Fully automated complete machining of turbine and special shafts – NILES-SIMMONS develops the new »CENTER AXIS ALIGNMENT« process

Dr.-Ing. Moritz Halle, Dipl.-Ing. Tho­mas Wächt­ler, NILES-SIMMONS Indus­trie­an­la­gen GmbH 

 

The field of application

In highly tech­ni­cal, inno­va­tive, and sen­si­tive indus­trial sec­tors such as the aero­space indus­try or the defense and energy sec­tors, the demands on the pro­duc­tion of com­plex com­pon­ents and the machi­ning of high-strength mate­ri­als are con­stantly incre­asing. In par­ti­cu­lar, the reduc­tion of error within pro­duc­tion pro­ces­ses for highly com­plex and cost-inten­sive work­pie­ces is beco­ming more important with regard to the »cost-per-part« and the accu­ra­cies to be achieved.

To meet these requi­re­ments, NILES-SIMMONS has deve­lo­ped the new fully auto­ma­ted and paten­ted machi­ning and mea­su­ring pro­cess of »CENTER AXS ALIGNMENT« spe­ci­fi­cally for the machi­ning of tur­bine shafts. This pro­cess enables the com­plete machi­ning of com­pli­ca­ted, deep-hole dril­led shaft-shaped work­pie­ces inclu­ding all in-pro­cess mea­su­re­ments wit­hout manual ope­ra­tor intervention.

 

Image 1 – Com­plete Machi­ning of Tur­bine Shafts wit­hout Ope­ra­tor Intervention

 

The aim of the machi­ning pro­cess is to adapt the outer con­tour of the work­piece exactly to the inner con­tour in order to achieve a uni­form wall thic­k­ness of the work­piece along its axis. The pro­cess is appli­ca­ble to all elec­tri­cally con­duc­tive mate­ri­als such as simple steels, but also for super alloys or nickel-based alloys such as Inco­nel 718. In addi­tion to the machi­ning of tur­bine shafts, it also applies to other deep-hole dril­led work­pie­ces up to two meters in length.

 

The machine configuration

The new pro­cess is exe­cu­ted on a NILES-SIMMONS N30MC machi­ning cen­ter with a cen­ter distance of 4500 mm and a swing dia­me­ter of 780 mm; the machine has been pur­po­sely con­fi­gu­red for this machi­ning ope­ra­tion. The spe­ci­fic equip­ment of the machine includes a main spindle, a tur­ning-mil­ling unit, a lowerable tail­stock, two ste­ady rest slides with one ste­ady rest and one dam­ping unit, and a bor­ing bar slide.

 

Image 2 – Pro­cess »CENTER AXIS ALIGNMENT« on a NILES-SIMMONS Machi­ning Cen­ter N30MC

 

Fur­ther­more, inde­pen­dent tool maga­zi­nes are available for both the bor­ing bar slide and the tur­ning-mil­ling unit. The maga­zine for the multi-axis tur­ning-mil­ling unit, pla­ced on the main spindle side, can be equip­ped with up to 144 tools. For the bor­ing bar slide, up to 16 posi­ti­ons are available in an addi­tio­nal bor­ing bar maga­zine on the tail­stock side. Sys­tem bor­ing bars up to two meters long, dri­ven bor­ing bars, sta­tic bor­ing bars, sta­tic bor­ing bars with con­troll­able cut­ting edge, mea­su­ring lan­ces, or a car­tridge with drive and chuck func­tion can be used.

With this con­fi­gu­ra­tion, and par­ti­cu­larly by using the lowerable tail­stock, all types of tur­bine shafts curr­ently available on the mar­ket can be machi­ned in dif­fe­rent lengths on one machine. Even par­ti­cu­larly long com­pon­ents can be easily machi­ned, espe­ci­ally due to this option, wit­hout having to choose a machine with a lar­ger footprint.

Fur­ther­more, all cut­ting tech­no­lo­gies such as tur­ning, mil­ling, dril­ling, gear hob­bing, tap­ping, thread mil­ling, thread tur­ning, rea­ming, spind­les, inter­nal machi­ning with indexa­ble inserts, power ski­ving, 5‑axis mil­ling, and deep-hole dril­ling up to 2000 mm depth can be map­ped in a pro­cess-relia­ble man­ner. In addi­tion, the machine inte­gra­tes the auto­ma­ted touch probe and opti­cal mea­su­re­ment of tools as well as the auto­ma­tic touch pro­bing of the work­piece. With that, it is pos­si­ble to achieve accu­ra­cies less than 5µm for the tur­ning and mil­ling pro­ces­ses. Due to the inte­gra­tion of all neces­sary tech­no­lo­gies in one machine, the auto­ma­ted too­ling, and the use of com­plex mea­su­ring tech­no­lo­gies, an unat­ten­ded com­plete machi­ning pro­cess is applied in a pro­cess-relia­ble manner.

 

Image 3 – Inter­nal Machi­ning with Sys­tem Bor­ing Bar with adjus­ta­ble Cut­ting Edge

 

To achieve increased tem­pe­ra­ture sta­bi­lity and to ensure the accu­racy requi­red by the cus­to­mer despite tem­pe­ra­ture fluc­tua­tions, we use a liquid-coo­led spe­cial con­crete machine bed. In addi­tion, the machi­ning cen­ters have dam­pe­ning and vibra­tion-redu­cing com­pon­ents such as FE-opti­mi­zed slide geo­me­tries, hydrau­li­cally clam­ped com­pon­ents of the work­piece sup­port com­pon­ents such as tail­stock and ste­ady rest slide, dam­pe­ning sur­faces in machi­ning direc­tion, and rol­ler gui­des of the machi­ning axes in size 45/55.

To ensure clear and simple ope­ra­tion of the machine, we use a Sie­mens OP19 with an addi­tio­nal touch screen for pro­cess monitoring.

 

The paten­ted mea­su­ring process

The key ele­ment of this inno­va­tive pro­cess is the new mea­su­ring pro­cess for deter­mi­ning the opti­mal shaft cen­ter axis. This pro­cess was deve­lo­ped and paten­ted by NILES-SIMMONS and is based on the appli­ca­tion of the eddy cur­rent mea­su­ring prin­ci­ple which mea­su­res the distance bet­ween the eddy cur­rent sen­sor and the workpiece.

Image 4 – Eddy Cur­rent Sen­sor for Deter­mi­ning the Opti­mal Work­piece Cen­ter Axis

 

This prin­ci­ple belongs to the non-cont­act induc­tive mea­su­ring prin­ci­ples, which can also mea­sure through non-con­duc­tive mate­ri­als wit­hout having any influence on the mea­su­ring result. The method is the­r­e­fore ide­ally sui­ted for use in harsh indus­trial envi­ron­ments. Dust, dirt, and oil do not influence the mea­su­re­ment. Tem­pe­ra­ture fluc­tua­tions are off­set by an effi­ci­ent tem­pe­ra­ture compensation.

Due to the fully auto­ma­ted mea­su­re­ment value recor­ding, the pro­cess can be car­ried out wit­hout any ope­ra­tor – from the first clam­ping of the work­piece until it is clam­ped in its new center.

A spe­cial eddy cur­rent sen­sor inclu­ding eva­lua­tion unit from µEp­si­lon is used here, which has been cali­bra­ted to the work­piece-spe­ci­fic pro­per­ties. This sen­sor covers a mea­su­ring range of up to 9 mm with a reso­lu­tion of less than one micrometer.

The applied sen­sor is moun­ted at the tip of a 2000 mm long car­bon lance, which is inte­gra­ted in an exch­an­geable modu­lar mea­su­ring cas­sette. Thus, the sen­sor is posi­tio­ned and moved via the machine axes of the bor­ing bar unit in the working area of the machine within the deep hole dril­led work­piece. Once the sen­sor is posi­tio­ned, the distances bet­ween the sen­sor and the work­piece can be mea­su­red with pre­cis­ion at any angle by rota­ting the workpiece.

 

Image 5 – Car­bon Mea­su­ring Lance in the »CENTER AXIS ALIGNMENT« Process

 

The cen­ter point of the con­side­red dia­me­ter is cal­cu­la­ted from these mea­su­red data. Along the lon­gi­tu­di­nal axis of the work­piece, any num­ber of cen­ter points can be deter­mi­ned with this method, which repre­sent the cur­rent course of the bore. Kno­wing the course of the bore, the ideal new course of the cen­ter axis is cal­cu­la­ted from the cal­cu­la­ted cen­ter points. This cen­ter axis then forms the basis for machi­ning the new clam­ping seats of the work­piece to accom­mo­date it in the new clam­ping operation.

This auto­ma­ted pro­cess mini­mi­zes the devia­tion of the outer con­tour line from the inner con­tour line, thus ensu­ring a uni­form wall thic­k­ness of the shaft along its axis.

 

The Value 

The main advan­tage of »CENTER AXIS ALIGNMENT« is the fully auto­ma­ted mea­su­re­ment, ali­gnment, and machi­ning of deep-hole dril­led work­pie­ces wit­hout ope­ra­tor intervention.

All steps neces­sary for the pro­cess run fully auto­ma­ti­cally within pro­grammed pro­cess limits. Faulty manual ope­ra­ti­ons or error-prone manual mea­su­ring pro­ces­ses, which were neces­sary in con­ven­tio­nal pro­ces­ses, are eli­mi­na­ted. This makes it pos­si­ble to reduce the pro­duc­tion of scrap parts to a mini­mum and to improve the qua­lity of the work­pie­ces signi­fi­cantly. Unsui­ta­ble raw parts are iden­ti­fied and rejec­ted at the begin­ning of the process.

The inte­gra­tion of all tech­no­lo­gies and mea­su­ring pro­ces­ses in one machine allows cycle times to be shor­tened and logi­stics and hand­ling pro­ces­ses to be reduced.

The mea­su­ring method is immune to envi­ron­men­tal influen­ces such as tem­pe­ra­ture fluc­tua­tions or for­eign sub­s­tances and can be used fle­xi­bly for a wide range of mate­ri­als. Due to the modu­lar design of the NILES machi­nes, dif­fe­rent types of work­pie­ces can be pro­ces­sed and in-pro­cess mea­su­re­ments taken on the same machine. This crea­tes maxi­mum fle­xi­bi­lity for the customer.

The pro­cess has alre­ady been suc­cessfully inte­gra­ted into tur­bine shaft pro­duc­tion on the market.

 

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