100 Tips and Techniques for Getting the Job Done Right by Tom Kendrick_6 doc

storage magazine. e latest tool presetting machines equipped with a full suite of tool management features and functions, can play a big role in improving shop: productivity/component quality, tool life, inventory control, whilst minimising down-time, reducing com- ponent cycle times and part scrappage. Mounting and Adjusting Milling Cutters Possibly the most crucial cutter body to correctly mount and adjust, for the individual cutting inserts, is that of a side-and-face cutter (Fig. 138). e reason why it is important to set the cutter assembly up cor- rectly, is that invariably the width of the slot in the ma- chined workpiece is identical to that of the respective rotating face widths of the cutting edges. Moreover, whole cutter assembly must ‘run true’ as it rotates on its arbor 39 – with no discernible ‘wobble’ – as this eective ‘wobbling’ will inuence the machined slot geometry. At its most extreme, some of these special-purpose slotting cutters can be >2 tonnes in weight and larger than 1.5 m in diameter, having segmented cartridges that are precisely and accurately tted onto the periph- ery of the cutter body. As a general ‘rule of thumb’ , most of these types of slotting cutters are used to ma- chine component features to a depth of four times their slot width 40 . If a deeper slot is required, then the cutter has to be ‘optimised’ in some way. Perhaps by using a smaller width cutter than that required for the component’s slot width and, if possible, cutting each slot face separately and eventually taking it to the de- sired width/depth – arbor interference permitting. Mounting cutting inserts in the case of the stag- gered-toothed side-and-face cutter body shown in Fig. 138, is relatively straight forward, due to the lateral adjustment available by the splined cartridge seatings. Here, it is important to ensure that the insert seat is thoroughly cleaned prior to commencing tment. Moreover, ensuring that the contact against the bot- 39 ‘Arbor’ , is the workshop term used for the extension from the machine tool’s spindle that the slotting-type cutter is located and driven from. It can be cantilevered – termed a ‘stub-ar- bor’ , or supported at its free-end, by an arbor-support – nor- mally tted with adjustable and suitable matched-bearing di- ameters. 40 When full slotting, using a side-and-face milling cutter at 40% of the maximum radial cutting depth, a typical feed per tooth would be around 0.25 mm tooth –1 . tom face of the seat occurs, prior to tightening the set screw – normally to a nal torque value of 5 Nm (i.e. illustrated in Fig. 138b). Each set screw should be lu- bricated with the recommended lubricant before re- use. In order to ensure that each cutting insert runs true, the slotting cutter, or face mill assembly, should be correctly mounted – in the former case, onto the ar- bor, the latter into the correct spindle nose taper – be- ing held on a suitable presetting machine. e whole assembly is then rotated to ensure that each cutting in- sert is both radially and axially positioned, thereby en- suring that no edges ‘stand-proud’ of each other and at the same time conrming that no discernible ‘wobble’ in the rotating assembly occurs (i.e see the deep-slot- ting cutter, held in a stub arbor with support, allowing the whole tooling assembly to be rotated and each cut- ting insert to be inspected/measured, in Fig. 139). Although cutter keyways are not strictly-speaking a mounting problem, the subject does need to addressed, as if the cutter’s diameter and its associated driving keys are not considered, this will limit the overall mill- ing performance of the cutter. With most slotting, and side-and-face cutters tted to arbors, they normally require a keyway/key for rotational driving purposes for the whole cutter assembly. Usually cutters that are <φ125 mm with insert sizes ranging between 6 to 8 mm , then one key will suce, but cutters >φ140 mm with insert sizes of between 11 to 14 mm, they would frequently need two keyways 41 . Cutter diameter and driving key limitations, are de- termined by the cutter’s bore and its connected key- way, together with the D OC being limited by several factors: the arbor OD, its mechanical strength, plus any deformation of the driving key(s). For vertical slotting applications, mounting the cutter on an large diameter arbor with the minimum of overhang is de- sirable. If the feed per tooth can be reduced – assum- ing component cycle-times will allow – then this will reduce the tendency of key deformation during mill- ing. Milling calculations and key strength, can be ob- tained from the following expressions and are valid for new cutting inserts: 41 Keyway positioning for two keys – is usually given by the dis- tance between them as: 180° minus half the peripheral pitch of adjacent cutting inserts – as shown in the diagrammatic sketch in Fig. 138a.  Chapter  Figure 138. The correct mounting and setting of a cutting inserts in a staggered-toothed side-and-face cutter body. [Courtesy of Sandvik Coromant] . Torque (T) = P [kW]/n [rpm] × 60,000/2π [Nm] Force (F) = T/d [mm] × 1,000 [N] Shear [keyway] stress (τ) = F/area = F/A × E [N mm –2 ]. NB As the cutting inserts wear, the above values will increase by approximately 30%, therefore, it is usual to add a ‘safety factor’ to the key(s) material shear strength, by multiplying this value by 1.5. Modular Tooling and Tool Management  Figure 139. Cutting inserts for large diameter cutters require pre-setting to mini- mise any run-out. [Courtesy of Starrag Machine Tool Co. and Sandvik Coromant] .  Chapter  If special-purpose applications are required, such as when form milling the ubiquitous ‘Vee-and-Flat’ con- guration for an conventional engine-/centre-lathe bed, ‘gangs’ 42 of: side-and-face, angled- and helical-cut- ters are deployed to form and generate these slideways. Here, it is important to ensure that when presetting the cutters on the tool presetter, that the whole cut- ter assembly is held in the exact manner that they will be utilised when ‘gang-milling’. is ‘gang-milling’ set- up, allows their dimensions and forms to be inspected/ measured, while slowly rotating the whole assembly. If two ‘helical cutters’ 43 are utilised in a ‘gang-milling’ op- eration, then their helices should be of the same pitch, but of dierent ‘hands’ (i.e. le-ward and right-ward respectively), as this arrangement will balance-out any end-thrust due to opposite cutter helices. Setting up ‘Long-edge milling cutters’ – these are sometimes termed ‘Porcupine cutters’ (i.e. see Fig. 124 – centre), which are normally required for the heavier and longer cutting applications, is quite a com- plex presetting process. As the individual cutting in- serts must be slowly rotated to ensure that axial and ra- dial run-out values are kept to a minimum. Otherwise those inserts ‘standing-proud’ of the remainder will suer from greater wear rates, thereby prematurely re- ducing the cutter’s eective life quite signicantly while milling an unwanted step into the machined sidewall. On standard face mills, ‘face run-out’ can be as high as >50 µm, so when close tolerances and good milled surface texture is mandatory, then extreme care must 42 ‘Gang-milling’ , is a complex forming process utilising two, or more milling cutters adjacent to one another. So, a side- and-face cutter, located directly together with a helical cutter, represents a ‘gang’ in its simplest form. is ‘gang’ of cutters, is normally permanently mounted together for re-grinding and tool presetting – this is assuming that the cutting edges are not made-up from a series of strategically-positions indexable inserts (see Fig. 76). NB ‘Straddle milling’ , should not be confused with ‘gang- milling’ , as here, it is normal to use two side-and-face cutters with spacing collars between them – of a specic and known dimensional size. erefore, the cutters ‘straddle’ the part – hence its name – while they machine two faces at the required distance apart in one pass along the workpiece. 43 ‘Helical cutters’ , are sometimes known as ‘Slab-mills’ , hav- ing either a le-, or right-hand helix, which ensures that the length of cut and its shearing mechanism are reduced by a ‘quick-helix’ , which is necessary for the milling of more duc- tile materials. be taken when presetting such tooling assemblies. In order to assist the presetting of such tooling on some face mills, ‘barrel screws’ allow ne adjustment to the cutting insert (Fig. 140a). Such ‘barrel screw’ designs are quite simply-designed, but surprising eective in both adjusting and retaining the cutting inserts, the following remarks explain how they are designed and their method of operation. ‘Barrel screws’ (Fig. 140a), are hardened to resist deformation and have a black- oxide nish to minimise corrosion. To prevent them from shiing during a face milling operation, a nylon pellet is embedded in the thread of the ‘barrel screw’. Right-hand cutting inserts use le-hand ‘barrel screws’ and vice versa, as this counter-acting rotation keeps the insert locked rmly in its pocket. e mating surface of a ‘barrel screw’ is reamed produce a minimum con- tact of 120° occurs, which ensures accuracy and preci- sion, while minimising wear. e ‘barrel screw’ hole is o-set toward the reamed surface, to provide positive contact with the mating surface throughout the range of adjustment of this screw. It should be noted, that these ‘barrel screws’ cannot adjust the eective ‘gauge- length’ of the tooling, as the amount of adjustment is limited by the position of the cutting insert’s clamping screw. e face-milling cutting inserts shown in Fig. 140a are tangentially-mounted, oering considerable sup- port and additional strength to the cutting edge. When presetting the face mill’s cutting edges when the cut- ter body is equipped with ‘barrel screws’ , the following procedure should be adopted: • To adjust the insert outward – leave the cutting in- sert tight and simply turn the ‘barrel screw’ to move the insert to the desired setting. NB Adjustment to the cutting insert’s position, should only be made in one direction only. • To adjust the insert inward – loosen both the cut- ting insert and ‘barrel screw’ , push the insert in - ward, then tighten the insert’s screw and adjust out again to the desired position. In Fig. 140b, the simple ‘ow-chart’ highlights why it is important to keep any face milling cutter insert’s run- out to a minimum. If the run-out of both the minor and peripheral cutting edges is large, then this can create several undesirable problems for the tooling as- sembly, including: • Poor surface nish – if a cutting insert ‘stands- proud’ of the others in the face mill, then it will cut Modular Tooling and Tool Management  Figure 140. Cutting inserts need to be precisely and accurately seated in their respective pockets of the cutter body, to eliminate potential run-out .  Chapter  in a similar fashion to that of a y-cutter, creating a periodically scored surface – aer each cutter revo- lution – degenerating the milled surface texture, • Chipping due to vibration – as all of the inserts are not set the same, then the most prominent one will take the largest cuts on both the minor and periph- eral cutting edges, causing shock loading as the cut is engaged, thereby increasing cutter vibration and potential thermal eects 44 creating the likelihood of chipping here on the most exposed cutting inserts, • Rapid growth of wear – because of a prominently set and poorly positioned cutting insert in relation to the others in the cutter body, it will absorb the greatest cutting loads, which will lead to shortened tool life, this being exacerbated by pronounced vi- brational tendencies, resulting from unbalanced cutting forces and torque. NB All of these factors will contribute to a short- ened cutter life. Conversely, if the face milling cutter’s insert run-out is small, then a good surface nish and stable and predict- able tool life will result. Mounting and Adjusting Single-Blade Reamers e cutting head of a single-blade reamer was previ- ously illustrated in Fig. 74a. e replaceable blade is positioned longitudinally by a blade end stop and 44 ‘ermal fatigue’ , can be present when cutting is interrupted – as is the case for milling with a prominently exposed ce- mented carbide cutting insert. Numerous cracks are oen ob- served at 90° to the cutting edge and are oen termed: ‘Comb- cracks’ – due to their visual appearance to that of a typical hair-comb. ese cracks, are the result of alternating expan- sion and contraction of the surface layers as the cutting edge is heated during cutting, then cooled by conduction into its body during intervals between cuts. is very fast alternating heating and cooling cycle, develops the cracks normally from the hottest region of the rake face – this being some distance from the cutting edge, which tends to spread across this edge and down the insert’s ank face. Once these cracks become quite numerous, they can join up and promote partial tool edging to break away – creating cutting edge chipping. NB Today, many cemented carbide tooling manufacturers use structures and compositions that are less sensitive to ther- mal fatigue, moreover, coatings also play a signicant role in reducing thermal fatigue eects, when milling. diametrically adjusted using the front and rear adjust- ing screws. e blade is micro-adjustable over a lim- ited range of radial movement and can be preset in a special-purpose setting xture (Fig. 141a and c), to ream the desired diameter that the tool can then con- sistently produce. is reaming blade normally has a back taper of: between 0.01 to 0.02 mm over a linear distance of between 10 to 25 mm, respectively – when positioned in the pre-setting xture (Fig. 141b shows a three-guide pad designed single-blade reamer). A fea- ture of the blade’s adjustment, is that it can be reset to compensate for any subsequent blade wear. A clamp, plus two clamping screws securely holds the blade in place, with the wedge-type clamp providing support along the entire blade length (Fig 74a). In the case of the single-bladed reamer design illustrated in Fig. 74a, the blade is located and positioned in the ream- ing head at an 12° positive rake angle. For this type of reamer design, additional standard blades can be t- ted, oering both 6° and 0° rake angles. Taper reaming setting can be achieved by mounting the taper reamer (i.e a taper reamer is shown ream- ing a component feature in Fig 73b), into the spe- cial-purpose setting xture (Fig. 141c). At least two dial-, or electronic-indicators are positioned along the blade’s length, then adjusted so that a very light pres- sure is applied to the cutting edge of the blade – to prevent it from inadvertently chipping. With the blade ‘semi-clamped’ , adjustment is made so that its is parallel along its length – relative to the tapered guide pads. Once the blade has been ‘fully clamped’ , adjustment occurs to position it higher than its guide pads’ diameter, by between 10 to 20 µm – all along the blade’s length, which achieves an accurate setting, but this setting will depend on both the workpiece mate- rial and the prevailing machining conditions 45 . .. Tool Store and its Presetting Facility – a Typical System In the worst case scenario, for many of the ‘old-style’ traditional workshops, the tools are as oen as not 45 Taper reamers – typical machining details: Cutting speed 4 to 20 m min –1 (Stainless steel 2 to 6 m min –1 ), Feed 0.2 to 0.8 mm rev –1 , Machining allowance 0.2 mm and up to 0.5 mm – for large taper reamers, plus Coolant soluble oil @ 10% dilution. Modular Tooling and Tool Management  Figure 141. Presetting equipment and ‘guidelines’ for the setting of single-bladed reamers.  Chapter  treated with almost contempt, until they are required for a repeat order, or utilised for a new machining op- eration. Here, when the tools are not in use, problems arise because of the following: • Wasted and poorly utilised space – tools are kept either simply ‘oating around’ in an ‘ad hoc’ sys- tem, or are just sitting on top of each other – dam- aging the precision-ground tooling surfaces – while being kept in the open, • Time is lost looking for tools – due to the lack of any form of tool management, tools must be looked for located, then assembled – under less than ‘ideal con- ditions’ – so the minimum of tool control occurs, • Lack of eciency – as a result, more eort is re- quired by personnel who must try to nd tools, changing front- and back-ends to suit the selected machine tool for the production run causing lead- times to lengthen. Considering that up to 10% of the machine tool cost is tied-up in the purchase of tooling, then tools need to be looked aer with some degree of care and atten- tion. An area adjacent to the workshop, should be set aside for the purposes of storing tools and associated equipment in purpose-built tooling cabinets (Fig. 142) and form a basis for tool presetting activities. ere are several advantages in utilising telescoping drawer cabinets for tool storage (Fig. 137a and b), these in- clude: • Increased tool storage density – allowing the drawer space to be completely eciently lled-up in the minimum of space, • All tooling is kept under cover – thereby avoiding tool damage, while keeping tools dust and debris- free, • All tools and ‘associated paraphernalia’ are read- ily to hand – tooling drawers can be completely open-up, so that the contents are both easy to see and to arrange, • Tooling components t into their respective places – the drawers appropriately sectioned, to to- tally enclose the tools and their component parts, making it impossible for them to drop out and be damaged, • An organised and practical tool management sys- tem is achieved – within the tool store and pre- setting facility. erefore, all of the tooling com- ponents can be classied and categorised in the respective drawers – with every tooling part clearly seen. As a result of this ecient tooling component lay- out and tool-kitting facility, consumable tools can be ‘tracked’ within the tool store, but when these consum- ables leave the store vicinity (Fig. 142c), they are to all intents and purposes ‘scrapped’ as far as the tool stores are concerned. Returnable tools destined for eventual re-use can be ‘tracked’ around the machine shop by a number of tool-identication means (i.e as seen in Figs. 116 and 117 – using ‘tagged tools‘), or at the most basic of identication levels, by judicious labelling, or bar-coding of tools, with feed-back of information to the tool stores. Oen, for the most frequently used tools, they are assembled into a composite forms, then issued as ‘grouped-tools’ in the form of kits for a spe- cic job (i.e see Fig. 142c). Sometimes, tools are individually issued to ma- chine tool setters/operators and are not assembled into ‘kits’ , under such circumstances, the stores will keep a record to show: to whom they were issued, the machine tool on which they will be used, the num- ber and identication of these tools, together with the date of issue. A major benet of creating an area set-aside close to the machine tools for dedicated tool management, is that tool kits can be made-up ahead of the time – this being dictated by master schedule, so that they are ready just-in-time before any machining commences. A result of this timely tooling strategy, the lead times 46 are reduced, which is of prime importance to a com- pany in a competitive fast-developing market. Oen, it is the case that all tooling is assembled in the tool stores /preparation facility (Fig. 142b). is advanced preparation means that metrology-based 46 ‘Lead times’ , refer to the time taken before manufacture of the part, or prior to a production run beginning. ese ‘times’ are dependent upon a range of interrelated factors, such as: component stock quantities and their availability, the machine tools that are available, plus ‘line-balance’* factors, etc. *‘Line of balance’ (LOB), refers to a technique which permits the calculation of the quantities of the particular activities, or components which must have been completed by a particular intermediate date, in order that some nal delivery schedule might be satised. erefore, in this instance, it can be con- sidered as a machine tool scheduling and a control technique. In most of the LOB activities undertaken concerning machine tools, plant utilisation levels are paramount and if possible, a smooth and consistent LOB across all of the production ma- chines is desirable – for both high eciency and consistent work-throughput. Modular Tooling and Tool Management  supplies such as ‘limit gauges’ 47 , together with jigs and xtures , are also the responsibility of the tool stores personnel, being despatched with the tool kits for a particular production run. When this is the case, to- tal packages are issued, containing: cutting-tool and work-holding kits, plus the limit gauges necessary for metrological checking/inspection. A tool store and prepartion facility with responsibility for all of these tooling-related aspects, becomes a ‘focal point’ for the machine shop for all matters relating to tooling, whether they are for breaking-down of previously used kits, calibration of gauges, or even purchase require- ments for the latest tool available. Specialist personnel in the tool stores/preparation facility, have consider- able responsibility in servicing tooling for the overall manufacturing resources on these machine tools and as a result, will have amassed a large working-know- ledge of the production tooling requirements, so their opinions should be sought prior to any purchasing de- cisions on new tooling. .. Computerised-Tool Management – a Practical Case for ‘Stand-alone’ Machine Tools If one considers the tooling requirement for a stand- alone machining centre, then today the market de- 47 ‘Limit gauges’ , are based upon the stated International Stan- dards agreed for ‘Limits and Fits’ for component toleranc- ing. e use of limit gauges, is a form of ‘attribute sampling’* where no attempt is made to determine the size of the work- piece toleranced feature, but they are simply utilised to estab- lish whether the component’s critical dimension is within the specied limits of size, or not. In practice, a component that has hole that has simply been drilled and reamed, might require a double-ended plug gauge, with one ‘Go’ end of the plug gauge being of full form and checking the maximum material con- dition and as many dimensions as possible, with the ‘Not go’ end checking the minimum material condition and only one dimension – which as its name implies, this latter end should not go into the reamed hole. is limit gauging technique ful- ls ‘Taylor’s eory of Gauging’. *‘Attribute sampling’ techniques, are a means of sampling im- perfections that are not in the strictest sense, measurable quan- tities. For example, a mirror-surface that has been produced, might be scratch-free, or may have other blemish marks, these factors might be cause for its rejection. Hence, ‘attribute sam- pling’ can be considered as a two-way classication system for either acceptance, or rejection of the workpiece. mands for its manufactured products has become much more diversied, with the number and multiplic- ity of tools required having also increased. As has been shown previously in this chapter in the preparation for workpiece machining, conrmation that all the tool- ing – including spares (i.e. ‘Sister-tooling’ – see Foot- note 1 in this chapter), must be loaded into the tool magazine. A computerised-tool management system (Fig. 143a), eliminates the possibility of mistakenly se- lecting the wrong tool and exacerbating the situation of placing it in the incorrect tooling pocket in the tool magazine. With these ‘tagged tools’ (Fig. 143d) having non-contacting read/write embedded microchips in say, the pull-stud region of the assembled tool – allow- ing coolant-through-spindle applications. e follow- ing tooling data can be automatically registered into the CNC memory (Fig. 143b), such as tool: number and its ID number; name and the nominal diameter; length, plus its ‘working-diameter’; thrust and power coecients; interference data, with ‘large diameter’ tool data – if required; life accumulated/actual usage time, wear and breakage ags. Many quite complex and sophisticated computer- ised-tool management systems exist, but essentially the practical system depicted in Fig. 143, can be use- fully applied to a machining centre in an ecient pro- duction environment. Here, the system comprises of three modules, these are: • Tool module – this being the smallest component of the tool management system, where the tooling data is both read/written at the machine magazine tool loading/unloading position (Fig. 143c). e tool data is automatically registered in the CNC memory at the push of a button, with this tooling- related data being continuously updated – as ma- chining continues, • Tool Management module – once this is combined with the ‘tool module’ (above), then tool manage- ment is conducted on a much larger scale, allowing not only all of the previous tooling data to be moni- tored and controlled, but additional information on the: toolholder’s bill of materials, insert inventory, and its location, together with a graphic tooling display of its build-up and information regarding the correct procedure to ensure fast and error-free tool measurement on the presetting machine (Fig. 143a), • Tool transportation module – consists of a tool transporter robot having high positional accuracy (i.e. not shown), which automatically transports  Chapter  . radially and axially positioned, thereby en- suring that no edges ‘stand-proud’ of each other and at the same time conrming that no discernible ‘wobble’ in the rotating assembly occurs (i.e see the. circumstances, the stores will keep a record to show: to whom they were issued, the machine tool on which they will be used, the num- ber and identication of these tools, together with the date. considers the tooling requirement for a stand- alone machining centre, then today the market de- 47 ‘Limit gauges’ , are based upon the stated International Stan- dards agreed for ‘Limits and Fits’ for