本科毕业论文---皮套圈座多轴钻孔专机设计.doc

编号

无锡太湖学院
毕业设计（论文）
相关资料

题目： 皮套圈座多轴钻孔专机设计

信机 系 机械工程及自动化专业

学 号： 　　　 0923176　　　　
学生姓名：
指导教师： 　 （职称：副教授 ）
（职称： ）

2013年5月25日

目 录

一、毕业设计（论文）开题报告
二、毕业设计（论文）外文资料翻译及原文
三、学生“毕业论文（论文）计划、进度、检查及落实表”
四、实习鉴定表

无锡太湖学院
毕业设计（论文）
开题报告

题目： 皮套圈座多轴钻孔专机设计

信机 系 机械工程及自动化 专业

学 号：
学生姓名：
指导教师： （职称：副教授 ）
（职称： ）

2012年11月14日

课题来源
无锡市江泰机械制造厂是一家专业从事外协件加工的企业，公司现采用加工中心加工纺织机械零件--皮圈架座上的三个孔,皮套圈座是纺织机械上一个异形件,加工精度高,用普通机床加工较困难，工装时间长，加工成本高，效率不高。因而需要设计一台专机达到提高工作效率，降低成本。
科学依据（包括课题的科学意义；国内外研究概况、水平和发展趋势；应用前景等）
普通机床加工零件时，不仅工人劳动强度很大，效率也不高，而且不利于保证产品加工精度。专用机床是按高度工序集中原则设计的，即在一台机床上可以同时完成许多同一种工序或多种不同工序的加工，它可以同时用多个刀具进行切削，机床的辅助动作实现了自动化，结构比普通机床简单，提高了生产效率。
专用机床与普通机床比较，具有以下特点：
⑴专用机床上的通用部件和标准零件约占全部机床零、部件总量的70%到80%，因此设计和制造的周期短、投资少、经济效益好。
⑵由于专用机床采用多刀加工，并且自动化程度高，因而比普通机床生产率高，产品质量稳定，劳动强度底。
⑶专用机床的通用部件是经过周密的设计和长期生产实践考验的，又有专门厂家成批制造，因此结构稳定，工作可靠，使用和维修方便。
⑷专用机床易于联成专用机床自动线，以适应大规模的生产需要。
随着社会经济的发展，机械制造业也愈来愈受到人们的关注。在皮套圈座方面，生产效率不仅严重地威胁着企业的经济情况，而且大量的工作危害着生产者的健康,立式多轴钻孔专机有效的缓解了这一现象。钻孔的要求越高,工人的工作量也就越大,针对手工钻孔的技术要求也就越高,工人保持长期的精力积中,容易出现生产安全事故,危害性较大.针对这一情况,各个企业采用了不同的方案,包括使用单一的钻床来减轻劳动者的疲劳度 ,这些措施在一定改善员工的作业要求,但还不能满足要求。因此,研究合适的皮套圈座立式多轴钻孔专机,降低了工作强度,特别是减缓工人的精力过度集中,对于防止企业的生产事故有明显的效果和保护作业人员的生命安全有十分重要的意义。
多轴钻孔最早出现在日本地区，后经台湾传入大陆。距今已有二十年的历史。
随着国家不断的加大对外开放,经济受到了剧烈的竞争,生产效率成为各个公司缓解压力的关键点,皮套圈座多轴钻孔专机面临着更广阔的应用空间。

研究内容
皮套圈座多轴钻孔专机的工作原理,结构组成,以及工作特点,控制系统;了解该系统机构的制造工艺,控制系统,安全装置的工作原理。
在前几年,手动钻孔机应用在我国较为广泛,随着竞争的不断加剧,机械加工精度要求不断地提高,手工钻孔逐渐被淘汰.单轴钻孔专机的出现越来越频繁,世界的一体化不断加剧,多轴钻孔专机取代了单轴钻孔专机受到越来越广的应用.随着多轴钻孔的兴起,多轴钻孔专机大体上分为两大类,可调式和固定式
多轴钻床按其加工件的硬度来划分，可分为中切削型、重切削型和强力超重切削型三类。中切削适用于铝、镁、铜等HB≤150以下的工件。重切削适用于孔数大于10个的软质件或7孔以下的钢、铁等HB≤265以下的工件。强力超重切削型试用于265≤HB≤330钢、铁等强硬度工件。
总之，综合考虑各种情况，得出一个最优设计方案，设计一个符合实际情况的皮套圈座立式多轴钻孔专机。

拟采取的研究方法、技术路线、实验方案及可行性分析
通过对多轴钻孔专机的实物研究和要加工产品的市场研究和产品分析,总结得出皮套圈座多轴钻孔专机的基本结构,工作方式与原理.然后根据考察的结果,再查阅相关书籍,确定基本的设计参数,进行初步的三维建模。交由指导老师检查,修改.完成后,再对主要载荷部件进行校核.最后出主要零件的零件图,编写设计说明书。
可行性分析：《我国多轴钻床行业2010年发展报告》指出2010年多轴钻床行业总产值上年增长20%，出口合同额比上年增长15%。目前，国内已有众多厂家在进行皮套圈座多轴钻孔专机等相关产品的生产研发工作，如无锡市，数家公司完成对此的研发，并成功用于产品的加工.由此可见，该设计方案切实可行。
研究计划及预期成果
研究计划:
2002年10月12日-2002年12月25日：按照任务书要求查阅论文相关参考资料。
2013年3月8日-2013年3月14日：按照要求修改毕业设计开题报告。
2013年3月15日-2013年3月21日：学习并翻译一篇与毕业设计相关的英文材料。
2013年4月12日-2013年4月25日：机床设计。
2013年4月26日-2013年5月21日：毕业论文撰写和修改工作。
预期成果：
此多轴钻孔专机的研究成功可以有效的降低工作强度,主要体现在下面几个方面:
(1)科学钻孔,降低对员工的技术要求。
(2)提高效率,增加经济效益.。
今年来我国生产事故不断，造成重大人民生命财产的损失，其中很多就是由于长时间的精力高度集中引起的。
特色或创新之处
近年来我国皮套圈座多轴钻孔专机有了较大的发展。动力系统,传动系统,钻孔的质量和技术水平都有较大的提高。特别在孔的精度上，达到了更高的水平。在其它方面均有较大的突破。
我设计的皮套圈座多轴钻孔专机的特色也在于此，即注重实用性和经济性；效率高；同时性价比高，成本低。
已具备的条件和尚需解决的问题
已具备的条件：设计过程中所需要的各种软硬件资源和相关产品实物照片。
尚需解决的问题：相关文献资料的缺乏，对一些结构设计部分的具体设计指导，以及三维软件的高级运用技巧。

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英文原文
Small-hole drilling in engineering plastics sheet and its accuracy estimation
Hiroki Endo and Etsuo Marui
Abstract
In recent manufacturing processes, the small diameter hole drilling process is frequently used owing to its good characteristics. The drilling process can easily be adapted to wide variations in lot size, processing accuracy, processing spot patterns where holes are made, and so on. Many machine elements, which have small diameter holes, are manufactured using engineering plastics of superior material and machining properties. However, it is not easy to drill holes with a diameter smaller than 1 mm, in recent machining technology as well. In this report, 1-mm diameter holes are drilled on two engineering plastics sheets and their drilling accuracy is discussed.
Keywords: Small diameter hole; Drilling; Engineering plastics; Machining accuracy

1. Introduction
Processing of small diameter holes is done in various materials, corresponding to the trend of downsizing or high accuracy in parts incorporated into electronic equipments, medical instruments or textile machineries. Many techniques are put to practical use, including drilling, ultrasonic machining, electric discharge machining, electrolytic machining, laser beam machining, electron beam machining, fluid or abrasive jet machining, and chemical blanking. Depending on the workpiece material, the machining accuracy, and the lot size, the best process for making holes of small diameter may be appropriately selected. Within these various machining processes, the drilling process can readily deal with a wide variety of machining conditions.

However, there are some difficult problems in drilling holes smaller than 1 mm in diameter. For example, a large load cannot be put on small drills, owing to their low strength and rigidity. Thus, the feed rate per unit drill rotation must be set small. The removal of drilled chips is difficult owing to the small drill flute area.

In many cases, engineering plastics are used in making various machine parts because they are light and have superior specific strength (that is, the ratio of tensile strength to density) compared with carbon steel. Also, the material cost of engineering plastics is competitive and their machinability is fairly good.

With these points as background, the orthogonal cutting of engineering plastics was investigated [1] and it was suggested here that the visco–elastic properties of engineering plastics have some effects on the magnitude of cutting force and the surface roughness of machined surfaces. There is a review paper [2] regarding the machining of engineering plastics. In this review paper, drilling process was also treated. It was pointed out that the heating up of the workpiece due to build-up of swarf on drill flutes is an obstacle to the drilling process of engineering plastics. Recently, some experiments have been attempted on drilling glass–fiber-reinforced engineering plastics sheets [3] and [4], and the thrust force and torque during drilling have been measured. In these papers, it was reported that the delamination phenomenon decreases the drilled hole integrity, when holes of about 5-mm diameter are drilled. However, the investigation on the accuracy in small hole drilling of engineering plastics is left pending.
Then in this paper, small diameter holes of 1 mm are drilled in two typical engineering plastics sheets, and the effect of spindle speed and feed rate on the accuracy (radius error) is estimated.
2. Workpiece materials
Two typical engineering plastics sheets, polyacetal (POM) and polyetherimide (PEI), were drilled. The materials properties are listed in Table 1.

Table 1.
Material properties of workpiece engineering plastics
Performance
Unit
POM
PEI
Specific gravity

1.41
1.27
Rate of water
%
0.22
0.25
Melting point
°C
165
210
Coefficient of linear thermal expansion
cm/cm/°C
9×10−5
5.6×10−5
Tensile strength
MPa
61
124
Tensile extension (Yielding point)
%
40
23
Bending strength
MPa
89
157
Bending elasticity
GPa
2.60
3.07
Compressive strength
MPa
103
118
Izote impact value
J/m
74
42
Rockwell hardness
M scale
119
127

Polyacetal is a crystallized engineering plastics material. The main raw materials are acetal co-polymer and homo-polymer. POM has good fatigue properties and machinability. Many cams, guides and liners are made of POM. Very high accuracy is needed in these machined parts. PEI is an amorphous engineering plastic having superior thermal resistance characteristics. Special electrical parts, for example, electric insulators, connectors, are made of PEI, which is superior in mechanical strength but inferior in machinability to POM.
The workpiece size was: length 100 mm, width 50 mm and thickness 0.8 mm.
3. Experimental apparatus and procedure
The drilling machine used is for small diameter holes, and is equipped with an automatic feed mechanism. A high-frequency induction motor positioned at the uppermost position of the main spindle drives the spindle. Maximum spindle speed is 12,500 rpm. The net spindle speed of the spindle during the drilling is measured by a tachometer, which counts number of the laser beam reflected from a reflective tape pasted on the scroll chuck.

A servomotor for drill feed drives the feed motion of the spindle. The feed is stepless, and a dial gauge equipped at the spindle head measures the length of the drill motion in the spindle axis direction. A stopwatch was used to measure the time needed for this length. The ratio of the moved length to the time is the substantial feed rate per unit time.

The spindle speed was varied between 1250 and 12,500 rpm. And also the feed rate per unit time was varied between 0.405 and 1.986 mm/s. Spindle speed was varied in keeping with the feed rate per unit time. Hence, the feed rate per unit drill rotation became small with the increase in the spindle speed of the drill.

The drill spindle end is attached to the scroll chuck. The drill used here is a conventional twist drill made of high-speed steel with a diameter of 1 mm. In some extra experiments, a 0.3 mm-diameter drill was also used. Such drills have no surface treatment. A dial gauge estimates deflection accuracy of the drill on the scroll chuck during rotation. Extreme care was taken so that the drill deflection was smaller than 5 μm.

The same drill made five holes under the cutting condition of the same spindle speed and the same feed rate. Another drill was used in the drilling under another cutting condition. Of course, the size accuracy of these drills exists within the above-mentioned size scattering. Any evidence of the wear of drills and the build-up of swarf on drill flutes were not recognized after five holes drilling.

Formerly mentioned workpiece of engineering plastics were set on the base of the drilling machine by clamping bolts. Dry cutting without fluid was performed.
4. Calculation of drilled hole shapes
The 1-mm diameter holes drilled on engineering plastics sheets by the process described above are not geometrically true circles, but have a small radial deviation. Shape accuracy of the drilled holes is estimated by the following process.

An optical microscope equipped with digital measuring device measures the shape of the drilled hole. The cross wire of the microscope is set at the circumference of the hole. Then, the coordinates (x,y) of the hole circumference are read. Dividing the circumference into 18 equal parts, the same measurements are then repeated on each spot on the circumference. Using these 18 sets of measured qualities, the equation of the circle that fits closely to the drilled hole is calculated. This is called a least square circle, and in the calculation, the least squares method is applied.

The equation of the least square circle is assumed as follows:
x2+y2+Ax+By+C=0 (1)
Owing to the shape error of the hole, the right hand side of Eq. (1) does not become zero when the above-mentioned measured qualities (xi,yi) are substituted. The residual in this case is vi and the following equation is obtained:
(2)
Here, the coefficients A, B, C in Eq. (1) are determined as the sum of the squared values of the residual vi becomes minimum. Values of these coefficients are obtained by solving the following simultaneous linear equations. In the calculation, N=18.

(3)

Moreover, the coordinates (x0,y0) of the center of the least square circle and its radius rm are obtained as follows:

Corresponding to the above process, the least square circles are described. An example is shown in Fig. 1, where the workpiece material is PEI, drill diameter: 1 mm, spindle speed: 12,500 rpm, and feed rate: 0.405 mm/s. The least square circle is indicated by the broken line.

5. Estimation of machining accuracy and experimental results
Machining accuracy of the drilled holes is estimated by the radius error obtainable from the least square circles. The calculation process of the radius error is given here.
Radius ri at the each measuring spot (xi,yi) is obtained from the coordinate of the least square circle center (x0,y0) of Eqs. (4) and (5) as follows:
(7)
Then, the radius error is calculated by the following equation. The parameter rm in the equation is the radius of the least square circle given by Eq. (6).
Δri=ri−rm (8)
And the position of that measuring spot on the circle is represented by the following angle θi.
(9)
The relation between Δri and θi obtained from the above method is shown in Fig. 2 as a radius error curve. The drilling conditions in this figure are the same as those of Fig. 1 Three concavities and convexities are recognized on the circumference. Then, the drilled hole shape is approximately triangular. Similar results were obtained in other workpiece materials for other drilling conditions. Furthermore, it is seen that the circumference of the drilled hole exists in the vicinity within ±0.02 mm from the least square circle. This drilled hole shape is similar to that produced by the so-called drill walking phenomenon [5]. The radius of the least square circle is slightly larger than that of the drill. The difference between them is about 10 μm.

Result of Fig. 2 is obtained in the measurement at the drill entrance into workpiece. Small burr was formed at the drill exist and the accuracy measurement could not carry out as it is. Then, the burr was forcibly removed and the accuracy was measured. Almost the same accuracy was confirmed, because the workpiece is thin (0.8 mm thickness).

These radius errors are rearranged as functions of the spindle speed or the feed rate for every workpiece material. The results are given in Fig. 3, Fig. 4, Fig. 5 and Fig. 6. Error bars indicate the distribution range of the experimental data. The radius error becomes small hyperbolically with the increase in the feed rate and becomes large linearly with the spindle speed. Small diameter drills were used in this experiment and their bending rigidity is low. Rotational cutting speed is almost zero near the chisel point. At that point, the drill has only a small axial velocity corresponding to the drill feed motion. Accordingly, the rate of penetration [6] is extremely small when the feed rate is small. As mentioned above, the walking phenomenon occurs owing to small errors in drill size. This phenomenon is compounded with the effect of small rate of penetration when small feed rate a