Exercise 4 Lecture in the Subject Manufacturing Technology I. Machinability and Machinability Testing Part B

Transkript

1 Lehrstuhl für Technologe der Fertgungsverfahren Laboratorum für Werkzeugmaschnen und Betrebslehre Exercse 4 Lecture n the Subject Manufacturng Technology I Machnablty and Machnablty Testng Part B!" #$%&' ()*+ *,-.*

2 Table of contents Table of contents 1. Introducton Force as evaluaton parameter Chp form as evaluaton parameter...11 Manufacturng Technology I - exerecse 4 2

3 Introducton 1. Introducton In ths exercse Machnablty and Machnablty Testng (Part B), the terms used to evaluate machnng propertes, force and chp form are explaned n detal. The other varables, tool-lfe and surface qualty were dealt wth n exercse 3. Manufacturng Technology I - exerecse 4 3

4 2. Force as evaluaton parameter In cuttng mechancs research has found that the force can be a good crteron for evaluatng the mechancal load of the cuttng part. The total force represents all mechancal loads concentrated at the selected pont of the cuttng edge. Research shows a dependency between the total force and the cross-sectonal area of the pass. The cross-sectonal area can be calculated wth the parameter undeformed wdth of cut and undeformed thckness of cut. In fgure 2.1 the terms are presented by the example of longtudnal cylndrcal turnng. rotary movement (workpece) snκ r = a p b κ r tool cuttng edge angle a p depth of cut f feed b undeformed wdth of cut h undeformed thckness of cut A cross-sectonal area of the pass b a p f feed movement (tool) snκ r = h f h fgure 2.1: Cross-sectonal area at longtudnal cylndrcal turnng In cuttng mechancs the term specfc force s often used. In general t stands for the reference of the force to the cross-sectonal area of the pass. n general: k F F = = wth: = c,f and p A b h The specfc force was scaled to the cross-sectonal area of 1 mm². k 1.1 = F 1mm 1mm wth: = c, f and p Manufacturng Technology I - exerecse 4 4

5 The frst explorer who has developed a method of calculaton by a potental functon n 1925 for perpheral mllng was SALOMON. Some years later KIENZLE has advanced ths method n 1952 for longtudnal cylndrcal turnng. Usng ths emprcal method, the specfc force components of the total force must be chart n a double logarthmc dagram lke fgure 2.2: kc / (N/mm²) 3270 c = -15,32 m c = -0, h / µm fgure 2.2: specfc force components The ndex stands for the components of the total force, c for cuttng force, f for feed force and p for back force. For analyss of the results, a lnear equaton s used n the double logarthmc dagram. Then the abscssa and ordnate sectons can be calculate by consderaton of the logarthmc scale: y m x + b logk = m logh + logk wth: = c, f and p = 1. 1 after applyng the logarthmc laws the result comes to: k = k. 1 m h 1 wth: = c, f and p Also the functon of approxmaton s a potental functon! The values of the specfc force components for a monc cross-sectonal area and of the slope of the lne can be meter-read drect form the dagram. Manufacturng Technology I - exerecse 4 5

6 the slope s: tan log A log B y y α = m = tan180 or log Bx log Ax m = log A y log B x log B y log A x After adoptng and changng of the values, the total force components comes to: F 1 m = k1. 1 b h wth: = c, f and p Ths equaton s advanced by the CHEMNITZER SCHULE wth a multple term to account for other boundary condtons to correct the equaton: 1 m 1. 1 b h C process wth: = c, f and p F = k Π The multple term s composed of correcton values lke those: Π C K process = γ o K v c K wear K SS K KSS K process correcton under consderaton of the tool orthogonal rake correcton under consderaton of the cuttng velocty correcton under consderaton of the tool wear correcton under consderaton of the cuttng materal correcton under consderaton of the coolng flud correcton under consderaton of the manufacturng process So t s clear that only a few parameters of acton can be consdered by emprcal equatons. Manufacturng Technology I - exerecse 4 6

7 a) Please wrte down and draw n the components of the total force you are knowng! fgure 2.4: components of the total force De Aktvkraft st de geometrsche Addton der Zerspankraftkomponenten Schnttkraft und Vorschubkraft. De Namensgebung kommt aus der Lestungsberechnung, da nur dese Kraftkomponente aktv be der Lestungsberechnung berückschtgt werden muss. De Passvkraft kann dazu unberückschtgt bleben, da se kene Bewegung als Ursache hat! b) What parameters nfluence the total force? Schnttbedngungen (v c, f, a p ) Schnedtelgeometre (β o,, ε r,, r ε ) Verfahrensknematk (α o, γ o,, κ r,, s ) Schnedstoff Werkstoff Manufacturng Technology I - exerecse 4 7

8 c) Why s t essental to have knowledge of the total force durng the cuttng process? Auslegung von Maschnenantreben Auslegung von Zerspanprozessen (Arbetsvorberetung) Vermedung unzulässger Verformungen an Werkstück, Werkzeug und Maschnen (Maßabwechungen am Werkstück) Vermedung des Regeneratveffektes Ermttlung und Erklärung der Belastungen des Schnedtels d) Please draw n the qualtatve trends of the total force components, cuttng force F c, feed force F f and back force F p, n dependency of the feed f, the cuttng velocty v c, the depth of cut a p and the tool orthogonal rake κ r. force force force force F F F F f v c feed velocty tool cuttng edge angle depth of cut κ r a p fgure 2.5: qualtatve trends of the total force components e) The cuttng force can be calculated approxmately by an emprcal equaton. Please wrte down ths equaton! f) For what stand the parameters k c1.1 and m c? De spezfsche Schnttkraft k c1.1 gbt de Schnttkraft an, de zum Abspanen enes Spans mt der Spanungsbrete b = 1 mm und der Spanungsdcke h = 1 mm erforderlch st. Der Exponent (1-m c ) gbt de Stegung der Geraden F c = f(h) m doppeltlogarthmschen System an. Man kann auch sagen: -m c des Exponenten gbt de Stegung Manufacturng Technology I - exerecse 4 8

9 der Geraden der spezfschen Schnttkraft k c = f(h) m doppeltlogarthmschen System an. For determnaton the monc specfc cuttng force k c1.1 and the slope m c of the lne n the double logarthmc dagram of the cast ron materal GJS-500 cuttng test was conducted wth the followng parameter: table 2.1: test condtons cuttng materal a p / mm v c / (m/mn) o / Grad o / Grad r / Grad s / Grad WC-K g) Please determne the monc specfc cuttng force k c1.1 and the slope of the lne m c of the machned materal GJS-500. Complete the table 2.2 and use the double logarthmc dagram n fgure 2.2. table 2.2: test results f / mm F c / N b / mm h / µm F c / (N/mm) 0,13 466,4 0, , , Manufacturng Technology I - exerecse 4 9

10 10000 kc / (N/mm²) h / µm fgure 2.6: specfc cuttng force n the double logarthmc dagram Manufacturng Technology I - exerecse 4 10

11 chp shape as evaluaton parameter 3. Chp form as evaluaton parameter a) What chp forms are evaluated as unfavourable for the automatsed producton? Please wrte down three forms and cause your answer! Bandspäne: Wrrspäne: Flachwendelspäne: Schäden an Maschne und Bedener Schäden an Maschne und Bedener Schäden am Werkzeughalter b) Please wrte down possbltes of dfferent knematcs whch avod bad chp forms! - Vorschub erhöhen (Erhöhung der Spanungsdcke) - Schnttgeschwndgket senken (Temperatursenkung n der Scherzone) - Werkzeug-Orthogonalspanwnkel verrngern (Vergrößern der Spankrümmung) - Ensatz von Werkzeugen mt Spanletstufen (Vergrößern der Spankrümmung) c) For evaluaton of the machnablty of a materal n respect of the chp formaton the term Z s s used. Please cause when the evaluaton of the term Z s s well? Z s st dann als gut anzusehen, wenn de Klebnegung des Werkstoffes gerng st, wenn sch kene Band- und Wrrspäne blden und wenn gratfree und glatte Werkstückoberflächen erzeugt werden. Manufacturng Technology I - exerecse 4 11