whether a large turnover ofsmall parts or low turnover of complex machinery,whether production is for the commercial market, orsuch as requires very high standards of accuracy in-volving a large inspection staff and equipment, suchas for the aircraft industry; the amount of machinery,and mechanical handling devices, directly engaged onproduction, and the number of technical staff re-quired on design, research and development. It willbe readily realised that these conditions varytremendously in different establishments and are suchas effect overhead costs to a marked degree.

PROGRESS CHART

NAME OF FIRM PERIOD

PART No NAME OTY JOB No OPERATIONS

FIG. IO

39