五噸單頭液壓放料機(jī)設(shè)計(jì)圖紙+論文+報(bào)告
五噸單頭液壓放料機(jī)設(shè)計(jì)圖紙+論文+報(bào)告,五噸單頭,液壓,放料機(jī),設(shè)計(jì),圖紙,論文,報(bào)告,講演,呈文
河南理大學(xué)本科畢業(yè)設(shè)計(jì)（論文）
磨削過(guò)程中應(yīng)力殘留
摘要：本論文闡述了對(duì)表面磨削殘留應(yīng)力的調(diào)查研究結(jié)果。功率密度加上磨輪/工件接觸時(shí)間形成系數(shù)因子B。論文描述了用于估測(cè)不同的加工材料，進(jìn)行本實(shí)驗(yàn)。實(shí)驗(yàn)估測(cè)出了加工參數(shù)對(duì)系數(shù)因子B及系數(shù)因子B與最大殘留應(yīng)力間關(guān)聯(lián)的影響。這種用于預(yù)測(cè)表面磨削殘留應(yīng)力的系數(shù)因子的可用性得到了證實(shí)。
關(guān)鍵詞：殘留應(yīng)力；磨削；磨輪/工件
1.序言
磨削適用于加工硬質(zhì)材料的最常用的方法之一，它常常是工藝流程中最后操作步驟之一。因此，磨削過(guò)程中的表層特性直接創(chuàng)建形成了工件的功能特性。如疲勞強(qiáng)度，磨蝕及腐蝕抗性等。
在磨削過(guò)程中，尤其是當(dāng)使用氧化鋁磨輪時(shí)，由于兩個(gè)相反的趨向，要形成理想的表面平整度是相當(dāng)困難的。一方面，為提高生產(chǎn)效率，需引入高加工參數(shù)，然而，這些參數(shù)往往會(huì)引起加工工件表面的磨削功率的提高。另一方面，磨削功率的提高使磨削溫度提高，可能造成（磨削）表層嚴(yán)重?fù)p壞。
由于在其他常規(guī)方法中缺少相對(duì)簡(jiǎn)單統(tǒng)一的措施，要在高生產(chǎn)效率和優(yōu)良的表層特性間找到平衡點(diǎn)是極其困難的。正是由于磨削步驟地重要性，許多研究中心已對(duì)這一過(guò)程進(jìn)行調(diào)查研究，一些常用的方法已被闡明。
方法之一：分析法[4，5]，依據(jù)數(shù)學(xué)方法，對(duì)表面形成過(guò)程中涉及的物理過(guò)程進(jìn)行描述。在磨削過(guò)程中熱效應(yīng)因子常常被描述。在對(duì)工件溫度分布的計(jì)算基礎(chǔ)上，對(duì)表層的微硬度、殘留應(yīng)力、微結(jié)構(gòu)等這些變化進(jìn)行估測(cè)。這種方法前景廣闊——但就目前而言，由于復(fù)雜的計(jì)算，以及對(duì)在極端磨削條件下材料反應(yīng)的有限認(rèn)知水平——僅限于理論上的調(diào)查研究。
實(shí)驗(yàn)法[1，7]以找磨削條件與表層參數(shù)間關(guān)聯(lián)為目標(biāo)。這是一種相對(duì)簡(jiǎn)單的方法，但存在一些缺陷。它通常是以時(shí)間—資本—消耗為過(guò)程，其應(yīng)用受到限制。而且，在不同的磨削方法與磨削條件下，推算實(shí)驗(yàn)結(jié)果可能受到限制。
針對(duì)表層形成控制問(wèn)題，還有第三種方法，將那些與表層特性關(guān)聯(lián)密切的磨削系數(shù)列入研究范疇[2，4]。這類(lèi)系數(shù)因子廣泛存在，其中最常見(jiàn)的有：相同碎片厚度（heq）和功率密度（p）。前者在磨削陶瓷制品時(shí)使用，后者常常應(yīng)用于當(dāng)使用氧化鋁磨輪時(shí)磨削的研究過(guò)程。
這兩種因子的主要缺陷是：測(cè)算時(shí)，必須對(duì)磨削有效深度或磨輪/工件有效接觸長(zhǎng)度進(jìn)行估算。而在實(shí)際的磨削過(guò)程中，這兩個(gè)量值又很難估算準(zhǔn)確。因此，仍然缺乏與表面平整參數(shù)密切相關(guān)且容易估算的磨削系數(shù)因子。就系數(shù)因子（功率密度與磨輪/工件接觸時(shí)間）與表面磨削殘留應(yīng)力之間的關(guān)聯(lián)，調(diào)查研究闡述如下：
2.磨削系數(shù)（功率密度與接觸時(shí)間）
實(shí)驗(yàn)證明，磨削后表層殘留應(yīng)力與最高磨削溫度密切相關(guān)。對(duì)磨削溫度計(jì)算方程式的分析表明，不僅是功率密度才影響磨削溫度，還有另外一個(gè)重要因子，即磨輪/工件接觸時(shí)間。在表面磨削過(guò)程中，具體工件與熱源（磨輪）間的接觸時(shí)間可通過(guò)以下方程式計(jì)算：
tc=le/vw ①
其中l(wèi)e——磨輪/工件有效接觸長(zhǎng)度；vw——工作速度
假設(shè)的磨削系數(shù)B由功率密度P和接觸時(shí)間tc構(gòu)成：
②
其中，p為磨削總功率；bd磨削寬度。
該系數(shù)因子的最大優(yōu)勢(shì)即是，在實(shí)際磨削過(guò)程中，方程式中所有的量（磨削功率，磨削寬度及工作速度）能夠很簡(jiǎn)單地被測(cè)算。
3.實(shí)驗(yàn)設(shè)置
本實(shí)驗(yàn)在以下磨削條件的基礎(chǔ)上進(jìn)行。
*加工材料（工件）：炭化鋼0.45%C,28HRC（標(biāo)注S）；合金鋼40H(0.38%C,0.9%Cr,0.28%N),48HRC;軸承鋼LH15(相當(dāng)于100 Crσ)62HRC(L)。
*磨輪：38A60J8V(J),99A80M7V(M)
*磨輪速度：26m/s(恒定)
*磨削深度：0.005—0.06mm
*工作速度：0.08—0.5m/s
*磨削液體：乳化劑或無(wú)
研究表明，主磨輪的驅(qū)動(dòng)功率，車(chē)床的速度調(diào)節(jié)范圍，及可能出現(xiàn)的，在表層形成的不可能接受的變化(如微裂痕，磨痕等)都限制這些磨削參數(shù)。
要估算系數(shù)因子B，必須測(cè)得磨削功率，工作速度及磨削寬度。測(cè)量磨削功率有兩種方法：通過(guò)測(cè)量磨輪主驅(qū)動(dòng)耗損（實(shí)際）（pm）,并同時(shí)測(cè)量相關(guān)的磨削力F1和磨輪速度V。由此，磨削功率可通過(guò)方程式來(lái)計(jì)算。由兩種方法獲得的實(shí)際結(jié)果對(duì)照如表1所示。從圖表中不難看出其中的關(guān)聯(lián)，表明了當(dāng)只有磨輪被主驅(qū)動(dòng)器驅(qū)動(dòng)時(shí)，只要測(cè)量磨輪主驅(qū)動(dòng)耗損功率即可準(zhǔn)確估算系數(shù)因子B。磨輪速度通過(guò)移位變極器測(cè)量，磨削寬度即場(chǎng)地樣品寬度。
4. 實(shí)驗(yàn)結(jié)果
通過(guò)測(cè)量表面磨削過(guò)程中p, vw和bd的值，在每次磨削試驗(yàn)中均可計(jì)算出系數(shù)因子B。在磨削過(guò)程中所測(cè)得測(cè)量值能夠便于估測(cè)磨削條件對(duì)系數(shù)因子B的影響（表2-7）。從表2，4。6中可看出有效磨削深度與B之間的線(xiàn)性依賴(lài)關(guān)系。這些直線(xiàn)的傾斜度主要由磨輪，工作速度(表2，6)，及磨削液體（表4）決定。以數(shù)字統(tǒng)計(jì)的形式近似的正確性——在所有情形下值都高于0.9。
工作速度對(duì)B的影響（表3，5，7）不像磨削深度的影響那樣始終不變。在一個(gè)低范圍工作速度，vw對(duì)B的影響很大，表明通過(guò)改變工作速度來(lái)影響系數(shù)因子B可能受到限制。對(duì)于調(diào)查研究的第三種加工材料——合金鋼(H),實(shí)驗(yàn)得到類(lèi)似的關(guān)系結(jié)果。
實(shí)驗(yàn)中，若不存在微裂痕和磨痕，殘留應(yīng)力分布的測(cè)量可通過(guò)熟知的材料移除法進(jìn)行。從每次磨削試驗(yàn)所得的殘留應(yīng)力——表面深度圖表中，可確定表層的最大殘留應(yīng)力。通常，在接近表面10—20um深度時(shí)，殘留應(yīng)力達(dá)到最大值（可伸縮量）.
對(duì)所研究的加工材料，系數(shù)因于B與最大殘留應(yīng)力間的關(guān)系如表8-10所示。在這些圖表中，不考慮其他磨削條件（磨輪特性，磨削液體，磨削參數(shù)），總結(jié)得出了各種加工材料的實(shí)驗(yàn)結(jié)果。在每種條件，以數(shù)字統(tǒng)計(jì)的形式稱(chēng)呈現(xiàn)各自的線(xiàn)性依賴(lài)關(guān)系（R0.8529-0.9074)。
這些數(shù)據(jù)表明，對(duì)于所給定的加工材料，殘留應(yīng)力-系數(shù)因于B曲線(xiàn)傾斜度呈現(xiàn)特征性，不受其他磨削條件的影響。軸承鋼（L）傾斜度最大表（10）。合金鋼（H）傾斜度最小表（9）。
挑查研究中的其他一些結(jié)果表明，應(yīng)用系數(shù)因于B預(yù)測(cè)或控制表層的微裂痕、磨痕或微結(jié)構(gòu)等變化化為可能。該系數(shù)因于在其他磨削方法中的可用性有待證實(shí) 。
5.結(jié)論
⑴磨削系數(shù)B(功率密度與磨輪/工件接觸時(shí)間)被用于預(yù)測(cè)表面磨削過(guò)程中的殘留應(yīng)力。
⑵實(shí)驗(yàn)發(fā)現(xiàn)系數(shù)因于B與最大殘留應(yīng)力間的線(xiàn)性相關(guān)，并經(jīng)多種加工材料證實(shí)。
⑶系數(shù)因于B與最大殘留應(yīng)力間的關(guān)聯(lián)似乎不受磨削條件的影響。
⑷系數(shù)因于B隨著磨削深度的加深而現(xiàn)行遞增，隨工作速度的提升而遞減，表明在較高工作速度范圍內(nèi)B反映不強(qiáng)烈。
⑸即使是在實(shí)際的工業(yè)應(yīng)用中，系數(shù)因于B也不難計(jì)算。
（6）系數(shù)因于B可能用于磨削過(guò)程中諸如微裂痕、磨痕、微結(jié)構(gòu)等表層特性的預(yù)測(cè)。
參考文獻(xiàn)：
附科技文原文
Abstract
Results of investigations on residual stress in surface grinding are presented in the paper. A coef?cient ``B'' combining power density and
wheel/workpiece contact time was developed. Experimental set-up and software to estimate the coef?cient during grinding are described in
the paper. Experiments were carried out for surface plunge grinding for several workmaterials in a wide range of grinding conditions. The
inˉuence of process parameters on the coef?cient B as well as the relation between B and maximum residual stress were experimentally
evaluated. The usefulness of the coef?cient to predict residual stress in surface grinding was proved. # 2001 Elsevier Science B.V. All
rights reserved.
Keywords: Residual stress; Grinding; Wheel/workpiece
1. Introduction
Grinding is one of the most popular methods of machining
hard materials. Because it is usually one of the ?nal operations
of the technological process, properties of surface layer
created in grinding inˉuence directly the functional properties
of the workpiece such as fatigue strength, abrasive and
corrosion resistance, etc.
Creating favourable surface integrity, especially in grinding
with aluminium oxide grinding wheels is dif?cult due to
two opposite tendencies. On one hand, high process parameters
are preferred in order to increase productivity.
Unfortunately, such parameters usually lead to the increase
of grinding power engaged in creation of the new surface of
the workpiece. On the other hand, the increase of grinding
power makes grinding temperatures grow, which may cause
a serious damage to the surface layer created in grinding.
Finding a compromise between high productivity and
advantageous surface layer properties is extremely dif?cult
due to the lack of relatively simple and universal routines,
among others. Because of the importance of grinding operation
the investigations of this process are performed in many
research centres. Some general approaches are observed in
these investigations.
The ?rst one, strictly analytical [4,5], is based on the
mathematical description of physical processes involved in
surface layer creation. In grinding thermal effects are usually
described. On the basis of the calculations of temperature
distribution in the workpiece, such changes in surface layer
like microhardness, residual stresses, microstructure, etc. are
estimated [5]. Such an approach is very promising but at the
present stage it is limited to theoretical investigations
because of complex calculations and still limited knowledge
about material behaviour in extreme grinding conditions.
The experimental approach [1,7] aims at ?nding a correlation
between grinding conditions and surface layer parameters.
This is a relatively simple method with some
disadvantages. Experimental works are usually time- and
capital-consuming which limits their application. Moreover,
there is a limited possibility to extrapolate the experimental
results on different grinding methods and grinding
conditions.
There is also a third approach to the problem of control of
surface layer creation, which involves a search for such
grinding coef?cients, which are strongly correlated with
surface layer properties [2,4]. There are many such coef?-
cients existing. The most popular are: equivalent chip
thickness (heq) and power density (P0). The former is proved
to be useful in grinding ceramics, the latter is often applied
when grinding with aluminium oxide grinding wheels is
investigated [2].
The main disadvantage of both coef?cients is that to
calculate them it is necessary to estimate the effective
grinding depth or effective wheel/workpiece contact length.
Both values are very dif?cult to estimate ``on-line'' grinding
accurately.
Thus, an ``easy-to-estimate'' grinding coef?cient, which
would be strongly correlated with surface integrity parameters,
is still lacking. The investigation on the correlation
between the coef?cient combining power density and the
wheel/workpiece contact time and residual stress in surface
grinding is described below.
2. Grinding coef?cient combining power density and
contact time
It was proved [3] that residual stresses in surface layer
after grinding are closely correlated with maximum grinding
temperature. The analysis of equations used for temperature
calculation in grinding [6] indicates that it is not only the
power density that inˉuences the grinding temperature but
there is also a second important factor D wheel/workmaterial
contact time. In surface grinding the contact time of
the particular workpiece point with heat source (grinding
wheel) can be easily calculated as
tc .
le
vw
(1)
where le is an effective wheel/workpiece contact length and
vw is the workspeed.
The proposed grinding coef?cient B is a product of power
density P0 and contact time tc:
B . P0tc .
P
bdle
le
vw .
P
bdvw
(2)
where P is the total grinding power and bd the grinding
width.
The ?rst advantage of this coef?cient is that all quantities
in this equation (grinding power, grinding width and workspeed)
are easy to measure ``on-line'' in a grinding process.
3. Experimental set-up
Experiments were carried out for the following grinding
conditions.
_ workmaterials: carbon steel 0.45% C, 28HRC (marked S),
alloy steel 40H (0.38%C, 0.9%Cr, 0.28% Ni) 48HRC (H),
bearing steel èH15 (equivalent to 100Cr6) 62HRC (L);
_ grinding wheels: 38A60J8V (J), 99A80M7V (M);
_ wheelspeed: 26 m/s (constant);
_ grinding depth: from 0.005 to 0.06 mm;
_ workspeed: from 0.08 to 0.5 m/s;
_ grinding fluid: emulsion or none.
Grinding parameters in these investigations were limited
by the power of the main wheel drive, table speed regulation
range and by the appearance of unacceptable changes in the
surface layer, microcracks and burns.
To estimate coef?cient B it was necessary to measure
grinding power, workspeed and grinding width. Grinding
power was measured in two different ways: by the measurement
of power consumed by wheel main drive (Pm) and
simultaneous measurement of tangential grinding force Ft
and wheelspeed vs. The grinding power can then be calculated
calculated
as Pc . Ftvs. The comparison of the results obtained
from both methods is shown in Fig. 1. A very good correlation
can be seen from this ?gure, which proves that measurement
of power consumption of wheel main drive is
accurate enough to estimate coef?cient B in the case when
only grinding wheel is driven by this drive. The wheelspeed
was measured by means of displacement transducer and
grinding width was taken as a width of the sample being
ground.
4. Experimental results
On the basis of measured values of P, vw and bd in surface
grinding, the coef?cient B was calculated in each grinding
test. Measurements carried out during grinding allowed, ?rst
of all, to evaluate the inˉuence of grinding conditions on the
coef?cient B, cf. Figs. 2±7. The linear dependence between
effective grinding depth and B can be seen from Figs. 2, 4
and 6. Slopes of these lines depend mainly on grinding
wheel, workspeed (Figs. 2 and 6) and on grinding ˉuid
(Fig. 4). The correctness of linear approximation was proved
in a statistical wayDvalues of R2 were higher than 0.9 in all
cases.
The inˉuence of workspeed on coef?cient B, Figs. 3, 5
and 7, is not as uniform as those obtained for grinding depth.
Much higher inˉuence of vw on B is observed for a lower
range of workspeeds. It indicates that there is a limited
possibility to inˉuence coef?cient B by changes of the
workspeed. Very similar dependencies were obtained for
the third workmaterial investigated D alloy steel (H).
For all experiments, in which microcracks and/or burns
were not present, residual stress distribution was measured
by means of the well-known material removal method. From
residual stress vs. depth below surface diagrams obtained for
each grinding test, maximal residual stresses in the surface
layer were determined. Usually, residual stresses reach their
maximum (tensile values) close to the surface on depths of
10±20 mm.
Relations between coef?cient B and maximum residual
stress for investigated workmaterials are shown in Figs. 8±
10. In these diagrams the results are summarised for each
workmaterial regardless of other grinding conditions (grinding
wheel properties, grinding ˉuid, grinding parameters). In
each case the linear dependence was assumed which was
proved in a statistical way (R2 from 0.8529 to 0.9074).
It results from these ?gures that the slopes of residual
stress-coef?cient B lines are characteristic for the given
workmaterial and seem to be independent of other grinding
conditions. The highest slope was obtained for bearing steel
(L), Fig. 10, and the lowest one for alloy steel (H), Fig. 9.
Some additional observations recorded during investigations
indicate that there is a possibility to use the coef?cient
B to predict and/or control such changes in surface layer like
microcracks, burns or microstructure changes. Additional
investigations are necessary to con?rm the usefulness of this
coef?cient in other grinding methods.
5. Conclusions
1. The grinding coef?cient B combining power density and
wheel/workpiece contact time was developed to predict
residual stress in surface grinding.
2. A linear correlation between coef?cient B and maximum
residual stress was found experimentally. It was
con?rmed for several workmaterials.
3. The relation between coef?cient B and maximum
residual stress seems to be independent of grinding
conditions.
4. Coef?cient B increases linearly with the increase of
grinding depth and decreases with the increase of
workspeed. This decrease shows less intensity in the
range of higher workspeeds.
5. The coef?cient B is easy-to-estimate, even on-line, in
industrial practice.
6. The coef?cient B may be useful in predicting such
surface layer properties in grinding like microcracks,
burns or microstructure changes.
References
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注： 11
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