Spotlight on cost-per-part in machining stator housings

When a machine tool manufacturer and a tool manufacturer known for boring and fine boring tools get together for a joint project, extraordinary results are guaranteed. NILES-SIMMONS and MAPAL have come together to develop a process that dramatically reduces the machining time of stator housings (or inner housing, cooling jacket, coolin sleeve, motor housing) for electric motors in the e‑mobility sector and also features innovative details.

Machi­ning the sta­tor housing includes inter­nal machi­ning with various sec­tions, machi­ning the smal­ler centre bore and machi­ning the out­side with its coo­ling ribs.

The tran­si­tion from con­ven­tio­nal com­bus­tion engi­nes to elec­tric dri­ves in the auto­mo­tive indus­try is beco­ming incre­asingly clear. NILES-SIMMONS is facing up to this change and tar­ge­ting machi­ning equip­ment for parts pro­duc­tion for the e‑mobility sec­tor with highly effi­ci­ent manu­fac­tu­ring pro­ces­ses – with the aim of seam­lessly fol­lo­wing on from the suc­cessful times of cranks­haft manufacture.

The majo­rity of machi­nes built by NILES-SIMMONS in Chem­nitz are used for the machi­ning of rota­tio­nally sym­me­tri­cal work­pie­ces. While tur­ning plays a key role here, MAPAL as a tool manu­fac­tu­rer focu­ses pri­ma­rily on cubic parts which are dril­led, rea­med and mil­led. In light of this, it’s little sur­prise that there had been few points of cont­act bet­ween the two com­pa­nies in the past. That chan­ged at the EMO 2019 trade show. At MAPAL’s stand, NILES-SIMMONS dis­co­vered an exhi­bit iden­ti­fied as a tur­ning work­piece: a sta­tor or motor housing for elec­tric motors. By then, MAPAL had estab­lished fine bor­ing tools for machi­ning parts on mil­ling cen­tres as a highly effi­ci­ent and ultra-pre­cise pro­cess in the industry.

A BENEFICIAL BLEND OF TURNING AND BORING OR FINE BORING

Soon, both sides had the impres­sion that a com­bi­na­tion of tur­ning, bor­ing and fine bor­ing could take machi­ning this key com­po­nent for e‑mobility to a new level. Fol­lo­wing the trade show, they set up a joint deve­lo­p­ment pro­ject. NILES-SIMMONS rebuilt a machine for the pro­ject and MAPAL sup­plied tools for pre‑, semi- and fine machining.

Pot-shaped parts like sta­tor housings are a fre­quently used design for elec­tric motors in the auto­mo­tive indus­try. The thin-wal­led alu­mi­nium housing fea­tures ribs on the out­side for the coo­ling cir­cuit and is instal­led in  the lar­ger motor housing. “Here, we have a rota­tio­nal work­piece  with a rear-side imba­lance that can be tur­ned, but, due to the high level of dia­me­ter accu­racy and the shape and posi­tion tole­rance requi­red by the mar­ket, must be bored and fine bored,” says MAPAL’s Area Sales Mana­ger André Ranke, describ­ing the start­ing point for the part­ner­ship. A cus­to­mer work­piece was not used for the tests car­ried out at NILES-SIMMONS with MAPAL tech­ni­ci­ans as part of the pro­ject. Ins­tead, MAPAL desi­gned a dummy that fea­tured all pro­duc­tion-ready requi­re­ments. The inner dia­me­ters vary bet­ween 220 mm and 231 mm, and the outer diameters
bet­ween 250 mm and 260 mm. Inner and outer fit tole­ran­ces in the IT6 range and cylind­ri­cal forms bet­ween 20 and 30 μm are requi­red. The con­cen­tri­city bet­ween the dif­fe­rent dia­me­ters is limi­ted in some cases to 0.05 mm.

Pro­ject­team (v.l.): Sales Mana­ger Tho­mas Lötzsch, Deve­lo­p­ment Engi­neer Tech­no­lo­gie Chris­tian Wink­ler, Pro­ject Mana­ger Daniel Pilz (all NILES-SIMMONS), Area Sales Mana­ger André Ranke, Tech­ni­cal Advi­sor Axel Schwarze und Appli­ca­tion Engi­neer Heiko Süß (all MAPAL). In the fore­ground, the MAPAL inter­nal machi­ning tools for (from left) pre-roug­hing, roug­hing, machi­ning the cen­ter bore and finis­hing, as well as the workpiece.

ALL OF THE TOOLS ARE ALREADY IN THE MACHINE

For the deve­lo­p­ment pro­ject, NILES-SIMMONS sel­ec­ted a DZS 315-type pick-up lathe from NSH sub­si­diary RASOMA, also based in Sax­ony. The machine has a modu­lar design and can the­r­e­fore be con­fi­gu­red pre­cis­ely to suit the rele­vant machi­ning pro­cess. The test set-up fea­tured a ver­ti­cal work­piece spindle at the top, a work­piece spindle under­neath, a tool con­sole and a tool revol­ver. Gene­rally spea­king, addi­tio­nal machining
units can be built into the machine, mea­ning all neces­sary tools can be housed in the machine, redu­cing set-up and non-pro­duc­tive time. The upper spindle picks up the work­piece and moves it to the sta­ti­ons one after ano­ther in a sin­gle clam­ping setup with the lathe slide.

There are advan­ta­ges to ver­ti­cal machi­ning. One of these is the space-saving inter­lin­ked setup of indi­vi­dual machi­ning units, opti­mum trans­port of chips and pro­ces­sing agents, and a com­pact design with a small instal­la­tion area, inclu­ding a pick-up system.

“The pick-up is a stan­dard solu­tion for tur­ning, as it is alre­ady widely used today for com­pa­ra­ble parts. This loa­ding solu­tion is per­fectly desi­gned for auto­ma­ted mass pro­duc­tion of sta­tor housings,” says Tho­mas Lötzsch, Sales Mana­ger at NILES-SIMMONS.

The key bene­fit of the newly deve­lo­ped pro­cess is the poten­tial boost in pro­duc­ti­vity. From the out­set, part pro­duc­tion time has alre­ady been cut by 50 per­cent in the com­bi­ned tur­ning and bor­ing pro­cess com­pared to the con­ven­tio­nal tur­ning pro­cess. Daniel Pilz, who mana­ged the pro­ject at NILES-SIMMONS, descri­bes how time is saved in each indi­vi­dual step, which, as the case may be, may involve the tur­ning of the work­piece, of the tool or of both.

left + cen­ter: The work­piece is clam­ped to the upper pindle and moved to the machi­ning sta­ti­ons one after ano­ther in one clam­ping setup.; right: The first step is roug­hing the inside of the housing.

NEW WAYS TO USE TRIED-AND-TESTED TOOLS

The first sta­tion turns the pro­cess pre­viously used by MAPAL on its head. Ins­tead of roug­hing the part with a rota­ting tool, the tool sits still in the machine, and it’s the work­piece coming from above that turns. As MAPAL’s tool is equip­ped with four blades, unlike a con­ven­tio­nal tur­ning tool, only around a quar­ter of the time is nee­ded to com­ple­tely pre-rough the various inner dia­me­ters on the part.

In the second machi­ning step, a bell-shaped tool deve­lo­ped by NILES-SIMMONS is used for the outer con­tour, while a MAPAL ISO bor­ing tool is used for semi-finis­hing the inner dia­me­ter. The inside and out­side of the work­piece are machi­ned at the same time. “What’s spe­cial is that a sta­tio­nary, ver­ti­cal exter­nal machi­ning tool is pla­ced to the spindle housing. The spindle dri­ves the inter­nal machi­ning tool,” says Daniel Pilz, describ­ing the setup. The work­piece dips into the annu­lar gap for­med by these two tools. All dia­me­ters are pro­du­ced with one sin­gle feed move­ment – for this spe­ci­fic part, this amounts to three inner and three outer dia­me­ters. Four blades are used for each dia­me­ter. “As well as being able to machine the inside and out­side simul­ta­neously, altog­e­ther we take just an eighth of the time we would need for con­ven­tio­nal tur­ning,” says Pilz. Other bene­fits include the following:

• Due to the coun­ter­ac­ting cut­ting forces of the inter­nal and exter­nal machi­ning, a lower tor­que must be main­tai­ned on the work­piece clam­ping device

• Vibra­ti­ons in the thin-wal­led part during machi­ning are absor­bed by the simul­ta­neous cut­ting action of the inserts on the inside and outside.

In this test, simul­ta­neous inter­nal and exter­nal machi­ning took place with a cut­ting speed of 700 m/min. Machi­ning using the sand­wich method with the work­piece in the middle ensu­res that the part is sta­bi­li­sed during machi­ning, as the inserts are cut­ting on both sides at the same time and thus gui­ding the part. Com­plex clam­ping tech­no­logy with vibra­tion dam­pe­ning is not requi­red, which has a noti­ceable impact on costs. While indus­try alre­ady uses MAPAL’s tool on hori­zon­tal machi­ning cen­tres for the inter­nal machi­ning of sta­tor housings, the bell-shaped exter­nal tool from NILES-SIMMONS was newly deve­lo­ped and a patent was filed for the inno­va­tive process.

The sub­se­quent fine machi­ning pro­cess uses an alre­ady tried-and-tes­ted MAPAL fine bor­ing tool with guide pads, which is ulti­m­ately used to fully finish the centre bore for the sta­tor bea­ring, inclu­ding all stages. MAPAL pro­du­ces the fine bor­ing tool used in various designs. A wel­ded design with blades and guide pads made from PCD was used for the tests in Chem­nitz. The dia­me­ter can be adjus­ted in the μm range.

left: The semi-finis­hing tool for inner machi­ning is clam­ped in the lower spindle. It is sur­roun­ded by the bell-shaped outer tool, which is secu­rely moun­ted; center: In simul­ta­neous machi­ning, the work­piece is moved into the annu­lar gap bet­ween the outer tool and the inner tool from above. Ple­nty of coo­ling lubri­cant is used for machi­ning.; right: Fine machi­ning of all inner dia­me­ters is done with a fine bor­ing tool.

STATOR HOUSING ARE THE NEW CRANKSHAFTS

NILES-SIMMONS expects the manu­fac­tu­ring of sta­tor housings or coo­ling jackets to become as important to elec­tric mobi­lity as cranks­hafts were to com­bus­tion engi­nes in the past. The expec­ted quan­ti­ties, cycle times and costs are in a com­pa­ra­ble range. “Enqui­ries for these parts amount to 250,000 parts per year,” says COO Klaus Krä­her. By 2030, there may be demand for as many as 20 to 50 mil­lion parts world­wide. “A 50 per­cent time saving is a
huge state­ment, espe­ci­ally as there is defi­ni­tely more poten­tial in our new pro­cess,” says Kräher.

In addi­tion to the suc­cessfully imple­men­ted ver­ti­cal con­cept, NILES-SIMMONS is also inves­ti­ga­ting the pos­si­bi­lity of refit­ting exis­ting hori­zon­tal machi­nes. The Chem­nitz-based com­pany has over 300 turn-broa­ching and cranks­haft mil­ling machi­nes curr­ently in use in car manu­fac­tu­r­ers’ cranks­haft pro­duc­tion lines world­wide. Both the inno­va­tive pro­cess and MAPAL’s tools can also be inte­gra­ted into a hori­zon­tal ver­sion of the concept.
MAPAL also offers the pos­si­bi­lity of using addi­tively-manu­fac­tu­red tools in which weight savings are not the sole focus and coo­lant out­lets can be geared even more spe­ci­fi­cally towards the cut­ting edge.

Apart from the machi­ning of sta­tor housings, the pro­cess can also be used for other work­pie­ces from a wide range of sec­tors, such as coo­ling ele­ments for hybrid engi­nes, pipe and flange cou­plings for the oil and gas indus­try, bea­ring and housing com­pon­ents for gene­ral machi­ning, and work­pie­ces for the pla­s­tics indus­try. This makes this pro­cess rele­vant for a very wide range of dif­fe­rent work­pie­ces with tube- and pot-shaped
geo­me­try requi­ring tole­ran­ces less than or equal to IT6 and with ultra-pre­cise shape and posi­tion tolerance.